## Wednesday, October 30, 2013

### galaxy rotation curves at large radii

can you give an expression $\upsilon_\mathrm{rot}(r)$ of how a galaxy rotation curve should look like far away from the centre of the galaxy?

## Wednesday, October 23, 2013

### cosmic neutrino background

can you estimate the amplitude of anisotropies in the cosmic neutrino background given the amplitude of CMB anisotropies?

## Wednesday, October 16, 2013

### shape of the Hubble-law

why does the Hubble law have to have the form $\vec{\upsilon} = H\vec{r}$? if it were of a different form, what would happen to the symmetry assumptions in the cosmological principle?

## Wednesday, October 9, 2013

### equation of state of baryons

can you estimate the equation of state parameter $w$ for the baryonic component in the Universe?

bonus question: how would $w$ change in time?

## Wednesday, October 2, 2013

### thermal wavelength

can you estimate the thermal wavelength of hydrogen atoms today? assume that there's no additional heat input so that you can predict the atom's temperature from the CMB temperature. are the atoms classical or does one have to use a quantum mechanical description?