I'll be teaching cosmology next month in my (high school) astronomy class.
The book I use discusses inflation and that the volume of the universe
during the Big Bang was less than the size of a proton! How can this be? I
realize the universe had a "hot" and "dense" beginning, but isn't there a
limit to how closely matter (made up of particles) can be packed together?
Particles take up space, so how could an object -- let alone the entire
universe -- have essentially "infinite" density (zero volume)?