Question: I am not able to understand one thing, when we say we saw a star exploded billions of light years away, does it mean it exploded billions of light years ago but the light reached to you just now. Aren’t we studying the phenomena which has happened billions of light years ago. Is it possible that another big bang has already happened, just the explosion light/energy has not reached to us yet? – Dipanshu
Answer: When we say that we have seen a star explode that is billions of light years ago, it means that it exploded billions of years ago since that light from that stellar explosion had to travel billions of light years to get to us. Note, though, that a stellar explosion is not the same as the big bang, in that the big bang expansion started everywhere at once, and was not characterized by an explosion at a single point.