Is the universe’s expansion accelerating? These scientists say no.

Researchers who won the 2011 Nobel Prize in Physics for their groundbreaking discovery that the universe has been expanding at an accelerating rate may have been wrong after all, according to new research published last week in the peer-reviewed online journal Scientific Reports.

Using an analysis of Type Ia supernovae, a type of exploding star that is as heavy as the sun but smaller in size than the Earth, the two separate teams honored by the Nobel Committee reported that weaker-than-expected light detections were evidence that the expansion of the universe was accelerating, and that this acceleration was driven by a substance known as dark energy.

Those observations found 50 Type Ia supernovae that appeared to be less luminous than expect, but as part of their new study, Oxford physicist Professor Subir Sarkar and his colleagues looked at 740 such supernovae and found that the evidence supporting the hypothesis that the universe’s expansion is accelerating may not be quite as strong as the authors of the earlier work thought.

As Professor Sarkar explained in a statement, he and his co-authors “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.”

“An analogous example… would be the recent suggestion for a new particle weighing 750 GeV based on data from the Large Hadron Collider at CERN,” he added. “It initially had even higher significance – 3.9 and 3.4 sigma in December last year – and stimulated over 500 theoretical papers. However, it was announced in August that new data shows that the significance has dropped to less than 1 sigma. It was just a statistical fluctuation, and there is no such particle.”

Scientists may have been ‘misled’ by Nobel Prize-winning discovery

While the professor admits that there is other evidence supporting the notion that the universe’s expansion is accelerating, including observations of the cosmic microwave background collected by the Planck satellite, he cautions that this data is “indirect, carried out in the framework of an assumed model, and the cosmic microwave background is not directly affected by dark energy.”

“So it is quite possible that we are being misled, and that the apparent manifestation of dark energy is a consequence of analyzing the data in an oversimplified theoretical model — one that was in fact constructed in the 1930s, long before there was any real data,” Professor Sarkar said. Adopting a new framework which does not assume that the universe is homogeneous and that its contents behave like ideal gases could explain all of these observations without the need for dark energy, he 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,” the Oxford physicist concluded. “Hopefully this will motivate better analyses of cosmological data, as well as inspiring theorists to investigate more nuanced cosmological models.”

So is the universe’s expansion accelerating or not? The definitive answer may have to wait until 2024, when construction of the European Extremely Large Telescope (E-ELT) observatory is expected to be completed. Located in Chile’s Atacama Desert, the ultrasensitive E-ELT will use a “laser comb” and adaptive optics to directly measure the expansion rate of the universe over a 10- to 15-year period, according to the research team.


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