TheRealOneTwo t1_ixidoqv wrote
MOND is not only controversial, it is outright garbage that most astrophysicists reject.
jwwetzel t1_ixiibqe wrote
total garbage
DeusExHumanum t1_ixlex6g wrote
total garbage is dark matter playing hide and seek perfectly
jwwetzel t1_ixng82x wrote
also total garbage lol but there are many many many distinct observations/reasons that support the dark matter hypothesis.
nonotan t1_iximbi4 wrote
As a mere hobbyist, why is that? Leaving aside the merits of this particular study, MOND seems like a mildly-promising (if arguably inelegant) approach that still leaves a few unanswered questions (as does standard GR, I should add), and which has had various potential modalities already invalidated by empirical evidence (which may not sound promising, but it means 1) at least it's a falsifiable theory that makes testable predictions, and 2) current evidence isn't able to entirely rule it out, and hey, there's only a single reality that needs to be explained)
From my perspective, I see it in a similar position to supersymmetry in QFT: an a priori reasonable attempt at addressing the issues in the standard model they are motivated by, with a not-so-great track record that makes them ever superseding the standard model look fairly unlikely right now, but still not within "statistical impossibility" territory. Except supersymmetry doesn't seem to get anywhere near as much hate.
sticklebat t1_ixjp9hu wrote
I mostly agree with you. I am glad people are working on MOND, because you never know. But as it stands, anyone who swears by it is delusional.
I think supersymmetry gets less hate because it is not a replacement for an existing, extremely successful model, but rather a very simple extension to the standard model of particle physics, with the potential to fill in a lot of holes. Many MOND proponents argue that dark matter’s existence is a poorly motivated and unrealistic postulate, but frankly that notion is just ignorant. And I think that attitude also sours people toward MOND, by extension.
pete_68 t1_ixjwijj wrote
We always talk about how successful it is, but it's got some serious problems. Not a hint of dark matter to be found, so far. Just a gravity effect we can't account for. A universe with accelerating expansion from dark energy that we also can't detect. Matter/antimatter asymmetry, neutrino mass, and the strong CP problem.
Oh, and let's not forget the elephant in the universe: gravity.
Those are some mighty big holes.
sticklebat t1_ixkxzz4 wrote
>We always talk about how successful it is, but it's got some serious problems.
It is very successful, even in the face of its shortcomings. That's the nature of science: there are always unresolved problems to figure out. Our most successful scientific models will always be incomplete. And usually it's that: it's more common for our models to be incomplete than flat out wrong.
>Not a hint of dark matter to be found, so far. Just a gravity effect we can't account for.
The word "just" is doing a hell of a lot of lifting in that sentence. And it's not just an effect, but many. There is missing gravity in the velocity dispersions of galaxies. There is missing gravity in the rotation curves of galaxies (but not all galaxies!). There is missing gravity in galaxy clusters. There is missing gravity related to gravitational lensing (or perhaps a better way of putting it is that in some cases, seemingly empty space strongly distorts the trajectory of light). There is missing gravity associated with the power spectrum of the CMB. There is missing gravity in the formation of structures like galaxies. There is missing gravity compared to the observed curvature of the universe. There is missing gravity in the large scale acoustic oscillations of the universe. There is missing gravity associated with redshift distortions of galaxy clusters and voids.
No attempt to explain all of those things as simply a misunderstanding of gravity has been successful, despite many decades of trying. Some of those phenomena have never been explained by any models of modified gravity ever (like the Bullet Cluster lensing, anomalous rotation curves of galaxies, and the CMB power spectrum). No such model has ever even come close to explain all of them simultaneously. On the other hand, all of them are well-explained by the existence of a consistent amount of dark matter, organized in ways consistent with each other (e.g. the dark matter distributions needed to explain rotation curves are consistent with the distributions needed to explain lensing, etc.), without having to even try being creative. It basically just works out.
Finally, not having detected dark matter directly in a lab setting is not really a problem for the ΛCDM model. The whole point is that it's dark. It cannot interact electromagnetically, and by that very nature it would be very hard to detect. So far we've only ruled out the lowest hanging fruit. It would've been nice if we got lucky and found it quickly, but expecting that to happen if dark matter exists is naive. And on a related note, detection of something via its gravitational effects is still detection. When talking about particles that interact primarily through gravitation, obviously we would first notice them by their gravitational effects... In particle physics we "detect" particles through their effects on other fields (e.g. no one has ever seen a top quark, we've only ever see the particles that they decay to and note that they're consistent with the standard model). Why should gravity be ineligible when we use the other fields for this purpose all the time?
> A universe with accelerating expansion from dark energy that we also can't detect.
This is a huge question mark not but it's not a failure. The cosmological constant is a simple solution that, as far as we can tell, is consistent with all of our observations and comes with a straightforward interpretation (though of course it's also at the heart of the problem of reconciling quantum mechanics and gravity). In many ways, the accelerating expansion itself can be considered a tentative detection of dark energy. Though of course there are other competing justifications for the acceleration that we aren't yet able to rule out, too.
>Matter/antimatter asymmetry, neutrino mass, and the strong CP problem.
All big questions! But no one is claiming we've finished cosmology. Those are all some of the most active areas of research, there are dozens of hypotheses attempting to address each of them. And more importantly, no other cosmological models attempt to explain those issues, either.
Deyvicous t1_ixl08th wrote
All this missing gravity, and gravity is the problem? The audacity of people xD.
I mean, yea it’s either there is extra mass or there is extra “gravity”. There’s been searches for both for decades, and while progress has been made, neither model has had much evidence…
sticklebat t1_ixm3ok9 wrote
Neither model has had much evidence? Y’all are too hung up on “direct” detection of dark matter. It would be nice but it isn’t necessary. The ΛCDM model has been around for decades and has been making predictions that whole time, and its predictions keep being verified. How is that not evidence??
There is a ton of evidence for dark matter and the ΛCDM model as a whole. The fact that it correctly predicted the CMB power spectrum so accurately is extremely compelling on its own, even if that were the only prediction that it made.
pete_68 t1_ixlrq99 wrote
But 95+% of physicists are working on SM and like 5 guys and a dog are working in a basement on MOND, I guess is my point and SM has made almost no progress on these things in a while. Might be time to start looking at alternatives to SM.
sticklebat t1_ixm51ox wrote
> I guess is my point and SM has made almost no progress on these things in a while. Might be time to start looking at alternatives to SM.
Um, what? First of all the SM of cosmology has come a very long way even in just the past couple of decades. It is not stagnant.
Second of all, most of the specific problems you highlighted are shortcomings of the standard model of particle physics, rather than of Big Bang cosmology itself. And if you think physicists aren’t looking for alternatives and extensions of the standard mode of particle physics then you’re confused. That’s what most particle physicists are trying to do every day. The problem is that it’s hard, it requires huge, expensive, and complex particle accelerators and detectors and that makes progress slow.
TL;DR Most physicists aren’t looking for alternatives of the Standard Model of Cosmology, because it works extremely well and its shortcomings are mostly shortcomings of the Standard Model of Particle Physics. Correcting the Standard Model of Particle Physics to account for its shortcomings is literally what most particle physicists are trying to do. Cosmologists switching gears to focus on something like MOND stands zero chance of addressing most of the problems you mentioned, since those problems are particle physics problems, not cosmology ones. You are confused.
scaratzu t1_ixlx7y0 wrote
My understanding is that dark matter is quite definitively "found", we can see the gravitational lensing effect it has, and can therefore locate where it is. We just don't know what it's made of.
​
Total untrained amateur though, so pinch of salt.
pete_68 t1_ixma6rt wrote
Yeah, I know. But all we see is the effect. My money is on primordial black holes, personally. But that's only one problem. I see the neutrino issue as more fundamental, but like you, untrained...
ThereOnceWasAMan t1_ixkhyoy wrote
The fundamental issue with MOND is that it purports to be a simpler model that doesn't require invoking the mysterious dark matter....except that it still requires dark matter to explain all of the observed phenomenology. MOND doesn't explain the observed gravitational lensing that we've seen, for example, so even MOND proponents admit that dark matter is needed to explain that. Similarly, phenomena like the bullet cluster are still explained by dark matter in the MOND context.
[deleted] t1_ixj6hi3 wrote
[removed]
Viewing a single comment thread. View all comments