Space-time ripples could help explain universe’s mysterious expansion

Dec. 28 (UPI) — Scientists have found most of the universe’s missing matter and explained how the early universe became reionized. Yet several of the cosmos’ mysteries remained unsolved — like why the universe continues to expand faster and faster over time.

The force explaining the universe’s accelerating expansion has long been considered one of the cosmos’ most important missing components — the missing link in the currently not-quite-right theory of the universe.

Some physicists estimate gravity is the secret sauce that ties it all together.

Now, in a new paper published this month in the journal Physical Review D, researchers suggest gravity’s role as cosmic binder could be revealed by slight ripples in the space-time continuum.

Scientists have previously offered all kinds of theories for the universe’s accelerating expansion.

“Many of these rely on changing the way gravity works over large scales,” study co-author Jose María Ezquiaga said Monday in a news release.

“So gravitational waves are the perfect messenger to see these possible modifications of gravity, if they exist,” said Ezquiaga, a NASA Einstein postdoctoral fellow in the Kavli Institute for Cosmological Physics at the University of Chicago.

When two large cosmic objects collide, like a pair of black holes, the crash creates ripples in the space-time fabric of the universe. These ripples, called gravitational waves, can be detected using LIGO, the Laser Interferometer Gravitational-Wave Observatory.

According to the new study, if these gravitational waves collide with a supermassive black hole or mass of galaxies, their signature should become altered.

If gravity was not a constant, but instead characterized by local differences, the change in gravity would be reflected in the gravitational waves’ altered signature.

Some scientists suggest a missing particle might explain the universe’s accelerating expansion. This extra particle would create a background “medium” around large objects, according to scientists.

If a gravitational wave collided with this medium, new waves would be generated, influencing the signature of the initial space-time ripple.

The gravitational wave, one intercepted by LIGO, might carry an “echo” of this collision and the particle responsible for the wave’s altered signature.

In the new paper, Ezquiaga and company lay out plans for identifying such effects in future LIGO datasets.

“In our last observing run with LIGO, we were seeing a new gravitational wave reading every six days, which is amazing. But in the entire universe, we think they’re actually happening once every five minutes,” Ezquiaga said. “In the next upgrade, we could see so many of those — hundreds of events per year.”