A Round Universe Would Be Bad News For Physicists

Hubble image of galaxy clusters and stars, including the PLCK G004.5-19.5 cluster discovered by Planck. (Image: ESA/Hubble)

Scientists analysing data from a defunct satellite say we should all consider that our universe might be round, rather than flat. The consequences, they explain in a new paper, could be crisis-inducing.

Current theories of the universe, which describe its age, size, and how it evolves over time, are built around a flat spacetime. A new paper reiterates that data from the final Planck satellite release might be better explained by a round universe than a flat universe. The authors write that the consequences of assuming a flat universe when the universe is actually round could be dire.

“The point isn’t really that the universe is closed,” or round, the study’s corresponding author Alessandro Melchiorri from Sapienza University of Rome told Gizmodo. Instead, he explained that if Planck data seems to prefer a closed universe, then the potential consequences and how they might butt up against cosmologists’ most popular theory of the universe must be “seriously investigated,” lest the theory fall apart.

The universe might come in one of three shapes: open, closed, or flat. Parallel lines in an open universe will always move farther apart; parallel lines in a closed universe will eventually meet (and single lines will eventually meet up with themselves); and parallel lines in a flat universe will stay parallel forever.

Scientists already knew from Planck satellite data that mass in the universe was warping the the cosmic microwave background radiation, the farthest radiation our telescopes can see, more than the standard theory of cosmology predicted. Perhaps this is a statistical fluctuation or something wrong with the way scientists are interpreting the data—but it would be an incredibly unlikely statistical fluctuation, with less than 1 per cent odds. Instead, the team led by Eleonora Di Valentino at the University of Manchester in the United Kingdom posited that the observation could be explained simply by a closed universe. This change, however, would put plenty of other measurements out of agreement with Planck’s data.

This tension falls on the heels of another important issue with the Planck data, called the Hubble tension. Experiments measuring the cosmic microwave background can’t seem to agree with experiments measuring closer objects when it comes to how fast the universe is expanding.

This new paper “would be a *really* big deal if true,” Dan Hooper, head of the Theoretical Astrophysics Group at the Fermi National Accelerator Laboratory told Gizmodo in an email. But he wasn’t completely swayed. “Overall, my view is that in order to convince me of something that is this surprising, one would have to present some very compelling evidence. At this time, the evidence that is available doesn’t reach this high standard.”

Others highlighted the fact that it may be too early to toss out what many scientists consider to be a core fact of the universe. “There are still things we don’t understand in the systematics,” meaning potential sources of error from the act of making the measurement, said Renée Hložek, professor at the Dunlap Institute for Astronomy & Astrophysics at the University of Toronto. She told Gizmodo that physicists need to be much surer about whether the issue arises from systematic errors or not before she’ll be convinced.

After all, aside from the Planck data, the lambda-CDM model, which is the standard model of the universe, seems to work really well. Using just six parameters, it seems to fit our observations of the universe, albeit a flat universe, nearly perfectly.

Melchiorri told Gizmodo that questioning prevailing theories is simply science, especially when, to his group, such a discrepancy appears to exist. “The point is to have an open mind,” he said. Several proposed experiments both on the ground and in space would take more measurements of the cosmic microwave background and either wipe out existing discrepancies as statistical flukes or show scientists that the universe is truly behaving in an unexpected manner.

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