 1zalo
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| 21 Mar 2012 04:03 AM
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The Universe is a term that refers to the totality of everything that exists, including planets, stars, galaxies, and all matter and energy.
The universe can be regarded as the entirety of physical existence or as a system bounded by unobservable space, time, or both. In practice, the universe is understood to mean the observable universe.
The Universe is constantly expanding according to the Big Bang theory, which is supported by most cosmologists. This means that light from distant objects will eventually become invisible, as it will have traveled so far that its redshift will shift the entire spectrum of light into radio frequencies.
The Universe may be infinite in extent or finite, but without global boundaries. The universe is also hypothesized to be flat, being neither positively curved (spherical-like) nor negatively curved (hyperbolic-like).
According to the Big Bang theory, the universe has been governed by the same physical laws and constants throughout its history. Over the long term, the gravitational attraction of matter results in the gradual formation of ever-larger units, which evolve until they become unstable and break up again. This process of galaxy formation occurs through the hierarchical organization of structure. This hierarchy has produced structures ranging from star systems to superclusters. There is no evidence for a force analogous to magnetic monopoles, which would exist if charge were not conserved. If a magnetic monopole existed, then it could not decay. Theories of the Big Bang describe a multiverse, with various universes evolving out of the initial state.
In this sense, the Big Bang theory does not describe the origin of the universe. In order to describe the origin of the universe, one must first ask: what came before it? According to the Big Bang theory, the answer is nothing: there was no time before the Big Bang, because time began as space expanded.
The Big Bang theory describes how our own observable universe has evolved since the event. Because we cannot observe anything beyond the observable universe, theories about the entire universe beyond this must be based on speculative extensions of the Big Bang model.
The standard Big Bang model assumes that the whole universe started expanding from a point, and that all the particles in the universe are expanding along with it. Since the universe's density fluctuates over time and space, matter clusters together by gravitation, creating galaxies, stars, planets, etc. Eventually, the expansion of space will cause these structures to break apart again. This model provides a framework for understanding many observations, such as the cosmic microwave background radiation, the large-scale structure of the universe, and the abundance of light elements.
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