What is the Size of the Universe?
Nobody knows the size of the universe but we know that the universe must have a certain mass in order for its attractive gravitational forces to slow the expansion of the universe which started at the big bang. We can precisely calculate the rate at which the universe is expanding currently, and how fast it has expanded in the past. From this we get the theoretical mass of the universe. This figure falls far short of the visible mass of the universe, which consists of stars, planets, and hot gas. This is how scientists are able to prove that we can only see about 5% of our universe.