Related topics: galaxies , dark energy , stars , black holes , big bang
Universe
hideThe Universe is defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, 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.
Current interpretations of astronomical observations indicate that the age of the Universe is 13.73 (± 0.12) billion years, and that the diameter of the observable Universe is at least 93 billion light years, or 8.80 × 1026 metres. (It may seem paradoxical that two galaxies on opposite sides can be separated by 93 billion light years after only 13 billion years, since special relativity states that matter cannot be accelerated to exceed the speed of light in a localized region of space-time. However, according to general relativity, space can expand with no intrinsic limit on its rate; thus, two galaxies can separate more quickly than the speed of light if the space between them grows.) It is uncertain whether the size of the Universe is finite or infinite.
According to the prevailing scientific model of the Universe, known as the Big Bang, the Universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable Universe was concentrated. Since the Planck epoch, the Universe has been expanding to its present form, possibly with a brief period (less than 10-32 seconds) of cosmic inflation. Several independent experimental measurements support this theoretical expansion and, more generally, the Big Bang theory. Recent observations indicate that this expansion is accelerating because of the dark energy, and that most of the matter and energy in the Universe is fundamentally different from that observed on Earth and not directly observable. The imprecision of current observations has hindered predictions of the ultimate fate of the Universe.
Experiments and observations suggest that the Universe has 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, although extremely small additional dimensions cannot be ruled out experimentally. Spacetime appears to be smooth and simply connected, and space has very small mean 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.
Throughout recorded history, several cosmologies and cosmogonies have been proposed to account for observations of the Universe. The earliest quantitative geocentric models were developed by the ancient Greeks, who proposed that the Universe possesses infinite space and has existed eternally, but contains a single set of concentric spheres of finite size – corresponding to the fixed stars, the Sun and various planets – rotating about a spherical but unmoving Earth. Over the centuries, more precise observations and improved theories of gravity led to Copernicus' heliocentric model and the Newtonian model of the Solar System, respectively. Further improvements in astronomy led to the characterization of the Milky Way, and the discovery of other galaxies and the microwave background radiation; careful studies of the distribution of these galaxies and their spectral lines have led to much of modern cosmology.
For more information about Universe, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with universe
Dark Energy v. The Void: What if Copernicus was Wrong?
Sep 26, 2008 |
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Dark energy is at the heart of one of the greatest mysteries of modern physics, but it may be nothing more than an illusion, according physicists at Oxford University. The problem facing astrophysicists is that they have ...
Scientists detect cosmic 'dark flow' across billions of light years
Sep 23, 2008 |
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(PhysOrg.com) -- Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), scientists have identified an unexpected motion in distant galaxy clusters. The cause, they suggest, is the gravitational ...
Looking for neutralinos at the Large Hadron Collider
Jul 09, 2008 |
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“We are looking at the heavens, and using the very biggest things to help up predict what will happen with the very smallest things,” David Toback tells PhysOrg.com. Toback is a professor at Texas A&M University in Colleg ...
Stars Fueled by Dark Matter Could Hold Secrets to the Universe
Nov 03, 2009 |
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(PhysOrg.com) -- The first stars in the universe may have been very different from the stars we see today, yet they may hold clues to understanding some of the mysterious features of the universe. These "dark ...
Searching for primordial antimatter
Oct 30, 2008 |
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Scientists are on the hunt for evidence of antimatter - matter's arch nemesis – left over from the very early Universe. New results using data from NASA's Chandra X-ray Observatory and Compton Gamma Ray Observatory ...
Physicists Calculate Number of Parallel Universes
Oct 16, 2009 |
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(PhysOrg.com) -- Over the past few decades, the idea that our universe could be one of many alternate universes within a giant multiverse has grown from a sci-fi fantasy into a legitimate theoretical possibility. ...
Can R2 gravity explain dark matter?
Apr 20, 2009 |
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(PhysOrg.com) -- "In many ways, the standard model of cosmology works very well," Jose Cembranos tells PhysOrg. "However, there are very basic features that we just do not know. We have dark energy and dark matter. They d ...
Astronomer Discovers Upper Mass Limit for Black Holes
Sep 05, 2008 |
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There appears to be an upper limit to how big the universe’s most massive black holes can get, according to new research led by a Yale University astrophysicist.
Texas School Standards: Age of the Universe Erased
Apr 07, 2009 |
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(PhysOrg.com) -- The fight over the new education and curriculum standards for the public schools in Texas has been long and publicized. Most of the publicity, though, focuses on the school board's focus on ...
What if there is only one universe?
Jun 04, 2009 |
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(PhysOrg.com) -- Lee Smolin, author of the bestselling science book The Trouble with Physics and a founding member and research physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, ...
Tackling the big questions -- approaching a revolution in our understanding of gravity
Nov 05, 2008 |
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(PhysOrg.com) -- The way galaxies move through the cosmos has recently begun to baffle scientists. Even when the gravitational theories of Newton and Einstein are taken into account, the universe is expanding and galaxies ...
Voiding the Cosmic Void: We're not at Center of the Universe After All
Dec 10, 2008 |
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Models of the universe that place us near the center of a large, sparse region don't jibe with astronomical observations. Cosmologists at the University of British Columbia reached the conclusion through a new analysis that ...
Dark Energy From the Ground Up: Make Way for BigBOSS
Aug 07, 2009 |
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(PhysOrg.com) -- Several ways have been proposed to examine dark energy, in hopes of finding out just what it is. One of them, "supernovae" for short, certainly works: it's how dark energy was discovered in ...
Dark Energy Found Stifling Growth in Universe
Dec 16, 2008 |
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(PhysOrg.com) -- For the first time, astronomers have clearly seen the effects of "dark energy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how ...
Galaxy Clusters Have a Mysterious Motion
Sep 24, 2008 |
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(PhysOrg.com) -- The stars are in motion, and on a much larger scale than can be explained with current theories, according to astronomers at NASA, the University of Hawaii and UC Davis. The finding could improve our understanding ...
