Universe Expanding Faster Than Expected

This image from the Hubble Space Telescope features the spiral galaxy Markarian 1337, which is roughly 120 million light-years away from Earth. In 2006, astronomers saw a certain kind of supernova explode in this galaxy, providing researchers with some of the data nee...IMAGE BY ESA/HUBBLE & NASA, A. RIESS ET AL.

The latest measurements with the Hubble Space Telescope suggest the universe is expanding faster than scientists' models predict—a hint that some unknown ingredient could be at work in the cosmos.

It’s one of the biggest puzzles in modern astronomy: Based on multiple observations of stars and galaxies, the universe seems to be flying apart faster than our best models of the cosmos predict it should. Evidence of this conundrum has been accumulating for years, causing some researchers to call it a looming crisis in cosmology.

Now a group of researchers using the Hubble Space Telescope has compiled a massive new dataset, and they’ve found a-million-to-one odds that the discrepancy is a statistical fluke. In other words, it’s looking even more likely that there’s some fundamental ingredient of the cosmos—or some unexpected effect of the known ingredients—that astronomers have yet to pin down.

“The universe seems to throw a lot of surprises at us, and that’s a good thing, because it helps us learn,” says Adam Riess, an astronomer at Johns Hopkins University who led the latest effort to test the anomaly.

The conundrum is known as the Hubble tension, after astronomer Edwin Hubble. In 1929 he observed that the farther a galaxy is from us, the faster it recedes—an observation that helped pave the way toward our current notion of the universe starting with the big bang and expanding ever since.

Researchers have tried to measure the universe’s current rate of expansion in two primary ways: by measuring distances to nearby stars, and by mapping a faint glow dating back to the infant universe. These dual approaches provide a way to test our understanding of the universe across more than 13 billion years of cosmic history. The research has also uncovered some key cosmic ingredients, such as “dark energy,” the mysterious force thought to be driving the universe’s accelerating expansion.

But these two methods disagree on the universe’s current expansion rate by about 8 percent. That difference might not sound like much, but if this discrepancy is real, it means the universe is now expanding faster than even dark energy can explain—implying some breakdown in our accounting of the cosmos.  READ MORE...