The Universe is all of space time and everything that exists therein, including all planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy. Similar terms include the cosmos, the world, reality, and nature.
The estimated diameter of the observable universe is about 93 billion light years or 28 billion parsecs. Scientific observation of the Universe has led to inferences of its earlier stages, which appear to have been governed by the same physical laws and constants throughout most of its extent and history. The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe, which is estimated to have begun 13.798 ± 0.037 billion years ago.
Scientists remain unsure about what, if anything, preceded the Big Bang. Many refuse to speculate, doubting that any information from any such prior state could ever be accessible. There are various multiverse hypotheses, in which some physicists have suggested that the Universe might be one among many, or even an infinite number, of universes that likewise exist.
The universe is composed of 4.9 percent atomic matter, 26.6 percent dark matter and 68.5 percent dark energy Observations of supernovae have shown that the Universe is expanding at an accelerating rate. There are several competing theories about the ultimate fate of the universe.
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