Planets, stars, galaxies, clusters, everything in the universe is spinning/rotating. Why?
In: Physics
Gravity pulls things towards each other.
Suppose you clear out the universe, and plonk a couple of big rocks in the middle of it. If you placed them to be perfectly still, they’d start to fall towards each other because of gravity. They’d collide, and either bounce away of smash together or something. Exactly what isn’t important.
Now suppose you try again. This time, the rocks are moving slightly with respect to each other. It doesn’t matter what direction they’re moving in, as long as it isn’t perfectly along the line between them. Gravity tries to pull them together. Specifically, it is always pulling in the direction of the line connecting them. But the rocks are already moving to the side, say. So the direction of gravity keeps changing as they move. Basically, they fall towards each other but miss.
That’s all an orbit is. Something is falling towards something because of gravity, but keeps missing. This results in the two rocks orbiting around each other, rather than colliding.
And that’s all that’s happening in the universe. Everything is being pulled towards everything else by gravity. But most of the time, things miss. This means they end up orbiting around each other.
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