Friday, January 22, 2010

The Millenium Simulation

My last couple posts on the Sloan Digital Sky Survey have made me want to discuss one more thing quickly: The Millenium Simulation.

The video below shows the results of this huge simulation.  Again, important things to notice:
  1. The cob-web structure dark matter takes on when it collapses.
  2. Now compare #1 to what Sloan got in my last post linked above. (You should conclude this simulation fits the data.)
  3. On large scales, what you see when the movie begins, the universe looks fairly uniform or homogeneous.
  4. As they zoom in, or on small scales, the universe departs from homogeneity.
  5. This has again been observed by Sloan and others.

Millennium Simulation from Kennislink on Vimeo.

The above points may be more important than the casual reader might realize.  Let's take the last points.  In many respects, the cosmological models we base so much off of stand or fall on the idea that on large scales the universe is homogeneous and isotropic and on small scales this no longer is the case.

If large scales aren't homogeneous we could throw our general relativity cosmology solutions out the window.  If on small scales we didn't depart from homogeneity, our theories could never account for for how things like galaxies or planets form.

On the first points, the cobb-web prediction is so important.  Visible matter doesn't collapse on it's own like this.  If the universe was not mostly dark matter we should not see this cobb-webb structure.

However, the cobb-webb structure is what a dark matter dominated universe predicts, and if you look closely at the Sloan pictures you see this is verified.  Dark matter continues to make predictions verified by experiments.

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