About 15 billion years ago, the universe bursts into existence in the Big Bang, which gives birth to space, time and all the matter and energy the universe will ever hold
The universe undergoes a brief, explosive period of inflation, growing from smaller than an atom to the size of a grapefruit. The inflationary expansion stops when the force driving it is transformed into matter and energy as we know them
Most of the energy is in the form of electromagnetic radiation‹visible light, X rays, radio waves and ultraviolet rays. Quarks clump into protons and neutrons, which later combine to make the nuclei of all atoms. The lightest nuclei‹helium, deuterium and lithium‹are forged in the first three minutes of cosmic history
Electrons combine with existing nuclei to form atoms, mostly hydrogen and helium. This raw material condenses into the first generation of stars during the first billion years. The galaxies also take shape during this window of time. Our sun and solar system were formed 4.6 billion years ago, and the first life-forms appeared on Earth a surprisingly short time afterward. Modern humans show up only 100,000 years before the present. Earth should remain habitable for another few billion years
This era extends to 10 trillion trillion trillion years after the Big Bang. Planets detach from stars; stars and planets evaporate from galaxies. Most of the ordinary matter in the universe is locked up in degenerate stellar remnants‹dead stars that have withered into white dwarfs or blown up and collapsed into neutron stars and black holes. Eventually, over spans of time greatly exceeding the current age of the universe, the protons themselves decay
This era extends to 10,000 trillion trillion trillion trillion trillion trillion trillion trillion years after the Big Bang. After the epoch of proton decay, the only large objects remaining are black holes, which eventually evaporate into photons and other types of radiation
Now only waste products remain: mostly photons, neutrinos, electrons and positrons, wandering through a universe bigger than the mind can conceive. Occasionally, electrons and positrons meet and form "atoms" larger than the visible universe is today. From here into the infinite future, the universe remains cold, dark and dismal
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