Wednesday, June 25, 2014

Newton's Indian rope trick

how long would a vertical rope need to be so that it is in dynamical equilibrium in the Earth's gravitational field with the centrifugal force?

Wednesday, June 18, 2014

asymptotic Hubble-function

what value will the Hubble-parameter reach asymptotically in the future in a $\Lambda$CDM cosmology? when are we within $10^{-n}$, $n=1,2,3$ of that value?

Wednesday, June 11, 2014

cosmic Unruh-effect

please estimate the temperature of the quantum vacuum which we observe due to peculiar acceleration of the Milky Way. how large would an acceleration need to be such that its assigned temperature became comparable to the CMB-temperature?

Wednesday, June 4, 2014

Dirac's large numbers

can you express the ratio between the size of the Universe and the size of the electron with fundamental constants and quote a numerical value?