Oxford University Physics Society: Professor Subir Sarkar "Beyond the Cosmological Standard Model"

The 'standard model' of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present — as was inferred from the Hubble diagram of Type Ia supernovae. There now exists a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these `standard(isable) candles’ indeed indicate cosmic acceleration. We find, rather surprisingly, that the inferred acceleration is mainly along the direction we seem to be moving with respect to the cosmic microwave background. It cannot therefore be due to the Cosmological Constant (aka vacuum energy), even though a variety of observations are supposed to have meanwhile confirmed its presence. This is an exciting time to be a cosmologist!