Isn't there a modified MOND which fits all the observation data?
Is dark matter’s “nightmare scenario” true?
101–110 of 183 posts
Re: Is dark matter’s “nightmare scenario” true?
#102Earlier quoted context omitted.
> You don't seem to quite understand the current cosmological models. You don't need special cases for every galaxy. No, he's correct that each galaxy does need tuning. Specifically, the amount of DM and it's specific distribution is tuned to match each observation, which is what the OP said. > but it is also true that anything that has to do with galaxy/star formation is immensely complicated as it involves a lot of…
> Specifically, the amount of DM and it's specific distribution is tuned to match each observation ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science?
Well, yes. That's because we have a pretty strong prior about the existence of planets orbiting stars. It was there before we started adding planets to explain the stars wobbles.
With DM the rationale goes the other way around. What means it's not a solid explanation.
That is perfectly fine, as long as proponents don't go saying it's settled knowledge and start fighting the people looking for alternatives. When they start doing that, they stop being scientists, and start being believers.
Re: Is dark matter’s “nightmare scenario” true?
#103Earlier quoted context omitted.
> You don't seem to quite understand the current cosmological models. You don't need special cases for every galaxy. No, he's correct that each galaxy does need tuning. Specifically, the amount of DM and it's specific distribution is tuned to match each observation, which is what the OP said. > but it is also true that anything that has to do with galaxy/star formation is immensely complicated as it involves a lot of…
A single variable being different for each galaxy isn't a problem per se. If a bunch of other factors work out with just that one adjustment, that's pretty good validation that that one adjustment is meaningful. If, on the other hand, your theory could be adjusted to allow for any possible combination of observations, that's when there's a problem. From what I've read, DM theories do a pretty good job of correlating…
> A single variable being different for each galaxy isn't a problem per se. If a bunch of other factors work out with just that one adjustment, that's pretty good validation that that one adjustment is meaningful.
I agree, but isn't that basically what MOND does too? It made one small tweak to gravity, and all of a sudden we can successfully predict a range of galaxy properties with a pretty tight margin for all galaxies, where LCDM can't make such precise predictions because each galaxy's DM distribution can only be tuned after its been observed, and the number of free parameters needed for tuning means the margin is very wide. That's great for MOND but doesn't bode well for LCDM.
From direct observations, MOND is strong where LCDM is weak and vice versa. I think LCDM just gets too much credit and more alternatives need to be tried. There's almost certainly something to MOND because the observations it matches and the successful predictions it made would be too coincidental otherwise.
Re: Is dark matter’s “nightmare scenario” true?
#104Earlier quoted context omitted.
Unless you have worked extensively with the data and math of modern cosmology I very much doubt your 'intuition' about 'dark matter' is anywhere close to the intended meaning.
Right? After quantum mechanics and relativity there's absolutely no reason to believe that our intuition is worth squat when it comes to how physics works.
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Re: Is dark matter’s “nightmare scenario” true?
#105Earlier quoted context omitted.
The minimum mass for a black hole is about 3 times the size of the sun. So we would definitely detect such an object. In fact it would have pretty catastrophic consequences if it entered the solar system...
You mean stellar black holes, right? Primordial black holes could be much smaller, if they exist. I just looked up what would happen in that case, and it sounds really bizarre: > Nevertheless, a PBH would have a notable local impact, Rahvar notes. “The passage of a black hole could melt a cylinder along the interior of the Earth with a radius of almost 10 cm. After a short time, this tunnel would freeze,” he explains…
The issue with that is you're really just talking about another form of dark matter: something else theoretically not impossible but also never observed despite decades of looking...
Re: Is dark matter’s “nightmare scenario” true?
#106Earlier quoted context omitted.
> You don't seem to quite understand the current cosmological models. You don't need special cases for every galaxy. No, he's correct that each galaxy does need tuning. Specifically, the amount of DM and it's specific distribution is tuned to match each observation, which is what the OP said. > but it is also true that anything that has to do with galaxy/star formation is immensely complicated as it involves a lot of…
A single variable being different for each galaxy isn't a problem per se. If a bunch of other factors work out with just that one adjustment, that's pretty good validation that that one adjustment is meaningful. If, on the other hand, your theory could be adjusted to allow for any possible combination of observations, that's when there's a problem. From what I've read, DM theories do a pretty good job of correlating…
> A single variable being different for each galaxy isn't a problem per se.
As John von Neumann said:
With four parameters I can fit an elephant to a curve. With five I can make him wiggle his trunk
Re: Is dark matter’s “nightmare scenario” true?
#107Earlier quoted context omitted.
*hypothesis Theory implies they found out what it is.
In physics, we have laws, rules, models, equations, theories, theorems, postulates, and maybe more. I can't think of one instance in which something has been "promoted" from one to the other after some data came in and couldn't even rank these in terms of certainty. We still call it Newton's law even though we know it's wrong. We still call it Born rule even though it's one of the most tested things we have. We still…
Thanks for expanding on my comment. You said it, bruh!
Re: Is dark matter’s “nightmare scenario” true?
#108Why do people in the comments always ignore that dark matter has way more evidence for it than just galaxy rotation curves (something very well explained in the article)? It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them.
Probably because it's the only piece of evidence you can understand with just high school physics. Most laypeople have trouble understanding that the universe is not expanding from a single point, so how would they be able to understand what the cosmic background radiation is, much less why its angular power spectrum has peaks at particular positions? It's a common pattern with crackpots as well, that they focus on "…
> Anyway, cosmology is a weird topic which not only HN reveals tons of arrogance over. Lots of misplaced skepticism. (Probably similar to the Covid topic.)
It's the curse of being clever. People believe that since they're clever and were able to be successful at what they do, it must be that all other topics are similarly easy. And with easy access (via the internet) to the most basic introductions for lay people to any topic, the Dunning Kruger effect really kicks in.
The more clever you are, the easier it is to fall into this trap. example: "Buy twitter and solve all its problems myself".
Re: Is dark matter’s “nightmare scenario” true?
#109> This isn't evidence against dark matter's existence,
If the repeated failure to find tangible evidence of something in the physical universe isn't evidence against its existence, then you're no longer doing science, but rather playing some religious game
Re: Is dark matter’s “nightmare scenario” true?
#110Why do people in the comments always ignore that dark matter has way more evidence for it than just galaxy rotation curves (something very well explained in the article)? It's quite tiresome to read the same objections as if physicists somehow hadn't thought of them.
Because dark matter is too convenient, and it's not like LCDM prediction are 100% on the money. http://backreaction.blogspot.com/2017/01/the-bullet-cluster-... Another big problem is that all LCDM predictions (MACHO/WIMP) were disproven but it still remains a theory. Now we need energy too high to use in universe. It's eerily similar to Phlogiston theory that at one point was considered to have negative mass.
MACHO/WIMP was one way to implement LCDM, but not a requirement for LCDM.