Sometimes, galaxies collide

Sometimes, galaxies collide.

A statement simple in its structure, but breathtaking in its profundity.

This was something not understood until later in the 20th century. It wasn't until the 1920s or so that we even understood that galaxies were entities separate from the Milky Way, colossal structures of their own with billons of stars in them. When this was finally grasped, the size of the Universe jumped by orders of magnitude in human understanding.

They're immense, tens or hundreds of thou...