General Relativistic Energy Conditions: The Hubble expansion in the epoch of galaxy formation

TL;DR

This paper examines how classical energy conditions in general relativity constrain the evolution of the universe during galaxy formation, revealing violations of the strong energy condition based on current observations.

Contribution

It demonstrates that energy conditions impose robust bounds on cosmological parameters and shows observational evidence for SEC violation during galaxy formation.

Findings

Strong energy condition is violated between galaxy formation and now.

Current data cannot be explained by normal matter alone.

Energy conditions provide useful bounds on density and look-back time.

Abstract

The energy conditions of Einstein gravity (classical general relativity) are designed to extract as much information as possible from classical general relativity without enforcing a particular equation of state for the stress-energy. This systematic avoidance of the need to specify a particular equation of state is particularly useful in a cosmological setting --- since the equation of state for the cosmological fluid in a Friedmann-Robertson-Walker type universe is extremely uncertain. I shall show that the energy conditions provide simple and robust bounds on the behaviour of both the density and look-back time as a function of red-shift. I shall show that current observations suggest that the so-called strong energy condition (SEC) is violated sometime between the epoch of galaxy formation and the present. This implies that no possible combination of ``normal'' matter is capable of fitting the observational data.