It seems clear that many of the pre-Copernican astronomers who made
earth-centered models gradually more complex to match better
observations thought - according to historians, anyhow - that they
were describing the phenomena, not explaining them. Are cosmologists
continuously re-editing an undeclared unsuccessful model of the
universe to accommodate it to new and unexpected observations?
(Disney 2007).
Several authors
(Horvath 2008)
are already declaring the crisis of the present cosmological model and
advocating for the need of a paradigm shift in a Khunian sense
(Khun 1962)
but, at the same time, the general adherence to the mainstream concordance
-CDM model does
not leave too much room for thinkers outside the accepted cosmic paradigm.
Does this mean that theorists or observers or both should give up on the universe and go back to studying cataclysmic variables (of which we are secretly very fond)? Certainly not! What it does mean, we think, is
1. Observers should be careful when combining many different sorts of data into a many-parameter model that they have not started off their minimization process from a place in the associated many-dimensional space that will trap them in a false minimum of values that seem to be the best possible fit but are far from the truth.
2. Theorists should put forward as many candidates as they want, but should ask whether their favorites (for instance w a smidge larger or smaller than -1) might have observable/testable consequences that can be extracted from programs and missions that have significant potential for learning other important things about the universe and its contents if the dark energy continues, as it has done so far, to act precisely like a pure, infamous cosmological constant. This, of course, especially true for candidates associated with various multiverse concepts.
As Rocky Kolb (private communication) has emphasised after reading a first draft of this manuscript: "Our goal must not be a cosmological model that just explains the observations, the ingredients of the cosmological model must be deeply rooted in fundamental physics. Dark matter, dark energy, modified gravity, mysterious new forces and particles, etc., unless part of an overarching model of nature, should not be part of a cosmological model. We may propose new ideas, but they must wither unless nourished by fundamental physics."
Acknowledgments. We thank Rocky Kolb, José Adolfo de Azcárraga, Ramon Lapiedra, María Jesús Pons-Bordería, and Alberto Fernández-Soto for many comments and suggestions. This work has been supported by the Spanish Ministerio de Ciencia e Innovación projects ALHAMBRA (AYA2006-14056) and PAU (CSD2007-00060), including FEDER contributions.