I just watched one of those videos that shows the scale of the universe, zooming out from one thing all the way out to the sphere that is thought to be the universe. However, they also showed other universes outside our own, and they made it seem like a universe is right next to others in space. I have often heard that our universe is expanding, so I just want to ask: What would happen if one universe expanded enough to collide with another, and what would this look like from inside one of the universes?
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The Universe is space and time.  If there are other universes they can't be "next to" ours, as "next to" is a statement about the relationship between things in space, and the Universe is not in space. It is space.
You can't have two universes colliding at a particular time, because time is a property of the universe.
Your mental image of universes as spherical bubbles floating in space is wrong. Unfortunately, there isn't a better visual image. The notion of being outside the Universe and looking at it seems to be fundamentally impossible, because "outside" is a property of space, and space only exists inside a universe.
The last part of the video does show "bubbles floating in space" but this is not intended to be a representation of the multiverse (if it exists) but a metaphorical symbolisation of it. It is something that is fundamentally unknown and unknowable. It is beyond our ability to visualise in a realistic way, so it must be visualised in an unrealistic way.
This is, at least, our best guess.  In fact questions of "outside the universe" are unanswerable.  If we could know about something outside the universe, then it wouldn't be outside, it would be part of our universe.
So ultimately, Mick is right: Nobody knows.
