The universe shouldn't be here. Everything scientists know about particle physics, summed up in a theory called the Standard Model, suggests that the big bang should have created equal quantities of matter and antimatter. A mirror version of matter, antimatter consists of partner particles for all the regular particles we know of, equal in every way but with opposite charge. When matter and antimatter particles collide, they destroy one another, so the mass created when the universe was born should have been completely wiped out, leaving an empty, featureless cosmos containing only light. That there was enough leftover matter after this great annihilation to form galaxies, stars, planets and even us but almost no antimatter is known as the matter-antimatter imbalance. This existential anomaly is one of the great outstanding mysteries of modern physics.
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