The First Three Minutes

Part 1: Inflation and the Hot Big Bang

The earliest instant we can model is not the reactions but a burst of expansion that preceded them. In the first sliver of a second, the universe underwent inflation: an episode of staggeringly fast, accelerating expansion that stretched a microscopic patch to cosmic size.

Inflation does two jobs worth keeping. It stretches space so smooth and so flat that it explains the flatness we measured last reading ($\Omega_\text{total} = 1$). And — more startling — it takes the unavoidable quantum fluctuations of the microscopic patch and stretches them to macroscopic size. Those frozen-in ripples became slightly denser and slightly emptier regions. They are the seeds gravity later grew into galaxies, clusters, and the cosmic web — and we have already seen their imprint, as the tiny temperature ripples in the cosmic microwave background. The largest structures in the universe are inflated quantum noise.

When inflation ended, the energy that drove it dumped into a hot soup of particles and radiation — the hot Big Bang proper. This is the moment to correct a stubborn picture.