# Einstein postulates of theory of relativity

Explanation of the negative results of the Michelson-Morley experiment:

As the theoretical results of the M-M experiment did not match with the experimental results (Theoretically fringe shift result was not zero, it was about 0.4 but the experimentally it was 0). Even then the scientists of that time had conviction that ether exist and earth moves with respect to it. Thus there was lot of debate and discussion regarding this as why there were negative results (that is why the theory and experiment result did not match?).

Following are the reasons given by the scientists:

1.  Ether Drag Hypothesis: The then scientists assumed that ether exits and it is attached with the earth. Thus it will be dragged with the earth so the relative velocity of ether and earth will be zero. If this is taken then theory and experimental will get matched. But this hypothesis is discarded as there was no proof for this.

2. Lorentz-Fitzgerald Hypothesis: Lorentz told that the length of the arm (distance between the pale and the mirror M2) towards the transmitted side should be L(√1 – v2/c2) but not L. If this is taken then theory and experimental will get matched. But this hypothesis is discarded as there was no proof for this.

Einstein explanation of negative results of M-M experiment:

Then Einstein gave his postulates by suggesting that there is no medium like ether. There are two postulates of the theory of relativity given by Einstein:

1.  Einstein’s First Postulate of theory of relativity:

All the laws of physics are same (or have the same form) in all the inertial frames of reference moving with uniform velocity with respect to each other. (This postulate is also called the law of equivalence).

2. Einstein’s second Postulate of theory of relativity:

The speed of light is constant in free space or in vacuum in all the inertial frames of reference moving with uniform velocity with respect to each other. (This postulate is also called the law of constancy).

## 3 Replies to “Einstein postulates of theory of relativity”

1. what about the turning the system by 90 degree …………….i can’t get it yet…..

1. amit says:

If you mean that Michelson and Morley turn the apparatus by 90 degree, then it means that they rotated the apparatus to change the positions of mirrors M1 and M2. This was done to do experiment accurately. Then the path difference is measured. Actually in research, the experiments are done repeatedly to improve the accuracy of results by averaging.

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