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Is dark matter’s “nightmare scenario” true?

bigthink.com

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Re: Is dark matter’s “nightmare scenario” true?

#31

Post by wruza »

ephimetheus wrote: post #22
miika wrote: post #7

Nightmare for who? How hard it is to admit that their equations are incorrect? Even amateur like myself can see that the dark matter is adhoc value that was calculated in order to patch the standard model. There are several better alternatives but do we need to wait until these stubborn believers have passed away until the world can move forward?

I guess the nightmare is more that it might be undetectable. There’s a real possibility that DM is real, but we hit the neutrino floor at some point without finding anything (maybe couplings are too weak). Until there’s an actual convincing alternative, that indeed is not as apparent as you make it out to be, that would be pretty terrible for a lot of physics.

Why isn’t it good for physics? It has found DM and can observe it via gravitational discrepancies, gets finally “solved” in this part. Does physics really need infinite modifications?

Re: Is dark matter’s “nightmare scenario” true?

#32

Post by stillworks »

aszantu wrote: post #3

I've been wondering for a while if light could be the thing that pushes away the boundaries of the universe and that's the reason for the expansion, if u can push a solar sail... anyways, I don't understand enough about this.

Would recommend reading Chapter 3 "From Eternity to Here" by Sean Carroll (or maybe read the entire book) for a "light weight" introduction. If you don't have the time then TL;DR : universe is expanding means literally that, i.e it is almost as if new space is getting created rather than "cosmological scale objects" hurtling away from each other because they "gained momentum (if one can even call it that)" because of that big bang.

Re: Is dark matter’s “nightmare scenario” true?

#33

Post by fsh »

habibur wrote: post #21

Dark matter and dark energy are like what if there was no Einstein to discover relativity in early 1900s. We later continue to discover that gravity can't explain planetary motions correctly and therefore search for any explanation. There are more laws of Physics waiting to be discovered. At least two big ones from what we currently observe.

You are cherry-picking one particular example. The neutrino and the planet Neptune were "dark matter" for decades until better detectors became available.

Re: Is dark matter’s “nightmare scenario” true?

#34

Post by namaria »

choeger wrote: post #30

My intuitive objection against dark matter is that it's basically an infinite amount of additional parameters to be fitted to the observations. Galaxy behaves weirdly? Add dark matter! It behaves as expected? It obviously has lost its dark matter! It stands to reason that for every possible observation, a particular DM configuration can be calculated. I fail to see how dark matter could ever be falsified. The best po…

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.

Re: Is dark matter’s “nightmare scenario” true?

#35

Post by doliveira »

Why 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.

Re: Is dark matter’s “nightmare scenario” true?

#36

Post by doliveira »

choeger wrote: post #30

My intuitive objection against dark matter is that it's basically an infinite amount of additional parameters to be fitted to the observations. Galaxy behaves weirdly? Add dark matter! It behaves as expected? It obviously has lost its dark matter! It stands to reason that for every possible observation, a particular DM configuration can be calculated. I fail to see how dark matter could ever be falsified. The best po…

Dark matter is the simplest theory.

Re: Is dark matter’s “nightmare scenario” true?

#37

Post by mr_mitm »

choeger wrote: post #30

My intuitive objection against dark matter is that it's basically an infinite amount of additional parameters to be fitted to the observations. Galaxy behaves weirdly? Add dark matter! It behaves as expected? It obviously has lost its dark matter! It stands to reason that for every possible observation, a particular DM configuration can be calculated. I fail to see how dark matter could ever be falsified. The best po…

There is only a handful of parameters. They describe the probability distribution of finding one particular matter configuration. We are simply observing one realization of that probability distribution, in which we should be able to calculate the percentage of galaxies with an unusual amount of dark matter for any definition of "unusual". We don't consider the position and momentum of every baryon a parameter of the standard model either, so why should we do so with DM?

DM can be falsified perfectly well. If the rotation curves of all observed galaxies behaved as predicted by Newton, there would be no DM and every reasonable physicist would consider DM falsified. DM simply passes a lot of falsification experiments.

If DM interacts purely gravitationally, then yes, considering it either matter or an artifact of space-time is merely a matter of preference. Simply move the DM part of the energy-stress tensor on the other side of the Einstein equation.

Differentiating it from MoND or similar theories will then be based purely on how well the theory fits.

However, while I'm only a cosmologist and not a particle physicist, I find the implied assertion by proponents of MoND, that the existence of non-interacting particles is impossible, questionable. Why shouldn't there be heavy particles that don't interact electromagnetically, like a heavy neutrino? Or particles that don't even interact weakly? Or at least, why should their abundance be low compared to baryons?

Edit: Regarding falsification of DM, it's not like DM isn't challenged anywhere. Like I mentioned above, we should be able to compute the abundance of galaxies of certain sizes (dark or not), and the dwarf galaxies are coming up short. It's called the dwarf galaxy problem and poses indeed a challenge to DM, albeit not as much as DM alternatives in the mind of most cosmologists. They think it will be solved eventually as our understanding of galaxy formation improves, but who knows, maybe it's the first glimpse at something bigger. https://en.wikipedia.org/wiki/Dwarf_galaxy_problem

Re: Is dark matter’s “nightmare scenario” true?

#38

Post by scotty79 »

doliveira wrote: post #35

Why 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.

Do you know of any good derivation of existence of dark matter a layman could follow through and be convinced?

Re: Is dark matter’s “nightmare scenario” true?

#39

Post by TEP_Kim_Il_Sung »

doliveira wrote: post #36
choeger wrote: post #30

My intuitive objection against dark matter is that it's basically an infinite amount of additional parameters to be fitted to the observations. Galaxy behaves weirdly? Add dark matter! It behaves as expected? It obviously has lost its dark matter! It stands to reason that for every possible observation, a particular DM configuration can be calculated. I fail to see how dark matter could ever be falsified. The best po…

Dark matter is the simplest theory.

*hypothesis

Theory implies they found out what it is.

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