Revealing the cosmic history with gravitational waves

The characteristics of the cosmic microwave background provide circumstantial evidence that the hot radiation-dominated epoch in the early Universe was preceded by a period of inflationary expansion. Here, we show how a measurement of the stochastic gravitational wave background can reveal the cosmic history and the physical conditions during inflation, subsequent pre-and reheating, and the beginning of the hot big bang era. This is exemplified with a particularly well-motivated and predictive minimal extension of the Standard Model, which is known to provide a complete model for particle physics-up to the Planck scale-and for cosmology-back to inflation.