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The AstronomersOur Universe with Sean Carroll
Our Universe with Sean Carroll
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Art spoke with physicist Sean Carroll about the origin and nature of the universe we live in. Carroll discussed the Big Bang, a scientific theory which proposes the universe came about from a tremendously dense and hot state about 14 billion years ago. He provided evidence for this theory, pointing out that the Big Bang model has been "established beyond reasonable doubt." Carroll covered other cosmological and theoretical physics topics, including the accelerating expansion of the universe, how space and time came into existence, 'quantum gravity,' parallel universes, string theory, and time travel. He also talked about the recent discovery of an Earth-like planet orbiting a red dwarf star 20 light-years away from our solar system. Carroll said it was unlikely there would be the kind of life there that we could find by using radio telescopes. Biography: Sean Carroll is a Senior Research Associate in Physics at the California Institute of Technology. His research involves theoretical physics and astrophysics, focusing on issues in cosmology, field theory, and gravitation. His current research involves models of dark matter and dark energy, cosmological modifications of Einstein's general relativity, the physics of inflationary cosmology, and the origin of time asymmetry. He has received research grants from NASA, the Department of Energy, and the National Science Foundation, as well as fellowships from the Sloan and Packard foundations. Wikipedia The universe is commonly defined as the totality of existence, including planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. Definitions and usage vary and similar terms include the cosmos, the world and nature. Scientific observation of earlier stages in the development of the universe, which can be seen at great distances, suggests that the universe has been governed by the same physical laws and constants throughout most of its extent and history. The universe is believed to be at least 10 billion light years in diameter and has existed for about 13.7 billion years, since it was created by the Big Bang. There are various multiverse hypotheses, in which physicists have suggested that the universe might be one among many universes that likewise exist. The farthest distance that it is theoretically possible for humans to see is described as the observable universe. Observations have shown that the universe appears to be expanding at an accelerating rate, and a number of models have arisen to predict its ultimate fate. The universe is immensely large and possibly infinite in volume. The region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years, based on where the expansion of space has taken the most distant objects observed. For comparison, the diameter of a typical galaxy is only 30,000 light-years, and the typical distance between two neighboring galaxies is only 3 million light-years. As an example, our Milky Way Galaxy is roughly 100,000 light years in diameter, and our nearest sister galaxy, the Andromeda Galaxy, is located roughly 2.5 million light years away. There are probably more than 100 billion (1011) galaxies in the observable universe. Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars, all orbiting the galaxy's center of mass. A 2010 study by astronomers estimated that the observable universe contains 300 sextillion (3×1023) stars. The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. Less than 5% of the universe is ordinary matter, a relatively small contribution. The observable matter is spread homogeneously (uniformly) throughout the universe, when averaged over distances longer than 300 million light-years. However, on smaller length-scales, matter is observed to form "clumps", i.e., to cluster hierarchically; many atoms are condensed into stars, most stars into galaxies, most galaxies into clusters, superclusters and, finally, the largest-scale structures such as the Great Wall of galaxies. The observable matter of the universe is also spread isotropically, meaning that no direction of observation seems different from any other; each region of the sky has roughly the same content. The universe is also bathed in a highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.725 kelvin. The hypothesis that the large-scale universe is homogeneous and isotropic is known as the cosmological principle, which is supported by astronomical observations. The present overall density of the universe is very low, roughly 9.9 × 10−30 grams per cubic centimetre. This mass-energy appears to consist of 73% dark energy, 23% cold dark matter and 4% ordinary matter.Thus the density of atoms is on the order of a single hydrogen atom for every four cubic meters of volume.
Added on Nov 27, 2012 by lonewolf
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Time: 01:18:41 | Views: 856 | Comments: 0
   
  Extragalactic astronomy  
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