Everything around you survived a cosmic wipeout by a margin of one in thirty million
In the searing first instants after the Big Bang, matter and antimatter were created and destroyed in almost equal amounts. Some unknown process tipped the balance by about one part in 30 million. When the pairs annihilated, that sliver of surplus matter was all that remained, and everything we see, including us, is built from it.
The Big Bang theory describes a universe expanding from an extremely hot, dense early state, roughly 13.8 billion years ago. Modern versions begin with inflation, an unimaginably short burst during which space kept doubling, over 80 times in a row, freezing tiny quantum ripples into the seeds of future galaxies. Inflation left space cold and empty, then a reheating event, whose mechanism is still unknown, turned its energy into a blistering plasma of particles.
The timeline after that is surprisingly precise. By around a millionth of a second, quarks had combined into protons and neutrons, and a mass annihilation left only about one in a hundred million of the original matter particles. A few minutes in, at about a billion kelvin, protons and neutrons fused into deuterium and helium, though most protons stayed as hydrogen. After about 380,000 years the universe cooled enough for electrons to join nuclei into neutral atoms. Space turned transparent, and the light released then still reaches us as the cosmic microwave background.
The idea took shape over a decade. Alexander Friedmann derived equations for an expanding universe in 1922, Edwin Hubble found in 1929 that more distant galaxies recede faster, and in 1931 Georges Lemaître proposed that everything emerged from a primeval atom. The microwave background, discovered by accident in 1964, clinched the case.
Plenty remains open. Nobody knows what caused the matter surplus, what dark matter is, or where dark energy comes from. Those unknowns dominate: ordinary luminous matter makes up under 5% of the universe's density, dark matter about 27%, and dark energy the remaining 68%.
Source: Big Bang
