# Understanding Temporal Dilation: The Time Vs. Velocity Equation

Updated on September 25, 2009

Science fiction has long delved into the mysterious world of time travel. Movies, books, television, and other stories have been warping captivated audiences into the future as well as transporting them to long forgotten civilizations of the past. Children daydream of traveling into the future or exploring the mysterious past, and there is always the new magazine article being written on where we will be in the next ten, fifty, or hundred years from now.

With Einstein's revolutionary special theory of relativity, he redefined the notion of space and time, drawing remarkable conclusions that in certain ways, would allow people to move forward in time. Now, with new experiments that are being conducted, that dream of accessing the past may now become a possibility, held up only by the advances that are needed in science.

In 1905 a Swiss patent clerk named Albert Einstein published a scientific paper that would soon shake up the world of physics and establish himself as the new great thinker of the twentieth century. The new theory that he developed would later be named the special theory of relativity. It completely overturned the established concept of a firm and rigid structure to space and time. Instead it portrayed Einstein's new space-time as a linked entity that was shifting and fluid. As a person moved through space, they would also be moving through time. The results showed that time was not a firmly established system, but, in fact, it was perceived differently by everybody depending on the speed that they were traveling.

The whole theory that Einstein developed is based on two postulates, which are things that must be accepted as true in order for the theory to work. The first postulate states: all the laws of physics are the same in any inertial frames of reference. This is a relatively straightforward statement. The only confusing part is "inertial frame of reference." Basically, an "inertial frame" is one that is either moving at a constant speed or not moving at all. In other words the laws that govern how objects behave are the same in every location that is neither accelerating nor decelerating. If a person throws a baseball in their backyard, on the twentieth floor of a New York skyscraper, or on an airplane going a constant speed of 300 miles per hour, the ball will behave in the same fashion. The physical laws that govern the world will not change because of the location. This is a perfectly reasonable assumption, but in conjunction with the second postulate, it will later lead to amazing consequences.

The second postulate states: the speed of light is constant for all observers. Light always travels at a constant 186,000 miles per second. This may seem like a logical thing to say, but if it is compared to something more ordinary, the strangeness of the statement will become more apparent.

For instance, Johnny is late for work and has just missed the bus. As the bus moves down the street at a steady 25 miles per hour (mph), Johnny chases after it at 10 mph. Jenny, an observer, sits on a bench laughing hysterically at the situation. From Jenny's point of view the bus is moving 25 mph, but from the point of view of Johnny, the bus is only moving 15 mph, since the bus is moving at 25 mph and he is chasing after it at 10 mph. The bus is moving away from Johnny at (25mph - 10mph) 15 mph. The speed of the object is all relative to the observer. Relative to Jenny the bus is going 25mph, but relative to Johnny the bus is only going 15 mph. That is why it is called the theory of relativity.

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