# From Newton to Einstein – Search for a Fundamental Frame of Reference

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It was on account on Newton’s insistence as to the existence of a fundamental or absolute frame of reference, called absolute space, that the search for it was carried on. This search resulted in the discovery, or rather the invention, of that monstrosity of a medium, Luminiferous Ether, as the following brief account will show:

Maxwell clearly demonstrated, in the year 1864, the inter-relationship between electricity, magnetism and light when, from the known properties of electricity and magnetism, he formulated his celebrated theory of electromagnetic radiation and have the well know equations of electromagnetic field which bear his name and are identical with those that represent a wave phenomenon. He thus established the presence of electromagnetic waves in space, travelling with the speed of light. In other words, he proved that light is an electromagnetic wave.
Since waves known hitherto (like sound and water waves) all required a material medium (air and water respectively) for their propagation, it was supposed that there must also be a suitable medium to carry there newly found electromagnetic waves, which travelled even through empty space between the stars and the earth. This intangible medium, though no one knew what it actually was, came to be referred to as luminiferous ether, pervading all space , empty or otherwise.

Further, to enable it to transmit light, a transverse wave, the ether had to be a rigid solid and, in view of the tremendous velocity of light, it had to have a large shear modulus and yet all material objects, like the earth and the planets and the stars etc, were to continue in their regular courses through it without encountering the slightest resistance. Utterly incredible as it seems to us today, no one seemed to object to its existence. On the other hand, it was felt that perhaps it was the absolute space or the fundamental frame of reference Newton was looking for and in which (or in a frame fixed relative to it) his laws of motion would hold perfectly.

On the face of it, it was such an inviting — and exciting– proposition and many a brilliant experiment were sought to be devised to establish the existence of this elusive medium, ether, and hence that of an absolute frame of reference. It was but natural that light water should be used for the purpose, since, after all, ether was little else but just a vehicle for them.

Now, the orbit of the earth around the sun having a radius of 150 million km, its orbital velocity works out to 30 km/s. So that, even assuming that the sun has no ether drift, the velocity of the earth through the ether must be this orbital velocity of 30 km/s and the same must, therefore, also be the velocity of the resulting ether drift. Since the velocity of light is (was) $3 \times 10^5$ km/s, it will be easily seen that the velocity of the expected ether drift is just $\frac {30} {3 \times 10^5}$ =1/10000th part of the velocity of light. Obviously, therefore a very sensitive apparatus was called for, if the experiment was to succeed.

Maxwell had actually despaired of any terrestrial methods being sensitive enough for the purpose and started looking for any astronomical evidence that may come his way in support. But A. A. Michelson of the United States, when he learnt about it in the year 1879, accepted the challenge, and along with his colleague E. W. Morley (at the Case Institute of Technology in Cleveland), succeeded in performing, in the year 1887, one of the most famous experiments in the history of the physics, which have a null result, striking at the very root of the ether hypothesis.