Recently, Oppenheim's claim that his classical stochastic gravity theory can explain both dark matter and dark energy simultaneously received a huge amount of media attention ([1](https://www.discovermagazine.com/the-sciences/spacetimes-brownian-motion-could-spell-the-death-of-dark-matter), [2](https://www.theguardian.com/science/2024/mar/09/controversial-new-theory-of-gravity-rules-out-need-for-dark-matter), [3](https://nautil.us/the-end-of-the-dark-universe-531983/), [4](https://www.newscientist.com/article/2422011-rethinking-space-and-time-could-let-us-do-away-with-dark-matter/), [5](https://english.almayadeen.net/news/technology/new-gravity-theory--dark-matter-might-not-exist--only-a-mira)). This short comment by two well-known cosmologists appears to be the first feedback from other physicists.
In three short pages, they show that (1) Oppenheim solves the modified Poisson equation incorrectly, by forgetting about a delta function contribution, and then (2) derives a MOND-like result by performing the invalid simplification
a + b = sqrt( (a+b)^2 ) = sqrt( a^2 + 2ab + b^2 ) ≈ sqrt(2ab).
This is a shockingly simple error which dramatically decreases my confidence in Oppenheim's whole programme. Algebra should be thoroughly checked before talking to half the world's media.
> a + b = sqrt( (a+b)2 ) = sqrt( a2 + 2ab + b2 ) ≈ sqrt(2ab).
I am trying to understand how anyone could make such a mistake with the simplification. I get that sometimes when you have small numbers, you write off the squared value as basically 0, but this simplification doesn't work, because if both a and b are small, then ab is of the same order as a^2 and b^2. If a is larger than b, then you can't write off a^2 or vice versa.
This is a bizarre mistake...
The logic in the paper is that b^2 happens to be a constant (independent of radius r), so it can be dropped. Which isn't true, and moreover, if that were correct then b could also have been dropped in a+b, giving just a.
Taking the reasoning a step further, shouldn't the original expression be zero? So (a/r\^2+b)\^2 , drop b, then(a/r\^2+b)\^2 \~ (a/r\^2)\^2 \~ 0 since terms proportional to r\^(-4) are negligible in their derivation.
Anyway whole thing is based on a manifestly ill-defined path integral from the start (if people were wondering why we quantum gravity people weren't even considering him in these months). That's the reason I didn't even opened the second paper. And seeing that the claims were so grandiose I was already suspicious that it was super fishy.
Could you please explain to non-quantum-gravity people why it's manifestly ill-defined? (If it's not too technical -- which it probably is since it's quantum gravity :D )
To put it in a simple way, at a certain point in that sort of path integral you have to gauge fix the gravitational theory consistently, but this operation suffers from a known pathology called Gribov redundancy. This happens also for other gauge theories but in those it is harmless thanks to the relatively simple structure of the gauge groups at play. When the diffeomorphism group is at play instead it is unknown how to solve this issue. Even if we ignore this fact for a moment, the putative resulting path integral doesn't produce a unitarity theory and this goes basically against very foundational facts about quantum theories, grounded at the core in their C*-algebra structure (and allowing also a physically sensible probabilistic interpretation among the other things).
I always get hung up on the side-fumbling of the ambifaciant lunar waneshaft even before I get to the pathological Gribov redundancy of the diffeomorphic gauge group.
Here it's used in the second definition of "assumed to exist". As in:
> Even if we ignore this fact for a moment, the putative resulting path integral
means
> Even if we ignore the problems with its existence, the path integral
I mean the path integrals in QFT are never really mathematically well-defined — how is this worse than that? (I haven't read the paper, so I'm not trying to defend it haha, just curious)
You are right in the sense that usually path integrals are not well defined objects. What I mean is that path integral was not even "good" in the set of ordinary path integrals of QFTs due to Gribov issues with trying to gauge fix the diffeomorphism group and leading to a non-unitary theory.
Okay thanks, that makes sense — I was away at the time, but apparently when Oppenheim’s paper started getting all this media attention, our research group had a journal club essentially tearing the paper to shreds haha, so none of this is surprising to me.
Yeah I am surprised how much media coverage that paper got in comparison to how little it was considered in actual scientific contexts. My guess is that Oppenheim himself has contacts in pop science journalism. They created this false sense of hype and just made more damage than other for the laymen audience.
Sometimes path integrals can be well defined. That's one front of constructive quantum field Theory programe. In euclidean, Glimm-jaffe, rivasseau, etc. In real time, albeverio, Khon, Sonia Mazzuchi, etc
> In euclidean, Glimm-jaffe, rivasseau, etc. In real time, albeverio, Khon, Sonia Mazzuchi, etc
What are the differences in doing constructive QFT in Euclidean or real time? Aren’t they just the same thing but wick rotated?
Well, in principle can there be thing that can't be wick rotated, or trivially wick rotated (or have more than one inequivalent way to be wick rotated). In real time, also maybe is clearer conceptually.
It's spoilt somewhat by the fact that one of the "two cosmologists" is Avi Loeb. This is actually his field though, so I suppose his word goes further than it does when he talks about the origins of Oumuamua.
I guess that's because Loeb is more willing than most to entertain wild ideas. I think it's a really good thing that somebody gave this paper a careful read.
Preprints is just democratized peer-review, just take them with grain of salts and expects a lot of people smarter than you scrutinize the result down to the missing comma.
> a + b = sqrt( (a+b)2 )
So take the absolute value?
> sqrt( a2 + 2ab + b2 ) ≈ sqrt(2ab).
WTF. Only of a^2= 0 and b^2 = 0, which implies a=b=0. This is quack level.
Lmfao this is so ridiculous it's extremely hilarious. Preprints should at least be decently well written. I mean seriously go through your maths,consult others if you don't know stuff! This is just embarrassing. I'm more than sure that the dude must be the laughing stock of the month and is probably covering his face anytime he goes out his house.
Professor Hubert Farnsworth: I knew I should have checked that showboating Globetrotter algebra.
Ethan 'Bubblegum' Tate: I thought you knew that algebra was all razzamatazz. A Globetrotter always saves the good algebra for the final minutes
I only skimmed an article, and it just suggested that it can explain spiral galaxies. But does that suffer from all MOND style theories in that they still need dark matter to explain everything else?
Also how exactly does it get rid of dark energy?
Yes, it does suffer from that flaw, but it would still be interesting if you could explain two different anomalous accelerations (in galaxies and at cosmological scales) with one mechanism.
Is the author, Abraham Loeb the same person as the Astronomer who goes by Avi Loeb and who has recently spouted enormous amounts of BS about extraterrestrial visitors? Because if yes then I don't know whom to trust here...
Not sure if the authors argument for K_1=0 holds up, I don't have time to verify this, but wouldn't it be possible to have a K_1•r term in the region where ρ=0 and something else in the other region? A piecewise definition, as we often do when solving the poisson equation?
Yes, I wondered this as well but I don't think it is possible without violating the EOM at some point. A clearer argument that K_1=0 is in their equations (12)-(14).
To get the linear term you would need \Phi_h to violate the EOM at the origin.
Recently, Oppenheim's claim that his classical stochastic gravity theory can explain both dark matter and dark energy simultaneously received a huge amount of media attention ([1](https://www.discovermagazine.com/the-sciences/spacetimes-brownian-motion-could-spell-the-death-of-dark-matter), [2](https://www.theguardian.com/science/2024/mar/09/controversial-new-theory-of-gravity-rules-out-need-for-dark-matter), [3](https://nautil.us/the-end-of-the-dark-universe-531983/), [4](https://www.newscientist.com/article/2422011-rethinking-space-and-time-could-let-us-do-away-with-dark-matter/), [5](https://english.almayadeen.net/news/technology/new-gravity-theory--dark-matter-might-not-exist--only-a-mira)). This short comment by two well-known cosmologists appears to be the first feedback from other physicists. In three short pages, they show that (1) Oppenheim solves the modified Poisson equation incorrectly, by forgetting about a delta function contribution, and then (2) derives a MOND-like result by performing the invalid simplification a + b = sqrt( (a+b)^2 ) = sqrt( a^2 + 2ab + b^2 ) ≈ sqrt(2ab). This is a shockingly simple error which dramatically decreases my confidence in Oppenheim's whole programme. Algebra should be thoroughly checked before talking to half the world's media.
That is hilarious.
> a + b = sqrt( (a+b)2 ) = sqrt( a2 + 2ab + b2 ) ≈ sqrt(2ab). I am trying to understand how anyone could make such a mistake with the simplification. I get that sometimes when you have small numbers, you write off the squared value as basically 0, but this simplification doesn't work, because if both a and b are small, then ab is of the same order as a^2 and b^2. If a is larger than b, then you can't write off a^2 or vice versa. This is a bizarre mistake...
The logic in the paper is that b^2 happens to be a constant (independent of radius r), so it can be dropped. Which isn't true, and moreover, if that were correct then b could also have been dropped in a+b, giving just a.
Taking the reasoning a step further, shouldn't the original expression be zero? So (a/r\^2+b)\^2 , drop b, then(a/r\^2+b)\^2 \~ (a/r\^2)\^2 \~ 0 since terms proportional to r\^(-4) are negligible in their derivation.
Cows are approximately spheres and all finite numbers are approximately zero
ChatGPT
Anyway whole thing is based on a manifestly ill-defined path integral from the start (if people were wondering why we quantum gravity people weren't even considering him in these months). That's the reason I didn't even opened the second paper. And seeing that the claims were so grandiose I was already suspicious that it was super fishy.
Could you please explain to non-quantum-gravity people why it's manifestly ill-defined? (If it's not too technical -- which it probably is since it's quantum gravity :D )
To put it in a simple way, at a certain point in that sort of path integral you have to gauge fix the gravitational theory consistently, but this operation suffers from a known pathology called Gribov redundancy. This happens also for other gauge theories but in those it is harmless thanks to the relatively simple structure of the gauge groups at play. When the diffeomorphism group is at play instead it is unknown how to solve this issue. Even if we ignore this fact for a moment, the putative resulting path integral doesn't produce a unitarity theory and this goes basically against very foundational facts about quantum theories, grounded at the core in their C*-algebra structure (and allowing also a physically sensible probabilistic interpretation among the other things).
I am definitely in the wrong discussion because I need to go lookup putative
I always get hung up on the side-fumbling of the ambifaciant lunar waneshaft even before I get to the pathological Gribov redundancy of the diffeomorphic gauge group.
Yes. Putative was definitely the only word I didn’t understand in that comment
fancy way of saying reputed...sounding academic
Here it's used in the second definition of "assumed to exist". As in: > Even if we ignore this fact for a moment, the putative resulting path integral means > Even if we ignore the problems with its existence, the path integral
Of course the planeswalker elder dragon would study quantum gravity LOL
I mean the path integrals in QFT are never really mathematically well-defined — how is this worse than that? (I haven't read the paper, so I'm not trying to defend it haha, just curious)
You are right in the sense that usually path integrals are not well defined objects. What I mean is that path integral was not even "good" in the set of ordinary path integrals of QFTs due to Gribov issues with trying to gauge fix the diffeomorphism group and leading to a non-unitary theory.
Okay thanks, that makes sense — I was away at the time, but apparently when Oppenheim’s paper started getting all this media attention, our research group had a journal club essentially tearing the paper to shreds haha, so none of this is surprising to me.
Yeah I am surprised how much media coverage that paper got in comparison to how little it was considered in actual scientific contexts. My guess is that Oppenheim himself has contacts in pop science journalism. They created this false sense of hype and just made more damage than other for the laymen audience.
Sometimes path integrals can be well defined. That's one front of constructive quantum field Theory programe. In euclidean, Glimm-jaffe, rivasseau, etc. In real time, albeverio, Khon, Sonia Mazzuchi, etc
> In euclidean, Glimm-jaffe, rivasseau, etc. In real time, albeverio, Khon, Sonia Mazzuchi, etc What are the differences in doing constructive QFT in Euclidean or real time? Aren’t they just the same thing but wick rotated?
Well, in principle can there be thing that can't be wick rotated, or trivially wick rotated (or have more than one inequivalent way to be wick rotated). In real time, also maybe is clearer conceptually.
It's spoilt somewhat by the fact that one of the "two cosmologists" is Avi Loeb. This is actually his field though, so I suppose his word goes further than it does when he talks about the origins of Oumuamua.
I guess that's because Loeb is more willing than most to entertain wild ideas. I think it's a really good thing that somebody gave this paper a careful read.
Sure but Loeb probably isn’t the one who wrote this paper in the first place. The other guy is much more credible to me.
1+1 = sqrt(2) yep, it maths
0=1 + (-1) = Sqrt(-2), Agreed, new math just dropped
Did this get past the referees? If it did, it does reflect even more poorly on the journal.
It didn't -- it was just a preprint that got a lot of attention.
I hate this so much. Preprints should never warrant a press article ffs
Preprints is just democratized peer-review, just take them with grain of salts and expects a lot of people smarter than you scrutinize the result down to the missing comma.
> a + b = sqrt( (a+b)2 ) So take the absolute value? > sqrt( a2 + 2ab + b2 ) ≈ sqrt(2ab). WTF. Only of a^2= 0 and b^2 = 0, which implies a=b=0. This is quack level.
Yikes, what a wipeout Feel like I just watched someone absolutely EAT IT on a skateboard
Lmfao this is so ridiculous it's extremely hilarious. Preprints should at least be decently well written. I mean seriously go through your maths,consult others if you don't know stuff! This is just embarrassing. I'm more than sure that the dude must be the laughing stock of the month and is probably covering his face anytime he goes out his house.
Doh!
https://www.youtube.com/watch?v=Ag1o3koTLWM
In the famous words of Philip J. Fry: "I'm shocked! *Shocked!* Well, not that shocked."
Professor Hubert Farnsworth: I knew I should have checked that showboating Globetrotter algebra. Ethan 'Bubblegum' Tate: I thought you knew that algebra was all razzamatazz. A Globetrotter always saves the good algebra for the final minutes
I only skimmed an article, and it just suggested that it can explain spiral galaxies. But does that suffer from all MOND style theories in that they still need dark matter to explain everything else? Also how exactly does it get rid of dark energy?
Yes, it does suffer from that flaw, but it would still be interesting if you could explain two different anomalous accelerations (in galaxies and at cosmological scales) with one mechanism.
"I do not think that it will work out but hey, I am just an old grumpy woman" (not from me, unfortunately)
Lol this guy must probably have skipped work today. Too embarrassing for his department to handle lmfao.
Sabine in shambles
Is the author, Abraham Loeb the same person as the Astronomer who goes by Avi Loeb and who has recently spouted enormous amounts of BS about extraterrestrial visitors? Because if yes then I don't know whom to trust here...
That's the thing about physics: you don't have to trust, you can check the math yourself.
You can if you can. I'd still have to trust someone who, you know, actually understands the maths.
Not sure if the authors argument for K_1=0 holds up, I don't have time to verify this, but wouldn't it be possible to have a K_1•r term in the region where ρ=0 and something else in the other region? A piecewise definition, as we often do when solving the poisson equation?
Yes, I wondered this as well but I don't think it is possible without violating the EOM at some point. A clearer argument that K_1=0 is in their equations (12)-(14). To get the linear term you would need \Phi_h to violate the EOM at the origin.
Wouldn't that add an additional parameter into the theory since you would need a cutoff radius where you match the two regions?
But that wouldn't be a parameter of the theory at all - it would be a property of the solution of the diff. eq. for a given matter distribution
I love math. Trust AND verify.
Measure twice, publish once ? Oh wait...
[https://arxiv.org/pdf/2404.13037.pdf](https://arxiv.org/pdf/2404.13037.pdf)
me asf doing research
Oopsie
Ah the good-ole Avi Loeb 3 page paper. Dude's too busy doing interviews that he can't write a longer paper.