Friday, May 15, 2020

Understanding Quantum Mechanics #2: Superposition and Entanglement

If you know one thing about quantum mechanics, it’s that Schrödinger’s cat is both dead and alive. This is what physicists call a “superposition”. But what does this really mean? And what does it have to do with entanglement? This is what we will talk about today.


The key to understanding superpositions is to have a look at how quantum mechanics works. In quantum mechanics, there are no particles and no waves and no cats either. Everything is described by a wave-function, usually denoted with the Greek letter Ψ (Psi). Ψ is a complex valued function and from its absolute square you calculate the probability of a measurement outcome, for example, whether the cat is dead or whether the particle went into the left detector, and so on.

But how do you know what the wave-function does? We have an equation for this, which is the so-called Schrödinger equation. Exactly how this equation looks like is not so important. The important thing is that the solutions to this equation are the possible things that the system can do. And the Schrödinger equation has a very important property. If you have two solutions to the equation, then any sum of those two solutions with arbitrary pre-factors is also a solution.

And that’s what is called a “superposition”. It’s a sum with arbitrary pre-factors. It really sounds more mysterious than it is.

It is relevant because this means if you have two solutions of the Schrödinger equation that reasonably correspond to realistic situations, then any superposition of them also reasonably corresponds to a realistic situation. This is where the idea comes from that if the cat can be dead and the cat can be alive, then the cat can also be in a superposition of dead and alive. Which some people interpret to means, it’s neither dead nor alive but somehow, both, until you measure it. Personally, I am an instrumentalist and I don’t assign any particular meaning to such a superposition. It’s merely a mathematical tool to make a prediction for a measurement outcome.

Having said that, talking about superpositions is not particularly useful, because “superposition” is not an absolute term. It only makes sense to talk about superpositions of something. A wave-function can be a superposition of, say, two different locations. But it makes no sense to say it is a superposition, period.

To see why, let us stick with the simple example of just two solutions, Ψ1 and Ψ2. Now let us create two superpositions, that are a sum and a difference of the two original solutions, Ψ1 and Ψ2. Then you have two new solutions, let us call them Ψ3 and Ψ4. But now you can write the original Ψ1 and Ψ2 as a superposition of Ψ3 and Ψ4. So which one is a superposition? Well, there is no answer to this. Superposition is just not an absolute term. It depends on your choice of a specific set of solutions. You could say, for example, that Schrodinger’s cat is not in a superposition of dead and alive, but that it is instead in the not-superposed state dead-and-alive. And that’s mathematically just as good.

So, superpositions are sums with prefactors, and it only makes sense to speak about superpositions of something. In some sense, I have to say, superpositions are really not terribly interesting.

Much more interesting is entanglement, which is where the quantum-ness of quantum mechanics really shines. To understand entanglement, let us look at a simple example. Suppose you have a particle that decays but that has some conserved quantity. It doesn’t really matter what it is, but let’s say it’s the spin. The particle has spin zero, and the spin is conserved. This particle decays into two other particles, one flies to the left and one to the right. But now let us assume that each of the new particles can have only spin plus or minus 1. This means that either the particle going left had spin plus 1 and the particle going left had spin minus 1. Or it’s the other way round, the particle going left had spin minus 1, and the particle going right had spin plus 1.

In this case, quantum mechanics tells you that the state is in a superposition of the two possible outcomes of the decay. But, and here is the relevant point, now the solutions that you take a superposition of each contain two particles. Mathematically this means you have a sum of products of wave-functions. And in such a case we say that the two particles are “entangled”. If you measure the spin of the one particle, this tells you something about the spin of the other particle. The two are correlated.

This looks like it’s not quite local, but we will talk about just how quantum mechanics is local or not some other time. For today, the relevant point is that entanglement does not depend on the way that you select solutions to the Schrödinger equation. A state is either entangled or it is not. And while entanglement is a type of superposition, not every superposition is also entangled.

A curious property of quantum mechanics is that superpositions of macroscopic non-quantum states, like the dead and alive cat, quickly become entangled with their environment, which makes the quantum properties disappear in a process called “decoherence”. We will talk about this some other time, so stay tuned.

Thanks for watching, see you next week. Oh, and don’t forget to subscribe.

120 comments:

  1. Hi Sabine,

    you have a typo with &Psi just after the movie. Then you have a superposition of typos in "But now you can write the original psi1 and psi2 as a superposition of psi3 and psi3" where the last one should be psi4; and I guess you mean \&Psi again..

    Well, it looks like this at least when I read it :)


    Best,
    J.

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    1. Hi akidbelle,

      Thanks for pointing out; I had forgotten to fix the formatting. I hope it displays correctly now!

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  2. Last, I think you also have a typo with the first particle decay (plus one and plus one).

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    1. Right... I have fixed this. Luckily I said it correctly. Thanks again for your attentive reading!

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  3. Minor typo?

    You say "But now you can write the original psi1 and psi2 as a superposition of psi3 and psi3" but I think the last psi3 should be psi4.

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    1. Yes, sorry, I have fixed this. Luckily it's correct in the video!

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  4. Isn't entanglement just a fancy name for correlation? One might think that these unexpected ("weird") correlations require a special name. Alternatively, we could learn to adjust our intuition (expectations). Our intuition is misled by wrong classical pictures that dominate our thinking.

    Wave functions (superpositions) are a way to express correlations. For example, the polarization state of a photon characterizes how the x- and y-components of the electric field are correlated. But it is a mistake to think of the wave function as representing an "individual" quantum system. Schrödinger's cat should have demonstrated that long ago, but apparently the message has not really sunk in. The wave function is but a single piece in a bigger statistical machinery, of which the Born rule is another important component.

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    1. If I tear a movie ticket into two and throw them in opposite directions, then yes, if the left half went in one direction, the right half went in the other.

      But in Bee's example, the spin 1 particles that went in the two directions need not be in definite states of spin that you choose to measure.

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    2. Werner wrote:
      >Wave functions (superpositions) are a way to express correlations.

      No. Bell's theorem.

      If you assume the values exist before they are measured and just happen to be correlated with each other (and, of course, no super-luminal interactions) then the Bell inequality has to be obeyed.

      Experimentally, it is violated. No, the wavefunction does not just describe the fact that we are ignorant of the true values until we measure them.

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    3. Arun wrote: "the spin 1 particles [...] need not be in a definite state of spin"

      Exactly. The results of the measurements depend on the detectors as much as on the properties (?) of the particles. Naively, we take spin to be a property of particles. This helps to explain that the measurements are (anti-)correlated. But if we think of properties of particles, Bell's inequality seems to imply superluminal communication between them when they meet the detectors. Yes, that's weird, entangled. Better not think of particles, but just describe the correlations.

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    4. PhysicistDave wrote: "If you assume the values exist before they are measured ..."

      That's precisely what I don't assume. And I don't think a "measurement" by some human is required, but just an interaction with a detector. The values come into existence at the detection event.

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    5. Werner wrote to me:
      >That's precisely what I don't assume. And I don't think a "measurement" by some human is required, but just an interaction with a detector. The values come into existence at the detection event.

      Well, unfortunately that does not work.

      The way the math works, a “detection event” just entangles the different possible states of the detector with the different possible states of the system. You need another “detection event” to make the values of the first detection event real. And so on and so on.

      An infinite regress.

      Also, no on has ever managed to figure out what counts as a “detection event.” If every interaction is a “detection event,” you will wreck superposition when you most assuredly need it! And, if not, then which interactions are true “detection events” and which are not?

      This stuff has been chewed over now for almost a century, and no one has managed to resolve such issues.

      You seem to think you have.

      I would suggest that you need to learn more about the failed attempts of the past, and then you will be less sure that your own attempts are not also failing.

      They are: you just know too little to see it.

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    6. PhysicistDave wrote: "unfortunately that does not work"
      "you know just too little to see it"

      Thank you for your rash assessment, Mr. Know-it-all. You haven't looked at the Schwinger/Keldysh formalism in the meantime, have you?

      "You need to learn more about the failed attempts of the past"

      You mean one should study all attempted answers before considering the possibility that one might be asking the wrong questions?

      "a 'detection event' just entangles the different possible states ..."
      "no on[e] has ever managed to work out what counts as a 'detection event'"

      I thought that physicists could agree on that a detection event is something physical that happens, for example, in a photomultiplier. You mean we don't have a theory how photomultpliers work? Of course, the terms "detector" and "system" carry connotations. Do you think the theory should reflect them? John Bell has warned against their use ("Against Measurement").

      Schwinger's paper is more than half a century old, and it did not specifically address the "measurement problem". But a formalism that combines unitary evolution and the Born rule without introducing the ad hoc term "measurement" should be of interest to everybody thinking that wave function collapse is necessary.

      "you just know too little to see it"

      Is it the wave function collapse that you want to see derived? Is that what makes you dismiss the closed-time-path formalism as one of those failed attempts? I certainly know too little about how you expect the "measurement problem" to be solved.

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  5. One thing worth mentioning is that quantum superpositions are real states, and not merely a reflection of our ignorance (they are pure, not mixtures). Going in the NW direction means you are going in a linear superposition of both N and W, but that's a real direction. Another interesting thing is that a maximally entangled pair of particles is just a single quantum state. As Susskind nicely put it, one can know everything about a system but nothing about its constituents.

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    1. No, a superposition of an N and W measurement is not an NW measurement. The one is a superposition of wave-functions which are vectors in Hilbert-space, the other is a sum of vectors that describe directions in space. These are two different things.

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    2. Sure, normal space is not Hilbert space, I was using a simple analogy. My point was you can create new vectors as linear combinations of basis vectors, in that case N and W (only with Hilbert spaces, the coefficients are complex) and that these states are actual real states, not proper mixtures.

      I meant quantum state before collapse. Measurement is a whole different discussion.

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  6. Entanglement for 2 identical "particles" is about experiments that yield two points in R^3; so, the correct configuration space is R^6/~, where ~ is equivalence under flip.

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  7. So, entanglement implies that conserved quantities are not conserved until someone makes a measurement.

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    1. Quantities aren't defined until someone makes a measurement.

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    2. You probably mean determined rathe
      than defined.

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    3. The language "aren't defined until someone makes a measurement" has always seemed funny to me, since to me "someone" refers to a human (not a a cat, or a rock, or whatever). So if there were no humans ever in the universe, that which "aren't defined until someone makes a measurement" are never defined, because are are no someones. The only way out is to assume that humans appearing in the universe to make measurements is a given.

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    4. Philip Thrift ,until there were researchers in quantum physics, before that there were billions of humans who could not define it, hahaha; Greetings

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  8. Somewhere I ran across an argument that there is really nothing objectively "real" about the wave function. It was interpreted as a way to characterize and quantify an observer's state of knowledge, or lack of it, regarding some system prior to measurement. Call that the observer's "epistemic state". This was supposed to trivialize the wave function collapse/measurement problem: what's problematic about, for instance, drawing a black marble out of a bag of multi-colored marbles? Before you draw, or make a measurement you have a known probability of an outcome. You pull a marble out of the bag and now you've got something with a definite color. What's the big deal? But it seems to me that entanglement shoots such ideas down and implies that there is something objectively real about the wave function-- it isn't just a way to characterize an observer's "epistemic state". On the other hand, wouldn't an epistemic state be objectively real?

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    1. You can view it as determining an objective probabilistic disposition.

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    2. Rick Lubbock wrote: "there is something objectively real about the wave function"

      Yes and no. What is real are physical correlations. But there is no one-to-one correspondence between an individual system and a wave function; the wave function always describes only a class (ensemble) of identically prepared systems. Conversely, an individual system must in general be described by a set of wave functions (a density matrix), and a trace (a sum over all possible states) needs to be taken before the formalism yields results that can be compared with experiment. A wave function by itself is meaningless.

      The wave function is a pedagogical device, a quasi-classical surrogate intended to help students absorb quantum theory. It is only half the story. Continuous and deterministic evolution according to Schrödinger's equation doesn't square with the discontinuity and randomness of real physical processes.

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    3. The Bohr interpretation of QM is ψ-epistemic that says the wave function is non-existent and is only a gadget, largely mathematical, that is used to compute things found in measurements. Sabine's statement about instrumentalism is in line with this. The many worlds interpretation is ψ-ontological that says there is something physically real about the wave or wave function.

      I think it is not possible to say which is true. Which ever is the case is a choice made by the analyst or experimenter.

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    4. I think it is not possible to say which is true. Which ever is the case is a choice made by the analyst or experimenter. (Lawrence Crowell)
      Exactly. One can always argue that QM is a belief system. If so, it is an extremely successfull belief system. A beautiful one too, depending on the eye of the beholder.

      QM promises action-at-a-distance. A wave function, scattered over space and time, in line with (almost) pointwise action. Einstein was a bit late with his EPR-argument. He had to come up with his objections way sooner.

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    5. Werner wrote:
      >The wave function is a pedagogical device, a quasi-classical surrogate intended to help students absorb quantum theory. It is only half the story.

      I have never heard any physicist express that perspective!

      In real physics research, yesh, sometimes the density matrix is used, though, frankly, it is very rare in the areas I am interested in.

      But the wavefunction is not just pedagogical: it is and long has been used in real research.

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    6. Lawrence Crowell wrote: "there is something physically real about the [...] wave function" and "it is not possible to say which is true"

      That's giving up way too quickly! You seem to be an adherent of Bohr's transcendentalism. :-)
      To me, the distinction between epistemic and ontological Psi seems misguided, because the wave function is not the whole story. It is a mere fragment of the theory. MWI says nothing else is required, whereas Copenhagen acknowledges that continuous and deterministic evolution according to Schrödinger's equation isn't everything, although "measurement" remains an undefined (primitive) concept.

      Epistemic/ontological is a false dichotomy. A statistical viewpoint may be seen to put me on the "epistemic" side, but I would also say that "there is something physically real about the wave function". Physically real in the same sense that a Maxwellian velocity distribution expresses something physical about the molecules in a gas. What it says about an individual molecule is limited, but it is physical information all the same. What is problematic in quantum theory is that many people are cavalier about the distinction between an ensemble and its members.

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    7. PhysicistDave wrote: "But the wavefunction is not just pedagogical."

      Sure. The wording was perhaps a bit too provocative. (I'm glad you took the bait!)

      It is a psychological fact that many physicists think of the wave function as the essence of quantum theory. Schrödinger's equation predicts the continuous and deterministic evolution of "something", whereas discontinuity and randomness are the hallmarks of quantum physics. How does that fit together? Moreover, Schrödinger's equation is a classical equation. If the wave function is the essence of quantum theory, why should second quantization be necessary?

      Some people think that quantum theory is beyond human understanding, and quantum field theory even more so. But the fundamental issues emerge more clearly if you turn to QFT.

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    8. The density matrix is not used a lot in QFT. In fact, in QFT quantum states are not so often used as are the field operators that act on a Fock basis to give states. The density matrix though is heavily used in a range of areas of physics. The density matrix ρ = |ψ⟩⟨ψ| is seen trivially to be a Hermitian operator, which gives real eigenvalues for the measure of observables pertaining a system. In this case the eigenvalues are probabilities. These also correspond on a 1 to 1 manner with other observables in the Born rule. However, that connection is not solidly understood. In a subtle way we can ask what is meant by a probability as an observable. Probabilities often make sense within some ensemble of outcomes. We can take a frequentist perspective on this, or with a succession of measurements a more Bayesian look. In this setting we might be at least somewhat tempted to say that if the density matrix corresponds to observables that this means quantum states have some ontology.

      Does the density matrix mean the proper interpretation of QM is ψ-ontic? I would be hasty to conclude such. QM is a theory of the dynamics of wave amplitudes, or a matrix of then in an exterior product we call the density matrix. These obey completely deterministic dynamics, given by the Schrödinger equation. This is not a stochastic theory at all. Things only appear stochastic when a measurement occurs, or in general there is some spontaneous loss of quantum phase into entanglement with a reservoir of states, The probabilities give a distribution of possible outcomes, and those probabilities only make sense in some ensemble or Bayesian updates. This is something outside of the wave dynamics of QM. When a measurement of an observable occurs, there is something outside of what we think of as QM. We have a classical-like process, say a nonlinearity of the quantum system that reduces the quantum state to some stable, or transiently stable, classical outcome. By transiently stable it means a quantum state reduction is rapidly decohered to the same eigenstate in a Zeno machine fashion, so on a large time scale there is some apparently stable classical (like) structure.

      The density matrix carries a lot of the geometry of QM and entanglement. The density matrix is a type of projector and this connects the quantum mechanics to a geometry of states with projective spaces and flag manifolds. It is worth noting that Penrose worked a variant of this called twistor theory, which is an aspect of quantum gravitation and will be once some complete theory of that is found.

      To say the wave function is real or that it is not requires some sort of strong result. As I see it none exists. We have competing interpretations of QM, or QM measurement, that people gravitate into. The four main camps now are the Bohr CI, QuBism, MWI, and GRW collapse interpretations. The first two of these are ψ-episatemic and the last two are ψ-ontic. There are five if one includes the deBroglie-Bohm theory, but that is a minority perspective. In none of these is there any proof or evidence

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    9. Werner wrote to me:
      >It is a psychological fact that many physicists think of the wave function as the essence of quantum theory. Schrödinger's equation predicts the continuous and deterministic evolution of "something", whereas discontinuity and randomness are the hallmarks of quantum physics. How does that fit together?

      Y'know, pretty much all physicists have been aware of that since 1926. Yes, how indeed does it all fit together? An awful lot of us, from de Broglie, Schrödinger, and Einstein, down to Sabine and, indeed, me have been mulling this over for a very, very long time. I myself have been doing so for fifty years -- more than half the time since 1926!

      Yes, we know he problem: no one has come up with a solution that satisfies most physicists.

      Werner also wrote:
      > Moreover, Schrödinger's equation is a classical equation. If the wave function is the essence of quantum theory, why should second quantization be necessary?

      You are very badly misinformed!

      Where, oh where, is the "classical" (non-quantum) system satisfying the Schrödinger equation?

      And, "second quantization" is not necessary. "Second quantization" is just (first) quantization of Maxwell's equations or other non-quantized field equations. The term is archaic and misleading.

      And, yeah, yeah, I know about "second-quantizing" Schrödinger's equation. It's a kludge. You should either deal with the non-relativistic Schrödinger's equation in 3N variables, or, better still, do the moral thing and go to QFT.

      What on earth are you reading that still talks about "second quantization"???

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    10. Lawrence Crowell wrote: "We have competing interpretations of QM"

      Actually we don't. We would like to understand QM, but none of the "interpretations" deserve the name, as is evident from the heat of the discussions about them.

      "These obey completely deterministic dynamics"
      "This is not a stochastic theory at all"

      Wouldn't a stochastic theory provide a better fit to reality? We seem to have fundamentally different views on physical theories: should they describe reality, or appeal to theoretical preconceptions? QM is a hugely successful theory, and I've never had any doubt that it is here to stay. But at bottom it's a statistical theory. Only the lopsided view on the "wave function" has led even educated people to think of it as deterministic.

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    11. PhysicistDave wrote: "Yes, we know [t]he problem"

      Yeah, just shrug it off. Couldn't it have some bearing on the question whether the wave function is physically real?
      Or has "physical reality" become meaningless, or a taboo-word for you too?

      "where is the classical (non-quantum) system satisfying the Schrödinger equation?"

      Of course there is no official definition what counts as a classical equation. You can insist that it is classical only if there's no h-bar in it. What I meant was that the equation for the H-atom was of the same kind as the familiar classical equations for drums or organ pipes. That's why wave mechanics immediately became popular.

      Mathematically, also the time-dependent Schrödinger equation is not really different from a heat or diffusion equation. If you think that the imaginary "i" makes a fundamental difference, consider the design of AC-circuits. Electrical engineers use the same "i" (or "j"), and for the same reason. Their "quanta" are just so tiny and numerous that it is pointless to count them! Or would you suggest that electrical engineers use quantum physics even at 60 Hz?

      "What on earth are you reading that still talks about 'second quantization'?"

      I confess that my first encounter with quantum theory was in the year 1972/73. But this shouldn't be held against me. :-) I agree that the term is archaic, but the mathematics is that of QFT. If it's "the moral thing" to go to QFT, don't you agree that it is only for didactic reasons that Psi is introduced as a classical field first?

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    12. " Schrödinger's equation predicts the continuous and deterministic evolution of "something" "

      The Something is Energy and Momentum.

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    13. No, it is not. How about you stop making ill-informed comments for some while. A long while, preferably.

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    14. Physicist Dave asks: "What on earth are you reading that still talks about 'second quantization' ???" Allow me to point out that two (very good) pedagogical textbooks refer to "second quantization." First, a 2013 textbook by Stefanucci and Leeuwen entitled Nonequilibrium Many-Body Theory of Quantum Systems (chapter one entitled Second Quantization).
      A second example is the 2014 text by Lancaster and Blundell, Quantum Field Theory For The Gifted Amateur (page 19, read: "second quantization, waves behave like particles.").
      I prefer Peskin and Schroeder: "This procedure is sometimes called second quantization, to distinguish the resulting Klein-Gordon equation (operators) from the old one-particle Klein-Gordon equation (wavefunctions). In this book we never adopt the later point of view, we start with a classical equation and quantize it exactly once." (1995, footnote, page 19).

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  9. Typo: "This means that either the particle going left had spin plus 1 and the particle going left had spin minus 1". I think the second "left" should be "right".

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  10. So, Hamlet is wrong after all...
    Many thanks, I love it!
    J.

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  11. Who can show that entanglement cannot be a interaction rhythm of space-time that conserves antipodal states?

    Once you measure a state observable you are part of that antipodal rhythm...

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  12. How should Psi be pronounced? Is it P-Si, Si, or a superposition of the two? Or is the word not pronounceable until it is spoken, like when Prince changed his name.

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    1. James,

      Well, I pronounce it the way that I have heard it most often which in English is "ps-ai" (in German it would be "ps-ee". The easiest way to find out I guess is to listen to the video? I have no idea which one is the "correct" pronunciation, given that it's Greek and I don't speak Greek, but I can tell you that if you pronounce it this way physicists will know what you are talking about.

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    2. The Greek is ps-ee. I leaned Greek after I learned basic math but before I learned quantum mechanics, so I will pronounce things incosnsistently: pi 'p-ai' but psi 'p-ee'. C'est la vie.

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    1. I would appreciate if you would read the book before guessing that the title and subtitle refer to. You got it badly wrong. You, as almost all hobby physicists, most of whom are bad at math, are hoping that I am criticizing the use of mathematics in physics, when in fact I am criticizing that physicists do not take math seriously enough.

      And needless to say, the 3rd law of motion is not the same as entanglement.

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    3. John,

      Let me see, you didn't read my book, but have opinions about it anyway. You didn't bother to actually learn the mathematics of quantum mechanics (that's pretty obvious) but have opinions about it anyway. Then you come here and expect that I answer your questions. Why the heck would I want to do that?

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    5. John wrote:
      >Superposition of something (Amplitude Modulation)
      -> The amplitude of a High Frequency signal varies in proportion to the transmitted message (Low Frequency)
      -> Here we have a superposition of a High (Carrier) with a Low Frequency (something) signal.

      Which proves that you know as little about the operation of AM radios as you do about physics.

      No: AM modulation consists of taking the baseband signal (plus a constant offset normally) and using that to multiply the carrier signal.

      Superposition is about adding not multiplying.

      Now, you can Fourier analyze, and then you will have "sidebands" at the frequencies fc-fb and fc+fb, where fc is the carrier frequency and fb the modulating frequency.

      But, trust me, that is way beyond you.

      John also wrote:
      >Entanglement of two superpositions of something
      -> The first superposition corresponds to one particle (actually particle and something else)
      -> The second one to the other particle (actually particle and something else)
      -> What does entanglement practically means? It means to find a mechanism to couple those two superpositions with each other
      ..etc.

      All just utter nonsense, John. Most of what you wrote is "not even wrong." It's Jabberwocky.

      John also wrote:
      >As you may understand, I like to put people to think on their feet (all other arguments are pure preheated food -> see established science) therefore according to my view, the today's description of both phenomena refer to the effect (there is nothing inside those expressions that refer to the cause).

      Also meaningless gobbledegook.

      John, I do have a question for you: is there any conceivable way to get you to understand that you have no idea what you are talking about at all and that even your questions are quite meaningless?

      No, I did not think so. Are you aware of the theological concept of "invincible ignorance"?

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    6. There is much to pick at in John's writing but I think to cut to the quick, his observation is correct and he just needs to accept it into his heart: Cause and Effect is a feature of story-telling and not of physics. Physics will say, F=ma, and someone will tell a story, a force causes an acceleration. It does not. Aristotle will encourage you to think of one of these as the 'logical prior,' but to heck with Aristotle, what did he know.

      There is a sense where beta decay, as a very simple and direct example of an uncased effect, is far more worldview shattering than some of the fancier results.

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    8. John wrote to me:
      >Thanks for your feedback (a little bit hard, actually) PhysicistDave!

      Tough love, John, tough love!

      Your latest post does sound as if you, uh, got more sleep than your first post.

      John wrote:
      >What I tried to share above (maybe in a not clear way) is we have two phenomena where the outcome (namely the effect) is probabilistic.

      Yes: the Schrödinger equation is deterministic, but quantum mechanics (and experiment) are probabilistic.

      That is one way of stating what the measurement problem is. Almost all physicists agree that somehow this has to be addressed, but they differ as to how to address it.

      A number of us physicists today -- including, it seems, Steve Weinberg, Sabine, and me -- feel that none of the widespread approaches for dealing with this really works.

      John also wrote:
      >The question is very simple and clear: Is the cause of a probabilistic effect also probabilistic? Of course not.

      I'm not sure I agree: the result of a roll of the dice is probabilistic; it has a probabilistic effect on whether I win or lose money.

      Why can't probabilistic effects have probabilistic causes?

      It sounds to me as if you are appealing to something like Einstein's "God does not play dice with the universe." It does seem to me that Bohr's reply is apt: who are you to tell God what he can do?

      John also wrote:
      >Actually, we could say the cause and the effect are fundamentally entangled with each other that means there is always a mechanism (which is intrinsic to the cause-effect). There is no cause without mechanism that implies no effect, and vice versa.

      I do not see why that has to be true either: why can't the laws of physics just be mathematical relationships without anything that strikes humans as a mechanism?

      Look: I suspect most physicists get into physics because, when they are young, they learn that some physical phenomena can be explained mechanistically and deterministically, and they have personalities that find this appealing (the word is "Aspergy," I think).

      So, yeah, most physicists would probably prefer that the world be as you suggest.

      But I do not see how we can insist on it: Nature does as she will, not as we wish.

      And thanks for writing more clearly!

      Dave

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    10. "Look: I suspect most physicists get into physics because, when they are young, they learn that some physical phenomena can be explained mechanistically and deterministically, and they have personalities that find this appealing."

      I've definitely met folks like that! I started my journey learning about EPR and inherent randomness in middle school, so this has always been an appeal. The desire to return to a more classical mechanistic view has always seemed weirdly retrograde to me.

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    11. John wrote to me:
      >Quantum Tunneling could be justified (without a Wave function) as a natural effect if and only if, there was an expression that would engage a reduction of the effective inertia (or the total energy of the particle) with barrier's height and width (this is what I call cause/mechanism).

      John, part of the problem that physicists, and scientists in general, have communicating with non-scientists is that the non-scientists do not have a broad overview of science nor do they understand the purpose of science.

      Our goal as physicists is not to explain one isolated phenomenon with some ad hoc mechanism.

      In the case of quantum mechanics, we have one single well-defined theory that does a good job of explaining hundreds (thousands?) of different phenomena. One of those happens to be quantum tunneling.

      Quantum theory was not designed to explain quantum tunneling.

      It just fell out of the theory after the theooy was created to solve other problems.

      That is the key point.

      There have been numerous debates among philosophers as to whether science is about prediction or explanation or better parametrizing data or whatever.

      And all those discussions miss the point.

      A good scientific theory ties together an overwhelming amount of data, phenomena, etc. to such a degree that it becomes silly to think that the theory is not telling us something about reality.

      Quantum mechanics does that: the explanation of tunneling is just one of many by-products of the theory.

      The same is true of the atomic theory, special relativity, evolution, the heliocentric theory, etc.

      The same is most certainly not true of your suggested idea to explain tunneling. We do not need your idea because we already have a perfectly good explanation. But more than that, your theory is just a "one-off": your theory does not also give a quantitative explanation of lasers, molecular bonding, high-energy particle physics, electron energy bands in semiconductors, etc. But quantum mechanics does all of that and more.

      John also wrote:
      >Mathematical relationships without cause/mechanism that describe natural effects lead to absurd. Natural effects presuppose causes/mechanisms.

      Why? How do you know?

      Look: when we talk about "mechanisms" we usually mean something somehow similar to the simple machines we know about in real life -- a can opener, say. Solid parts that push or pull on each other through direct contact, etc.

      But we know that the subatomic world is not like that. Why should it be? The properties of macroscopic solid objects are weakly emergent from the subatomic world. The parts govern the whole, not the other way around.

      And we now understand in substantial detail how that works.

      At some level, physics has to reduce to simple brute facts about how the smallest known constituents of matter behave. And those brute facts may indicate that those smallest constituents do not behave much like the parts of a can opener: i.e., they do not meet your criteria for being a "mechanism."

      That seems to be what the world is really like.

      Now, there is indeed a problem with quantum mechanics, as Sabine and I and many other physicists have pointed out: the measurement problem. But the problem there is not the lack of “mechanism.” The problem is that if you take the theory that works so well for subatomic phenomena and try to explain macroscipic phenomena with the same theory it all works really great with one exception: the measurement postulate – Schrödinger's cat and all that.

      We actually have a perfectly consistent theory that solves that problem – Bohm-de Broglie mechanics. But the way that Bohmian mechanics interacts with relativity, while perfectly consistent, is so kludgy that most of us believe that Bohmian mechanics is not true.

      Therefore, we consider the measurement problem unsolved.

      Otherwise, quantum mechanics is cool, completely cool: we have no need for ad hoc ideas like your tunneling idea.

      Dave

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    14. John wrote to me:
      >Well I picked those two effects because of blog's limitation. There are more inconsistencies in QM (and in general Physics) like the Casimir effect.

      Well... about all I can say is that what you think are inconsistencies aren't.

      John also wrote:
      > I am speaking about something so simple and fundamental that exists in classical physics for centuries but overlooked that potentially may affect all areas of Physics...

      John, almost everyone (as far as I know, zero exceptions!) who thinks that way is a crackpot. I do not mean to be rude, but no one that I know of has made a significant contribution to physics for more than a century unless they had pursued physics seriously at least to the level of being a grad student.

      If you are a normal person, you should think about that and realize that your belief that you know something that has been overlooked for centuries is more likely to be a delusion than a real insight.

      And if you would seriously take that approach in dealing with us physicists and say, "Guys, can you tell me where I am missing the boat in thinking __________" you'd be more likely to get a positive response.

      John also wrote:
      >Your argumentation (most physicists do this mistake) mixes the measurement problem with the essence of the effect (better cause-effect).

      See: again you just assume you know more than professionals in a field you clearly do not understand rather than considering that maybe you are wrong.

      Or you insult physicists by saying:
      >It seems to those who do not want to think on their feet because they feel/afraid any out of the box proposal is futile and may also cost their career.

      John also wrote:
      >The easiest answer (that you may probably agree) is such arguments like those I propose (but not exposed yet) are nonsense. Is this scientific? NO. What is scientific is to present a counter-argument that must be consistent.

      No, we do not owe you a counter-argument.

      Look: do you go online and lecture brain surgeons and tell them that they are full of nonsense and you know their field better than they do?

      I very much doubt you do. And you know how they would respond if you did.

      But, somehow, you think that you can do this to physicists and they will accept it.

      They won't, John. You'll notice that i am engaging you more than any other physicist here, mainly because I am intrigued about whether there is some way to reach out to people who are delusional. I keep thinking there must be, despite all the evidence to the contrary!

      But, again, just think about why you do not behave this way to brain surgeons or auto mechanics or airline pilots and then, perhaps, you can see why this behavior is not going to get physicists to listen to you.

      Or not.

      Dave

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    17. John wrote to me:
      >I have written a paper and is already under review in the Journal Foundations of Physics (Springer) since mid March. I have faith to expect something good (approved) but as you may understand even if I am right, would they give me the chance (no institutional affiliation as also I am not a Physicist) to publish my paper in their Journal? Or would you?

      John, I know of FoP: they are somewhat more open to “speculative” ideas then, say The Physical Review. However, I strongly suspect that your ideas will go far beyond their accepted bounds. The fact that you have no degree in physics, no academic position, and no publishing record in physics is not going to help either.

      Odds are they will turn it down.

      And that is not unreasonable. Even established physicists such as Max Tegmark or John Wheeler would have trouble getting ideas published that strike the editors as goofy (and Tegmark and Wheeler both have had a few pretty goofy ideas!). But at least, the editors might say to themselves that they know Wheeler or Tegamrk has done some pretty good work and maybe the editor is missing something.

      You will not have that benefit of the doubt.

      Your list of “discoveries” is also going to spook most physicists.

      I mean, when Schrödinger published his famous equation, I do not believe he said, “And this will solve the problem of chemical bonding, explain the behavior of electrons in semiconductors, create a framework for understanding a whole new zoo of elementary particles, etc.” even though it did do all those things.

      All physicists know that almost always when someone claims all the discoveries you claim, they are simply wrong. Even worse, much of what you claim goes against very well-established physics.

      Why not just start up a blog and post it? It only takes a few minutes. And if you link to the blog in your blogger profile any of us can get to it. Sabine does not want a link here, but if you just say, “Hey, click on my profile and go to my blog” anyone can find it.

      If you do that, I'll look at it. I assume that you do know already that my comments will almost certainly consist of: this part disagrees with known empirical facts, that part is meaningless math, etc.

      One of the problems that amateurs like you have is failing to understand that even if a professional such as Sabine or Peter Woit were to post an ambitious new theory, almost certainly the rest of us physicists would be able to prove that it was wrong.

      Almost all radically new ideas do turn out to be wrong.

      Physicists understand and accept that.

      I'm afraid most of you amateurs do not. You think that when we “kick the tires” and poke holes in your carefully crafted theories, we are being mean. No, that is how science works. The guy who proves you wrong has shown you a lot more respect than the guy who kindly says “Now that is really interesting!” and nothing more – the latter guy is just being patronizing.

      Alas, it seems impossible to get this through to non-scientists.

      Dave

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  14. I think if I need the wave function to understand the end result in an entangled particle system; so somehow the wave function is something real, or has real components; the phenomenon works as if each of these were the observer of the other, without the need for our consciousness or presence; if there is a mathematical form that describes it; then that form must have something of real; I suppose?.

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    1. "Each of these the observer of the other"-- yes, and consciousness is absolutely unnecessary. Consciousness really plays no role. It should be regarded as epiphenomenal and merely along for the ride in certain instances. Each the observer of the other might as well be framed as each the cause of the other. It amounts to the same thing. Actually, I think this sort of view fits well into a super deterministic picture.

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    2. Rick Lubbock hi, i realized that you said something similar; Yes, it seems that nature already has its own "surveillance system" hahaha. I don't know how a superdeterministic theory works; but my belief (it is only belief) is that the particles, the fields and the space are forms of existence of matter, if each one of them could be formulated mathematically, then the equations would be solved in order to preserve the symmetry; Although I do not believe that such a system can be built with fundamental lengths, it is trying to explain quantum physics with a type of classical physics that would not work.

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    3. Drs Hossenfelder and Palmer have a paper on superdeterminism that is well worth reading. I think she has a link to it somewhere on this blog.

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  15. Schrodinger writes (1935): "Best possible knowledge of a whole does not include best possible knowledge of its parts--and that is what keeps coming back to haunt us." (page 167, Zurek & Wheeler, Quantum Theory and Measurement). Interestingly enough, in this famous "cat paradox" paper, Schrodinger provides a simple argument for the necessity of discreteness coupled to measurement (page 164).

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  16. It's never been clear to me that "(e)verything is described by a wave-function," rather than fundamental entities like photons or leptons or whatever. Though saying being fundamental means that you can write a wave function for it is the same thing?

    At any rate, it is hard to imagine *a* wave function for a dead cat. But if there are multiple wave functions, questions about reality are not even asked. But then, the mathematically equivalent not superposed not-dead-or-alive clearly has no properties, thus cannot be real. But if you do ascribe some thing you label reality to a part of the wave function, as far as I can see, you get virtual universes...but no singular real universe.

    Guessing that the "prefactors," (coefficients in equations according to Google,) are supposed to have something to do with "realistic?" The instrumentalist meaning seems to be, prefactors are coefficients that give correct predictions, since I can't make heads or tails of what point there is to arbitrary prefactors. This sounds like an iron commitment to the proposition that "science" isn't about describing reality but correlating readings on instruments in specified experimental setups. I have no idea how this is reconcilable with the claim predictions aren't everything.

    "You could say, for example, that Schrodinger’s cat is not in a superposition of dead and alive, but that it is instead in the not-superposed state dead-and-alive. And that’s mathematically just as good." It is no doubt good mathematics, and good anti-realism too. But the "state dead-and-alive" begs the question of what the body temperature of the dead cat is when the death chamber is opened, doesn't it? Measurement not only determines the state of the cat now, but in the past too!

    As to entanglement, the issue with decoherence is, where does the environment come from? If decoherence is what disentangles, how long after the Big Bang did an environment emerge?

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    1. S Johnson wrote:
      >At any rate, it is hard to imagine *a* wave function for a dead cat.

      Only for those who lack imagination, or a basic knowledge of physics.

      SJ also wrote:
      >It's never been clear to me that "(e)verything is described by a wave-function," rather than fundamental entities like photons or leptons or whatever. Though saying being fundamental means that you can write a wave function for it is the same thing?

      You are really betraying your ignorance of physics here!

      It is routine to (successfully) use wavefunctions for things much, much bigger that a single photon or lepton.

      SJ also wrote:
      >Guessing that the "prefactors," (coefficients in equations according to Google,) are supposed to have something to do with "realistic?" The instrumentalist meaning seems to be, prefactors are coefficients that give correct predictions, since I can't make heads or tails of what point there is to arbitrary prefactors.

      You are babbling meaninglessly.

      As you say, you cannot make "heads or tails" of what you are talking about.

      SJ also wrote:
      >As to entanglement, the issue with decoherence is, where does the environment come from? If decoherence is what disentangles, how long after the Big Bang did an environment emerge?

      Just no. Really: no.

      Look: if you have read some definite thing that confuses you that you can quote briefly, then politely ask a question.

      But for you to make these unbearably silly statements as if you might actually be doing anything except stringing words together, you are just demeaning yourself.

      "It is better to remain silent and be thought a fool than to open one's mouth and remove all doubt." Mark Twain.

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    2. S Johnson wrote: "it is hard to imagine *a* wave function for a dead cat"

      I agree. Also for a live cat.

      PhysicistDave, in his characteristically outspoken, just "mildly" insulting way wrote: "Only for those who lack imagination, or a basic knowledge of physics."

      Of course he cannot imagine such a wave function either. It's an empty claim -- all he can do is write down a rather meaningless string of symbols: |dead>.

      S Johnson: "what point there is to arbitrary prefactors"

      Very good question! Discussions of Schrödinger's cat invariably involve the most notorious of irrational numbers: the square root of 2. This has to do with unitarity, of course. But one never sees |dead> subtracted from |alive>, or even multiplied with an imaginary "i". According to the rules, those would be different states. Of course, the phase factors could be included in the definitions of |alive> and |dead>. But are these really *two* states that can be coherently superposed?

      It is distracting that Schrödinger thought of such a ridiculous case. Instead of the cat he could have chosen a calorimeter, where triggered by the Geiger counter, a small volume of water would be heated from 14°C to 15°C. Would people constructing kets from dead and alive cats dare to write down
      |Psi> = (|14°C> + |15°C>) / sqrt(2) ?
      This is clearly an abuse of notation. Using Boltzmann's famous formula you find for 1cc of water an entropy increase ln W = S/k of the order of 10**23. And that's just the *logarithm* of the number of states! The sqrt(2) is clearly suspicious. I find these "superpositions" utterly meaningless, but perhaps Mr. Know-it-all can reveal the deeper meaning to us fools.

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    3. "It is routine to (successfully) use wavefunctions for things much, much bigger that a single photon or lepton." Although I've mentioned both superpositions and entanglements, plainly I am aware that wavefunctions address more than single photons or leptons. The "single" was just made up by you, a hostile mis-reading. No argument will ever survive shameless malice. Thus there is no reason for anyone to value your opinion, though perhaps the host is gratified. If you didn't understand why it was "*a*" wave function, rather than simply "a" wave function, you should have asked.

      Your best bet for fame and glory is to write the wave functions for a dead cat and a live cat, respectively. (Not clear that density matrices count as rigorous argument...)

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    4. S. Johnson wrote to me:
      > I am aware that wavefunctions address more than single photons or leptons.

      The wavefunction refers also to a whole lot of things besides leptons and photons.

      You have no idea what you are talking about, you are just making things up, and you have proven yourself to be completely ignorant on this subject.

      SJ also wrote:
      > Thus there is no reason for anyone to value your opinion, though perhaps the host is gratified.

      As opposed to you who is just spouting silly nonsense?

      Look: what I quoted from you is the following:
      >SJ also wrote:
      >It's never been clear to me that "(e)verything is described by a wave-function," rather than fundamental entities like photons or leptons or whatever. Though saying being fundamental means that you can write a wave function for it is the same thing?

      As far as we know, everything is made up of "fundamental entities" such as leptons, quarks, etc. We have not detected anything else in the universe. And, as far as we know, everything can therefore be described by a wavefunction.

      I know you are ignorant of that fact, but that just is the basis of modern science.

      Chem, astronomy, and geology reduce to physics and, aside from the still unsolved problem of quantum gravity, physics just is quantum mechanics. And biology reduces to chem and physics.

      For better or worse, this just is twentieth-century science.

      And your silliness about "prefactors" sounds as if you are high or something. For example, I did a search on "prefactor" in Weinberg's Lectures on Quantum Mechanics: nothing came up. This is not a standard issue in quantum mechanics: it is just your weird delusion. (Yes, I know the word "prefctor" will sometimes show up in papers on QM, just as the word "left" sometimes shows up in papers on quantum mechanics -- you want to refer to the left side of an equation, then the word "left" is useful, and if you want to refer to a factor that comes before something else, the word "prefactor" might be useful. But "prefactor" has no deep meaning or relevance in quantum mechanics, contrary to your weird musings.)

      Do you do this to brain surgeons or auto mechanics? Do you just spout nonsense about their field of expertise and then insult them when they quite correctly admonish you for spouting nonsense?

      Frankly, I really hope you do, because you will then get exactly the amount of help from surgeons or auto mechanics that you truly deserve.

      I sincerely hope you have to live with those consequences someday.

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    5. PhysicistDave wrote: "I sincerely hope you have to live with those consequences someday."

      Dave,

      what made you so upset? Leaving the content aside, just looking at the language: you have really soiled yourself. It may be too much to expect an apology, but possibly you find the "Delete" button.

      Away from ad personam remarks, back to science: As you indicated, it is important to remember the lessons of the past. In an essay, Walter Elsasser wrote (1971):

      Within classical physics, symbols may quite legitimately be taken as representing objects, and indeed often representing all available knowledge about the objects. But in quantum mechanics the relationship is not so simple because the most common symbol, a wave function, does not refer to an individual object at all; it describes the statistical distribution of a large number of equivalent objects, a class, and contains very little information about an individual object considered by itself, apart from the class.
      ("Perspectives in Quantum Theory", p.213, Elsasser's emphasis)

      I thought that was common knowledge in the seventies, but it seems largely forgotten now. Concerning the mantra that every physical system is described by a wave function, S Johnson touched a crucial point. Nowadays, many physicists apparently take it to mean: "A wave function represents an individual system." But thinking of the wave function as representing an ensemble of identically prepared systems is the only decent way to dispose of Schrödinger's cat. If you can think of another way, I'd be eager to hear about it.

      Sincerely,

      Werner

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    6. Since it was the post that brought up prefactors, you can argue the irrelevance/meaninglessness of prefactors with our host, the author of the post. The question mark and the work "guessing" in my original comment clearly showed to honest eyes that I didn't understand their role in somehow making superpositions easy, common sense ideas either. Trying to take me task for the same problem in understanding what the business about prefactors is an egregious example of meaningless babble.

      Worse than meaningless, the assertion everything reduces to physics is aspiration. Astronomy needs General Relativity, so this is witless nonsense on that ground alone. Given the role of thermodynamics in chemistry, not sure that chemistry reduces to quantum mechanics either, inasmuch as I'm shaky on how "information is never lost" implies "information is always lost." Or for that matter how "time reversible" leads to the "arrow of time," which geology uses without thought. As for biology...your real problem is you're using "reduces to" in an incompetent way, a sciency sounding substitute for thought.

      The only true thought in this response is the malicious joy in fantasizing physical harm to me, for some offense or other. You have nothing else positive to say, only content free invocation of your personal superiority and malice. You could be Lubos Motl under a pseudonym!

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    7. Werner wrote to me:
      >what made you so upset?

      You mean aside from the fact that you arrogantly say things that are not true, indeed that yoou know are not true?

      For example, above you said:
      >The wave function is a pedagogical device, a quasi-classical surrogate intended to help students absorb quantum theory.

      But you later admitted that you knew that was not true:
      > The wording was perhaps a bit too provocative. (I'm glad you took the bait!)

      No it was not "too provocative" -- it was a lie. And I "took the bait"? Yeah, because I call you out as a liar.

      Or when you said:
      > Schrödinger's equation is a classical equation.

      You clearly know that is a lie, too.

      Yeah I know: you consider lying to be a way of being "provocative" and of setting out the "bait."

      I don't: I consider it to just be lying.

      I hate liars and con artists, Werner. I have hated liars since I was a very young child. And I hope bad things happen to them.

      I therefore despise you as a human being.

      No doubt, as a liar and con artist yourself, you cannot grasp this, but that is the answer to your question.

      I hate and despise people like you. As do all decent human beings.

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    8. S. Johnson wrote to me:
      >You could be Lubos Motl under a pseudonym!

      Nah – I lack Lubos' Central European sense of savoir faire! But thanks for the compliment!

      SJ also wrote:
      >Since it was the post that brought up prefactors, you can argue the irrelevance/meaninglessness of prefactors with our host, the author of the post. The question mark and the work "guessing" in my original comment clearly showed to honest eyes that I didn't understand their role in somehow making superpositions easy, common sense ideas either.

      Okay, now I see what you are getting at.

      The answer is that in certain situations it is fairly straightforward to prepare a system in such a way that we know what the coefficients (“prefactors”) are. Explaining why is complicated, which is, I suppose, why Sabine did not explain it in detail. Basically, a state that in one representation only has one “prefactor,” basically set equal to “1”, is in another representation, a superposition with a variety of coefficients determined by the theory.

      And, indeed, in many cases, one gets that superposition by just waiting for time to pass.

      How do we know this “really” happens? Well, the theory predicts that when this happens, certain experimental results will occur, and those predictions have been born out to very high accuracy.

      SJ also wrote:
      >Worse than meaningless, the assertion everything reduces to physics is aspiration.

      It is an aspiration that has been achieved to a stunning degree.

      Call it a hypothesis if you will, a hypothesis that has been confirmed again and again and again and, thus far, never refuted.

      The reductionist program really has been stunningly successful.

      If you are not aware of that, you know almost no science at all.

      There are really only three serious current problems with the reductionist program: the quantum measurement problem, the problem of quantizing gravity, and the problem of consciousness. A very large number of physicists – most certainly including Sabine and me – have acknowledged all of those problems. I think most physicists think all three can be solved within the framework of physics. I am a bit of a heretic because I have argued at length in many places, including Sabine's comment section, that the problem of consciousness probably cannot be solved by physics as we know it.

      SJ also wrote:
      >Given the role of thermodynamics in chemistry, not sure that chemistry reduces to quantum mechanics either...

      A good example: modern statistical mechanics is simply applying quantum mechanics to systems with many, many components. Nothing more.

      SJ also wrote:
      >As for biology...your real problem is you're using "reduces to" in an incompetent way, a sciency sounding substitute for thought.

      Your ignorance of science, again.

      SJ also wrote:
      >The only true thought in this response is the malicious joy in fantasizing physical harm to me, for some offense or other.

      Physical harm??? You are paranoid. I merely suggested that if you behave in an obnoxiously contemptuous way towards surgeons or auto mechanics, they will treat you as you deserve. That is, they will not provide you with the services or assistance you might want: as I said above, “you will then get exactly the amount of help from surgeons or auto mechanics that you truly deserve.“

      Not “fantaiszing physical harm” to you (!), but just hoping that people treat you as you treat them.

      And that is why you probably do not treat surgeons or auto mechanics with contempt.

      But you think you can arrogantly make statements to physicist that simply display your ignorance of modern science and the physicists will tolerate it in a way surgeons or auto mechanics would not.

      Physicists are not as forgiving as you seem to think, indeed not noticeably more forgiving than surgeons or auto mechanics. Treat us with contempt, and we are happy to return the favor.

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    9. Dave,

      as is evident from your other comments, you know the difference between being dishonest and being deluded. Instead of clearing up my delusions, you attack me as a liar. In my comments I have carefully explained why I believe what I have written -- it is there for everybody to see and read it. Your replies to my comments invariably target the peripheral, irrelevant, or personal. Why is that? The only reason I can think of is that you don't have any scientific arguments to place against mine, and are too vain to admit it.

      I bet you have nothing scientific to reply, and it'll be safe to ignore it.

      You wrote: "I hate and despise people like you."
      I wish you the very best.

      Werner

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    10. PhysicistDave3:04 AM, May 19, 2020

      "As far as we know, everything is made up of "fundamental entities" such as leptons, quarks, etc. We have not detected anything else in the universe."

      So you do agree that conscious experience is physical, as far as we know! You've checkmated yourself, Dave ;)

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    11. Physicist Dave lies about how he doesn't fantasize about physical harm to people he can't give sensible answers to. Then it is stated that thermodynamics is simply QM, which rather makes one wonder how thermodynamics preceded QM. The quick answer is that Physicist Dave's hand waving version of "reductionism" pretends there is no question of how thermodynamics quantum mechanically creates the arrow of time. And his insistence that he's already found the fundamental secret of what to reduce to, QM, has already succeeded, hasn't been demonstrated.

      And Physicist Dave shows the incompetence of his idiosyncratic version of reductionism even more clearly when he claims there is a grave difficulty in explaining consciousness. No, there is no supernatural explanation. His version of reductionism thinks there is, but he's full of shit.

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    12. @ Steven Evans,

      You're giving a classical description. Quantum theory is best understood as a form of perspectivism.

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    13. Steven Evans wrote to me:

      >[Dave]"As far as we know, everything is made up of "fundamental entities" such as leptons, quarks, etc. We have not detected anything else in the universe."

      >[Steve]So you do agree that conscious experience is physical, as far as we know! You've checkmated yourself, Dave ;)

      Hey, Steve! Hope you are doing well.

      Nope: how consciousness works, as I have said again and again, is not one of the things we know -- that point has, after, all been my major theme on the subject.

      Yeah, among all the things we know "as far as we know," leptons, quarks, etc. are all that is there.

      But, my whole point is that consciousness is further than we know.

      Neither I nor you nor anyone else can say what else is there with consciousness.

      In fact, if you recall, I have emphasized again and again that perhaps all that is going on with consciousness is that, in addition to physics, you need a “translation dictionary” to tell you what physical states are associated with what experiential states.

      In that case, there would be something physics does not know (the translation dictionary) but no substance there beyond physical objects.

      (For our cognoscenti, all I have really done is explain in concrete terms what the theory philosophers call “dual-aspect theory” would mean scientifically.)

      So, if my minimalist “translation-dictionary” theory is true, there is nothing there except quarks and leptons, etc., but there are emergent properties of quarks and lepton in bulk in certain unusual situations that cannot be explained by current physics – you need the translation dictionary.

      Could even be true – though I doubt it: as you know I doubt all theories of consciousness including my own.

      As we have discussed, I slightly prefer my “consciousness is to brain as candle flame is to candle” theory. In that case, I suppose there is something there besides quarks and leptons, but it is not, in philosophical terms, “self-subsistent”: concretely, the mind dies if detached from the brain just as a candle flame cannot exist without a candle.

      Pretty metaphor, don't you think?

      Of course, it is probably false: have I mentioned that I doubt all theories of consciousness including my own?

      I have spun out various other theories, all of which I suspect are false.

      The difference between a scientist and a crackpot is that a scientist is skeptical of his own theories.

      As my teacher Dick Feynman liked to say, “The first principle is that you must not fool yourself — and you are the easiest person to fool.“ (I was there in the audience, by the way, when Feynman gave that “cargo-cult science” talk at 'Tech's 1974 commencement.)

      Alas, Steve, you are not skeptical of your own theories!

      All the best,

      Dave

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    14. PhysicistDave11:53 PM, May 21, 2020

      "But, my whole point is that consciousness is further than we know."
      That's an assumption. You need to be more critical of your theories, Dave.

      "Neither I nor you nor anyone else can say what else is there with consciousness."
      The evidence tells us nothing else is there currently.

      "In that case, there would be something physics does not know (the translation dictionary) but no substance there beyond physical objects."
      An assumption. You need to be more critical of your theories.

      "For our cognoscenti, all I have really done is explain in concrete terms what the theory philosophers call “dual-aspect theory” "
      Wow! Amazing! I feel like I'm imbibing really deep intellectual knowledge here. So there are 2 aspects to matter. And then? What are the facts derived from this idea? Not a single one. The dual-aspect theory, dear, oh, dear.

      Delete
    15. Prof. David Edwards12:25 PM, May 21, 2020

      "You're giving a classical description. Quantum theory is best understood as a form of perspectivism."

      Did I. Of what?

      Delete
    16. S. Johnson wrote to me:
      >Then it is stated that thermodynamics is simply QM, which rather makes one wonder how thermodynamics preceded QM.

      For simple historical reasons: everyone with any serious interest in science knows that thermodynamics was worked out phenomenologically before Maxwell, Boltzmann, et al. figured out how to derive thermodynamics from statistical mechanics. And statistical mechanics was worked out before quantum mechanics was discovered.

      But nowadays statistical mechanics really is just figuring out the results of quantum mechanics for systems with a very large number of components.

      I know you are too ignorant of science and the history of science to know this, but that is not my fault.

      What is your fault is your extreme rudeness to people who point out your egregious errors because they know a lot more than you do. I truly do hope that this is how you treat surgeons and auto mechanics when you need their help.

      SJ also wrote to me:
      >No, there is no supernatural explanation. [Dave's] version of reductionism thinks there is, but he's full of shit.

      A supernatural explanation would not be reductionist at all, quite the opposite in fact. Re-read Sabine's post on reductionism. You are confused.

      Consciousness is the one area in which I suspect reductionism will fail.

      But, I have no “supernatural explanation” for consciousness – indeed, I have no explanation at all.

      There are, quite obviously, some things humans do not know, though the area of human ignorance has shrunk a great deal in the last century.

      I merely note that the explanations people have tried to concoct to explain consciousness do not work.

      I am just the fellow who comes around after the party, picks up the trash, and tosses it into the dumpster.

      And you are the guy who is very badly confused.

      And very, very rude.

      Delete
  17. The Shrodinger's cat is as imaginary as the multiverse, or as imaginary as a "universal wavefunction", all these cases are typical examples of how meaningless you can get when your reductionist mindset is unbounded.
    Shrodinger's cat is meaningless simply because a real cat is not a quantum object that can be described by a Shrodinger equation, not even in principle.

    Sugar molecules of around 40 atoms already exhibit parity symmetry breaking, a living cat is a lot more complex than sugar molecules with lots of dynamic irreducible emergent properties, the "state" of a cat is not a superposition of an assembly of atoms quantum states.

    Still many have not internalized that the level of information(complexity) encoded in your assumptions(axioms) bounds the level of information encoded in your conclusions/results.

    Chaitin's: "if one has ten pounds of axioms and a twenty-pound theorem, then that theorem cannot be derived from those axioms."

    By the same argument any theory always has a limited range of applicability because anything with more information content(complexity) than its assumptions will be irreducible formally from that theory unless its assumptions are modified.

    And obviously there is a lot of more information content in a living cat structure than in Quantum Mechanics assumptions. A living cat dynamic structure is well beyond Quantum Mechanics range of applicability.

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    1. I suppose Bee's punishment for writing engaging and popularly-accessible physics is to be hounded eternally by cranks and know-nothings.

      Delete
  18. Werner:
    "The wave function is a pedagogical device, a quasi-classical surrogate intended to help students absorb quantum theory."

    This is not so. Physicists use the wave function in their research all the time. Search 'wave function' in arXiv and you'll see tons of professional researchers using the idea. Just a few weeks ago I attended a talk at an online conference that focused on the wave function of a certain nucleus.

    You can argue whether physicists should be doing this if you like, but it's a fact that the wave function is not just a pedagogical device.

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    1. "First Approximation":

      I know all this. You can find my reply in the original thread.

      Delete
  19. The difficulties with understanding quantum mechanics are that it violates so much of our ordinary expectation of things. This is not only from our ordinary experience of the physical world, but from our classical understanding. However, it really has to be pointed out that classical mechanics is not entirely easily understood either and was doubly difficult in the late 17th century and early 18th century. In fact, scientific theories and results often counter human expectations or desires. If one looks at renaissance art it is filled with pictures of people, and even entities presumed to be at the foundations of reality, angels and gods or God, are depicted as people. The scientific revolution came out of the renaissance and put together a mental image of the world that was quite different.

    The ideas of medieval physics, say from Oresme, Grosseteste, Averroes etc. tended to see the motion of an object as requiring a constant force. There was some sort of aether or fluid in space that acted on any moving object, say a projectile thrown by a person or a trebuchet. This included the motion of planets, which of course at that time were thought to revolve around Earth. This picture from the time of Copernicus, to Galileo and Kepler and culminating with Newton was a thrown in disarray. Newton said a body remained in a constant state of motion, on a straight path with constant velocity, unless acted on by a force. Gravitation was even stranger, for now there is some invisible net of force emanating from a gravitating body that we directed radially and not angularly. This was hard for people to grapple with. There were following issues with Newton’s “fluxions” in his calculus, which Leibnitz made a bit more exact, but this lead to developments in calculus, mostly in Germany and culminating with Weierstrass which lead to deep mathematics on integration by French mathematicians culminating with Lesbegue.

    Classical physics is not that intuitive, and teaching basic physics is hard if one tries to keep as many students on board as possible. Even for those who learn physics and then become astronauts it requires 10s of millions of dollars of education to train them to work in outerspace. The simple fact is that we are on an experiential level Aristotelians. Medieval physics, or really pre-physics, is based on Aristotle’s physics, he even penned a book Physics, that served one of the bases for medieval pre-science. Even Penrose, Witten, as were past luminaries Feynman, Einstein and Hawking, are from an experiential level Aristotelians. Those who have been in prolonged weightlessness in outerspace say the experience has a permanent mental imprint that moves them away from being Aristotelians. I would love to join that club, but my prospects are nearly infinitesimal, even though I learned to pilot airplanes.

    Quantum mechanics takes us a step further away from our ordinary experience of things. It is where not only our intuitive experience of the world fails, but now our classical mechanical understanding fails. From a mathematical perspective we shift from a real valued understanding to a complex valued system. In classical physics complex number show up, but the physical observations are all the real part. We have something similar in QM, with the modulus square of amplitudes, but we are more centered in a view of the world that is complex valued or that is given by holomorphic manifolds. Our ordinary intuition is left way behind. This is a problem that continues with quantum physics and has lasted longer than confusions with classical mechanics. By the mid-18th century confusions with classical physics were largely settled. We continue to have problems with QM, and the industry of quantum interpretations is one aspect of this. Quantum interpretations are built up largely to make QM more intuitive. Also the more they satisfy intuitions the more difficult they are, such as the deBroglie-Bohm.

    ReplyDelete
  20. follow on from above because of space limit:

    Quantum gravitation will take us further in this direction. In particular it will shred our ideas of locality in QFT and the ontology of space and time. I will not go into what I think will occur here, but it will be a further leap away from our understanding of things. It brings forth a sense of Alice in Wonderland and believing 6 impossible things before breakfast.

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    1. It has lately seemed to me that field theories signaled the end of classical physics. The decline of mechanism and the rise of the field concept and the associated mathematics may have been the beginning of the end.

      Delete
    2. Like Maxwell's Theory, followed by General Relativity, followed by QED, followed by The Standard Model,...

      Delete
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    4. @ John

      "I understand the gist of your speculation, it is most likely nuncupatory"

      (Rhialto the Marvellous)

      Delete
    5. Classical mechanics is not going away. Dynamics described by a convex set is determined by an L^p integration measure. One case of this is L^2 that describes a Gaussian interval in relativity, such as proper time. There is also a duality with 1/p + 1/q = 1, which means there is another L^2 system, and physics provides quantum mechanics. This is a part of my motivation for saying that QM and GR are dual or equivalent systems. Now, GR is a classical system. It is though different from standard classical mechanics. We can consider then a p = 1 system, which corresponds to a classical probability system. We have then the summation of probabilities or in a continuous measure L^1 it is a classical probability system. The dual system is q → ∞, which can be interpreted as a classical deterministic system such as Newtonian mechanics or the mechanics of a Turing machine.

      There are then the dual systems (½, ½) and (1, ∞) and in both of these the respective systems are not going away any time soon. The trace of a density matrix serves to be a map ½ → 1 for probability theories, and the connection with Zurek we have a connection to the classical system or “q = ∞.” These are matters not yet understood fully,

      Delete
    6. This comment has been removed by the author.

      Delete
    7. There are a lot of ways to describe the difficulties with quantizing gravitation. Quantum field theory computes the propagation of a field in space with time. Yet with gravitation the field you are propagating is space and you are propagating space, well … through space. With a source of gravitation, a spherically symmetrical mass etc, if that mass is quantized then it can exist in a superposition so it can occur at different locations in space. But, wait! that means the curvature of space or spacetime associated with that mass is also in a superposition of configurations. We have a sort of entanglement, but where again we have a curious idea of spacetime having "such and such" a configuration in these regions of spacetime.

      Quantum mechanics has a nonlocality to it that then means the location of space or spacetime is itself nonlocal. That is a rather odd development and it has a bootstrap aspect to it that seems both tautological and paradoxical. When on looks at this mathematically it does lead to a bit snarl. In particular in a QFT situation it means Feynman diagrams for a graviton couple to all others and there is no scheme for renormalization.

      Delete
  21. Entanglement:

    If we want to understand entanglement by physical causality and not merely as a mathematical formalism, then this is a surprising phenomenon indeed. A striking property of it is the fact that it can only be observed statistically. One single measurement does not show any entanglement; the experimenter has to perform a number of measurements and then to analyze these measurement statistically.

    Could it be an explanation of this phenomenon that our treatment of statistical processes is at some point erroneous?

    ReplyDelete
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    1. Physicist doesn't want to understand statistical correlation as causality. I wonder if antipodes are conserved and organized in rhythmical spacetime... ;)

      It's more fruitful to focus in mechanisms than in magic philosophy.

      Delete
    2. No! There is no problem!! A quantum theory of two particles simply means a quantum theory whose fundamental observable yields a point in R^6.

      Delete
    3. By a causal explanation I do not mean a formal description as we get it from Quantum mechanics; but a physical explanation where the cause of this phenomenon is visible.

      Such cause could be that there is a transmission in space which is not limited to c but is restricted to transmissions which do not mean a transport of energy. To set a spin in free space does not mean a change of the energy of the system.

      However, we do not have an independent indication that such a process exists.

      Delete
    4. We do have several independent indications that when entangled correlation there is nothing to do with causality. It's one a phenomenon spreaded by spacetime without cause xand effect.

      Delete
  22. …”we will talk about just how quantum mechanics is local or not some other time.”

    …”“decoherence”. We will talk about this some other time”…


    I like the article thank you; I am looking forward to the future talks you mentioned.

    ReplyDelete
  23. Hi, Sabine, I love your blog!!!! I think you repeated the "left"particle in the first Entanglement paragraph...

    Regards, Jose.

    ReplyDelete
  24. 19-MAY-2020

    I don't surf, but I lived for a short time in southern California,
    and would hang out at Huntington Beach or Seal Beach, watching people
    ride waves.

    The really proficient ones seem to dance on the crests as the water
    becomes shallow and the wave rises up. First they catch the mean of
    a moving normal distribution called a "swell." There's a "sweet spot"
    where you need to be, to be properly accelerated. A surfer wants to
    be where the wave can be most precisely "measured." Statistically you
    wish to find the mean of the ensemble. We surf information, don't we?

    A wave is an ensemble of parcels; same with the atmosphere, measured
    in parcels. You can't evade a huge number of samples to find the mean.

    You know you're entangled with a wave, when you can stand up and ride
    it all the way to shore.


    Cheers,
    mj horn

    ReplyDelete
  25. Dear Sabine,

    In Monday lecture you have admitted that superdeterministic models are time-symmetric.
    Here is recent Ken Wharton paper showing that, among others, with superdeterminism you cannot escape retrocausality: https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.92.021002

    Time-symmetry is in CPT theorem, path integrals, Lagrangian formalism etc., directly gives Born rule: one amplitude from past propagator, second from future (or left/right in Ising), allows for Bell violation constructions, has superdeterminism as a property.

    I would say they are basically equivalent - do you see superdeterminism and time-symmetry as essentially different philosophies?

    All the best,
    Jarek

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    1. Jarek,

      I have not "admitted" that superdeterministic models are "time-symmetric", I have explained that my superdeterministic model is time-reversible.

      I am well aware of Wharton's papers. As we have explained in our paper, Wharton uses a notion of causality (Pearl's) that is fundamentally meaningless. There is, for what fundamental physics concerned, nothing "retrocausal" going on in any of these models. In fact, fundamentally the term doesn't even make sense.

      "I would say they are basically equivalent - do you see superdeterminism and time-symmetry as essentially different philosophies?"

      That a time-evolution can be reversed does not mean it is invariant under time-reversal.

      Delete
    2. Dear Jarek

      Greetings.

      The deadline for scoring essays in the recent FQXi competition has just passed. I had an essay showing how Bell's Theorem could be circumvented using time reversal, but that reversal required retrocausality. For me that means that a wave travelling from the future causes something to occur in the past/present. In Feynman's QED thesis an advanced wave from the future is (suggested as being?) required to make an emitting electron recoil in the present i.e. exactly at the time of emission. In my paper the effect of time reversal was to cause the paired measurements not be carried out on entangled pairs. A measurement on pairs, yes, but the time reversal meant that one measurement was made before the pair became entangled. That bypassed the conditions for the Bell Inequality to apply.

      However, I have my own doubts about it. In my preon model I do not have spontaneous emission of photons, and also weak isospin is conserved in my model of particle interactions. So I wonder about the elephant in the room, the higgs field. In my model, an electron interacts with a higgs and changes the spin of the electron and emits a photon. And maybe the electron gets an instant and local recoil from the higgs, rather than from an advanced wave from the future?

      A second problem IMO for my idea is that in my preon model There are antiparticles (antipreons) within all particles so that time reversal should be happening within all particles, and not just for the positrons in my version of the Bell experiment.

      A third problem is that although I can imagine antiparticles travelling backwards in time, and particles travelling forwards in time, causality at macroscopic level does seem to be only forwards-in-time along with entropy increase. So I imagine time being level-dependent. The universe has its own (macroscopic) time while the particles acting as quasi universes have their own internal times which can project along or against the universe's time direction. Not sure where that leaves causality?

      Austin Fearnley

      Delete
  26. Dr. H, an off-topic question , but the boys are back in town with "The Cosmic Revolutionary's Handbook" by Barnes and Lewis, published by the CUP, bizarrely. How can cranks and fraudsters like this be stopped from polluting physics? The CUP publishes their rubbish, Physics Today praises their nonsense in reviews and every other popular physics author praises the nonsense, presumably in return for having their own nonsense praised.
    Are there openings in the market for honest versions of Physics Today and the Cambridge University Press with actual standards do you think? Cranks like Lewis and Barnes undermine the work of real physicists by telling bare-faced lies to the public about physics.

    ReplyDelete
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    1. Steven Evans,

      Concretely, what do you dislike about their book? Glancing through it on amazon, it just looks like a pop-sci book. Am I missing something?

      Or do you just trash any book by authors whose religious or political beliefs differ from yours? Certainly a way to shorten your reading list!

      Of course, you do give these guys an awful lot of free publicity! Are they paying you? I'm thinking about reading their book myself since you brought it up.

      Dave

      Delete
    2. Reading ABOUT the book, and viewing interviews with the authors, it seems to serve a useful purpose: kind of encapsulating the historical/scientific process of understanding how the universe works and is configured, and why modern big bang cosmology is the best model thus far. I don't see anything wrong with that, unless someone has a strong bias against the scientific consensus on issues of cosmology, and doesn't want to be exposed to evidence. I'll probably get the book myself. The title is misleading. The book seems to be anti-crank. I did not get that impression from the title.

      Delete
    3. Rick Lubbock3:29 PM, May 20, 2020

      The point is the wider picture. Their first book made the trivially erroneous claims that universal fine-tuning was true and that the multiverse and some primitive fairy tale were possible explanations. Maybe lying like this is not a breach of their employment contracts, but they should have received a hammering in the physics community for the lies. Instead, an actual Physics Nobel Laureate wrote a bizarre, mistake-ridden introduction for the book, Physics Today and the Observatory wrote whitewash reviews failing to point out there was no evidence for the 2 big scientific claims and that positing the truth of a fairy tale as physics is pure insanity. And now their second book is published by the CUP, lauded by the BBC and other popular science authors like Sean Carrol, and while the new book appears to be not complete nonsense like their first book, of course it further drives the anti-scientific agenda of their first book by bringing them further unwarranted publicity.

      Physics Today, the BBC and CUP have completely failed in their quality control, and Brian Schmidt has lost all credibility.
      What needs to happen is the lies need to be withdrawn by Barnes and Lewis. They have got away with it so far due to the quality control failures of the physics community, but it seems unlikely they can keep these lies up forever.

      (The even wider picture is that this is but one example of Templeton Foundation money, which itself is the profits of tax-dodging, corrupting science.)

      Do get the book, though. The higher they rise, the bigger will be their ultimate fall, and the bigger the warning to cranks and fraudsters not to try to corrupt science in the future. I look forward to the denouement.

      Delete
    4. From the intro to "Cosmic Revolutionary's Handbook":

      "The universe we are told was born almost 14 billion years ago in a hot and fiery event, cheekily named the big bang. At its beginning, everything was compressed into a point of infinite density and infinite temperature."

      These 2 guys are absolute cowboys. This is a complete misrepresentation of the actual observations that make up the theory in the title of the book.
      The observational evidence tells us that the observable universe has expanded from a tiny dense soup of quarks about 14 billion years ago until today. It is not known empirically that there was a "beginning" and "infinite" temperatures and densities are meaningless in physics. This observation of the expansion will not go away, it will only be added to or made more precise.
      They are talking about overthrowing a theory they have got completely wrong. And the observations that have already been made cannot be dismissed - they are encouraging a common misunderstanding among lay people that physics is just theories which can be shown to be completely wrong. And we all know why Luke Barnes is doing this. There is a growing cancer in physics that needs cutting out.

      I look forward to Philip Helbig's review of this drivel in The Observatory.

      Delete
    5. @ Steven Evans,

      1. The early description of the Big Bang as a quark-gluon plasma is part of a quantum field theory in a curved spacetime model. In such a model the observables are potential phenomena, not actual small objects.

      2. Using the super-classical limit of the standard model one gets a cyclic Universe with a big bounce instead of a big bang.

      Delete
    6. Prof. David Edwards9:49 AM, May 22, 2020

      David, Yes, gluons, too of course. I am vaguely aware that Physicists describe this situation with QFT. The point I am making is that CUP has published 2 purported Physics books by these cowboys that are riddled with errors and even present primitive fairy tales as Physics:
      There is no empirical evidence that the observable universe had a beginning, strictly speaking.
      There is no empirical evidence of universal fine-tuning.
      Infinite densities and temperatures are physically meaningless.
      There is no empirical evidence of a multiverse.
      There is no empirical evidence of Gods, demi-gods or angels or whatever other nonsense is swimming around Luke Barnes' muddled mind.

      There *is* empirical evidence that the observable universe expanded from a very small but non-zero spacial extent around 14 billion years ago. This is the mis-named Big Bang theory of physics - it is a collection of observations, as with all Natural Science.

      2. Yes, famously Hawking and later Turok brought out theoretical papers extrapolating observations backwards in time - Hawking coming up with the smoothed-off universe and Turok coming up with the bouncing universe (presumably Dark Energy would be fatal to the bouncing universe idea). But these are just models, of course, unsupported by observation. Which is another of my complaints about Barnes and Lewis - they are making claims about the nature of the universe based only on noddy models - yes, you can change the value of the Cosmological Constant in a header file in a computer program, but it doesn't mean that change is physically possible. (Of course, Hawking and Turok make clear that their papers are theoretical and their models are extrapolations of observations using GR, QFT and the latest Maths, not a gormless schoolboy misunderstanding of modus ponens as with Lewis and Barnes.)

      It's quite bizarre that CUP have published purported Physics books by 2 clowns who don't know the basic facts of their own field, and one of whom is apparently the 13th disciple.

      In the end, Dr. H. is right - there is a market for BS. At least, Lewis and Barnes will never, ever publish anything even remotely scientifically significant in a journal. Ever. This is a comfort.

      Delete
  27. This comment has been removed by the author.

    ReplyDelete

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