Saturday, February 25, 2012

Minkowski metric

why is the Minkowski metric not the solution to the Einstein equations for empty space? (or equivalently, why is the empty space of special relativity not the empty space of general relativity?)

Monday, February 20, 2012


inside a void, does time pass faster or slower? by how much?

bonus points: what's $\cos(i)$ with $i = \sqrt{-1}$?

Friday, February 17, 2012

Schwarzschild radius

estimate the Schwarzschild-radius $r_S$ of the Universe!

Friday, February 10, 2012

distance measures

which of the cosmological distance measures are additive, $D(z_1,z_2) + D(z_2,z_3) = D(z_1,z_3)$ and which ones are monotonic, $dD/dz > 0$?

and for bonus points, like always: what's $i^i$ with $i = \sqrt{-1}$?

Friday, February 3, 2012


why does structure formation in the linear regime conserve Gaussianity? does it conserve other statistical properties of the initial density field?