For many decades, it’s been a premise of cosmology – the science of the universe as a whole – that our universe is the same in all directions. It may look clumpy on small scales, for example, the scale of our solar system or Milky Way galaxy or even Local Group of galaxies. But on the largest possible scales, the scale of the whole universe, all is expected to be uniform. This assumption fuels the vast majority of calculations made about our universe. If it’s not true, our whole picture of the universe might be wrong. Now scientists from University College London and Imperial College London have put this assumption through what they say is “its most stringent test yet” and found only a 1 in 121,000 chance that the universe is not the same in all directions. Phew.
This work was published in the peer-reviewed journal Physical Review Letters in September 2016.
To test the idea of a universe with “no direction,” as they describe it, these scientists used maps of the cosmic microwave background (CMB) radiation: the oldest light in the universe created shortly after the Big Bang. ESA’s Planck satellite made the measurements that created the maps between 2009 and 2013, which, the scientists said in a statement:
… provide a picture of the intensity and, for the first time, polarization (in essence, the orientation) of the CMB across the whole sky.
Previously, scientists had looked for patterns in the CMB map that might hint at a rotating universe.
The new study considered the widest possible range of universes with preferred directions or spins and determined what patterns these would create in the CMB. For example, a universe spinning about an axis would create spiral patterns, while a universe expanding at different speeds along different axes would create elongated hot and cold spots.
Dr Stephen Feeney, from the Department of Physics at Imperial, worked with a team led by Daniela Saadeh at University College London to search for these patterns in the observed CMB. The results show that none were a match, and that the universe is most likely “directionless,” these scientists said. Feeney explained:
This work is important because it tests one of the fundamental assumptions on which almost all cosmological calculations are based: that the universe is the same in every direction. If this assumption is wrong, and our universe spins or stretches in one direction more than another, we’d have to rethink our basic picture of the universe.
We have put this assumption to its most exacting examination yet, testing for a huge variety of spinning and stretching universes that have never been considered before. When we compare these predictions to the Planck satellite’s latest measurements, we find overwhelming evidence that the universe is the same in all directions.
Lead author Daniela Saadeh from University College London added:
You can never rule it out completely, but we now calculate the odds that the universe prefers one direction over another at just 1 in 121,000. We’re very glad that our work vindicates what most cosmologists assume.
For now, cosmology is safe.
Bottom line: Scientists at University College London and Imperial College London tested the assumption that, on the largest scales, our universe has no direction. They found only a 1 in 121,000 chance that the universe is not the same in all directions.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.