Yogesh

“During the early universe, when everything was a seething cauldron of energy, matter and antimatter would spontaneously pop in and out of existence, transforming back and forth into photons—light energy. But as the universe expanded and cooled, there would be one last time that a photon became a matter-antimatter particle pair. Except that one in a hundred million of the photons mysteriously created a lone particle without an annihilation partner, which would evermore remain adrift in space with an empty dance card. The rest would find partners and annihilate, becoming photons one last time. That one-in-a-hundred-million particle was made of matter, with no antimatter particle to match it. Nobody knows how or why that happened. But it did, leaving us with a universe of a hundred million photons for every particle of matter. And no antimatter. Without that tiny asymmetry, the universe would contain only photons and no matter, and we wouldn’t exist. So we’re glad for the asymmetry, but the question remains, what caused it? Where did the antimatter particles go, if in fact they were created at all? And most importantly, did Aliens gather them up and create an anti-universe of their own? On the off chance that your first encounter is with an Alien made entirely of antimatter, always carry something in your pocket that you can toss. A coin will do. If, upon catching it, the Alien spontaneously explodes with the power of two hundred million sticks of dynamite, then it was made of antimatter. Otherwise, you’re good to go.”
― Neil deGrasse Tyson, Take Me to Your Leader: Perspectives on Your First Alien Encounter