Saturday, August 15, 2020

Understanding Quantum Mechanics #5: Decoherence

[Note: This transcript will not make much sense without the graphics in the video.]


I know I promised I would tell you what it takes to solve the measurement problem in quantum mechanics. But then I remembered that almost one of two physicists believes that the problem does not exist to begin with. So, I figured I should first make sure everyone – even the physicists – understand why the measurement problem has remained unsolved, despite a century of effort. This also means that if you watch this video to the end, you will understand what half of physicists do not understand.

That about half of physicists do not understand the measurement problem is not just anecdotal evidence, that’s poll results from 2016.This questionnaire was sent to a little more than one thousand two hundred physicists, from which about twelve percent responded. That’s a decent response rate for a survey, but note that the sample may not be representative for the global community. While the questionnaire was sent to physicists of all research areas, forty-four percent of them were Danish.

With those warnings ahead, a stunning seventeen percent of the survey-respondents said the measurement problem is a pseudoproblem. Even worse: twenty-nine percent erroneously think it has been solved by decoherence. So, this is what I want to explain today: What is decoherence and what does it have to do with quantum measurements? For this video, I will assume that you know the bra-ket notation for wave-functions. If you do not know it, please watch my earlier video.

In quantum mechanics, we describe a system by a wave-function that is a vector and can be expanded in a basis, which is a set of vectors of length one. The wave-function is usually denoted with the greek letter Psi. I will just label these basis vectors with numbers. A key feature of quantum mechanics is that the coefficients in the expansion of the wave-function, for which I used the letter a, can be complex numbers. Technically, there can be infinitely many basis-vectors, but that’s a complication we will not have to deal with here. We will just look at the simplest possible case, that of two basis vectors.

It is common to use basis vectors which describe possible measurement outcomes, and we will do the same. So, |1> and |2>, stand for two values of an observable that you could measure. The example that physicists typically have in mind for this are two different spin values of a particle, say +1 and -1. But the basis vectors could also describe something else that you measure, for example two different energy levels of an atom or two different sides of a detector, or what have you.

Once you have expanded the wave-function in a basis belonging to the measurement outcomes, then the square of the coefficient for a basis vector gives you the probability of getting the measurement outcome. This is Born’s rule. So if a coefficient was one over square root two, then the square is one half which means a fifty percent probability of finding this measurement outcome. Since the probabilities have to add up to 100%, this means the absolute squares of the coefficients have to add up to 1.

With these two basis vectors you can describe a superposition, which is a sum with factors in front of them. For more about superpositions, please watch my earlier video. The weird thing about quantum mechanics now is that if you have a state that is in a superposition of possible measurement outcomes, say, spin plus one and spin minus one, you never measure that superposition. You only measure either one or the other.

As example, let us use a superposition that is with equal probability in one of the possible measurement outcomes. Then the factor for each basis vector has to be the square root of one half. But this is quantum mechanics, so let us not forget that the coefficients are complex numbers. To take this into account, we will put in another factor here, which is a complex number with absolute value equal to one. We can write any such complex number as e to the I times theta, where theta is a real number.

The reason for doing this is that such a complex number does not change anything about the probabilities. See, if we ask what is the probability of finding this superposition in state |1>, then this would be (one over square root of two) times (e to the I theta) times the complex conjugate, which is (one over square root of two) times (e to the minus I theta). And that comes out to be one half, regardless of what theta is.

This theta also called the “phase” of the wave-function because you can decompose the complex number into a sine and cosine, and then it appears in the argument where a phase normally appears for an oscillation. There isn’t anything oscillating here, though, because there is no time-dependence. You could put another such complex number in front of the other coefficient, but this doesn’t change anything about the following.

Ok, so now we have this superposition that we never measure. The idea of decoherence is now to take into account that the superposition is not the only thing in our system. We prepare a state at some initial time, and then it travels to the detector. A detector is basically a device that amplifies a signal. A little quantum particle comes in one end and a number comes out on the other end. This necessarily means that the superposition which we want to measure interacts with many other particles, both along the way to the detector, and in the detector. This is what you want to describe with decoherence.

The easiest way to describe these constant bumps that the superposition has to endure is that each bump changes the phase of the state, so the theta, by a tiny little bit. To see what effect this has if you do a great many of these little bumps, we first have to calculate the density-matrix of the wave-function. It will become clear later, why.

As I explained in my previous video, the density matrix, usually denoted with the greek letter rho, is the ket-bra product of the wave-function with itself. For the simple case of our superposition, the density matrix looks like this. It has a one over two in each entry because of all the square roots of two, and the off-diagonal elements also have this complex factor with the phase. The idea of decoherence is then to say that each time the particle bumps into some other particle, this phase randomly changes and what you actually measure, is the average over all those random changes.

So, understanding decoherence comes down to averaging this complex number. To see what goes on, it helps to draw the complex plane. Here is the complex plane. Now, every number with an absolute value of 1 lies on a circle of radius one around zero. On this circle, you therefore find all the numbers of the form e to the I times theta, with theta a real number. If you turn theta from 0 to 2 \Pi, you go once around the circle. That’s Euler’s formula, basically.

The whole magic of decoherence is in the following insight. If you randomly select points on this circle and average over them, then the average will not lie on the circle. Instead, it will converge to the middle of the circle, which is at zero. So, if you average over all the random kicks, you get zero. The easiest way to see this is to think of the random points as little masses and the average as the center of mass.

Now let us look at the density matrix again. We just learned that if we average over the random kicks, then these off-diagonal entries go to zero. Nothing happens with the diagonal entries. That’s decoherence.

The reason this is called “decoherence” is that the random changes to the phase destroy the ability of the state to make an interference pattern with itself. If you randomly shift around the phase of a wave, you don’t get any pattern. A state that has a well-defined phase and can interfere with itself, is called “coherent”. But the terminology isn’t the interesting bit. The interesting bit is what has happened with the density matrix.

This looks utterly unremarkable. It’s just a matrix with one over two’s on the diagonal. But what’s interesting about it is that there is no wave-function that will give you this density matrix. To see this, look again at the density matrix for an arbitrary wave-function in two dimensions. Now take for example this off-diagonal entry. If this entry is zero, then one of these coefficients has to be zero, but then one of the diagonal elements is also zero, which is not what the decohered density matrix looks like. So, the matrix that we got after decoherence no longer corresponds to a wave-function.

That’s why we use density matrices in the first place. Every wave-function gives you a density matrix. But not every density matrix gives you a wave-function. If you want to describe how a system loses coherence, you therefore need to use density matrices.
br> What does this density matrix after decoherence describe? It describes classical probabilities. The diagonal entries tell you the probability for each of the possible measurement outcomes, like in quantum mechanics. But all the quantum-ness of the system, that was in the ability of the wave-function to interfere with itself, have gone away with the off-diagonal entries.

So, decoherence converts quantum probabilities to classical probabilities. It therefore explains why we never observe any strange quantum behavior in every-day life. It’s because this quantum behavior goes away very quickly with all the many interactions that every particle constantly has, whether or not you measure them. Decoherence gives you the right classical probabilities.

But it does not tell you what happens with the system itself. To see this, keep in mind that the density matrix in general does not describe a collection of particles or a sequence of measurements. It might well just describe one single particle. And after you have measured the particle, it is with probability 1 either in one state, or in the other. But this would correspond to a density matrix which has one diagonal entry that is 1 and all other entries zero. The state after measurement is not in a fifty-fifty probability-state, that just isn’t a thing. So, decoherence does not actually tell you what happens with the system itself when you measure it. It merely gives you probabilities for what you observe.

This is why decoherence only partially solves the measurement problem. It tells you why we do not normally observe quantum effects for large objects. It does not tell you, however, how it happens that a particle ends up in one, and only one, possible measurement outcome.

The best way to understand a new subject is to actively engage with it, and as much as I love doing these videos, this is something you have to do yourself. A great place to start engaging with quantum mechanics on your own is Brilliant, who have been sponsoring this video. Brilliant offers interactive courses on a large variety of topics in science and mathematics. To make sense of what I just told you about density matrices, for example, have a look at their courses on linear algebra, probabilities, and on quantum objects.

To support this channel and learn more about Brilliant, go to brilliant.org/Sabine, and sign up for free. The first two-hundred people who go to that link will get twenty percent off the annual Premium subscription.

224 comments:

  1. One should read "Geometry of Quantum Theory" by V. S. Varadarajan for a much deeper and more coherent approach to quantum theory!

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    1. During this Covid lock down last spring I read Geometry of Quantum States by Bengtsson and Zyczkowski. I found this to be very good.

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  2. Nice mini-tutorial! You have compactly and understandably captured both the power of the decoherence model and, more importantly, what it emphatically does not explain. (By the way, I hope you are also writing on such topics for Brilliant.org.)

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  3. Hi Sabine,
    Decoherence is like the process that leads to the manifestation in the classical world after a measurement has taken place. Apparently, decoherence does not give an answer to the measurement problem as you also presented on that video.

    From Wikipedia we read:"...meaning that the measurement "did something" to the system that is not obviously a consequence of Schrodinger evolution. The measurement problem is describing what that "something" is, how a superposition of many possible values becomes a single measured value."

    Furthermore:"....the Schrodinger wave equation determines the wave function at any later time. If observers and their measuring apparatus are themselves described by a deterministic wave function, why can we not predict precise results for measurements, but only probabilities? As a general question: How can one establish a correspondence between quantum and classical reality?".

    Conclusions:
    a) the evolution of the Schrodinger equation says nothing about the inner mechanics of quantum reality (that implies ignorance of the mechanism), pointing to an incompleteness of Schrodinger's equation. This is exactly what Einstein's was also thinking about and today's QM proponents still fail (failed to understand the essence of the problem (the measurement problem itself, the justification of the outcome)) to acknowledge.

    b) when one speaks about the mechanism of inner quantum reality, QM proponents use the wave function collapse (nothing to do) as counterargument. The discovery of the mechanism has nothing to do with the wave function itself (see above) and certainly the answer is classical and not quantum.

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    1. Bell’s theorem demonstrates locality and realism cannot be true of a quantum system. If one performs measurements of observables, eigenvalues that real, then locality does not apply. Wigner’s friend argument illustrates how we can show reality may be abandoned. The following experiment illustrates this. Two observers may witness nature in ways that are not commensurate with each other. The observer then cannot be completely removed from nature.

      https://arxiv.org/abs/1902.05080

      This is a Bell type of experiment where locality is imposed, but two observers witness two different version of reality. There is then a loss of objectivity to reality, which is the flip side or dual to the standard Bell inequality violation used to demonstrate nonlocality.

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    2. Lawrence Crowell,

      "Bell’s theorem demonstrates locality and realism cannot be true of a quantum system. If one performs measurements of observables, eigenvalues that real, then locality does not apply."

      This is incorrect. Bell theorem is a refinement of the EPR argument which proves that locality can only be maintained if QM is supplemented with deterministic hidden variables. So, local non-realism has been ruled out since 1935 by EPR.

      Bell investigates the remaining local option, local realism and proves that locality can only be retained in superdeterministic theories.

      To say that "Bell’s theorem demonstrates locality and realism cannot be true of a quantum system" is deeply misleading because it creates the illusion that one can save locality by rejecting realism which is false.

      Tim Maudlin's paper:

      What Bell Did

      https://arxiv.org/abs/1408.1826

      is the best treatment of the subject I know of, except for his take on superdeterminism which he unjustly considers to be non-scientific.

      "Wigner’s friend argument illustrates how we can show reality may be abandoned. The following experiment illustrates this. Two observers may witness nature in ways that are not commensurate with each other. The observer then cannot be completely removed from nature.

      https://arxiv.org/abs/1902.05080"

      Wigner’s friend argument is based on a false assumption, that is possible in principle to isolate a system from its environment. All matter contains massive and electrically charged particles, and those particles will interact with the environment gravitationally and electromagnetically. So the assumption in this paper that:

      "From outside the closed laboratory, however, Wigner must describe his friend and her quantum system as a joint entangled state."

      is false. Both Wigner and his friend have the same information about the system.

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    3. I am thinking of Bell more than EPR. The EPR paper argued for the necessity of local hidden variables. This was argued to give the Bertelsmann’s socks argument. Bell then asked what happens when one Stern-Gerlach apparatus is set to π/2 relative to the other. This leads to the violation of inequalities of probabilities that are classical.

      This Wigner friend problem is realistic if we consider the decoherence of states as due to further entanglement. We ordinarily think of localization of a quantum state or particle is associated with collapse. With this decoherence comes a loss of quantum correlation or phase. However, if we have two observers looking at a quantum state there are entanglements with needle states. We can think of Alice and Bob as an entanglement and Debbie and Charlie as entanglements. This is then a 4-tangle of needle states. The problem is that any one of these states is entangled with the other 3. We cannot consider this as an entanglement of any of these states with each of these three individually. As such Charlie is entangled with the triplet (ABD) and Debbie is entangled with (ABC). Consequently, there is no way we can think of Charlie and Debbie as having states that are equivalent.

      I draw little quarter for Maudlin. I honestly think he is simply dead wrong on much of what he argues. My time is a bit tight right now, so I am not able to get into this. However, I for the time will just say I reject references to him.

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    4. Lawrence Crowell,

      "The EPR paper argued for the necessity of local hidden variables. This was argued to give the Bertelsmann’s socks argument."

      Right, EPR proved that locality can only coexist with a deterministic hidden-variable completion of QM. Hence local-nonrealism has been proven wrong. Bell does not discuss this option because it does not make any sense to beat a dead horse.

      " Bell then asked what happens when one Stern-Gerlach apparatus is set to π/2 relative to the other."

      Yes, and he concludes (assuming that his theorem applies - it does not for superdeterministic theories) that QM must be non-local, not that it must be non-realistic. Just read the abstract of his paper.

      "However, if we have two observers looking at a quantum state there are entanglements with needle states."

      I have provided a strong argument that macroscopic superpositions are not possible due to the impossibility of shielding gravitational or electric fields. So, the observer outside the lab and the one inside agree on the state of the needle. The one inside just looks at the needle, the one outside can determine the needle state by a measurement of the gravitational field associated with this needle. So, there is no such thing as a superposition of needle states, hence no entanglement. Your argument just falls apart.

      "I draw little quarter for Maudlin. I honestly think he is simply dead wrong on much of what he argues."

      His analysis on Bell, or the one on quantum logic is solid. When you have time I would be interested to hear where you think he gets wrong.

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    5. I have not read Maudlin in many years, but I think he introduces local HV implicitly. I am not sure I have time to slog through his stuff. The problem is that he is somebody who is taking a conservative stance on QM. This happens right at a time when with quantum gravitation we most likely need a more radical perspective. The concept of an event or the meaning of localizing any event is incomplete.

      You can shield against electric fields. A Faraday box isolates the interior region from electric fields. The conducting shell redistributes electrons on its surface to counter an electric field. The electric potential in the interior is then constant. This is a standard Gauss' law result. Gravitational fields are more nuanced. A spherical shell of matter has a constant gravitational potential in the interior. A large piece of sheet metal give partial protection from lightning, which means it gives a less varying electric potential that can induce an electric strike. A large sheet of matter is similar, but if there is a gravitating body nearby it falls towards it, as does the test mass.

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    6. Lawrence Crowell,

      "You can shield against electric fields. A Faraday box isolates the interior region from electric fields. The conducting shell redistributes electrons on its surface to counter an electric field. The electric potential in the interior is then constant. This is a standard Gauss' law result."

      This only works to a certain approximation. It assumes that charge is continuous while in reality it is quantized. Magnetic fields are not shielded in this way at all.

      I do not understand your point about gravity. Do you agree or not that it is possible to detect the mass distribution inside the lab by a measurement of the gravitational field from the exterior? This is a common technique to understand the interior of the planets by analyzing the orbit of a spacecraft.

      In regards to Tim Maudlin, my point is that he provides a good account on EPR and Bell. I do not see how this relates with quantum gravity. Anyway, do you still maintain that the conclusion of EPR + Bell is that you can have local non-realism? Why? Can you provide a local and non-realistic account of the EPR correlations?

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    7. A magnetic field can be shielded. A metal with a large magnetic permeability μ, called a high-μ metal in a cylindrical or pipe configuration will channel most magnetic field lines into it. The region of space in between may have little magnetic field.

      Bell formulated his theorem with hidden variables. The existence of these hidden variables is the assumption of realism and counterfactual definiteness. The hidden varlable is λ ∊ Λ, exists in this space Λ of probabilties, where the stochastic outcomes of QM come from a random sampling of λ. We then have the Alice-Bob setting with their respective functions on the sphere of Stern-Gerlach detector directions (or think spin direction such as on a Bloch sphere) and this sample space A,B:S^2×Λ --> {-1, 1}. The values that Alice and Bob measure with detector settings a, b are then A(a,λ) and B(b,λ). Quantum correlations are determined by A(x,λ) = -B(x,λ) for x ∊ S^2, such that we have the expectation of a random variable X on Λ as

      〈X〉 = ∫X(λ)p(λ)dλ

      for p(λ) is a probability density. This then establishes local realism.

      This is used to compute the inequalities. QM is then found to violate this. What is then evident is this assumption of local realism fails in either locality or in realism. If I can find the time, maybe Saturday, I can go further into this. One of these two assumptions is then false in QM. The usual situation is where locality is abandoned. We may alternatively abandon realism.

      This is where superdeterminism enters into the picture. The assumption of realism or counterfactual definiteness is countered by superdeterminism (sup-d). Sup-d means there is no choice one has for performing an experiment, there is no alternative to a process (no I could have done this and gotten that) and this leads to the curious idea of ‘t Hooft. Hossenfelder and Palmer wrote an FQXi paper on this, which invokes somewhat nonstandard version of incomputability on a fractal set. I wrote a paper that invoked a more standard idea of incomputability, and how I see these as complementary. The HP paper is one that abandons realism, whereas mine abandoned locality. These two approaches are dual to each other.

      The result of

      https://arxiv.org/abs/1902.05080

      is a Bell type of experiment where locality is imposed, but two observers witness two different version of reality. There is then a loss of objectivity to reality, which is the flip side or dual to the standard Bell inequality violation used to demonstrate nonlocality. This is then a Bell-theorem where locality is imposed, but where realism fails. In many ways this happens with black hole complementarity. An observer who remains outside a black hole witnesses one set of events, while another observer who enters the BH another. The exterior point o has a future time development I^+(p) that is not identical to the causal development J^(p), at least what is accessible to an exterior observer. The observer who enters the BH reports something different.

      LC

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    8. Lawrence Crowell,

      Thanks for spending your time explaining Bell's theorem to me but it was not necessary. My point is not that realism/hidden variables are not assumed by Bell, they are. My point is that non-realist theories have already been proven to be non-local by EPR. Let us read the abstract of Bell's paper "On the Einstein Podolsky Rosen paradox":

      "THE paradox of Einstein, Podolsky and Rosen was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality."

      OK, so why are the hidden-variables necessary? To restore locality. In other words, without hidden variables QM is non-local, hence non-realism is non-local.

      Bell then studies if locality can actually be restored by hidden variables and he concludes that it cannot. But this does not magically revive local non-realism which was killed by EPR already.

      Let me repeat the argument using Bohm's version of the experiment:

      At two distant locations (A and B) you can measure the X-spin of an entangled pair. QM predicts that:

      P1: If you measure the X-spin at A you can predict with certainty (probability 1) the X-spin at B.

      Let’s exclude non-locality:

      P2: the X-spin at B is not determined by the measurement at A.

      From P1 and P2 it follows that there was something at B that determined the result of the B measurement. EPR named that “something” an “element of reality”. So:

      P3: There is an element of reality at B that determines the measurement result at B.

      You may observe that there is no other logical option available (unless you think that it’s by pure luck that we manage to always predict with certainty the X-spin at B, which is rather absurd).

      From P1 and P3 it follows:

      P4: there was an element of reality at A that determined the measurement at A.

      This is because once we’ve established that the measurement at B was fixed (P3) it’s impossible that the measurement at A could have been different, right?

      OK, so P3 and P4 lead to:

      C: The X-spin of both particles, at A and B were determined before any measurement took place (deterministic realism).

      If you believe that local non-realism can survive the above argument please explain!

      In regards to the paper "Experimental test of local observer-independence" my argument, that one cannot isolate a system from an outside observer still stands. Yes, you can shield EM fields to a certain degree, but you cannot do it completely and there is no way to shield gravitational fields. So, those experiments are not possible, even in principle.

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    9. If QM obeyed the Bell inequalities your P4 would be correct, at least tentatively. The violation of the inequalities falsifies P4.

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    10. Lawrence Crowell,

      If P4 is false, as you claim, it means that either P4 does not follow from P1 and P3 or that P1 or P3 are false. Please explain your choice.

      Anyway, P4 cannot be proved false by Bell's theorem because superdeterminism is a valid option being compatible with all known physics. But you are invited to try.

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    11. P1 is where things go wrong. This only holds if I have my Stern-Gerlach apparatuses measuring spin A and B in the same direction. What if I decide to orient B in a direction orthogonal?

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    12. Lawrence Crowell,

      "P1 is where things go wrong. This only holds if I have my Stern-Gerlach apparatuses measuring spin A and B in the same direction."

      P1 is a verified prediction of QM and it is assumed to be true by Bell's theorem as well. So, P1 is true. So, my argument holds.

      If B is orthogonal we have 1/2 probability to get spin up and 1/2 probability spin down. So what? How is this in contradiction with my argument?

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    13. P1 only holds for the special case of the two SG apparatus aligned in the same direction.

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    14. Lawrence Crowell,

      "P1 only holds for the special case of the two SG apparatus aligned in the same direction."

      This complaint is most bizarre. Of course P1 only holds for same measurement orientation, this is what P1 is about. I only need it to be true as defined. My argument does not make any assumption in regards to a different experiment, when the orientations are different.

      To make an analogy, you may also say that the proposition:

      P1': Trump is the president of US.

      is problematic because it only holds for Trump.

      So, do you accept that P1, as defined in my argument, is true or not?

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    15. It is really seen in the mathematics of quantum states. QM is sort of weird. I do not have time to go into that right now. Your argument for P1 might be called classical.

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    16. @ Lawrence Crowell,

      A quantum state is just a probability measure on the quantum logic (=generalized probability space).

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    17. Lawrence Crowell,

      There is no "argument for P1", classical or quantum. You either can predict the X-spin at B from the X-spin measured at A or you cannot. Just make your choice, it's not that difficult.

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    18. Edwards in part has it. Look, Bell's theorem tells us that classical probability conditions fail. That is all, and orienting the SG results in violations of inequalities for classical probabilities. This is all there is to it. You are thinking in a pure classical way. Sorry, I rest my case.

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    19. Prof. David Edwards,

      "A quantum state is just a probability measure on the quantum logic (=generalized probability space)."

      The EPR-Bohm argument presented above does not depend on any assumption regarding the nature of the quantum state. The only assumptions are locality and the existence of the EPR correlations (which are by now an established experimental fact). This means that no interpretation that does not include hidden variables can be local. So, you can have your quantum logic approach, but it is non-local.

      Lawrence Crowell,

      "Edwards in part has it."

      Edwards proposed another non-local interpretation. So what? The point of our discussion was about local non-realism. Non-local non-realism is certainly a possibility even if I cannot understand the appeal of such a proposal.

      "Look, Bell's theorem tells us that classical probability conditions fail."

      No, it does not. It allows you to chose between non-locality (Bell's choice) or superdeterminism ('t Hooft and Sabine's choice). You seem to side with Bell but you don't like to admit it. As proven by the above argument you could not refute, without hidden variables you have a non-local theory. Quantum logic does not provide an escape from this.

      "You are thinking in a pure classical way."

      I'm not sure what you mean by that. Classical physics is not an assumption of the argument. The only assumptions are locality and the existence of EPR correlations.

      "Sorry, I rest my case."

      Well, your case only consists in vague, unsupported assertions that are completely ineffective against the EPR-Bohm argument. No premise has been shown to be wrong so, even if you do not like the conclusion, you should accept it.

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    20. @ Andrei,

      Newton's gravitational theory is non-local. To get a "local" quantum theory one should use relativistic QFT.

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    21. @ Andrei: As I said you are implicitly making classical assumptions.

      @ Edwards: Locality in QFT is not entirely the same as locality in QM, though I think these are related. Nonlocality in QM pertains to quantum superposition and entanglements which occur in a way so that observables are not uniquely defined in some small region or a point in spacetime. Nonlocality in QFT involves the Wightman condition that harmonic oscillator amplitudes and their operators at different points of space, a spatial surface in spacetime, are commutative. There has been a lot of work over this, where this zero commutation condition tends to remove the whole quantum mechanical condition such as [x, p] = iħ. It appears quantum mechanics holds largely on and in the light cone. However, this is skirted because information of quantum nonlocality is only verified by classical signals that occur on light cones. The assumption of locality on spatial surfaces is made up for then by light cone conditions. There has been a lot of work on this with axiomatic QFT that has not lead to clear conclusions.

      I am not sure what is meant by nonlocality of Newtonian gravitation. Locality in general relativity is a statement that a Gaussian or Birkhoff surface on a spatial surface can be used to estimate the ADM mass in that region. This can happen with type D solutions such as black holes where Gaussian surface can be place far enough away to where the curvature of spacetimes asymptotes to flatness. In general any such Gaussian surface will exhibit diffeomorphisms of the Lorentz group so there are connection terms that render any calculation frame dependent. Newtonian gravitation is a case of asymptotic spacetime for type D solutions.

      There is a general problem with understanding what is meant by locality or nonlocality. Are these all related? Probably, but this is something not entirely understood. Holography and AdS/CFT duality make these issues even more interesting.

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    22. Prof. David Edwards,

      "Newton's gravitational theory is non-local."

      Sure, I've never claimed otherwise. I do not see the relevance of this, but it is true.

      "To get a "local" quantum theory one should use relativistic QFT."

      As proved above, any theory must involve hidden variables in order to be local, QFT included.

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    23. @ Andrei:
      I am a bit under the impression that you are tilting at windmills, just as Maudlin in the (very entertaining although depressingly pointless) discussion with Werner in the follow up to his article you cited above, which I mention because I am under the impression that Lawrence Crowell's arguments here are exactly the same as what Werner tried to argue against Maudlin.

      As someone who has no particular sympathy for Bohmian Mechanics but clearly favours an ontologically well-defined approach to physics, it is somewhat disturbing how two (or more) intelligent people, both with profound knowledge in quantum physics can fail so badly in understanding each others arguments about such a seemingly simple question.
      Already the terminology used by Werner for the assumption that somehow the dichotomy that you either can or cannot predict the outcome at A indicates, that he does not fully grasp the depth of the commitment he is making, calling it (C) for classical (as does Lawrence here), where many refer to it as realism and I would actually prefer the letter (S) - either for "scientific" or for "sensible". At the same time, I also had the feeling that Maudlin does not make a fully committed attempt to understand Werner's argument (I think is argument is not convincing, but it would help to fully grasp it to give a convincing rebuttal).

      My personal suspicion is, that scientists like Werner, who are deeply familiar with details of operational quantum mechanics but fail to understand the argument for non-locality, split in two groups:
      The first (often without admitting it, even to themselves) adopt a many worlds view, in which the answer to your question whether you can or cannot predict the X-spin at B from the X-spin measured at A is indeed that both are equally true (in parallel worlds, if you wish).
      The second (to which Werner seems to count) opt for the perspective that the only reality are observed outcomes of measurements, and therefore the very discussion of properties like predictions for the X-spin at B is meaningless without measurement. As Werner writes in his reply to Maudlin's reply (arXiv:1411.2120): "... any description in terms of properties, thought to pertain to the system itself, and independent of the experimental arrangement and the choice of subsequent measurement, presupposes C."
      This is fine, but in my opinion with this one is (probably again without admitting to oneself) adopting a de-facto Copenhagen view, in which only "measurements" matter - and one ends up with the usual demarcation problem that there is no reasonable criterion within the quantum formalism that distinguishes between a measurement and non-measurement processes. In my opinion, this problem is way more crucial than the problems that come with giving up locality (in the non-signalling EPR meaning of the word).

      More importantly, none of the two views is truly local. It is simply that in both views a sensible definition of locality beyond the no-signalling condition cannot be formulated.

      I referred to the criterion that Werner and Crowell call "classicality" as "scientific", because I don't consider the lack of an explanation of the observed universe (Born rule) in the many worlds approach and the lack of a well-defined ontology in the Copenhagen approach as natural science - in the original meaning of the word as gaining knowledge about nature.

      In this sense, I would suggest as a compromise that there is a choice; however it is not between non-local realism and local non-realism but between a non-local scientific theory and a non-scientific theory that is agnostic about locality.


      Disclaimer: I am neither a trained philosopher, nor did I put nearly as much effort into this post as I would have for a research paper, and English is not my native language, so please forgive semantical imprecission. I hope the point I am trying to make became clear, nonetheless.

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    24. PS @Sabine:
      I think, when pressing the "Preview" button in the comment field, it goes directly to Publish? Sorry for the double posting, in case my comment shows up twice.

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    25. Lawrence Crowell,

      " As I said you are implicitly making classical assumptions."

      Yes, you said that, but you failed to point out where exactly in my argument I make such an assumption and how, by rejecting that assumption the argument fails. For now you only precise complaint was:

      ""P1 only holds for the special case of the two SG apparatus aligned in the same direction.",

      but as P1 is only intended in my argument to hold in that situation we are in agreement that P1 is true.

      So, where is this "classical assumption" you are referring to?

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    26. André

      “I am a bit under the impression that you are tilting at windmills, just as Maudlin in the (very entertaining although depressingly pointless) discussion with Werner in the follow up to his article you cited above, which I mention because I am under the impression that Lawrence Crowell's arguments here are exactly the same as what Werner tried to argue against Maudlin.”

      I think we should discuss my argument presented above, not Maudlin’s. That paper is quite large and I am not willing to defend it. I do not know what Lawrence Crowell had in mind but what he said in regards to my argument cannot qualify as a rebuttal, let alone a valid one. He simply asserted that I assume something classical, without pointing out exactly where this assumption appears in my argument or how this hypothetical assumption is going to render my argument unsound.

      “My personal suspicion is, that scientists like Werner, who are deeply familiar with details of operational quantum mechanics but fail to understand the argument for non-locality, split in two groups:

      The first (often without admitting it, even to themselves) adopt a many worlds view, in which the answer to your question whether you can or cannot predict the X-spin at B from the X-spin measured at A is indeed that both are equally true (in parallel worlds, if you wish).”

      This is not true. In MWI you can always predict the X-spin at B from the X-spin at A. It just postulates that there are two “worlds”, one where you have spin-up at A and spin-down at B and another one where you have spin-down at A and spin-up at B. But the perfect anticorrelation exists in both worlds. Anyway, MWI is not a counterexample to my argument since it is a realistic, deterministic theory. Lawrence Crowell goes for a non-realist one.

      “The second (to which Werner seems to count) opt for the perspective that the only reality are observed outcomes of measurements, and therefore the very discussion of properties like predictions for the X-spin at B is meaningless without measurement.”

      But my argument does not make use of such “predictions without measurements”. You measure X-spin at A and get “up”. You can predict that a measurement at B will be “down”. The measurement at B is actually performed and confirms your prediction. Please read carefully my argument as it is different than EPR’s. EPR intended to show that non-commuting properties exist simultaneously. My argument does not say such a thing. So, as long as Werner accepts the reality of the measurements that are performed and properly recorded and eventually published he has to accept the conclusion of my argument that locality can only exist in a hidden-variable theory.

      “As Werner writes in his reply to Maudlin's reply (arXiv:1411.2120): "... any description in terms of properties, thought to pertain to the system itself, and independent of the experimental arrangement and the choice of subsequent measurement, presupposes C."

      1. My argument does not require that any properties are “independent of the experimental arrangement”, so it does not presuppose C – classicality

      2. I actually think the opposite is true. The fact that the properties of the system under observation do depend on the measurement context is a requirement of classical physics as well. The reason for this is that all particles interact by infinitely range fields (electromagnetic, gravitational).

      “In this sense, I would suggest as a compromise that there is a choice; however it is not between non-local realism and local non-realism but between a non-local scientific theory and a non-scientific theory that is agnostic about locality.”

      Please read carefully my argument. The choice is not between local non-realism and non-local realism, but between local-realism and non-locality (either realistic or not). My argument proves that a local non-realistic theory is not possible.

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  4. The reduction of states induces a_1a_2*e^{iφ} and its complex conjugate a_1*a_2e^{-iφ} to zero without |a_1|^2 and |a_2|^2 being zero. This does reduce the system to a classical-like probability. Yet this process is nonunitary and it is not hard to see that Trρ = Tr(ρ^2) = Tr(ρ^n) = 1 prior to the measurement and after Tr(ρ^n) ≠ 1 for n > 1. So, the system after measurement is in separable states. This is a statistical mixture that has aspects of classicality.

    In general though, what is occurring is the initial quantum state is coupled to other states. We may consider a needle state as an idealization so that

    a_1|1⟩ + a_2e^{-iφ}|2⟩ → a_1|1⟩|↑⟩ + a_2e^{-iφ}|2⟩|↓⟩

    for the needle state with ⟨↑|↓⟩ = 0. We have an expanded density matrix then, where if we trace over the needle states Tr_↕ρ =ρ_{½, -½ }. We are then in effect making an effective theory where the needle states, usually for a more massive system with frequencies or energy much larger than for the system of interest, are ignored. These needle states sample the phase of the system of interest around the unit circle in the Argand plane in a time much smaller than the angular frequency of the phase. I am making a time argument here, and the discussion was for a time independent system, but we can replace time with momentum or wave vector k. So, what has happened then is this precious quantum phase has been transferred to the needle states, and if we trace them over or out then we miss them. This is analogous in ways to coarse graining in statistical mechanics.

    The separable states or classical-like probabilities have for N trials 2^N possible configurations, which is a Kolmogorov complexity. So, if I throw a bag of pennies on a table and blindly sample them for heads or tails, we have this measure of complexity. For the quantum system the maximal complexity is exp(2^N) for all possible phase configurations. This is an enormous number for N at all large. In fact for N = 7 this is 3.9×10^{55} while 2^N is just 128. We then have transferred in our measurement above this phase to a needle state, or one that we generally consider to be more massive. We then have measurements of the needle state, such as an avalanche in a phototube detector, where this avalanche amounts of a massive number of entanglements, or an entanglement with a system that is massive. This connects with gravitation, and this tracing over means what we observe is no longer a superposed distribution. The gravitation of the system, say superposed masses in different locations, is transferred to needle state information or what we in a trace over system might be a very weak IR graviton. We are now on the verge of talking about ER = EPR.

    The wave function then in one sense never really collapses. It assumes a different form, and how we report this is dependent upon the sort of detection we make. Maybe we choose to measure the needle state as well, which leads to measurement of a measurement. Maybe we choose to detect, if it were really possible, that very weak IR graviton. How this outcome is interpreted is then dependent upon what experimental action the observer takes.

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    1. Lawrence

      I read your comment with Penrose's Conformal Cyclic Cosmology in mind and making (amateur) analogies between large-scale universe and small-scale electron, with my idea that the electron hypothetically has its own internal and independent arrow of time. In CCC, a cycle ends at a needle state with all contents in a condensate of photons all in one state. I think it is supposed to have unitarity so that no content from the universe is lost when transitioning between cycles. This leads to a similar problem of how does the electron retain all its content during collapse of its contents to a point (= single state) when the contents were earlier distributed everywhere. In CCC at the very end of cycle, the individual photons have very low energy and an almost infinite wavelength. There are no fermions left and it is assumed that fermions are required to maintain the spacetime metric. What is the speed of light in this metric, and is it still c when the metric of distance is being continually undermined to a limit of no metric? So maybe a failing/fading metric in CCC allows the photons to fix on a single place to collapse at without being restricted to speed c. Similarly for an electron collapse by analogy assuming equivalence of universe and electron form. That is, where the contents of the electron are collapsing within the electron's own hypothetical 'internal' failing/fading spacetime.

      But what of the loss of unitarity in going from quantum to classical? Or in CCC terms going from mid cycle to end of cycle. My hypothetical electron does not spontaneously collapse from quantum to classical as it needs an interaction with the outside world. My hypothetical incoming electron is different from my outgoing electron in a way that is not just a tweak of its arrangement of contents. It has, in my amateur preon model, at least 25% new contents and maybe up to 75%. So that is a swap of contents and a loss of unitary. Likewise, I suspect that the universe will not end its cycle merely from internal effects. The electron changes spin by + 1 or - 1 (which is given off in a photon) and changes by + 0.5 or -0.5 of weak isospin which is not conserved in interactions in the Standard Model. Even in the Standard Model there is an incoming electron being replaced by an outgoing electron plus a photon, so the electron may be seen to be having have a non-unitary interaction event?

      I saw Susskind's video lecture on ER = EPR a few years ago, so I think you may be referring to two possible outcome states of a particle being connected at-a-distance? Like two black holes maybe being connected by a wormhole. Or like Alice's measurement outcome in a Bell Experiment instantly influencing Bob's measurement outcome.

      I agree that in the CCC the collapse point is not spookily different from other times in the evolution of the cosmos although it does have the seemingly difficult-to-explain aspects of loss of space and time metrics at that event. I use Rasch measurement theory to justify, in general terms, such a loss of metric.


      Austin Fearnley

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    2. The Conformal Cosmological Cycle of Penrose is sort of interesting, but I suspect it is not going to win the day. As an undergraduate I remember at a “bull session,” which included pitchers of beer, we were in discussions on physics where I argued that if the universe reached a complete heat death there could be no clock and this would render time undefinable. This seems to have maybe some connection to the instability of de Sitter vacuum and spacetime. Yet spacetime is such that thermal equilibrium is not possible. A black hole with a temperature T in a cosmic background of the same temperature is not at equilibrium. The emission or absorption of a boson will respectively increase and decrease the temperature of the black hole. In a stochastic setting there is a probability the black hole will now wander away form the temperature of the background. The issue is then what is meant by thermal equilibrium in a cosmology.

      The subject of quantum entanglement is vast. One can look at it according to geometry, such as in the elementary case the Fubini-Study metric space. Another approach is algorithmic complexity, such as the work of Aaronson. There is also an interesting development of late called MIP* = ER, which states the class of entangled multiple interactive proof (MIP), where entangled is MIP*, is equivalent to the set of recursively enumerable (RE) algorithms. Recursively enumerable problems are those that can execute an output, but have no terminus. Algorithms that compute fractals are RE, because the fractal has infinite complexity in principle. This means that in principle a Mandelbrot set contains information equivalent to a type of entangled system.

      The ER = EPR is interesting and if one looks at the elementary Penrose diagram for the Schwarzschild black hole there is a lower triangle region bounding the two spacetime diamonds where particles escape from and the upper triangle region where particles enter. These two triangles are the white hole and black hole. It is in parallel or analogous to a^† and a in quantum mechanics. The two diamond regions then observe black holes that are entirely equivalent. In fact, they are entangled.

      The quantum complexity problem is where the complexity of a classical problem, say the set of binary strings that is 2^N, is the exponential of that, say exp(2^N). The collapse of a quantum wave, say of the form |ψ〉 = a_1|1〉 + a_2e^{-iφ}|2〉, is such that the phase for any set of outcomes is random and the sum over all possibilities is zero. This is a where there is not just bit error from decoherence but phase error as well. This is what makes quantum complexity so absolutely enormous.

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    3. Taking CCC with quantum complexity ...

      I often mention CCC but I know it is not the answer to everything, and may not be correct. If I assume that there is an equivalence, in some sense, of form between electron and universe, then to see how an electron is measured we can look at how the universe is measured, or brought to a single state. And where is that point/state located? The CCC universe has eons of time to come to that point [by calculation or otherwise] though that duration may be observer dependent.

      Quantum entanglement ...

      I have spent time, on and off, across ten years, on computer simulations of Bell's Theorem. I started by translating De Raedt's Fortran code (on time windows for detection of particle pairs) into Visual Basic. Then helped some Bell disbelievers.

      I have always pretty much accepted Bell's Theorem as true because in its simplest, skeletal form I cannot defeat it in a local hidden variables simulation. So for a long time I thought that real experiments must be using loopholes to get S values greater than S = 2. Also, correlations of real-valued vector pairs give cos theta but if you replace the real values by integer approximations then surely the correlation will be reduced by attenuation. So Bell's Theorem is understandable as the reduction in correlation brought about by using integer-valued vector approximations to the real-valued ones.

      It was also difficult to understand the idea that quantum randomness can somehow restore a higher correlation. To my mind randomness, on the contrary, lowers a correlation.

      Next I found a duality in results for a Bell experiment and for Malus's Law. 'Bell' results in a 2x2 table while 'Malus' results in a 2x1 table. So you put two Malus results together to get an equivalent Bell table. Malus's Law takes an incoming beam and measures how much of the beam passes a filter set at angle theta to the incoming polaristion angle. The Malus results are precisely what is needed in the Bell table. That implies that Alice is measuring a beam pre-polarised along Bob's filter's vector setting. And vice versa for Bob's measurement.

      So how can the particle pairs (electrons and positrons) in a Bell experiment be pre-set in polarisation? Very frequently I see a Feynman diagram with positrons indicated as travelling backwards in time. So non-spooky entanglement passes the polarisation of the positron to the partner electron. So Malus's Law is the real source of the cos theta correlation. Entanglement is required but is not the prime source of the correlation. And randomness is present because of Malus's Law which is based on a beam and not on individual particle outcomes.

      So how do I see entanglement now? Not really sure yet. At the moment I see it as a sort of Monty Hall effect. It can be very complex mathematically/statistically but one is maybe dealing with probabiities that can travel faster than light (for Wigner's friends?) rather than physical entities that travel faster than light.


      Austin Fearnley

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    4. I read two snippets today which maybe relevant to the end-of-cycle of the universe (and IMO maybe to the end of an electron at a measurement). 1. An article about massive gravity (Claudia de Rham) in Quanta which has gravity dwindling with distance where the distance depends on the mass of the graviton. (And there is an online video by de Rham, too.) 2. Reading from Penrose' The Emperor's New Mind.

      Penrose used U to represent linear processes and R for non-linear (maybe it is more complex than that but I am an amateur). The R enters the picture at a measurement and is necessary to cope with obtaining observed outcomes. Quantum Mechanics only uses U. I wondered if de Rham's 'dwindling point' corresponded with a transition to or acquisition of R? This could also be a transition point in the metric of the universe? Which maybe weakens, but not reverses, the arrow of time. This might have an effect on the long-term stability of black holes which need to evaporate before the end of cycle in CCC, despite them being high entropy objects. This dwindling gravity transition seems to be non-linear?

      (A side note is that in one version of my preon model I have a dwindling point for attractive coloured-gravitation and beyond that a repulsive neutral-coloured gravitation. Also, in a different model, a transition from a nearby zone of positive mass particles to a far zone of negative mass particles could be separated by a dwindling point for gravitation.)

      Austin Fearnley

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  5. Dr. Hossenfelder,

    I appreciate this posting because of the lack of math used and I understood it just fine without the video. I have been reading multiple books about diversified topics in modern physics, (advantage of being retired). The one thing that fascinates me is that no matter what so many authors say about providing a simple and easily understood manuscript on a complex topic, without fail they bog down their books with so much math which really just confuses the information. You on the other hand are able to provide a description of complex concepts without having to throw in a bunch of confusing math.

    Words are just a powerful as mathematics and you have used words alone to bring understanding to a lot of things, thank you so much for that. Maybe I focused too much on the title of your book, but that is the philosophy I have been following.... yes, math is needed, but do not get lost in it because there is so much that can be learned by simply looking at what has already been found. To me it looks like so many are looking only at the math and not what is already there and what we already know means or where it can lead us.

    Something I have read in more than one book, in the beginning of quantum Niels Bohr and his followers had an iron grip on the direction that quantum was going to go. What if they were wrong on something or their was an error on one of their concepts...I hate to say it but I will, kinda sounds like the 50 years of string theory we have today.

    The current book I am reading about the Standard Model, the author made the following statement about a concept/physical characteristic, it "turns out to be essentially an accident rather than a fundamental feature of nature." In other words, it was all about the math and nature had nothing to do with this observed physical concept.

    Thank you Dr. Hossenfelder

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  6. > this would correspond to a density matrix which has one diagonal entry that is 1 and all other entries zero. The state after measurement is not in a fifty-fifty probability-state, that just isn’t a thing. So, decoherence does not actually tell you what happens with the system itself when you measure it. It merely gives you probabilities for what you observe.

    Indeed that last little bit of quantumness, going from probabilities to actualities, is the biggest unsolved mystery in... well, all of fundamental physics. And it doesn't even require high energies or super-small or large scale to experiment with. I'd guess that something interesting is bound to pop up before the entangled "particle" count gets close to the Planck mass/proton mass, or about 10^19. Still 15 orders of magnitude higher than the current fullerene record, but maybe the planned cat state experiments with cantilevers or mirrors can hit it from the other direction. Wish there was more effort spent in this area. Here is to hoping.

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    1. There are parallels between decoherence Hawking radiation, quantum black holes and probably quantum gravity. In particular the unitarity enforces Trρ = Tr(ρ^2) = Tr(ρ^n) = 1 whereas decoherence results in Tr(ρ^n) ≠ 1 for n > 1. This occurs with black holes, where pure quantum states with Tr(ρ^n) = 1 for n > 0 that enter a black hole emerge as Hawking radiation with Tr(ρ^n) ≠ 1 for n > 1.

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  7. My thought is that electrons, or whatever they are, have bosons orbiting them in orbitals. Maybe SUSY bosons. When these bosons jump from a normal state to and excited state, to a higher orbital, we have the electron that we know an love. Kind of a correlation to the de Broglie hypothesis.

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    1. The closest I can get to giving a tepid thumb’s up on this is the Higgs field does something like this with fermions. There are Yukawa Lagrangians of the form ℒ = gγ^0ψ^†Hψ, that are an interaction between the scalar boson Higgs field and a fermion ψ. The Higgs field is a doublet of Goldstone bosons and the fermion is similarly a doublet (ℓ, ν) for a lepton and its neutrino pair, or a pair of quarks (u, d), (s, c) or (b, t). This is equivalent to a Lagrangian term ½m^2 ψ^†ψ when the Goldstone boson components are on the degenerate vacuum state. This is how leptons and quarks get their mass, and the electron is a lepton.

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  8. Dr. Hossenfeldsr — in the third paragraph you refer to “braket notation.” Is this intended to read “bracket notation,” or is it a term I’m simply not familiar with? I look forward to watching the video.

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    1. Thanks for the clarification. The spacing when I read it on my tablet left it unclear as to its status as a word hyphenated by design or by text layout.

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    2. @Friar:

      Bra-Ket is a word hyphenated by design by Dirac.

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    3. ...who invented this notation for his flavour of QM.

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  9. Im not so surprised that the majority of contemporary physicists do not care about the measurement problem (either explicitly or implicitly by too easily assuming that decoherence solves the problem). Reason is their lack of interest in the fundamentals of physics (or the philosophy of physics). When I studied electronics, our professor of quantum mechanics said that the difficulties in understanding it just followed from our intuition being based on our day to day experiences in the macroscopic world, and we should just drop that intuition. Understandable advice in an applied sciences environment, but if Newton and Einstein had not followed their intuition, they would never have done their great discoveries.

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  10. Sabine,

    defining the problem is the hardest part. It is not clear how Feynman would have responded to the poll, who wrote: "I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem".
    So you're in good company.

    But the problem with quantum mechanics is not about measurement. It is often said that only through measurement do the intermediate states disappear and a change becomes physically manifest ("real"). Through the fleeting presence of a W-meson the collision of two protons leads to the occasional production of a deuteron in the sun. But it would be absurd to say that the reaction requires "measurements" or even observers. A free neutron will also decay regardless of the presence of a Geiger counter. This is not reflected at all in the continuous, deterministic change of its wave function on the time-scale of minutes, whereas the decay products leave the scene within microseconds. Schrödinger's equation doesn't square with the observed granularity and randomness in the microworld.

    You said: "the density matrix in general does not describe a collection of particles or a sequence of measurements". I strongly disagree. One should not aggravate the problem by denying the statistical character of quantum theory. The idea that there is an exact correspondence between the wave function and an individual quantum system is spurious metaphysical "überbau", a serious misconception. The formalism does not require this, as can be seen in the Heisenberg picture. (And all textbooks agree that the Heisenberg picture is mathematically equivalent to the Schrödinger picture.) In the Heisenberg picture the state vectors remain constant, and all the time-dependence is in the operators. Nobody ever suggested that an operator represents an "individual" quantum system. They describe statistical ensembles, and like any decent statistical theory, quantum theory permits the calculation of expectation values. It is quite sufficient to know the decay rate of a neutron, and extremely unlikely that we will ever have a theory that predicts the exact time of its decay.

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  11. Before you comment, please read the comment rules. The only links I approve are those to scientific journals, the arXiv, or major news pages whose names I immediately recognize. I do not have time to check other links and will therefore not approve comments that contain other links.

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  12. Hello Sabine,

    I always get the impression you see physics as a game of chess.
    The one who knows the rules best will win.
    The one who can best combine the rules will win.
    Oh, yes.
    It's a good idea to get top grades in school and university.
    And it's also appropriate for many areas of physics.
    But it's not appropriate for the double-slit experiment.
    The double-slit experiment is more comparable to the "Kobayashi Maru" test.
    Here the candidate is in a "no win" situation.
    And only those who succeed in changing/breaking the rules will pass the test.

    Have fun
    Stefan

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  13. Sabine, I think you're attacking a straw man here. I would bet more than half the physicists who say that the measurement problem is "not a problem" don't cite decoherence as the reason it's not a problem (but the minority who do are certainly misguided).

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    1. Peter,

      I have shown you the poll results. That's the best information I have. I don't know what "straw man" you are talking about.

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    2. Why don’t you bring up in the video the linearity vs non-linearity problem of using schrodinger’s equation and then the measurement takes place? That was by far the most effective way I understood your definition of the measurement problem and I have yet to see a satisfactory response..

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    3. manyoso asked: "Why don't you bring up the linearity vs non-linearity problem of using schrodinger's equation and then the measurement takes place?"

      The wave function is not the whole story. It is a mistake to ignore the statistical character of quantum theory and to think of the wave function as representing an "individual" quantum system. This is a common misunderstanding, but Sabine seems to share this view. (It is slightly ironic that her series of blog posts carries the title "Understanding Quantum Mechanics"!)
      I pointed this out in my comment of August 16, but apparently Sabine was too busy to reply.
      @Sabine: It would be nice if you could clarify your position (or rectify my misunderstanding).

      Best wishes,
      Werner

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    4. Wenrer wrote:
      >The wave function is not the whole story. It is a mistake to ignore the statistical character of quantum theory and to think of the wave function as representing an "individual" quantum system.

      That could be -- physicists brighter than you or me have believed as much (Einstein, de Broglie, etc.). But if it is not the "whole story" then what is the rest of the story?

      The obvious answer is "hidden variables." I assume you know that hidden-variable theories have been worked out (e.g., by Bohm and Ed Nelson) that do reproduce the experimental results of QM... but those theories have some real issues.

      So, in all seriousness, what do you yourself think is the rest of the story? Do you think the electron always really does have a definite position in space, even though that is not given by the wave function? And, if so, what are the laws of motion that determine how that position changes in time?

      These are not rhetorical questions -- after all, Bohm and Ed Nelson actually gave logically possible answers.

      But Bell's theorem seems to say that any such answers are going to be pretty strange, one way or another.

      So how do you answer such questions yourself?

      Dave

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    5. PhysicistDave asked: "then what is the rest of the story?"

      The rest of the story, as far as the bare formalism is concerned, is Born's rule. Many people believe (as I did) that it should somehow be derivable from Schrödinger's equation. But it really is a separate component of the formalism. In Schwinger's closed time-path formalism the two components are neatly combined. There's no need to talk about two different kinds of evolution of the wave function. Focus on the wave function is misguided -- in the Heisenberg picture the state vectors play a peripheral role, because they are always traced over. Quantum mechanics is a statistical theory that lets us compute expectation values and correlation functions.

      Dave also asked: "Do you think the electron always really does have a definite position in space?"

      No. And I don't think it is necessary to assume that an electron always exists, i.e. that its world line is continuous (charge conservation notwithstanding). An electron can be conceived of as a series of points in space-time, statistically described by the Feynman propagator. It has always puzzled me how particles could be identical, if their existence were continuous in time. By following the world lines, Nature would always "know" which electron interacted with which photon. But as you surely know, Nature isn't like that. By drawing propagators, events in space-time can be connected in many different ways, and there's not one that is the "correct" one. All Feynman diagrams have to be added up to arrive at the S-matrix. Or, rather, the "square" of the S-matrix in the closed time-path formalism.

      To summarize: I agree that there is a quantum measurement problem, but it's not about measurement. It's about the ontology of quantum theory. The theory should say what it is about, and I think it is foolish to say that it is about "particles" and "measurements".

      Werner

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    6. @ Werner,

      1.The Born rule is derived in the book "The Geometry of Quantum Theory" using the quantum logic approach.

      2. There is no measurement problem if one stops thinking about "quantum objects" and just works with phenomena and theory.

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    7. Prof. Edwards,

      1. Surely it is possible to repackage any theory around other concepts that seem more reasonable.

      2. I agree that talk of "quantum objects" is harmful, because the term is ill-defined. And "phenomenon" is vague too. How about "events"?

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    8. @ Werner,

      I actually have relativistic quantum theories of "events", "trajectories", etc. Experiments and their results is a good alternative to observables and measurements. The primitive, undefined notions of any theory are liable to be a bit vague.

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    9. Werner wrote to me:
      >To summarize: I agree that there is a quantum measurement problem, but it's not about measurement. It's about the ontology of quantum theory. The theory should say what it is about, and I think it is foolish to say that it is about "particles" and "measurements".

      Well, I suppose the one point on which one could achieve a near-universal agreement among physicists is that there is not agreement among physicists on the “ontology of quantum theory”!

      Which raises the question: do you think you have the answer to the question of the ontology of quantum theory, and, if so, what is your answer?

      Full disclosure: I myself do not, and I rather doubt anyone does. But I am open to being surprised.

      Werner also wrote:
      >The rest of the story, as far as the bare formalism is concerned, is Born's rule.

      Well, yes, we all know the textbook approach – we have all learned, in Dave Mermin's immortal words, to “shut up and calculate.”

      But, the problem is that Born's rule, in all the formulations I have ever seen and certainly in the standard textbook formulations, refers explicitly to “measurement.”

      Which puts us back where we started: the infamous measurement problem.

      And that really is a problem. The issue is not simply a problem of economy in the axioms of quantum theory. The problem is that no one has ever been able to explain exactly what counts as a measurement and when it occurs.

      We train students to sort of intuit this, “for all practical purposes,” and most advanced physics students sort of get it. But in principle? Does a hydrogen atom perform a measurement on a photon when it absorbs it? Does an electron perform a measurement in Compton scattering? Or does it take a “macroscopic” device? And, if so, what counts as “macroscopic”? And why should that matter, since macroscopic devices are made up of atoms, and, in principle, describable by quantum mechanics?

      Actually think about such questions long enough, and you get a headache and yell out is desperation, “Just shut up and calculate!”

      But yelling is not an answer. Something is missing in our current understanding of quantum mechanics.

      For a long time, physicists succeeded in bullying students into just not asking such questions. But late in the darkness of night, if they are honest with themselves, they have to admit that they do not really know what is going on with quantum mechanics.

      Dave

      Delete
    10. @ PhysicistDave,

      You write:

      "Which raises the question: do you think you have the answer to the question of the ontology of quantum theory, and, if so, what is your answer?

      Full disclosure: I myself do not, and I rather doubt anyone does. But I am open to being surprised."

      I believe that quantum theory is best understood as a form of perspectivism not physicalism; hence, no ontology! For details see my essay "The Mathematical Foundations of Quantum Mechanics" on my website.

      Delete
    11. Prof. David Edwards,

      "I believe that quantum theory is best understood as a form of perspectivism not physicalism; hence, no ontology!"

      Please explain how perspectivism evades the EPR-Bohm argument below:

      At two distant locations (A and B) you can measure the X-spin of an entangled pair. QM predicts that:

      P1: If you measure the X-spin at A you can predict with certainty (probability 1) the X-spin at B.

      Let’s exclude non-locality:

      P2: the X-spin at B is not determined by the measurement at A.

      From P1 and P2 it follows that there was something at B that determined the result of the B measurement. EPR named that “something” an “element of reality”. So:

      P3: There is an element of reality at B that determines the measurement result at B.

      You may observe that there is no other logical option available (unless you think that it’s by pure luck that we manage to always predict with certainty the X-spin at B, which is rather absurd).

      From P1 and P3 it follows:

      P4: there was an element of reality at A that determined the measurement at A.

      This is because once we’ve established that the measurement at B was fixed (P3) it’s impossible that the measurement at A could have been different, right?

      OK, so P3 and P4 lead to:

      C: The X-spin of both particles, at A and B were determined before any measurement took place (deterministic realism).

      This argument proves that ontology is required to keep locality, which is an established physical principle. How is perspectivism better?

      Delete
    12. PhysicistDave asked: "Does an electron perform a measurement in Compton scattering?"

      As I've vainly tried to explain, this is a meaningless question. In the Schwinger/Keldysh formalism there's no mention of "measurement", it's just about statistics and evaluating correlation functions. (The Born rule is implicit in the formalism.) I think there's broad consensus that there's no place for the concept of measurement in a fundamental theory.

      Dave also asked: "What is your answer?"

      My answer is embarrassingly simple, and I'd thought I've already explained it several times. With the help of a little drawing, a child could understand it, but for quantum dogmatists it seems to be a lot harder.

      Can you think of a synthesis of the wave and particle concepts? Of course you can't, if you have absorbed Bohr's transcendental philosophy of complementarity. It has been declared impossible by the master. Yet it is possible, and I'll try once more to explain.

      Imagine a snapshot of the molecules as a sound wave passes through a gas. There are tiny variations of density, and "only" of a statistical nature, since density is a macroscopic concept. In reality there are only molecules. Now just label one direction in this picture "time" and think of it as a distribution of events in space-time. This is what I call a wave pattern. A particle pattern is even simpler to construct: just think of a dotted line, which will always look like a solid line at coarse enough (time) resolution, and might be called the world line of a particle. There you are: waves and particles are just names we attach to patterns of events in space-time.

      In the case of sound we are aware that at the fundamental level there are only atoms. But in the case of photons and electrons most physicists regard them as fundamental, rather than derived concepts describing the correlations between events. It is the Bell-type experiments which (in my view) force us to treat events as fundamental. Photons with undefined-unless-measured polarization states engaging in superluminal communication are superfluous metaphysical baggage.

      Fields describe correlations between events, and QFT is a machinery for calculating correlation functions. Incidentally, the absorption of a photon is a composite event and should not be thought of as instantaneous. And points in space-time carry more than space and time coordinates; for something resembling QED also a phase factor and a time tag are necessary. But the details are something I can't squeeze into this comment.

      Dave also wrote: "I am open to being surprised."

      I hope so.

      All the best,

      Werner

      [Btw, I'll be offline next week, so you don't need to rush with your reply.]

      Delete
    13. Werner asked me:
      >Can you think of a synthesis of the wave and particle concepts? Of course you can't, if you have absorbed Bohr's transcendental philosophy of complementarity.

      Uh, well, yeah, I can. I suppose almost all physicists can. It's trivial.

      The "wave" aspect is the quantum amplitude, which obeys the wave equation. The "particle" aspect is the thing the quantum amplitude gives us probabilities about. That is elementary QM. (Very few physicists really take Bohr all that seriously anymore, you know.)

      Now, of course, if you do QFT, you have the fields as the primary object and quantum amplitudes relating to the state of those fields. Simple as pie.

      Now, I know you will not like what I just said, but it is simple textbook QM. So, if you do not like it, don't yell at me but take it up with Feynman, Weinberg, Schiff, Baym, et al.!

      Wave-particle "duality" is no more a mystery today than the question of why the people Down Under do not fall off the planet is a mystery!

      Werner also wrote to me:
      >As I've vainly tried to explain, this is a meaningless question. In the Schwinger/Keldysh formalism there's no mention of "measurement", it's just about statistics and evaluating correlation functions.

      But statistics of what? In standard textbook QM, it is statistics of measurements. In Bohmian QM, it is statistics about the "hidden variables."

      In your theory, I honestly do not understand what the statistics refer to.

      Please let us know.

      Werner also wrote:
      >Imagine a snapshot of the molecules as a sound wave passes through a gas. There are tiny variations of density, and "only" of a statistical nature, since density is a macroscopic concept. In reality there are only molecules. Now just label one direction in this picture "time" and think of it as a distribution of events in space-time.

      Well, for the gas, there are "hidden variables," the positions of the gas particles. This makes it sound is if you think you have some hidden-variable theory.

      Werner also wrote:
      >In the case of sound we are aware that at the fundamental level there are only atoms. But in the case of photons and electrons most physicists regard them as fundamental, rather than derived concepts describing the correlations between events.

      Well, are your events only events we measure, AKA "measurements," or are they something else?

      You seem to think the word "event" makes what you are thinking clear. It does not.

      Werner, I truly think you have some vague words but no actual theory. But show I am wrong: answer my specific questions about your theory.

      Werner also wrote:
      >Fields describe correlations between events, and QFT is a machinery for calculating correlation functions.

      Correlation functions in what situation? The textbook answer would be "measurements."

      Werner also wrote:
      >Incidentally, the absorption of a photon is a composite event and should not be thought of as instantaneous. And points in space-time carry more than space and time coordinates; for something resembling QED also a phase factor and a time tag are necessary. But the details are something I can't squeeze into this comment.

      Ummm... have you actually worked this out mathematically and written it up? Because if you know more about the interaction between photons and electrons than all the rest of us know -- I mean really know not just vague words -- you ought to write it up and collect your Nobel prize!

      Dave

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    14. PhysicistDave wrote: "almost all physicists can [think of a synthesis of the wave and particle concepts]. It's trivial."

      What a shallow notion of "synthesis"! So QM is about particles on Mondays, Wednesdays, and Fridays, about waves on Tuesdays, Thursdays, and Saturdays, and on Sundays we lament on the "measurement problem".

      > "Are your events only events we measure, AKA "measurements", or are they something else?"

      I know of no definition of the term "event" that does not attribute to it a definite place and a definite time. So think of points in space-time. As I reject the term measurement, I also object to singling out some events as measurements.

      You may think there's no physics left if all there is are scattered points in space-time. But consider a mixture of hydrogen and oxygen. It is only a statistical regularity in the positions of the atomic nuclei that distinguishes it from water vapour. It's the different arrangements of the nuclei that theory must describe. Likewise, it's the different arrangement of quarks and leptons that distinguishes your brain from a brick. There's a place for statistics even without "hidden variables".

      > "But statistics of what? In standard textbook QM it is statistics of messurements."

      Gordon Baym's wording is more careful. There's no mention of wave function collapse, or of measurement as some additional process or ingredient of the theory:

      "This connection between physical quantities and operators, the eigenvalues and the possible values of the physical quantities, and the eigenstates and the probabilities of having one of the possible values, is true in all cases in quantum mechanics, not merely for the particular case we have considered. It is the basis for calculating the expected results of measurements made on quantum mechanical systems." (p.17)

      > "I truly think you have some vague words but no actual theory."

      Right. There is no need for a new theory. It is well known under the name QED, and it's extraordinarily successful. But I have more than vague words. Can I dare to call it a "heuristic viewpoint"?

      > "have you actually worked this out mathematically and written it up?"

      No, not to the level of detail that you probably expect. But I invite you to read up on the closed time-path formalism. In my previous life as an astrophysicist I published a paper containing a pedestrian application of the formalism to the calculation of photon absorption and scattering coefficients (J.Phys.A: Math.Gen. 21, 407-418). The paper also discusses the role of interference terms and the distinction between real and virtual intermediate states.

      Werner

      Delete
  14. Stefan,,
    "Changing/breaking the rules" may succeed where following them, as in chess, may not.
    "Oh, yes."
    But, your impression of Sabine may be wrong.
    This QM series is part of a blog which increases the understanding and use of physics among the rest of us. Sabine may have already made the transition your comment may suggest, possibly when she chose to write "lost In Math."
    "Oh, yes."

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    1. Hello, Bert,

      if you solve the Schrödinger equation for the H atom and consider only the ground state,
      you get a spherical wave function with an exp(-r/a) decrease.
      a is the Bohr radius and about a = 50 pm
      a depends on the mass of the electron and some other constants.

      Now we make some scattering experiments with such an atom.
      We let the atoms fly through a double slit or a lattice.
      We will see interference fringes after the summation of many atoms behind the lattice.

      But to understand the streaks, we need a completely different explanation, the de Broglie wavelength.
      The de Broglie wavelength depends on the mass of the proton and the velocity od the atom.
      So the de Broglie wavelength has nothing to do with the 1s-H-atom-wave function.
      But if you look in a table for lattice constants, you will find l~300pm for some metals,
      which is in the order of Bohr's radius.

      In summary:
      We have solved the basic equation of quantum mechanics and obtained a wave function.
      But this solution has nothing to do with the double slit experiment.
      And also strange: The wave function solves a problem that we did not ask for.

      So I wonder how anyone can love this theory.

      Have fun!
      Stefan

      Delete
  15. If the solution to the measurement problem you will offer is superdeterminism I have no problem with that. For whatever it might be worth I think you and Tim Palmer have done something elegant. I've just read a long involved thread following a critique of superdeterminism as you and Palmer presented it (https://mateusaraujo.info/2019/12/17/superdeterminism-is-unscientific/), and I must say I found it depressing. Apparently, in theoretical physics, even people who understand the math very well find certain concepts impenetrable, and fail to agree even on the meaning of the math. Palmer made a good defense, I thought, but it either wasn't understood or there were flaws I couldn't see that the critic saw. I thought the critic misunderstood Palmer's point. I found another critique recently of superdeterminism and I think the gist is that it violates what should be invariant time ordering of events in certain Lorentz frames. I tried to find that paper again but couldn't-- wanted to provide a link. At least you've got a lively discussion going, and I hope something fruitful results. I'm naive enough to think that if you've got the math down then it should all be cut and dried. Apparently not.

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    1. Violations of Bell's inequalities are usually cited for nonlocality.Yet this illustrates really how locality and reality are not compatible concepts. This experiment

      https://arxiv.org/abs/1902.05080

      violates Bellinequalities and enforces locality. This is then the Wigner's friend experiment that demonstrates a failure of objective reality. This is dual or complementary to nonlicality.

      Nondeterminism can be said to be dual to stochasticity and is a way that what appears random can be seen to be a sort of illusion. However, objectivity itself is a sort of illusion. This may appear to be a highly inconveninet way of looking at QM, but it may have some utility.

      Delete
    2. Didn't you mean that determinism is dual to stochasticity?

      Delete
    3. That is a writing glitch. Yes that is the case, and even more with superdeterminism.

      Delete
  16. https://www.nature.com/articles/s41567-020-0990-x

    A strong no-go theorem on the Wigner’s friend paradox

    Nearly 60 years ago, the Nobel prize-winning physicist Eugene Wigner captured one of the many oddities of quantum mechanics in a thought experiment. He imagined a friend of his, sealed in a lab, measuring a particle such as an atom while Wigner stood outside. Quantum mechanics famously allows particles to occupy many locations at once -- a so-called superposition -- but the friend's observation "collapses" the particle to just one spot. Yet for Wigner, the superposition remains: The collapse occurs only when he makes a measurement sometime later. Worse, Wigner also sees the friend in a superposition. Their experiences directly conflict. Now, researchers in Australia and Taiwan offer perhaps the sharpest demonstration that Wigner's paradox is real. In a study published this week in Nature Physics, they transform the thought experiment into a mathematical theorem that confirms the irreconcilable contradiction at the heart of the scenario. The team also tests the theorem with an experiment, using photons as proxies for the humans. Whereas Wigner believed resolving the paradox requires quantum mechanics to break down for large systems such as human observers, some of the new study's authors believe something just as fundamental is on thin ice: objectivity. It could mean there is no such thing as an absolute fact, one that is as true for me as it is for you.

    If somehow observation and the data that comes from it is not absolute, than what is science all about?

    ReplyDelete
    Replies
    1. Wigner's paradox illustrates a major difference between the standard/Bohr interpretation and the rest: observer dependence. Hidden Variables theories, MWI, Superdeterminism, and Objective Collapse all rescue this principle in different ways. It's a fascinating ongoing debate as to whether or not the attempts are successful.

      Delete
    2. It is interesting some reactions to this. I am seeing a lot of people scream as if the barbarians are at the gates about the burn down the libraries. If you want reality or objective facts then you choose to explore nature without locality. With nonlocality one has Bell's nonlocal hidden variables that serve to define reality, at least within QM.

      Delete
    3. Axil wrote: "It could mean there is no such thing as an absolute fact, one that is as true for me as it is for you."

      Also experiments require interpretation. Michelson thought to establish facts concerning the speed of the aether.

      Quantum mechanics is not so mysterious if you know how to apply it. But these new experiments really shed much darkness on the matter. :-)

      Delete
    4. Wignwe is also famous for bringing consciousness within the process of measurement/interaction. It's something that I find quite strange - surely there was a universe around before man was around to observe it.

      Delete
  17. Quantum emitters demonstrate two separate modes of emissions: a dark mode and a bright mode. These modes of emission are carried over to the Bose condensates that these quantum emitters can form. There is a structured level of quantum coherence that these condensates can establish so that the quantum behavior of the quantum emitter becomes observable at the macro scale.
    It is my belief that the dark mode state of this emitter is actually a result of a state of superposition where energy is pumped into it but no energy comes out of it. This leads to the possibility that when in dark mode these macro systems dispose of energy to an unobservable destination. Only when the macro system is exposed to a decoherence producing stimulus does the macro quantum emitter condensate show energy production.

    The strange thing about this case is that the dark mode state can persist indefinitely. We can pump energy into this dark mode macro system till the cows come home and not see any energy exit the dark mode. One does not expect to see this type of behavior in a macro system.

    ReplyDelete
  18. From Griffith News(shown in full to avoid rejection of this post due to unfamiliar web link)

    New quantum paradox reveals contradiction between widely-held beliefs

    Quantum physicists at Griffith University have unveiled a new paradox that says, when it comes to certain long-held beliefs about nature, “something’s gotta give”.

    Quantum theory is practically perfect at predicting the behaviour we observe when we perform experiments on tiny objects like atoms. But applying quantum theory at scales much larger than atoms, in particular to observers who make the measurements, raises difficult conceptual issues.

    In a paper published in Nature Physics, an international team led from Griffith University in Australia has sharpened those issues into a new paradox.

    “The paradox means that if quantum theory works to describe observers, scientists would have to give up one of three cherished assumptions about the world,” said Associate Professor Eric Cavalcanti, a senior theory author on the paper.

    “The first assumption is that when a measurement is made, the observed outcome is a real, single event in the world. This assumption rules out, for example, the idea that the universe can split, with different outcomes being observed in different parallel universes.”

    “The second assumption is that experimental settings can be freely chosen, allowing us to perform randomised trials. And the third assumption is that once such a free choice is made, its influence cannot spread out into the universe faster than light,” he said.

    “Each of these fundamental assumptions seems entirely reasonable, and is widely believed. However, it is also widely believed that quantum experiments can be scaled up to larger systems, even to the level of observers. But we show that one of these widely held beliefs must be wrong! Giving up any one of them has far-reaching consequences for our understanding of the world.”

    The team has established the paradox by analysing a scenario with well-separated entangled quantum particles combined with a quantum ‘observer’ – a quantum system which can be manipulated and measured from the outside, but which can itself make measurements on a quantum particle.

    “Based on the three fundamental assumptions, we have mathematically determined limits on what experimental results are possible in this scenario. But quantum theory, when applied to observers, predicts results which violate these limits. In fact, we have already performed a proof-of-principle experiment using entangled photons (particles of light),” said Dr Nora Tischler, a senior experimental author. “And we found a violation just as quantum theory predicted.”

    “But our ‘observer’ had a very small ‘brain’, so to speak. It has just two memory states, which are realised as two different paths for a photon. That’s why we call it a proof-of-principle experiment, not a conclusive demonstration that one of the three fundamental assumptions in our paradox must be wrong,” she said.

    “For a more definitive implementation of the paradox, our dream experiment is one where the quantum observer is a human-level artificial intelligence program running on a massive quantum computer,” said Professor Howard Wiseman, the leader of the project and Director of Griffith’s Centre for Quantum Dynamics, where the theoretical and experimental teams are based.

    “That would be a pretty convincing test of whether quantum theory fails for observers, or whether one of the three fundamental assumptions is false. But that’s probably decades away.”



    “It has long been recognized that quantum computers will revolutionise our ability to solve hard computational problems,” Professor Wiseman said.

    “What we didn’t realise until we started this research is that they may also help answer hard philosophical problems – the nature of the physical world, the mental world, and their relationship.”

    ReplyDelete
    Replies
    1. "“For a more definitive implementation of the paradox, our dream experiment is one where the quantum observer is a human-level artificial intelligence program running on a massive quantum computer"

      Is that all you need.

      Delete
  19. Hi Sabine, thanks for this. Here is a suggestion for a future video that I think really gets to the heart of it:

    "Admit we have a measurement problem or give up on scientific reductionism... pick one!" and then reiterate your very crucial point about the non-linear character of the measurement postulate, how this postulate is critical to describe what we observe, and how it is incompatible with the linear evolution of the wave function. Thanks!

    ReplyDelete
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    1. @ manyoso,

      1. Even if classical atomism was correct (i.e., neglecting QT); it wouldn't be capable of classifying those complex, dynamic patterns that correspond to "living persons"!

      2. In my approach (perspectivism) there is no "measurement problem" (see my paper "The Mathematical Foundations of Quantum Mechanics" on my website.)

      Delete
    2. manyoso: Aren't you just describing the video we just watched?

      She doesn't need to hand out any fallacious ultimatums (fallacy of the excluded middle, the either-or fallacy).

      She just said many physicists think decoherence solves the problem, and then demonstrated mathematically what decoherence is and that it does not solve the problem; in fact it clarifies the problem in stark terms.

      I fail to see why the video you suggest would not just be redundant.

      Delete
    3. The difference is this video she did not emphasize what I see as her key point: disputing that we have a measurement problem is tantamount to giving up on scientific reductionism. Sabine *has* emphasized this in the past, but not in this video. And I really do believe it is the crux of her argument. Scientific reductionism demands that we admit there is a measurement problem.

      Delete
  20. If we regard the measurement as a perturbation, forcing a linear process into a non-linear excursion whose details we do not understand because that excursion is brief and complex? That is not unheard of in thermodynamics. What the wave equation would correspond to is a description of an equilibrium state. I think others have pointed out parallels to thermodynamics. For me, going off in this direction looks interesting but whether it would clarify anything I don't know.

    ReplyDelete
  21. Sabine wrote:

    “The idea of decoherence is then to say that each time the particle bumps into some other particle, this phase randomly changes and what you actually measure, is the average over all those random changes.”

    You don’t even need external particles or random changes. All you need to get decoherence is to require that the states you are measuring should NOT be eigen-states of the Hamiltonian. Then, time evolution would mix up the phases and give you decoherent states.

    ReplyDelete
    Replies
    1. Udi Fuchs wrote:
      >You don’t even need external particles or random changes. All you need to get decoherence is to require that the states you are measuring should NOT be eigen-states of the Hamiltonian. Then, time evolution would mix up the phases and give you decoherent states.

      No, Udi that is a mistake.

      Take an electron in a magnetic field: two states with different energies, so that the phases constantly change over time. As long as your state is not an eigenstate of the Hamiltonian (i.e., spin aligned or anti-aligned with the B field), then, yes, the state will change with time.

      But that is not what physicists mean by "decoherence." Yes, in that case the relative phases change over time, but in a completely predictable and simple manner. Indeed, in that case we periodically get the original state back.

      Sorry, but you are missing the point: decoherence is more subtle than you envision it. In principle, decoherence never really occurs. But, for all practical purposes, in complicated systems in which it is impossible to accurately account for all interactions or keep accounting for all the phases, then you have decoherence.

      Delete
    2. As Dave said.

      But let me add (though it should be obvious) that the explanation in my video is illustrative (I hope) but somewhat vague on what is mathematically really happening, namely you create an entangled state with the environment and then average over ("trace out") the environment. In the simplest case though, this has the very effect that I am talking about. I couldn't think of a good way to explain "tracing out" without significantly increasing the math load first. So, sorry about being somewhat sketchy.

      Delete
    3. Udi Fuchs,

      I hope it is clear that neither I nor Sabine is accusing you of being foolish! There are some subtleties involved here that I am not sure anyone really fully grasps.

      As Sabine said:
      > you create an entangled state with the environment...

      Indeed. But what exactly is "the environment"??? Well, for all practical purposes, that is usually obvious. But in principle... ? Such questions tend to boil down ultimately to the (in)famous measurement problem.

      Incidentally, for anyone who wants to pursue this in detail, the standard text is Schlosshauer's Decoherence and the Quantum-to-Classical Transition, very detailed and relatively readable, considering the subject (best if the reader is at least an advanced undergrad in physics, though parts are accessible to interested laypeople). Schlosshauer is remarkably honest in making clear that decoherence does not fully solve all the foundational and conceptual issues, though I think it is fair to say that most of us physicists think that people who do not understand decoherence may have trouble really dealing with such issues.

      I should admit that I myself have not fully absorbed the book (although I have read the more entertaining chapters).

      All the best,

      Dave

      Delete
    4. PhysicistDave9:36 PM, August 19, 2020

      Dave, you are a proven liar. You literally wrote the opposite answers to the same question asked at different times.

      It's good to see you spending your last days correcting people who aren't very good at Physics to make you feel good about yourself, but you are a proven, barefaced liar. You have reached the end of your life, and all you are is a liar.

      PhysicistDave4:56 AM, July 30, 2020
      SE: 'you claimed that you could refute by logical proof the possibility of conscious experience being weakly emergent from a physical brain.....'

      DM: "Yes, I have such a proof,"

      PhysicistDave12:50 AM, August 07, 2020
      SE' You claim to have a "logical proof" that mind cannot be emergent from matter, but have provided no proof.'

      DM "Where have I said that????"


      Hume's ought/is argument and the fact the term "conscious" doesn't appear in Physics show that the mind cannot be emergent from the brain, don't they, Dave?

      Dear, oh dear.

      I see why you failed at Physics - you're completely thick as well as a liar.

      Delete
    5. Let me add that Schlosshauer has a pdf of the book on the arXiv, you find the link in the information below the video on YouTube.

      Delete
    6. PhysicistDave12:22 AM, August 20, 2020

      "I hope it is clear that neither I nor Sabine is accusing you of being foolish! "

      Dave, I hope it is clear that I am accusing you of being a barefaced liar:

      PhysicistDave4:56 AM, July 30, 2020
      SE: 'you claimed that you could refute by logical proof the possibility of conscious experience being weakly emergent from a physical brain.....'

      DM: "Yes, I have such a proof,"

      PhysicistDave12:50 AM, August 07, 2020
      SE' You claim to have a "logical proof" that mind cannot be emergent from matter, but have provided no proof.'

      DM "Where have I said that????"


      You, Dave Miller, are a barefaced liar. This will be your soon-to-appear epitaph.

      Delete
    7. Dave,

      You wrote on Aug 4, 12:53am

      "What I have proven is that the currently known laws of physics cannot explain consciousness."

      As I have said before, I don't like Steven's aggressive mode of argumentation, but I am with him on this. You have not provided a proof, and unsurprisingly, because there is no proof. Instead, I have proved over and over again that for all we currently know about the laws of nature consciousness is weakly emergent. If it wasn't, this would be in contradiction with the standard model.

      I know that a lot of people find this hard to grasp because they don't understand how effective field theories work, but I was hoping that's a problem I wouldn't encounter with you.

      Delete
    8. Steven Evans,

      You are still in a really bad mood, son, aren't you?

      The lockdown giving you cabin fever?

      Look: as I have explained, more than once, different people use "weak emergence" in different ways, and I therefore try not to use the phrase myself.

      I do have a preferred meaning of "weak emergence" and, yes, by my preferred meaning, I have proven that consciousness cannot “weakly emerge” from physical processes as currently explained by the currently known laws of physics. But other people mean other things by the phrase, and I am not dogmatic about the "true" meaning. My proof may or may not apply to some other uses of that phrase.

      It is not lying for me to ask you where I said something. I will note that in the case you cite, it was you, not I, who chose to use the phrase "weak emergence." (And, yes, you can probably dig up some place on the Web where I did use the phrase myself, even though I generally try not to because I know it is used by different people with different meanings.) As far as I can see, in the comment thread you cite, I did not choose to use the phrase myself, and, in fact, in the comment that you cite, after quoting your statement about "weak emergence," I did make very, very clear what I was claiming in my proof, so that no one need be confused by miscommunication involving the phrase "weak emergence."

      In fact in a comment in the same thread you quote from, I explained why I try to avoid this phrase and did my best to clear up any confusion.

      Words can be confusing and can be used in different ways. But if I say I left my money in the bank, and you complain that I did not in fact leave it on the edge of the river, it is you who is being disingenuous. I have gone out of my way, including in the comment from which you quote, to express myself in a way that is unlikely to be misconstrued by any honest person.

      Steve also wrote:
      >It's good to see you spending your last days correcting people who aren't very good at Physics to make you feel good about yourself, but you are a proven, barefaced liar.

      Steve, I am pretty sure that you are not really so nasty that if you really thought I was in my "last days" you would be so crude as to harp on the matter. Now, I could be nasty in return and suggest that, unlike you, I have actually been shaving for more than five years!

      Kinda silly, eh? Anyway, I will try not to hold your youth and inexperience against you.

      In any case, you are just playing silly little gotcha word games to no purpose. That is obviously because you know I did prove something of significance, which you cannot seriously refute, and so you are reduced to silly word games.

      You used to have some interesting comments.

      But, now, Steve, you are becoming boring. Very, very boring.

      Steve, really: what did religious believers do to you that you are so consumed with hatred that you are driven mad by the possibility that physics as it now exists cannot explain consciousness? Why does that make you so rabid?

      I have known a lot of religious nuts, but very few who are as consumed with their dogmas as you are!

      Calm down and take better care of yourself, Steve. Maybe getting outside and getting some fresh air will help. The lockdown will not last forever.

      All the best,

      Dave

      Delete
    9. PhysicistDave5:14 AM, August 20, 2020

      Yes, yes, Dave, turn it on me - what a cunning troll you are. Writing 30 comments repeating the same illogical nonsense and attempting lame smears of me. You earned a couple of digs about your age.

      And unfortunately, you are now on the record as a proven, barefaced liar:

      PhysicistDave4:56 AM, July 30, 2020
      SE: 'you claimed that you could refute by logical proof the possibility of conscious experience being weakly emergent from a physical brain.....'

      DM: "Yes, I have such a proof,"

      PhysicistDave12:50 AM, August 07, 2020
      SE' You claim to have a "logical proof" that mind cannot be emergent from matter, but have provided no proof.'

      DM "Where have I said that????"


      Got a proof, not got a proof? Which is it, Dave?

      Do you want to explain your blatant, barefaced lie, you naughty, little boy?

      You were lying all along and well we both know it. You can't get an "ought" from an "is" therefore the mind 100% cannot be emergent from the brain? The most stupid non-sequitur in the history of the world.

      No wonder your Physics career was a failure. You don't even understand basic logic.

      Delete
    10. Sabine Hossenfelder4:55 AM, August 20, 2020

      "As I have said before, I don't like Steven's aggressive mode of argumentation, "

      Soz, Dr. H. But I am still way behind the benchmark set by Luke Barnes of fantasising about killing me because I pointed out his book was complete nonsense:

      "lukebarnes6:20 AM, December 04, 2018
      When I am Supreme Emperor of Spacetime, there will be a law that says: on pain of death, the sentence "I haven't read the book" must be followed by "and so I don't have an opinion about it.""

      What a psycho lunatic fantasist Bible Boy is.
      Maybe that's why Phillip Helbig gave the book a whitewash review - he was worried for his life.

      "but I am with him on this."

      Read it and weep, Dave. You don't get to write your bizarre married couple-sounding "Sabine and I" about this one, as if the whole Physics world is on the side of your ludicrous "ought/is" non-sequitur.

      Delete
    11. If I were monitoring this blog these sorts of kvetching, kibitz, quibbling screeds would be deleted.

      Delete
    12. If you want to moderate my comment section, you are more than welcome. Trust me, I can think of better ways to spend my time.

      Delete
    13. Sounds as much fun as a visit to the dentist.

      Delete
    14. Sabine,

      Re Sabine Hossenfelder 4:55 AM, August 20, 2020:

      Only the information content of consciousness can potentially be explained by physics and logic. E.g. consciousness of a tree in one’s surroundings is clearly a result of the brain/mind (in effect) analysing photon interactions with the eyes. This information content can potentially be represented as a new category of information “emerging” due to new relationships/ equations and logic. What “emerges” is new categories of information, i.e. new information content.

      But the feeling/ subjective experience of the information content is an aspect of consciousness that can’t be explained by physics and logic. There are seemingly only 2 choices:

      1. Posit that subjective experience of primitive-level information content is already present in particles.
      and/or
      2. Acknowledge that nothing can ever be proved. Just like one can’t prove that particles do (or don’t) subjectively experience information, one can’t prove that subjective experience of information content could ever emerge.

      Delete
    15. Lawrence Crowell12:50 PM, August 20, 2020

      "If I were monitoring this blog these sorts of kvetching, kibitz, quibbling screeds would be deleted."

      I'm not sure you would make a wholly impartial monitor.
      Would you also delete the "puerile" (your word) comments pointing out the rather critical point that there is no empirical evidence for MWI or inflation, and would you delete my corrections to your several basic Maths blunders?

      The facts are the facts. Dave's a proven liar and Luke Barnes is a lying sociopath and Templeton-funded fifth columnist.

      Delete
    16. Dave wrote:

      “There are some subtleties involved here that I am not sure anyone really fully grasps.”

      I’m saying exactly the opposite. Decoherence is fairly simple. Decoherence due to interaction with external particles can get really complicated. But to understand the fundamental reason why an interference pattern disappears, you don’t need to worry about all these complications.

      Dave wrote:

      “the standard text is Schlosshauer's Decoherence and the Quantum-to-Classical Transition”

      I looked at this paper from 2014 and the expanded version from 2019. In the introduction he writes:

      “The key insight in addressing the problem of the quantum-to-classical transition was first spelled out almost fifty years ago by Zeh [1], and it gave birth to the theory of quantum decoherence, sometimes also called dynamical decoherence or environment-induced decoherence[1–9].”

      First it explain one misunderstanding, that when he talks about decoherence, he actually means “environment-induced decoherence”. I just wished that he would have introduced simple decoherence, before going into environmental decoherence. At the end of the day, Environmental decoherence essentially ends up with an estimate of a decoherence timescale, which is equivalent to the decoherence you get from a simple Gaussian wave packet.

      Schlosshauer paper mostly concentrates on environmental decoherence, which is an interesting subject, which is very relevant to many quantum experiments.

      What I am saying is that for understanding the conceptual issues in quantum mechanics that Sabine is talking about, there is no need to go into these complications. The simple decoherence of the wave packet encapsulates all the relevant parts.

      Delete
    17. Lawrence Crowell wrote:
      >If I were monitoring this blog these sorts of kvetching, kibitz, quibbling screeds would be deleted.

      Well, Lawrence, if I were moderating the blog, I would let Steve's comments through, even though I am currently the main person he is spewing invective at (I am comfortable with the fact that Steve puts me in the same category as Phil Helbig and Luke Barnes – okay guys to associate with!).

      Steve's comments are self-revealing: he is actually damaging his own position.

      The sad thing is Steve is not actually a moron. He does sometimes raise valid points. I have actually sharpened and clarified some of my own arguments by thinking about and responding to some of his criticisms.

      Steve has some personal issues with religion, I suspect as a result of childhood experiences. I do, too: to this day I resent the people who caused me to have terrifying nightmares about Hell because they were literally trying to “scare the Hell out of me.”

      Although I do hope my public approach to religious believers is a bit more restrained than Steve's.

      Anyway, maybe that is why I am willing to cut Steve some slack.

      All the best,

      Dave

      Delete
    18. Steven Ecans wrote:
      >[Steve] But I am still way behind the benchmark set by Luke Barnes of fantasising about killing me because I pointed out his book was complete nonsense:

      "lukebarnes6:20 AM, December 04, 2018
      >[Luke] When I am Supreme Emperor of Spacetime, there will be a law that says: on pain of death, the sentence "I haven't read the book" must be followed by "and so I don't have an opinion about it.""

      Luke was joking, Steve.

      That was quite obviously a joke: you see, Luke knows that he will never be “Supreme Emperor of Spacetime.”

      Calm down, Steve: Luke is not going to kill you!

      Delete
    19. PhysicistDave3:13 AM, August 21, 2020

      That's right, Dave. It is perfectly normal for a scientist to fantasise in public about killing the critics of his book rather than answer the criticisms.

      Like Bible Boy, you are just angry that you have lost an argument and been ridiculed and humiliated. It's better just to admit you were wrong and move on than repeat the same lie 30 times like a maniac.

      Delete
    20. PhysicistDave3:11 AM, August 21, 2020

      Dave, you are a proven liar. Everybody can see:

      PhysicistDave3:25 AM, April 29, 2020
      "I have hated and despised pathological liars and con artists since I was a very young child in grade school six decades ago."

      PhysicistDave4:56 AM, July 30, 2020
      SE: 'you claimed that you could refute by logical proof the possibility of conscious experience being weakly emergent from a physical brain.....'

      DM: "Yes, I have such a proof,"

      PhysicistDave12:50 AM, August 07, 2020
      SE:' You claim to have a "logical proof" that mind cannot be emergent from matter, but have provided no proof.'

      DM: "Where have I said that????"


      Hoisted by your own petard, Dave "I have hated and despised pathological liars since I was a very young child" Miller caught in a blatant lie.

      You don't have that long, Dave.

      You will feel much better about yourself if you now make your deathbed confession to me, admit you have been a heinous liar and ask for my forgiveness.

      Hume's ought/is argument does not imply the mind cannot be weakly emergent from the brain. Don't be daft.

      Confess, Dave - you're a liar and a troll! (but have a solid background in QM)

      Delete
    21. PhysicistDave3:11 AM, August 21, 2020

      "Well, Lawrence, if I were moderating the blog, I would let Steve's comments through,"

      Well that's extremely generous of you. Fortunately the blog is run by Dr. H. who understands basic logic, unlike you, Dave, and understands the requirement for empirical evidence in Physics and has studied some Maths, unlike Lawrence apparently.

      You know you are trolling and lying, here and about the ought/is nonsense. I know it. And Dr. H. knows it.

      Who do you think you are kidding, Dave? Get a check for Alzheimer's - I think you are losing your mind.

      Delete
    22. Lorraine Ford10:51 PM, August 20, 2020

      "But the feeling/ subjective experience of the information content is an aspect of consciousness that can’t be explained by physics"

      How. do. you. know. this. Lorraine?

      Are you in possession of a complete blueprint of the brain which rules out an emergent mind? I don't think so.

      Do you have evidence of some input into the mind other than the brain? No.

      So what are you talking about in your thousands of comments? You just keep repeating your claim with no evidence.

      You have said before that reproducing human intelligence in silicon is impossible, but here is how to instantiate your brain in silicon:

      For i = 1 to the heat death of the universe
      Print "Consciousness can't emerge from a physical brain";
      Read response; //ignore contents of response
      Next i

      Your brain is a trolling bot that can be written in 4 lines of C.

      Delete
    23. There is a podcast of Sean Carroll and Luke Barnes on premierchristianradio website. They argue over the issue of fine tuning. I do not include the actual website, but one can look that up.

      Delete
    24. Calm down Steven: You might burst a blood vessel, or give yourself a stroke or a hernia, or something.

      Delete
    25. Lawrence Crowell6:44 AM, August 22, 2020

      "There is a podcast of Sean Carroll and Luke Barnes on premier christian radio website."

      And there is a steaming dog turd on the pavement in the middle of my street.

      I remember listening to this. The website should be renamed after the host - Smug Christian T**t radio. At least the media whore Carroll stops his media whoring for long enough to point out that Bible Boy doesn't have any evidence for his whacko delusion. You are in trouble if even Sean "no tenure" Carroll can spot your theory has no empirical evidence - he promotes all kinds of evidence-free garbage usually.

      In reply, Bible Boy lamely claims that we should consider the possibility anyway. And given the Templeton Foundation have given Bible Boy $500,000+ to consider the possibility, one can see why. It's called corruption.

      The money keeps Bible Boy in pies and pizza. If you listen carefully during the recording, you can hear Bible Boy getting even fatter as he munches on his 10,000th Templeton-funded pie.

      Being a corrupt liar is hungry work.

      Delete
    26. Lorraine Ford9:46 AM, August 22, 2020

      What a relief - it looks like an exception has been thrown in your brain's programming and you have exited your infinite loop. Has the comment section been saved from another thousand "IF...THEN" unjustified claims?

      Delete
    27. @ Evens: Wow, you need to take a vacation or maybe you are in dire need of making hot love. One of the smartest physicists I have ever met was Marlin Scully, and he is religious. It happens, Don Page is rather on the religious side.

      I am not a strong upholder of theistic ideas. If there is some sort of master conscious intelligence behind existence I think it is most likely to be far different than any perspective of God in religions. It seems rather strange that a God that generates all of existence is foaming out the mouth with vengeance if I put on a dress and attend a drag show, or eternally damns anyone who has not accepted Jesus and so forth. What is really funny is how so many think God is like somebody watching a football game rooting for Republicans in the next election.

      Theism tends to suggests things are upside down. It is almost similar to the idea ancient astronauts made pyramids and so forth, which BTW are preposterous. Existence appears most plausible to have a foundation on the most simple of things, say an elementary vacuum, and complexity by combinatorial interactions builds up. Theism works the other way, and everything we find tells us otherwise.

      However, one has to have some measure of tolerance with these things. Generally I tend not to talk that often about religion with people. In fact I try to avoid the topic like death itself.

      Delete
    28. @Crowell:

      Serious theism has had quite a number of attempts at characterising the relationship between God and the world, and none of them include ancient astronauts.

      The most believable of them is that Gods Will manifests itself in the world as the laws of nature - this is in Spinoza for example.

      As for God regulating what people wear, this is about the nafs, or ego; in a word - greed - which in more contemporary capitalist discourse that has become comfortable with this is translated as desire - live your desires, be what you desire, max out your desires, you can never have too much etc, etc, etc.

      It's not for the good of God that these 'regulations' were set down, but for the good of man. Perhaps he'll get a chance to reflect on them after his desires have burnt up the earth and there isn't much of an earth to desire over.

      Delete
    29. Mozibur: I don't believe in ancient astronauts, but a belief in them as an explanation of "Gods" is actually not any form of theism at all. Ancient Astronaut Theorists are making a scientific hypothesis, that Fermi's Paradox is wrong: Advanced technological life evolved elsewhere, perhaps many millions of years before humans, and that helps to explain many actual ancient technological mysteries (as well as a host of faux mysteries, I will readily agree).

      But it is not theism. If anything it is atheism, I haven't heard any Ancient Astronaut Theorists expressing any belief in actual Gods, to them the "Gods" were evolved aliens either intentionally posing as Gods or mistaken by primitive humans for Gods; because as Arthur C. Clarke said, "Any sufficiently advanced technology is indistinguishable from Magic."

      Delete
    30. Sabine wrote to me:
      >You have not provided a proof, and unsurprisingly, because there is no proof. Instead, I have proved over and over again that for all we currently know about the laws of nature consciousness is weakly emergent. If it wasn't, this would be in contradiction with the standard model.

      Well, Sabine, different people mean different things by "weak emergence," and I have found it fruitless to argue about which meaning is "right."

      All I claim to have proven is a very simple, almost trivial application of a basic theorem about formal logic: a conclusion to a proof cannot include terms that are not included in the axioms or the premises, except tautologically of course.

      Going back to Galileo, we physicists have intentionally eschewed mentalistic terms (primary and secondary qualities and all that) in our physics theories, quite wisely of course. (No doubt this has a bit to do with the fact that many of us who are attracted to physics: do not really want to talk that much about "feelings"!)

      You cannot derive a conclusion that is about something not present in the axioms or premises.

      I assume it is obvious how to prove this theorem about formal logic. You can just do it by induction on the length of the proof. There are also model-theoretic ways to prove it. It is so trivially obvious that most logicians would not even bother to give a detailed proof.

      Our friend, Dr. AMC, has raised the question of whether definitions can be used to evade this basic principle of logic. In formal logic, definitions are just convenient abbreviations. “Expand out” the definitions and the theorem still holds.

      I think you, and probably my friend Steve Evans, want to attribute to me a grander claim than I am making. I am not talking about what other people may mean by “weak emergence,” as I have explained to Steve again and again. I am merely talking about the very narrow issue of what can in fact be derived from existing physical theories as a matter of logic. I think you mean something more than that when you talk of “weak emergence,” though I am not clear what that is.

      As to whether my point would disprove the Standard Model, it would merely show that the Standard Model is incomplete, which of course everyone already knows (quantum gravity and all that).

      As I have said many times, this incompleteness of the Standard Model might consist in the almost trivial fact that we need a "translation dictionary" that tells us what physical states of the brain correlate to what conscious experiences.

      Neuroscientists are busy at work on such a "translation dictionary" right now, of course, and while it would, in some sense, be an extension to the Standard Model, it would not be inconsistent with the Standard Model at all.

      Even so, it would raise some interesting questions: e.g., how does this "translation dictionary" apply to jellyfish or silicon intelligences, or whatever.

      But, yes, I do also leave open the possibility that understanding consciousness will change the Standard Model: I do not know and neither does anyone else.

      After all, we all expect (and hope) that there will be future extensions and corrections to the Standard Model. If understanding black-body radiation was sufficient to trigger the quantum revolution, who knows what understanding consciousness will trigger?

      Maybe nothing more than the obviously necessary "translation dictionary." Or maybe something bigger.

      Neither you nor I nor anyone else knows. "Prediction is hard -- especially of the future!"

      All the best,

      Dave

      Delete
    31. Dave,

      "You cannot derive a conclusion that is about something not present in the axioms or premises."

      Of course you can. I can prove that there exists no holomorphic function on the entire complex plane that's not just a constant. It follows that Dave is not a non-constant, holomorphic function on the entire complex plane. I can draw that conclusion despite Dave not being in the assumptions.

      For the same reason I can make a statement about consciousness. Nothing is strongly emergent. Hence, consciousness is not strongly emergent.



      Delete
    32. @PhysicistDave: Dr. AMC has raised the question of whether definitions can be used to evade this basic principle of logic."

      This is false. I did not "raise the question", I stated categorically you left it out and it is disproves your logic.

      As Dr. Hossenfelder notes (as I see it), there is also the fact of implicit definition; she doesn't have to define "Dave" in the premises or axioms in order to make a conclusion about "Dave", any rational person reading her proof already knows who Dave is.

      Your claim "In formal logic, definitions are just convenient abbreviations" is also false, as I demonstrated.

      Many definitions simply rely on human experience, we know what the "Northern Lights" are by seeing them. We knew what "dogs" were and could study them before we had any notion of evolution or genetics that might precisely define "dogs". We could track and record and predict the positions of Constellations 5000 years before we knew what stars were, there was no definition of the constellation Sagittarius other than "that pattern of stars right there, next to those other patterns of stars."

      The axioms and definitions you use are flawed, so you come to wrong conclusions.

      A definition of the Northern Lights only needs to distinguish the consensus of what investigators consider IS the phenomenon from what IS NOT the phenomenon, based on their experience, for the purpose of relevant study. That definition may be refined as more is learned about the phenomenon.

      If we study dogs, we don't need a formal definition of what "ears laid back" or "bared teeth" mean, those are labels for a generalized version of experiences we have agreed upon. And we can formally reason using those definitions, without substituting any other words; fellow researchers agree on what is and is not "bared teeth." A happy dog may expose its teeth, but that is not 'bared teeth'.

      Definitions are ultimately grounded in experience, not logic, and can themselves therefore be axiomatic, even if unstated in a theorem. The Northern Lights means what it means, it is a label for a human experience; and there many centuries there was description but no precise definition of this experience, while it was being scientifically studied.

      Delete
    33. To be more specific about consciousness, what type of thing is consciousness supposed to be? Is consciousness like: 1) matter; or like 2) lawful relationships, variables, and numbers (or information derived from lawful relationships, variables, and numbers)?

      If one said that consciousness is LIKE a type 2 thing possessed by a type 1 thing, i.e. like mass or velocity, you’d have to wonder why consciousness would generate such a controversy.

      But if one said that consciousness is OF a type 2 thing possessed by a type 1 thing, you’d have think that consciousness is exactly what it seems to be.

      Delete
    34. Sabine wrote to me:
      >For the same reason I can make a statement about consciousness. Nothing is strongly emergent. Hence, consciousness is not strongly emergent.

      Oh, I agree. I think the phrase “strongly emergent” is meaningless. It applies to nothing, just as “gifferish” applies to nothing. I have never seen anyone give a coherent explanation as to what “strongly emergent” is supposed to mean.

      I think that “weakly emergent” is next to meaningless also, which is why, as I have said again and again and again, I try to avoid it.

      On the other hand, I trust that you agree with me that QCD is neither weakly nor strongly emergent from QED. QCD is certainly not predicted nor explained by QED. It is just a different law of nature.

      Same for consciousness. It is neither weakly nor strongly emergent from the laws of physics as they are now understood.

      I think we are dealing with a rather bizarre intellectual opinion on the part of (some) physicists that everything must somehow emerge, weakly or strongly, from currently known laws of physics as they are known in 2020

      But none of us really believes that. We do not believe that, in 1960, physicists should have acknowledged that QCD was implied, weakly or strongly, by the laws of physics known in 1960. Clearly it was not. QCD was something physicists just did not know in 1960.

      Similarly, almost no one today believes that quantum gravity is either weakly or strongly emergent from the laws of physics as we currently know them. Quantum gravity is just something beyond the laws of physics as we now understand them.

      The same is true of consciousness: it is like QCD in 1960 or quantum gravity today. It is just something that is not explained by the laws of physics as we know them today.

      There is, I am afraid, a rather strange insecurity among (some) physicists in being reluctant to concede that there are things about reality that are not explained by the laws of physics that we currently understand.

      I know that reductionism has been stunningly successful: in 1900, the laws of physics that were then known in 1900 could not explain what made the stars shine or what caused atoms to form chemical bonds or why some materials were metals and some were insulators. Of course, all of that, and much, much more, can now be understood in terms of the laws of physics as they are understood in 2020.

      Similarly, in 2020, there are three “dark clouds” upon the distant horizon that cannot be explained by the currently known laws of physics, as they are understood in 2020: the quantum measurement problem, quantum gravity, and consciousness.

      Perhaps (I certainly hope so!), as physics changes wildly and dramatically in the next 100 years, just as it has changed since 1900, the new physics of 2120 will indeed explain the quantum measurement problem, quantum gravity, and indeed consciousness.

      But not yet. Not with the laws of physics as they are currently understood in 2020.

      That is all I am saying. If you think I am saying more than this, you misunderstand me.

      I find it quite bizarre that this is even controversial. Historically, this has always been the case. Today, everyone agrees that, say, quantum gravity is not explained by the currently known laws of physics. And, today, no one even has a serious stab at explaining consciousness in terms of physics.

      When I point out that the laws of physics as currently understood do not explain consciousness, this really should elicit a bored, “Well of course – what else is new?”

      You and I know a very bright blogger (if I mention his name it seems to trigger trauma in some of the commenters here!) who is absolutely sure that superstring theory has been proven to be correct. As much as I like and respect this fellow, on this he is mistaken, and I do not think it is helpful to physics to deny that superstring theory is still unproven.

      Similarly, it is not helpful to physics to claim that the currently known laws of physics can explain consciousness.

      All the best,

      Dave

      Delete
    35. PhysicistDave7:56 PM, August 25, 2020

      Stop your lying and trolling.

      It is absolutely not possible for the mind to be describable in terms of the current laws of Physics. You have a "logical proof" of this, you claim... depending on the day.

      ** Nobody believes you **

      **** Except Lorraine ****

      So provide the proof or withdraw the lies. Everybody here will concur if it is an actual "logical proof" as you have repeatedly claimed.

      So let's have it. Provide your "logical proof".

      Delete
    36. PhysicistDave says: Same for consciousness. It is neither weakly nor strongly emergent from the laws of physics as they are now understood.

      That is an assertion without proof.

      Emergent simply means new properties or types of behavior that are the result of interacting components.

      A motor is composed of parts, none of which provide movement on their own. When the parts are properly arranged, then that arrangement allows interactions and the motive power of a motor emerges.

      One could say the same thing about atoms in iron; in the wrong arrangement they are not a magnet, when properly arranged they have an emergent magnetic power more extensive than any individual iron atom.

      One could say the same thing about fluids. The individual molecules of H2O do not obey the laws of fluid dynamics, because those assume interactions of proximity to other H2O molecules. Arranged together in a liquid state in certain conditions of gravity and pressure, while still obeying the laws of physics, they will also obey the laws of fluid dynamics, which themselves are emergent statistical approximations of the outcome of many trillions of interactions obeying the laws of atomic physics.

      You cannot prove that consciousness is anything different. You cannot prove that physics needs an overhaul or needs to "change wildly and dramatically" in order to explain consciousness. You cannot prove consciousness is anything but emergent from biology which is emergent from chemistry which is emergent from the laws of physics as we know them now.

      To make a scientific claim about the non-emergence of consciousness, you must prove that it has some property or capability that is categorically not possible within the laws of physics as we know them. And you (and Lorraine) have certainly not done that.

      It is because of that your claim should not be taken seriously.

      We all know that the measurement problem is (apparently) unexplainable by the current laws of physics, as is Dark Matter and Dark Energy and the infinite densities and attractions of General Relativity that might be solved by a quantum theory of gravity.

      Unlike those, consciousness may be a mystery, but there is nothing about it that seems categorically in violation of the laws of quantum or macro physics, quantum chemistry or biology, or is categorically unexplainable or in violation of those sciences.

      You can't even define "consciousness" in any terms that would let you prove it is incompatible with those sciences; like the Northern Lights, it is an experience we can recognize and label, without any formal criteria.

      You don't get to just assert something is true without evidence. Show your work.

      Delete
    37. Dr Castaldo,

      There are 2 issues:

      First, there is the issue of what information actually exists, and from whose point of view it exists. E.g. binary digits only exist from the point of view of the 100% lawful human mind/brain structure: there is no such law-of-nature lawful “binary digit” information that exists from the point of view of a computer.

      The only information that exists is lawful information: your idea that “arrangement” could somehow be lawful information that lawfully causes outcomes is just rubbish; “arrangement” is only information from the point of view of the human mind/brain, or other living things, that can somehow analyse lawful information coming from their surrounding environment.

      Second, we know that lawful information exists, but

      consciousness of lawful information

      is not the same as

      the existence of lawful information.

      Delete
    38. PhysicistDave7:56 PM, August 25, 2020

      More lies and breadcrumbing. You are utterly shameless.

      " And, today, no one even has a serious stab at explaining consciousness in terms of physics."

      Nobody in these comments has written otherwise, so why do you write these irrelevances? It's just breadcrumbing.

      "When I point out that the laws of physics as currently understood do not explain consciousness, "

      More lies. Everyone knows that conscious experience *hasn't* been explained in terms of the current laws of Physics.

      But you are claiming that conscious experience ** cannot ** be explained in terms of the current laws of Physics. Further, you make the insane claim that you have a "logical proof" of this.

      Now, of course, I know, you know and everybody else knows - you have no proof; you just don't want to admit you have made a very, very stupid claim.

      It is absolutely bizarre behaviour.

      Delete
    39. Dr. A.M. Castaldo,

      "We all know that the measurement problem is (apparently) unexplainable by the current laws of physics"

      Not at all, it's only a problem of some interpretations. If one takes the position that QM is a statistical, non-fundamental theory there is no measurement problem.

      Delete
    40. @ Andrei,

      There is also no measurement problem if one takes the position that QM is a statistical, fundamental theory; just experiments and their results.

      Delete
    41. Prof. David Edwards,

      If QM is fundamental it has to be non-local. Locality is, I think, quite well established so I see little reason to chose this option. There is also a lack of explanatory power implied by such a theory.

      Delete
    42. "First, there is the issue of what information actually exists, and from whose point of view it exists. E.g. binary digits only exist from the point of view of the 100% lawful human mind/brain structure: there is no such law-of-nature lawful “binary digit” information that exists from the point of view of a computer."--Lorraine Ford

      Humans are made of quarks and gluons and leptons. So are computers. The processes which take place in human nervous system can be simulated or accomplished in different ways in computers (e.g., video cameras and microphones instead of eyes and ears).

      Currently no super computer has the full range of sensory and processing capability (equivalent neurons and synapses) as a functioning human, by many orders of magnitude. However, they have proved themselves capable of performing specific, limited cognitive tasks as well as or better than humans (e.g., Go).

      What are the objections to the possibility of computers with the full intelligence of a human?

      1) That we don't understand how intelligence works well enough to implement it in hardware.

      This is possible, but from the neuroscientific study of neurons we have been able to simulate them as neural networks in computers, with promising results. It appears, to me at least, that biological evolution, over billions of years and an average of over a trillion tries (genetic variations) per minute has found a system (neural network) which can learn new things by a process of trial and error, induction, and abstraction; and we have been able to implement that process in computers.

      2) That even if a computer appears to know something (e.g., how to play Go at a high level), it will never really know that it knows, as we do. I think this is Searle's argument.

      Here I think we need to ask ourselves with humility, what does it mean to know that we know? The sense I have of that is that we are certain of something, such as that 1+1=2; and how did we reach that certainty? I beiieve by trial and error, induction, and abstraction. We observe that one apple plus one apple is two apples, and the same for oranges, or elephants, and so on. This is exactly how a neural network can be trained in a computer. At the end of the training process, a computer will be as certain as us that 1+1=2, and for the same reason. (Note: as with humans, biased training can produce wrong conclusions.)

      We may be endowed at birth with certain evolved instinctual forms of knowledge, but of course similar principles can be and are programmed into computers.

      3) The human race may lack the intelligence, will, desire, or sustained civilization to produce a computer with general intelligence.

      That wouldn't surprise me very much.

      To the extent that I think I know anything, I think I know that computers have the potential for general intelligence. (Perhaps my neurons have been trained incorrectly, though.)

      Delete
    43. @ Andrei,

      My paper "The Mathematical Foundations of Quantum Mechanics" is totally coherent, mathematically rigorous, and computational powerful! It's also very well-written! So just start it and you'll be hooked!!

      Delete
    44. Steven,

      I would think that conscious experience and feelings can’t ever be explained in terms of the laws of physics.

      New categories of information can potentially be explained as deriving from existing categories of information, perhaps via new mathematical or logical relationships, or perhaps, like temperature, being a higher-level description of lower-level events. But an experience/ feelings/ knowledge “dimension” (so to speak) BY matter, OF its own categories of information, can’t be explained.

      Delete
    45. JimV,

      On the issue of what information actually exists, and from whose point of view the information exists:

      1. Voltage represents lawful information, but binary digits (0s and 1s) are codes, not lawful information:

      --- Depending on the threshold voltage of the transistor, and whether the integrated circuit design engineer is using positive logic or negative logic, 3 volts might represent the binary digit 0, and <3 volts might represent the binary digit 1. I.e. the binary digit symbols don’t match up with the voltages.
      --- A string of the above binary digit symbols is a pattern of zeroes and ones that symbolise (e.g.) numbers and words. These patterns are codes, not lawful information.

      2. The lawful information that is acquired by the sensory systems of living things is a type of universally understood information from the point of view of the particles, atoms and molecules in the sensory system. This information is further analysed by the mind/brain. But the inputs to computers (i.e. binary digit codes) are not universally understood information: the man-made codes can’t be decoded or interpreted by the computer to find out what words or numbers the codes are supposed to represent.

      Delete
    46. Lorraine Ford12:08 AM, August 28, 2020

      Back to the infinite loop of your bot brain..

      "I would think that conscious experience and feelings can’t ever be explained in terms of the laws of physics."

      I know you think this. Because you have written it 10,000 times. But you haven't provided any argument to support thinking it, and all the empirical evidence suggests you may well be wrong.

      "But an experience/ feelings/ knowledge “dimension” (so to speak) BY matter, OF its own categories of information, can’t be explained. "

      Unless it can in a way that you, undoubted omniscient genius though you are, can't imagine. You are extremely tiresome.

      Where is the empirical evidence for your claim? You have none. Please stop just writing your unjustified claim. Enough now.

      Delete
    47. I will second that. No one cares whether you think consciousness can't ever be explained in terms of the laws of physics. The world is full with people who think that and not a single one of them has even a hint of an argument to support this claim. It's about as scientific as believing in god. So please stop repeating what you "think" if you have no argument to support your "thinking".

      Delete
    48. Prof. David Edwards,

      "My paper "The Mathematical Foundations of Quantum Mechanics" is totally coherent, mathematically rigorous, and computational powerful!"

      On page 97 you write:

      "The measurement problem is avoided by not introducing the notion of the "system itself. Our fundamental axioms relate directly to the structure of the deep logic which itself represents interlocking modes of perceiving. EPR type paradoxes are avoided in a similar fashion"

      Your problem here is my argument:

      At two distant locations (A and B) you can measure the X-spin of an entangled pair. QM predicts that:

      P1: If you measure the X-spin at A you can predict with certainty (probability 1) the X-spin at B.

      Let’s exclude non-locality:

      P2: the X-spin at B is not determined by the measurement at A.

      From P1 and P2 it follows that there was something at B that determined the result of the B measurement. EPR named that “something” an “element of reality”. So:

      P3: There is an element of reality at B that determines the measurement result at B.

      You may observe that there is no other logical option available (unless you think that it’s by pure luck that we manage to always predict with certainty the X-spin at B, which is rather absurd).

      From P1 and P3 it follows:

      P4: there was an element of reality at A that determined the measurement at A.

      This is because once we’ve established that the measurement at B was fixed (P3) it’s impossible that the measurement at A could have been different, right?

      OK, so P3 and P4 lead to:

      C: The X-spin of both particles, at A and B were determined before any measurement took place (deterministic realism).

      Look carefully at this argument. It does not assume the existence of the "system in itself", neither the existence of unmeasured properties. Its conclusion, however is that if you want your theory to be local you need the existence of the "system in itself". Hence, you are not avoiding EPR, you are tacitly accepting non-locality.

      Delete
    49. Sabine,

      I know that no one cares what I think. But as far as I know, you haven’t tried to define consciousness (sorry if you have, and I’ve missed it). This is all in the context of Dr Castaldo asserting things about a consciousness which, as far as I can see, he hasn’t attempted to define; and JimV asserting that computers could be intelligent (he has previously asserted that they could be conscious, without even trying to define consciousness, as far as I remember).

      But I have sort-of made an attempt to describe/define consciousness as being possessed/ experienced by matter, and that consciousness is experience of categories/ relationships (as opposed to consciousness itself being a category/ relationship that has emerged/ evolved). I can’t see the point of your (and Steven’s) putting down what I say, when seemingly no one else here has tried to describe/define what they mean by the word “consciousness”, as far as I remember.

      Delete
    50. Hello Sabine,
      "in terms of the laws of physics"
      do you mean the today physics laws?
      Or do you include future laws as well?
      Have fun
      Stefan

      Delete
    51. Lorraine,

      (a) I have previously given you a reference with my definition of consciousness. Here it is again.

      (b) It does not matter how I define consciousness, as I have pointed out repeatedly, because I have explained why nothing is strongly emergent, hence consciousness is not strongly emergent *regardless of how you define it*.

      It is not a difficult argument and the fact that you have still not been able to grasp it makes me think you are either unable or unwilling. Let me say this once again: All your talk about what consciousness is or isn't is entirely utterly and totally irrelevant.

      "I can’t see the point of your (and Steven’s) putting down what I say, when seemingly no one else here has tried to describe/define what they mean by the word “consciousness”, as far as I remember."

      This is wrong, Lorraine. I have literally published a paper that defines consciousness, and also, it is irrelevant how it is defined to state that it cannot be strongly emergent, because nothing is strongly emergent. Did this get through now?

      Delete
    52. Stefan,

      As I have said over and over and over again, everything I say is referring to our current best knowledge.

      Delete
    53. Dr. Hossenfelder: Bad Link: Your link above to your definition of Consciousness is in error, it goes to the essay 2876 by Sophia Magnusdottir. Unless it is your intent to subscribe to her definition of Consciousness. (Which, in fact, is quite similar to my own, and the one referred to by Lorraine.

      I did not find you as an author of an essay for that contest; but there are some interesting essays there. https://fqxi.org/community/forum/category/31425

      Delete
    54. Lorraine says This is all in the context of Dr Castaldo asserting things about a consciousness which, as far as I can see, he hasn’t attempted to define.

      Incorrect, I did not assert anything not already known to science and common sense, and I detailed a hypothesis for which there is plenty of evidence in published cognitive research (including 'priming' experiments in psychology).

      Unlike you, I described consciousness purely in physical terms of a system of neural models as we understand them now, no special sauce or new physics to discover or new dimensions or new fundamental forces or fields or properties. Just plain old chemistry. In fact, much like the 11 page essay to which Dr. Hossenfelder linked.

      Delete
    55. Lorraine Ford5:21 AM, August 28, 2020

      "I know that no one cares what I think. "

      You have been asked dozens of times to provide evidence for your claim. How much attention do you want for making an unjustified claim?

      Everybody has conscious experiences presumably - we seem to be aware of certain actions of the brain.

      You claim that these conscious experiences absolutely cannot consist solely of the matter in the brain. But you have never provided any evidence for this strong claim. Just saying that you can't see how it can be so is not an argument.

      Remember you and Dave are making the strong claim here. Dr. H. states that *as far as we know* conscious experience is weakly emergent from the brain - this does not rule out the possibility of strong emergence or indeed some future discovery of some other input to the mind other than the brain. (Don't hold your breath, though.)

      But you and Dave claim that conscious experience absolutely cannot be emergent from the brain, but you refuse to share with the class how you know this. Not that anyone thinks either of you has a shred of evidence.

      Delete
    56. @ Andrei,

      As you are surely aware, QT predicts the correct experimental results. Nothing more is required. (In the EPR situation, Bohr got it right! There is only one complicated experiment; not two experiments in a row!

      Delete
    57. Dr Castaldo,

      It is not an error. I wrote this essay under a pseudonym. I have explained this all multiple times before. It doesn't even matter, just believe me that I subscribe 100% to Dr. Magnusdottir's definition of consciousness.

      Delete
    58. Dr Hossenfelder: Oops. I either missed that explanation, or forgot it. Apologies for the irritation.

      Delete
    59. Prof. David Edwards,

      Bohr was responding to the EPR setup, my argument is based on the EPR-Bohm one which is free from the problem of not being able to prepare an initial state of known momentum and known position, hence Bohr's rebuttal does not apply. I am also not arguing for the mutual existence of non-commuting properties as EPR did. My argument is different, simpler, and in my opinion, stronger. So, please present a rebuttal or accept that your theory is non-local!

      I certainly agree QM gives correct predictions. My argument actually depends on that.

      Delete
    60. Sabine,

      Your essay says:

      1. “consciousness is relational: Its origin lies in the relation between a system, its environment, and its subsystems.” I.e. just like mass and velocity are simple relationships, consciousness is an elaborate version of this same type of relationship. I.e. consciousness is comparable to mass and velocity.

      2. “experience is hugely beneficial …[but] Experience … isn’t necessary”. At no point do you attempt to give a genuine reason for the existence of subjective experience and feelings. I.e. subjective experience and feelings can’t (ever) be explained in terms of the laws of physics.

      Delete
    61. Lorraine:

      You claimed I do not have a definition. I demonstrated that this is wrong. Now you complain that you do not like the definition. I could not care less. As I have said more times than any sensible person can bear: It is entirely irrelevant how you want to define consciousness. It is not strongly emergent because nothing is strongly emergent.

      Delete
    62. I’ve long held the assumption that consciousness has facets that are not obviously explainable by the laws of physics we currently understand. At the risk of sounding repetitive, on an earlier blogpost here I mentioned the experience of my late mother dreaming about the earthquake, and subsequent landslide, in Chile in the Spring of 1960, the night before it occurred. Such seemingly precognitive dreams or, for example, apparent avoidance of future danger even in the waking state, are common in the literature. One such case during the London Blitz involved a family pet (a cat I think), who refused to enter the family’s garden shelter when sirens sounded. Prodded by the cat’s behavior the family found shelter elsewhere. The garden shelter subsequently received a direct hit from a bomb. Somehow the family pet ‘sensed’ the danger in the very near future, saving the lives of the entire family.

      In my own very non-professional opinion, I suspect some as yet unknown aspect of Quantum Mechanics underlies the seeming capacity of living organisms to detect future events that could impact the organism’s survival. The process of evolution began when living things were limited to very small molecular assemblies that had the ability to replicate. But this is the size regime where quantum behavior tends to dominate. Should some feature of QM provide a ‘window’ into future happenings, exploiting this information would confer a distinct survival advantage to an organism. As organisms evolved into more complex multi-cellular structures selection pressure would have preserved this facility. So, perhaps what we define as consciousness is indeed emergent from the laws of nature, but contemporary science hasn’t completed the inventory of those laws.

      Delete
    63. I have one minor semantic quibble with the excellent paper on consciousness, this statement: "Consciousness, hence isn’t binary but continuous..." which seems to me to imply that those are the only two possibilities. Binary imples to me two states (on or off), continuity an infinite and uncountable number of states. There are also large numbers of states, more than two but less than infinite, which I think is the actual case for consciousness.

      So I would have (if capable of writing such an essay, condition contrary to fact) written: "Consciousness is not binary but has a much larger scale", or something like that. Still, I understood what was meant. But I like to support Zeno by hammering away at the bias for continuity when I can.

      "At no point do you attempt to give a genuine reason for the existence of subjective experience and feelings."--Lorraine Ford

      As also explained many times, science is not and cannot be in the business of giving reasons why, for example, quarks exist or F=MA exists. It is in the business of studying what does exist and what correlations can be measured among things that exist. One can speculate about such things but such speculations which cannot be tested are not scientific.

      As also explained, if "feelings" or experiences in general did not exist, evolution could not have produced us. Also, since such things are the results of interactions among particles (e.g., chemicals in the nervous system), a universe without such things would probably be a universe with no interactions among particles. One could perhaps define feelings and experiences as complex interactions among systems of particles, but again, the question of why particles can interact in this universe cannot be answered.

      Delete
    64. JimV,

      Thanks for the thoughtful comment. I think I see what you mean. The statement didn't so much refer to the number of possible ways of being conscious being infinite, as opposed to it being an "on-off" condition. Ie, the answer to the question "Is it conscious" may not be "Yes" or "No" but maybe "a little" or "in some sense". Saying it's "not continuous" may not have been a good way to express this. I will keep it in mind. Best,

      Sabine

      Delete
    65. Sabine,

      Re Sabine Hossenfelder 11:15 AM, August 28, 2020:

      In your essay, the word “consciousness” describes a category which consists of law-of-nature lawful relationships and interactions, just like mass, temperature and velocity are relationships and interactions, but more elaborate than those for mass, temperature and velocity. In other words, your essay seems to be saying that the categories/ relationships that exist are the substance of consciousness. I.e. there is nothing essentially different about consciousness: consciousness is just a label for a particular set of normal relationships and interactions.

      So your essay doesn’t explain the defining feature of consciousness, which is the feeling, subjective experience and knowledge of the above-mentioned categories/ relationships that exist. (These categories/ relationships presumably contain necessary-for-survival information about the surrounding environment of a living thing).

      Laws of nature are about objective aspects of the world (categories/ relationships, numbers and interactions) not about subjective aspects of the world (feelings, experience and knowledge), so it is not surprising that the subjective aspects can’t be explained by the laws of nature. Presumably, these difficult-to-prove subjective aspects never emerged: they were always there.

      Delete
    66. Lorraine,

      There is nothing to explain which is not in my essay. You are inventing something that does not exist and then insist it needs "explanation". And in any case, as I have said like a dozen of times it is irrelevant whether you like my definition of consciousness. I have provided it merely because you falsely claimed I do not have one. The definition of consciousness is unnecessary to know that it is not strongly emergent.

      It is not a difficult argument, really. If you could maybe try to at least think about it instead of insisting that it must be wrong because you do not like the conclusions that would help.

      Delete
    67. Dr. A.M. Castaldo wrote to me:

      > Your claim "In formal logic, definitions are just convenient abbreviations" is also false, as I demonstrated.

      I am sorry, but on this you are just indicating your ignorance of the modern formal logic of axiomatic systems.

      Please note that I am referring to formal axiomatic logic a la Gödel et al. And I am referring to the use of definitions in a system of formal logic (the most obvious such system being first-order predicate logic).

      Strictly speaking, in a formal axiomatic system, there are no definitions at all: there are merely undefined terms (variables, relations, etc.) and logical operators. But of course, for practical purposes, humans find it convenient to use abbreviations: we do not wish to restate the axioms for group theory every time we refer to a group, so we come up with an abbreviation, say “Group(x)” that can always, in principle, be expanded so as to eliminate the word “Group.”

      For example, if you google the notes for the Washington University class “PHIL 410A:  HANDOUT ON REASONING IMPORTANT TERMS AND ABBREVIATIONS,” you will find the following:

      Definitions. A definition of a term T states its meaning in more basic terms. Example: sister =df female sibling. An acceptable definition of a term T provides necessary and sufficient conditions for T.” I trust it is obvious why a term defined in such a way can always be replaced by the "more basic terms" for which it is an abbreviation.

      This is supposed to be known and well-understood by anyone with any familiarity with modern formal logic, or, indeed, higher math.

      For example, it is a commonplace that Zermelo-Fraenkel set theory with the Axiom of Choice (ZFC) can be used to derive just about all of contemporary mathematics. But there are no definitions within ZFC, just the undefined variables for sets and the undefined relation “is an element of” and the logical operations.

      So, how can we talk about integers, real numbers, vector spaces, etc. in ZFC?

      In ZFC, “x is an integer” is simply an abbreviation for a series of statements about “x” that state that x is an ordinal (“x is an ordinal” is in turn an abbreviation for a series of elementary statements about x) and that no subset of x can be put in one-to-one correspondence with x itself (the latter also being an abbreviation for a set of elementary statements about x).

      The statement “x is an integer” therefore expands into a very large number of elementary statements about x, but in ZFC “integer” is always just an abbreviation that can be expanded out into the full elementary statements.

      Look at, for example, Section 4.1 of the sixth edition of Mendelson's Introduction to Mathematical Logic to see how this works for an alternative axiomatization of set theory: the definitions are just abbreviations.

      That all this works is the major development in the foundations of mathematics in the last hundred fifty years. It leads to some very counter-intuitive theorems in the foundations of mathematics: for example, the Löwenheim–Skolem theorems. And it is essential to Gödel's Completeness Theorem (note: that is not a typo – I do not mean the “Incompleteness” theorem!), Cantor's independence proofs, and much else.

      I know about the philosophical debates: I have read my Kripke – I read "Naming and Necessity" decades ago. I know about the debate about the phrase "the present king of France" and the "morning and evening star" discussion and all the rest.

      None of that has anything to do with what I am talking about because it has nothing to do with formal axiomatic logic.

      I am talking about the issue of how formal axiomatic systems work, which simply has nothing to do with anything you have said or anything the philosophers have said.

      On this particular point, I am not going to argue with you or anyone else. Go to a decent university library and read about it.

      Delete
    68. PhysicistDave2:15 AM, August 29, 2020

      Another long irrelevant trolling post about the basics that even a primary school child would know.

      Blah, blah, blah, troll, troll, troll.

      "I am talking about the issue of how formal axiomatic systems work,"
      Good. Then you can write down the formal logical proof that conscious experience cannot be derived from the current laws of physics, which you claim to possess.

      Stop lying and trolling and write down your proof, old man. You haven't got long left.

      Delete
    69. Sabine wrote to me:
      >Of course you can. I can prove that there exists no holomorphic function on the entire complex plane that's not just a constant. It follows that Dave is not a non-constant, holomorphic function on the entire complex plane. I can draw that conclusion despite Dave not being in the assumptions.

      Great question, Sabine! Unless you object, I plan on using this example in the paper and book I am doing, because it does help explain the theorem about formal logic.

      I have tried always to add the phrase “except tautologically” to my claim that a term cannot show up in the conclusion of a valid theorem if it does not show up in the premises or the axioms (assuming of course each defined term has been expanded out into its definiens, as I have to keep telling Dr. AMC).

      Sometimes I have neglected to spell out all those conditions carefully when I repeat the point, but I have said them so often that they should be clear. And your example illustrates the “except tautologically” condition very nicely.

      What makes your point amusing of course is that you are not really giving any information specific to “Dave”: you could just as easily have substituted “Sabine” or “King Kong” or “slithy toves” (my favorite example).

      Since nothing in the argument you appeal to (the proof about holomorphic functions) refers to “Dave,” if you were justified when you first introduce the term “Dave” into the argument, you would have been equally justified in introducing any other term not used elsewhere in the argument (“Sabine,” “King Kong,” “slithy toves,” etc.).

      In fact, the specific rule of axiomatic logic that you are implicitly using is the “Rule of Specialization,” which says that from “for all x f(x),” one may deduce “f(c),” where “c” is any constant (see Rule E on p.10 of the 1966 edition of Cohen's Set Theory and the Continuum Hypothesis).

      I hope you can now easily see how this works in my argument that one cannot explain consciousness from the currently existing laws of physics. Suppose you have an argument of the following form:

      (Premises that make use of some of the current laws of physics but do not mention consciousness or related terms such as “conscious”)
      .
      .
      (A deductive chain)
      .
      .
      (Conclusion that does refer to consciousness)

      At whatever stage in the logic the term “consciousness” first shows up, one could, just as easily, have used any other term not already referred to, just as you could have referred to “Dave” or “slithy toves” or “King Kong” in your own example. For if consciousness has not been mentioned at all up to that point, there is nothing to privilege the term consciousness over “King Kong” or “slithy toves” or, indeed “God.”

      This can, in an obvious way, be rigorously proved by induction on the length of the proof and by inspection of the rules of deduction. But the induction is only needed to make sure that there is a “first time” that the term “consciousness” is used, and I trust everyone will accept that the term “consciousness” is not used or singled out in any of the standard rules of inference for deductive systems!

      I had thought this was all quite obvious, but you have made it clear I will have to really spell it our carefully in the paper and the book.

      So, we can indeed conclude that if the laws of physics as currently known do indeed predict or explain consciousness, then they also equally predict or explain any term at all that we put in place of consciousness: “slithy toves,” “King Kong,” or, indeed, “God.”

      Of course in some tautologically trivial sense, you can deduce statements about such terms:
      From F=ma, conclude that either toves are slithy or they are not slithy.
      From F-ma, conclude that either King Kong is an ape or he is not an ape.
      From F-ma, conclude that either God exists or God does not exist.

      All valid deductions because all tautologically true.

      If a term does not occur in the axioms or the premises, it cannot occur in the conclusion except in a trivial manner, as in your example. QED

      Delete
    70. Lorraine Ford12:55 AM, August 29, 2020

      "Presumably, these difficult-to-prove subjective aspects never emerged: they were always there. "

      Yes, and these "subjective aspects" have only ever been reported related to brains on Earth. But, yeah, these aspects are everywhere and have always been there. There is consciousness on Mars, there is consciousness in the Andromeda galaxy, there was consciousness 13.7 bya in the quark-gluon soup.

      Yes, this is an eminently reasonable conclusion to reach based on the empirical evidence. It's not that conscious experience in brains hasn't yet been explained because brains evolved over hundreds of millions of years, are hugely complex and their analysis far from complete. No, the answer is - consciousness is everywhere, always - with not a shred of evidence to support this mental claim.

      Delete
    71. PhysicistDave2:15 AM, August 29, 2020

      "On this particular point, I am not going to argue with you or anyone else."
      That's the whole point, old man, you haven't provided any argument. You claim to have a "logical proof" in around 100 long, trolling comments and counting, and you still fail to provide it.

      You are just a silly old man who is too proud to admit you made a stupid, stupid claim. Nobody has made a claim more stupid in these comments - you are the King of the stupid.

      Provide your "logical proof", King.

      Delete
    72. PhysicistDave2:15 AM, August 29, 2020

      You have repeated 2 equally embarrassingly stupid non-points, King, in your 100 comments.

      1) You claim that terms that don't appear in the laws of Physics can't be derived from the laws of Physics.

      So what are Chemistry and Biology? The term "cell division" does not appear in the laws of Physics, but clearly cell division is ultimately just atoms moving around according to the laws of Physics. So why not "conscious experience", too?

      2) You claim that "you can't get an "ought" from an "is"" implies the mind cannot ultimately be described in terms of Physics.

      The delicious irony here, and the reason that you truly are the absolute King of the Stupid, is that Hume was warning people against non-sequiturs.
      Yet your gormless point is a complete non-sequitur!
      How does it follow that assuming the mind is emergent from the brain is an example of an "ought" from an "is", King? Please show your working here.

      Delete
    73. Sabine,

      You don’t actually have a definition, you have an essay, which I have boiled down to the following definition: 1) consciousness is a (seemingly undefinable) set of normal lawful mathematical relationships and interactions; and 2) “Experience … isn’t necessary”, and it doesn’t need an explanation.

      Its not a matter of ME “not like[ing] the conclusions”, it’s a matter of YOU denying that subjective feelings, experience and knowledge need an explanation.

      Delete
    74. Dave,

      "So, we can indeed conclude that if the laws of physics as currently known do indeed predict or explain consciousness, then they also equally predict or explain any term at all that we put in place of consciousness: “slithy toves,” “King Kong,” or, indeed, “God.”"

      No, that conclusion is wrong because you left out a rather important fact namely: We have observational evidence that consciousness exists. We do not have observational evidence that God or King-Kong exist and I don't know what slithy toves is supposed to mean.

      A scientific theory cannot "explain" something for which there is no observational evidence. If you think so, you have used a meaningless definition of the word "explain".

      The correct conclusion of your logic is that the laws of physics predict or explain everything for the existence of which we have observational evidence.

      That's the same as saying there's no strong emergence.

      With best regards,

      Sabine

      Delete
    75. Lorraine,

      You falsely claimed I have no definition of consciousness. I pointed you towards that definition. You clearly neither understand nor like it, but who cares.

      Delete
    76. Lorraine Ford5:04 AM, August 29, 2020

      How do you know that a satisfactory (for you and Dave, too) explanation of conscious experience will not be achieved in terms of the physical structure of the brain?
      Have you completely analysed the brain and all its possible emergent processes and ruled this out?
      No, of course you haven't. You and Dave know close to nothing about neuroscience.

      So you are simply saying, as is Dave, that you *personally* can't see how conscious experience arises in the brain.

      In other Earth-shattering news - my dog can't prove the Riemann Hypothesis.

      There are brilliant neuroscientists who have studied the brain for decades who can't figure it out, so how on Earth do you and Dave think you are going to come up with the answer after a few minutes' inexpert consideration?

      Anyway, you and Dave have been told enough times. The conclusion is

      either
      Lorraine and Dave are insane trolls
      or
      Dr. H., Dr. C. and I are insane trolls

      I'm happy in the group I'm in.

      Delete
    77. PhysicistDave says: A definition of a term T states its meaning in more basic terms.

      And thus you have the obvious proof by an impossible infinite descent: Either there are some most basic terms that are not defined, or definitions are circularly defined.

      The latter tends to be the case in dictionaries, all words are ultimately cyclically defined; which means you just have to pick some point visited on the circle and use that as a definition with no further explanation of what it means; other than personal experience or a description thereof.

      Go ahead, look up "pain." The first definition is "suffering." The first definition of "suffer" is "pain". Although many words CAN be explained in more basic terms, but at its core language is just a synonym dictionary, which is obviously a cyclical graph that ends in a tautology: Pain is pain. But it is not meaningless, it is a label for a human experience.

      Those little cycles at the bottom, like for "pain", all represent labels for human experience. Loud is loud, funny is funny, fright is fright.

      The same thing goes for "person", eventually you will find the cycle of "human" -> "homo sapien" -> "group to which humans belong".

      This is important to your argument: They may have definition in synonymous words or phrases, but they have no definition in more basic terms.

      Which in turn means references to human experience are already present in formal logic, without being stated as axioms, and are thus fair game.

      Consciousness is one such experience, definitions will (currently) devolve into a cycle that represents a fundamental human experience (undoubtedly shared with other species).

      The same was once true for the Northern Lights; which is why I used it; it represented a distinct and fundamental human experiences which could not (at the time due to lack of scientific knowledge) be further explained.

      Like the Northern Lights, or pain, or humor, human experience X CAN be studied logically without a precise definition of what it is, as long as researchers can agree on what is X, and what is not X.

      I don't think you understand the structure of language at all.

      Please refrain from using it until you do.


      Delete
    78. I'm not sure we can explain electrons as to what they are, much less why they exist. That being the case I don't see the point of worrying about why consciousness exists. (Although I think it traces back to interacting particles.) We know enough about electrons to make use of them, and we know enough about the neuroscience of consciousness to try to generate it mechanically in computers, using neural networks. Like everything we develop, starting with the wheel, it will probably be a long process of trial and error.

      That means unless some unknown magic is involved, which has never been reliablely demonstrated in controlled tests (rather than relying on random coincidences which are bound to occur occasionally--see Littlewood's Law of Miracles), we ourselves are biological machines, developed by random evolution, and what random evolution can do is possible for us to duplicate (given enough resources and trials).

      The benefit of doing this might be to have impartial judges and advisors who do not act out of fear or prejudice. (Of course everything we make can be used harmfully also.)

      I am sorry if I come off as a jerk for espousing this and other views. My intent is not to insult anyone who has different views but to clarify how I disagree with them, and demonstrate that contrary opinions exist, in need of consideration or education. Also, I have too much free time at this point.

      Delete
    79. Sabine,

      Your essay describes how consciousness works; it is a considered view of the structure of consciousness, most of which no one could disagree with.

      But there is an issue with subjective feelings, experience and knowledge. They undeniably exist, I think most people would agree that subjective feelings, experience and knowledge genuinely exist. And clearly, subjective feelings, experience and knowledge cannot have strongly emerged; there is nothing that can have caused them to emerge.

      Whereas your solution to the experience “problem” is that experience is not necessary, another solution is that experience (of structure, relationships and numbers) was always there. There is seemingly an increasing number of people that have a pan-experientialist view of the world. Clearly, a knowledge/ experience aspect could only ever exist if it were necessary to make the physics of the system work; the only reason why a knowledge/ experience aspect could ever exist is that the system needs to somehow know its own relationships and numbers.

      Delete
    80. Dave,

      I think the best explanation for Steven’s lunatic ravings against you and me was given by Lawrence. Steven’s each and every “contribution” seems to be entirely content-free because it is so overwhelmed by the wall of abuse against those he disagrees with. Unsurprisingly, I no longer bother to attempt to glean possible valid content underlying the abuse.

      Delete
    81. Lorraine,

      Yes, subjective feelings exist. They are some pattern in your brain. There is nothing, absolutely nothing, in "subjective feelings" that physics cannot handle.

      I certainly didn't say anything of the type that experience is not "necessary".

      And in any case, you still have not been able to understand, evidently that it is entirely irrelevant whether you like my definition of consciousness or not. Consciousness is not strongly emergent, regardless of how you define it, because nothing is strongly emergent.

      Delete
    82. Sabine,

      As you know, the imaginary philosophical zombies don’t experience anything. But one wouldn’t know this because every other aspect of them is exactly like their experiencing counterparts. In the context of discussing philosophical zombies, your essay says “Experience, hence, isn’t necessary”. And I would agree that we haven’t really found a use for subjective experience: every objective physical outcome can be seen as a zombie outcome that can be theoretically explained as just mathematical laws and logic, and interactions, taking their natural course.

      And I agree that strong emergence of experience/ consciousness is not possible. It is only possible that experience/ consciousness could “emerge” in the same sense that law of nature relationships and associated initial number assignments “emerged” in the world. I.e. like laws and numbers, experience/ consciousness would have to be a given characteristic of the system.

      So is there a genuine use for subjective experience/ knowledge? One could probably say that a knowledge aspect of the world is necessary in the following sense: the physics of the world seemingly can’t work without the world in some sense knowing its own relationships and numbers, as opposed to zillions of other sets of mathematical relationships and number assignments that might be theoretically possible.

      But, being an interior subjective aspect of the world, a match between an objective physical aspect of the world, and a subjective experience/ knowledge aspect of the world can’t actually be proved, except maybe for human beings who can report on their experience (as long as they are not zombies who say they are experiencing, when they are not).

      Delete
    83. Suppose it's possible to make a catalog of every possible type of elementary interaction, like a lot of Feynman diagrams. An animist might say that the elements of these interactions are aware of each other, and know how to behave under various circumstances. A panpsychism enthusiast might say that conscious is built from these components when assembled into complex systems, especially evident when those systems are recursive and self-referential. You would probably then have to give some objective standing to gestalts. The "problem" of subjectivity can go in crazy directions. A case could be made that subjective consciousness/experience is no more than an epiphenomenon, a bit of fluff, like navel lint, along for the ride while the zombie mechanism does all the work. Still, it would be nice to know where the fluff comes from.

      Delete
    84. @ Rick Lubbock,

      You're talking about "elementary interactions" as if they were classical! Quantum theory is best understood as a form of perspectivism not physicalism. From this point of view, it is the "physical world" that is epiphenomenal and "reality" is a society of minds!

      Delete
    85. Prof. David Edwards5:50 AM, August 31, 2020

      "Quantum theory is best understood as a form of perspectivism not physicalism."

      And now the Prof. Edwards bot. If superdeterminism were true, for example, which isn't ruled out by the empirical evidence, then perspectivism would be absolutely the wrong approach.

      I've told you this before. Your claim is facilely shown to be unjustified. Please update your bot program accordingly.

      Delete
    86. @ Steven Evans,

      "In quantum mechanics, superdeterminism is a loophole in Bell's theorem, that allows one to evade it by postulating that all systems being measured are causally correlated with the choices of which measurements to make on them.[1]"
      https://en.wikipedia.org/wiki/Superdeterminism

      My approach doesn't use the notion of "systems"; just experiments and results! It's the use of "systems" that yields all the confusion in understanding QT!

      Delete
    87. Prof. David Edwards7:07 AM, August 31, 2020

      Jolly good. But it's nature that decides whether superdeterminism is true or perspectivism, so you don't get to claim that quantum theory is "best understood" by perspectivism because there is no empirical evidence that is the case.
      Can you stop making your unjustified claim now?

      Delete
    88. @ Steven Evans,

      Nature can't decide this since both theories make the same predictions! I'm a published researcher in the foundations of QT and make the professional judgement that: "Quantum theory is best understood as a form of perspectivism not physicalism."

      Delete
    89. Prof. David Edwards,

      "My approach doesn't use the notion of "systems"; just experiments and results! It's the use of "systems" that yields all the confusion in understanding QT!"

      Your approach is obviously nonlocal. My argument presented here:

      http://backreaction.blogspot.com/2020/08/understanding-quantum-mechanics-5.html?showComment=1598604494865#c6670103904840114451

      prooves it.

      But even without that argument, it stands to reason that if nothing exists besides the macroscopic states of the instruments, the only way to explain the EPR correlations is to posit that the measurement at A causes instantly the result at B. And this non-local behavior comes with no explanatory power. We get no explanation for why those detectors behave as they do.

      Delete
    90. @ Andrei,

      Your confusions are caused by using the word measurement and thinking of the situation as 2 experiments instead of 1 combined experiment.

      Delete
    91. Prof. David Edwards,

      How exactly does my argument depend on how you define "experiment" and how many of them are?

      Delete
    92. Prof. David Edwards8:57 AM, August 31, 2020

      'Nature can't decide this since both theories make the same predictions!'

      Currently maybe, but there is the possibility that the competing interpretations could be distinguished by future observations (e.g. observation of a quantum-gravitational environment or observations in a working quantum computer).

      MWI, Superdeterminism and Perspectivism all fit with current data, so why is Perspectivism "best"?


      ' I'm a published researcher in the foundations of QT and make the professional judgement that'

      Good for you. But you haven't provided a justification for the use of "best". Gleason's theorem depends on an assumption of non-contextuality which would be ruled out if superdeterminism is true. Your "best" theory depends on an assumption.

      Delete
    93. Lorraine Ford9:30 PM, August 29, 2020

      "I think the best explanation for Steven’s lunatic ravings against you and me was given by Lawrence. "

      Don't cry.
      You are welcome, Lorraine, to provide an argument for your claim that the mind cannot be weakly emergent from the brain anytime you like. You have failed to do so in 100 posts.

      Dave is welcome to provide the "logical proof" that he has been ridiculed by everyone for claiming he has any time he likes. He has failed to do so. Instead he writes long, irrelevant, trolling, lying posts as is the wont of old men.

      Lawrence is welcome to provide evidence of inflation or MWI, but he hasn't.

      Off you go. Provide your evidence. Break a leg.

      Delete
  22. Dave wrote:

    “But that is not what physicists mean by "decoherence." “

    Decoherence is the loss of coherence. A laser loses its coherence after a certain distance (it’s coherence length) even if it propagates in the vacuum with no particle interaction. Interaction with external particles will cause decoherence. But decoherence can occur without external particles.

    Dave also wrote:

    “Yes, in that case the relative phases change over time, but in a completely predictable and simple manner. Indeed, in that case we periodically get the original state back.”

    If there is a finite number of energies eigen-states and these energies have a rational ratio, you will indeed periodically get the original state back. Still, it would require extreme fine tuning to restore an interference pattern in such a system.

    In practice, every somewhat realistic system would have continuous energy eigen-states. For example, the spin-states in the Stern-Gerlach experiment, have continuous eigen-states once you take into account the fact that they need to be positioned in a wave-packet.

    I do agree that the phase would change in “a completely predictable and simple manner” (for some definition of simple). This is exactly my point. There is nothing mysterious about decoherence, it is all straightforward math.

    Sabine,

    Tracing out the interacting particles is required for calculating decoherence in the case of interacting particle. My point is that you can get decoherence without additional interacting particles.

    ReplyDelete
    Replies
    1. Hello Udi,

      if you have a HeNe-laser and send the laser light from earth to the moon is will travel round about 380000 km. If there is an interferometer on the moon you will be able to see interference fringes. So the light will be coherent although the HeNe-laser has only a coherence length of about 1km.
      Have fun
      Stefan

      Delete
    2. Stefan Freundt wrote:

      “if you have a HeNe-laser and send the laser light from earth to the moon is will travel round about 380000 km. If there is an interferometer on the moon you will be able to see interference fringes. So the light will be coherent although the HeNe-laser has only a coherence length of about 1km.”

      If I understand correctly, the experiment you are suggesting is beaming an HeNe-laser from earth to a small interferometer on the moon. In that case, you are correct that we will be able to see an interference pattern. The reason is that the relevant length is the distance from the beam splitter to the screen.

      On the other hand, if the interferometer arms are longer than 1km, there will be no interference pattern. This calculation is straightforward and does not involve any interaction with external particles.

      Delete
    3. Hello Udi, so do you continue beliving that coherent ligth can decay to decoherent light?
      Have fun
      Stefan

      Delete
    4. There are two meanings to the word coherent. In QM coherence means there is a quantum phase associated with superposition or entanglement. Completely separable states or mixed states have lost this coherence. Coherence of laser states of lights is an overcomplete set of states that are identical. These are states |α⟩ = e^{αa^† - α* a}|0⟩ of the operator D(α) = e^{αa^† - α* a} that under a Taylor series, exercise to reader, gives a massive set of identical states.

      Delete
    5. Lawrence Crowell:
      "... that under a Taylor series, exercise to reader, gives a massive set of identical states."

      Physicists love approximations.
      Keeping in mind that the distance travelled by a particle in circular motion is Rα=vt while the distance travelled by the center of its field, moving tangential to the circle, is Rtanα = vt, we find that the condition for coherence states is based on α=tanα=arctanα, which results in an infinitive number of not identical states with v a little bit slower or faster than the speed of light c.
      This means that both Einstein's E=mc2 and Planck's
      E=hf are just approximations. Exercise accomplished.

      Delete
    6. I suppose I do not follow this argument for coherent states.

      We can go back to Einstein’s coefficients, where he showed that photons have statistics that is both random or blackbody, and in a coherent form. Laser coherent states are modelled as this idealization, where realistically it is not possible to have absolutely, God-assured pure coherent states of light. It is interesting that today I got an email from someone on whether thermal sources are purely blackbody and carry only temperature as information. This too is an approximation, and frankly with Hawking radiation as well. Einstein in a way got some of this a long time ago --- Big Al was a serious genius.

      Lasers generate coherent states of photons by pumping atomic states from the ground to some level that is usually separated by other states by some appreciable energy gap. When these atomic states transition back to the ground state they emit photons that entangle with other excited states or their photons so a mass avalanche of photons occur in the same quantum state. There are a number of things that can muddy these waters. One is the Heisenberg uncertainty principle tells us the excited states can include other atomic states. Another is that since the laser cavity, usually linear, is finite there exists in effect an ensemble of coherent states with slightly different k propagation direction and thus slightly different polarizations. If you have worked with lasers, and I am an industry guy who has done a fair amount, you may have noticed in laser optics a speckle pattern in laser light. Run a laser mean through a lens and you can see this on a screen. This occurs because there are interferences between these coherent states in this ensemble. So, from a practical perspective these laser coherent photons are not perfectly coherent.

      A friend works with serious high-powered lasers at Sandia Nat’l labs. The goal of course is to make this a weapon, where the COIL chemical laser is being used in trials. The problem is that lasers heat the atmosphere, and this destroys the coherence of a laser beam. This is not due to some spontaneous breakdown of coherence, but is due to an interaction. Because photons are massless and these coherent states of light are a type of Bose-Einstein condensate the physics is such that can happen in principle for T = 0. Pure coherent photons are zero temperature, at least in principle, and heat is only generated if the beam interacts with matter.

      Delete
    7. Coherence in laser technology and in physics have different meanings.
      In physics coherence means that two wave sources produce waves of identical frequency and waveform with a constant phase. The problem is that you cannot observe such coherent states because two waves with a constant phase of Pi interfere destructive to zero.

      Sabine said in her video:
      "Here is the complex plane. Now, every number with an absolute value of 1 lies on a circle of radius one around zero. On this circle, you therefore find all the numbers of the form e to the I times theta, with theta a real number. If you turn theta from 0 to 2 \Pi, you go once around the circle. That’s Euler’s formula, basically."
      These simple sentences reveal that physicists in general have not the faintest idea of what you can do with Euler's formula when any kind of oscillation or circular motion is involved.
      Basically it defines an angle as a length on the unit circle ranging from -infinity to +infinity, meaning that a straight line has an infinitive number of intersections with a circle.

      Transformations based on Euler's formula are widely used in electrical engineering, e.g. Fourier transform, Laplace transform and z-transform.
      Remember that GPS works exact while physics still uses approximations - for military and religious reasons.

      Delete
    8. Stefan Freundt wrote:

      “so do you continue beliving that coherent ligth can decay to decoherent light?”

      A perfectly coherent light, will stay coherent forever. But in the real world you cannot have perfect coherent light. Every laser has a finite decoherence length.

      I asked you a very specific question about the details of the interferometer experimental setup and you ignored it. This gives the impression that you are just citing something you read and that you don’t really understand what you are talking about.

      Delete
    9. Lawrence,

      The equations you wrote down are just the equations for the coherent state of the harmonic oscillator. Only your states are in Fock space, as it should be for describing a laser.

      A coherent state will stay coherent only if the potential is a harmonic oscillator or in the case of Fock space, if we are dealing with a free particle.

      Coherent states and energy eigen-states are two different entities. Both are stable states and for both you can describe the unstable state (what we refer to as decoherence) by introducing a wave packet.

      There are many other sources of instability. All I am saying is that the simple math of a wave packet is enough to understand the relation between decoherence and quantum measurement. There is a misconception that decoherence requires randomness or some external influence. Neither of these are necessary.

      Delete
    10. Hello Udi, now I got it. Thanks for your interesting comment. Stefan

      Delete
  23. Thank you for the excellent tutorial video! Your proof rules out the idea that decoherence leads to a system that remains in only a single eigenstate. However, what I think a lot of physicists think of when they say decoherence solves the measurement problem, is that the observer becomes entangled with the system. The decoherence then corresponds to the two states of observer+system becoming disentangled. This leads to an Everett type many worlds scenario, and seems consistent with a diagonal density matrix.

    ReplyDelete
  24. It is clear that the integral of exp(iθ) over a 2π cycle is zero. Mathematically zero.

    But exp(iθ) or cosθ + i sinθ in the range 0 to 2π draws a circle in the complex plane. The set of points traced out in that cycle by exp(iθ) does not contain the point zero.

    By analogy an average family, mathematically or statistically, has 2.5 children. But if a particular, individual family had 0.5 of a child you would think that unrealistic. Likewise I suspect that it is unrealistic to suppose that a particular electron has an average value of exp(iθ) which is zero. A series of buffetings should merely move the path traced out along the circle for a single individual particle?

    Austin Fearnley

    ReplyDelete
  25. There seems to be an irreconcilable incompatibility between the language of biology and that of quantum mechanics similar to the situation holding between quantum mechanics and general relativity. It is not just that the reduction of biology to physics has
    not been worked out. Rather it would appear that such a reduction is impossible in principle. As another example, a geologist wants to say that India collided with Asia, throwing up the Himalayas. He does not want to use probabilistic language. For him this
    event is a fact which he can almost see. The physicists language becomes even more inappropriate when applied to history or to Wigner's friend.

    ReplyDelete
  26. The various sciences do not fit together into a single coherent picture. In fact, incompatibilities are commonplace even within a single science and often even within a single scientific paper. Moreover, these incompatibilities are often not to be viewed as
    defects needing remedy, but, instead, as rational responses to a very complex situation.

    ReplyDelete
  27. A close study of the various electron models reveals tremendous differences. The differences between the Schrodinger, Dirac, and Feynman theories of an electron appear to us as huge as the differences between the Freudian, Skinnerian and Piagetian theories of human behavior. In studying complex phenomena there are always a variety of possible approaches. Too much of an insistence on consensus results in very impoverished starting points such as those taken by Russell and Carnap . From such starting points it is very
    difficult to get anywhere. But the other extreme often results in a tower of Babel where each scientist has not only his own theories but his own scientific methodology and logic. To paraphrase Goethe: One can convince one self while viewing a great collection of scientific works that nearly each master had a different way of approaching nature. In our opinion, what is required in science is the same thing that is required in art, namely "taste" and "judgment."

    ReplyDelete
  28. My understanding of the history of science leads me to expect the opposite of what Pierce expected; in the long run our network of scientific theories don’t converge on the truth, but, instead, become richer and more complex, requiring intellectual ecology to comprehend. The network of scientific theories moves towards looking like a rainforest! A good example is optics. Geometrical optics goes back to at least Euclid; wave optics to Huygens; then we have Maxwell’s electro-magnetic theory and its’ classical competitors the
    Feynman-Wheeler theory and the Maxwell-Dirac theory. Onwards to Einstein’s photon theory and later to quantum electro-dynamics. If one examines an optician’s handbook one will find many ad hoc theories; similarly for treatises on computer graphics. The following collection of theories exhibits an even more
    frightening possibility, tangled hierarchies: The Theory of Mind;
    Neuroscience; Molecular Biology; Particle Physics; Quantum
    Theory. Sometimes I feel that only Hegel is crazy enough to
    incorporate quantum theory.

    ReplyDelete
    Replies
    1. Laplace always said to his students:"Read Euler". That's what physicists also should do instead of believing in effects caused by approximations (E=h*f) or invalid conversions (the relativistic root as a replacement of a circular function).
      Compared to Euler Einstein's genius is only relative.

      Delete
    2. Basically Euler defines a set of vectors based on the unit vector e^(i*α)=cos(α) + i*sin(α), with α as a distance on the unit circle, that use the trigonometric functions and extend them to circular functions.

      There are two vectors in x-direction
      cos(α)=(e^(i*α)+e^(-i*α))/2
      cot(α)=cos(α)/sin(α)

      two in y-direction
      i*sin(α)=(e^(i*α)-e^(-i*α))/2
      i*tan(α)=i*sin(α)/cos(α)

      and another two in radial direction
      sec(α)*e^(i*α)=(1/cos(α))*e^(i*α)=1+i*tan(α)
      csc(α)*e^(i*α)=(1/sin(α))*e^(i*α)=i+cot(α)

      Euler's formulas are like an all-in-one tool (in German: eierlegende Wollmilchsau) where you can arbitrarily mix Cartesian coordinates with cylindrical coordinates.

      Some operations, though, are not allowed, esp. those which destroy the periodic nature of circular functions.
      One example is the Lorentz factor, where Einstein derived from sin(α)=v/c the relativistic root. He should have used the secants instead.

      Euler would have disproved special relativity in the time between noon and lunch. Others need longer.

      Delete
  29. Decoherence does not explain what a superposition state of "up" and "down" of a spin actually means.

    There is no understanding at all in the physics community of how "mysteriously" (+1)+(-1) somehow "magically" does does not equal 0.

    The real mystery is why so many "physicists" parrot the statement that it is so.

    Not to mention spending billions in funding on an entire technology ("quantum computing"), solely on the uncritical supposition that the results of the Bell experiments and entanglement etc require any such self-contradictory bizarre 'interpretation'!

    This is the REAL mystery!

    Particularly when there exists a perfectly non-self-contradictory explanation OF those very same mathematical facts!

    That's what's truly mind-boggling, that such a herd-mentality could exist within the physics community.

    ReplyDelete
    Replies
    1. Wave-functions are vectors. There is absolutely nothing "mysterious" about the fact that one step sideward and one step backward does not return you to the starting point.

      And please refrain from enlightening us with your "explanation" of "mathematical facts" that you clearly don't understand in the first place, thank you.

      Delete

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