The theory that dark energy is forcing the universe to expand at an accelerating pace is one of the most important concepts of modern physics.
Revealed in 1998, it led to frenzied scientific inquiry, a Nobel prize, and even a prediction for the universe’s ultimate destiny – a protracted, icy death.
But now researchers at Oxford University think it could be wrong.
A new study published in Scientific Reports suggests that the universe is actually expanding at a constant, rather than accelerating, rate, indicating that dark energy might not exist after all.
It’s based on analysis of thermonuclear explosions – supernovae – of 740 dying stars, pictured by the Hubble Telescope.
That’s more than ten times the number of supernovae catalogued in the study which won the Nobel five years ago.
Oxford physics professor Subir Sarkar said in a statement: “We 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.”
However, supernovae are not the only evidence to suggest that the universe’s expansion is accelerating.
Information on the cosmic microwave background - the after glow of the Big Bang - backs up the theory.
Sarkar called into question this evidence: “All of these tests are indirect, carried out in the framework of an assumed model, and the cosmic microwave background is not directly affected by dark energy.
“Actually, there is indeed a subtle effect, the late-integrated Sachs-Wolfe effect, but this has not been convincingly detected.
“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.”
He called for scientists to explore an alternative model for the cosmos:
“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.”
Professor Sarkar added: “Naturally, a lot of work will be necessary to convince the physics community of this, but our work serves to demonstrate that a key pillar of the standard cosmological model is rather shaky.
“Hopefully this will motivate better analyses of cosmological data, as well as inspiring theorists to investigate more nuanced cosmological models.”
Professor Sarkar suggested that the European Extremely Large Telescope would make “significant progress” in observing whether the expansion rate is accelerating when it comes online.