Hi, I didnt see specific relative theory and time mentioned on this site that tries to explain the nature of time: http://www.thisistime.co.uk/7.html [Broken] I can understand the part of motion and change, which defines time. But the problem is that relative theory of time is used on GPS navigation to correct signal processing and timing. So it seems time is something real thought relative, it can slow down as per Einstein. "Atomic clocks have been used on jet planes and satellites to verify Einstein's theory of relativity, which states that time slows down as the velocity of one object relative to another increases." - http://science.jrank.org/pages/618/Atomic-Clock.html "Einstein showed that the only way this can happen is if time intervals and/or lengths change according to the speed of the system relative to the observer's frame of reference. This flies against our everyday experience but has since been demonstrated to hold in a number of very solid experiments. For example, scientists have shown that an atomic clock travelling at high speed in a jet plane ticks more slowly than its stationary counterpart." - http://archive.ncsa.illinois.edu/Cyberia/NumRel/SpecialRel.html "Special relativity predicts that the frequency of the atomic clocks moving at GPS orbital speeds will tick more slowly than stationary ground clocks." - http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System I can find statements, that its been proved by atomic clocks on airplanes and satellites. Now question is, if the ticking cycle of the objects is changed by gravity and speed of the vehicle, which gives the illusion of time is changing OR is time real after all no matter what clock, atomic, mechanical or biological you use, it will be affected? Does Einsteins theory also mean, that aging process is slower on high speed, less gravital force affected vehicles? One can think of chemical reactions as a biological clocks... And finally when traveller jumps back to the earth from high speed vehicle, I guess the velocity of the earth around the sun and its own axis is still same and traveller and people on earth jumps back to the same time?