Eternal inflation is a hypothetical inflationary universe model, which is itself an outgrowth or extension of the Big Bang theory.
Paul Steinhardt, one of the original researchers of the inflationary model, introduced the first example of eternal inflation in 1983,[1] and Alexander Vilenkin showed that it is generic.
[4] The basic idea was that the universe underwent a period of rapidly accelerating expansion a few instants after the Big Bang.
The basic idea was to have a continuous "slow-roll" or slow evolution from false vacuum to true without making any bubbles.
Quantum fluctuations in the hypothetical inflaton field produce changes in the rate of expansion that are responsible for eternal inflation.
As a simplified example, suppose that during inflation, the natural decay rate of the inflaton field is slow compared to the effect of quantum fluctuation.
[7] In 1980, quantum fluctuations were suggested by Viatcheslav Mukhanov and Gennady Chibisov[8][9] in the context of a model of modified gravity by Alexei Starobinsky[10] to be possible seeds for forming galaxies.
[11] The average strength of the fluctuations was first calculated by four groups working separately over the course of the workshop: Stephen Hawking;[12] Starobinsky;[13] Guth and So-Young Pi;[14] and James M. Bardeen, Paul Steinhardt and Michael Turner.
[15] The early calculations derived at the Nuffield Workshop only focused on the average fluctuations, whose magnitude is too small to affect inflation.
Paul Steinhardt, who produced the first example of eternal inflation,[1] eventually became a strong and vocal opponent of the theory.
The universes which are generated on the plane are described using a redefinition of the no-boundary wavefunction - in fact the theory requires a boundary at the beginning of time.
[24] Stated simply Hawking says that their findings "imply a significant reduction of the multiverse" which as the University of Cambridge points out, makes the theory "predictive and testable" using gravitational wave astronomy.