The Apparent Incompatibility of The Law Of Propagation of Light with The Theory of Relativity
Hello Friends, in this section we will study about how the most simple law of Physics i.e. The Law of propagation of Light which seemed to be incompatible with The Theory of Relativity.Every child studying in a school believes that he knows that light travels with a velocity which is equal to c (30,00,00,000 m/s) but the theory of relativity was not seeming to be much favorable to the law. In his famous Double Star experiment the Dutch Astronomer,DE Sitter, had also shown that velocity of light does not depend on the state of motion of the body. For the better understanding of the thing, let us come back to our embankment. Now , we remove all the air above the embankment and put a source of light above the embankment. If I ask you what is the velocity of light with respect to the embankment , the answer comes out to be 'c' which is the correct one. But now, I will complicate the situation a bit. What if I introduce back our old friend i.e. the railway carriage , and tell you that it is travelling with a velocity V in the direction of propagation of light with respect to the embankment.If I ask you now that what is the velocity of light with respect to the carriage. Let us call this velocity as W. The answer that one's intuition gives or the answer that one will give after studying the section "The Theorem of Addition of Velocities" comes out to be like this.
W= c - V
And hence the velocity comes out to be somewhat less than c , which actually contradicts The Law of Propagation of Light. And now comes a conclusion that either the theory of Relativity is wrong or The law of propagation must be something else for a moving body like the railway carriage.Those who have studied carefully, till here, must be thinking the Relativity should retain and The Law of propagation of Light must be replaced by something more complicated.But this path could not be pursued. The works and investigations of H.A Lorentz on the Electrodynamics and optical phenomenon show that experience in this domain leads to such a theory of electromagnetic phenomenon for which The Law of propagation of light must hold true.This made the part of Relativity weaker and it came on the verge of rejection. But due to the analysis of physical conceptions of space and time (which we will read about in the next sections) , both of these laws came out to be compatible and the theory made by merging these laws was known as 'THE SPECIAL THEORY OF RELATIVITY.'
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