General relativistic energy conditions: The Hubble expansion in the epoch of galaxy formation

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 behavior of both the density and look-back time as a function of redshift. I shall show that current observations suggest that the so-called strong energy condition (SEC) is violated at some time 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.