Timothy Clifton (London):
Does Dark Energy Exist?
Abstract:
Cosmological observations, when
interpreted within the framework of a homogeneous and isotropic
FriedmannLemaitreRobertsonWalker (FLRW) model, suggest that the Universe
is entering a period of accelerating expansion. This is usually taken to mean
that the expansion of space itself is accelerating. In a general spacetime,
however, this is not necessarily true.
In this talk I will attempt to
clarify this point by considering a handful of local and nonlocal measures
of acceleration in three different inhomogeneous cosmological models. Each of
these measures reduce to the same quantity in the limit of exact spatial
homogeneity and isotropy, but in spacetimes that are only statistically
homogeneous and isotropic it can be shown that the acceleration inferred from
observations made over large scales does not necessarily imply that the
expansion of space itself is accelerating. This demonstrates that observations
made in an inhomogeneous universe can imply acceleration without the existence
of dark energy.
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