Researcher discusses how gravitational waves hint at dark matter and Big Bang mysteries

Gravitational waves are ripples in space-time predicted by Einstein nearly a century ago and first detected in 2015. A new study led by Yanou Cui, an associate professor of physics and astronomy at the University of California, Riverside, suggests that an extremely simple form of matter could create a detectable gravitational wave background shortly after the Big Bang.

“This mechanism that produces a detectable gravitational wave background may help explain the puzzling gravitational wave signal recently captured by the Pulsar Timing Observatory,” Choi said. “Another intriguing implication is that this very same form of matter may be identified as dark matter, a mysterious substance that has puzzled scientists for decades and is thought to make up most of the mass in the universe.”

the study, Published in Physics Review Letteris paving the way to new fundamental physics using the largest laboratory in the universe itself. In the following Q&A, Choi answers some questions about his research.

What are these very simple forms of matter?

The simplest form of matter is a type of ultralight scalar field matter. Scalar means that the matter has no internal rotation (spin) and is similar to the Higgs boson. These forms of matter are extremely light, each with a mass one millionth or billionth of that of an electron. Because their mass is so small, they behave more like waves than particles and permeate the universe.

of Gravitational waves (GW) must have sufficient strength, Electromagnetic wavesCurrent experiments need to be sensitive enough to capture gravitational waves, and the waves must be within the frequency band that these experiments can sense. So far, technological limitations have meant that we can only detect a certain range of gravitational wave frequencies.

Could these simple forms of matter have generated a radiation background of gravitational waves that could only be detected immediately after the Big Bang?

Yes, gravitational waves are generated at the epoch when the expansion rate of the universe is roughly the same as the mass of the scalar field. Beyond this point, gravitational waves stop because internal mechanisms stop particle production. Just after the Big Bang, which is still just a split second afterwards, gravitational waves can be generated much later from astrophysical sources such as merging black holes, as observed by the Laser Interferometer Gravitational-Wave Observatory.

Why were these simple forms of matter unknown until now?

These don’t interact with known matter in any way other than through ultra-weak gravitational interactions. The gravitational wave signals that we’ve demonstrated are a way to detect these. But if these are dark matter, we know about them from the general evidence for dark matter. Again, they only interact gravitationally with visible matter, and very weakly, which is why we didn’t know much about them until now.

You say identifying this simple substance as dark matter is exciting because we finally know what dark matter is made of?

Yes, this is one of the highlights, but it is very difficult to produce detectable gravitational waves, and we have only just discovered a possibly simple form of matter. Dark matterThe ability to generate such gravitational waves is a major theoretical achievement, and as mentioned above, this mechanism also helps explain last year’s puzzling discovery of the timing of pulsars.