Oxford scientists call into question the idea that the universe’s expansion is accelerating
- By Jessica Hall on October 26, 2016 at 1:15 pm
Type Ia supernovae are affectionately called “standard candles” in astronomy. They’re blessedly predictable, so we use them to measure distances.The 2011 Nobel Prize in Physics went to three astronomers who used standard candles to reach the same conclusion based on the same data: namely, that the universe is expanding at an ever-accelerating rate. But a team of cosmologists from Oxford have done a new analysis using an expanded library of supernovae, and their results cast doubt on the Nobel-winning conclusions.
When the Oxford team did their own analysis of the universe’s expansion scenarios, their best-case, most-certain outcome was much less confident that the universe is expanding at an accelerating rate. Instead, the data “lends itself” to the conclusion that the rate of expansion is constant.
Possible models of the expanding universe. Image credit: The Cosmic Perspective / Jeffrey O. Bennett, Megan O. Donahue, Nicholas Schneider and Mark Voit.
It all hinges on the idea of sigmas. Like p-values, sigmas are meant to convey a measure of the confidence scientists have in their data. Higher sigma values, like lower p-values, mean greater confidence. The conclusions on the expansion of our universe that won the Nobel had a five-sigma confidence rating. The Oxford scientists got just three sigma in their most confident model. While that doesn’t just tear down the current standard model of cosmology, it does raise the possibility that we should run a sanity check. If the data that we have isn’t a representative sample of the behavior of our standard candles, then we really need to go check out what other hypotheses we’ve based on that data set.
“An analogous example in this context would be the recent suggestion for a new particle weighing 750 GeV based on data from the Large Hadron Collider at CERN,” said lead author Subir Sarkar in a statement. “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.”
Sarkar noted that dark energy could be so difficult to find because it doesn’t actually exist. The problem in our hypotheses that we solved using the concept of dark matter might just be an artifact of doing our major cosmological theories in the 1930s, “long before there was any real data.”
Naturally, Sarkar says, a lot of work will be necessary to sell the physics community on these ideas. “Hopefully this will motivate better analyses of cosmological data, as well as inspiring theorists to investigate more nuanced cosmological models,” added Sarkar. “Significant progress will be made when the European Extremely Large Telescope makes observations with an ultrasensitive ‘laser comb’ to directly measure over a 10 to 15-year period whether the expansion rate is indeed accelerating.”