The Big Bang and the Quantum

TL;DR

This review discusses how loop quantum cosmology replaces the classical big bang with a quantum bounce, resolving singularities and providing natural initial conditions for inflation, thus offering new insights into early universe physics.

Contribution

It highlights recent advances showing that quantum geometry effects can resolve big bang singularities and alter early universe dynamics, challenging classical predictions.

Findings

The big bang is replaced by a quantum bounce.

The horizon problem disappears due to quantum effects.

A super-inflationary phase occurs immediately after the bounce.

Abstract

This short review is addressed to cosmologists. General relativity predicts that space-time comes to an end and physics comes to a halt at the big-bang. Recent developments in loop quantum cosmology have shown that these predictions cannot be trusted. Quantum geometry effects can resolve singularities, thereby opening new vistas. Examples are: The big bang is replaced by a quantum bounce; the `horizon problem' disappears; immediately after the big bounce, there is a super-inflationary phase with its own phenomenological ramifications; and, in presence of a standard inflaton potential, initial conditions are naturally set for a long, slow roll inflation independently of what happens in the pre-big bang branch.