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Originally Posted by Fortis
Ten or fifteen years ago, was dark energy "mainstream" cosmology?
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I think the answer here is not so black and white. I don't think all ideas can fit into a simple "mainstream" or "against the mainstream" dichotomy. When Reiss et al (1998) provided supernova results that suggested an accelerated expansion, many cosmologists were already well prepared to make the jump to a universe with a non-zero cosmological constant. It was well established by 1998 that there were observational difficulties for the standard inflationary CDM cosmology that could be alleviated by the re-introduction of a non-zero cosmological constant (lambda).
For example
Efstathiou (1995) discussed several problems that persist for the CDM cosmology if the cosmological constant is zero. The biggest of these problems was that the ages of the oldest stars (in globular star clusters) were difficult to reconcile with a Hubble constant of ~70 km s-1 Mpc-1 - the old age crisis whereby the universe would be younger than its oldest stars. This problem was also discussed by
Krauss in 1998 among numerous other authors during the 90's. Another problem that had come to a head by that time was that observations indicated a matter density too low to account for Omega=1 as required by inflation (see for example Carlberg et al 1996 study on the matter density of the universe from galaxy clusters).
A nice review of the Cosmological Constant was provided in 1992 by
Carroll&Press In their conclusion they state:
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Originally Posted by Carroll&Press
In terms of ruling in a nonzero cosmological constant, the situation now is not too different than it has been in the past. A high value of H0 (>80 km/s/Mpc, say), combined with no loss of confidence in a value of 12-14 Gyr as a minimum age for some globular clusters would effectively prove the existence of a significant Omega-lambda term. Given such observational results, we would know of no convincing alternative hypotheses.
What is most different now from in the past, and what provides hope for breaking the seemingly endless alternation between Lamda-fashionability and Lamda-rejection, is the existence of a new set of tests - gravitational lens statsistics - that have the ability to rule out a dominant omega lamda contribution.
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The point here is that the cosmological constant term has always been in the equations and whether or not its value is zero had been a topic of serious discussion in mainstream journals long before 1998.
In the end, the supernova results were the final piece needed for cosmologists to abandon the occam's razor excuse and adopt the cosmological constant as a means of saving CDM cosmology from other observational difficulties.
So I don't buy the argument that has been made here in the past that cosmologists had to be dragged kicking and screaming to dark energy. It's not that simple. Were they cautious? Yes. Were they hoping they could get away without it? Probably. Are they concerned about the fine-tuning problem it presents? Certainly. But when the time came, the community of cosmologists readily accepted the cosmological constant and dark energy because observations suggested it exists and not inconveniently it provided a means of rescuing CDM cosmology from other troubling observations.
I don't think there will be agreement on this thread regarding the issue of whether or not cosmologists are dogmatic or open minded where new ideas are concerned. People have well staked out positions on that matter. The lesson from the cosmological constant, is simply that cosmologists are willing to modify theory when observational results demand it. The reason ATM ideas are often taken less seriously is that they typically require more dramatic modifications to what is accepted than the cosmological constant did (for example).