It seems to a not physicist or mathematician that dark matter is just a stand in for something that Einstein missed in explaining gravity. Newton physics explained most, but not all observations of gravity, Einstein refined these explainations and expanded on them, leading to new experimental technology to confirm the theory
Alas, such minds don’t come around very often. But perhaps one day.
“Quantum foam” wouldn’t behave like dark matter. It would behave like dark energy, at least qualitatively… but quantitatively, it’s the biggest embarrassment in the history of science, past, present, or probably future. See, we can’t actually calculate how large the “quantum foam” should be, but we can at least estimate it. And our best estimates are about 120 orders of magnitude too large. Note, that’s not a factor of 120, that’s a factor of 10^120. As in, you would need a 120 digit number to say how far wrong those estimates are. Now, given that it’s only an estimate, one wouldn’t be surprised if it turned out to actually work that all of the different effects exactly canceled out, so that the total was zero… but it would be extremely surprising if they cancelled out 99.999…%, with 120 nines, but not 100%.
Other universes on adjacent branes are a completely different issue. Those could maybe account for dark matter… except that the stuff within them would still have to be very different than the stuff in our Universe. We’ve made enough observations of the effects of dark matter to say that not only does it not interact significantly with our kind of matter, but it also doesn’t interact with itself very much (certainly not nearly as much as our kind of matter does).
ohiomstr2, certainly many people have tried to come up with alternate models of gravity that would explain away the need for dark matter. And some of them work pretty well… for some situations. But none of them works for all situations, and any model that works for one of them fails spectacularly in others. Besides which, what’s so weird about dark matter, anyway? In some ways, it’d be weirder if it didn’t exist. Why should we expect that everything would interact electromagnetically?
Einstein didn’t so much as refined and expanded Newton’s gravitation (which really didn’t explain anything about how gravity worked other than that it related the attractive force to the product of the masses over the square of the distance between them) as gave an entirely new definition (the curvature of the underlying plenum of spacetime) which also accounted for changes in spacetime itself due to peculiar motions of masses and other disturbances.
The idea of the apparent mass of ‘dark matter’ as being a result of some kind of modified Einstein gravity (general relativity) is not new—there are dozens, and perhaps hundreds of variations of proposed modified Einstein gravity models (and even modified Newtonian-based models)—but the problem is that none of these models really work well over all scales, whereas Einstein gravity has been demonstrated to a pretty high degree of precision over all visible scales save for behavior that very much looks like some non-visible, weakly interacting mass. No physicist or cosmologist is going to declare that the problem of (missing) dark matter (MDM) is in any way solved or properly understood, but overservationally it seems to work well within general relativity without requiring arbitrary modifications at differeing scales without any rhyme or reason.
Stranger
Dark Matter got its name in the first place from the presumption that it was probably WIMPs: Weakly Interacting Massive Particles. That was a very attractive idea because some speculations of particle physics beyond the Standard Model were based on supersymmetry- the hypothesis that everyone observed fermion particle has a boson counter-particle, and vice-versa. It would have made a lot of sense from the theoretical standpoint if this had been born out. The problem is that supersymmetric particles have not appeared despite intensive searches for them. The low-hanging fruit of the most likely possibilities have been ruled out. Most searches for WIMPs now presume they’re some speculative particle or another unrelated to supersymmetry.
“For the moment we might very well call them DUNNOS (for Dark Unknown Nonreflective Nondetectable Objects Somewhere).” -Bill Bryson
Non-Euclidian geometry didn’t exist in the time of Newton, and despite his impressive work on Calculus the tools simply didn’t exist for him to discover Relitivity. QFT is based on algebra, General Relativity is geometry.
Einstein didn’t predict dark matter, but some observations of ‘dark matter’ require General Relativity to be properly described. A quantum theory of gravity probably is need needed to reconcile general relativity with QFT, but a usable quantum gravity theory may not be unifying. But some posts seem to think GR needs to be replaced to explain dark matter and that is not true.
All popular current potential models of quantum gravity still have have major formal and conceptual problems and none should be “believed in” today.
The things Einstein missed in explaining gravity is really failing to come up with a unifying theory. The constraints on alternative theories for General Relativity and the Standard Model are getting tighter, and some ideas like supersymmetry which are required for a lot of the ideas above are suffering serous constraints.
Supersymmetry seems to be edging on being a failed theory, which is going to be a real bummer for some of the above ideas.
https://www.nature.com/articles/s41586-018-0599-8
But we will have to see.
kthx.
WRT extraterrestrials creating dark matter, is there any evidence that the effects of dark matter are something “new” with regards to the age of the universe? If dark matter is an alien construct, then it’s effects would only go back to the time it was created and not all the way back to the big bang. As far as I know, the effects of dark matter go all the way back to the big bang and don’t start suddenly, say 8 or 9 billion years ago.
I dunno, but good point.
This is the latest idea that caught my interest to solve the missing matter mystery. Forgive me as I butcher recounting it:
Spontaneous(?) emission relies on an atom’s electron increasing its energy level momentarily when it randomly absorbs a photon; then emitting a photon as the level decreases again at some random time. But, what if there was no electron?
The idea was that many galaxies may have massive filaments of totally ionized particles spanning the gaps between them. But, lacking any electrons, they are unable to emit photons as we know normal matter to do.
If 25% of all the energy in the universe were in the form of positive ionized particles wouldn’t that be immediately noticeable and detectable, since ordinary matter is neutral? And where would those zillions of electrons go and wouldn’t they be noticeable?
And that’s besides their imprint on the CMB.
Although only electrons (and leptons like short-lived muons and tau leprons) emit photons in the visible and radio frequency bands, any charged particle can emit electromagnetic radiation from decay or interaction with electromagnetic fields, e.g. bremsstrahlung or synchrotron radiation. And technically, only atoms and molecules can be ionized by definition.
Dark matter (or as I refer to it, “atramentous corporeity”) is something very different from normal baryonic matter, both in distribution and behavior. Or it is something else entirely which needs a new physics paradigm to describe it. But it isn’t just normal cold baryonic matter, and likely isn’t just some modification of Einstein gravity.
Stranger