Albert Einstein conceptualized the theories of general relativity and special relativity. He came to realize that the universe was not made up of three dimensional space as was commonly accepted, but four dimensional space-time. The fourth dimension being that of time. .
Objects move through space and time. Time is not a universal quantity which exists on its own, separate from space. Rather, future and past are merely directions like up and down, left and right, forward and back in what is referred to as space-time. One can only travel in the future direction in time but one can travel on an angle. ( John Gribbin, 1990, p. 1).
Einstein made other great discoveries, such as the speed of light. How can observers moving at different speeds all measure light at the same speed? The answer is that they cannot, not if the normal ideas of space and time hold true. However, in the famous paper of 1905, Einstein stated that it is possible if they abandoned the idea of a universal time. Instead, all the observers would have their own individual time, measured by a clock they each carried. The times on these clocks would measure the same if they were all moving at the same speed "but the times would differ significantly if the clocks were moving at different speeds. (Stephen Hawking, 1993, p. 73) .
This aforementioned effect has been measured and proven correct. One clock was placed in a stationary position on the ground, while another clock "synchronized with the stationary clock "was placed in a commercial airliner. The clock on the airliner was found to run slightly slower when compared to the stationary clock.
The difference between the rates of clocks are very small for normal speed of travel. One would have to fly around the world four hundred million times to add one second to their life. But this time-dilation effect would show up dramatically in very fast space travel.
