WASHINGTON — The universe is expanding faster than it used to, meaning it's about a billion years younger than we thought, a new study by a Nobel Prize winner says. And that's sending a shudder through the world of physics, making astronomers rethink some of its most basic concepts.

At issue is a number called the Hubble constant, a calculation for how fast the universe is expanding. Some scientists call it the most important number in cosmology, the study of the origin and development of the universe.

Using NASA's Hubble Space Telescope, Johns Hopkins University astronomer Adam Riess concluded in this week's Astrophysical Journal that the figure is 9% higher than the previous calculation, which was based on studying leftovers from the Big Bang.

The trouble is, Riess and others think both calculations are correct.

Confused? That's OK, so are the experts.

They find the conflict so confounding that they are talking about coming up with "new physics," incorporating perhaps some yet-to-be-discovered particle or other cosmic "fudge factors" like dark energy or dark matter.

"It's looking more and more like we're going to need something new to explain this," said Riess, who won the 2011 Nobel in physics.

NASA astrophysicist John Mather, another Nobel winner, said this leaves two obvious options: "1. We're making mistakes we can't find yet. 2. Nature has something we can't find yet."

Even with the discovery, life continues on Earth the way it always has. But to astrophysicists trying to get a handle on our place in this expanding universe, this is a cosmic concern.

To come up with his measurement of the Hubble constant, Riess looked to some not-so-distant stars.

Riess observed 70 Cepheid stars — stars that pulse at a well-observed rate — calculated their distance and rate, and then compared them with a certain type of supernovae that are used as measuring sticks. It took about two years for the Hubble telescope to make these measurements, but eventually Riess calculated an expansion rate of 74.

Using that 74 figure means the universe is somewhere between 12.5 billion and 13 billion years old. That's much younger than the established estimates of 13.6 billion to 13.8 billion.

"Hey, it's good news. Everybody likes to look younger," Riess said.

In 2013, the European Planck satellite helped scientists come up with a much slower expansion rate of about 67, but that was done in an entirely different, more complicated and less direct way and by looking at a much earlier time, when the universe was just a toddler.