Some experiments just seem a bit too dangerous to try. Mixing chemicals can start fires. Testing big weapons can put the lives of many people at risk. But what about colliding two galaxies together? That's taking it to a whole different level, not to mention how difficult this sort of experiment would be to set up given that we have no control over these sorts of things.
Nevertheless, our galaxy, the Milky Way galaxy, is expected to collide with the "nearby" Andromeda galaxy in about 3 billion years. What will this mean for both galaxies and anything that happens to inhabit them at that time? Is there any way that studying such a collision could improve our understanding of physics? The video focuses on the Milky Way galaxy as the Andromeda galaxy makes two passes through it: the first is a glancing blow while the second results in a merging of the two into a single galaxy.