Question

A very short period of extremely rapid expansion, called , is thought to have occurred when the universe was about 10-38 second old.

Answer 1

Inflation is a sudden and extremely rapid expansion of the universe that occurred in a tiny fraction of a second during the universes's first second to existence. More specifically, inflation is thought to have occurred as the strong and electroweak forces, froze out, from the GUT force when the universe was a mere 10-38 second old.