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The special theory of relativity is based on two postulates:
1. In any relative inertial frame of reference, all observers are
subject to the same laws of physic.
2. The speed of light is always a constant in a vacuum,
no matter how the light source moves. This means when an object
approaches the speed of light, the mass of the object becomes
infinite; it will also not be able to go faster than the speed of
light. Important to notice is that the object also expands in the
direction of motion.