What is Special Relativity?

Isaac Newton's law of motion governed the way scientist thought of motion until the late 1800's when a bright young scientist by the name of Albert Einstein challenged these laws. He proclaimed these laws to be subsets of a grander scheme. That is, he thought that Newton's laws were not applicable when speeds approached the speed of light. In 1905 he presented the world with his paper "On the Electrodynamics of Moving Bodies" which contained the Special Theory of Relativity. As of today this theory still governs all motion regardless of its speed. In addition to changing the way the world looked at motion he also predicted some "strange" things to occur when traveling near the speed of light. These changes include a "slow down" of time (called time dilation), an increase in mass and a decrease in length (parallel to the direction of motion) as observed by a person in another reference frame. We will expand on these ideas later in our discussion.

The Basics of Special Relativity!

Einstein's Special Theory of Relativity contains two postulates, they are as follows:

1. The laws of physics are the same in all inertial reference frames.

That is to say regardless of weather you are stationary or moving with constant speed the laws of physics are still applicable and that there is no "correct" reference frame. Let's look at the following two examples. A boy standing on the ground throws a ball straight up into the air and as expected returns to his hand, as seen by him the ball moves up and down. Example two has A girl who is standing in a box car of a train moving with a constant velocity of 20 m/s .She also throws a ball straight up into the air and as expected it returns to her hand. The girl sees her ball go up and down in a straight line also. Once again the laws of physics have prevailed. Therefore, even though the boy and the girl are in two different reference frames they both observer the same observations when performing identical experiments. This evidence illustrates that absolute motion has no meaning, which is what the first postulate is addressing.

To continue the example let's "look" at what the boy will see (standing on the ground) as the girl performs her experiment in the train. As the girl passes by and throws the ball up he sees a different motion, he sees the ball move in a parabolic path instead of up and down, as seen by the girl in the train. The good thing is that although each person "sees" something different they are both correct according to the laws of physics. That is to say what you "see" depends on which frame of reference you are in, and as Einstein stated in his first postulate the laws of physics are applicable in both, because there is no absolute reference frame!