The Problem of Averaging in Cosmology – seminar by Tim Clifton

This week our speaker, Tim Clifton of CERN and Oxford, took us through the difficult problem of averaging in cosmology. Tim presented the various current methods of averaging, pointing out some problems with them such as the dependence of averaged quantities on the foliation of three dimensional space, how to maintain covariance when averaging non-scalar quantities and the fact that, in general, averaging and time-evolution does not commute.

Tim’s approach, which uses no averaging, is to assume that spacetime is filled with regularly spaced, discrete equal mass objects such that when you zoom out to large scales, it looks like a FLRW universe. While this model is not a realistic model of the cosmos, it is very useful for investigating the impact of inhomogeneities on average observations.

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