Understanding Dark Matter: Theories and Effects on the Cosmos

[matt.o]

I'm not sure that it is worthwhile comparing the density of the ICM to that of the quantum vacuum. My point was just that the ICM is not very dense.

 

[Chronos]

The average mass density of the universe [conventional] is around 1 hydrogen atom per square meter. The intergalactic medium is thought to be in the range of 10 - 100 H atoms per cubic meter. Intercluster mass density might be ~5 times denser, on average. It is a very difficult thing to model. The classical approach is based on Newtonian gravity [most of this stuff does not move fast enough to worry about relativistic effects]. Dark matter is what plugs the gap to explain the apparent gravitational attraction observed, but not otherwise accounted for. DM is a rather unsavory explanation, but is more consistent with observation than the competing theories [MOND in particular]. Finding the DM particle in the lab is, however, a huge issue. It hasn't been done yet. It may also never be feasible. The energies necessary may not be achievable by any known technologies.

 

[Garth]

It is a very difficult thing to model. The classical approach is based on Newtonian gravity [most of this stuff does not move fast enough to worry about relativistic effects].

However the non-linear GR effects of orbiting gravitating matter may be significant.

Dark matter is what plugs the gap to explain the apparent gravitational attraction observed, but not otherwise accounted for. DM is a rather unsavory explanation, but is more consistent with observation than the competing theories [MOND in particular]. Finding the DM particle in the lab is, however, a huge issue. It hasn't been done yet. It may also never be feasible. The energies necessary may not be achievable by any known technologies.

In which case, if the DM particle is never found, what would be the scientific status of such DM?

Garth

 

[matt.o]

However, the non-linear effects have no bearing on the ICM, which also requires DM to explain why it hasn't evaporated into inter-cluster space.

 

[Garth]

However, the non-linear effects have no bearing on the ICM, which also requires DM to explain why it hasn't evaporated into inter-cluster space.

I totally agree - see my post #4 in More about the Cooperstock and Tieu model

Garth

 

[Mike2]

I've gotten the energy density for black body radiation for a given temperature. And we have the Unruh temperature for a given acceleration. But in order to apply this Unruh temperature to the acceleration due to gravity (as required by the equivalence principle. Is this DM) I need to calculate the emount of acceleration at each point for a given mass distribution. I could try to use the inverse square law, but this goes to infinity at r=0. And points in the second iteration would then be inside the new distribution when calculating second order effects. So does anyone have a formula for the acceleration felt by test particles calculated by using the gravitational potential for a given arbitrary mass density formula? Thanks.

I'm seriously tempted to consider the energy density of the Unruh radiation applied to the acceleration due to gravity as possibly the source of Dark Matter? It would seem like an easy calculation to find out. First find the energy density of this assumed Unruh radiation. This would involve an integral of Planck's density spectrum over all frequencies. I've looked at this, and I think I can find a definiate integral formula to accomplish this. This would give us an energy formula at temperature. That energy can be converted to mass, and the additional gravitational effects could be calculated from that. But you'd have to find the acceleration for the Unruh formula at a given radius from the galactic center. I suppose one could use Newton's inverse squared law as a good approximation. Then apply the equation for the Unruh temperature. Then one could construct an integral over all space of this extra mass density produced by the Unruh effect applied to acceleration due to gravity.
I suppose this might seem like a very small effect; but that's a lot of space, and I've not done the calculation yet. Not only that, but once you have a first approximation, then you'd have to do it all over again since now you have to take into account the existence of this first approximation results. Your galaxy just acquired more mass, so it will produce more gravitational acceleration that you realized, which requires another iteration of the process. I suppose you'd have to do this 4 or 5 times to see how quickly the series converged.

 

[Mike2]

Isn't this calculation worth doing for its own sake? If the Unruh effect of acceleration can be applied to gravitationally accelerated reference frames due to the equivalence principle, then should we try to see how much of an effect this would have?