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Physics + MathPhysics & Math

Universe Is Expanding Faster Than Expected, and We Don’t Know Why

ByTim De ChantNOVA NextNOVA Next

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In what may be the biggest correction of all time, astronomers have adjusted the rate of expansion of the universe.

Stars and galaxies are flying apart 9% faster than previously thought, and physicists don’t know what’s behind it. The new estimate was made by studying the distance from the Hubble Space Telescope to 2,400 stars and 300 supernovae in 19 different galaxies. Physicists and astronomers now say the universe’s rate of expansion is 45.5 miles per second per megaparsec. (One megaparsec is 3.26 million light years.)

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UGC 9391
Stars and supernovae in galaxy UGC 9391 were among those used to calculate the rate of expansion of the universe.

The new figure doesn’t jibe with previous estimates made using data collected on the cosmic microwave background, the radiation left over from the Big Bang. The mismatch has astrophysicists scratching their heads.

“You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,” Adam Riess, a professor of physics at Johns Hopkins University, said in a statement . “But now the ends are not quite meeting in the middle, and we want to know why.”

So far, they have a few candidates. One is that dark energy is more powerful than we thought. Another is that dark matter may have some unknown property that’s driving the expansion. And a third suggests that it might be due to an undiscovered particle that’s a type of dark radiation.

While the new estimate does suggest there’s a part of physics our current models can’t explain, it doesn’t mean we’re completely in the dark. Here’s Josh Sokol,

reporting for New Scientist :

Hints of this problem have been brewing since 2011 , and the most recent results have only made the problem worse. Still, we could do away with the issue if one of the two benchmark measurements is just a little bit wrong, says David Spergel of Princeton University in New Jersey.

“Right now I think the discrepancy is at the level of, ‘This is interesting, it’s worth thinking about’,” he says. “But it’s not yet, ‘Let’s panic, we know that our current model must be wrong.’”

Even if the new figure doesn’t lead to a new model for the universe, scientists on the project say that solving the discrepancy could shed light on the dark parts of nature—dark energy, dark matter, and dark radiation.

Photo credit: NASA, ESA, and L. Frattare (STScI)