## Wednesday, April 30, 2014

### coasting dark energy universe

following up on the CQW from last week: is it possible to construct a dark energy component with an equation of state that would provide a stable balance between acceleration and deceleration and lead to a constant expansion speed?

bonus question: in what ways would this model be distinguishable from a universe with pure curvature?

## Wednesday, April 23, 2014

### Ricci-scalar in a FLRW-universe

CQW celebrates $10^{4.5}+$ views in 28 months of running the blog! we would like to thank our followers and remind you that if you'd like to propose a question yourself, you're invited to mail us your suggestions to cosmologyquestionoftheweek["AT"]gmail["DOT"]com.

can you express the Ricci-scalar in a FLRW-universe in terms of the Hubble function and the deceleration parameter?

## Wednesday, April 16, 2014

### Wien displacements in many dimensions

can you show that the Wien displacement law for frequencies for a Planck-spectrum in $n$ dimensions is identical to the displacement law for wave lengths in $n+2$ dimensions?

## Wednesday, April 9, 2014

### braking by scattering

can you estimate the time-scale on which a cluster of galaxies slows down due to the kinetic Sunyaev-Zel'dovich effect? (PS: there's something remarkable about the solution if one assumes small velocities and if CQW didn't make a mistake)

## Wednesday, April 2, 2014

### Planck, Bose and Boltzmann

the Planck-spectrum is determined by the Bose-distribution for indistinguishable integer-spin particles and not by the Boltzmann-distribution for classical distinguishable particles. can you show that the difference between the Stefan-Boltzmann-laws derived with both distributions vanishes in the limit of many dimensions? can you show this mathematically and give an intuitive argument?