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tycon69
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I was simply wondering if dark matter is most-likely a Solid, Liquid, Gas, or Plasma.
If plasma is hot, it emits light.tycon69 said:... or Plasma.
mgb_phys said:It depends what type of dark matter, there are two main theories:
MACHOS (Massive astrophysical compact halo object) are regular star/planet stuff that is too cool to glow in visible light. So these are solids (dust/planets/rocks) or gas (brown dwarfs) or degenerate matter (neutron stars)
Parlyne said:If this were the case and there were enough of these to account for the missing mass in our own galaxy, we should expect to see some amount otherwise inexplicable gravitational lensing of light from outside our galaxy. We don't.
It depends on the mass of the individual 'particles'.FTL_Diesel said:Indeed, I think the latest results from the microlensing surveys is that only 25-50% of dark matter can be accounted for by MACHOs.
Garth said:It depends on the mass of the individual 'particles'.
If much larger then the dark mass would require fewer of these objects and fewer lensing events would be detected.
If MACHOs do not fit the bill then IMBHs might.
Garth
They would also be further away on average.Parlyne said:There would be fewer lensing events; but, wouldn't the lensing in what events there were be stronger?
jdg812 said:If plasma is hot, it emits light.
If plasma is cold, it recombinates and becomes gas.
staf9 said:It's not something I'm well versed on at all, but couldn't dark matter be manipulated into any state of matter?
tycon69 said:I was simply wondering if dark matter is most-likely a Solid, Liquid, Gas, or Plasma.
delta_moment said:But, yeah: Right now I'd say it behaves like matter in that it influences motions of visible matter somehow. Like gravity does. Only, it ain't really there. Like matter. But, causes similar behaviors, as matter.
tycon69 said:I was simply wondering if dark matter is most-likely a Solid, Liquid, Gas, or Plasma.
You are if the alternative theories fly enough to have been published in peer reviewed journals.notknowing said:here exist several alternatives, such as the MOND theory and also a number of other alternatives (which I am not allowed to provide in this forum).
Rudi Van Nieuwenhove
tycon69 said:Hhhhm... would be cool if it were to include a 5th force.
Accepting dark matter as a proven entity (such that one can start studying its properties) can be considered to be misleading as wellGarth said:You are if the alternative theories fly enough to have been published in peer reviewed journals.
The problem is with the mountain of crackpot 'theories' out there. We haven't the strength to point out the obvious flaws with all of them and discussion about them might well mislead newbies who come to these Forums to actually learn some science.
The evidence that something, which is labelled 'Dark Matter', is out there does not just depend on galactic rotation curves, but also galactic cluster binding masses, cluster gravitational lensing masses, large scale structure formation and the CMB anisotropy power spectrum.
Garth
Agreed.notknowing said:Accepting dark matter as a proven entity (such that one can start studying its properties) can be considered to be misleading as well
Gravitational lensing does not depend on 'gravitational force' but space-time curvature. For example, if GR is wrong and space-time is flat, so gravitational forces are some Newtonian force effect, then you could model galactic rotation curves with a suitable MOND type force but you might have no gravitational lensing at all.The other indirect evidence you mentioned (galactic cluster binding masses, lensing, etc.) in fact also relate to the effect of the gravitational force. So, if the gravitational force is calculated wrong, this evidence disappears as well. I'm not sure about the CMB anisotropy spectrum. The interpretation of the latter is of course depending an a cosmological model which might be wrong as well ...
At some point in time, I will come back with some peer reviewed altnerative theory.
Rudi Van Nieuwenhove
Yes, I was wrong to use the term "gravitational force" but that does not really change the argumentation. I could equally well argue that GR does not describe well gravitation at large distances. Both Newton's law (of gravitation) and GR have only been verified experimentally at relatively short distances (size of solar system) and assuming that the same laws hold when extrapolating to distances which are much much larger represents a very optimistic point of view. I agree of course that one has to fit the astrophysical data. Regarding the "cosmological data", things are (in my view) much more confuse. The interpretation (such as of the CMB) depends on the chosen cosmological model which in turn depends on GR or on assumptions whether or not inflation actually is a valid theory.Garth said:Agreed.
We must always be critical of our conceptual models, especially while DM remains undiscovered in the laboratory. But something is out there.Gravitational lensing does not depend on 'gravitational force' but space-time curvature. For example, if GR is wrong and space-time is flat, so gravitational forces are some Newtonian force effect, then you could model galactic rotation curves with a suitable MOND type force but you might have no gravitational lensing at all.
If you then invoked a pseudo Newtonian-SR light bending effect it would produce only half the observed light deflection by the Sun.
Remember you have to fit local experimental data as well as astrophysical and cosmological data.
Garth
I agree that the need for DM and DE to make the standard [itex]\Lambda[/itex]CDM model fit the data may indicate that GR breaks down at cosmological distances.notknowing said:Yes, I was wrong to use the term "gravitational force" but that does not really change the argumentation. I could equally well argue that GR does not describe well gravitation at large distances. Both Newton's law (of gravitation) and GR have only been verified experimentally at relatively short distances (size of solar system) and assuming that the same laws hold when extrapolating to distances which are much much larger represents a very optimistic point of view. I agree of course that one has to fit the astrophysical data. Regarding the "cosmological data", things are (in my view) much more confuse. The interpretation (such as of the CMB) depends on the chosen cosmological model which in turn depends on GR or on assumptions whether or not inflation actually is a valid theory.
Not so many years ago, (nearly) everybody was convinced that 99 % of the mass in the universe was in the form of dark matter and you would be attacked strongly to claim otherwise. Now, this is reduced to 23 % (with the invention of dark energy). This demonstrates the loose ground on which the concept of dark matter rests.
Rudi Van Nieuwenhove
Dark matter is a type of matter that is thought to make up about 85% of the total matter in the universe. It does not interact with light, which is why it is invisible, and its presence is inferred through its gravitational effects on visible matter.
It is currently unknown what state of matter dark matter is in. It does not behave like any of the known states of matter, so scientists are still trying to understand its properties and composition.
Scientists study dark matter through its gravitational effects on visible matter, such as stars and galaxies. They also use particle accelerators and other advanced technologies to search for dark matter particles.
As dark matter is still not fully understood, it is currently impossible to create or destroy it. It is believed to have existed since the early universe and will continue to exist unless we find a way to manipulate it.
Understanding dark matter is crucial for understanding the universe and how it evolved. It also has implications for the future of the universe and the fate of galaxies. Additionally, studying dark matter can lead to advancements in physics and technology.