Gravitational waves, ripples in space-time first predicted by Einstein nearly a century ago, were finally detected in 2015.
Now, a new study led by Yanou Cui, an associate professor of physics and astronomy at the University of California, Riverside, suggests that simple forms of matter could create detectable gravitational waves soon after the Big Bang.
“This mechanism of creating detectable gravitational waves might help explain the mysterious gravitational wave signals recently captured by pulsar timing observatories,” Cui said.
“Another exciting possibility is that this same form of matter could be dark matter—the mysterious substance believed to make up most of the universe’s mass and which has puzzled scientists for decades.”
The study, published in Physical Review Letters, opens the door to discovering new fundamental physics using the universe as a giant laboratory. Here, Cui answers some questions about this groundbreaking research.
What Are These Simple Forms of Matter?
The simple form of matter in question is a type of ultra-light scalar field matter. “Scalar” means the matter has no internal spin, similar to the Higgs boson.
These particles are incredibly light, with masses a millionth or even a billionth of an electron’s mass. Due to their small mass, they behave more like waves than particles and fill the entire universe.
For gravitational waves to be detected, they need to be intense enough, similar to strong electromagnetic waves.
Additionally, they need to fall within the frequency ranges that current technology can detect. So far, only certain gravitational wave frequencies can be observed due to technological limitations.
Do These Simple Forms of Matter Generate Gravitational Waves Only Shortly After the Big Bang?
Yes, these gravitational waves are produced during a specific period when the universe’s expansion rate matches the mass of the scalar field.
This production stops after a certain point because the internal mechanism shuts down particle production.
When we say “shortly after the Big Bang,” it’s still a fraction of a second after it happened. Much later, gravitational waves can also be produced by events like black hole mergers, which have been observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO).
Why Were These Simple Forms of Matter Not Known Until Now?
These forms of matter don’t interact with known matter except through very weak gravitational interactions.
The gravitational wave signals we demonstrated provide a way to detect them.
If these forms of matter are indeed dark matter, we’ve known about their existence from general evidence of dark matter. However, because they only interact with visible matter through gravity, which is extremely weak, we haven’t known much about them until now.
Why Is It Exciting to Identify This Simple Form of Matter as Dark Matter?
Identifying this simple form of matter as dark matter would be a major breakthrough because it would finally reveal what dark matter is made of.
Additionally, it’s remarkable that this simple form of matter can produce detectable gravitational waves.
This is a significant theoretical achievement. Moreover, the puzzling pulsar timing findings from last year could be explained by this mechanism.
This new study led by Yanou Cui provides fascinating insights into the early universe and the nature of dark matter.
By exploring how simple forms of matter can generate gravitational waves, scientists are uncovering new ways to understand the universe’s mysteries. This research highlights the exciting potential for future discoveries in fundamental physics and cosmology.
