10-19-05, 05:34 PM
The apparent missing mass that many scientists are looking for may be in part an underestimation of the mass of light in the universe. Think about it: The thousands of tons of hydrogen that is converted into helium every second in just our sun, tons of which is converted into light. This light has mass - in fact there may have been little mass change if any. In every point in the universe at any time, there is light from most every direction traversing through the universe. This is a tremendous amount of energy if you think about it. It takes billions of years for light to traverse just a small fraction of the universe - The end effect is energy permeating practically everywhere in the form of light.
10-19-05, 05:46 PM
Actually, it turns out that even with a very rough estimate (one which is almost certainly extremely generous), the energy density of light emitted by all stars for all time is only a few percent of the energy stored in the Cosmic Microwave Background. The energy of the CMB is known from its temperature and is .262 MeV/m^3. This energy density is itself a tiny fraction (~ 5.8 * 10^(-5)) of the critical density needed to produce a spatially flat universe. Given these observations, it seems impossible to imagine that the missing mass could come from light.
10-21-05, 03:31 AM
Could the missing mass actually be a product of a failed formula and not missing at all?
I assume that the formula E=mc^2 is of primary concern. Could it be wrong?
Noting that just because it appears to work locally doesn't necessarilly extend to it being a universal truth.
What if the formula is not complete in some way?
Or what if the missing 5 to 20 times more mass than is observed and reasonably speculated is missing because the formula known as Geometrodynamics ( General Relativity ) is not complete or is wrong in some way? :eek:
10-21-05, 08:59 PM
It is certainly possible that GR may need modification at large scales, but there is no solid evidence that this is the case. Various theories like MOND, tired light, etc have been put forward, but observational data is always turning up that agrees with GR and constrains the possibility of alternative theories. The fact that GR does so well is especially impressive since it has no free parameters (except the cosmological constant).
GR has predicted every "small scale" effect so far including perturbed orbits in the solar system, binary decay due to gravitational wave emission, GPS, deflection of starlight, and a host of others. GR also seems to allow us to understand cosmological observations like the nearly uniform CMB, etc. Perhaps most importantly, while GR does require "missing mass", this isn't necessarily a bad thing. Almost everyone is convinced by now of the reality dark matter and dark energy, and we would be surprised now if nothing was found, especially since many people expect supersymmetry, etc in the LHC or residually in current experiments. Missing mass may be one of GR's greatest predictions rather than its greatest flaw.
10-21-05, 09:08 PM
Hmmm you make a strong case Physics Monkey! I'm inclined to agree with you. It's been said that (M theory I think) that: be there many dimentions, gravity may be suseptable to influence from these. But let us not forget that it may be both. We could have still underestimated the mass of the energy in light form, and other dark matter still exist.
10-21-05, 09:18 PM
Indeed, Tortise, it turns out that the place to look for interesting new gravitational physics may be the very small rather than the very large. In fact, very recently Eric Adelberger's Eot-Wash group out at the University of Washington, Seattle observed possible deviations from the inverse square law at short distances (~ 100 microns). Confirmation work needs to be done before any definite statement can be made, but this could be big (or small as the case may be ;) ).
10-24-05, 04:36 PM
But I'm sure that you will agree with me that many of the calculations were based on a smaller universe. It is now calculated that the universe may be some 20 billion light years across (estimates keep getting bigger). Wouldn't this make a difference in the energy content and the deeper meaning of the question of dark matter? Or rather it may have changed slightly the nature of the question with respect to the data.
10-24-05, 04:52 PM
Hi, Tortise, I would hesitate to categorically say no, but the relevant parameter is energy density rather than energy per se. Since energy density is independent of volume for a homogeneous universe, it shouldn't matter how big the universe is.
10-26-05, 11:43 PM
Yes, I'm sure you're right. Thank you.