Hello Physicists First time poster. To give you some background I'm an electrical engineer so i have some basic understanding of physics up through relativity/quantum. I had a thought just occur to me that isn't very easy to google an answer for so i thought I'd come to the experts here. my attempt to articulate it follows: I understand the basic concept of the big bang theory. red spectrum doppler shifts in light indicates all matter in the universe is moving away from eachother. logically if you were to reverse time this motion would go in the other direction forcing all matter to get closer together. What i don't understand is how we can state with certainty that if time were to reverse for long enough(~14 billion years) all this matter would converge into a single pint of infinite mass and energy. Is it not possible that the universe expanded from a concentration of mass with a diameter much larger than the infinitaly small point at a more recent time? For example, how do we know that the big bang wasnt actually the expansion of a sphere of matter/energy already 2 billion light years in diameter and that the expansion started 12 billion years ago instead of starting from a single point 14 billion years ago? any explanation would be appreciated, this has been driving me nuts all day.