I just started a book entitled Maps of Time, An Introduction to Big
History by David Christian. David Christian is an historian who began
teaching "Big History" at the university level in 1989. In the book he
states that just prior to the big bang, the universe was the size of an
atom. I have heard this kind of statement many times--that the universe
was tiny or infinitesimal in size and I have always taken it as a
misinterpretation of the idea that the density of the universe was
infinite or as the result of treating that part of the universe which is
observable to us today as the entire universe. My question is, does our
current understanding of cosmology suggest that the entire universe was
infinitesimal or very small when it was most recently most dense? What
does it even mean to say that the universe was the size of an atom?