Our universe is much more “homogenous” than would be expected, scientists have said after producing a detailed map of matter in the cosmos.
The findings could suggest that there is something deeply strange about our understanding of the universe, which could require a new kind of physics or fundamentally alter our understanding of dark matter.
The new results come from the Kilo-Degree Survey, or KiDS, which uses the European Southern Observatory’s Very Large Telescope to map the distribution of matter across our universe. So far, it has charted roughly 5% of the extragalactic sky, from an analysis of 31 million galaxies that are as much as 10 billion light years away.
Producing such a detailed map allows scientists to examine the “clumpiness” of how galaxies are distributed through the cosmos. That allows researchers to build up a picture of all matter in the universe, of which some 90 per cent is invisible, made up of dark matter and tenuous gas.
That in turn allows astronomers to watch the processes that gradually make the universe less homogenous, or evenly distributed: parts of the universe that have more than the usual mass attract matter from their areas around them, which makes them less similar to those other parts. The expansion of the universe counteracts that growth.
Since both of those processes are driven by gravity, they can be used to test the standard model of cosmology and the assumptions underlying our physics. Since that allows us to predict the way that the variations in density would change as the universe aged, those predictions can be put to the test by examining how homogenous or differently clumped the universe really is.
The new study found, however, that those predictions were wrong. The universe is almost 10 per cent more homogenous than our current understanding of physics suggests.
Like other recent findings, such as the mysterious discrepancy in the expansion rate of the universe or Hubble constant, the data could be yet another crack in the standard model of physics, and could require us to rethink our picture of the universe.
“The question is whether these can be solved with a small adjustment, for example with a somewhat more complex behavior of dark matter than the simple hypothesis of totally inert ‘cold dark matter’,” said Tilman Tröster, from the University of Edinburgh, in a statement.
But the change could be far more fundamental, suggesting for instance that Einstein’s general theory of relativity could need replacing.
The researchers behind the new observations were keen to stress that their focus was on accurately taking the measurements, rather than making any leaps about what they could tell us about the universe – or what they could tell us about what we have got wrong about it.
“As an observing cosmologist, you try to remain impartial and make the measurements as accurate as possible without theoretical prejudices,” said Hendrik Hildebrandt from Ruhr University Bochum.
“One thing is clear: we live in exciting times!”
Astronomers will need more data to be sure that their results are correct. There is still a one in 1,000 chance that the results came about because they looked at an especially strange part of the universe.
That extra data will arrive soon, when the final “legacy” KiDS map is published. That will be 30 per cent larger than the current one, and will include all of the KiDS observations, allowing for further study.
Astronomers around the world are also launching new projects to map the distribution of matter – and dark matter – through the universe, which could shed light on the current findings as well as potentially offering some explanation for them.