K
kmarinas86
Guest
Gravity slows down the speed of light, physically:<br />http://en.wikipedia.org/wiki/Shapiro_effect<br /><br /><font color="yellow">In General relativity, the Shapiro effect, or <b>gravitational time delay</b>, is one of the four classic solar system tests of general relativity. It says that a radar beam (or light beam) which passes near a massive object as it travels from some observer's location to a target and returns to the observer, takes slightly longer to make the round trip (as measured by the observer) than it would if the object were not present.<br /><br />More generally, the "travel time" of any signal moving at the <b>local speed of light</b> can be affected by the gravitational field in regions of spacetime through which it travels. In general relativity (and in most other gravitation theories), the <b>local speed of light</b> is a constant of nature, but the time delay effect implies that the effective <b>global speed of light</b> is path-dependent.<br /><br />The time delay effect was first noticed in 1964, by Irwin I. Shapiro. Shapiro proposed an observational test of his prediction: bounce radar beams off the surface of Venus and Mercury, and measure the round trip travel time. When the Earth, Sun, and Venus are most favorably aligned, Shapiro showed that the expected time delay, due to the presence of the Sun, of a radar signal traveling from the Earth to Venus and back, would be about 200 milliseconds, well within the limitations of 1960s era technology.<br /><br />The first test, using the MIT Haystack radar antenna, was successful, matching the predicted amount of time delay. The experiments have been repeated many times since, with increasing accuracy.</font><br /><br />Velocity time dilation deals with the clocks of objects with mass.<br />Gravitational time dilation deals with the clock of the space time fabric itself!<br /><br />http://www.google.co</safety_wrapper