Monday, March 23, 2020

Are dark energy and dark matter scientific?

I have noticed that each time I talk or write about dark energy or dark matter, I get a lot of comments from people saying, oh that stuff doesn’t exist, you can’t just invent something invisible each time there’s an inconvenient measurement. Physicists have totally lost it. This is such a common misunderstanding that I thought I will dedicate a video to sorting this out. Dark energy and dark matter are entirely normal, and perfectly scientific hypotheses. They may turn out to be wrong, but that doesn’t mean it’s wrong to consider them in the first place.


Before I say anything else, here is a brief reminder what dark energy and dark matter are. Dark energy is what speeds up the expansion of the universe; it does not behave like normal energy. Dark matter has a gravitational pull like normal matter, but you can’t see it. Dark energy and dark matter are two different things. They may be related, but currently we have no good reason to think that they are related.

Why have physicists come up with this dark stuff? Well, we have two theories to describe the behavior of matter. The one is the standard model of particle physics, which describes the elementary particles and the forces between them, except gravity. The other is Einstein’s theory of general relativity, which describes the gravitational force that is generated by all types of matter and energy. The problem is, if you use Einstein’s theory for the matter that is in the standard model only, this does not describe what we see. The predictions you get from combining those two theories do not fit to the observations.

It’s not only one prediction that does not fit to observations, it’s many different ones. For dark matter it’s that galaxies rotate too fast, galaxies in clusters move too fast, gravitational lenses bend light too strongly, and neither the cosmic microwave background nor galactic filaments would look like we observe them without dark matter. I explained this in detail in an earlier video.

For dark energy the shooting gun signature is that the expansion of the universe is getting faster, which you can find out by observing how fast supernova in other galaxies speed away from us. The evidence for dark energy is not quite as solid as for dark matter. I explained this too in an earlier video.

So, what’s the scientist to do when they are faced with such a discrepancy between theory and observation? They look for new regularities in the observation and try to find a simple way to explain them. And that’s what dark energy and dark matter are. They are extremely simple terms to add to Einstein’s theory, that explain observed regularities, and make the theory agrees with the data again.

This is easy to see when it comes to dark energy because the presently accepted version of dark energy is just a constant, the so-called cosmological constant. This cosmological constant is just a constant of nature and it’s a free parameter in General Relativity. Indeed, it was introduced already by Einstein himself. And what explanation for an observation could possibly be simpler than a constant of nature?

For dark matter it’s not quite as simple as that. I frequently hear the criticism that dark matter explains nothing because it can be distributed in arbitrary amounts wherever needed, and therefore can fit any observation. But that’s just wrong. It’s wrong for two reasons.

First, the word “matter” in “dark matter” doesn’t just vaguely mean “stuff”. It’s a technical term that means “stuff with a very specific behavior”. Dark matter behaves like normal matter, except that, for all we currently know, it doesn’t have internal pressure. You cannot explain any arbitrary observation by attributing it to matter. It just happens to be the case that the observations we do have can be explained this way. That’s a non-trivial fact.

Let me emphasize that dark matter in cosmology is a kind of fluid. It does not have any substructure. Particle physicists, needless to say, like the idea that dark matter is made of a particle. This may or may not be case. We currently do not have any observation that tells us dark matter must have a microscopic substructure.

The other reason why it’s wrong to say that dark matter can fit anything is that you cannot distribute it as you wish. Dark matter starts with a random distribution in the early universe. As the universe expands, and matter in it cools, dark matter starts to clump and it forms structures. Normal matter then collects in the gravitational potentials generated by the dark matter. So, you do not get to distribute matter as you wish. It has to fit with the dynamical evolution of the universe.

This is why dark matter and dark energy are good scientific explanations. They are simple and yet explain a lot of data.

Now, to be clear, this is the standard story. If you look into the details it is, as usual, more complicated. That’s because the galactic structures that form with dark matter actually do not fit the data all that well, and they do not explain some regularities that astronomers have observed. So, there are good reasons for being skeptical that dark matter is ultimately the right story, but it isn’t as simple as just saying “it’s unscientific”.

163 comments:

  1. scientific -

    based on or characterized by the methods and principles of science.

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  2. Maybe someday dark energy and dark matter are not dark anymore.

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  3. For a theory to be scientific, you might want to be able to answer the question "When can it be proved wrong?"

    If the answer is "never", maybe it's not that scientific after all. It seems to me Dark matter is pretty close to this status. Perhaps that's where opinions differ.

    About Dark Energy, the Cosmological Constant explanation seems completely satisfying, as long as it fits the data.

    (Sorry if double post)

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    1. dlb,

      First, as I have said many times, strictly speaking you cannot falsify a theory, you can only implausify it until everyone loses interest. You can, eg, never rule out that there is not some small amount of dark matter hiding somewhere you haven't looked, but that isn't a particularly interesting theory.

      Having said that, dark matter, for example, predicts that the 2nd peak of the CMB is suppressed, which it is. The suppression fits to the amount that is needed for other explanations. If it hadn't been suppressed that would have ruled this explanation out. It would not, as I said, have ruled out that there cannot be some small amount of dark matter somewhere.

      Now look, many smart scientists have criticized the way that dark matter has been used to explain galactic structures and indeed in this case it is hard to avoid the impression that the theory is being amended each time an observation does not fit.

      However, there now seem to be a lot of ill-informed people with their home-made dark matter ideas who repeat this totally out of context.

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    2. I don't understand. A theory can be ruled out but not falsified strictly speaking ? That is because we do not speak about the same "theory". Here the theory which explain inexistence of the second peak via DM, and some other theory which would explain another thing with DM. DM itself is not a theory.

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    3. "Implausify it until everyone loses interest" -- good one Sabine -- You've got a gift with words, apparently in any language!

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  4. I agree they are not "unscientific" however, speaking for myself and guessing what others might really mean, they are certainly ad-hoc. Let's face it, science history is full of ad-hoc explanations because observation didn't conform with the periods current accepted physics, Newtonian mechanics is a good example. While I think there is more of a case for dark matter actually existing regardless, the most rational conclusion is GR needs to be replaced as extensively as it replaced Newtonian mechanics. Sadly there is a lot of evidence pointing to the foundational direction that holds the most promise for that however it will be be resisted for many of the same human reasons that you often write about in your blog.

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  5. It took over 50 years to 'prove' gravity waves, and 20 years to demonstrate the Higgs particle. How do you decide, a priori, whether or when a theory "can be proved wrong"?

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  6. “A scientist, an artist, a citizen is not like a child who needs papa methodology and mama rationality to give him security and direction; he can take care of himself, for he is the inventor not only of laws, theories, pictures, plays, forms of music, ways of dealing with his fellow man, institutions but also of entire world views, he is the inventor of entire forms of life.”
    ― Paul Karl Feyerabend, Science in a Free Society
    https://www.goodreads.com/author/quotes/85302.Paul_Karl_Feyerabend

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    1. Amen. Feyerabend was a very smart person, but its not a warrant to avoid big mistakes as his idea of ​​the "Galilée's propaganda". A theory is not merely "a form of live" because it try adequately representing a external reality. Even if a scientist (as Einstein) does not follow a constant methodology, he cannot forget rationality. A theory has to fit experience AND has be mathematically, logically and conceptually consistant.

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    2. "be mathematically, logically ... consistant"

      That part has no foundation, that I can see.

      Cf. Quine, Two Dogmas; and https://www.iep.utm.edu/math-inc/

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  7. "Let me emphasize that dark matter in cosmology is a kind of fluid. It does not have any substructure. Particle physicists, needless to say, like the idea that dark matter is made of a particle". Quite. In 1916 Einstein said “the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy”. Gravitational field energy causes gravity, and it isn’t made up of WIMPs. It's spatial energy. It's dark matter of sorts.

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    1. No, it is not. As I said, dark matter is a technical term. It means something specific. The energy of the gravitational field is not dark matter.

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    2. Btw, just for completeness let me add that there is like a 100 years long debate on how to properly define the energy of the gravitational field to begin with. But you don't actually need to know what it is to use GR. Saying that the gravitational energy gravitates merely means the theory must be non-linear, which it is.

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    3. You're missing the significance of what Einstein said. A region of space causes gravity because the spatial energy density in that region is greater than in the surrounding region. So what's going to happen if a region of space is gravitationally bound by a galaxy, and does not expand while the surrounding space does? Don't forget that we have no certain knowledge of any situation where conservation of energy does not apply.

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    4. In all honestly, I care very little what Einstein said. Einstein himself did not, could not, know what we do today. Every student today knows more about GR than Einstein. I like to think he would have been happy about that.

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    5. I urge students to study two different books: Ta-Pei Cheng's "Einstein's Physics" and Robert Kennedy's "A Student's Guide to Einstein's Papers." (both Oxford University Press, 2013, 2012). As is my preference, I try to avoid all-encompassing words such as "every." However, it is simply a delusion to believe that "every" student today knows more about General Relativity than Einstein. There is much of continuing value to be uncovered through his "words." So, contrariwise, I care very much about what Albert Einstein said--placed within the context of his own time, not ours.

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  8. " For dark matter it’s that galaxies rotate too fast, galaxies in clusters..."

    Is it possible that *all* these discrepancies could be explained away by the possible mis-application of GR equations that you mentioned in the earlier dark matter post (namely, the assumption that the GR equations can be applied linearly is incorrect and this leads to the discrepancies between model and observations, and in fact dark matter may not be implied)?

    "The evidence for dark energy is not quite as solid as for dark matter."
    Is this because no-one has actually measured the purported acceleration directly except maybe in a few thousand cases?

    Why does Physics present dark matter and dark energy to the public as empirical facts when they are clearly as yet unconfirmed hypotheses?

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    1. Steven,

      Well, yes, it is possible because no one really knows what the correct equations look like. Some people would argue, however, that it isn't very plausible because the corrections (that unquestionably exist) would be too small.

      Dark matter and dark energy are hypotheses that are well supported by evidence, as I just said. Though I certainly wish that scientists wouldn't overstate the case as much as they do. The damage this will do if one of these hypothesis turns out to be wrong is substantial.

      (Fwiw, I think it's much worse for inflation. The evidence is far worse and yet the conviction that it's right much higher.)

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    2. Observations are always made and interpreted within the context of some model or theory. Ideally, a theory should be crafted with some observations in mind ...
      (I'm not sure this was the case for GR)
      It is all a bit circular. The circle can be viscous or virtuous.

      If you subscribe to GR then dark matter and dark energy are exciting discoveries.

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    3. Greg Feild 2:14 PM, March 24, 2020

      "Observations are always made and interpreted within the context of some model or theory. "
      Really? What about Newton's apple falling from the tree? Also, if no-one had come up with GR, people would still eventually have noticed that atomic clocks on orbiting satellites ran faster than atomic clocks on the Earth's surface. No inference from a model is required to observe the physical phenomenon of time dilation, just a couple of clocks. This is why I'm suspicious of dark energy claims unless they directly measure the claimed acceleration. I accept that most physicists believe there are hints that dark energy exists, as with the blog post.

      " dark matter and dark energy are exciting discoveries. "
      They are exciting questions. The exciting discoveries will be determining the gravitational and energy sources whose effects have *possibly* been observed. Then we really will be able to believe the claims.

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    4. "This is why I'm suspicious of dark energy claims unless they directly measure the claimed acceleration"

      People don't measure acceleration.
      They measure red shifts.

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    5. The atoms in 'moving' clocks are more massive than the atoms in a 'stationary' clock, hence they oscillate at a different frequency.

      No gravity is required for this interpretation.

      Time dilation is not a really real thing.

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    6. Greg Feild9:41 AM, March 26, 2020

      "They measure red shifts. "
      I'm happy to accept the Doppler effect. I've heard an ambulance siren.

      "The atoms in 'moving' clocks are more massive than the atoms in a 'stationary' clock"
      If you are talking about a clock on a satellite in orbit above the Earth, the relativistic time dilation due to the velocity of the satellite would slow the clock and the gravitational time dilation due to the reduced gravitational potential would speed it up. Presumably

      "Time dilation is not a really real thing. "
      Is it not? So why do GPS systems have to take the discrepancy due to time dilation into account to provide accurate coordinates?

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    7. Time dilation means the clock runs slower.

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    8. Greg Feild2:00 PM, March 26, 2020

      "Time dilation means the clock runs slower."

      . The point was that Newton came up with the idea of universal gravity by a simple direct observation with no inferences. And that gravitational time dilation would have been noticed as a physical phenomenon in GPS systems just by comparing 2 clocks even if no-one had come up with the theory of GR, because it really is real. You claimed otherwise.
      According to Phillip Helbig you can't just measure the change in redshift from all galaxies over time to directly measure the acceleration of the universe. I'll take his word for it, but I don't really see why you can't in principle.

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    9. "According to Phillip Helbig you can't just measure the change in redshift from all galaxies over time to directly measure the acceleration of the universe. I'll take his word for it, but I don't really see why you can't in principle."

      There are two points. First is the question how indirect a measurement is allowed to be. Acceleration is a change in velocity with time, so that means measuring a velocity at at least two different times. Does measuring a redshift directly measure a velocity in a cosmological context? No. It tells you the ratio of the scale factor of the universe to the time when the light was emitted. That's it. (Even this makes some assumptions.) If you a) assume an FRW model and b) know the parameters, then you can calculate the velocity at various times. (But you have to define "velocity"; there are many distances in cosmology, and acceleration is change in velocity with time, but you have to say which velocity, and perhaps which time as well.) But measuring the redshift does not imply measuring the velocity in any meaningful sense.

      Second, the redshift drift is proportional to 1 - x/y, where x is the ration of the Hubble constant at the redshift in question to its value today and y = 1+z, where again z is the redshift. It is not obvious to me whether the sign of this effect uniquely maps to the sign of the acceleration, even assuming FRW. (This is left as an exercise to the reader.) But even if so, point 1 above still stands.

      See, e.g., https://arxiv.org/abs/1712.07555.

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    10. "According to Phillip Helbig you can't just measure the change in redshift from all galaxies over time to directly measure the acceleration of the universe."

      I hope that this will follow up on a comment which at the time of writing has not yet been approved.

      Look at Eq. (7) https://arxiv.org/abs/1712.07555. Consider the de Sitter model (Omega=0, lambda=1), which is always accelerating. Since the Hubble constant doesn't change with time in this model, the expression 1 - x/y is always positive, whatever the redshift. Let's then take the Einstein-de Sitter model (Omega=1, lambda=0), which is always decelerating. Here, the E(z) is (1+z) to the 3/2 power. Dividing by (1+z), the fraction is the square root of (1+z). So, the expression is always negative.

      So, can we say positive means acceleration now and negative deceleration now? In general, E(z) is the square root of Omega*v**3 - (Omega+lambda-1)v**2 + lambda, where v=1+z. (All values of Omega an lambda---which in general change with time---refer here to the present-day values, usually denoted with subscript 0.) Any model with q = Omega/2 - lambda < 0 is accelerating now. Are there any models with q < 0 where the expression is positive? Consider Omega=2 and lambda=1. This has q=0 so, if the assumption above applies, the expression in this case should always be zero, but one can easily see that it is not.

      This all assumes FRW, so it doesn't even work in this case, much less if one does not assume FRW. And point 1 above still applies.

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    11. I think to make this simple, the Hubble relationship v = Hd gives not just a linear relationship between distance and velocity, but given a distance d and d = ct we have v = Hct and the faster the velocity the further back in time one is observing. Departures from this would then be at least an indirect observation of acceleration with time. The more distant galaxies have velocity that increases faster than this linear relationship.

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    12. Phillip Helbig10:16 AM, March 27, 2020

      Cheers. I started getting lost in the double asterisks in the last para, but the spectroscopic velocity shift is a function of the change in red shift and this E(z) which is a function of things like matter density, dark energy density.
      So you give examples of the spectroscopic velocity shift being +ve in a simple model of an accelerating universe and -ve in a simple model of a decelerating universe. But this correlation isn't necessarily true for more realistic models.
      So from what you are saying, even with the SDSS data for redshift from 3 million objects it would be tricky to conclude acceleration because change in redshift is tied into all these factors like matter density, etc. So I accept that a direct measurement to confirm acceleration may not be possible. And the supernovae data are just for a few thousand galaxies. So it looks like acceleration is an unconfirmed hypothesis at the moment with some positive evidence. I don't get a feel how necessary dark energy is in all this. Maybe the model is screaming out for it and that's why you are all so convinced.

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    13. Greg Feild wrote:
      >Time dilation means the clock runs slower.

      Yes, but “slower” relative to what?

      In the case of gravitational time dilation, the answer is slower relative to an observer very far from the gravitational source, “at infinity,” as we say.

      The deeper you are in the gravitational well, the more time is slowed.

      The formula is well-known -- see any standard text: if one clock is at radius r0 and the other at r1, r0 < r1, then the clocks at r0 run slower by a factor of sqrt[( 1- 2GM/(r0 c^2))/( 1- 2GM/(r1 c^2))].

      Plug in r0 for the surface of the earth and r1 for the radius at geosynchronous orbit, and you get that time runs faster by about 0.6 parts per billion for a stationary clock sitting at the geosynchronous radius compared to one on the earth's surface.

      The higher up you are, the faster clocks run.

      On the other hand, a clock in low earth orbit runs slower than a clock on the earth's surface due to special-relativistic time dilation: the formula is of course the familiar sqrt(1-(v/c)^2). Plug in the numbers, and a rocket in orbit near the earth's surface runs slower by about 0.3 parts per billion compared to a clock at rest on the earth's surface.

      Get it?

      Stationary clocks at rest at the GEO radius run faster than clocks here on earth. Clocks in low earth orbit run slower than clocks here on earth.

      Here is a calculation for the GPS satellites, which are in neither low earth orbit nor GEO.

      Greg also wrote:
      >Time dilation is not a really real thing.

      Gee, that's funny, since really real measurements have really been made that show that it really is a really real thing!

      Didn't you once claim that you actually had some sort of physics education?

      Really?

      Steven Evans 1; Greg Feild 0.

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    14. My bad. I was too brief.

      GEO satellites are continually being accelerated which introduces complications of course.

      (In SR, with 'no acceleration') Two observers moving with some relative velocity will each say the other's clock is running more slowly.

      It is all Relative. There is no prefered reference frame in this case.

      To say Time is dilated is meaningless.

      PS - length contraction isn't real either.

      Greg



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    15. Dave said:

      In the case of gravitational time dilation, the answer is slower relative to an observer very far from the gravitational source, “at infinity,” as we say.

      ...

      This is really the whole problem for a theory with no preferred reference frame.

      It is just the "fixed stars" in a new guise.

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    16. Lawrence Crowell 7:23 PM, March 27, 2020

      "but given a distance d and d = ct we have v = Hct and the faster the velocity the further back in time one is observing. Departures from this would then be at least an indirect observation of acceleration with time. "

      But you'd need the distance to calculate H, wouldn't you? And where this was obtained using the brightness of the supernovae as a proxy, it was only done for a few thousand galaxies, wasn't it? Out of 100 billion. Presumably if good evidence were found of acceleration that would necessarily imply a supply of energy like dark energy.

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    17. Greg Feild wrote to me:
      >GEO satellites are continually being accelerated which introduces complications of course.

      >(In SR, with 'no acceleration') Two observers moving with some relative velocity will each say the other's clock is running more slowly.

      >It is all Relative. There is no prefered reference frame in this case.

      >To say Time is dilated is meaningless.

      What a remarkably foolish statement!

      It's like saying the so-called "twin paradox" does not have a definite answer. But it does: the traveling twin ages less, as seen in all reference frames. (Proper time is a relativistic invariant, simply because the spacetime interval is a relativistic invariant.)

      Special Relativity has no problem at all dealing with accelerated motion, as everyone who legitimately passed an undergrad class on relativity knows.

      Time passes more slowly for satellites in LEO than for clocks on the ground, in all frames of reference: it's no more complicated than the so-called twin paradox.

      It's been measured, Greg.

      Greg also wrote:
      >In the case of gravitational time dilation, the answer is slower relative to an observer very far from the gravitational source, “at infinity,” as we say.

      >This is really the whole problem for a theory with no preferred reference frame.

      It's been measured, Greg, Pound-Rebka and a great deal more.

      Two posts from Greg, both betraying grotesque ignorance of physics.

      Score now: Steven Evans 3, Greg Feild 0.

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    18. Since the acceleration is very small it makes little contribution to the expansion of a local region with z relatively small, say much less than 1. The Hubble v = Hd is a linear form of the FLRW metric factor exp(t√(Λ/3)) ≈ 1 + t√(Λ/3)t + ½t^2(Λ/3) + … . The Hubble factor is H = √(Λ/3), and v/c = t √(Λ/3) and we see simply v = Hd. The second order term corresponds to deviations form this which are accelerations. Evidence for this involves larger time or equivalently larger distance.

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    19. Hi Steven Evans,

      I think we agree!

      If one interprets redshifts in terms of GR then one assumes expansion and/or acceleration. I will leave expansion alone for right now, but I think we both agree acceleration seems unlikely.

      As for Newton, he was a Genius, but he did not work in a vacuum. He knew of Kepler, the one over R squared law was in the air, etc.

      Finally, I did not mean to say that people cannot or do not make new observations, but they are only useful or surprising against some expected result.

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    20. Dave,

      So, there is an absolutely fixed reference frame against which all acceleration is measured... ?

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    21. Greg Feild 9:12 AM, March 28, 2020

      "To say Time is dilated is meaningless."
      But there is a physical phenomenon termed gravitational time dilation, and this can easily be observed if you are in possession of 2 clocks - 1 on the Earth's surface, 1 on a satellite - and have never heard of GR. Which was the original point. Are you saying there is no such physical phenomenon as gravitational time dilation, that this cannot be observed?



      Greg

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    22. I agree that the clocks will run at different rates and will show different times when reunited.

      However, to say that Time
      (with a metaphysical capital T)
      was 'dilated' or physically different in some way, in the interim, or along the way, seems nonsensical to me.

      The moving clock runs slower than the reference frame clock in terms of the 'stationary reference frame' time.

      So, in this example, there is only one relevant time frame, and only one time.

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    23. Greg said:
      > So, there is an absolutely fixed reference frame against which all acceleration is measured... ?

      Did it ever come to your mind that there are always counterpart when something accelerated? It's interaction. They are many different masses and always common origin of masses conserves its motion state...

      Does it ever come to your mind that interactions define spacetime with its coordinates not vice versa?

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    24. "I started getting lost in the double asterisks in the last para"

      The double asterisks are Fortran for raising something to a power. It's not always clear how much HTML is allowed in blog comments.

      "but the spectroscopic velocity shift is a function of the change in red shift and this E(z) which is a function of things like matter density, dark energy density.
      So you give examples of the spectroscopic velocity shift being +ve in a simple model of an accelerating universe and -ve in a simple model of a decelerating universe. But this correlation isn't necessarily true for more realistic models."


      Right.

      "So from what you are saying, even with the SDSS data for redshift from 3 million objects it would be tricky to conclude acceleration because change in redshift is tied into all these factors like matter density, etc. So I accept that a direct measurement to confirm acceleration may not be possible."

      Directly measuring acceleration in any meaningful sense might never be possible. On the other hand, if we have a theory which explains everything else and this theory predicts acceleration, that should be good enough.

      There are two things interesting about the redshift-drift idea. First, it rules out most other explanations of the redshift, because these predict no drift. Second, by measuring the redshift drift at different redshifts, one can in principle measure lambda and Omega, just from the redshifts---no other observations are needed. So this is a high-redshift cosmological test which is completely unaffected by evolutionary effects, selection bias, small-scale perturbations (most tests assume that the universe is effectively homogenous, at least with regart to light propagation), and so on. With time, the results will get better and better. Ultimately, all the other cosmological tests will be interesting only for historical reasons, though one might turn them around and learn something about evolution, selection effects, small-scale inhomogeneities etc. by using very well measured cosmological parameters as input and seeing what other assumptions are needed to make them compatible with observations.

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    25. Greg Feild asked me:
      >So, there is an absolutely fixed reference frame against which all acceleration is measured... ?

      In Special Relativity, any inertial frame will work: they are all equivalent in terms of measuring 4-acceleration.

      But you are missing the point: measuring acceleration does not matter in the cases we were discussing.

      It's like the so-called twin paradox: the twins start out next to each other and compare watches, and then they end up next to each other and compare watches. No need to worry about which frame of reference is being used: the watches are right next to each other and can be directly compared by anyone in any frame of reference.

      Exactly the same thing is true for an observer in very low orbit vs. one on the ground: the guy in orbit keeps circling back so that he is right next to the guy on the ground -- it's just like the so-called twin paradox;

      And, in principle, a similar thing can be arranged for gravitational time dilation: just climb up the stairs slowly and then sit at the top of the Empire State Building for a year and then climb back down slowly and compare your watch to the fellow on the ground.

      Yes, in relativity you need to be careful about talking about phenomena that are independent of the frame of reference. But this can be done. Indeed all knowledgeable people have known how to do it for a hundred years. The so-called twin paradox is one example. I just gave two others.

      You can't do this. I know. That is why you are not a physicist and were never really a (competent) physics student.

      What amazes me is that you are so sure of yourself when your knowledge and understanding are so non-existent. That level of totally unjustified self-assurance must be a real gift, Greg.

      A real gift.

      I assume you have made a lot of money off of it.

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    26. Greg Feild11:28 AM, March 29, 2020

      " but I think we both agree acceleration seems unlikely."
      Acceleration of the universe? I have no idea, but it seems that a complex situation can be summarised, as described in the blog post, as being that acceleration is a possibility due to the supernovae data, but that more data and analysis are required to be confident.

      "As for Newton, he was a Genius, but he did not work in a vacuum. He knew of Kepler, the one over R squared law was in the air, etc."
      True. And he made the standing on the shoulder of giants comment. But my point is that there are physical phenomena which can be viewed directly (gravity) or with little equipment (SR or GR time dilation), whereas cosmology involves a rather complex model.

      "Finally, I did not mean to say that people cannot or do not make new observations, but they are only useful or surprising against some expected result. "
      Although the apple falling from the tree probably wasn't wholly unexpected by Newton. But fair enough. Our pointless internet discussion is complete ;)

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    27. Lawrence Crowell 8:30 AM, March 29, 2020

      Cheers for the comment. I don't completely understand it, but I will investigate.

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    28. "though one might turn them around and learn something about evolution, selection effects, small-scale inhomogeneities etc."

      Sweet.

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    29. Dave ranted hysterically:
      Blah blah blah

      Most people agree that one has to accelerate to change velocity.

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    30. "I think to make this simple, the Hubble relationship v = Hd gives not just a linear relationship between distance and velocity, but given a distance d and d = ct we have v = Hct and the faster the velocity the further back in time one is observing. Departures from this would then be at least an indirect observation of acceleration with time. The more distant galaxies have velocity that increases faster than this linear relationship."

      As Einstein said, make it as simple as possible, but not simpler. :-)

      With your example, assuming that H is known and v is estimated from the redshift (how?), then how could you possibly observe any deviation?

      But the whole concept is wrong. See the great article by the late Ted Harrison for details.

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    31. Hello Eusa,

      That is exactly what I think.

      That is my Thesis !

      Greg

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    32. Philip wrote:

      "Directly measuring acceleration in any meaningful sense might never be possible."

      Hi Philip,

      I believe angular acceleration is the only true and unambiguous acceleration.

      It is observable from any reference frame; inertial frames and accelerating frames.

      Delete
    33. Greg Feild wrote to me:
      >Dave ranted hysterically:
      >Blah blah blah [referring to what Greg could not understand -- i.e., anything having to do with physics whatsoever]
      >[Greg]Most people agree that one has to accelerate to change velocity.

      Greg, you are obnoxious, rude, and ignorant, but most especially ignorant: indeed, “Blah blah blah” is the absolute peak of your intellectual powers, the most significant thing you are capable of expressing.

      In fact, Special Relativity easily deals with acceleration/change in velocity.

      As Sean Carroll put it in his textbook Spacetime and Geometry (p.11:

      >"The notion of acceleration in special relativity has a bad reputation, for no good reason. Of course we were careful, in setting up inertial coordinates, to make sure that particles at rest in such coordinates are unaccelerated. However, once we've set up such coordinates, we are free to consider any sort of trajectories for physical particles, whether accelerated or not. In particular, there is no truth to the rumor that SR is unable to deal with accelerated trajectories, and general relativity must be invoked. General relativity becomes relevant in the presence of gravity, when spacetime becomes curved. Any processes in flat spacetime are described within the context of special relativity..."

      Indeed, Misner, Thoren, and Wheeler devote a whole chapter (Chapter 6) to describing how Special Relativity deals with accelerated motion. Thiis is not just a bizarre intellectual exercise. Indeed, they point out that one effect of accelerated motion in Special Relativity, the “Thomas precession,” is in fact a significant matter in atomic physics.

      Indeed, the whole point of the "Equivalence Principle" is to compare a frame in Special Relativity undergoing uniform acceleration to the situation in a static gravitational field. If Special Relativity could not deal with accelerated motion, the Equivalence Principle could not exist.

      All competent physics students know about this.

      But you don't: to you it is all just, to use your own mindless verbal ejaculations, “Blah blah blah...”

      You've soiled yourself, Greg. To any normal person, you are a disturbingly sick little puppy inexplicably dirtying itself in its own waste -- its own "Blah blah blah," like an animal unable to express itself in human speech.

      Why do you do this? What is wrong with you?

      What happened to you to make you so contemptuous towards people who know things of which you are utterly and completely ignorant?

      How did you become so sadly twisted?

      Yeah, I know your answer, “Blah blah blah.”

      Pitiable.

      Delete
    34. Helbig wrote,"With your example, assuming that H is known and v is estimated from the redshift (how?), then how could you possibly observe any deviation?"

      Maybe I should have elaborated, but with v - Hd astronomers use red shift information to infer v and some other standard candle to get d. This is where SN1 data comes in. Perlemutter et al found this deviation from this linear relationship. The drop off in SN1 relative luminosity provided information for this acceleration.

      Delete
    35. "Maybe I should have elaborated, but with v - Hd astronomers use red shift information to infer v and some other standard candle to get d. This is where SN1 data comes in. Perlemutter et al found this deviation from this linear relationship. The drop off in SN1 relative luminosity provided information for this acceleration."

      That is not how it works. Yes, there is a linear relationship between redshift an apparent magnitude which, at low redshift, can be converted to a relationship between velocity and distance. Yes, at higher redshift it is no longer linear and, yes, this can be used to determine the cosmological parameters. Two points. First, where is any measurement of acceleration in the above? (One determines the parameters and infers acceleration since in such a model there is acceleration.) Second, note that the velocity is exactly proportional to distance for all distances and at all redshifts, though this is the proper distance and its derivative with respect to cosmic time.

      Please, read the paper by Harrison which I have linked to. Please.

      Delete
    36. As I said, SN1 data leads to a departure from the linear Hubble relationship. You saying I am wrong and then your statements are pretty much what I just wrote. All I am talking about is the inference of acceleration inferred by departures from a linear v = Hd.

      Delete
    37. I have read Harrison's paper to sec 3.2. The argument there surrounding equation 18 assumes the cosmological constant is truly constant. However, with the EW theory the false vacuum has symmetries of the Lagrangian, while the physical vacuum constrained away from these symmetries has a different energy. The same is likely the case with the cosmological parameter, where the constant is just its value on the physical vacuum. There is then an RG flow involved with the inflationary expansion of the universe and the basin of attraction for gauge coupling and particle masses.

      Delete
    38. Lawrence Crowell wrote:
      >The same is likely the case with the cosmological parameter, where the constant is just its value on the physical vacuum. There is then an RG flow involved with the inflationary expansion of the universe and the basin of attraction for gauge coupling and particle masses.

      Lawrence, do you have any references on this?

      This question has caused me to scratch my head for some time. On the one hand, if the CC depends on some effective spatial cutoff at small distances, and the scale factor of the universe expands, wouldn't the effective cutoff length expand in the same way?

      On the other hand, whether or not the universe is "expanding" is largely a matter of how one slices spacetime: most obviously, in the "Milne universe," space is "expanding" if you use the Milne coordinates (comoving/cosmic time and the corresponding hyperbolic spatial slices), but the universe is not "expanding" at all if you just use the standard Minkowski coordinates.

      (For those who are not aficionados of the Milne universe, it is just an alternative set of coordinates for flat Minkowski spacetime. But with the Milne coordinates, space appears to be non-Euclidean and to be expanding. It is a good approximation to an expanding universe with very low energy density and zero cosmological constant. Most importantly, it illustrates the dangers of not thinking carefully about how you choose your coordinates!)

      Of course, everyone just seems to assume this question is obviously irrelevant. Perhaps it is.

      Dave

      Delete
    39. "As I said, SN1 data leads to a departure from the linear Hubble relationship. You saying I am wrong and then your statements are pretty much what I just wrote. All I am talking about is the inference of acceleration inferred by departures from a linear v = Hd."

      The point is that departure from linearity does not imply acceleration. In general, there is a departure at higher redshift. In fact, the only model in which there is no departure from linearity even at high redshift is the de Sitter model, which is expanding exponentially!

      In other words, yes, from the relation between apparent magnitude and redshift (which, in general, is linear only at low redshift) one can determine the cosmological parameters; if Omega/2-lambda is less than 0 then the Universe is accelerating. But a) there is no "direct" measurement of acceleration here and b) by itself non-linearity in this relation does not necessarily imply acceleration.

      Delete
    40. Greg asked me:
      >So, there is an absolutely fixed reference frame against which all acceleration is measured... ?

      I don't see that anyone has answered that question.

      In Special Relativity, there is an objective fact of whether your frame of reference is accelerated or non-accelerated (AKA inertial), and a non-accelerated frame is global, covering the whole universe.

      In General Relativity, there is also an objective distinction between accelerated frames and non-accelerated frames (AKA free fall), but, in a gravitational field, the non-accelerated frames are only local (like calculus -- limit as Δx goes to zero and all that) and do not fit together to form a global non-accelerated frame.

      Gravity just is this failure of inertial frames ot fit together into one global inertial frame.

      Decent modern textbooks explain this: yes, I know you can find lots of books, especially pop-science books, that make all this as clear as mud -- I would avoid such books.

      Incidentally, one of the reasons I get annoyed at the false claim that Special Relativity cannot describe accelerated motion is that the first serious physics problem I solved for myself was figuring out how long it would take to get to Alpha Centauri if one had a starship that could accelerate and decelerate at a comfortable 1 g.

      I solved the problem, using the knowledge of Special Relativity I had taught myself in junior high from Bondi's Relativity and Common Sense. Years later, I found advanced texts that confirmed that I had done it right.

      Now all I need to do is build the starship...

      So not only is it the case that Special Relativity can describe accelerated motion, but I myself did it, successfully, as a high-school student.

      People who claim otherwise are either ignorant or simply fools.

      Delete
    41. Physicist Dave, your words have compelled me to dig deeper, as I located (archive.org) a pdf copy of Milne: "Relativity, Gravitation and World-Structure" (1935). I note, Milne's book is an unusual document (idiosyncratic). Also, an article by Possel, "Teaching cosmology with special relativity-- Piecewise inertial frames as a model for cosmic expansion," (arXiv:1811.09524v1) with abstract: "The model can be viewed as a toy version of the Milne universe."
      Possel writes: "On larger scales, the toy model corresponds to a purely kinematical description of the universe, with gravity switched off." (page 17).

      Delete
    42. A reference for inflationary cosmology is.

      A. Guth, The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Basic Books (1997).

      The FLRW metric coefficient is exp(Ht) and the Taylor expansion is

      exp(Ht) = 1 + Ht + ½H^2t^2 + …,

      where the first order term is velocity, or with t = d/c it is a term v/c, and the second order term is, even with elementary physics, a change of that or acceleration. The SN1 data and the drop off in luminosity gave information on the second order term.

      The Milne cosmology is a special relativity-like spacetime with a negative curvature. This give FLRW-like spacetime is pure vacuum, while FLRW has a mass-energy density. The data better matches FLRW and the negative curvature of the Milne spacetime has not been found.

      Delete
    43. Gary Alan wrote to me:
      >Physicist Dave, your words have compelled me to dig deeper, as I located (archive.org) a pdf copy of Milne: "Relativity, Gravitation and World-Structure" (1935). I note, Milne's book is an unusual document (idiosyncratic).

      Now, that's a diplomatic way of putting it!

      I think Milne was actually viewed as a bit of a kook (perhaps unfairly). As I understand it, his whole model went beyond what is now called the "Milne universe," and almost no one ever took the whole model seriously, except Milne of course.

      However, the Milne universe per se (i.e, the alternative coordinates for Minkowski space) is a valid (trivial) solution to the Einstein field equations and is a useful toy model for helping students grasp the issues involved in General Relativity.

      It is getting more attention in recent textbooks just for that pedagogical purpose: e.g., Sean Carroll mentions it in his Spacetime and Geometry, and it is discussed in a bit more detail in George Ellis and Ruth Williams' Flat and Curved Space-Times. In my opinion, the space-like slices in the Milne universe are actually the simplest way to understand hyperbolic geometry (the isometries of this 3-D hyperbolic space are just the homogeneous Lorentz transformations, so for those of us comfortable with Lorentz transformations, it makes hyperbolic geometry almost obvious).

      And if the cosmological constant turns out to be zero and if the energy density turns out to be below the critical value, the Milne universe would be a good approximation to the real universe sometime long in the future (but not now).

      All the best,

      Dave

      Delete
    44. "The FLRW metric coefficient is exp(Ht)"

      During inflation you have an exponential expansion. As I've showed---even giving examples---in general the drop off in luminosity, while it does give some information on the second-order term, does not automatically indicate acceleration.

      Delete
    45. The whole point of (special) relativity is that the same laws of physics apply in all inertial reference frames moving relative to one another. Only the bookkeeping varies.

      How the relative velocities are obtained is not considered.

      If you want to attibute some incontestable physical change due to the relative velocities, then some work must be done. There must be some acceleration.

      There must a preferred reference frame.

      Delete
  9. 1. Are the observations of gravitational waves by LIGO being implausified?

    2. Einstein famous quote: "It is the theory that describes what we can observe". Was Einstein a scientist?

    3. Dark energy and dark energy are just mainstream fallacies.

    4. When you claim that roughly 68% of the universe is dark energy, 27% of it is Dark matter, and the rest is ordinary matter, what you actually are claiming is that your ignorance about the universe is just 95%, and the rest is what you think you know, but that's not necessarily the truth.

    ReplyDelete
  10. There is a paper entitled "How Dark Matter Came To Matter" (arXiv:1703.00013v2) where we find: "the story of dark matter cannot be reduced to a narrative in which ‘theories’ or their ‘elegance’ were the sole guide, nor indeed can it be framed as an exemplar of falsification-alism; its many interlocking components suggest a much richer texture that should forewarn one from constricting debate along the lines of ‘testability’."
    There read: "we need to understand why certain observations were eventually conceived as ‘evidence’ of anything in the first place." (page 12).

    ReplyDelete
    Replies
    1. i.e. science is just one of the many stories we tell ourselves ...

      Delete
    2. "i.e. science is just one of the many stories we tell ourselves ..."

      That is called "throwing the baby out with the bathwater".

      Delete
  11. Thanks for the explanation of DM/DE and perhaps just as importantly, the way science works to arrive at these conjectures.

    It sounds like what you are saying is that just because a hypothesis or idea is scientifically derived, it doesn't mean its right, but it means we are thinking about it the right way and are best positioned to figure out if its right or not.

    Looking at DM/DE from the viewpoint of the educated, non-expert public, it seems to me the physics community has a messaging problem. Instead of focusing on "we don't know what it is", more emphasis should be made on "we know what it does" (and are learning more all the time).

    ReplyDelete
  12. > First, the word “matter” in “dark matter” doesn’t just vaguely mean “stuff”.

    I disagree.
    I think a priori it does just mean "stuff".

    > Dark matter behaves like normal matter, except that, for all we currently know, it doesn’t have > internal pressure.

    A lack of internal pressure is not a necessary a priori property of any "dark matter". Take neutrino dark matter in galaxy clusters: it does have a large internal pressure.

    > The other reason why it’s wrong to say that dark matter can fit anything is that you cannot
    > distribute it as you wish. Dark matter starts with a random distribution in the early universe.

    Again an orgin in the early universe is not a necessary a priori property of any "dark matter".
    A much later origin (e.g. like from Hoyle's matter creation field in the steady state
    theory) would not a priori disqualify it as "dark matter".

    What makes dark matter "scientific" is not some a priori
    "specific behaviour" but that some
    a priori arbitrary behaviour that is stated in
    scientific (here physical, i.e. mathematical) terms
    eventually explains some observations.

    Franzi

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    Replies
    1. You are disagreeing with yourself. Neutrino dark matter is not just "stuff", it has very specific properties which is my point. The second quote refers to the presently most widely accepted dark matter model. The same goes about your remark about other variants. This is not a survey of variations on LCDM.

      Delete
  13. I am not sure if this has been done, but it is a thought I have had. There was the ekpyrotic theory of dark energy that posited a spatial variation to dark energy or the vacuum energy of the universe. This idea advanced by Steinhardt and Turok was somewhat popular last decade. I have never been a big panegyric of this idea. Also, I can think of potential problems with saying DM is ekpyrotic DE. However, if we think of the cosmological constant Λ = Λ(φ, ∂_μφ), the dilaton or inflaton field φ serves to cause a “flow” of space. This flow is mostly outwards, but for spatial variations that are highly local this might be a source of DM.

    I can of course hear problems, such as making this idea fit observations is once again a lot of form factor fiddling. But it would mean DM is fluid-like. It is sourced to the same field φ in a Brans-Dicke √(g)φR Lagrangian, A spatial variation or evolution of the vacuum |Ω⟩ → |0⟩ could produce particles, maybe these are axions which are related to dilatons by an entanglement change in an underlying gauge-like field. See the appendix in vol 1 of Green-Schwarz-Witten Superstring Theory on SO(24) SUGRA. This might be one way that DM could be a distributed field or vacua that also corresponds to particles. Of course, how a “vacuum” here can remain different from a vacuum “there” is hard to understand. It is a bit as if a wall of water with a large potential energy can stand without a dam. Maybe solitons are at work.

    Anyway, this is more of a question and not some theory I am thinking of in any serious way.

    Since the early days of the Swiss astronomer Zwicky it has been clear there is some source of gravitation that is not visible luminous matter. There is either some sort of matter particles that sit outside the standard model, or there is some form of space or spacetime physics outside of GR, This is one of the ideas Verlinde has been advancing. We really do not know the relationship between gravitation or quantum gravity and the nature of the quantum vacuum. In fact, how DE gives this tiny cosmological constant Λ ≈ 10^{-54}m^{-2}, when a straight up summation of QFT zero point energies gives a huge number, is not known. All of these questions are where science is the most interesting, which is the unknown.

    ReplyDelete
    Replies
    1. "All of these questions are where science is the most interesting, which is the unknown."
      And it is crucial to admit when you don't know (like inflation) ;)

      Delete
    2. Inflation has evidence for it. The support for inflation is though admittedly not conclusive. Inflation solves some problems, such as the flatness problem. The anisotropy of the CMB is consistent with inflation.

      The clincher will be to find B-modes in the polarization of the CMB. This was thought to have been found in 2015 with BICEPII, but the polarizing influence of galactic dust was reconsidered and the sigma 6 result suddenly collapsed to sigma 3. This is not bad evidence, but not enough to be conclusive. It would be like getting a 99.9% on a test, not bad but no cigar at this point. Work is ongoing to improve these observations. So as with most of science it comes down to measurement and observation.

      Delete
    3. Lawrence,

      The flatness problem is not a scientific problem, it is an aesthetic problem. Scientists should stop talking about it. I have explained this here.

      B-modes will not tell us anything if not found because it's easy enough to fumble with inflation models so as to accommodate whatever will be observed. That's one of the reasons why I am saying the methodology in this disciple is broken and needs to be fixed.

      Delete
    4. The flatness problem and similarly the horizon problem are related to a fine-tuning question. The critical value for energy density of the universe in inflation is reasoned with the exponential expansion under a huge vacuum energy. The stretching out of space by 60 e-folds means that any global curvature that existed prior to inflation was ironed out so such curvature, if it exists, is beyond the cosmic horizon. Similarly, the horizon problem on how disparate regions of the universe have the same homogeneity and isotropy is also solved with regions prior to exponential expansion being in causal contact. It is clear that one can impose initial or boundary conditions on a model of the early universe that give the same result. However, now one really has a fine-tuning, for one might ask where these come from. With inflation what ever “higgly-piggly” initial values were existent in the first 10^{-35}sec are not entirely relevant.

      This is admittedly not empirical evidence that gives confirmation of inflation. There are of course alternatives that can be considered. The difficulty I see is that these lead to more in the way of auxiliary or ad hoc conditions imposed. So I tend to see flatness and horizon problems as at least addressed by inflation to a minimal degree of sufficiency to keep inflation on the cosmological docket.

      Delete
    5. Lawrence Crowell8:10 AM, March 29, 2020

      But you mentioned before that B-modes, if discovered, would represent a successful prediction of inflationary theory; while Dr. H is saying that even if B-modes are found not to exist, inflationary theorists will just tweak their models and continue on their merry exponential way. You can't have it both ways.

      "However, now one really has a fine-tuning, for one might ask where these come from."
      I don't think it makes any sense to call this "fine-tuning". Current theoretical explanations for the flatness include exponential inflation or a set of boundary conditions. One could similarly claim that inflation is a kind of fine-tuning as it is required to be exponential rather than linear or logarithmic. There is no information on which is more likely out of inflation or boundary conditions, but tagging one of them as "fine-tuning" suggests the latter is more unlikely which is completely unknown.

      Delete
    6. "The flatness problem and similarly the horizon problem are related to a fine-tuning question."

      While Sabine and I disagree on the reasoning, we both agree that the flatness problem is not a problem. For a definitive account, including many references (also to some of my papers), check out the very thorough paper by Marc Holman. The real flatness problem is people not reading the literature. :-)

      Delete
    7. What are B-modes? Bekenstein’s rule is entropy of a black ho;e with area A = 4πr^2 = 8πm^2 is S = A/4ℓ_p^2 for ℓ_p = √(Għ/c^3) the Planck length. This can also hold for a cosmology with the area A = 3/Λ. The cosmological constant is in the early universe a parametrized function of the inflaton field Λ = Λ(φ, φ’) for φ’ the time derivative of the inflation field. In the early universe this parameter was huge, about 110 orders of magnitude larger than now. It means the area was much smaller and entropy low. This is in line with observations that strongly suggest a low entropy for the early universe. This mean the area of the horizon was semi-classical and the Bousso bound, similar to Bekenstein’s is

      S = ⟨A⟩/4ℓ_p^2 + quantum corrections,

      for ⟨A⟩ the quantum expectation of the cosmological horizon area. These quantum corrections are entropy contributions similar to the von Neumann or Renyi entropy from density matrix of QM. These might be called quantum fluctuations, which with the end of inflation leave a metric finger print.

      These metric fluctuations are gravitons. This quantum correction is a form of expansion of a metric according to the Planck length g = g0 + ℓ_p/L + O(ℓ_p^2) or

      g_{ab} = g0_{ab} + g(ħ^½)_{ab} + g(ħ)_{ab} + ….

      Where the second term is for free gravitons and the last stated term is for quantum gravitation field coupled with matter. These free gravitions have two degrees of polarization and most have circular poliarization. This means the metric has signatures of these polarized gravitons, which are “blown up” into large scale metric signatures at the end of inflation. Then things get messy, where metric signatures influence the distribution of matter and acoustical waves and these leave a signature in the CMB. This last statement involves a lot of phenomenology that I can’t go through in a blog entry.

      The BICEPII announced the discovery of B-modes in the CMB back in 2015. This was heralded as a breakthrough. However, electromagnetic radiation and light can be polarized by dust in a way that appears similar to B-modes. This muddied up the data, so σ = 6 data fell to σ = 3 or so. This now requires a more comprehensive set of observations to separate out the contribution of dust, which can be in part found by looking at different angles of inclination relative to the galactic plane, from B-modes should they really exist.

      Maybe inflation produced graviton B-modes do not exist. We will have to see. The theory and complex phenomenology are pretty well understood, so they are reasonable. Then of course nature might not be so cooperative.

      Delete
    8. It might depend on what you call a problem. Robert Dicke in the 1960s observed that to get the degree of homogeneity or flatness observed at large would have required an extraordinary measure of fine-tuned initial conditions. The one thing that inflation does do is with its 60 e-folding of space is to “iron things out” so that what ever initial conditions there were, are not as significant. If one rejects the idea in its entirely there is a problem or question on fine tuning, then indeed this is a “non-problem.” Even still, inflation smooths over what ever initial conditions there may have been in the pre-inflationary cosmos.

      There seem to be two uncomfortable approaches to fine-tuning. One is to say this can only be solved with an intelligent designer, and thus opens up the door to theology. The second is to say this is a non-problem, which has a sort of sterile logical positivism to it. It may be this is something we can never know, so these two philosophical stances may be what are left to us.

      I think half of physics is about counting and combining degrees of freedom, or equivalently about the dynamics of quantum information. With the early universe if the cosmological horizon were very small, say with a radius of ≈ 100ℓ_p, the most expected entropy would then be k⟨A⟩/4ℓ_p^2 ≈ 10^{-20}j/K, or less than 1eV/K. These DoFs expanded into a region about a meter in diameter. This scrambling lead to the appearance of much more entropy, but far less than what is given by the cosmological horizon length. The universe then started with extraordinarily low entropy, but the pre-inflationary quantum information is now mixed up. This is in part what inflation does do; it gives some credence to an hypothesis the observed universe has some level of generic qualities.

      Delete
    9. Lawrence Crowell 2:03 PM, March 30, 2020

      "One is to say this can only be solved with an intelligent designer, and thus opens up the door to theology. The second is to say this is a non-problem"
      Or we could state current knowledge: there is zero evidence of universal fine-tuning, so nobody knows if the universe is fine-tuned or not; ditto for the multiverse; and, theology is a fairy tale and fairy tales are not true. This is what we know.

      "This is in part what inflation does do; it gives some credence to an hypothesis the observed universe has some level of generic qualities. "
      How does it do that if it's an unconfirmed physical theory? And isn't genericness a quality that physicists should be beware of being impressed by, like naturalness?

      Delete
    10. The value of coupling constants at low energy is a consequence of the renormalization group flow for gauge parameters. How these running parameters terminate at the value they do is a profound question. In the transition from a false or high energy vacuum to the physical vacuum of broken symmetry these gauge parameters reached attractor points. How is this so?

      It is becoming fashionable to sweep a lot of things away, and while I too have some issues with the idea of fine tuning, particularly with strong AP or theistic ideas of a fine tuner, I think there is a deep question here. Instead of just saying this question does not exist as a proper question we might be more honest in admitting that physics has failed in its main objective.

      Delete
    11. Lawrence Crowell9:37 PM, March 31, 2020

      We really don't seem to be making any progress. You've mentioned these attractor points before. There may be a perfectly good non-tuning physical explanation. It is not known that this is a fine-tuning. Do you agree?

      Universal fine-tuning is pure hypothesis with no evidential support. AP is a simple tautology. Both ideas have been around for decades and have led to **zero** physical facts. Given physicists know there must be quantum-gravitational phenomena, now does not appear the right time to up tools and declare the current fundamentals to be explained by fine-tuning. And how is AP ever going to help anyone discover a physical fact? Physics has reduced the question of how the observable universe came about to a few fundamental laws and constants and a soup of quarks. How will considering complexity at much later times in chemistry or biology help? You cannot watch a YouTube video and determine whether the chip is ARM or Intel. (Of course, putting forward ideas of fine-tuning and AP could bag a researcher 1 million quid from the Templeton Foundation, even if they are intellectual dead-ends.)

      Theism is a fairy tale. Why bring it into a discussion about reality?

      "I think there is a deep question here"
      And are you also thinking hard about the route to observational confirmation? Otherwise you might end up solving a Pure Maths problem and accidentally win the Abel Prize or something...

      Delete
  14. Among the measurable effects of Dark Matter that Sabine enumerated in her video is enhanced gravitational lensing above what it would be if only normal matter existed in galaxies and galaxy clusters. This evidence for Dark Matter strikes me as the most difficult to accommodate in non-Dark Matter models. A long standing non-Dark Matter model that gets the rotation curves in galaxies right, fails to explain gravitational lensing when considering the Bullet Cluster, according to the article linked below.

    Another idea, which electrified me when I first heard about it - Jamie Farnes negative mass model - as I had an idea along similar lines, (albeit amateur grade), runs into problems of instability and energy conservation, as Sabine pointed out in a December 7, 2018 post. I just scanned Jamie’s paper on the arXiv, but only the section titles, and couldn’t find any mention of how his model deals with gravitational lensing. But going by his diagram 1, where the force between negative and positive aggregates of matter are repulsive, I assume that inward of the negative matter halo, surrounding a galaxy, light rays will be given an extra degree of curvature simulating the existence of more positive matter within the galaxy proper.

    Meanwhile our region has received a 7 inch coating of unwelcome White Matter. Just wish it was as invisible as Dark Matter and only interacted by its gravitational potential.

    ReplyDelete
  15. Forgot to put in the link which shows that the Bullet Cluster, and similar clusters, are incompatible with MOND with respect to gravitational lensing.

    https://archive.briankoberlein.com/2014/08/17/gravitational-models-dont-work/index.html

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    Replies
    1. I seem to have been in a mental fog for a stretch, but yesterday, and today, it appears to have cleared up, maybe due to taking a vitamin pill yesterday with breakfast. So belatedly, Sabine, I was reading the link you provided: "The Bullet Cluster as Evidence against Dark Matter". Reading that I see that I got things backwards - Modified Gravity can handle the dynamics of this system, whereas DM runs into significant problems. I have a simple, home-brewed idea that might be the missing ingredient to enable Mordehai Milgrom's MOND theory to account for the CMB spectrum. Of course it's quite amateur, and I won't go into details to comply with rules here.

      Delete
  16. Sabine,
    I like your blog a lot, it's really great!

    You wrote:
    "It’s a technical term that means “stuff with a very specific behavior”.
    Dark matter behaves like normal matter, except that, for all we currently know, it doesn’t have internal pressure."

    In the above quote you claim that "dark matter"
    means "stuff without internal pressure".

    I made you aware of the fact that neutrino
    dark matter has internal pressure. Therefore
    what you wrote above is incorrect.

    Your answer:
    "Neutrino dark matter
    is not just "stuff", it has very specific properties
    which is my point."

    does not make sense because it would of course
    equally wrong to claim that dark matter
    is "stuff with internal pressure".
    Dark matter just means "stuff".
    Tell me any "specific behaviour" it _needs_
    to have a priori.

    Franzi

    ReplyDelete
    Replies
    1. Franzi,

      I have already responded to these comments above. I will say it once more: I am, needless to say, talking about the concordance model of cosmology, also known as LCDM. My video is not about all the possible variations of dark matter that people have thought up. For the record, I am myself working on a type of dark matter that has pressure. This is an educational video that communicates the basics, not a review article.

      I will not publish another repetition of your comments which I have now responded to twice. Please stop wasting my time.

      Delete
  17. Much (most?) of what we know about the world outside of human-scale is through indirect observation. We can't watch directly, so we observe the behavior of what we can see and infer underlying mechanisms. In principle, watching the way stars and galaxies behave through telescopes of all sorts and watching the way subatomic particles behave in the Large Hadron Collider are the same.

    ReplyDelete
  18. What does it mean when you say that dark matter has no internal pressure? That dark matter doesn't gravitationally attract itself? That it doesn't interact with itself frictionally?

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    1. It means p=0. p are the diagonal entries of the stress-energy tensor. No, it does not mean that dark matter does not gravitationally attract itself, of course it does.

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    2. Could you imagine that neutrino-mixing off-diagonal entry has something to do with the dark matter and gravitational "field"?

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    3. Eusa,

      Anything could have "something to do with" anything else.

      But the "neutrino-mixing off-diagonal entry" is just physicists' way of talking about the fact that the weak interaction interacts with mixed states of neutrinos that have different masses.

      You could try to make "naturalness" arguments (of the sort Sabine has criticized!) to argue that this mixing and the small but non-zero neutrino masses is a surprise that requires some explanation.

      Or not. Maybe it just is.

      In any case, to tie it somehow to dark matter or gravitation, you'd need some detailed theory.

      (Of course, astrophysicists have considered the possibility that the dark matter just is the known neutrinos. There are good reasons to doubt this, which Phil or JeanTate could explain better than I.)

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  19. Dr. Hossenfelder,

    What an absolutely fascinating piece and discussion. I find it very interesting how the argument that dark matter and dark energy represents something made up simply to provide answers for observations that are not complete understood yet, so it has no basis or value.

    You know I have search all over and asked many mathematicians and physicists where it is in either quantum and/or relativity that require unification of these two things. It seems to me that since there is nothing in any science anywhere that requires unification of quantum and relativity all GUTs and TOEs could also be considered "made up." This in turn begs the question if dark matter and dark energy are made up, shouldn't we also consider string theory made up? I am just asking the question.

    Dr. Hossenfelder, as always, thank you for an interesting discussion. As a favor I would like to ask you to keep "shaking the tree" as you get some wonderful things to fall out

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  20. Dr. Hossenfelder: You say about dark energy:

    “Dark energy and dark matter are entirely normal, and perfectly scientific hypotheses.”

    “… the so-called cosmological constant. This cosmological constant is just a constant of nature and it’s a free parameter in General Relativity. Indeed, it was introduced already by Einstein himself. And what explanation for an observation could possibly be simpler than a constant of nature?”

    Simple - yes. But does this indeed mean a serious theory? Also a constant of nature should have a logical place in a theory, it should point at a physical cause of it. Such connection is nowhere visible in this case. So the present use of the constant is on the same level like fitting a polynomial of an arbitrary degree to a sequence of measurements.

    At least if we have the expectation to have a reductionist physics we should try to refer this constant to a theory or a process in a next layer. I think that even in a first step we should demand a better approach to call this procedure a theory.

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    1. I partially agree. Mathematical consistency does not suffice at all in Nature's sciences. A physical meaning is required for Lambda. But in a first time a formal trick can make the job perfectly just as the Planck's constant made another job in her time.

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    2. antooneo wrote:
      >Simple - yes. But does this indeed mean a serious theory? Also a constant of nature should have a logical place in a theory, it should point at a physical cause of it.

      The physical cause is energy that is invariant under Lorentz transformations.

      A term like the lambda term is the only way to get this, since stress-energy must be a second-order symmetric tensor, and the only candidate tensor that is Lorentz invariant is the metric itself.

      You could play with lambda varying over space and time, but then you would need a theory of how that worked -- much more complicated (and with no motivation).

      In more detail, you need a term with negative pressure (to explain what seems to be the cosmic acceleration) but not negative energy (no evidence for negative energy particles, and if they existed they could make the vacuum unstable).

      The cosmological constant fits the bill perfectly. If you have any other plausible (and motivated!) idea that works and that fits in with our best current theories of nature (such as relativity), let us know.

      I know enough about your work to know you don't.

      Delete
    3. PhysicistDave7:18 PM, March 25, 2020

      "I know enough about your work to know you don't."

      Yes, but, Dave, you have your own misconceptions, in that you think it is not known one way or the other whether a consciousness can exist "before" or "outside" observable space-time.

      But it is an irrefutable empirical fact that consciousness only exists in evolved complex brains on Earth. Anyone, claiming otherwise without evidence is simply wrong. It would be like claiming that an elephant's trunk (another thing that happened to evolve on Earth) might exist outside observed space-time.

      Do you agree?

      Delete
    4. Steven Evans wrote to me:
      >Yes, but, Dave, you have your own misconceptions, in that you think it is not known one way or the other whether a consciousness can exist "before" or "outside" observable space-time.

      Steve, I rather doubt that any sort of god or other disembodied consciousness exists. But I don't know.

      I'm afraid that you are a bit more confident on this issue than I am! I think you will find many scientists share my reticence on the matter.

      Steve also wrote:
      >But it is an irrefutable empirical fact that consciousness only exists in evolved complex brains on Earth. Anyone, claiming otherwise without evidence is simply wrong.

      Well, it sort of seems that way. But, you know, I do not know whether superdeterminism is right or wrong or whether string theory is right or wrong or whether the "firewall" does or does not occur around black holes or many other things in my own field of expertise.

      So, I pause before answering grand questions about the ultimate nature of the universe that go far beyond my area of expertise.

      Is much of the Bible mythical and the product of historical development? Sure, all educated people know that. Truth be told, lots of self=proclaimed fundamentalists know that -- they get uncomfortable if you start asking about how the vengeful and parochial God of the Old Testament turned into the universal and merciful deity of the New Testament. You can almost see them thinking, "Well, people changed their idea of God, but we are not supposed to say that publicly."

      I do not find it admirable that they say something different from what they think, but I know some of them well enough to feel sadness for the situation they find themselves in.

      Anyway, for myself, I honestly do not know how consciousness fits into the physical world: all the attempts I have seen to answer that question in detail seem to me unconvincing.

      So, both religious believers and dogmatic materialists think I am close enough to their position that I should join them. But, I fear the only honest thing I can do is say, "Sorry, but I just don't know."

      All the best,

      Dave

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    5. Einstein introduced the term “cosmological constant” to have a stable universe in his equation. He was aware that this was a poor ad-hoc assumption. Because when Hubble presented a solution for this problem, Einstein called his cosmological constant the “worst folly” in his life.

      Here Einstein was right, it was a folly. And with respect to the logical context this judgement applies also to the continued use of the cosmological constant.

      Is there a better solution? I have stated earlier that the whole problem of dark energy is immediately gone if we accept that the speed of light was slightly higher in former times. With a value of c greater than today by e.g. 2% for a time a billion years ago, the Doppler Effect yields a greater speed for old stars. So there is no acceleration to be assumed and no dark energy necessary.

      A small drift of c with time would be no problem for GR. Einstein’s formalism does not depend on a specific numerical value of c. Also there is no evidence for a strict constancy of c over time. And as said earlier, I had the occasion to ask Saul Perlmutter if this assumption could solve the problem of dark matter. Perlmutter did not like it, but he did not have serious arguments against it.

      For the other question by which mechanism c could change: this is a more fundamental question. Present physics do not even know why c has the value which it has. Einstein did not give an explanation but only postulated the constancy of c and the value which it has.

      I know a model which explains c and its dynamic behavior, even semi-quantitatively, but that is not main stream.

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    6. antooneo wrote to me:
      >Einstein introduced the term “cosmological constant” to have a stable universe in his equation. He was aware that this was a poor ad-hoc assumption.

      No, it is not an ad hoc assumption -- the cosmological term belongs in the field equation. It is logically possible that lambda is equal to zero, but that appears not to be the case.

      And, as Sabine keeps pointing out, modern physicists just do not care what Einstein thought on some particular issue. Physics is not theology where we have to go keep going back and engaging in deep exegeses of the inner meaning of the writings of the founder.

      We honor Einstein for his achievements but we do not need to appeal to the writings of St. Albert when we know enormously more than he ever did: the CMB, the Standard Model in particle physics, and all the rest.

      You are like the Creationists who insist on quoting and analyzing some obscure statement from Darwin, thinking they thereby disprove evolution. Modern evolutionary biology does not hinge on whether or not Darwin got everything exactly right (he certainly did not). It rests on an enormous amount of data that Darwin himself was never aware of.

      One of the reasons you are not a scientist is that you insist on quoting Einstein, Lorentz, or whomever, as if the words of Holy Scriptures of our forefathers tell us the ultimate truth.

      The Book of Nature is written in mathematics and empirical observations, not in some confused or misunderstood comments by some of the early pioneers in the field.

      antooneo also wrote:
      >Present physics do not even know why c has the value which it has.

      Of course we do -- by definition the speed of light in vacuo is 299,792,458 m/s: definition of the meter.

      Yes, I am being facetious -- we can define the meter that way because we have good reason to believe the speed of light in vacuo is constant. But there is a serious point to the joke: no theory can predict the speed of light for the simple reason that it is not a dimensionless number. Speed compared to what??? Only dimensionless ratios can be predicted by a theory in principle: otherwise, a mere change of units would falsify the theory.

      antooneo also wrote:
      >Einstein did not give an explanation but only postulated the constancy of c and the value which it has.

      You know that is false: Einstein did not "postulate" the value of c: he just accepted that it is what it is.

      antooneo also wrote:
      >I know a model which explains c and its dynamic behavior, even semi-quantitatively, but that is not main stream.

      And that is your problem: semi-quantitatively.

      Because we have a theory that predicts what is going on quantitatively, not just semi-quantitatively. We have no need for your semi-theory.

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    7. “antooneo wrote to me:
      >Einstein introduced the term “cosmological constant” to have a stable universe in his equation. He was aware that this was a poor ad-hoc assumption.

      No, it is not an ad hoc assumption -- the cosmological term belongs in the field equation. ….”

      >> I recommend to look into the books in which Einstein described how he developed relativity. He concluded from his GR field equation that the universe has to collapse. This was in conflict with observation, so he added – without any physical idea about it – a term which formally worked into the other direction. - This is a really bad case of an ad-hoc solution. Which Einstein normally rejected. So he was later ashamed to have done it.

      “And, as Sabine keeps pointing out, modern physicists just do not care what Einstein thought on some particular issue. Physics is not theology where we have to go keep going back and engaging in deep exegeses of the inner meaning of the writings of the founder. … “

      >> I would strongly appreciated if the physical community would not take relativity as a religion with Einstein as the leader. But this is not done. If relativity would be related to facts, the community would end up at the Lorentzian relativity. Also Sabine should appreciate this because Lorentz’s is a reductionist theory whereas Einstein is based on postulates, called principles.
      I had once a long discussion about Einstein vs. Lorentz (with respect to dark matter) with our leading professor for cosmology. He had a lot of arguments in disfavor of Lorentz. I could refute all his arguments what he accepted. At the end his last argument was that he still prefers Einstein because of the beauty of his version. - What can one say to this argument? - And further, he found Einstein’s RT simpler than the Lorentzian. - Funny indeed, because that means that the Riemannian geometry is simpler than the Euclidean.

      “You are like the Creationists …
      The Book of Nature is written in mathematics and empirical observations, not in some confused or misunderstood comments by some of the early pioneers in the field.”

      >> The book of nature is written in mathematics? Very funny! So elementary particle and field elements are intelligent enough to follow mathematically formulated rules and demanding principles? I would be curious to meet a particle (e.g. an electron) which knows what a mathematical formalism is.

      “antooneo also wrote:
      >Present physics do not even know why c has the value which it has.

      Of course we do -- by definition the speed of light in vacuo is 299,792,458 m/s: definition of the meter.

      …..”

      >> Why have physicists made an enormous effort to measure the value of c if it is so simple to just define it to have some value, and everybody is happy? So let’s define any physical parameter we need and the work is done! Funny understanding!

      “antooneo also wrote:
      >Einstein did not give an explanation but only postulated the constancy of c and the value which it has.

      You know that is false: Einstein did not "postulate" the value of c: he just accepted that it is what it is.”

      >> Please read carefully: Einstein has defined the *constancy*. But which process in nature has caused c to have that value which it has, that was the question here. And why is it constant. Can you answer it?

      “antooneo also wrote:
      >I know a model which explains c and its dynamic behavior, even semi-quantitatively, but that is not main stream.

      And that is your problem: semi-quantitatively.

      Because we have a theory that predicts what is going on quantitatively, not just semi-quantitatively. We have no need for your semi-theory.”

      >> If you have or know a model which yields exactly the value of c, as we know it, from basic facts, then please tell us. The model which I have mentioned needs at least the absolute density of elementary objects immediately after the Big Bang. Then c can be determined quantitatively and also its further development. I understand that you can do it? Then please to ahead!

      Delete
    8. PhysicistDave7:09 AM, March 26, 2020

      "disembodied consciousness"
      The term "disembodied consciousness" while grammatically correct is semantically meaningless. The endless production of such grammatically correct but meaningless terms is carried out in the field of philosophy.

      "I'm afraid that you are a bit more confident on this issue than I am! I think you will find many scientists share my reticence on the matter."
      Brian Schmidt and Crazy Luke maybe. Not Steven Weinberg, I bet.

      S: "But it is an irrefutable empirical fact that consciousness only exists in evolved complex brains on Earth."
      D: "Well, it sort of seems that way."
      Yes, it sort of seems that way in the way that it sort of seems that electrons exhibit quantum behaviour i.e. it's an empirical fact. Billions of brains are known to experience consciousness, anything without a brain is known not to be conscious. Empirical fact.

      "So, I pause before answering grand questions about the ultimate nature of the universe that go far beyond my area of expertise."

      Does one have to be an Intel engineer to know that the quantum behaviour of an electron is confirmed in transistors quadrillions of times a day? Consciousness is the one thing we are all experts in anyway.

      "Anyway, for myself, I honestly do not know how consciousness fits into the physical world: all the attempts I have seen to answer that question in detail seem to me unconvincing."
      There isn't a confirmed explanation of the quantum behaviour of an electron (maybe its MWI, maybe it's superdeterminism), but it's still an irrefutable empirical fact that the electron exhibits quantum behaviour. Similarly, it's an irrefutable empirical fact that consciousness is the function of an evolved brain.

      "But, I fear the only honest thing I can do is say, "Sorry, but I just don't know.""
      But empirically you know. You know there was no consciousness in the soup of quarks 13.7 billion years ago; you know there was no consciousness in bacteria on Earth a few billion years ago; you know the Sun and the Moon aren't conscious; you know consciousness only exists in evolved brains.

      Delete
    9. Steven Evans wrote to me:
      >[Dave] "I'm afraid that you are a bit more confident on this issue than I am! I think you will find many scientists share my reticence on the matter."
      >[Steve Evans] Brian Schmidt and Crazy Luke maybe. Not Steven Weinberg, I bet.

      Well, actually, Steve, I took QFT from Steve Weinberg and have followed his public statements over the decades. Naturally, he and I do not agree on everything (I think he is a bit to the left of me politically, for example), but we do tend to have similar perspectives on the "Big Issues." Our views on the foundations of quantum mechanics, for example, have converged over the decades.

      Here is s discussion of Steve's views on religion: I think he and I are in broad agreement on the topic.

      As to your attacks on "Crazy Luke," I suppose you and I agree that he should have shown more "reticence," don't we?

      Steve Evans also wrote:
      >Billions of brains are known to experience consciousness, anything without a brain is known not to be conscious. Empirical fact.

      Sure, but exactly what is the connection between the physical world and consciousness? Can a computer be conscious? When you trash an old computer, have you committed murder? Do the intricate interactions among phonons in a big rock embody a primitive form of consciousness?

      Really: no one can definitively answer such questions. Hence, my reticence.

      Maybe you and I differ simply as a matter of temperament? You seem eager to declare iron-clad definitive answers. I am more cautious. Or maybe I am just older and have had time to make so many mistakes that I have learned from experience to sometimes withhold judgment!

      All the best,

      Dave

      Delete
    10. antooneo wrote to me:
      >> I recommend to look into the books in which Einstein described how he developed relativity. He concluded from his GR field equation that the universe has to collapse. This was in conflict with observation, so he added – without any physical idea about it – a term which formally worked into the other direction. - This is a really bad case of an ad-hoc solution. Which Einstein normally rejected. So he was later ashamed to have done it.

      Yes, antooneo, we all know the history. Everyone knows the history.

      But, you see, we just don't care.

      Really bugs you, doesn't it??

      Einstein did indeed make a mistake in claiming the lambda term was a mistake! It belongs there: we even have a bit of a toy model as to how to get it -- the zero-point energy of the vacuum. (Yes, yes we all know it isn't really the zero-point energy, but that is an example of how you could get a term like the cosmological constant.)

      I sincerely wish you could see that a big part of what is going on here is that you somehow think that the truth of a scientific concept hinges on its history and development, much like the truths of Christian theology (supposedly) depend on the history reported in the Bible.

      No scientist thinks that way: that is theology, not science. We just do not care if Darwin worded some idea in a sloppy manner or Einstein wrongly disavowed the cosmological constant or if Dalton had a screwed-up picture of atoms or whatever.

      By treating science as if it were theology, you risk making a laughingstock of yourself, old friend.

      antooneo also said:
      >>> I would strongly appreciated if the physical community would not take relativity as a religion with Einstein as the leader.

      But, we are the folks who just do not care what Einstein said on the issue. You are the one who thinks what Uncle Al said is of crucial importance.

      You treat his words as Gospel; we just don't care.

      Come to think of it, I have never read a book by Einstein. Probably never will. I care about physics, not some old dead guy.

      You are the would-be theologian; we are scientists.

      antooneo also wrote:
      >I had once a long discussion about Einstein vs. Lorentz (with respect to dark matter) with our leading professor for cosmology. He had a lot of arguments in disfavor of Lorentz. I could refute all his arguments what he accepted. At the end his last argument was that he still prefers Einstein because of the beauty of his version.

      To be completely honest, I do not believe you. Who was this supposed "leading professor for cosmology"? You have not behaved honestly, and I do not believe you.

      antooneo also wrote:
      >The model which I have mentioned needs at least the absolute density of elementary objects immediately after the Big Bang. Then c can be determined quantitatively and also its further development.

      You cannot derive a speed solely from a density: dimensional analysis prevents it.

      I do not believe you are even trying to tell the truth.

      But, by all means, prove me wrong: tell us the title and author of the paper that proves I am wrong.

      Delete
    11. > I took QFT from Steve Weinberg
      Way to go, Dave. Being taught by physics royalty.

      "Sure, but exactly what is the connection between the physical world and consciousness?"
      The brain. A functioning physical brain gives its owner a feeling of consciousness. Empirical fact. The electron exhibits quantum behaviour - another, also as yet unexplained, empirical fact.

      " Can a computer be conscious?"
      Yes, if you can recreate the structure of the brain in silicon. But then you would have a brain in silicon rather than just a computer - the iBrain.

      " When you trash an old computer, have you committed murder? "
      No, because current computers are finite state automata. If we can describe functions completely and none of the functions are consciousness then we have no consciousness.

      "Do the intricate interactions among phonons in a big rock embody a primitive form of consciousness?"
      Obviously not, because they may be intricate but they are nowhere near intricate enough to represent the states of a conscious brain. Empirically speaking, you can't get consciousness in just physics, just like you can't get a functioning microprocessor in a random piece of silicon. To get consciousness you need to build up the physics into chemistry and then cells and then neurons in various complex structures, and you can achieve consciousness. Just like in computing you build up from transistors to logic gates to latches to registers, etc. all the way to a microprocessor. You can't achieve a microprocessor through a random scattering of transistors on silicon, you have to go through the hierarchy to achieve complexity; similarly you can't achieve the complexity of the brain with just a collection of not very structured atoms like in a brick.

      Empirically speaking, consciousness has only been reported/observed in brains with this hierarchical build up of complexity.

      I think you underestimate ways of knowing. I know the Battle of Stalingrad happened, but I wasn't there.


      Delete
    12. > I took QFT from Steve Weinberg
      Way to go, Dave. Being taught by physics royalty.

      Nice !

      Delete
    13. PhysicistDave 5:18 AM, March 29, 2020

      Alright, Dave. I have a convincing argument. This is my last attempt.
      Do you know that orcs depicted in "Lord of the Rings" don't exist in reality?
      Yes. Because you know that Tolkien imagined these beasts. If someone claimed that Tolkien alone might have seen one, or that orcs had once roamed the Earth, or orcs might possibly have evolved elsewhere in the universe, then you would surely say the chances of this are nil based on scientific and societal knowledge. Chances are nil = you know it.

      Similarly for a god (disembodied consciousness). You know it is a mythical being. You know that the chances that a mythical being actually exists is nil, by the above argument. And in the case of a god, because of the advances of scientific knowledge, the claim has had to be pared back from a physical being with amazing powers living in the sky to a "disembodied consciousness" (meaningless) existing "outside space-time" (meaningless). So as with the orcs, because of your knowledge of how the idea came about and the lack of any evidence, you know the chances of the idea being true are nil, especially given in its pared back form the idea is meaningless.
      Quod erat demonstrandum?

      Delete
    14. Dave,

      you write that the cosmological constant is not at all an ad-hoc idea but a necessary part of the field equation. But obviously this term was not a necessary part earlier, before Riess and Perlmutter made their detection. And now it is all of a suddenan intrinsic part of the field equation?

      This is indeed a very special kind of logic in a physical theory.

      And btw, religion is the reference to principles, not the use of reductionism which I follow.

      Delete
    15. "But obviously this term was not a necessary part earlier, before Riess and Perlmutter made their detection. And now it is all of a suddenan intrinsic part of the field equation?"

      This is wrong on many levels. At best (but even that really doesn't hold up) one could argue that the supernova projects first determined that the cosmological parameters was non-zero. Before that, observations just weren't good enough to say. There is an urban legend that someone invented the cosmological constant to explain the supernova data. This is just wrong.

      Delete
    16. "that the cosmological parameters was non-zero" should be "that the cosmological constant was non-zero"

      Delete
    17. Steven Evans wrote to me:
      >Alright, Dave. I have a convincing argument. This is my last attempt.

      >Do you know that orcs depicted in "Lord of the Rings" don't exist in reality?

      >Yes. Because you know that Tolkien imagined these beasts.

      Indeed. And I grant you your analogy: we know a good deal about how humans invented Yahweh (much of it is actually documented in the Old Testament, in parts True Believers tend to ignore!) and similarly how the myth of the Christ was created by human beings (that is very well-documented in the writings of the "Church Fathers").

      So, we therefore know that Yahweh and his Christ are not real (I take no stand as to whether the human Jesus of Nazareth was real, but his alter ego, Christ the Son of God, is of course make-believe).

      However, to continue with your Tolkien analogy, suppose I told you that paleo-anthropologists had found fossils of beings that were not really "hobbits" but who resembled hobbits enough to be given that nickname. Would you argue that this is impossible because true hobbits are, of course, make-believe?

      I trust you know what I am referring to: Homo floresiensis, which was indeed given the nickname of "hobbits."

      Your argument does not show that there cannot be something in the real world similar to something first conceived in fiction, and, indeed, we could give endless counter-examples: air-flight, flight to the moon, etc.

      So, yes, your argument proves that Yahweh, Zeus, Harry Potter, Superman, etc. can never really exist simply because, by definition, the real Superman is fictional -- we know he was created as a fantasy by human beings.

      But whether there is something in the real world that has a close enough resemblance to Zeus, Yahweh, etc. that he could reasonably be called "God," sorry, but your argument is just too weak for that.

      Do I think such a "God" exists? No, I don't. But I am relying on the empirical absence of evidence: quite often, absence of evidence really is evidence of absence (despite the mindless repetition of the contrary by so many pseudo-intellectuals!).

      Truths about the real world have to rely on empirical facts about the real world. The mere analytical fact that, by definition, "orcs" are fictional tells us nothing about the real world.

      All the best,

      Dave

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    18. PhysicistDave 2:50 AM, March 31, 2020

      " quite often, absence of evidence really is evidence of absence"
      But in this case it's absence of meaning even. What is even meant by a disembodied consciousness?

      "Truths about the real world have to rely on empirical facts about the real world."
      Exactly. And the empirical facts tell us that consciousness is a function of complex,long-evolved brains on Earth. Why would one abstracted function of an evolved Earth brain exist outside space-time from 13.7 billion+ years ago and was it the first member of Mensa?
      Empirical facts tell us this has probability zero, not that disembodied consciousness and outside space-time even mean anything empirically. Probability zero because conscious brains have arisen in a particular environment via innumerable steps in a process of evolution. So it is not clear what one abstracted aspect of a conscious brain would be doing floating around in nothingness 13.7 billion+ years ago. Does this not cross the line of empirical knowledge?
      Are you saying, for example, that you don't know that clairvoyance is not real? Is it possible that the disembodied consciousnesses of the dead communicate with consciousnesses of the living?
      Again, I say that I know clairvoyance is not real, because I know dead people aren't conscious.
      I understand obviously you will be extremely skeptical of clairvoyance, but do you know it's not true? Is there anybody there.....?

      Delete
    19. PhysicistDave 2:50 AM, March 31, 2020

      Dave, I guess I'm just arguing a strong version of Russel's teapot, though I would claim Russel didn't make full use of all the data. Russel claimed that the burden of proof rests on a person claiming a teapot is in solar orbit between Mars and Earth; but I am saying that based on all our knowledge (of teapots, the solar system, etc.), we know there is no teapot there.

      Do you know that there is no teapot in solar orbit between Mars and Earth?

      Delete
    20. Steven Evans wrote to me:
      >Empirical facts tell us this has probability zero, not that disembodied consciousness and outside space-time even mean anything empirically. Probability zero because conscious brains have arisen in a particular environment via innumerable steps in a process of evolution.

      Well, Steve, maybe you took different classes on probability than I did! But how do you get probability zero from empirical data?

      As you know, for a long time, people in Europe observed whit swans but nary a black swan at all. Does that mean that the probability of black swans was zero?

      But then it turned out there actually are black swans Down Under!

      Steve also wrote:
      >So it is not clear what one abstracted aspect of a conscious brain would be doing floating around in nothingness 13.7 billion+ years ago. Does this not cross the line of empirical knowledge?

      Yes, indeed it is not clear, and empirical knowledge does indeed suggest it did not happen.

      What I am not so clear on is why you are absolutely certain of something like this this rather than simply thinking it has high probability.

      Steve also wrote:
      >Are you saying, for example, that you don't know that clairvoyance is not real? Is it possible that the disembodied consciousnesses of the dead communicate with consciousnesses of the living?

      Well, I doubt it because, as you know, people have actually looked for evidence of these things and failed to find any convincing evidence.

      Steve asked me:
      >I understand obviously you will be extremely skeptical of clairvoyance, but do you know it's not true?

      Well, I think it is not true, and indeed it probably is untrue, so I guess you could say I "know" it: I mean, if Biden loses in November, I could say, "Yeah, I always knew he'd lose!" since I do honestly think he will lose.

      On the other hand, perhaps it would be more honest for me to say, "Back at the end of March I thought Biden was down by 3:2 odds and he sure did lose," which is in fact my current best guess. (Note: this has nothing to do with whom I will vote for. This is just my current guess as to what will actually happen. Reality may surprise me.)

      Feynman once said that he was comfortable living in a universe in which there were many things he did not know. I guess I share his sentiment.

      You seem to not only want to be absolutely certain about many empirical facts on your own account but also to want others who largely share your views to be equally certain.

      I confess that this perplexes me, though I know that many (most?) people feel as you do, not as Feynman and I do.

      Since childhood, I have been perplexed by people who say things like "That's life!" I remember as a pre-schooler wondering how they knew everything about life, since that seemed a rather large subject to fully encompass.

      I still think that way.

      C'est la vie.

      Dave

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    21. PhysicistDave 11:59 PM, March 31, 2020

      You didn't attend the Feynman lectures, too, did you?

      I take all your points but I think we have the knowledge to say we know the Battle of Stalingrad happened, and that the Russelian teapot isn't there and that disembodied consciousness isn't a thing. Though I wouldn't want to write out the full argument;)

      Do you know Harry Potter in the books is a fictional character, or would you need to go to England to check?
      That's the way in which I know disembodied consciousness isn't a thing i.e. I know it.

      Delete
  21. Dear Sabine! Dark Matter truly doesn't exist. It derives from Einstein's interpretation about what is and how works Gravity, and it is an absolutely absurd claim. In 'Einsteinianism' many things that appear to resemble something are declared to be true. This is as silly as go to circus and declare that the rabbit, which appeared to disappear by a magician, truly disappeared. Nothing of that is true.

    I will give you one clear story about where science has failed a lot, and no scientists have realised the blunder right in front of their eyes. It is the claim of Einstein that the speed of light is constant for any frame of reference. For this claim to be true, the Aether as it was understood in the days of Michelson and Morely, has to be accepted as existing. But its existence has been rejected by virtually all scientists. And this creates an absurd conundrum - Einstein's claim is only true if that specific Aether exists, but the same experiment that Einstein is using for his claim is also used to declare that it doesn't exist. But that is absurd.

    Just think about it. How can it be that Einstein had this claim? What experiments proved this correct? If the Aether doesn't exist, then there is no other experiment that would lead to Einstein's claim... No wonder Einstein himself in 30-ties declared that the universe without the Aether is unimaginable. But he was ignored on this. And scientists up to this day live with these two, mutually excluding claims and teach them as both true at the same time. And the whole science of theoretical physics is the same...

    I sent you am email few days ago about the true Pattern of Magnetic field. As it turns out, some important info was missing there. So I changed the article and will send it to you again.

    And no, Dark Matter/Energy and Einstein's Gravity don't exist. And in due time i am going to prove this all...

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    Replies
    1. George,

      It's ill-informed nonsense like yours that prompted this video.

      Delete
    2. Your initial premise shows that you not only failed to understand relativity, you failed even to read this history correctly. In fact relativity got rid of the aether by building the idea of propagation directly into the geometry - the Minkowski geometry of spacetime instead of the 3+1 Euclidean geometry with universal time.

      The real damage people do with such balled-up arguments is that all of us who question the rationale behind dark matter and energy, even those with expert-level understanding of gravitation and relativity that we got by hard work and long study, are lumped into the same bin with loonies who make arguments that have nothing whatsoever to do with the actual problems, like this one.

      -drl

      Delete
  22. @Sabine.
    "Dark matter behaves like normal matter, except that, for all we currently know, it doesn’t have internal pressure".
    I do not think that being pressureless is an intrinsic property of DM. A fluid with no pressure is simply a cold fluid. That's why we talk about cold dark matter (CDM) in the standard LCDM model. Now, if being cold was an intrinsic property of DM, we would not need to put the adjective "cold" in front of it. Indeed, people have studied models of warm DM ans wavelike DM (you had a post on this some time ago), both of which have some kind of pressure. Cold DM happens to be better at fitting the observations, but it's not a fundamental property of DM.
    The real intrinsic property of DM is, well, that it is dark, ie, that it does not couple to photons, so we can't see it. This is actually a bit of a misnomer, because we do see dark objects! (because they absorb the light coming from behind them). DM does not absorb light and therefore is more transparent than dark.
    To add even more confusion, "dark" in Dark Energy does not mean the same! For all I can think, it just means that it is an unknown kind of energy.

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    Replies
    1. Opamanfred,

      Needless to say, I am talking about the currently most widely accepted standard model of cosmology, ie LCDM.

      Delete
    2. @opamanfred
      no, "that it does not couple to photons"
      is also no necessary intrinsic property
      of "dark matter". Take planets which might
      be an imporant fraction of the dark
      matter in galaxy cluster. Of course they
      "couple to photons". "Dark matter" needs
      to have properties such that "it has
      not been seen in the EM spectrum up to now".
      But the latter is no property in itself.
      There is no a priori property dark
      matter needs to have. A priori it
      just means "stuff".

      Delete
    3. @Franzi. Planets are made of baryonic matter, so it's not dark matter. Dark does not mean "hitherto unseen".

      @Sabine. I still think your paragraph is ambiguous. Warm and wavelike dark matter are they dark matter or not then?

      Delete
    4. @opamanfred
      > Dark does not mean "hitherto unseen".

      You're mistaken, it means exactly this.

      > Planets are made of baryonic matter, so it's not dark matter.

      Look: there is dark matter in galaxy clusters.
      If that would turn out to consist of
      planets, this dark matter would be planets.

      "Not being baryonic" is also no a priori
      property of dark matter ;-).

      Delete
  23. Maybe it would help in understanding the relationship between a field and source to think of electromagnetism. A static electric field is associated with a charge. If that charge is moving there is also a magnetic field, so a current gives a magnetic field. There is of course the issue of special relativity, for it one boosts themselves to a frame moving with the charge the magnetic field “goes away” and is replaced with more electric field. So, we have

    Electric, magnetic fields ↔ charge, current.

    These static or stationary fields are strictly tied to a source.

    Now if the charge is accelerated or suddenly shifted to another region by a force, the radial electric field adjusts by wiggling in a pulse the propagates outwards. This is associated with a magnetic field as well. This is an electromagnetic field that propagates outwards at the speed of light. In the so-called far field region, as the name suggests far from the charge or current that oscillates or forced to move, the time varying electric and magnetic field exists without a charge.

    General relativity is similar. A static gravity field is associated with a distribution of mass. The rotation or motion of a mass results in a gravitation analogue of the magnetic field. Thus, if there is some stationary or static gravity field the Einstein field equations, just as with Newton, tell us there must be some matter source for the gravitational field. The rapid change in mass distribution, say the collision of black holes etc, results in gravitational waves, which are entirely analogous to electromagnetic waves.

    It is then a very reasonable, at least what we might call a first order hypothesis, that dark matter is some sort of mass. Matter is considered or modeled as made of particles, which has been the dominant paradigm since the early 20th century. As a result, the idea of ΛCDM is reasonable. This does not guarantee of course this is correct, but in science you go with what tools and knowledge base you have.

    For something beyond this, consider John Wheeler’s hypothesis that electric charge is really a sort of wormhole. In this idea lines of electric field weave through tiny wormholes which gives the appearance of charge. Then charge is a topological quantity. With dark matter it is possible that something similar occurs. For the MOND field with potential V(r) = V_0 log(r) with force F = -V_0/r has characteristics of two-dimensional space, which might reflect some sort of topological field effect with space or spacetime. This sort of physics may be present in reality, and it may as with Wheeler’s suggestion have a correlation with point-like particles.

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  24. John Wheeler writes: "The charge, or wormhole flux, is unquantized. It can have one value as well as another. It has nothing whatsoever directly to do with the quantized charge observed on the elementary particles of quantum physics." (page 232, 1957, Classical Physics as Geometry, Reprinted: Geometrodynamics, 1962).

    ReplyDelete
    Replies
    1. I am referring to Misner Thorne Wheeler Gravitation on page 1200 figure 44,1. This is based on the Misner-Wheeler article. The physics gives a classical idea of charge because the EM and GR concepts are all classical. There is though nothing, except for quantum gravity and one that might violate Hawking-Penrose energy conditions, that demands it is impossible for some quantized version of this.

      Delete
  25. "As the universe expands, and matter in it cools, dark matter starts to clump and it forms structures. Normal matter then collects in the gravitational potentials generated by the dark matter."

    Why would DM clump faster than baryonic matter? Would kind of mean it curves spacetime more eV for eV, wouldn't it? There are reasons normal matter at some point stops collapsing (outside fringe conditions). What, if anything, is stopping / slowing DM collapse? They both rotate (most likely), that's true but, again most likely, at same speed.

    And if it is clumping faster than normal matter how come DM halos are larger than baryonic stuff they've corralled? One could conjure a scenario where normal matter feels gravitational pull of DM but not vice versa although I find that bit shoehorned.

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    1. Because it doesn't have internal pressure.

      Delete
    2. For those who are having trouble visualizing a pressure-less fluid, think of a lot of stars in a cluster. Ignoring the rare collision they do not impact so as to give a pressure. In fact given a trillion stars that fall inwards, this a galaxy worth of stars, they could gravitationally contract without interacting. Once this cluster clumps in, remember without pushing on each other, to about half a light year there will be the formation of a black hole. This happens without any pressure.

      Delete
  26. Unscientific is as you say the wrong word, but some can be wrong-headed and still scientific - the best examples come from the early days of relativity and quantum theory - the deformable electron in the ether, and the Bohr-Sommerfeld elliptical orbits. You can even get right answers, for the wrong reason, e.g. the value of the fine structure constant.

    -drl

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  27. One should keep in mind that dark matter has a very long history, both in the sense of matter which does not emit light (but, in contrast to modern cosmological dark matter, absorbs it)---dust, dark nebulae, and so on---as well as matter deduced from its gravitational interaction. In the context of our galaxy, other galaxies, and galaxy clusters, this goes not back just to Smith in 1936 (Virgo cluster) and Zwicky in 1933 (Coma cluster), but earlier to Lundmark (1930), Oort, Kelvin, Poincaré, sometimes even with the speculation that there might be more dark matter than luminous matter. Companions of stars were found because of their gravitational influence of proper motion on other stars, and of course Neptune was postulated and found because of its gravitational influence on Uranus. Even some ancient Greeks had an invisible counter-Earth, which is arguably a form of dark (and transparent) matter. So it is an old idea which has been invoked---and found to be the best explanation---many times.

    On the other hand, even before Milgrom there were speculations that Newton's law of gravity might not hold. These were usually based on the idea of it not applying at large distances. Milgrom's idea that it breaks down at low accelerations has proved amazingly productive.

    Don't fall for the false dichotomy---both might be right: some cosmological dark matter and also some sort of modified gravity.

    There was a dark-matter prediction which didn't pan out: Vulcan. The answer here: modified gravity (general relativity).

    Newton did a large part of his important scientific work while in home office during the plague. Maybe the corona virus will prove as productive. :-)

    ReplyDelete
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    1. "Don't fall for the false dichotomy---both might be right: some cosmological dark matter and also some sort of modified gravity."

      And don't ignore any cases - modified gravity and no dark matter is a possibility.

      Delete
    2. "modified gravity and no dark matter is a possibility"

      If so, it would have to be some sort of modified gravity which is yet unknown. Note also that there is no debate that there is baryonic dark matter; no-one claims that everything glows. As for non-baryonic dark matter, even most MOND enthusiasts admit that there are areas where it works and MOND doesn't, particularly in cosmological structure formation. (Also in galaxy clusters, but there not that much is need and the cluster dark matter could actually all be baryonic.)

      I recommend the (semi-)popular books by Bob Sanders. He is one of the leading MOND people, and two of his books, The Dark Matter Problem: A Historical Perspective and Deconstructing Cosmology are in some sense advertising for MOND, but he takes a balanced approach on the whole. (Another book, Revealing the Heart of the Galaxy: The Milky Way and its Black Hole is actually about a large chunk of dark matter which might have been formed completely out of baryons but also might have been seeded by a primordial (and thus non-baryonic, since formed before big-bang nucleosynthesis) black hole.)

      Delete
  28. "Why would DM clump faster than baryonic matter?"

    Baryonic matter is prevented from clumping due to interaction with radiation before decoupling. This is some of the strongest evidence for dark matter. We know the size of fluctuations at the redshift of the CMB. There hasn't been enough time for structure to form if there is only baryonic matter; it works only because dark matter gets a head start because it doesn't interact with radiation.

    "And if it is clumping faster than normal matter how come DM halos are larger than baryonic stuff they've corralled?"

    By faster we mean that things roughly the size of galaxies develop in dark matter faster than baryonic matter can collapse (so the baryons fall into the potential wells of the dark matter). But how much dark matter collapses depends on what it is made of. In fact, a popular idea is that it is an extremely lightweight particle with a Compton wavelength larger than a galaxy, so essentially the exclusion principle keeps it from collapsing more.

    The details of galaxy formation probably depend more on baryonic than on dark matter.

    ReplyDelete
    Replies
    1. Phillip Helbig 8:26 AM, March 27, 2020

      "This is some of the strongest evidence for dark matter. We know the size of fluctuations at the redshift of the CMB. There hasn't been enough time for structure to form if there is only baryonic matter; it works only because dark matter gets a head start because it doesn't interact with radiation."

      Interesting. Is it possible that the dark energy factor in the model forces this conclusion incorrectly, though?

      Delete
    2. "Interesting. Is it possible that the dark energy factor in the model forces this conclusion incorrectly, though?"

      How?

      Dark energy (or the cosmological constant---there is no evidence that dark energy is anything other than the cosmological constant) has only a very small effect on structure formation. Its main effect in a cosmological context is that it affects the expansion history of the universe, but a positive cosmological constant provides more time for structure to form, so it actually helps a bit (but not enough by a long stretch).

      Delete
    3. I see (I was thinking that no dark energy or CC might mean baryonic matter could be closer together and more easily able to form structures, but no.)

      Delete
    4. Luminous and dark matter clump depending on energy or the temperature of the early cosmos. This gets into a lot of phenomenology I am no expert on, so pardon me in advance if I get something wrong here. In the radiation dominated phase of the universe charged particles were Compton scattered by radiation. Dark matter conversely is not causally affected by radiation. The clumping of DM in the early universe is thought to be due to acoustic modes in the early universe. These were produced by “valleys” in the metric of the early universe produced by anisotropies left over from inflation. This may include B-modes. These were converted to acoustical modes. Interestingly gravitational radiation in matter is similar to acoustical waves, where the coupling of the two converted early gravitational radiation to acoustical waves. So in the later radiation dominated phase of the universe these acoustical waves with high and low pressure regions would heat luminous matter (LM) more “here” and less “there.” Where the luminous matter was less hot it would clump more. The gravitational interaction of DM and LM would cement LM around DM this way.

      With the end of the radiation dominated phase came the matter dominated phase. At this point the universe was no longer an opaque plasma and LM could now clump much further and radiate energy by emitting photons. Now LM clumps far more than DM. DM is in these galactic haloes and LM clumps into the galaxies. Then a lot of further galactic phenomenology enters in with density waves and so forth. This removes me further from my detailed understanding. How galaxies organized themselves into these spiral structures is a bit of a mystery to me, and from my understanding is not at all well understood.

      Delete
    5. Lawrence Crowell9:13 AM, March 30, 2020

      I see. So DM had a 300,000 year head start to form structures. There is the possibility though that inflation didn't happen and what you are explaining by inflation could be explained by boundary conditions, and that dark matter doesn't exist and what you are explaining by dark matter is explained by modified gravity. Yes?

      Delete
  29. Dr. Hossenfelder;

    Forgive my delayed response. I simply wanted to take a moment to wish you the best of luck with any and all research in the area of dark matter and dark energy. If we really want to be honest dark matter and dark energy really represent the only areas of possible new theories and discoveries in physics. Back in 1933 Fritz Zwicky theorized dark matter and it in essence has been ignored until now because "something" (that really has not given us anything useable) was more important. In my humble opinion this is not how science, and in particular physics should work. So, I wish you the best of luck and would request that you think out of the box a bit and do not look at anything as being too crazy.

    Speaking about history, what if T. Kaluza was right about a 4th dimension above our current 3 dimensions? As I believe I have read, the same physicists of the time that gave us Copenhagen also told him he could not be right because physics would see this other dimension. The question becomes, how would physics see this other dimension?

    Again, good luck Dr. H. and thank you for taking the time to try and find something new as it has been a long time since any new useful discoveries.

    ReplyDelete
    Replies
    1. Back in 1933 Fritz Zwicky theorized dark matter and it in essence has been ignored until now because "something" (that really has not given us anything useable) was more important.

      As noted in my other comment, Zwicky was not the first to suggest that a substantial fraction of the Universe might be in dark matter, but he was probably the first to do so in connection with galaxy clusters.

      But where do you get the idea that it has been ignored? Several books have been written about it; there have been a large number of conferences on it; many have dedicated their careers to it. Whatever one thinks of it, it certainly hasn't been ignored.

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

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  31. Undoubtedly, adding a constant to make the equation hit - is scientific.

    But when we study physics as manifold of interactions, a constant (dark matter, dark energy, lambda) is due either to need for degree of freedom (like causality speed) or to need of emergency (like specific heat capacity). in a sense they are probably two manifestations of the same thing ...

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  32. 1. Sabine, you spoke recently with Subir Sarkar, where do you see the weakness in his arguments that there might be no dark energy.
    2. The discussion about Laniakea supercluster, the great attractor, is very much depended of the existence of dark energy: with dark energy we may not be a part of the Laniakea supercluster in the “Long run”. With no dark energy or less dark energy we, the lokal group (in 2-3 billion years maybe one galaxy) could mostly be influenced by the Laniakea supercluster (and in a distant future be one cluster/galaxy with a gigantic central black hole). What is your comments to this discussion among astronomers, Sabine?

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  33. Before humans sailed around the world, maps were published with dragons swimming far offshore. Near the dragons it would say, "Beyond here there be dragons." So there you have it, dark energy, dark matter, dragons.

    ReplyDelete
  34. It doesn't matter whether Russell's teapot is filled with dark tea or not.

    ReplyDelete
  35. So it cooled down slower since it doesn't radiate. Which would left it with higher kinetic energy. Which would make it more resistant to gravity.
    Or are you saying it is so exotic that it came into existence already cold?
    Then there's spontaneous collapse of cold hydrogen clouds into protoplanetary discs and (warm) DM's role there. Then there's it's role when collapse is caused by external pressure which doesn't affect it, cold or warm. Then there's the fact that folks were searching for decades for DM particle that would cause every non-Black-Hole object in the universe to have a ball of DM in its centre (packed to density of a neutron star?) which doesn't screw up radiation/gravity balance at all, right? And would have most of DM locked up in BHs anyway.
    It explains some observations. Doesn't mean it exists. Could exist, sure. But it would be so nice if we went back to times when people, when coming up with a solution, came up with a solution and not just vague apparition of one.
    I get it, you (theoretical scientists) have to eat. An environment was created, let's not go into "by whom", where papers are produce. Of course, we could have society where smart and educated people earned their living by teaching and have theoretical exercise as a hobby. But then they'd have to deal with unfulfilled egos, modest living standards and overcrowding. Societal norms' pressure notwithstanding. Won't happen. It's kind of what's happening with scientific data gathered. Often we hear about papers based on 10+ years old data. Why have we built better instruments when data gathered with old ones hasn't been used fully yet? Again pointless mental exercise. Of course we'll build bigger, better, more expensive. Everybody benefits from it, right? Let us all drive sports cars, reach a destination as fast as possible so we can rush to the next one and damn the scenery. Just don't forget to take a selfie when you get there!
    If only I could earn my living by telling concerned customer their problems are caused by computer gremlins and it will take me 7 years to prove their existence and few more to get rid of them :)

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    1. Olmo Sirk wrote:
      >I get it, you (theoretical scientists) have to eat. An environment was created, let's not go into "by whom", where papers are produce.

      Well, I'll grant you that there is more than a bit of truth in that!

      Olmo also wrote:
      >Of course, we could have society where smart and educated people earned their living by teaching and have theoretical exercise as a hobby.

      Well, of course neither Einstein nor Darwin had an academic position when they did some of their most important work.

      One of the odd things is that the modern world is much richer than the world of Einstein or Darwin and so it should be more possible for there to be "gentlemen scientists" today than back then. But it does not seem to happen often.

      Olmo also wrote:
      >Often we hear about papers based on 10+ years old data. Why have we built better instruments when data gathered with old ones hasn't been used fully yet? Again pointless mental exercise. Of course we'll build bigger, better, more expensive. Everybody benefits from it, right? Let us all drive sports cars, reach a destination as fast as possible so we can rush to the next one and damn the scenery. Just don't forget to take a selfie when you get there!

      Well, that is sorta the point Sabine has made about the proposed FCC: as you imply, it has not won her a lot of friends among "Big Science" academic physicists.

      If you want to read an analysis of Big Science by an early critic, check out Leo Szilard's satiric short story, "The Mark Gable Foundation."

      I fear he was prophetic.

      Dave

      Delete
    2. One of the odd things is that the modern world is much richer than the world of Einstein or Darwin and so it should be more possible for there to be "gentlemen scientists" today than back then. But it does not seem to happen often.

      I don't know. There are many such people who are often guest scientists at an institute, or have an adjunct position but no other position, or whatever. They usually don't advertise the fact widely, but neither do they hide it. Sometimes, there are "code words" for such positions, such as "senior research associate". Keep in mind, though, that the same expression might imply a salaried position elsewhere. These days, an institutional affiliation is nice for access to journals and so on---not everything is available free of charge, and it is too expensive for most people to buy it themselves. But also for face-to-face contact. Back in the days of Darwin and Einstein, there wasn't that much literature, and it was all on paper, so one could have private subscriptions. Also, for people doing ground-breaking work like Darwin and Einstein, there was little need for face-to-face interaction.

      Also, there is more to know now. Not that long ago, one could know all that was known in a given field, enough to make original contributions, without being a full-time academic. That is hardly possible today. Many gentlemen scientists weren't so rich that they didn't have to earn money at all, but rich enough that they didn't have to spend all of their time earning money.

      Occasionally, one sees papers published with what are obviously private addresses as the institutional affiliation.

      Delete
  36. Sehr geehrte Frau Hossenfelder,
    Ihre Kolumnen in "Bild der Wissenschaft" haben meine Aufmerksamkeit geweckt und ich habe daraufhin Ihr Buch "Das hässliche Universum" mit Vergnügen gelesen. Mir gefällt die erfrischend skeptische Analyse der neuesten Forschungsergebnisse über die Quantenphysik. Ich bin kein Physiker und daher nicht interessiert an der Finanzierung von Forschungsprojekten oder der Zustimmung renommierter Fachleute. In meinem Beruf als Informationstechniker war ich aber auch viele Jahre mit physikalischen Phänomenen in der Hochfrequenztechnik und der Sende- und Empfangstechnik beschäftigt. Dadurch entwickelte sich eine Neugier auf physikalische Grundlagenforschung und ich habe entsprechende Bücher und Fachliteratur verschlungen. Das ist nur mein Hobby, und ich würde mich nicht in den Disput der Fachleute einmischen, aber je mehr ich über die Jahre gelesen habe, desto mehr Widersprüche und offene Fragen sind für mich entstanden. Ich hoffe, dass Sie mir etwas weiterhelfen können, da Sie mehr Gedankenfreiheit in der Diskussion einfordern. Ich hätte einige dumme Fragen, aber hier möchte ich gerne nur über das Thema Lichtgeschwindigkeit und Raumbeschaffenheit etwas mehr Klarheit bekommen. Ich würde mich sehr freuen, wenn Sie bereit wären, meine Gedanken darüber zur Kenntnis zu nehmen und meine Fragen zu beantworten.
    Mit freundlichen Grüßen Reimund
    P.S. Mit Ihrem Einverständnis würde ich diese Fragen kurzfristig in Ihren Blog senden.

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    1. Reimund:

      Danke für Ihr Interesse. Ich habe leider keine Zeit, um Fragen zu allgemeinen Themen der Physik auf meinem Blog zu beantworten. Ich kann Sie aber an einen Kollegen aus meinem "Talk to a Scientist" Programm weiter vermitteln (allerdings bieten wir diesen Service derzeit nur in Englisch an). Weiter Information finden Sie hier. MfG, Sabine

      Delete
  37. Is the measurement problem in quantum mechanics a bias, which is the product of the detector-hardware-program? That is, measurement itself is a bias.
    Thinking of Einstien in the picture: Let's say that acceleration got a body to possess the matter and mass that it possesses. That is, acceleration or through acceleration the body gained mass and matter--by gobbling up space-time. Forget gobbling up for the moment. So, this formation of matter becomes inertia, the inertia of acceleration. Inertia because it resists change and tends to continue in a state or a pattern. This inertia of acceleration is gravity.

    Looking at it from another point of view. We said that energy in a pattern is matter. We also said that matter is a record of this pattern of energy and that matter is a program. The programming of energy led to matter. A programming without the programmer. There was no programmer. Now, the inertia of this programming is gravity.

    We can also say that acceleration is programming matter. Initial velocity followed by acceleration, then resistance of the body to acceleration as inertia, followed by removing acceleration which results in a final velocity. This final velocity is the new inertia. That is the new state of the body's motion. This new state is the modified program. Hasn't acceleration led to the increase in mass of the body however negligible it may be together with length contraction and time dilation however negligible these may me? What I mean is matter has been programmed by acceleration, rather, acceleration is programming. And the inertia of acceleration or programming is gravity.

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    1. Gokul wrote:
      >Looking at it from another point of view. We said that energy in a pattern is matter. We also said that matter is a record of this pattern of energy and that matter is a program.

      With all due respect, who is this "we" who "said" these things?

      What you have written is what is commonly called "word salad," English words fit together in a grammatical way but without any actual meaning.

      Of course, maybe your posts are merely sly satire......

      Delete
    2. No, No Sirs, this is not sly satire. There are no hidden or double meanings. There are no allusions or cynicism. I am only an elementary mathematics student.

      Its like this Sirs: you Sirs come along and ask me Gokul now tell us what is 2/1; 2/(1/2); 2/6; 2/(1/4). After racking my brains I say Sirs the answers are 2; 4; 0.33; 8. I give four answers for 4 question--again sirs there is no double or hidden meaning trust me. You sirs tell me there are no four things 2; 4; 0.33; 8, rather they are all the same thing. Then you Sirs explain to me that, Gokul my boy, when we introduce the denominator or reference or frame of reference the same thing looks like four different things because of four different denominators. Gokul my boy, remove the denominator, that is, replace the denominator by 0, then what happens? Removing the denominator or reference or frame of reference or observer or replacing the denominator by 0 means that you cannot define the thing. Which means the thing is an abstraction that comes into being when we introduce a denominator. It is the denominator or reference or frame of reference or observer that abstracts. The thing: it is what it is because of the denominator or reference or frame of reference or observer. So there is only one thing that appears as different things with respect to different frames of reference or observers or denominators. Gokul my boy just go away.

      Delete
    3. Gokul wrote to me:
      >I am only an elementary mathematics student.

      Gokul, if you are really under college age (under age 18( and interested in learning more about physics, I and other people here will give you some suggestions. I can only tell you that the approach you are taking is not productive.

      Gokul also wrote:
      > It is the denominator or reference or frame of reference or observer that abstracts. The thing: it is what it is because of the denominator or reference or frame of reference or observer.

      To the degree that this makes any sense at all, it is not true.

      If you would like some advice, part of your problem is that you are too focused on the meaning of "abstraction" and other words and too little focused on solid math and on what we actually know about the real physical world.

      I realize that, prior to the rise of modern science, this game of "what do words really mean" was often viewed as the highest intellectual endeavor. It worked out badly, and that is not how science proceeds.

      Gokul also wrote:
      >Gokul my boy just go away.

      Nah, Sabine is pretty tolerant, she runs the place, and I doubt she will tell you to go away.

      But if you have any desire to actually learn about science, you are going to have try out a different way of thinking.

      Sort of like different skills are needed for soccer than for the high jump.

      Dave

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    4. Sir, I am not under 18; I am a middle aged bloke. I graduated in Physics, but am passionate about elementary mathematics. And I don't know why you mentioned high jump; I am an athlete, and stood third in "HIGH JUMP" in inter school sports in my district and North zonal first way back in the late 1980s and early 1990's. Your mentioning high jump is it an uncanny coincidence or is there something going on?

      Delete
  38. We spoke of inertia of acceleration or inertia of programming or inertia of a program in my previous comment. Likewise, can we speak of the forces in the Standard Model? I am only wondering aloud.

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  39. Steven Evans,
    I suppose that like you I am an atheist. However, I am not certain that i would still be an atheist if I were in an ICU on a ventilator. Its the contingency of life that keeps certainty at a distance.

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    Replies
    1. Steve Bullfox 6:18 PM, April 02, 2020

      You sound like a bit of a fair-weather atheist. "Atheist" is a redundant term anyway - "sane" will suffice.

      "Its the contingency of life that keeps certainty at a distance."

      Are you sure about that? You need to read Dr. H's theory of superdeterminism.

      Keep safe during the pandemic! We don't want you turning into a religious looney.


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  40. Steve E.,
    I am far from being a religious looney. I am not a fan of religion on both scientific and moral grounds. But I know people in seriously reduced circumstances whose main strength in crisis is religion. So if they want to be a religious looney, if it gets then through the day, I am ok with that.

    In the meantime, stay healthy.

    ReplyDelete

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