Strange they didn't mention in this article that the discrepencies in the galactic rotation curves can actually be explained without any novel physics or particles ("dark matter"):
This paper is very weird. They basically assume we are rotating with respect to the center of a galaxy and that is why the see different rotational velocity compared to when we would not be in a rotating frame. This could be the case for a single galaxy. But how can we be in a rotating frame towards the center of all galaxies? That doesn't make sense to me.
So the math would be correct for a single galaxy, but this cannot happen for all galaxies at the same time.
What is interesting though, that they basically find a model with a single additional parameter per galaxy (angular velocity omega) that fits most of the rotation curves very well. However the most simple explanation how we get this omega is not by assuming fictitious forces from rotation frames, but simply real forces from dark matter.
So, actually the paper isn't saying that we are all spinning in sync with the center of every galaxy out there. What it's really getting at is that each galaxy might be spinning or moving in its own special way because of the specific gravitational forces acting on it locally.
It isn't surprising to me because the standard of journalism seems to be one of "debunking". In this approach you start with something that you don't like, in this case Mond, something you do like, usually the status quo, and then throw a bunch of pasta at the wall in the hope that something will stick with the reader. There is usually little to no attempt at an honest review, only a biased statement salad. It's pretty depressing, but I guess it sells ads and doesn't bother the establishment.
Can someone ELI15? Does this work claim that because galaxies fly around each other, potentially around some bigger center of mass, rather than in straight lines, their rotation curves look differently/are actually different, and nobody checked before?
Disclaimer: the authors are good friends of mine and I'm a computer scientist, not a physicist, so I'll try my best to explain it:
The basic idea here, is that the reference frames used to measure galaxy rotation curves may not be inertial. that is, they might be influenced by rotational or other accelerative forces due to the galaxies' motion in the universe. Traditionally, it's assumed these frames are inertial, meaning they are free from such influences, which simplifies calculations but might overlook significant effects, and that's the key point that has been missed and is addressed by the paper, showing that you can't overlook those effects.
if we consider these non-inertial effects akin to acknowledging that galaxies might not be moving in straightforward, stable paths but could be "flying around" each other or a common center, then we can account for the observed rotation curves differently. They suggest that the forces arising from these complex motions could mimic the effects attributed to dark matter.
AFAIK, this has not been rigorously checked in the past. However, there are several other phenomenon that are explained by dark matter / dark energy besides this discrepency, so people in the field are not very eager to give up on dark matter just yet
My very casual understanding is that Mond really has been mostly discarded. The article says it's 'in trouble'.
We see some galaxies whose gravity is near the baryonic prediction and others where it is not.
- explaining this with dark matter is easy: some galaxies have a lot of dark matter and some have little.
- explaining this with Mond seems impossible. If there is some gravity law we don't understand, how can it have different effects on different galaxies?
- how do we explain the famous bullet cluster finding?
Well, attributing it to dark matter is easy. It's not really explaining anything though, until you can say what dark matter is and why it's there. At this point it's basically just an abstract parameter that we assume, without any direct evidence, is in fact some kind of matter and not, well, something else. Maybe spacetime just have different geometry in different places? Maybe the assumption that it would be flat in the absence of matter is wrong? It could very well be that the neutral shape of spacetime in some places is more or less curved than we currently assume.
Then there are fun ideas like large masses permanently deforming spacetime. Going with the famous rubber mat analogy, what if the mat gets permanently stretched and even once the mass that stretched it is dispersed the sag remains?
That's of course assuming there even is such a thing as spacetime. Which, btw, sounds like a reasonable assumption. However, just because the math works doesn't mean it's a physical reality, it merely points to it.
The analogies literally don't matter though. If it behaves "matter-like" enough, then it's matter. We generally regard this to mean entities which can have an independent momentum and position.
Hence: dark matter - because the effect we observe seems to behave that way. MOND is distinct because it declares what we're seeing is not a bunch of entities with that character.
It's worth noting we also talk about a lot of things like this even though strictly speaking they're not: i.e. electron-holes in semiconductors can be perfectly well modeled as their own form of matter - they can't just leave the semiconductor environment. But they do have momentum and position.
Dark matter could literally be the same type of effect, but if you're a wrinkle in space-time then it doesn't matter unless that description has some sort of experimental reality, and we currently do not observe it to do so. It is not like physicists would not rush to test any experimental formulation of dark matter as such that was accessible with current or near-future instruments.
Isn't all that the same idea? If you ignore nomenclature and interpretations, DM basically says there's "a thing", opposed to "a law". Like actual trees vs aerodynamics. "There's trees" doesn't explain anything either, but if there's no trees and spacetime just remembers something, that is a thing as well, not a law. Just dark. A thing is a memory of spacetime.
Nice theory! That would help explain the Great Attractor. The Universe could actually be a deformed blob of spacetime and the Big Bang and its development just happens to be the result of this blob's movements.
There are rogue blackholes, maybe they leave spacetime deformations behind them that could be observed?
I wouldn’t expect to find any “empty” spacetime deformations, since by their very nature they would attract matter. I would however expect more gravity than the presently observable matter could explain.
I wonder if that can explain some of the large scale filament type structures we see.
That's the problem. It lumps unexplained phenomena into a luminiferous aether 2.0. The most likely explanation is our model of gravity isn't yet good enough and so perhaps RelMOND is worth a look.
Probably not. There were hopes that dark matter might arise from supersymmetry, and that if so the LHC might be able to create it.
Thus far they haven't found it, which is a big strike against supersymmetry, as well as a loss of an avenue for exploring dark matter. So back to the drawing board.
At that drawing board, they have other tools to look at. Often, they're astronomical and cosmological. One big clue is the "Bullet Cluster", where two galaxies collided, and the regular mass smashed into each other but the dark matter kept going. And they can look at the distribution of the Cosmic Microwave Background, which would show the influence of early dark matter.
Using that they know that dark matter must be "cold", i.e. not moving near the speed of light. So it must be fairly heavy -- heavier than neutrinos, at least, another particle that's maddeningly hard to detect. (They do have neutrino detectors that also hope to spot a dark matter collision event, but it's unlikely.)
If supersymmetry doesn't cut it, they'll need a new way to fix other problems with the Standard Model. Those would hopefully predict another dark-matter-like particle (massive, weakly interacting), which in turn would point in the direction of a detector. But there aren't any front-runners at the moment.
Dark matter is more of an observation than a theory. The gravitational motions of galaxies doesn't really make sense without it (and with dark matter + General Relativity, it fits perfectly, so we have good reason to believe it exists).
There are a few different theories on what dark matter is; there's axions, supersymmetry (from string theory), cold dark matter and more.
Dark Matter is not the same as antimatter, which CERN did produce.
There are speculations if there are antimatter galaxies out there and that they are in fact the dark Matter that we search for.
But dark matter is in essence matter that should be there, e.g. because a solar system behaves like it is in its gravitational field, but cannot be detected by our instruments.
Maybe it is a flaw in our theory, like the time we found out that newtons physic has some flaws, or we can't detect it because it is made of stuff that we can't measure yet.
Enter Mills classical theory of atomic structure that predicts dark matter is just hydrogen with the electron in a lower orbit that doesn't radiate (hence dark). This stuff has been created in the lab and measured every which way, for example in a gas chromatograph where it flows through faster than normal hydrogen. https://brilliantlightpower.com/theory/
https://www.mdpi.com/2075-4434/9/2/34