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There's something distinctly unsatisfying about this sort of paper, because the number of potential solutions to the problem they're trying to solve is in princ

There's something distinctly unsatisfying about this sort of paper, because the number of potential solutions to the problem they're trying to solve is in principle vast, and you can arrive at any number of them if you laboriously work backwards and fit your equations to the data. Without very rigorous efforts towards empirical validation, in novel ways if required, this sort of thing is just another wholly speculative theory to add to the large and growing pile. The interesting thing, as far as I'm concerned, is the size and shape of the answer space. How many theoretical solutions can be coaxed to fit the cosmological data? It can't be infinite, but it seems as though it's a rather large number.

szundi 3y ago
This is exactly what Sabine Hossenfelder is talking about for years now.
- naasking 3y ago
  Indeed, and even she thinks this is at least a fairly novel approach in this space which hasn't seen much new thinking recently (20+ years).
hnaccount_rng 3y ago
To be fair, everything that astrophysics comes up with will be massively under constrained. For all intents and purposes we work with a single datapoint and try to infer dynamics.
- Nevermark 3y ago
  Exactly. A few "data points", i.e. unexplained effects, and then Occamm's razor, parsimony, etc. I really like the parsimony of this paper. If a very small detail of space-time, i.e. stochastic behavior at the Planck scale, results in an emergent effect that explains something on the cosmological scale, that is explaining a lot with a little. Stochastic might not even mean random or non-deterministic (as I understand - and as the paper suggests, i.e. non-quantum), it could just be chaotic. Which would be very parsimonious. So many seemingly different effects we observe are the result of very simple things, under stochastic, statistical, entropy, thermodynamic type situations.
sebzim4500 3y ago
I'm far from an expert, and I'm still struggling my way through this paper, but from what I can see they are only intruducing one new free parameter, the same number as lambda CDM.
eigenket 3y ago
I agree with your point in general, but in this case specifically I strongly disagree. The idea worked out by Oppenheim and his colleagues/students is a fairly concrete theory which aims to marry quantum mechanics and general relativity. They're working on a bunch of approaches to turn their model into testable predictions in different regimes. They have a bunch of different papers with different ways their model could be falsified. None of them are at the level where you could falsify their model with current technology but they're seriously working on the theory required to make their ideas potentially testable. I went to a talk a couple of years ago at a conference by Oppenheim and he is very clear that what they're looking for is to make concrete predictions which can be tested. Edit: you can see here for another paper where they try to push their theory towards producing some testable predictions https://arxiv.org/abs/2203.01982 https://arxiv.org/abs/2203.01982
BlueTemplar 3y ago
Correct me if I am missing something, but it seems like the speculative bit was Milgrom noticing that coincidence in 1983, and now they are trying to explore the consequences of assuming that it's not just a coincidence... hopefully with testable predictions coming out of this ? How else should they go about it ?
- zikzak 3y ago
  I forget who said it but asking "hm, what's causing this anomaly in my experimental results" is how science progresses.
  - webmaven 3y ago
    ISTR someone saying that the most common words spoken prior to a breakthrough aren't "Eureka!" or "Aha!" but instead "That's strange..."
    - mkl 3y ago
      Often atrributed to Asimov, but it doesn't seem to have been him: https://quoteinvestigator.com/2015/03/02/eureka-funny/?amp=1 https://quoteinvestigator.com/2015/03/02/eureka-funny/?amp=1
    - devmor 3y ago
      Coincidentally (or not) those also seem to be the words spoken during computer programming right before you figure out something you never understood before.
keepamovin 3y ago
I think you're missing the point: you can say this about any theory. At least ones that attempt to deal with something significant and difficult. It's therefore not a very perceptive critique to make to say the problem with this specific theory is that it is one of many possible ones. It's more meaningful to compare such wide-aperture theories like this to their actual alternatives, rather than distrust them on principle because the space of potential hypotheses in which they carve out a specific model is so large. Funnily, your observation could be said to be an instance of itself: in that it is an overly general appraisal unrooted in pertinent specifics, therefore mostly divorced from explanatory power - akin to what you're misjudging this theory to be. I don't know if this theory will pan out, but it seems more interesting than you say. While different to the paper, I have the following related thoughts to offer: I've often thought gravity makes sense, not as a fundamental force, but as an emergent metric, rooted in randomness (perhaps the informational content of matter, for which mass is, normally but not always, useful proxy?), similar to how temperature is merely an emergent property that we can measure that arises from (and reflects) the microstates/ensembles of gigantic numbers of particle interactions, owing to their energy content. I wonder if a "time" or "age" factor could be needed in revised calculations of gravity to account for the plausible way in which information increases over time (if we assume, without trying to understand, that the history is recorded somewhere, somehow), and if that's why these very old and very distant galaxies bork our normal (non dark matter fudged) calculations of gravity, because they are so old that the time accrual of information is an effect which begins to come into play.
- A_D_E_P_T 3y ago
  > I think you're missing the point: you can say this about any theory. At least ones that attempt to deal with something significant and difficult. Hardly. In fact, just the opposite is true: You can say it about virtually no theories outside a niche within modern physics. The great theories of 20th century physics were empirically validated almost immediately. Even their thought experiments were subjected to intense scrutiny and debate. Now those theories are fodder for engineers who tinker with material devices like MRI machines. In other disciplines, e.g. biology or chemistry, it's effectively forbidden to work backwards from data and come up with a "solution" that fits but can't be validated in any way. Chemical space is vast; if you have a complex molecule, there are any number of ways retrosynthesis will work; finding one such way, without empirically validating it, is of near-zero value. > I've often thought gravity makes sense, not as a fundamental force, but as an emergent metric, rooted in randomness (perhaps the informational content of matter, for which mass is, normally but not always, useful proxy?) The randomness of what now? How do you reconcile this with the frame-dragging effect? Namely, in that it shows that the distribution and movement of mass (not just the presence of mass/entropy) can influence the curvature of spacetime and thereby gravitational effects. > I wonder if a "time" or "age" factor could be needed in revised calculations of gravity to account for the plausible way in which information increases over time Information is degraded over time; the universe will eventually contain zero useful information content ("heat death") and will then be modellable as a homogeneous space subject to statistical fluctuation.

szundi 3y ago

This is exactly what Sabine Hossenfelder is talking about for years now.

naasking 3y ago
Indeed, and even she thinks this is at least a fairly novel approach in this space which hasn't seen much new thinking recently (20+ years).

hnaccount_rng 3y ago

To be fair, everything that astrophysics comes up with will be massively under constrained. For all intents and purposes we work with a single datapoint and try to infer dynamics.

Nevermark 3y ago
Exactly. A few "data points", i.e. unexplained effects, and then Occamm's razor, parsimony, etc. I really like the parsimony of this paper. If a very small detail of space-time, i.e. stochastic behavior at the Planck scale, results in an emergent effect that explains something on the cosmological scale, that is explaining a lot with a little. Stochastic might not even mean random or non-deterministic (as I understand - and as the paper suggests, i.e. non-quantum), it could just be chaotic. Which would be very parsimonious. So many seemingly different effects we observe are the result of very simple things, under stochastic, statistical, entropy, thermodynamic type situations.

sebzim4500 3y ago

I'm far from an expert, and I'm still struggling my way through this paper, but from what I can see they are only intruducing one new free parameter, the same number as lambda CDM.

eigenket 3y ago

I agree with your point in general, but in this case specifically I strongly disagree. The idea worked out by Oppenheim and his colleagues/students is a fairly concrete theory which aims to marry quantum mechanics and general relativity. They're working on a bunch of approaches to turn their model into testable predictions in different regimes. They have a bunch of different papers with different ways their model could be falsified. None of them are at the level where you could falsify their model with current technology but they're seriously working on the theory required to make their ideas potentially testable. I went to a talk a couple of years ago at a conference by Oppenheim and he is very clear that what they're looking for is to make concrete predictions which can be tested. Edit: you can see here for another paper where they try to push their theory towards producing some testable predictions https://arxiv.org/abs/2203.01982 https://arxiv.org/abs/2203.01982

BlueTemplar 3y ago

Correct me if I am missing something, but it seems like the speculative bit was Milgrom noticing that coincidence in 1983, and now they are trying to explore the consequences of assuming that it's not just a coincidence... hopefully with testable predictions coming out of this ? How else should they go about it ?

zikzak 3y ago
I forget who said it but asking "hm, what's causing this anomaly in my experimental results" is how science progresses.
- webmaven 3y ago
  ISTR someone saying that the most common words spoken prior to a breakthrough aren't "Eureka!" or "Aha!" but instead "That's strange..."
  - mkl 3y ago
    Often atrributed to Asimov, but it doesn't seem to have been him: https://quoteinvestigator.com/2015/03/02/eureka-funny/?amp=1 https://quoteinvestigator.com/2015/03/02/eureka-funny/?amp=1
  - devmor 3y ago
    Coincidentally (or not) those also seem to be the words spoken during computer programming right before you figure out something you never understood before.

keepamovin 3y ago

I think you're missing the point: you can say this about any theory. At least ones that attempt to deal with something significant and difficult. It's therefore not a very perceptive critique to make to say the problem with this specific theory is that it is one of many possible ones. It's more meaningful to compare such wide-aperture theories like this to their actual alternatives, rather than distrust them on principle because the space of potential hypotheses in which they carve out a specific model is so large. Funnily, your observation could be said to be an instance of itself: in that it is an overly general appraisal unrooted in pertinent specifics, therefore mostly divorced from explanatory power - akin to what you're misjudging this theory to be. I don't know if this theory will pan out, but it seems more interesting than you say. While different to the paper, I have the following related thoughts to offer: I've often thought gravity makes sense, not as a fundamental force, but as an emergent metric, rooted in randomness (perhaps the informational content of matter, for which mass is, normally but not always, useful proxy?), similar to how temperature is merely an emergent property that we can measure that arises from (and reflects) the microstates/ensembles of gigantic numbers of particle interactions, owing to their energy content. I wonder if a "time" or "age" factor could be needed in revised calculations of gravity to account for the plausible way in which information increases over time (if we assume, without trying to understand, that the history is recorded somewhere, somehow), and if that's why these very old and very distant galaxies bork our normal (non dark matter fudged) calculations of gravity, because they are so old that the time accrual of information is an effect which begins to come into play.

A_D_E_P_T 3y ago
> I think you're missing the point: you can say this about any theory. At least ones that attempt to deal with something significant and difficult. Hardly. In fact, just the opposite is true: You can say it about virtually no theories outside a niche within modern physics. The great theories of 20th century physics were empirically validated almost immediately. Even their thought experiments were subjected to intense scrutiny and debate. Now those theories are fodder for engineers who tinker with material devices like MRI machines. In other disciplines, e.g. biology or chemistry, it's effectively forbidden to work backwards from data and come up with a "solution" that fits but can't be validated in any way. Chemical space is vast; if you have a complex molecule, there are any number of ways retrosynthesis will work; finding one such way, without empirically validating it, is of near-zero value. > I've often thought gravity makes sense, not as a fundamental force, but as an emergent metric, rooted in randomness (perhaps the informational content of matter, for which mass is, normally but not always, useful proxy?) The randomness of what now? How do you reconcile this with the frame-dragging effect? Namely, in that it shows that the distribution and movement of mass (not just the presence of mass/entropy) can influence the curvature of spacetime and thereby gravitational effects. > I wonder if a "time" or "age" factor could be needed in revised calculations of gravity to account for the plausible way in which information increases over time Information is degraded over time; the universe will eventually contain zero useful information content ("heat death") and will then be modellable as a homogeneous space subject to statistical fluctuation.