If our current understanding of the universe is correct, it should not even exist. The very fact that planets, stars and galaxies exist undercuts one of the most fundamental premises of particle physics — that the Big Bang, which created our universe 13.8 billion years ago, created equal amounts of matter and antimatter.
If this really happened, it begs the question — why, given that matter and antimatter particles annihilate each other when they collide, is there something rather than nothing in the universe? Why do you and I exist when the laws of physics, as we know them, seem to dictate that the cosmos should be nothing but a wasteland strewn with leftover energy?
Obviously, as attested by the fact that we exist, there is a fundamental asymmetry between matter and antimatter. Either significantly more matter was created by the Big Bang, or there is a fundamental, as-of-yet-undiscovered asymmetry between matter particles and their antimatter counterparts — one that would have given the former an edge over the latter in the race for survival.
On Saturday, a team of researchers at the international T2K Collaboration in Japan announced that they had detected evidence of such matter-antimatter asymmetry — in this particular case, an asymmetry between neutrino and antineutrino oscillation.
Neutrinos — once described as “the most tiny quantity of reality ever imagined by a human being” — are perhaps the most exotic and least understood of all known subatomic particles. Produced by the decay of radioactive elements, these particles rarely, if ever, interact with matter, making them extremely hard to detect and study. Every second, billions of neutrinos travelling at nearly the speed of light pass through Earth.
Neutrinos, and their antimatter counterpart antineutrinos, exist in three types, or “flavors” — electron, muon and tau. Each of these flavors can change into the other, “oscillating” spontaneously as the particles travel over long distances.
At the T2K experiment, researchers looked for a difference between neutrinos and antineutrinos oscillations. Their findings, announced at the International Conference on High Energy Physics in Chicago, suggest that there are — more muon neutrinos were found changing into electron neutrinos than muon antineutrinos changing into electron antineutrinos.
The researchers, who had expected to detect 23 electron neutrinos and seven electron antineutrinos, observed 32 electron neutrinos and 4 electron antineutrinos.
However, given that the results were derived from relatively few data points, there is still a one in 20 chance that random chance may have caused the difference.
If confirmed with a greater level of certainty, this would point to a violation of charge-parity (CP) symmetry in neutrinos. CP symmetry tells us that a system remains unchanged even if two fundamental properties — charge and parity, which refers to a 180-degree flip in spatial configuration — are reversed. If a violation of CP symmetry is confirmed, it would not only hint at the existence of physics beyond the Standard Model — a theory of almost everything — it would also help us understand why the universe is completely devoid of antimatter.
“This is an important first step towards potentially solving one of the biggest mysteries in science,” Morgan Wascko from the Imperial College London and the international co-spokesperson for the T2K experiment, said in a statement. “T2K is the first experiment that is able to study neutrino and antineutrino oscillation under the same conditions, and the disparity we have observed is, while not yet statistically significant, very intriguing.”