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# What is gravitational time dilation?

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Gravitational time dilation refers to the slow-down of time which occurs in the vicinity of a mass exerting a gravitational pull. The phenomenon was originally predicted by Einstein in his theory of relativity and later confirmed with the Pound-Rebka experiment.

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Credit: ANDRZEJ WOJCICKI Science Photo Library Getty Images

Time is a relative construct which is wrapped up in and inseparable from its brother dimension, space. Masses like planets and stars exert large gravitational pulls and send "ripples" through the dimension of space-time, warping it. In theory, this means that time operates in a unique way at every separate point in space depending on its relation to the various gravitational pulls of celestial entities.

When near masses exerting powerful gravitational fields, it has been observed that time moves slower relative to areas with less gravitational interference. This has been demonstrated with synchronized atomic clocks. A clock in an airplane moving around the planet will gradually move ahead of another clock left on the ground. The clock in the air is experiencing a faster relative time because it is further away from the gravitational pull of the Earth. The difference here is minuscule -- measured in nanoseconds -- but the experiment nevertheless confirms the existence of time dilation.

A larger, theoretical example involves a black hole, which is an object exerting so much mass that its gravitational pull does not even allow for the escape of light. The gravitational field of a black hole is so powerful that it warps space-time completely, and a clock near a black-hole would cease its ticking completely. Time, effectively, would stop.

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