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?