When considering the immense size of the cosmos, it's pretty remarkable what scientists have been able to discover from our pale blue dot. For example, back in the 1990s, three astronomers used an analysis of so-called "type Ia" supernovae — binary star systems where one star triggers another into a supernova explosion — to determine not only that the entire universe is expanding, but that it is expanding at an accelerating rate. The discovery was granted the Nobel Prize.
The revelation was so profound that the idea of an accelerating expansion has become standard theory, but not without a hitch. In order to account for accelerating expansion, scientists have had to posit the existence of an invisible form of energy that permeates all of space: dark energy. But despite the spooky, elusive nature of dark energy, the idea enjoys widespread acceptance because of the respectability of the standard model of cosmology.
That whole model could soon be called into question, however. A team of scientists led by Professor Subir Sarkar of Oxford University has performed a new analysis on type Ia supernovae that seems to suggest that the original, Nobel Prize-winning research may have been in error. The universe might not be expanding at an accelerating rate after all, reports Phys.org.
It's a bold claim, but not one without ammo. Sarkar's analysis took into account 10 times more type Ia supernovae than the original research did. It's therefore possible that the difference in results could be one of sample size.
"We analyzed the latest catalogue of 740 Type Ia supernovae... 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," explained Sarkar.
In other words, it's still possible that the universe is expanding at an accelerating rate, but the evidence we have is too weak to make a claim one way or the other. Of course, if an accelerated expansion isn't necessary to believe in, then neither is mysterious dark energy. Maybe dark energy is so elusive because it simply doesn't exist in the first place.
"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," said Sarkar.
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. Hopefully this will motivate better analyses of cosmological data, as well as inspiring theorists to investigate more nuanced cosmological models."
The new data is humbling. It reminds us that regardless of whether the universe is expanding at an accelerating rate, it's still a very big place. The things we've been able to discover from our tiny orb are remarkable, but for now we're simply going to have to keep looking up.