The early universe resembled an overheated cauldron, seething with quantum fluctuations (random bursts of energy). In this chaos, like steam over boiling water, a special field, the scalar field, condensed. It became the 'engine' that made space expand at an incredible rate. This process is called inflation.
The authors showed that such a field need not be introduced artificially. It arises on its own, as a collective behavior of many quantum particles. Using ideas from statistical physics and quantum field theory, they derived the condition under which expansion proceeds exactly as observed in the cosmic microwave background. This condition links the rate of change of the field to the expansion rate.
This approach turns inflation from a hypothesis into a consequence of the quantum nature of the universe. The entire observable universe is but foam left after the quantum 'cauldron' spilled its contents into the classical world.
Inflation lasted a tiny fraction of a second, but during that time the universe expanded by a factor of $10^{26}$—as if a grain of sand became the size of a galaxy.