  Using new cosmological doomsday argument Page predicts that the maximal
lifetime of de Sitter universe should be $t_{max}=10^{60}$ yr which is way too
small in comparison with strings predictions ($t_f>$googleplex). However, since
this prediction is dependant on the total number of human observations, we show
that Page arguments results instead in astounding conclusion that this number
is the quantum variable and is therefore much greater then Page's estimation.
Identifying it with the number of coarse-grained histories in de Sitter
universe we get the lifetime of the universe comparable with strings
predictions. Moreover, it seems that this result can be considered as another
one of the observational evidences of validity of the many-worlds quantum
theory. Finally, we show that for the universe filled with phantom energy
$t_{max}\sim t_f$ up to very high precision.
