# Cosmological Constant

1. Jul 19, 2006

### wsdisman

In using Einstein's Cosmological Constant, what is the significance of 8pi in the equation? What effect does this factor account for in the movement of time and space? What outome would come from manipulating this number?

2. Jul 20, 2006

### wsdisman

I have seen 8 pi used in String Theory equations as well, but I am unsure if its applications are the same in this field. I believe when it is used in Einstein's Constant it infers a cyclical universe. I realize it must have something to do with the geometry of the universe.

3. Jul 20, 2006

### pervect

Staff Emeritus
I suppose you are talking about the 8 pi in

$$G_{\mu\nu} = 8 \pi T_{\mu\nu}$$

?

The cosmological constant is a different, additive constant. Anyway, this is just a convention, it's a consequence of setting G=1 in geometric units.

4. Jul 20, 2006

### wsdisman

In electrodynamics, it is common to produce factors of 4 pi using Maxwell's Field equations because it represents the area of the unit sphere. When you derive the inverse square law from these equations, 4 pi represents the spherical path of the electric field. In GR, is the cosmological constant trying to bridge the gap between electromagnetism and gravity? If so, I do not understand the significance of the factor of two in making 4 pi into 8 pi.

5. Jul 21, 2006

### wsdisman

I am new to this forum so this will be my first attempt at Latex:

$$\Omega = \frac{8 \pi G }{3 H^2 }\rho$$

This is Friedmann's equation of determining the density parameter of a cosmological model. It uses H as the Hubble expansion parameter, G as the gravitational constant, and rho as the density of the system. Again, the use of 8 pi delivers a spherical progression of the system. Like the cosmological constant it assumes a uniform cyclical expansion. Is there any other model that could explain our universe without assuming geometric symmetry?