English: A blackboard used by Albert Einstein in a 1931 lecture in Oxford. The last three lines give numerical values for the density (ρ), radius (P), and age of the universe. The blackboard is on permanent display in the Museum of the History of Science, Oxford

The formulae are:

D = 1/c 1/l dl/dt = 1/c 1/P dP/dt
D^2 = 1/P^2 (P0-P)/P ~ 1/P^2 (1a)
D^2 = k rho/3 (P0-P)/P ~ k rho (2)
D^2 ~ 10^-53
rho ~ 10^-26
P ~ 10^8 L.I. [or y.? then L.y. = light-year.]
A ~ 10^10 (10^11) I [or y.? = year => an estimate for the age of the universe.]