Difference between revisions of "Gravitational waves"

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(Gravity waves have never been observed, and have even been the subject of a hoax in 2010.)
(You can't "disfavor" a wave--like electromagnetic waves, they travel right through you, whether you like them or not. And they are as real as neutrinos or Higgs bosons.)
 
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'''Gravity waves''' are predicted by the [[Theory of Relativity]], which claims that distortions in space travel at the speed of light away from a mass that moves.  
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:::''Gravitational waves are often incorrectly called "[[Gravity waves]]".  See that page for a discussion of this point.''
  
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Gravity waves have never been directly observed, and have even been the subject of a hoax:<ref>http://discovermagazine.com/2014/april/23-20-things-you-didnt-know-about-hoaxes</ref>
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'''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, they were first observed, and their existence confirmed, in early 2016. <ref>http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102</ref>
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{{cquote|In 2010 researchers from the Laser Interferometer Gravitational-Wave Observatory detected the first direct evidence of gravitational waves — crucial proof of relativity. After thousands of hours of verification, they learned that the signal was a “blind injection,” an authorized prank by colleagues to check their work.}}
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In 2016, demands immediately rang out for a [[Nobel Prize]] to be awarded for an anomalous "chirp" detected in LIGO.<ref>[http://www.bbc.co.uk/news/science-environment-19408363] Gravitational waves spotted from white-dwarf pair, BBC</ref><ref> [http://www.bbc.co.uk/news/science-environment-35524440] Gravitational waves from black holes detected, BBC</ref>
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==Description==
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== See also ==
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*[[Relativity]]
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Gravitational waves are "ripples", similar to the ripples made in a pond when a pebble is tossed in, but on a cosmological scale.  The masses in question are binary systems - pulsars, neutron stars, or black holes - which orbit around each other.  According to Einstein's [[General relativity|General Theory of Relativity]], both objects emit gravitational waves and lose energy as they gradually approach, eventually resulting in a collision, and emitting a final, very strong burst of gravitational waves
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As part of his relativity theory, Einstein came up with his "quadrupole formula", which describes the rate of wave emissions from a system of astronomical masses based on the change of the mass itself, what he called the "quadrupole moment". His formula as originally postulated was
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:<math> \bar{h}_{ij}(t,r) = \frac{2 G}{c^4 r} \ddot{I}_{ij}(t-r),</math>
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Where
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:<math> \bar{h}_{ij} </math> is the gravitational wave
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:<math>I_{ij}</math> is the mass quadrupole moment.
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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>
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== The LIGO observations ==
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Because gravitational waves from distant (billions of light years away) phenomena are incredibly faint, detecting them has been a daunting task.  Decades of work have gone into the development of sufficiently sensitive detectors.  In 2015, the [[LIGO]] detectors (one in Hanford, Washington and one in Livingston Louisiana) made the first detection of the waves. <ref>http://www.ligo.org/news/pressreleases.php</ref>
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=== The event of September 14, 2015 ===
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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>
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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.
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Unlike most astronomical wave phenomena, the gravitational waves from black hole mergers are approximately in the audible range.  With only a small amount of signal processing, the signal was made audible; it's sort of a "chirp".<ref>https://www.ligo.caltech.edu/video/ligo20160211v2</ref>  For a while this "chirp" became something of an internet sensation.
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Other articles:  [https://www.nbcnews.com/science/science-news/gravitational-waves-ripples-space-time-detected-first-time-n516566], [https://www.youtube.com/watch?v=aEPIwEJmZyE]
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=== The event of December 26, 2015 ===
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A second black hole merger was detected two months later.<ref>https://www.nbcnews.com/science/science-news/it-wasn-t-fluke-scientists-see-black-holes-collide-again-n593156</ref><ref>https://www.cbsnews.com/news/scientists-detect-second-gravitational-wave-einstein-predicted/</ref><ref>https://www.ligo.caltech.edu/news/ligo20160615</ref>
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Here is a comparison of the "chirps" from the two events.  The December event was significantly less powerful that the September one.  It was 1.4 billion light years away.<ref>https://www.ligo.caltech.edu/video/ligo20160615v2</ref>
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=== The event of January 4, 2017 ===
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A third event was detected in early 2017.  This one was 3 billion light years away.<ref>https://phys.org/news/2017-06-gravitational-insight-black-holes.html</ref>
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===Further events ===
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Since those very early announcements, further observations of gravitational waves have continued to come in.<ref>https://ligo.org</ref>  In August 2019 the first detection of the gravitational waves from the merger of a [[black hole]] and a neutron star occurred.<ref>https://ligo.org/news/index.php#O3updateAug19</ref>  This was event S190814bv, 870 million light years away, and hence actually occurred 870 million years ago.<ref>https://www.extremetech.com/extreme/296902-scientists-detect-first-ever-collision-between-black-hole-and-neutron-star</ref>
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== The LISA project ==
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An even more ambitious and sensitive detector, previously called LISA and now called eLISA (Evolved Laser Interferometer Space Antenna), is being designed by an international consortium of agencies.  This one involves satellites in heliocentric orbit, using laser interferometers to measure changes in the distance between "test masses" inside the satellites.
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A test of the underlying test mass technology, called the LISA Pathfinder test, succeeded on June 6, 2016.<ref>https://www.bbc.co.uk/news/science-environment-36472434#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa</ref>
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== See also ==
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*[[LIGO]]
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*[[Theory of relativity]]
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*[[Counterexamples to Relativity]]
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*[[Essay:Rebuttal to Counterexamples to Relativity]]
  
 
==References==
 
==References==
 
<references/>
 
<references/>
  
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[[Category:Relativity]]
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[[category:physics]]<nowiki></nowiki>
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[[Category:Physics]]

Latest revision as of 03:23, January 1, 2022

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, they were first observed, and their existence confirmed, in early 2016. [1]

Description

Gravitational waves are "ripples", similar to the ripples made in a pond when a pebble is tossed in, but on a cosmological scale. The masses in question are binary systems - pulsars, neutron stars, or black holes - which orbit around each other. According to Einstein's General Theory of Relativity, both objects emit gravitational waves and lose energy as they gradually approach, eventually resulting in a collision, and emitting a final, very strong burst of gravitational waves

As part of his relativity theory, Einstein came up with his "quadrupole formula", which describes the rate of wave emissions from a system of astronomical masses based on the change of the mass itself, what he called the "quadrupole moment". His formula as originally postulated was

Where

is the gravitational wave
is the 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"),[2] but serious errors led him to a revision, published in 1918 as Über Gravitationswellen ("About Gravitational Waves").[3]

The LIGO observations

Because gravitational waves from distant (billions of light years away) phenomena are incredibly faint, detecting them has been a daunting task. Decades of work have gone into the development of sufficiently sensitive detectors. In 2015, the LIGO detectors (one in Hanford, Washington and one in Livingston Louisiana) made the first detection of the waves. [4]

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.[5] 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.[6] 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.

Unlike most astronomical wave phenomena, the gravitational waves from black hole mergers are approximately in the audible range. With only a small amount of signal processing, the signal was made audible; it's sort of a "chirp".[7] For a while this "chirp" became something of an internet sensation.

Other articles: [1], [2]

The event of December 26, 2015

A second black hole merger was detected two months later.[8][9][10]

Here is a comparison of the "chirps" from the two events. The December event was significantly less powerful that the September one. It was 1.4 billion light years away.[11]

The event of January 4, 2017

A third event was detected in early 2017. This one was 3 billion light years away.[12]

Further events

Since those very early announcements, further observations of gravitational waves have continued to come in.[13] In August 2019 the first detection of the gravitational waves from the merger of a black hole and a neutron star occurred.[14] This was event S190814bv, 870 million light years away, and hence actually occurred 870 million years ago.[15]

The LISA project

An even more ambitious and sensitive detector, previously called LISA and now called eLISA (Evolved Laser Interferometer Space Antenna), is being designed by an international consortium of agencies. This one involves satellites in heliocentric orbit, using laser interferometers to measure changes in the distance between "test masses" inside the satellites.

A test of the underlying test mass technology, called the LISA Pathfinder test, succeeded on June 6, 2016.[16]

See also

References

  1. ↑ http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102
  2. ↑ Einstein, Albert. "Näherungsweise Integration der Feldgleichungen der Gravitation"; Proceedings of the Royal Prussian Academy of Sciences (1916), Berlin, Germany.
  3. ↑ Einstein, Albert. "Über Gravitationswellen"; Proceedings of the Royal Prussian Academy of Sciences (1918), Berlin, Germany.
  4. ↑ http://www.ligo.org/news/pressreleases.php
  5. ↑ http://journals.aps.org/prl/pdf/10.1103/PhysRevLett.116.061102
  6. ↑ https://www.ligo.caltech.edu/image/ligo20160211a
  7. ↑ https://www.ligo.caltech.edu/video/ligo20160211v2
  8. ↑ https://www.nbcnews.com/science/science-news/it-wasn-t-fluke-scientists-see-black-holes-collide-again-n593156
  9. ↑ https://www.cbsnews.com/news/scientists-detect-second-gravitational-wave-einstein-predicted/
  10. ↑ https://www.ligo.caltech.edu/news/ligo20160615
  11. ↑ https://www.ligo.caltech.edu/video/ligo20160615v2
  12. ↑ https://phys.org/news/2017-06-gravitational-insight-black-holes.html
  13. ↑ https://ligo.org
  14. ↑ https://ligo.org/news/index.php#O3updateAug19
  15. ↑ https://www.extremetech.com/extreme/296902-scientists-detect-first-ever-collision-between-black-hole-and-neutron-star
  16. ↑ https://www.bbc.co.uk/news/science-environment-36472434#sa-ns_mchannel=rss&ns_source=PublicRSS20-sa
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