Sentence that I find odd


So the title of a video I've watched for immersion
(<https://www.youtube.com/watch?v=qmd_p5qnzCM>) is the following :
天の川がアンドロメダと衝突したとき何が起こるか

I would translate it to something like "When the milky way collided with
Andromeda, what happens" and that makes no sense to me. The problem is, it has
not yet happened ( I'm talking about the andromeda and milky way collision),
so I thought it shouldn't be present?

Can you explain this to me?

