In 1867, Lord Kelvin had a strange idea. Atoms, he proposed, were nothing more than tiny knots tied in an invisible substance called the aether. Picture it like twisting a rubber band into loops that somehow hold their shape forever. Different elements, he reasoned, were simply different kinds of knots.
Scientists quickly proved him wrong. Atoms turned out to be made of subatomic particles, not twists in space. Kelvin’s elegant vision was tossed aside, a curious footnote in the history of physics.
But what if he wasn’t entirely off the mark?
A team of Japanese physicists recently dusted off Kelvin’s forgotten concept and gave it a modern makeover. Their work, published in Physical Review Letters, suggests that knotted structures may have existed in the earliest moments after the Big Bang. And these “cosmic knots” might hold the answer to a question that has puzzled scientists for decades. Why does anything exist at all?
A Universe That Shouldn’t Be Here
Here’s a problem that keeps physicists awake at night. When the Big Bang happened, it should have created equal amounts of matter and antimatter. Every particle of matter has an antimatter twin with the same mass but opposite charge. When they meet, both vanish in a flash of pure energy.
If the Big Bang played fair, every bit of matter would have found its antimatter partner. Everything would have been annihilated. Nothing would remain but a sea of radiation drifting through space. No stars. No planets. No galaxies. No you. Yet here we are.
Look around, and you’ll notice something strange. Almost everything in the observable universe is made of matter. Antimatter is vanishingly rare. Simple math tells us why we exist at all. For every billion matter-antimatter pairs created in the early universe, just one extra particle of matter survived. One in a billion. That tiny surplus became every atom in every star, every planet, every living thing.
“This study addresses one of the most fundamental mysteries in physics: why our Universe is made of matter and not antimatter,” said Muneto Nitta, a professor at Hiroshima University’s International Institute for Sustainability with Knotted Chiral Meta Matter. “This question is important because it touches directly on why stars, galaxies, and we ourselves exist at all.”
Our best theory of particle physics, called the Standard Model, cannot explain where that extra matter came from. Its predictions fall short by a staggering margin. Finding the source of this imbalance, a process scientists call baryogenesis, remains one of the biggest unsolved puzzles in all of physics.
Enter Two Forgotten Symmetries
Nitta and his colleagues, Minoru Eto of Yamagata University and Yu Hamada of Germany’s Deutsches Elektronen-Synchrotron, believe they’ve stumbled onto something important. By combining two extensions of standard physics that others had studied separately, they found a way for stable knots to form in the fabric of the early universe.
One extension is called the Peccei-Quinn symmetry. It was invented to solve a different puzzle entirely, explaining why neutrons don’t behave the way theory predicts they should. As a bonus, it predicts the existence of a hypothetical particle called the axion, which happens to be a leading candidate for dark matter.
Another extension involves something called B-L symmetry, short for Baryon Number Minus Lepton Number. It explains why neutrinos, those ghostly particles that can pass through entire planets without bumping into anything, have mass at all. Both ideas have been around for decades. But nobody had thought to put them together. “Nobody had studied these two symmetries at the same time,” Nitta said. “That was kind of lucky for us. Putting them together revealed a stable knot.”
Cracks in Space Itself
To understand how these knots formed, imagine the universe just after the Big Bang. Everything was unimaginably hot and dense. As the cosmos expanded and cooled, it went through a series of dramatic shifts, similar to water freezing into ice.
But when water freezes unevenly, you get cracks. Something similar may have happened to the universe. As different symmetries broke down at different times, the process may have left behind thin, thread-like defects in spacetime itself. Scientists call these hypothetical objects cosmic strings.
Picture a crack running through a crystal, except this crack runs through the fabric of reality. Cosmic strings would be thinner than a proton, yet incredibly dense. Just an inch of cosmic string could weigh as much as a mountain. As the universe grew, a tangled web of these strings would have stretched and twisted, like spaghetti being pulled apart.
Now here’s where it gets interesting. Breaking the B-L symmetry produced one type of string that acts like a magnetic tube. Breaking the Peccei-Quinn symmetry produced a completely different type, a superfluid vortex with no magnetic properties at all.
You might think such different objects would have nothing in common. But their differences are exactly what allowed them to fit together. One type of string gave the other something to grab onto. In return, the second type pumped electric charge into the first, fighting against the tension that would normally cause loops to snap apart. When these two types of strings are linked together, they create something stable. A cosmic knot.
When Knots Ruled the Cosmos
Radiation loses energy as the universe expands. Light waves stretch out, becoming weaker over time. But the knots didn’t fade so easily. Like ordinary matter, their energy density dropped much more slowly than radiation’s.
At some point in cosmic history, the knots took over. Their stored energy outweighed everything else in the universe. For a brief window, perhaps just a flash on cosmological timescales, knots were the dominant force driving how the universe evolved. But nothing lasts forever, especially not in the violent conditions of the early cosmos.
A Quantum Magic Trick
Eventually, the knots came undone through one of nature’s strangest phenomena. Quantum tunneling allows particles to pass through barriers they shouldn’t be able to cross, like a ball rolling through a wall instead of bouncing off it. Through this process, the knots collapsed. And when they did, they released a shower of particles.
Among the debris were heavy right-handed neutrinos, massive cousins of the ghostly neutrinos we detect today. These particles are special because when they decay, they don’t treat matter and antimatter equally. They have a slight preference for creating matter over antimatter.
As these heavy neutrinos broke down into lighter particles like electrons and photons, they passed along that tiny bias. A cascade of decays followed, each one tipping the scales just a bit more toward matter. Eventually, that microscopic preference added up to the matter-filled universe we see today.
Yu Hamada, one of the study’s co-authors, put it in memorable terms. “In this sense, they are the parents of all matter in the universe today, including our own bodies, while the knots can be thought of as our grandparents.”
Running the Numbers
Good ideas in physics need more than poetry. They need math that actually works out. When the researchers traced through their model’s predictions, they tracked how many right-handed neutrinos the knots would produce, how massive those neutrinos would be, and how much heat their decays would dump back into the universe.
Plugging in realistic numbers, they assumed the heavy neutrinos weighed about 10¹² giga-electronvolts, roughly a trillion times heavier than a proton. If the knots transferred most of their stored energy into creating these particles, the model predicted the universe would reheat to about 100 giga-electronvolts.
That number turns out to be significant. It matches the temperature below which certain reactions in the early universe would have shut down permanently. Below 100 GeV, the specific processes that convert an imbalance in neutrinos into an imbalance in ordinary matter stop working. Any later, and the universe would have missed its window.
In other words, the model naturally hits the sweet spot. It creates matter at exactly the right moment, in exactly the right way.
Listening for Echoes of Ancient Knots
Most theories about baryogenesis have a frustrating feature. They describe events so far in the past, at energies so high, that testing them seems nearly impossible. But the cosmic knot model offers a rare opportunity.
Reheating the universe to 100 GeV would have left a mark on something scientists can actually detect. Gravitational waves, ripples in spacetime itself, carry information about the conditions that created them. A knot-dominated era followed by sudden collapse would have shifted the background hum of gravitational waves toward higher frequencies.
Several detectors planned for the coming decades could pick up that signal. LISA, a European space-based observatory, will listen for gravitational waves from its orbit. Cosmic Explorer in the United States and DECIGO in Japan will add their own ears to the search.
If the knots really existed, their gravitational signature might still be echoing through the cosmos, waiting for us to tune in.
Minoru Eto pointed out another encouraging feature of the theory. Cosmic strings and knots belong to a category called topological solitons. Their stability comes from mathematical properties that remain unchanged no matter how you twist or stretch them. Because the underlying math is robust, the team’s conclusions don’t depend on getting every detail of their model exactly right.
An Old Vision Finds Its Moment
For now, the cosmic knot theory remains exactly that, a theory. Nobody has detected cosmic strings, let alone the specific knotted configurations the researchers describe. But the model offers clear predictions and, crucially, ways to test them.
Nitta outlined the road ahead. Researchers will need to refine simulations of how knots form and decay. They’ll need to calculate more precisely what signals to look for. And they’ll need to wait for the next generation of gravitational wave detectors to come online.
If those detectors find the predicted signature, it would be a stunning confirmation that Lord Kelvin’s discarded idea, reimagined for the modern era, helped explain why anything exists at all. Our grandparents, it turns out, may have been knots.
