Question: How do you make your universes on the super computers?

Julian Onions answered on 11 Nov 2014:

I take what I think the conditions are soon after the big bang (which is a much simpler universe than now!). I make a description of this using positions and mass in what is effectively a large box, with bits of matter placed in it.
Then I tell the computer how these things affect one another – big masses pull more than small masses, and so on. Then I let it run by doing these calculations over and over, each time moving these bits of matter by a little bit. Then it recalculates where they should be next based on where they are now, and so on. For about 14 billion years. However I jump in time by a few million years each time rather than doing it second by second, else we’d still be here before the universe ended!