Ideas of time travel have existed for centuries, but when Albert Einstein released his theory of special relativity, he laid the foundation for the theoretical possibility of time travel.

As we all know, no one has successfully demonstrated time travel, but no one has been able to rule it out either. Time has fascinated people throughout the dawn of civilization. People have spent their life thinking about these concepts and the ideas behind them.

As the boundaries of physics are pushed back and back it is becoming clear that whoever understands the laws of physics best will be able to travel through time and space, easily gaining a dominant position in the known Universe. Indeed that race which can move from universe to universe will get to control all universes! We must therefore double our efforts to ensure that it is we and not some other race who gains understanding first! Or we will end up playing second fiddle for rest of time!

We have constantly come up with every increasingly more complex and accurate ways to measure the passing of this thing which we call time. However, I wonder how many people realize that time itself is not exactly the same wherever you are. Albert Einstein was the first to show in his Theory of Relativity that time was not, in fact, a smooth river, constant in its flow, but something that could be affected by motion and by gravity - an effect known as time dilation. Einstein did not consider time and the three spatial dimensions as being separate, but as being linked to form a four-dimensional quantity known as space-time.

Einstein's theories of relativity have been proved by numerous experiments, including one in 1971 in which highly accurate atomic clocks were placed aboard two high-speed aircraft, with another one at an airbase. Despite staying in the same location, the ground clock was not stationary, since it was traveling at the same rate as the Earth spins. One aircraft flew eastwards from the base, traveling in the rotational direction of the earth and so moving faster than the ground clock, while the other flew westwards and so moved relatively slower. After the flight, the eastbound aircraft's clock had lost time relative to a ground-based atomic clock, while the opposite was true of the westbound aircraft's timepiece. Amazing eh? The only constant in the theory of Special Relativity is that the relative speed between any observer - regardless of his or her own motion and any ray of light is always 300,000 kilometers per second (186,000 miles per second). The consequence of this theory, once the equation has been balanced, is that not only is time different for a faster observer, but also lengths and mass change.

Let's see something about the most talked about fuss called 'theory of Relativity'. The theory of relativity is in fact two theories. The special theory of relativity (1905) and the general theory of relativity (1915). The special theory gives a unified account of the laws of mechanics and of electromagnetism. Einstein rejected the concepts of absolute space and time and made two postulates (a) the laws of nature are the same for all observers in uniform relative motion and (b) the speed of light is the same for all such observers.

The transformation of time implies that two events that are simultaneous according to one observer will not necessarily be so according to another in uniform relative motion. It will appear to two observers in uniform relative motion that each other's clock runs slowly. This is the phenomenon of time dilation.

In 1915, Einstein developed his ideas to form the General Theory of Relativity, in which he considered objects that were being accelerated with respect to one another. He compared the forces of acceleration and gravity and found them to be indistinguishable. For example, an astronaut standing in a rocket on a launch pad would feel himself pressed against the floor because of gravity. If the same rocket was in outer space and not affected by gravity, but with its engines turned on so that it was accelerating, the astronaut would again be pressed against the floor. If the acceleration due to the engines were the same as the acceleration due to gravity, the astronaut would have no way of telling whether the rocket was at rest on the earth or accelerating in outer space unless the looked out of the window. Einstein stated that the attraction to the Earth of a rocket that is resting on a launch pad is equivalent to the acceleration of the rocket. So although in three-dimensional space, the rocket remains stationary, in four-dimensional space-time the rocket is in motion along its world line. The upshot of this motion in space-time is that gravity also makes time run slower.

While writers have produced some great ideas for time machines over the years, a real-life time machine has yet to be built. Most theories of time travel don't rely on machines at all. Instead, time travel will probably be done by way of natural phenomena that will transport us instantly from one point in time to another. These space phenomena, which we are not even sure exist, include Rotating black holes, Wormholes, Cosmic strings.

A black hole is a dying star that has collapsed under the weight of its own spent fuel, with the result that its gravity field is so strong, not even light can escape its pull. The edge of a black hole is called an event horizon, since that is where light cannot escape. Compared to such forces, the Earth's escape velocity is paltry in comparison. A spacecraft needs a mere 11.2 kilometers per second to break free of our planet's grip. As the edge of a black hole - known as the event horizon - is neared, time slows down relative to areas, which are distant from the hole. Some scientists believe that within the event horizon, all matter collapses into a dimensionless object of infinite density known as a singularity.

However, others argue that no such collapse occurs and that space-time forms a closed surface without a boundary. In effect a black hole would then not be a rip in space-time, but would be more like the hole of a donut. This second theory opens the possibility of using black holes to link to other parts of the universe through tunnels in space-time known as wormholes. By entering one end of a wormhole a traveler might be able to take a shortcut through space-time to another part of the universe. In a similar way, the shortest route between one side of a donut to the other is through the hole in the center, rather than around the rim. Einstein's General relativity equations do not rule out the possibility that these wormholes might not only provide a tunnel through space, but also a tunnel through time.