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Gravitational time dilation is a form of time dilation, an actual difference of elapsed time between two events as measured by observers situated at varying distances from a gravitating mass. The stronger the gravitational potential (the closer the clock is to the source of gravitation), the slower time passes. Albert Einstein originally predicted this effect in his theory of relativity〔 * A. Einstein, "Relativity : the Special and General Theory by Albert Einstein."Project Gutenberg. This has been demonstrated by noting that atomic clocks at differing altitudes (and thus different gravitational potential) will eventually show different times. The effects detected in such earth-bound experiments are ''extremely'' small, with differences being measured in nanoseconds. Demonstrating greater effects would require greater distances from the earth and/or a larger gravitational source. Gravitational time dilation was first described by Albert Einstein in 1907〔A. Einstein, "Über das Relativitätsprinzip und die aus demselben gezogenen Folgerungen", Jahrbuch der Radioaktivität und Elektronik 4, 411–462 (1907); English translation, in "On the relativity principle and the conclusions drawn from it", in "The Collected Papers", v.2, 433–484 (1989); also in H M Schwartz, "Einstein's comprehensive 1907 essay on relativity, part I", American Journal of Physics vol.45,no.6 (1977) pp.512–517; Part II in American Journal of Physics vol.45 no.9 (1977), pp.811–817; Part III in American Journal of Physics vol.45 no.10 (1977), pp.899–902, see (parts I, II and III ).〕 as a consequence of special relativity in accelerated frames of reference. In general relativity, it is considered to be a difference in the passage of proper time at different positions as described by a metric tensor of spacetime. The existence of gravitational time dilation was first confirmed directly by the Pound–Rebka experiment in 1959. ==Definition== Clocks that are far from massive bodies (or at higher gravitational potentials) run more quickly, and clocks close to massive bodies (or at lower gravitational potentials) run more slowly. For example, considered over the total lifetime of the earth (4.6 Gyr), a clock set at the peak of Mount Everest would be about 39 hours ahead of a clock set at sea level. This is because gravitational time dilation is manifested in accelerated frames of reference or, by virtue of the equivalence principle, in the gravitational field of massive objects.〔(id=MBjkuQAoyZIC&pg=PA28&lpg=PA28&dq=%22gravitational+time+dilation%22+indistinguishable+%22rotating%22+reference+frame&source=bl&ots=9v3ikTLcgo&sig=se7viP4NsHBJSGzOK1yfuNR0_KQ&hl=en&sa=X&ei=j8v3UtL4O6K07Qae24CICA&ved=0CEMQ6AEwBw#v=onepage&q=%22gravitational%20time%20dilation%22%20indistinguishable%20%22rotating%22%20reference%20frame&f=false John A. Auping, ''Proceedings of the International Conference on Two Cosmological Models'', Plaza y Valdes, ISBN 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gravitational time dilation」の詳細全文を読む スポンサード リンク
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