4 ms·

This would be an incredible result and probably the biggest experimental physics discovery in decades (bigger than gravitational waves and the Higgs). But MOND

This would be an incredible result and probably the biggest experimental physics discovery in decades (bigger than gravitational waves and the Higgs). But MOND has so many problems on so many levels and some of the people who promote it in the scientific community are borderline crackpots. So I'd treat this veeeeery carefully until confirmed by independent groups and measurements. For the moment, this is like the room-temp superconductor: Revolutionary if true, but I'd still bet on poorly executed measurements in combination with unknown errors as the real explanation.

topspin 3y ago
> But MOND has so many problems The fact that the results happen to fit some MOND model(s), while interesting, doesn't really mean much: these results could be 100% correct and all of MOND a pipe dream at the same time. The crucial question is, is the analysis correct?
- sigmoid10 3y ago
  If the results are correct, it means that extreme weak field gravity laws are actually in need of modification. I'd be very surprised if any existing variant of MOND got it right, but it would still mean that the premise of MOND is correct, which would be a huge deal.
  - V1ndaar 3y ago
    > premise of MOND is correct Well, typically the term MOND refers to very specific modifications of Newtonian gravity and doesn't even take into account GR. So I'm not sure I would agree with the statement in general terms (note, I haven't read the paper so far, so I don't know what they claim). There's _plenty_ of extensions of GR though that modify gravity. That in itself isn't really that surprising. Scalar-Tensor theory and the like. And there's a reason these are usually not called MOND. Some go by "MOG" for modified gravity.
    - sigmoid10 3y ago
      The paper actually mentions a specific form of MOND called AQUAL [1]. The original version of MOND was a very specific, simple modification of Newton's laws, but over the decades it has become more of a synonym for all attempts at modifying gravity at long distances. Especially since all of these attempts modify the weak field regime, which is equivalent to modifying Newton's law of gravity. [1] https://en.m.wikipedia.org/wiki/AQUAL https://en.m.wikipedia.org/wiki/AQUAL
    - AnimalMuppet 3y ago
      This particular proposed modification is for very weak accelerations. That's where Newtonian gravity is least corrected by GR.
  - naasking 3y ago
    > I'd be very surprised if any existing variant of MOND got it right I'm not sure why this would be surprising, MOND has made many more successful predictions than DM.
    - sigmoid10 3y ago
      That is simply not true. Like, it's literally the opposite of the truth.
      - naasking 3y ago
        Don't confuse post-hoc curve fitting with predictions: From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity, https://arxiv.org/abs/2110.06936 https://arxiv.org/abs/2110.06936
        sigmoid10 3y ago
        You should read up on how DM is fitted vs how MOND is fitted. But neither preceded the data in the way you imply and DM is vastly more successful at predicting all observations with a single fit.
        naasking 3y ago
        What I know is that MOND predicted the high redshift galaxies we're now seeing 20 years ago, and DM did not: https://tritonstation.com/2022/01/03/what-jwst-will-see/ https://tritonstation.com/2022/01/03/what-jwst-will-see/ There are many instances like this as outlined in the paper I linked.
- MattPalmer1086 3y ago
  But if the analysis is correct, it does mean that general relativity will need to be different to the current formulation and that dark matter is unlikely to be the (entire) explanation for observed galactic rotations.
  - naasking 3y ago
    No, some form of dark matter could have interactions that produce MOND dynamics in the correct regime. This is compatible with GR. For instance, various superfluid dark matter proposals that are being researched.
    - MattPalmer1086 3y ago
      My understanding is that dark matter cannot explain this motion in wide binaries, which is why these are interesting observations.
      - naasking 3y ago
        Dark matter is not one theory, but a class of theories. The point of superfluid dark matter proposals is that it reproduces MOND dynamics, therefore it would explain these observations.
        MattPalmer1086 3y ago
        The paper states: "First of all, the gravitational anomaly in the dynamics of binary stars cannot be attributed to dark matter because the required amount is absurd, and thus there is no way to save the standard theory of gravity."
        naasking 3y ago
        Which applies to classical dark matter theories, not ones that naturally reproduce MOND dynamics.
- taylodl 3y ago
  If these observations are confirmed, then Newton is wrong (which we already knew), GR is wrong, and MOND is wrong. I don't think the solution is going to be tweaking GR - it's going to be something radically different. This could be so big we might even uncover something causing us to re-think QFT and then put all the forces on equal footing. That would be huge, because where we are now we're stuck. We've been looking for hints for how to move forward, this could be it.
vfclists 3y ago
> some of the people who promote it in the scientific community are borderline crackpots Is the astronmer making this particular "claim" among the borderline crackpots? Why don't you check the claims yourself before making such a comment? You seem to be one of those people who are afraid that their cherished orthodox views may not hold, and so respond by bring up the crackpot angle.
- sigmoid10 3y ago
  It's always funny when people accuse physicists of cherishing old views and not wanting change, when in fact any real good physicist loves to see conflicting data, because this is the only way progress is made. In fact, we have been hoping for someone to show how gravity breaks for more than a century. I don't think anyone wants this to be false. But good physicists are also very careful and reserved about analyses like these, because they know how difficult they are and exactly how much can go wrong. It wouldn't be the first time that a trivial bug in some self written software causes a fantastic publication, only to get trashed when other people try to replicate it. And unfortunately there are also bad physicists who actually trim data, which made the good ones even more careful and reserved. And if the academic MOND literature is known for anything, it's trimming data. So yes, I would love for this to be true, but no, I will not believe it until there is independent confirmation.
hilbert42 3y ago
"So I'd treat this veeeeery carefully until confirmed by independent groups and measurements." So would I, and most would especially with the LK-99 incident fresh in our minds. I'm not an astrophysicist, so it would be stupid of me to discuss the specifics of MOND, so I'll just make a few observations from the perspective of a lay observer. First, I have no fixed position on the matter except to say that if MOND were determined as fact then it would only be so after possibly the most extensive verification process yet undertaken in science—and it would upend everything, and science would be in turmoil for years. That said, being an outsider, I have the luxury of having an opinion that if wrong won't wreck my career—no one would care, not even I. That preface was necessary because I come at physics from a slightly different perspective to many. Decades ago I spent much of my professional life trying to make electronic circuits, amplifiers etc., as linear and distortion free as possible and it's not an easy task. When one gets distortion figures down to -120dB and below even capacitor dialectics conspire against one by exhibiting nonlinear responses that contribute distortion. That experience instilled a distrust in me that made me question even the intrinsic nature of the physical constants, their stability over time, variation with energy levels etc. Sure, the transfer characteristics of the electronic circuits I was working with were way, way up the chain from any physics that could be responsible for variations in the physical constants—so far as to be irrelevant—and their properties were emergent anyway. What mattered was my perception of the physical world changed. Let me give you an example: take a large volume of space somewhere in the universe that's free of physical matter, over time dust and matter drifts in and a star forms and eventually dies and forms a black hole and after 10^xyz eons it evaporates and we are left with empty space again (all else being equal of course). Can we say for certain that that volume of space is absolutely identical to that before the dust drifted in? Specifically, is spacetime perfectly elastic and that the black hole left no distortion in its fabric—not even the most infinitesimal amount? Same goes for physical constants, are we certain the electric constant (vacuum permittivity), ε0, is immutable and has never changed (since the end of inflation anyway), if it has then so has c changed. Same goes for the cosmological constant and we still have the problem of the 'vacuum catastrophe' to contend with. Then there's alpha, α, the fine structure constant, we have its precision to nine or more digits, but there are still questions whether it varies over time and or by location, and its liable to vary with energy levels. If α changes so does the electric charge, e, and also does c. (Simply, it's unlikely every constant is immutable and perfectly linear/predictable over almost 'infinite' time and scale.) Now to the gravitational constant, we have its accuracy to only about five digits, some four orders of magnitude less than, say, c and α, which is a bit of a worry. Thus it seems to me there's potential wiggle room in those constants, and whilst it's unlikely MOND has substance, we shouldn't rule it out without further research.

topspin 3y ago

> But MOND has so many problems The fact that the results happen to fit some MOND model(s), while interesting, doesn't really mean much: these results could be 100% correct and all of MOND a pipe dream at the same time. The crucial question is, is the analysis correct?

sigmoid10 3y ago
If the results are correct, it means that extreme weak field gravity laws are actually in need of modification. I'd be very surprised if any existing variant of MOND got it right, but it would still mean that the premise of MOND is correct, which would be a huge deal.
- V1ndaar 3y ago
  > premise of MOND is correct Well, typically the term MOND refers to very specific modifications of Newtonian gravity and doesn't even take into account GR. So I'm not sure I would agree with the statement in general terms (note, I haven't read the paper so far, so I don't know what they claim). There's _plenty_ of extensions of GR though that modify gravity. That in itself isn't really that surprising. Scalar-Tensor theory and the like. And there's a reason these are usually not called MOND. Some go by "MOG" for modified gravity.
  - sigmoid10 3y ago
    The paper actually mentions a specific form of MOND called AQUAL [1]. The original version of MOND was a very specific, simple modification of Newton's laws, but over the decades it has become more of a synonym for all attempts at modifying gravity at long distances. Especially since all of these attempts modify the weak field regime, which is equivalent to modifying Newton's law of gravity. [1] https://en.m.wikipedia.org/wiki/AQUAL https://en.m.wikipedia.org/wiki/AQUAL
  - AnimalMuppet 3y ago
    This particular proposed modification is for very weak accelerations. That's where Newtonian gravity is least corrected by GR.
- naasking 3y ago
  > I'd be very surprised if any existing variant of MOND got it right I'm not sure why this would be surprising, MOND has made many more successful predictions than DM.
  - sigmoid10 3y ago
    That is simply not true. Like, it's literally the opposite of the truth.
    - naasking 3y ago
      Don't confuse post-hoc curve fitting with predictions: From galactic bars to the Hubble tension: weighing up the astrophysical evidence for Milgromian gravity, https://arxiv.org/abs/2110.06936 https://arxiv.org/abs/2110.06936
      - sigmoid10 3y ago
        You should read up on how DM is fitted vs how MOND is fitted. But neither preceded the data in the way you imply and DM is vastly more successful at predicting all observations with a single fit.
        naasking 3y ago
        What I know is that MOND predicted the high redshift galaxies we're now seeing 20 years ago, and DM did not: https://tritonstation.com/2022/01/03/what-jwst-will-see/ https://tritonstation.com/2022/01/03/what-jwst-will-see/ There are many instances like this as outlined in the paper I linked.
MattPalmer1086 3y ago
But if the analysis is correct, it does mean that general relativity will need to be different to the current formulation and that dark matter is unlikely to be the (entire) explanation for observed galactic rotations.
- naasking 3y ago
  No, some form of dark matter could have interactions that produce MOND dynamics in the correct regime. This is compatible with GR. For instance, various superfluid dark matter proposals that are being researched.
  - MattPalmer1086 3y ago
    My understanding is that dark matter cannot explain this motion in wide binaries, which is why these are interesting observations.
    - naasking 3y ago
      Dark matter is not one theory, but a class of theories. The point of superfluid dark matter proposals is that it reproduces MOND dynamics, therefore it would explain these observations.
      - MattPalmer1086 3y ago
        The paper states: "First of all, the gravitational anomaly in the dynamics of binary stars cannot be attributed to dark matter because the required amount is absurd, and thus there is no way to save the standard theory of gravity."
        naasking 3y ago
        Which applies to classical dark matter theories, not ones that naturally reproduce MOND dynamics.
taylodl 3y ago
If these observations are confirmed, then Newton is wrong (which we already knew), GR is wrong, and MOND is wrong. I don't think the solution is going to be tweaking GR - it's going to be something radically different. This could be so big we might even uncover something causing us to re-think QFT and then put all the forces on equal footing. That would be huge, because where we are now we're stuck. We've been looking for hints for how to move forward, this could be it.

vfclists 3y ago

> some of the people who promote it in the scientific community are borderline crackpots Is the astronmer making this particular "claim" among the borderline crackpots? Why don't you check the claims yourself before making such a comment? You seem to be one of those people who are afraid that their cherished orthodox views may not hold, and so respond by bring up the crackpot angle.

sigmoid10 3y ago
It's always funny when people accuse physicists of cherishing old views and not wanting change, when in fact any real good physicist loves to see conflicting data, because this is the only way progress is made. In fact, we have been hoping for someone to show how gravity breaks for more than a century. I don't think anyone wants this to be false. But good physicists are also very careful and reserved about analyses like these, because they know how difficult they are and exactly how much can go wrong. It wouldn't be the first time that a trivial bug in some self written software causes a fantastic publication, only to get trashed when other people try to replicate it. And unfortunately there are also bad physicists who actually trim data, which made the good ones even more careful and reserved. And if the academic MOND literature is known for anything, it's trimming data. So yes, I would love for this to be true, but no, I will not believe it until there is independent confirmation.

hilbert42 3y ago

"So I'd treat this veeeeery carefully until confirmed by independent groups and measurements." So would I, and most would especially with the LK-99 incident fresh in our minds. I'm not an astrophysicist, so it would be stupid of me to discuss the specifics of MOND, so I'll just make a few observations from the perspective of a lay observer. First, I have no fixed position on the matter except to say that if MOND were determined as fact then it would only be so after possibly the most extensive verification process yet undertaken in science—and it would upend everything, and science would be in turmoil for years. That said, being an outsider, I have the luxury of having an opinion that if wrong won't wreck my career—no one would care, not even I. That preface was necessary because I come at physics from a slightly different perspective to many. Decades ago I spent much of my professional life trying to make electronic circuits, amplifiers etc., as linear and distortion free as possible and it's not an easy task. When one gets distortion figures down to -120dB and below even capacitor dialectics conspire against one by exhibiting nonlinear responses that contribute distortion. That experience instilled a distrust in me that made me question even the intrinsic nature of the physical constants, their stability over time, variation with energy levels etc. Sure, the transfer characteristics of the electronic circuits I was working with were way, way up the chain from any physics that could be responsible for variations in the physical constants—so far as to be irrelevant—and their properties were emergent anyway. What mattered was my perception of the physical world changed. Let me give you an example: take a large volume of space somewhere in the universe that's free of physical matter, over time dust and matter drifts in and a star forms and eventually dies and forms a black hole and after 10^xyz eons it evaporates and we are left with empty space again (all else being equal of course). Can we say for certain that that volume of space is absolutely identical to that before the dust drifted in? Specifically, is spacetime perfectly elastic and that the black hole left no distortion in its fabric—not even the most infinitesimal amount? Same goes for physical constants, are we certain the electric constant (vacuum permittivity), ε0, is immutable and has never changed (since the end of inflation anyway), if it has then so has c changed. Same goes for the cosmological constant and we still have the problem of the 'vacuum catastrophe' to contend with. Then there's alpha, α, the fine structure constant, we have its precision to nine or more digits, but there are still questions whether it varies over time and or by location, and its liable to vary with energy levels. If α changes so does the electric charge, e, and also does c. (Simply, it's unlikely every constant is immutable and perfectly linear/predictable over almost 'infinite' time and scale.) Now to the gravitational constant, we have its accuracy to only about five digits, some four orders of magnitude less than, say, c and α, which is a bit of a worry. Thus it seems to me there's potential wiggle room in those constants, and whilst it's unlikely MOND has substance, we shouldn't rule it out without further research.