Purpose/1. The Universe/Introduction/The Universe/What Happened After The Big Bang
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The Big Bang theory postulates that the universe came into being when what amounts to an infinitely large amount of energy suddenly appeared as an infinitesimally small speck (fittingly called a singularity). Where this energy came from—no one knows.[21] How so much energy could occupy next to zero volume—no one knows. One theory postulates the existence of another universe, vastly bigger than the one we inhabit and hidden in additional space/time dimensions, and suggests that it could have created and fed the singularity. This background universe could be periodically “blowing bubbles” that inflate into universes.[22] Our (relatively small, on this scale) universe could have originated within one of these bubbles.[23] Superstring Theory (see The Conservation Laws, a postscript to Chapter Seven ) supports the existence of many universes (of which ours is one), each being formed from, and eventually returned to, empty space.
Regardless of what actually occurred to “begin our universe,” and what was needed before this event to cause it to happen, scientists can account for what is seen today simply by postulating that everything came from a single point in one Big Bang then applying some known laws of physics.
Rather than making guesses about what might have happened beyond and before our universe began (guesses that can never be substantiated—see section six of this chapter), let us start with what is generally accepted—a Big Bang/Inflationary origin to our universe. This theory is able to explain much that we observe, and it yields accurate predictions, hallmark properties of a good scientific theory. Assuming that the laws of physics as we know them today also applied almost immediately following the Bang,[24] we can reconstruct the history of the universe. This has been carried out by various people over the past fifty years, with modifications and revisions being made each time someone was able to improve the fit between astronomical observations and theory. Today, scientists think that something very like the following occurred.
Immediately upon the original insertion of energy, time in this continuum began, and space was created by separating energy components. This was followed by an extremely rapid expansion. Starting about 10-37 of a second after the Bang,[25] and lasting until about 10-34 of a second,[26] this minute bubble of pure energy that was to become our universe inflated to 1050 times its previous size.[27]
For the first one hundred seconds or so following the Bang, only energy (in various forms of radiation) could have existed.[28] Continued expansion and further cooling of this hot dense ball of energy continued until, after about 300,000 years,[29] the temperature was low enough (about 3,000°C) for atoms of hydrogen (and helium, the next lightest element) to remain intact. From this time onward the universe would contain matter.[30]
These atoms of hydrogen and helium[31] continued to move apart, and the temperature of the universe continued to drop. Gravitational forces pulled wisps of atoms closer together, forming tremendous, irregularly shaped clouds, and these eventually further condensed to form many giant gas balls. Condensation continued, with the gases at the centre of each ball forming first black holes, then supermassive black holes.[32] Electrically charged gases (spiralling ever faster and faster around these holes before being swallowed) emitted intense electromagnetic radiation fields that pushed the surrounding gases away. Clouds of these gases then themselves condensed to form additional smaller balls. As gravity pulled the gases in each of these balls tighter together they began to heat up. Eventually the temperature within each became so high that thermonuclear reactions occurred, and the gas balls began to emit light. These high-temperature, hydrogen-gas balls, are called stars.[33] The large collections of stars that rotate around supermassive black holes are called galaxies.
