#leptogenesis

SNO+ | Sudbury Neutrino Observatory [Canada, 2025 | SNOLAB]

How Did The Matter In Our Universe Arise From Nothing?

“[Y]ou can start with a completely symmetric Universe, one that obeys all the known laws of physics and that spontaneously creates matter-and-antimatter only in equal-and-opposite pairs, and wind up with an excess of matter over antimatter in the end. We have multiple possible pathways to success, but it's very likely that nature only needed one of them to give us our Universe.

The fact that we exist and are made of matter is indisputable; the question of why our Universe contains something (matter) instead of nothing (from an equal mix of matter and antimatter) is one that must have an answer. This century, advances in precision electroweak testing, collider technology, and experiments probing particle physics beyond the Standard Model may reveal exactly how it happened. And when it does, one of the greatest mysteries in all of existence will finally have a solution.”

On one hand, we have all the stars, galaxies, gas, plasma, and the great cosmic web, all made out of matter and not antimatter. On the other hand, we have the laws of physics, which are almost completely symmetric between matter and antimatter, so much so that we’ve never created or observed more matter than antimatter in any reaction throughout human history. Yet somehow, such a reaction must have occurred, since the Universe exists as we see it: made of matter. So how did it get to be this way? How did a completely symmetric, early Universe give rise to a matter-dominated existence, complete with two trillion galaxies, each containing billions of stars? Believe it or not, we’re closer than ever before to answering this question, and the 21st century is poised to be the one where the answer to this existential question goes from speculative to solid.

LEGEND–200 | Gran Sasso National Laboratory [Italy, 2023]