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In 1905 Albert Einstein published a theory that comotionated the concepts of physics: The Special Theory of Relativity. This theory wasn't accepted by all scientist because it affirmed that time wasn't an absolute dimention, but a relative one, however this idea now is widely accepted. Einstein's theory was so revolutionary that it marked a change of era for physics, the era after Einstein is know as Modern Physics. Before Einstein two great scientists (Galileo Galilei and Issac Newton) discovered and studied the laws that acted as a basis for all modern science. Newton got most of the credit for the advances he made using as a basis Galilei's work and he expressed the basic laws of mechanics, now known as Newtonian Mechanics. In Classical Physics every single motion was to be analyzed in four dimentions: three positional ones and time. This works well. Also in Classical Physics time is the only absolute of the dimentions, it is the same for every particle or object in all motion states. The other three remain relative to something else, because it is known that we can't find a frame of reference which is static and can act as the 'true' frame of reference. What Einstein proposes in the theory is that the fourth dimention (time) is relative to the motion-state of the observer relative to the time measuring unit (clock). The Postulates The Special Theory of Relativity has two postulates: The Principle of Relativity holds valid and correct for every single natural event. The speed of light in the vacuo or in any inercial frame of reference is always the same, regardless of the motion of the light source relative to the inertial frame of reference. Both of the postulates have been explained and demonstrated already in previous lessons, specially in the one about Classical Relativity. Mathematically the Special Theory of Relativity is really simple, it doesn't involve much more than elemtal algebra, however to understand all the phyisical reasoning can be hard. It is always important to say that an open-mind is really important to understand the theory, specially because there are somethings that go against our intuition and logic, also because sometimes it looks like what is being said is an absurd, when this happens we ask you to read again and think it all over starting by thinking that everything is relative to something else.
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