How do astronomers observing distant galaxies talk about looking backward in time?
The speed of light is not infinite. Light takes time to travel from distant galaxies to our eyes here on Earth. If a galaxy is 1 billion light years away, it has taken 1 billion years for the light emitted by said galaxy to reach us here, so (obviously) we are seeing the light emitted 1 billion years ago. In a sense, we are seeing 1 billion years into the past at the light emitted by that galaxy.