For purposes of weights and measures, a standard gravity value is defined by the International Bureau of Weights and Measures, under the International System of Units (SI). That value, denoted g, is g = 9.80665 m/s2 (32.1740 ft/s2). The standard value of 9.80665 m/s2 is the one originally adopted by the International Committee on Weights and Measures in 1901 for 45° latitude, even though it has been shown to be too high by about five parts in ten thousand.
Gravity has an infinite range, although its effects become weaker as objects get further away. Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass.
The issue was resolved in 1915 by Albert Einstein's new theory of general relativity, which accounted for the small discrepancy in Mercury's orbit.
On 11 February 2016, the LIGO and Virgo collaborations announced the first observation of a gravitational wave. Alexander Friedmann in 1922 found that Einstein equations have non-stationary solutions (even in the presence of the cosmological constant).
In 1927 Georges Lemaître showed that static solutions of the Einstein equations, which are possible in the presence of the cosmological constant, are unstable, and therefore the static Universe envisioned by Einstein could not exist.
The expansion of the Universe discovered by Edwin Hubble in 1929 confirmed this prediction. The theory's prediction of frame dragging was consistent with the recent Gravity Probe B results. General relativity predicts that light should lose its energy when traveling away from massive bodies through gravitational redshift.
Later, in 1931, Einstein himself agreed with the results of Friedmann and Lemaître.
This was verified on earth and in the solar system around 1960. ===Gravity and quantum mechanics=== An open question is whether it is possible to describe the small-scale interactions of gravity with the same framework as quantum mechanics.
Shapiro in 1964 in interplanetary spacecraft signals. Gravitational radiation has been indirectly confirmed through studies of binary pulsars.
Another astrophysical system predicted to lose energy in the form of gravitational radiation are exploding supernovae. The first indirect evidence for gravitational radiation was through measurements of the Hulse–Taylor binary in 1973.
This research was awarded the Nobel Prize in Physics in 1993. The first direct evidence for gravitational radiation was measured on 14 September 2015 by the LIGO detectors.
This research was awarded the Nobel Prize in physics in 2017. , the gravitational radiation emitted by the Solar System is far too small to measure with current technology. ===Speed of gravity=== In December 2012, a research team in China announced that it had produced measurements of the phase lag of Earth tides during full and new moons which seem to prove that the speed of gravity is equal to the speed of light.
The team's findings were released in the Chinese Science Bulletin in February 2013. In October 2017, the LIGO and Virgo detectors received gravitational wave signals within 2 seconds of gamma ray satellites and optical telescopes seeing signals from the same direction.
This research was awarded the Nobel Prize in Physics in 1993. The first direct evidence for gravitational radiation was measured on 14 September 2015 by the LIGO detectors.
On 11 February 2016, the LIGO and Virgo collaborations announced the first observation of a gravitational wave. Alexander Friedmann in 1922 found that Einstein equations have non-stationary solutions (even in the presence of the cosmological constant).
This research was awarded the Nobel Prize in physics in 2017. , the gravitational radiation emitted by the Solar System is far too small to measure with current technology. ===Speed of gravity=== In December 2012, a research team in China announced that it had produced measurements of the phase lag of Earth tides during full and new moons which seem to prove that the speed of gravity is equal to the speed of light.
The team's findings were released in the Chinese Science Bulletin in February 2013. In October 2017, the LIGO and Virgo detectors received gravitational wave signals within 2 seconds of gamma ray satellites and optical telescopes seeing signals from the same direction.
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