as you go backwards in time, to say the first minute of the universe's life, the density is not absurdly high, it's only a little more than that of water, but the density of radiation is much, much higher — it's a million times higher — and the temperature is like the inside of a nuclear reactor, so one of the interesting things is that when we get back to just a minute, say, after the apparent beginning of the expansion, we're not yet dealing with any bizarre physics, we're dealing with conditions that we know and understand on earth.