In Cosmology books and tv programs it is mentioned the galaxies are accelerating and running away from us. My question relates to this observation. When they are looking through telescope to the edges of visible universe, they find extremely bright supernova or "celestial candles", calculate its speed and then find the acceleration. But those are billions of light years away. So what they are looking at is the position and speed of that supernova as it was billions of years ago (since light took that much time to reach us). All they can say is those galaxies were accelerating billions of years ago. They don't know where those galaxies are now, so no way to tell if they continued acceleration, slowed to static speed or started collapsing. For example if you are obseverving some galaxy 10 billion light years away, you are looking so far into the past it takes you closer to big bang (13.7 billion). That time, of course, you would expect the universe to be much different and show strange things. How can somebody know what is happening right now. If they cannot know, how can they use this observation to postulate presence of dark energy (right now)? Thanks in advance.