Ripples in space-time could explain the mystery of why the universe exists

Inflation stretched the tiny universe into a macroscopic size and turned cosmic energy into matter. But it likely created an equal amount of matter and antimatter. It's not clear why but the authors probe one theory that a phase transition after inflation led to a tiny bit more matter than anti-matter and also created cosmic strings which would produce slight ripples in space-time known as gravitational waves. (Image credit: R. Hurt/Caltech-JPL, NASA, and ESA Credit: Kavli IPMU - Kavli IPMU modified this figure based on the image credited by R.Hurt/Caltech-JPL, NASA, and ESA)

A new study may help answer one of the universe's biggest mysteries: Why is there more matter than antimatter? That answer, in turn, could explain why everything from atoms to black holes exists.

Billions of years ago, soon after the Big Bang, cosmic inflation stretched the tiny seed of our universe and transformed energy into matter. Physicists think inflation initially created the same amount of matter and antimatter, which annihilate each other on contact. But then something happened that tipped the scales in favor of matter, allowing everything we can see and touch to come into existence — and a new study suggests that the explanation is hidden in very slight ripples in space-time.

"If you just start off with an equal component of matter and antimatter, you would just end up with having nothing," because antimatter and matter have equal but opposite charge, said lead study author Jeff Dror, a postdoctoral researcher at the University of California, Berkeley, and physics researcher at Lawrence Berkeley National Laboratory. "Everything would just annihilate."

Obviously, everything did not annihilate, but researchers are unsure why. The answer might involve very strange elementary particles known as neutrinos, which don't have electrical charge and can act as either matter or antimatter.

One idea is that about a million years after the Big Bang, the universe cooled and underwent a phase transition, an event similar to how boiling water turns liquid into gas. This phase change prompted decaying neutrinos to create more matter than antimatter by some "small, small amount," Dror said. But "there are no very simple ways — or almost any ways — to probe [this theory] and understand if it actually occurred in the early universe."

But Dror and his team, through theoretical models and calculations, figured out a way we might be able to see this phase transition. They proposed that the change would have created extremely long and extremely thin threads of energy called "cosmic strings" that still pervade the universe.

However, when the team modeled this hypothetical phase transition under various temperature conditions that could have occurred during this phase transition, they made an encouraging discovery: In all cases, cosmic strings would create gravitational waves that would be detectable by future observatories, such as the European Space Agency's Laser Interferometer Space Antenna (LISA) and proposed Big Bang Observer and the Japan Aerospace Exploration Agency's Deci-hertz Interferometer Gravitational wave Observatory (DECIGO).

"If these strings are produced at sufficiently high energy scales, they will indeed produce gravitational waves that can be detected by planned observatories," Tanmay Vachaspati, a theoretical physicist at Arizona State University who wasn't part of the study, told Live Science.

Editor's note: This story was updated to correct the organizations in charge of LISA. It is run by the European Space Agency, not NASA, which is a collaborator on the project.

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Originally published on Live Science.

Yasemin is a staff writer at Live Science, covering health, neuroscience and biology. Her work has appeared in Scientific American, Science and the San Jose Mercury News. She has a bachelor's degree in biomedical engineering from the University of Connecticut and a graduate certificate in science communication from the University of California, Santa Cruz.