Weird quantum objects known as Q balls could explain why we exist
Theoretical “lumps” called Q balls formed in the moments after the Big Bang.
One of the most puzzling cosmological mysteries is why the universe contains far more matter than antimatter, and thus why we exist. A group of theoretical physicists claims to have discovered the solution. All they have to do is detect gravitational waves emitted by bizarre quantum objects known as Q balls.
Every conventional matter particle has an antimatter partner with opposing characteristics, and when matter and antimatter interact, the two annihilate each other. That fact makes our existence a mystery, because cosmologists believe that at the beginning of the universe, equal amounts of matter and antimatter were created; those matter and antimatter partners should have all annihilated each other, leaving the universe empty of any matter at all. But matter exists, and researchers are slowly uncovering the reasons why.
Q balls, hypothesized “lumps” that formed moments after the Big Bang before the cosmos inflated rapidly like a balloon, could be one possible explanation. These objects would have their own matter-antimatter asymmetry, which means that each Q ball would have differing amounts of matter and antimatter.
When these Q balls “popped,” they released more matter than antimatter, causing gravitational ripples in space-time. According to a paper published in the journal Physical Review Letters, if these objects did exist, we could detect them using gravitational waves.
The fabric of the cosmos, according to particle physics, is covered by various quantum fields, each of which describes some feature (such as electromagnetism) at all points in space. These fluctuations give rise to the basic particles that constitute our physical reality. Consider a trampoline with a bowling ball in the center to demonstrate how these fields work.
The bowling ball’s shape on the trampoline reflects how much energy each location on the field contributes to the universe — the closer to the center depression, the more potential energy. The “shape” of a field determines its behavior, just as the shape of a trampoline’s surface governs how a marble glides around a bowling ball.
One theory, proposed in 1985 by Princeton University physicists Ian Affleck and Michael Dine, seeks to explain the universe’s matter-antimatter asymmetry by claiming that the fields that governed the universe’s early balloon-like inflation had to be relatively shallow in order for that inflation to happen — in other words, the bowling ball in the center of the trampoline wasn’t very heavy. And, much as a marble rolling around a bowling ball’s shallow depression doesn’t gain or lose much speed, the field’s shape meant that the energy driving the universe’s inflation stayed constant.
Because inflation requires this uniformity, the field cannot interact with other fields (essentially other trampolines) too strongly in order to produce particles. However, according to Affleck and Dine’s theory, this field interacted with others in such a way that more matter particles were formed than antimatter particles. The field contained such particles in “lumps” to retain that consistent shape.
“These lumps are called Q balls. They’re just lumps of field,” said lead author Graham White, a physicist at the Kavli Institute for the Physics and Mathematics of the Universe.
These Q balls persisted as the universe expanded. “And eventually, they become the most important part of the universe in terms of how much energy is in them compared to the rest of the universe.”
But they don’t last forever. When the Q balls disappear, filling the cosmos with more matter than antimatter, they do so with such power that sound waves are generated. According to the study, the sound waves operate as a cause for the ripples in space-time known as gravitational waves. If gravity waves exist, they can be detected by detectors like NASA’s Laser Interferometer Space Array (LISA) and the underground Einstein Telescope, according to White’s team.
This isn’t the only theory to explain the matter-antimatter asymmetry of the universe. But White said that’s okay since we’re at an interesting point when we can probably prove one of these paradigms is correct. “[There are] a whole bunch of machines we’re turning on in the 2030s which can hopefully see these gravitational waves,” White said.
“If we do see them, that’s really exciting.” Even if detectors fail to detect these Q-ball ripples, that’s good news since it suggests that simpler hypotheses are more likely to be correct — and those are easier to test, he says. “So in some ways it’s a bit of a no-lose.”