OK, if we want to talk about getting back to basics, let's look at some things here. The universe is homogeneous and isotropic, but we have to get to particular scales for that (after all, my room isn't isotropic and homogeneous, neither is the Earth, neither is the solar system, neither is the Milky Way Galaxy, neither is the local cluster, etc.)
The universe starts being homogeneous and isotropic at when we bound a few hundred Mpc (that's megaparsecs). Once we look at a slice of the universe that's a few hundred Mpc, then we'll get a good idea of the entire universe. So what's the energy density of, say, stars within a few hundred Mpc?
We can use the mass to light ratio for this job. If every star were like Sol, this would be (1.1 x 10^8 M_sun/Mpc^3) through a typical B-filter. But the sun isn't the most common type of star (lower mass stars are), so we use stars within about a kpc because they have good parallax distances to determine an average ratio (because of O-types and such, this ratio turns out to be about 4 M_sun/L_sun). So we get something like 4 x 10^8 M_sun/Mpc^3. This gives a density parameter (when compared to the critical density) of 0.003: stars only make up about 0.3% of the mass needed to produce the geometry of universe that we see.
Conclusion: the mass isn't in stars.
OK, so where else would it be? The next place to look would be gas. This does turn out to be where most of the baryonic matter is, and we can use nucleosynthesis based on element abundances to figure this out. The density parameter for baryons is about 0.048; so ALL baryons (in principle, including stars) only gives us about 4.8% of the mass needed to get a universe with the geometry that we see.
Let's also consider the motion of galaxy clusters. As with an individual galaxy's rotation curve, we can measure the dispersion in the radial velocity of galaxies in clusters and use the Virial Theorem purely in terms of mechanical and potential energy (we get masses much greater than we would get if we were to mass the baryonic matter). What about the gas? It's actually supported from gravitational infall by its own pressure, so we can figure this out using hydrostatic equilibrium techniques. It's actually a pretty cool technique by which you can constrain the mass enclosed as a function of radius and temperature (you'd be amazed at how difficult it is to mass galaxies).
Meow Mix, All this sounds as you´ve got the entire universal picture quite right and on the very brink of a Theory of Everything, but what is the big problem in all this since this is not the case?
How can you make a conclusion of "
the mass isn't in stars" as these usually are measured, explained and compared in masses?
Since velocity dispersion and temperature both trace the underlying gravitational potential, we'd predict that they should trace each other, right?
Agreed in this - but from what dynamic approaches, forces and reasons?
Well, guess what:
They do. (This is
velocity dispersion vs. x-ray temperature relation).
Does this graphic plot contains "dark matter" issues too?
I have no reasonable doubts of this measuring plot. But I have doubts about the standing theory and causes in general.
"Velocity connects to x-ray temperature".
Well, unless you have the weak gravity to produce the much stronger EM x-rays, you´re explanation here are disconnected from fundamental forces facts, I´m afraid.
The mass-to-light ratio for most galaxies is around 400, and it's not because of interstellar gas.
Interesting indeed.
Otherwise, "interstellar gas" (and dust) is in "standard models" thought to play the main reason for the formation of the Solar System, and as this is located in our Milky Way galaxy, this formative process is obviously taking part in galaxies in general. The entire formation and motion is exactly "because of the interstellar gas" and cannot be ruled out at all.
There is nothing about vague-ish E&M ideas (that you can't or won't quantify) that would explain this.
I hope you´re aware that all atoms have E&M qualities and have circuital E&M motions? That all atoms can be affected by electric forces and magnetic fields?
When you observe strong gamma- and x-rays beaming out of galactic poles, why is it then that standing cosmological models are holding onto an assumed "g"-force which isn´t explained, and even is defined to be the by far weakest of all fundamental forces?
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From your second post:
There's also gravitational lensing. If we know the redshift of the lens and the source and the Einstein radius, we can get a very accurate (and direct) measurement of the mass enclosed. When we compare this to the baryonic, visible mass, it never matches up.
This is not "gravitational lensing". You forget and excludes the E&M bending of E&M light around other electromagnetic spheres. (Or simple refraction in gaseous atmospheres)
And when "it doesn´t compute in baryonic/visible mass", it´s simply because "gravity" don´t work at all, and you should have made some E&M measuring instead in these cases.
For you to wave all of this away and say, "no, it's this mysterious E&M action that I can't even quantify," you'd have to explain why completely independent methods give the same results, and that none of these results could be obtained by a mysterious plasma ether.
What do you mean by "completely independent methods"?
If the used method is based on only 1 of the 4 fundamental forces (and "dark matter"), this method are BASICALLY DEPENDENT of this exclusive approach, and cannot be taken as evidence for a reliably universal test at all.
"Plasma" is mysterious at all: You find it naturally in our E&M Sun and in the beautiful polar Northern and Southern Lights. And you can find plasma in neon tubes as well.
It´s only in the consensus gravitational world such natural phenomena are mysterious.
So much for MY "natural back to basics" for know