Would it be possible to point a telescope to a particular direction, where our own galaxy once was, and see ourselves in the past?
We can’t directly see past versions of the Milky Way because light travels at extraordinarily fast speeds (300 million meters per second), much faster than the Milky Way. In other words, the light that was emitted by the Milky Way say, 10 million years ago, has already traveled far beyond us. We would need the Milky Way to outrun its own light in order to see it in the past, which unfortunately isn’t possible! That being said, because light travels at a fixed speed, when we look at other galaxies we are seeing light they emitted thousands to millions of years ago. By observing galaxies at different distances from us, we can see galaxies at different life stages, which allows us to infer how galaxies change over time. This gives us clues about the Milky Way’s history. Another method we can use to study the Milky Way’s past is to measure the motions of stars in both the Milky Way and nearby galaxies. The Milky Way sits in a group of galaxies, and the relative motions of stars in these galaxies tell us about where the galaxies used to be, and where they’re going.