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In physics, gravitational waves are ripples in the curvature of spacetime which propagate as waves, travelling outward from the source. Predicted in 1916 by Albert Einstein to exist on the basis of his theory of general relativity,〔(The Detection of Gravitational Waves using LIGO, B. Barish )〕 gravitational waves theoretically transport energy as gravitational radiation. Sources of detectable gravitational waves could possibly include binary star systems composed of white dwarfs, neutron stars, or black holes. The existence of gravitational waves is a possible consequence of the Lorentz invariance of general relativity since it brings the concept of a limiting speed of propagation of the physical interactions with it. Gravitational waves cannot exist in the Newtonian theory of gravitation, in which physical interactions propagate at infinite speed. Although gravitational radiation has not been ''directly'' detected, there is ''indirect'' evidence for its existence.〔 For example, the 1993 Nobel Prize in Physics was awarded for measurements of the Hulse–Taylor binary system which suggest that gravitational waves are more than theoretical concept. Various gravitational-wave detectors are currently under construction or are in operation, such as Advanced LIGO which began observations in September 2015. On 17 March 2014, astronomers at the Harvard–Smithsonian Center for Astrophysics erroneously claimed that they had detected and produced "the first direct image of gravitational waves across the primordial sky" within the cosmic microwave background, providing flawed evidence for inflation and the Big Bang.〔http://www.theguardian.com/science/2014/jun/04/gravitational-wave-discovery-dust-big-bang-inflation〕 On 19 June 2014, lowered confidence in confirming the cosmic inflation findings was reported and on 19 September 2014, a further reduction in confidence was reported. On 30 January 2015, even less confidence yet was reported; ''Nature'' went as far as publishing a news article entitled "Gravitational waves discovery now officially dead". == Introduction == In Einstein's theory of general relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass. Generally, the more mass that is contained within a given volume of space, the greater the curvature of spacetime will be at the boundary of this volume.〔 As objects with mass move around in spacetime, the curvature changes to reflect the changed locations of those objects. In certain circumstances, accelerating objects generate changes in this curvature, which propagate outwards at the speed of light in a wave-like manner. These propagating phenomena are known as gravitational waves. As a gravitational wave passes a distant observer, that observer will find spacetime distorted by the effects of strain. Distances between free objects increase and decrease rhythmically as the wave passes, at a frequency corresponding to that of the wave. This occurs despite such free objects never being subjected to an unbalanced force. The magnitude of this effect decreases inversely with distance from the source. Inspiralling binary neutron stars are predicted to be a powerful source of gravitational waves as they coalesce, due to the very large acceleration of their masses as they orbit close to one another. However, due to the astronomical distances to these sources the effects when measured on Earth are predicted to be very small, having strains of less than 1 part in 1020. Scientists are attempting to demonstrate the existence of these waves with ever more sensitive detectors. The current most sensitive measurement is about one part in () provided by the LIGO and VIRGO observatories. The lack of detection in these observatories provides an upper limit on the frequency of such powerful sources. A space based observatory, the Laser Interferometer Space Antenna, is currently under development by ESA. Gravitational waves should penetrate regions of space that electromagnetic waves cannot. It is hypothesized that they will be able to provide observers on Earth with information about black holes and other exotic objects in the distant Universe. Such systems cannot be observed with more traditional means such as optical telescopes or radio telescopes, and so gravitational-wave astronomy gives new insights into the working of the Universe. In particular, gravitational waves could be of interest to cosmologists as they offer a possible way of observing the very early Universe. This is not possible with conventional astronomy, since before recombination the Universe was opaque to electromagnetic radiation. Precise measurements of gravitational waves will also allow scientists to test the general theory of relativity more thoroughly. In principle, gravitational waves could exist at any frequency. However, very low frequency waves would be impossible to detect and there is no credible source for detectable waves of very high frequency. Stephen W. Hawking and Werner Israel list different frequency bands for gravitational waves that could be plausibly detected, ranging from 10−7 Hz up to 1011 Hz.〔Hawking, S. W. and Israel, W., ''General Relativity: An Einstein Centenary Survey'', Cambridge University Press, Cambridge, 1979, 98.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravitational wave」の詳細全文を読む スポンサード リンク
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