Reply #5: Neutrinos almost certainly have mass

[caraher]

Under the current understanding of neutrino oscillation the three known flavors of neutrinos only mix because they have nonzero masses. At the same time, attempts to measure neutrino mass have only yielded upper limits; as far as I know there's nonzero lower limit on mass established by experiment.

I think you're overestimating the effect of neutrinos. 10% of matter is not the same as 10% of the total energy... I'm not sure how soon after the Big Bang this 10% figure refers to, but in the very early universe far, far more energy was in the form of radiation than matter. So that 10% is a larger piece of a much smaller pie. And we do understand neutrinos well enough to calculate with pretty good confidence their effects on the expansion of the universe, and apparently neutrinos don't really make much of a dent in the "missing mass" problem.

But I think you're probably right as far as the big picture... recent observations showing the expansion of the universe accelerating suggest that there's a LOT we don't really understand. When I was in grad school not that long ago one day a high energy theorist would assure us that the Standard Model is the final word on everything and is basically complete, and the only important parameter to measure is the mass of the Higgs boson. Then the next day the astrophysicist confess we don't know what most of the matter in the universe really is... And of course, there's the ongoing problem of developing a theory of gravity that works at the Planck scale, and a slowly but steadily growing awareness of the Pioneer anomaly.