Example is andromeda is about to collied with us in 4 billion years but that light needs to travel then has it already happened but we wouldn’t see it since light needs to travel.
Sorry for bad English and grammar.
In: 0
Sort of. Andromeda is 2.5 million light years away, so its light takes 2.5 million years to reach us, so we do see it as it was 2.5 million years ago, not as it is ‘now’. Aliens living in Andromeda right now live in a galaxy that looks 2.5 million years older than the galaxy ‘andromeda’ that we see, and if they sent us a signal, it would take 2.5 million years to reach us, and our whole civilization (or theirs) might disappear before it even reaches us.
But Andromeda is actually getting closer to our galaxy, and that lag time will decrease over time. When andromeda does actually collide with the milky way, any observers left in the galaxy will see the galaxies collide in much closer to ‘real time’ – except not really because the distances between stars are still dozens of light years.
Latest Answers