I just thought I'd share this simulation from the Khan Academy website that shows how particles may interact gravitationally, to give an idea of how galaxies and solar systems form etc. You get a different result everytime you play it. It also allows you to play around with the source code, so if you're a competent programmer you can change the conditions of the simulation to see what happens.
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Here is a video where Sal Khan talks about what the simulation shows.
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Here is a video where Sal Khan talks about what the simulation shows.