Does the universe expand forever, or contract and expand in an infinite series of big bangs? We don’t know yet, but here’s how we will find out:

Either way, here is a related question because we know that our galaxy is expanding right now:

How do galaxies collide? If things started in the Big Bang – moving away from every thing else – what would cause a mass the size of a galaxy to change direction and move into another galaxy?

See also: When galaxies collide

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