# Increased Expansion Rate

1. Feb 11, 2006

### porquat

Hello all...
Hope you'll allow a complete novice to sneak in for a moment or two with a couple of questions:

(1)Disregarding any preferential viewpoint, like Earth, and at any instant, is universal expansion velocity the same?

(2)In what way(s) does the recently discovered increased universal expansion rate affect the Hubble Constant value.

(3)What is the value of the above increased expansion rate?

Easy enough questions I'm sure, but the hard part is putting any answers into simple language that an idiot like me can understand

2. Feb 12, 2006

### Chronos

1] there is no preferential point.
2] the hubble constant is constant
3] the universe is expanding

Welcome to PF, porquat! Good questions. There are many studies that affirm what I claimed. And there are other studies that attempt to refute those claims. You have the freedom of choice to take sides.

3. Feb 13, 2006

### hellfire

At a given instant of time, the expansion velocity per unit length is the same for every observer that measures a homogeneous and isotropic distribution of matter at large scales (this means that the cosmological principle applies).

The Hubble parameter does always decrease or remains constant, if the universe does not contain phantom energy (that leads to a big-rip). In the current cosmological model, the universe contains dark energy in form of a cosmological constant, that comprises 73% of the energy density, and it contains also matter, comprising 27% of the energy density. The matter content makes the Hubble parameter decrease. However, the contribution of the cosmological constant to the energy density will become dominant in future tending to 100% of the energy density (the distribution of matter decreases its density as the universe expands, whereas the energy density of the cosmological constant remains constant). In that a limit the Hubble parameter will become a constant in time.

Considering that $\ddot a / a = - H^2 q$, with q = -0.6 (current deceleration parameter) and H = 71 Km / s per Mpc (current Hubble parameter) you get about 4.3 × 10-35 s-2. This is about 1.3 × 10-15 km / s2 per Mpc. (1 Mpc = 326 million lightyears).

Last edited: Feb 13, 2006