Conformal Cyclic Cosmology

Originally written in December 2014 for an upper-division physics course in General Relativity, this paper provides a brief overview of my personal favorite cosmological theory: conformal cyclic cosmology. This theory, first hypothesized by Nobel laureate Roger Penrose, attempts to explain the origins and evolution of the universe while taking into account the second law of thermodynamics, i.e. the need for the entropy of the universe to increase over time. This requirement leads him to the belief that the universe exists on a cycle, where the expansive heat death of the previous universe leads directly into the birth of the next.

Abstract

Proposals for describing the early state of the universe rarely address a fundamental conundrum, that of the second law of thermodynamics. According to the second law, the entropy of the universe basically increases monotonically with time, where the term entropy refers to a measure of disorder or lack of specialness in the state of the universe. Entropy increases with the positive flow of time, which means that the beginning of the universe must have been the most special. Any proposal for the initial universe must account for this extreme specialness. The currently popular “inflationary model” and the previously popular “chaotic cosmology” both suggest that the universe started in a random state, and was then shaped via various physical mechanisms into the somewhat special state in which it actually appears to have been at slightly later stages. But random means “not-special” to an extreme degree, which would imply a violation of the second law in order to reach the later, more special state. Conformal Cyclic Cosmology (CCC) is a countertheory to the inflationary model of the universe that addresses the existence of the second law of thermodynamics.