What is "dark energy", really?
Well, everybody (including Mozina) seems to at least accept that the accelerating expansion interpretation of cosmological data is reasonably acceptable (source papers:
Riess, et al., 1998,
Perlmutter, et al., 1999 and the several thousand references thereto). Generally speaking, the words "dark energy" are nothing more than a place-holder for whatever it is that causes the accelerating expansion. This may be an unfortunate choice of words, for if the cause is found to be, for instance, a cosmological constant, then it is not "energy" at all, at least in classical general relativity, but rather simply an artifact of the geometry of space. Of course, given a quantum theory of general relativity one might reconsider the cosmological constant as a true force.
Now, given that we accept an accelerating expansion, what can we hold responsible for this? If we are constrained to stick tightly only to the physics we know well, then we can start with the realization that there are only 4 known "forces": gravity, electromagnetism, and the strong & weak nuclear forces. If it's not one of these 4 forces that causes the accelerating expansion of the universe, then I think it is safe to say that "physics as we know it" is not responsible, and "new physics" must be derived to explain the observations.
Classical Maxwellian electromagnetism can be ruled out at once by the simple observation that the expansion treats charged particles (i.e., plasma) and neutral material in identical fashion. I don't know how to get classical electromagnetic fields to couple to neutral matter with the same strength as they couple to electrically charged matter, and I am unaware of anyone else professing an ability to describe this. However, there are polarization states in quantum electrodynamics that do not couple to electric charge, but only via gravity. These electromagnetic states are under investigation by some groups as a plausible physical basis for "dark energy" and the accelerated expansion of the universe (i.e.,
Novello, et al., 2004;
Jimenez & Maroto, 2009a;
Jimenez & Maroto, 2009b and
Labun & Rafleski, 2008).
The data are most consistent with a cosmological constant in Einstein's equations being the root source of the accelerating expansion and therefore the physical basis of dark energy (i.e.,
Wood-Vasey, et al., 2007 and
Davis, et al., 2007 and the numerous references thereto). A classical electromagnetic field cannot effectively mimic a cosmological constant since it couples strongly only to electric charges and not to neutral matter. Furthermore, a "cosmological constant" is so named because it is in fact
constant in its effect throughout the entire universe. It's hard to imagine any
realistic classical electromagnetic field owning up to such a stringent constraint.
There are hordes of papers on all aspects of dark energy, but a few good general treatments of the topic (or so it appears to me) are
Basilakos, 2010;
Clarkson, 2009;
Urban & Zhitinsly, 2009;
Sami, 2009a;
Sami, 2009b. And see
Freiman, Turner & Huterer, 2008 for an extensive review of the topic of dark energy, the most extensive recent review that I am aware of.
So it is my position that the lack of strong coupling between classical electromagnetic fields and neutral matter, along with the requirement that the accelerating effect be constant (at least within observational constraints) throughout the universe, leads to a confident ruling out of classical electromagnetic fields as the physical basis for dark energy.
It's an analogy ben.
