Changes

:::''Gravitational waves are often incorrectly called "[[Gravity waves]]".  See that page for a discussion of this point.''

:::''Gravitational waves are often incorrectly called "[[Gravity waves]]".  See that page for a discussion of this point.''

'''Gravitational waves''' are distortions in space that travel at the speed of light away from a mass that accelerates.  Predicted by [[Albert Einstein]]'s [[Theory of Relativity]] in 1916, gravitational waves had never been observed until 2015, when the first evidence of their existence was confirmed<ref>http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102</ref>.

'''Gravitational waves''' are distortions in space that travel at the speed of light away from a mass that accelerates.  Predicted by [[Albert Einstein]]'s [[Theory of Relativity]] in 1916, gravitational waves had never been observed until 2015, when the first evidence of their existence was confirmed.<ref>http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102</ref>

==Description==

==Description==

:<math> \bar{h}_{ij} =</math> gravitational wave, and <math>I_{ij} =</math> mass quadrupole moment.

:<math> \bar{h}_{ij} =</math> gravitational wave, and <math>I_{ij} =</math> mass quadrupole moment.

The results of his findings were published in 1916 as ''Näherungsweise Integration der Feldgleichungen der Gravitation'' (''"Approximate Integration of the Field Equations of Gravitation"''),<ref>Einstein,  Albert.  "Näherungsweise Integration der Feldgleichungen der Gravitation"; ''Proceedings of the Royal Prussian Academy of Sciences'' (1916), Berlin, Germany.</ref> but serious errors led him to a revision, published in 1918 as ''Über Gravitationswellen'' (''"About Gravitational Waves"'')<ref>Einstein, Albert.  "Über Gravitationswellen"; ''Proceedings of the Royal Prussian Academy of Sciences'' (1918), Berlin, Germany.</ref>.

The results of his findings were published in 1916 as ''Näherungsweise Integration der Feldgleichungen der Gravitation'' (''"Approximate Integration of the Field Equations of Gravitation"''),<ref>Einstein,  Albert.  "Näherungsweise Integration der Feldgleichungen der Gravitation"; ''Proceedings of the Royal Prussian Academy of Sciences'' (1916), Berlin, Germany.</ref> but serious errors led him to a revision, published in 1918 as ''Über Gravitationswellen'' (''"About Gravitational Waves"'').<ref>Einstein, Albert.  "Über Gravitationswellen"; ''Proceedings of the Royal Prussian Academy of Sciences'' (1918), Berlin, Germany.</ref>

== The LIGO observations of 2015 ==

== The LIGO observations of 2015 ==

=== The event of September 14, 2015 ===

=== The event of September 14, 2015 ===

This event was observed shortly after turning on the enhanced version of the LIGO detection system, and reported in January 2016.<ref>http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102]</ref>  It was the merger of two black holes, each about 30 times the mass of the Sun, about 1.3 billion light years away and hence 1.3 billion years ago.  Making sure that it wasn't a detection of random noise required comparing the waveforms with the predicted waveforms from theoretical calculations of the final approach and "ringdown" of a merger of two black holes.  The signal closely matched theoretical predictions.<ref>https://www.ligo.caltech.edu/image/ligo20160211a</ref>

This event was observed shortly after turning on the enhanced version of the LIGO detection system, and reported in January 2016.<ref>[http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102]</ref>  It was the merger of two black holes, each about 30 times the mass of the Sun, about 1.3 billion light years away and hence 1.3 billion years ago.  Making sure that it wasn't a detection of random noise required comparing the waveforms with the predicted waveforms from theoretical calculations of the final approach and "ringdown" of a merger of two black holes.  The signal closely matched theoretical predictions.<ref>https://www.ligo.caltech.edu/image/ligo20160211a</ref>

The match showed a confidence of better than "five sigma", that is, a probability of less than one in a million that this was a coincidence.  The same event was detected at both observatories, a small fraction of a second apart, as the wave passed through the Earth.

The match showed a confidence of better than "five sigma", that is, a probability of less than one in a million that this was a coincidence.  The same event was detected at both observatories, a small fraction of a second apart, as the wave passed through the Earth.

[[Category:Relativity]]

[[Category:Relativity]]

[[category:physics]]

[[Category:Physics]]