# Using stars random distribution to determine presence of gravity

1. Jan 11, 2010

### tmh556

Hi, I'm sure this has been tried but I was just wondering if it's possible to use the distribution of stars and planets in the sky and see how much that deviates from true randomness. With that calculation in mind, I would then think it's possible to determine the gravitational force present since I believe that would be the main factor altering pure randomness. That said, I don't really know what I'm talking about so I could be completely off. Just wondering if there has been any approaches like this.

2. Jan 11, 2010

### marcus

That kind of analysis has been done a lot and has gotten highly sophisticated.
It comes under the heading of early universe "structure formation".

You should google "Smoot TED" and watch the 18 minute video of Nobelist George Smoot explaining with excellent slides and computer animations. He explains how we study structure formation and how we observe it.

It is a way of checking that the gravity works the way our model says it should, and also of checking that the estimate of unseen matter is right.

The very early universe matter was close to uniformly spread out. Even distribution. No structure. We can observe how it gradually collapsed into sheets and strands and clumps and clusters. So it took on a kind of cobwebby appearance, and then galaxies formed in the denser parts.

The cobwebby mess that we observe is actually just what our theory of gravity says should condense out of a uniform cloud. And you can run computer sims based on our gravity equations and they approximately duplicate the appearance of what we see, in a qualitative sense. The results look the same. It is an impressive demonstration of how good the basic einstein model of gravity is, when you add dark matter to it.

Without dark matter there would not have been enough ordinary matter to have done this and condensed that way and be looking like this. So it helps confirm that as well.
Check out Smoot's talk.

Last edited: Jan 11, 2010
3. Jan 11, 2010

### ideasrule

Relating to what Marcus said, check out the Wikipedia article on the Millennium Run.

Not relating to what Marcus said, the stars that you see when you look up at the sky are certainly not random. The stars are clearly denser towards the center of the Milky Way, and in general, along the galactic plane.

4. Jan 11, 2010

### Chronos

The Faber-Jackson relationship comes to mind.