I was just watching a video in which the famous physicist Brian Greene was interviewed about his book The Hidden Reality. During this interview, Greene said that it is a matter of significant debate among cosmologists about whether the size of the universe in finite or infinite. In Stephen Hawking's book A Brief History of Time, Hawking says that the universe expanded at a finite rate after the Big Bang. If the universe expanded at a finite rate after the Big Bang, how can the universe now be infinitely big? Before I saw this interview of Brian Greene, I thought that no cosmologist who believes in the Big Bang Theory would think that the universe was infinitely big. My sources on this are the interview of Brian Greene that I watched on youtube and Stephen Hawking's A Brief History of Time.