Ekpyrotic: Encyclopedia II - Ekpyrotic - Introduction

Ekpyrotic - Introduction

Brane cosmology assumes that the visible universe lies on a four-dimensional brane which moves in higher dimensional space. Our brane may be one of innumerable others moving through these extra dimensions. The ekpyrotic scenario was proposed by Khoury, Ovrut, Steinhardt and Turok in 2001. It suggests that the visible universe was empty and contracting in the distant past. At some time, our brane collided with another, parallel "hidden" brane, which caused the contracting universe to reverse and begin expanding. Hot matter and radiation was created in the collision, which started the hot big bang from which the present-day universe originated. The brane collision, from the four-dimensional perspective of the visible brane, looks like a big crunch followed by a big bang.

The scenario is appealing because it replaces cosmic inflation with a theory that achieves many of the same successes in a framework that seems compatible with string theory. An important distinction between the ekpyrotic scenario and cosmic inflation is that in the ekpyrotic scenario, the primordial nearly scale invariant spectrum of quantum vacuum fluctuations, which is the seed for all structure in the universe today, is generated in a contracting universe, before the big crunch. In cosmic inflation they are generated immediately before the big bang, in an expanding universe.

Adapted from the Wikipedia article "Introduction", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki