In ekpyrotic theory, however, there is no beginning of time, and the Big Bang is replaced with a bounce between two ‘branes’ – three-dimensional worlds in a five-dimensional space-time.

The structure of the current Universe is determined before this bounce, so the need for inflation is avoided.

The theory also avoids the inconvenient singularity in standard cosmology, when the Universe was somehow all crushed down to a single point before exploding in the Big Bang.