All electromagnetic waves involve periodic changes in the strengths of electric and magnetic fields. Any accelerating particle, generates electromagnetic waves. Measurements of these waves agree perfectly with the theory of electromagnetism, which predicts them.
The modern theory of gravity - Einstein's theory of relativity - also predicts waves that move through space. Gravitational waves are "ripples in the curvature of spacetime". A gravity wave is much like other types of waves. In fact, it is the gravitational counterpart of an electromagnetic wave. A gravity wave, or gravitational radiation, results from a change in the strength of a gravitational field. In principle, any time an object of any mass accelerates, a gravity wave should be emitted at the speed of light. the passage of a gravity wave should produce small distortions in the space through which it passes. Gravity is an exceedingly weak force compared with electromagnetism, so these distortions are expected to be very small - in fact, much smaller than a diameter of an atomic nucleus for the waves that might be produced by Galactic sources.
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