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?

# cosmology question of the week

CQW is an educational resource for theoretical astrophysics and cosmology. we post a new question every week for students to get and for teachers to stay in shape.

## Wednesday, February 25, 2015

## Wednesday, February 18, 2015

## 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?

## Wednesday, January 28, 2015

### cosmology in SI-units

can you formulate the speed and acceleration of a FLRW-universe in human-understandable units? what would be your favourite choice?

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