3 ms·

> I'm getting interested now, the comments have alleged several predictions MOND made. On the other hand I'm pretty sure the evidence for dark matter is pretty

by burnte 2y ago

> I'm getting interested now, the comments have alleged several predictions MOND made. On the other hand I'm pretty sure the evidence for dark matter is pretty strong as well (I believe there are several ways to calculate the amount of dark matter, all of which agree). > Can you give an example of MOND falling apart? One that requires so much fine-tuning that it cannot be adequately explained, or one requiring a violation of one of the more fundamental laws of physics? Pick any MOND theory you like, it all fails when it hits relativity, which is a theory with an embarrassment of riches of evidence in its favor, and can't be reconciled with relativity either. So while it explains galactic rotational speeds, it then fails to explain lots of other things, so it's a huge step backwards. It's the equivalent of saying Newtonian physics is wrong because it can't explain Mercury's precession, so let's go back to epicycles. To favor MOND we give up tremendously more than we gain. MOND CAN explain things, if I have been interpreted to say it never predicts anything, that was never my intent. The problem is that MOND can't explain much else, so rather than making our theories simpler (which usually means we're in the right direction) it complicates things. To make relativity work for the things MOND looks at, we only add 1 thing, WIMPs, particles we theorize but haven't seen. We've predicted lots of particle and found them, so this isn't a problem. chances we have missed a particle that turns out to be highly non-interactive? High. It took us ages to really solve the missing neutrino problem by discovering them, and we predicted the Higgs boson with high accuracy too. So this is a road we've been down before. To make MOND work, we throw out a lot of theory, and we have nothing to replace it with under MOND. Chances all those other theories are wrong even though they work great? Low. Dr Becky is amazing with her MOND analyses. Here's one of the latest: https://www.youtube.com/watch?v=HlNSvrYygRc https://www.youtube.com/watch?v=HlNSvrYygRc

shiandow 2y ago
Do tell me if I'm completely wrong but isn't part of the problem there that you're simply expecting too much from MOND? I mean a theory that is a modification of classical dynamics is not going to work well in a relativistic regime. That just means that somehow the classical limit ends up being slightly different from what we thought it was for reasons we don't know yet. I've always viewed MOND as more of an empirical law that we don't have a good explanation for yet. To me at least it seems obvious it will be deficient when you extrapolate too far and it can't replace more fundamental models. That MOND can't handle relativity is not a direct reason to dismiss it. It would be a problem if relativity can't handle MOND (i.e. relativity cannot result in a MOND like theory) but I can't tell if that is the case. We could also dismiss MOND if it didn't explain anything, but as you said that's not quite the case either. So yeah, dark matter seems more reasonable, but it's hard to completely ignore a theory seems to have more predictive power (even if we know it is flawed).
- burnte 2y ago
  > Do tell me if I'm completely wrong but isn't part of the problem there that you're simply expecting too much from MOND? No, and the reason is because MOND is a fundamentally flawed path. We're fairly sure unified theories are the way the universe works, MOND sticks out of that like a sore thumb. If MOND wants to explain one thing, then it has to fit everything else that effects or it's wrong. Really, for a theory to overturn a preferred one, it has to be better in some way. MOND isn't, it's explains few things than dark matter, and less well. At no point have I ever heard anyone state that MOND has a better predictive power than any other accepted theory, so I'm not sure what you're referring to there. In fact, that's the primary issue with MOND theories is that they ALL fail to meet dark matter with parity, none exceed it's predictive qualities.

by burnte 2y ago

shiandow 2y ago

Do tell me if I'm completely wrong but isn't part of the problem there that you're simply expecting too much from MOND? I mean a theory that is a modification of classical dynamics is not going to work well in a relativistic regime. That just means that somehow the classical limit ends up being slightly different from what we thought it was for reasons we don't know yet. I've always viewed MOND as more of an empirical law that we don't have a good explanation for yet. To me at least it seems obvious it will be deficient when you extrapolate too far and it can't replace more fundamental models. That MOND can't handle relativity is not a direct reason to dismiss it. It would be a problem if relativity can't handle MOND (i.e. relativity cannot result in a MOND like theory) but I can't tell if that is the case. We could also dismiss MOND if it didn't explain anything, but as you said that's not quite the case either. So yeah, dark matter seems more reasonable, but it's hard to completely ignore a theory seems to have more predictive power (even if we know it is flawed).

burnte 2y ago
> Do tell me if I'm completely wrong but isn't part of the problem there that you're simply expecting too much from MOND? No, and the reason is because MOND is a fundamentally flawed path. We're fairly sure unified theories are the way the universe works, MOND sticks out of that like a sore thumb. If MOND wants to explain one thing, then it has to fit everything else that effects or it's wrong. Really, for a theory to overturn a preferred one, it has to be better in some way. MOND isn't, it's explains few things than dark matter, and less well. At no point have I ever heard anyone state that MOND has a better predictive power than any other accepted theory, so I'm not sure what you're referring to there. In fact, that's the primary issue with MOND theories is that they ALL fail to meet dark matter with parity, none exceed it's predictive qualities.