Wednesday, February 25, 2015

recollapsing FLRW-universes

can you construct a FLRW-universe with dark matter and dark energy (with constant equation of state $w$) that recollapses? what's a suitable condition?

Wednesday, February 18, 2015

just two equations?

why are there exactly two Friedmann equations and not more (or less)?

Wednesday, February 11, 2015

FLRW-universes with no big bang

is it possible to set up a FLRW-model with dark matter and dark energy that has a finite size in the inifinite past, i.e. a universe without a big bang?

Wednesday, February 4, 2015

ambiguity in the Planck-units?

the Planck-units are defined using the great constants of Nature: $c$ from relativity, $\hbar$ from quantum mechanics, $k_B$ from thermodynamics and finally $G$ as the gravitational coupling constant. but gravity brings a long a second coupling constant, the cosmological constant $\Lambda$, which now makes the Planck system of units overdetermined: is there a way to resolve this?