Chalnoth said:
But for there to be one near the edge of our observable universe without seeing any sign of it within our observable universe is very unlikely.
The problem is that we are talking about scales that cannot be seen in principle, neither directly not indirectly. A structure just beyond the particle horizon will influence visible objects via gravity, but in an
infinite universe we must talk about
arbitrary large structures which are
arbitrary far away! You can't ever see them. So you have to make an assumption. You will never be able to prove or disprove this assumption but you must honestly admit that you made an assumption.
Chalnoth said:
Now you're getting about as absurd as saying that you can't prove neutrinos exist.
No, certainly not. Neutrinos have been detected, so there's no doubt about their existence. And of course I will change my mind as soon as one is able to demonstrate the existence of dark matter. But currently there is no proof, therefore it's allowed to be skeptical and to think about alternatives.
Chalnoth said:
a) Inhomogeneities have been ruled out as an explanation for the accelerated expansion, as I posted earlier:
http://arxiv.org/abs/1007.3725
I know this paper; I would like to wait for some more responses and discussions before calling it a disproof.
Chalnoth said:
b) I'm just not impressed at all at people claiming to have found such inconsistencies. Such observations are liable to help us nail down the precise nature of dark matter, but other observations have already confirmed beyond any reasonable doubt that it exists.
I think the real reason of disagreement between us is a different conception of science, here especially about
existence. I absolutely agree that observations have confirmed the existence
of an effect that cannot be explained via standard hadronic matter and standard GR. But that is
not a confirmation of the existence of dark matter itself. (as an example: the observation of beta decay did not proof the existence of the neutrino; it simply revealed an effect that was not compatible with the models known at that time and that required new physics w/o any indication regarding violation of conservation of energy or the existence of a new particle; the proof of the existence of the neutrino was a second, independent experiment). In the same way DM will not be proven by using it as a parameter to fit the data.
Chalnoth said:
c) ... The LHC is a very poor dark matter detector, by the way.
The LHC and the detectors are especially designed and constructed to detect light SUSY particles (e.g. the neutralino, depending on the specific model like MSSM; mainly by detecting missing energy) which are the best candidates for DM; is there any other experiment that could do the job?
Btw.: is there a preferred mass scale for light SUSY particles to explain DM? What happens of the LHC disproves the existence of SUSY particles below 14 TeV; is (C)DM compatible with much larger SUSY mass scales?