For almost 20 years, our understanding of the universe suggested that the universe is expanding at an ever-increasing. But what if we are wrong? A team of scientists led by Subir Sarkar at Oxford University have now found the proof on which this idea is based is not as solid as previously thought.
In a recent study issued in Scientific Reports, researchers looked at the evidence originally used to prove the universe is expanding at an accelerating rate. This was grounded on the study of Type Ia supernovae – exploding dying stars. After this observation, the data set of this kind of supernovae has improved vastly, letting researchers to reconsider the initial proofs based on more evidence.
There now exists a much bigger database of supernovae on which to perform rigorous and detailed statistical analyses. We analysed the latest catalogue of 740 Type Ia supernovae – over ten times bigger than the original samples on which the discovery claim was based – and found that the evidence for accelerated expansion is, at most, what physicists call '3 sigma'. This is far short of the '5 sigma' standard required to claim a discovery of fundamental significance.
So instead of accelerating, the results are more reliable with a constant rate of expansion. Although there is other indication to point to an accelerating universe – counting the information on cosmic microwave background – all these proofs are "indirect", Sarkar said.
He said a massive amount of work will be required to satisfy others of their findings, but if it turns out to be accurate a massive amount of study carried out over the last two decades might be based on inappropriate models.
The discovery of the accelerating expansion of the universe won the Nobel Prize, the Gruber Cosmology Prize, and the Breakthrough Prize in Fundamental Physics. It led to the widespread acceptance of the idea that the universe is dominated by 'dark energy' that behaves like a cosmological constant – this is now the 'standard model' of cosmology.
It is quite possible that we are being misled and that the apparent manifestation of dark energy is a consequence of analysing the data in an oversimplified theoretical model – one that was in fact constructed in the 1930s, long before there was any real data.
A more sophisticated theoretical framework accounting for the observation that the universe is not exactly homogeneous and that its matter content may not behave as an ideal gas – two key assumptions of standard cosmology – may well be able to account for all observations without requiring dark energy. Indeed, vacuum energy is something of which we have absolutely no understanding in fundamental theory.