## Friday, January 6, 2012

### Hubble function

in cosmology we can measure the Hubble function $H(a)$ and the growth function $D_+(a)$. do they carry the same information? could one compute $D_+$ with the knowledge of only $H$ and vice versa? are there cosmologies where this is NOT possible?

#### 1 comment:

1. the Hubble function H(a) and the growth function D+(a) contain the SAME information and one can be derived from the other as long 1. all of structure formation is only driven by gravitational forces (i.e. there are no pressure forces or similar things) and 2. structure growth is linear (meaning that nonlinearities are small).