Recent progress in observational cosmology, and especially the forthcoming
PLANCK mission data, open new directions in so-called precision cosmology. In
this paper we illustrate this statement considering the accuracy of
cosmological determination of the two-quanta decay rate of 2s hydrogen atom
state. We show that the PLANCK data will allow us to measure this decay rate
significantly better than in the laboratory experiments.Comment: v2: matched with the version accepted in JCAP (minor changes
