Mach’s Principle and Einstein’s theory of the Aether

In the following analysis we demonstrate that Einstein’s theories of Special and General Relativity were constrained by his far-reaching insights concerning the Aether.

Summary:

An investigation of Einstein’s insights concerning the nature of the Aether suggest that his conceptual framework for Special and General Relativity was constrained by his understanding of the Aether as a physical entity devoid of mechanical properties. Furthermore, the clearest mathematical generalization of Einstein’s notion of the Aether appears to have been realized by Emmy Noether.

The analysis is based almost entirely upon Einstein’s influential essay[1], although Einstein’s analysis is indebted to the analyses of Isaac Newton and Ernst Mach’s consideration of Mach’s Principle.

Mach’s Principle and Einstein’s theory of the Aether:

1. The notion of the Aether emerged from Newton’s mysterious theory of action-at-a-distance and later Maxwell’s field theory for electromagnetic waves which forced scientists to reflect upon the mystery of light’s propagation through space.

2. Newton’s theory of gravitation first assigned a cause for gravity by interpreting it as action-at-a-distance, proceeding from point masses. However, this theory provoked a sense of discomfort among Newton’s contemporaries as it appeared to be in conflict with the principle that there may be reciprocal action only through contact and not through immediate action-at-a-distance.

3. In the time of Newton and Maxwell, this led to two orthogonal analyses concerning the Aether:

   1. The path taken by Newton’s followers who assumed that all contact forces are actually Newtonian action-at-a-distance.
   2. Those who assumed that Newtonian action-at-a-distance is only immediate action-at-a-distance in appearance but actually conveyed by a medium permeating space.

4. While Einstein’s Special Relativity appears to dismiss the possibility of an Aether, the objective measurability of rotating frames requires it. Thus, we may associate the notion of absolute space with the Aether. But, what are its properties?

5. The Aether of General Relativity is a medium which is itself devoid of mechanical and kinematic properties but helps to determine the effects of inertia. Thus, we may think of the Aether as a Platonic Demiurge which guarantees the comprehensibility of the Universe.

Discussion:

Upon closer inspection, relativity theory implies invariance relative to a certain group of transformations which was carefully considered by Emmy Noether. But, why should this hold and where does this lead us?

Einstein’s careful considerations actually lead us to the hypothesis that local physical laws are determined by the large-scale structure of the Universe. To be precise, we are led to conjecture the homogeneity and isotropy of space-time which we may identify with the Universality of the Aether.

References:

1. Albert Einstein. Ether and the Theory of Relativity. Methuen & Co. Ltd, London. 1922.

2. Julian B. Barbour; Herbert Pfister, eds. (1995). Mach’s principle: from Newton’s bucket to quantum gravity. Volume 6 of Einstein Studies. Boston: Birkhäuser.