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In physics, gravity (from Latin gravitas 'weight' [1]) is a fundamental interaction primarily observed as mutual attraction between all things that have mass.Gravity is, by far, the weakest of the four fundamental interactions, approximately 10 38 times weaker than the strong interaction, 10 36 times weaker than the electromagnetic force and 10 29 times weaker than the weak interaction.
The appearance of the comet in 1759, now named after him, within a month of predictions based on Newton's gravity greatly improved scientific opinion of the theory. [106] Newton's theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted by the actions of the ...
This effect has been observed by the European Space Agency astrometric satellite Hipparcos. It measured the positions of about 10 5 stars. During the full mission about 3.5 × 10 6 relative positions have been determined, each to an accuracy of typically 3 milliarcseconds (the accuracy for an 8–9 magnitude star). Since the gravitation ...
This formulation is dependent on the objects causing the field. The field has units of acceleration; in SI, this is m/s 2. Gravitational fields are also conservative; that is, the work done by gravity from one position to another is path-independent. This has the consequence that there exists a gravitational potential field V(r) such that
For the Moon–Earth system, this effect has been measured with the help of lunar laser ranging. [102] More recently, it has been measured for test masses aboard the satellite Gravity Probe B to a precision of better than 0.3%. [103] [104] Near a rotating mass, there are gravitomagnetic or frame-dragging effects. A distant observer will ...
As for Brans–Dicke (which has a tunable parameter ω such that ω = ∞ is the same as general relativity), the amount by which it can differ from general relativity has been severely constrained by these observations. Many other alternatives to general relativity have also been ruled out by analyses of the neutron-star merger GW170817.
[249] [250] LIGO-VIRGO and Fermi constrain the difference between the speed of gravity and the speed of light in vacuum to 10 −15. [251] This marks the first time electromagnetic and gravitational waves are detected from a single source, [ 252 ] [ 253 ] and give direct evidence that some (short) gamma-ray bursts are due to colliding neutron ...
The first direct observation of gravitational waves was made on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016. [3] [4] [5] Previously, gravitational waves had been inferred only indirectly, via their effect on the timing of pulsars in binary star systems.