The Melting Point of Atoms

If we look at our universe today, there seems to be a lot more energy stored in matter than there is in radiation. But since radiation loses energy faster than matter during expansion, this means that if we go back in time far enough, the universe was much hotter billions of years ago. And it turns out that a few thousand degrees isn't just any old temperature, it's a very special temperature. I'm fond of calling it the melting point of atoms.