# How can I apply probability to the cosmological constant?

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1. Sep 19, 2015

Hello! me and my friends were discussing a few ideas earlier this week and then we suddenly started talking about Einstein's biggest mistake. I was a bit lost because Im not all that familiar with the Cosmological constant and I was wondering how can probability be applied to that mistake?? I would love and appreciate some light in this >.<

2. Sep 19, 2015

### Hornbein

I have a masters degree in probability and I say that probability has nothing to do with the cosmological constant.

3. Sep 21, 2015

### Garth

First, as Hornbein said, probability has nothing to do with the Cosmological Constant, except that is in the estimation of error in the evaluation of its energy density from cosmological observations.

However beginning from square one, a constant can appear in Einstein's Field Equation as a kind of integration constant - the mathematics allows it - and Einstein used it to obtain a static model (which later was shown to be unstable in any case).

Without such a constant the universe could not be static because it would be under the influence of the gravitational forces within it and tend to collapse, or if expanding it would decelerate and possibly then collapse.

Later Hubble's observations of galaxy red shifts showed the universe was actually expanding - as Einstein might have predicted from his field equation without the constant - it was this oversight that Einstein called his blunder.

Subsequently the constant was generally set to zero until 1998 when observations of distant type Ia super novae found they were fainter than expected and we inferred that the universe was actually accelerating in its expansion - so the cosmological constant did actually exist and Einstein was right after all.

The cosmological constant could be in the form of 'Dark Energy' and actually might be not constant and this is an active field of research today - all evidence so far indicates that it is constant and its energy density comprises of 68% of all the density of the universe - so quite important then!

I hope this helps,
Garth