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A 'Gravity wave' is a wave in the gravitational field. Gravitational radiation is the overall result of gravity waves in bulk and refers to the concept for the phenomenon known as gravity. According to general relativity, gravityThis article covers the physics of gravitation. See also gravity (disambiguation). Gravitation is the tendency of masses to move toward each other. The first mathematical formulation of the theory of gravitation was made by Sir Isaac Newton and proved ast can cause oscillationSee Oscillator (disambiguation) for particular types of oscillation and oscillators. Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. The term vibration is sometimes used more narrowlys (or waves) in spacetimeIn special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional manifold called spacetime . A point in spacetime may be referred to as an event . Each event has four coordinates t x y z ; or which can transmit energy.
Roughly speaking, the strengthIn physics, the field strength of a field is its force per unit mass or charge at a point. Gravitational field strength The gravitational field strength, E at a point is the force per unit mass acting on a body arising from another object's mass. When a f of gravityThis article covers the physics of gravitation. See also gravity (disambiguation). Gravitation is the tendency of masses to move toward each other. The first mathematical formulation of the theory of gravitation was made by Sir Isaac Newton and proved ast will vary as a gravitational wave passes, much as the depth of a body of water will vary as a water wave passes. More precisely, it is the strength and direction of tidal forces (measured by the Weyl tensor) that oscillate, which should cause objects in the path of the wave to change shape (but not size) in a pulsating fashion. Similarly, gravitational waves will be emitted by physical objects with a pulsating shape, specifically objects with a nonzero quadrupole moment .
The Einstein field equations imply that any accelerated mass radiates energy, but the gravitational interaction's coupling strength is small in comparison to electromagnetism: It is 1038 times weaker. This means (a) that only oscillating masses of astronomical sizes will radiate significant amount of energies and (b) that even so powerful waves are hardly noticeable because their coupling with matter is so small.
Gravitational radiation differs from electromagnetic radiation (such as light) in that electromagnetism contains both positive and negative charges and hence can radiate in a dipole mode. Gravity is only attractive, and hence can only radiate in a weaker quadrupole mode. As with electromagnetic radiation and the photon, gravitational radiation is expected to be quantized with the quantum being the graviton. However, unlike electromagnetic radiation, there is no general accepted theory of quantum gravity.
The existence of gravitational radiation with the features described above is predicted by the physical theory of general relativity, which describes gravitation in general. The equations of this theory are nonlinear, so that; [1] The solutions to the equations cannot be superimposed (added together) to produce new solutions. This makes solving the equations much harder than in linear analogues, such as the theory of electromagnetic radiation, and; [2] Gravitational waves interact with each other (not just with other physical objects). This is unlike, for instance, the interaction of two wave pulses travelling down a string, which can pass through each other without interference. However, weak gravitational waves can be described to a good approximation by linearised general relativity , which is linear.