The Universe comprises everything that is perceived to physically exist, the entirety of space and time, all forms of matter and energy, and the physical laws and constants that govern them. However, the term Universe may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world, or Nature.
Throughout recorded history, various cosmologies and cosmogonies have been proposed to account for observations of the Universe. The earliest quantitative geocentric models were developed by the ancient Greeks. [citation needed] Detailed observations and improved theories of gravity then led to Copernicus' heliocentric model and the Newtonian model of the Solar System, respectively. Observations led to the characterization of the Milky Way and the discovery of other galaxies. Studies of the distribution of these galaxies and their spectral lines have led to much of modern cosmology.
The prevailing scientific model of the Universe is known as the Big Bang. In this model, the Universe expanded from an extremely hot, dense phase called the Planck epoch. Since this epoch, the observable universe has been expanding to its present form, possibly with a 10−32 second period of cosmic inflation. Examination of the cosmic microwave background radiation and other experiments support this theoretical expansion and, more generally, the Big Bang theory. Interpretations of astronomical observations indicate that the age of the Universe is (13.73 ± 0.12) billion years old,[1] and that the diameter of the observable universe is at least 93 billion light years, or 8.80 ×1026 metres.[2] Observations indicate that the expansion is accelerating because of dark energy, and that most of the matter and energy in the Universe is fundamentally different from that observed on Earth. The imprecision of current observations has hindered predictions of the ultimate fate of the Universe.
The Universe appears to have been governed by the same physical laws and constants throughout its extent and history. The dominant force at cosmological distances is gravity, and general relativity is currently the most accurate theory of gravitation. The remaining three fundamental forces and all the known particles on which they act are described by the Standard Model. The Universe has at least three dimensions of space and one of time. This spacetime appears to be smooth and simply connected, and space has a minimal curvature, so that Euclidean geometry is accurate on the average throughout the Universe. Conversely, on a quantum scale spacetime is highly turbulent.
The word Universe is usually defined as encompassing everything. However, using an alternate definition, some have speculated that this "Universe" is just one of many disconnected "universes", which are collectively denoted as the multiverse. For example, in bubble universe theory, there are an infinite variety of "universes", each with different physical constants. Similarly, in the many-worlds hypothesis, new "universes" are spawned with every quantum measurement. These universes are usually thought to be completely disconnected from our own and therefore impossible to detect experimentally.
- ^ Chang, Kenneth (2008-03-09). "Gauging Age of Universe Becomes More Precise". New York Times. Retrieved 2008-09-24.
- ^ Lineweaver, Charles (2005). "Misconceptions about the Big Bang". Scientific American. Retrieved 2008-11-06.
{{cite web}}: Unknown parameter|coauthors=ignored (|author=suggested) (help)