AC130Nav said:
So cosmology is fine and just needs a little tweaking? Isn't that what they said about epicycles? Again a case where math tried to trump reason.
People have been making this sort of accusation for some time about dark matter and dark energy in particular. But I have been quite confused as to why they think the situation is in any way reasonable.
To take the example of epicycles, for instance, there were some massive conceptual problems. The first one is that when the observations became more and more precise, more and more epicycles had to be added to make them work. To contrast this with dark matter, the simplest model for dark matter, a perfectly collisionless, zero-temperature massive particle, has passed with flying colors every observation that it so far would have impacted. There are potential issues where our understanding of the physics in question is otherwise poor (such as the centers of galaxies), but in every case where the physics is relatively well-controlled, where we have a reasonably good handle on the systematic errors, this simplest model of dark matter works fantastically.
Of course, for theoretical reasons we don't expect any real dark matter to actually have zero temperature or be perfectly collisionless. And we hope to one day be able to exploit these non-idealities in order to determine more explicitly the nature of dark matter. But there most definitely hasn't been a need to continually add new properties to dark matter to explain observations.
With dark energy you might have more of a point, but there I'm starting to think that our original assumption that the cosmological constant just had to be zero was based on faulty thinking. Since we actually have no indication from theory that this parameter should have been zero, we should have expected a non-zero value, and thus should, had we paid attention to our equations, have expected to at some point observe some accelerated expansion.
Edit: I'm also confused that when claiming that we can be pretty sure dark matter is a WIMP, and dark energy is the cosmological constant, that this is equated to "everything being okay" with cosmology. No, not at all. Provided you are talking in terms of knowing everything about cosmology, just knowing that dark matter is some sort of WIMP doesn't in any way say what dark matter actually
is, it just narrows down the possibilities. Stating that dark energy is actually the cosmological constant doesn't in any way say why it takes this particular value, something which definitely would require new physics to explain. It just narrows the focus to what sorts of new physics we should be looking for. Observational cosmology is by no means close to finished, but we have answered some questions.