The Big Bang Theory states that the Universe began in a single "explosion," or inflation event from which all of matter-energy and space-time took form. The latest estimates pinpoint this inception moment to have occurred about Your very thoughtful question presupposes that this inflation happened at a specific point in space. In fact, the Big Bang Theory states that space, itself, was created in this event.
So, there was no space in which the Big Bang could have occurred. Unfortunately, this answer is aggravatingly counter intuitive, as we all envision explosions or inflations to happen relative to something else.
For instance, when one inflates a balloon in a room, the balloon membrane approaches the walls as the balloon inflates. Assuming that the balloon remains steady, the center maintains a constant position and all points within the balloon have a specific distance from it.
In the first moments after the Big Bang, the universe was extremely hot and dense. As the universe cooled, conditions became just right to give rise to the building blocks of matter — the quarks and electrons of which we are all made.
A few millionths of a second later, quarks aggregated to produce protons and neutrons. Within minutes, these protons and neutrons combined into nuclei. As the universe continued to expand and cool, things began to happen more slowly. It took , years for electrons to be trapped in orbits around nuclei, forming the first atoms. These were mainly helium and hydrogen, which are still by far the most abundant elements in the universe.
Present observations suggest that the first stars formed from clouds of gas around — million years after the Big Bang. However, after this point, the universe was plunged into darkness, since no stars or any other bright objects had formed yet. About million years after the Big Bang, the universe began to emerge from the cosmic dark ages during the epoch of reionization.
During this time, which lasted more than a half-billion years, clumps of gas collapsed enough to form the first stars and galaxies, whose energetic ultraviolet light ionized and destroyed most of the neutral hydrogen.
Although the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity, about 5 or 6 billion years after the Big Bang , according to NASA, a mysterious force now called dark energy began speeding up the expansion of the universe again, a phenomenon that continues today. A little after 9 billion years after the Big Bang, our solar system was born.
The Big Bang did not occur as an explosion in the usual way one think about such things, despite one might gather from its name. The universe did not expand into space, as space did not exist before the universe , according to NASA Instead, it is better to think of the Big Bang as the simultaneous appearance of space everywhere in the universe. The universe has not expanded from any one spot since the Big Bang — rather, space itself has been stretching, and carrying matter with it.
Since the universe by its definition encompasses all of space and time as we know it, NASA says it is beyond the model of the Big Bang to say what the universe is expanding into or what gave rise to the Big Bang. Although there are models that speculate about these questions, none of them have made realistically testable predictions as of yet.
In , scientists from the Harvard-Smithsonian Center for Astrophysics announced that they had found a faint signal in the cosmic microwave background that could be the first direct evidence of gravitational waves, themselves considered a " smoking gun " for the Big Bang. The findings were hotly debated , and astronomers soon retracted their results when they realized dust in the Milky Way could explain their findings.
The universe is currently estimated at roughly In comparison, the solar system is only about 4. This estimate came from measuring the composition of matter and energy density in the universe. This allowed researchers to compute how fast the universe expanded in the past. With that knowledge, they could turn the clock back and extrapolate when the Big Bang happened.
The time between then and now is the age of the universe. Scientists think that in the earliest moments of the universe, there was no structure to it to speak of, with matter and energy distributed nearly uniformly throughout. According to NASA, the gravitational pull of small fluctuations in the density of matter back then gave rise to the vast web-like structure of stars and emptiness seen today.
Dense regions pulled in more and more matter through gravity, and the more massive they became, the more matter they could pull in through gravity, forming stars , galaxies and larger structures known as clusters, superclusters, filaments and walls , with "great walls" of thousands of galaxies reaching more than a billion light years in length.
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