The fate of the universe just became a little less certain. Thatās due to a disagreement between a map of the early universe and a new map of todayās universe. If the mismatch stands the test of future measurements, we might have to rewrite physics. But that is a pretty big if.
The , which are part of the ongoing Dark Energy Survey (DES), charted the distribution of matter across 26 million galaxies in a large swathe of the southern sky.
āThis is one of the most powerful pictures of the universe today that weāve ever had,ā says at the University of Chicago, who is a part of the 400-person DES collaboration but wasnāt involved in this work.
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It is so powerful because knowing the distribution, or clumpiness, of galaxies helps us better understand the cosmic game of tug of war as dark energy ā a mysterious force that causes the universe to accelerate ā pulls each galaxy apart, and dark matter ā a theoretical but still unseen form of matter ā pushes each galaxy together.
Cosmic selfie
These results are based on data from the 4-metre Victor M. Blanco Telescopeās first observing season for the DES, which lasted a mere six months. The survey is slated to run for five years, meaning that DESās measurements can only improve. But its first results have already revealed a tension with earlier findings.
What we know makes up 5 per cent of the universe ā what is the other 95 per cent made of?
In 2013, astronomers revealed the results of charting the universeās dark contents across the early cosmos ā 380,000 years after the big bang, to be exact ā with the help of the Planck satellite.
āWeāve had really good baby pictures of the universe and now, with this, itās like the first time weāve had really good selfies,ā Scolnic says.
Comparing the two allows us to piece together how the universe evolved from its early state to the present ā and make predictions about the future. Many astronomers believe that dark energy is a constant force and didnāt think these results would change over time. DESās first findings, however, might suggest otherwise.
Take dark matter, for example. Planck pegged it at 34 per cent of the energy of the early universe, but DES finds that today it only amounts to 26 per cent. That could mean dark matter is losing the cosmic game of tug of war to dark energy ā a result that would force a radical rewrite of physics.
āIf [the two different answers] donāt go away, weāre seeing the first signs of what could be a very serious problem in the cosmological model,ā says at Princeton University.
Balancing act
Astronomers are hesitant to make too grandiose a claim based on the first data set. Statistically speaking, thereās only a slight tension between the results relating to todayās universe and the early universe. But Scolnic points out that this tension is one in a line of many tensions. Results from the South Pole Telescope, for example, similarly disagree with Planck.
āItās hard to believe that this is a coincidence,ā Scolnic says. And if it isnāt a coincidence, the results could mean that dark energy actually grows stronger with time ā an idea that has wild implications for our future.
Before, we assumed that although the universe would continue to expand, galaxies would remain forever bound. But should dark energy increase with time, then one day galaxies ā plus stars, planets and even the atoms within us ā will also expand until they are torn to shreds.
āThat would be a disturbing conclusion,ā Spergel says. But he advises against panicking just yet.
The latest mismatch could mean that one or both of the measurements is wrong. If so, it might disappear with more data. Then again, it might not. And the fate of the universe hangs in the balance.
Read more: Dark energy could signal collapse of the universe
Article amended on 8 August 2017
We corrected the contribution of dark matter to the make-up of the early universe
