One day, this is what the night sky will look like. Yup, that’s a galaxy (Andromeda, to be specific) headed straight for … our galaxy!
Andromeda’s rushing towards us at the crazy fast speed of 250,000 miles per hour. Luckily, it is a galaxy far, far away, and so it will take 3.75 billion years to get close enough to present as it does in the above illustration, which NASA rigged up based on data from the Hubble telescope.
Despite the speed at which all these balls of matter are moving, the collision of the two galaxies would feel incredibly slow to a human being. The sun will likely be flung out to one of the furthest corners of the new galaxy, informally dubbed Milkomeda. But the Earth will still revolve around the sun! All of this change will take a billion years or so to settle in.
Of course, by the time any of this happens, we will have either left Earth or evolved into creatures that breath carbon dioxide and feast on chemicals we now consider toxic. But perhaps one of these creatures will point up at the galaxy looming in the night sky and tell its offspring that the ancients (us!) predicted that this event would come to pass. And then they will fight with light sabers.