What happens when parallel universes collide?

What would happen if two universes collide? Did our universe collide with another universe at some point in the past? If yes, what scar would that collision leave on our universe? And how that scar would look like?
Professor Hiranya Peiris, British astrophysicist at University College London, best known for her work on the cosmic microwave background radiation, explains.
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Видео What happens when parallel universes collide? канала Science & Cocktails