The Big Bang occurred 13.7 billion years ago, starting as a point of high density and expanding outward, causing space to expand. The Planck epoch, the grand unification epoch, and the inflationary epoch followed, with the universe growing rapidly. The universe is now at least 92 billion light-years in size.
The Big Bang is the origin of the universe, which occurred about 13.7 billion years ago. It began as a point of nearly zero volume and tremendous density. Then this point started to extend outward in all directions, not expanding into space but causing the space itself to expand.
The first period of time immediately following the Big Bang is known as the Planck epoch, which occurred in the first 10-43 seconds thereafter. Little is known about this period, because our current physical theories cannot probe time scales smaller than this. It is thought that all four fundamental forces – strong nuclear, weak nuclear, electromagnetism and gravity – were unified at this point, serving as one superforce. Scientists are working on physical theories to help describe this era. At the end of the Planck era, the force of gravity separated from the other three, creating gravity and the so-called electronuclear force.
After the Planck epoch came the epoch of the grand unification, which occurred from 10-43 to 10-35 seconds after the Big Bang. The universe was smaller than a quark (a type of subatomic particle) with temperatures above 1027 K. This is about 1012 times more energetic than the collision points inside the largest particle accelerators. As the universe expanded and cooled, and the electronuclear force broke down into its constituents: the strong nuclear force, the weak nuclear force, and electromagnetism. At the end of the epoch of grand unification, the universe was about the size of a proton.
The epoch of grand unification was followed by the epoch of inflation, during which the universe grew by a factor of at least 1026, and perhaps much larger. The inflationary epoch only lasted about 10-32 seconds, but during that time the universe grew from the size of a proton to the size of a grapefruit or more. Its volume increased by a factor of at least 1078. The universe expanded many times faster than the speed of light, explaining that space itself was expanding, even though nothing within the space broke the speed limit universal.
After the inflationary era, the universe continued to expand, eventually becoming what it is today: a behemoth the size of at least 92 billion light-years, and perhaps much more.
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