Re: Curious about response to Fermilab's proposal of unecessariness of dark energy...

From: Phillip Helbig---remove CLOTHES to reply (helbig_at_astro.multiCLOTHESvax.de)
Date: 03/27/05 

Date: Sun, 27 Mar 2005 08:56:22 +0000 (UTC)

In article <1111784369.091750.88880@l41g2000cwc.googlegroups.com>,
online@redpicture.com writes:

> http://www.fnal.gov/pub/presspass/press_releases/darkenergy_3-16-05.html

I think there is a lot of confusion in the popular press due to
nomenclature. In particular, some people use the term "dark energy" to
mean the same thing as "cosmological constant", some use it in a more
general sense (arbitrary equation of state, that of the cosmological
constant being fixed, and/or variation with time, the cosmological
constant being, well, constant), some in a more restricted sense (e.g.
the result of some particular mechanism, whereas the cosmological
constant could be "caused" by any number of things).

As far as I know, there are no observations which cannot be explained by
a classical cosmological constant, i.e. one with the pressure being the
negative of the energy density and which is fixed with time. Of course,
one should allow for the possibility that this is not the case, and see
if something else fits the data better, but at the moment this doesn't
seem to be the case. This is a phenomenological point of view. A
completely different question is what is the CAUSE of the cosmological
constant.

I think it is good to keep the two things separated. With regard to
dark matter, everyone agrees to use the term "dark matter" to refer to
it, and the question of what it actually is composed of is a different
question. With regard to "dark energy", things aren't so clear-cut,
especially in popular accounts.

I'm a bit suspicious of Rocky Kolb being on the press release. He
sometimes seems to go overboard in his support of inflation. As late as
the late 1990s, he was still convinced that Omega_matter is 1, even
though already by that time there was massive evidence against this.
His motivation was that "the simplest models of inflation" predict this.
Inflation is difficult to prove, so it's logical that he would embrace
tying it in to something more "mainstream", such as observations of an
accelerating universe. Also, if the idea is so simple as they claim,
why didn't they come up with it before the discovery of accelerated
expansion, and hence predict that accelerated expansion should be
observed?