Albert Einstein was one of the greatest, most creative thinkers of all time. Some of his ideas were that mass could be converted to energy and energy to mass (E = mc^2), that light was actually made out of particulate photons, that gravity was not a force but a curved field in space time, and that everything is relative. This brings us to the Special Theory of Relativity. This theory is based on two postulates (assumptions). The first of these is the relativity principle.
- If two frames of reference move with constant velocity relative to each other, then the laws of physics will be the same in both frames of reference.
If there was ever a frame of reference that was fixed, it would become the absolute reference frame. This absolute reference frame is light because the measured speed of light relative to the earth is the same whether the earth was moving toward the source of light or away from it. The second postulate of this theory is:
- The speed of light in space is the same for any observer no matter what the velocity of the observer's frame of reference is, and no matter what the velocity of the source of the light is.
According to this theory, time is also relative. For example, a clock that is moving will run slightly slower. The stretching of time is called "time dilation". Another statement made by this theory is that objects at high speeds will be measured to be shorter then when they are at rest, and that objects can not go faster then the speed of light.
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