Thursday, January 21, 2010

More On Sloan

I'm going to start with a numerical simulation showing how dark matter collapses into what is known as large scale structure.   Note a few important things:

  1. At early times the universe was very uniform without much large scale structure.
  2. As time evolves, dark matter begins to gravitationally collapse into distinct structure.
  3. Side note: since dark matter is the dominant form of matter, visible matter should align itself with the collapsed dark matter.  This means where dark matter has collapsed, visible matter should collapse there too. (More or less, without going into galaxy bias.)

Before experiments like Sloan, and no offense to the numerical world, this was just theoretical. Numerical simulations are just working out the fine details of a theory which may or may not be correct. As nice and clever as the codes are, the universe may not look like this.

However, enter Sloan.  Here is an example image taken from the Sloan data: (Click to see larger.)

If you look closely you can see that far away, at the edges representing the universe long ago. the universe is indeed more smooth without much definite structure.  Close up, at the center depicting  more modern times, the universe is not as smooth and indeed has more well defined structure.

So the numerical simulations, and therefore the theories behind them, seem to be supported by the data indeed.  As I said in my last post, Sloan is a very priceless survey.

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