Physicist’s 150-year-old knot hypothesis could hold the key to why the universe exists
In 1867, Lord Kelvin envisioned atoms as intricate knots in the aether. This theory was quickly disproven, but it may have an enduring impact on cosmology.
Now, more than 150 years later, a team of Japanese physicists are resurrecting the concept to solve one of cosmology’s longest-standing riddles: Why does the universe teem with matter, but shun antimatter?
In a new study, the team posits that “cosmic knots” – topologically stable tangles in spacetime – emerged in the very early universe. These may have collapsed in ways that favored matter over antimatter. They have also left behind a unique hum in spacetime that future detectors might be able to record.
The mystery of matter-antimatter asymmetry
In theory, the Big Bang should have produced an equal amount of matter and antimatter. Each particle would then have destroyed its twin until only radiation remained. However, observations reveal a stark asymmetry: for every billion matter-antimatter pairs, one matter particle endured. The universe is overwhelmingly made of matter, which is responsible for visible structures ranging from atoms to galaxies, and quarks to quasars.
Despite its success in describing the fundamental building blocks of matter, the Standard Model of particle physics cannot account for the discrepancy seen between matter and antimatter. The answer to this question has long eluded the scientific community, but it strikes to the core of our very existence.
“This study addresses one of the most fundamental mysteries in physics: why our Universe is made of matter and not antimatter,” corresponding author Muneto Nitta, a professor at Hiroshima University explained in a press statement. “This question is important because it touches directly on why stars, galaxies, and we ourselves exist at all.”
Nitta and a team from Hiroshima University believe they have found a potential answer to the discrepancy, which is known as baryogenesis. The team combined a gauged Baryon Number Minus Lepton Number (B-L) symmetry with the Peccei–Quinn (PQ) symmetry. This showed that knots could form naturally in the earliest days of the universe, generating the surplus of matter.
The PQ symmetry addresses the strong CP problem. It also introduces axions, a leading dark matter candidate. The B-L symmetry, meanwhile, explains why neutrinos, or “ghost particles”, are capable of passing through matter almost undetected.
Listening to the universe’s gravitational wave chorus
This updated framework explains how, as the early universe cooled, phase transitions produced thread-like defects called cosmic strings. These are hypothetical cracks in spacetime that many scientists believe may still be out there. The combination of flux-carrying B-L strings and superfluid-like PQ vortices could allow for the emergence of stable knot solitons.
“Nobody had studied these two symmetries at the same time. Putting them together revealed a stable knot,” Nitta explained.
Eventually, the knots decayed due to quantum tunneling. This, in turn, produced heavy right-handed neutrinos, ultimately producing more matter than antimatter.
The team’s calculations showed that the typical mass of the heavy neutrinos and the energy released from knot collapse led to the universe reheating to 100 GeV. This is the precise threshold for lasting matter formation.
The scientists also theorize that the process altered the universe’s “gravitational wave chorus”, shifting it toward higher frequencies. They believe that future observatories such as the Laser Interferometer Space Antenna (LISA) in Europe, Cosmic Explorer in the United States, and the Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO) in Japan could one day record this subtle shift.
Source: Interesting Engineering
Physicist’s 150-year-old knot hypothesis could hold the key to why the universe exists