Ether and General Relativity

The idea of the ether comes from:

• the theory of action at a distance
• the properties of light which have led to the undulatory theory

Outside of physics, we know nothing of action at a distance*.

It seems to us that there are only actions of immediate contact:

• collision
• push and pull
• heating or inducing combustion by means of a flame, etc.

Weight is action at a distance. It plays a very important part.

But since we experience weight constantly we do not speculate as to the cause of gravity. Therefore we do not become conscious of it as action at a distance.

In Newton’s theory, the cause of gravity is mass.

• Yet Newton’s contemporaries were uneasy with this because experience teaches that movement comes from contact.

Contact Forces vs Action at a Distance

This means that either:

1. Contact forces are really distant forces at small distances. This is what Netwonians favored.

2. Newtonian action at a distance [gravity] is really contact force from afar, conveyed by a medium permeating space This led to the ether hypothesis.

The ether hypothesis did not at first bring with it any theory of gravity*. It became customary to treat Newton’s Laws as axioms not further reducible.

The ether hypothesis found fresh support in the first half of the 19th century when light was proven to be elastic waves in ponderable bodies.

Light became a vibratory process in an elastic, inert medium filling up universal space. Light can be polarized. It follows that the ether must be a solid body. This is because transverse waves are not possible in a fluid, but only in a solid.

This led to the theory of the “quasi-rigid” luminiferous ether. Relatively to one another, it only carried the small movements of deformation which correspond to light-waves.

Fizeau’s experiment is fundamental to both:

• the ether and
• Special Relativity.

It showed that the ether does not take part in the movements of bodies.

The phenomenon of aberration also favoured the theory of the quasi-rigid ether.

Maxwell and Lorentz

Maxwell and Lorentz developed the theory of electricity which gave an unexpected turn to the ether.

For Maxwell, the ether still had purely mechanical properties, although much more complicated than the mechanical properties of tangible solid bodies.

But neither Maxwell nor his followers could elaborate a mechanical model for the ether which might furnish a satisfactory mechanical interpretation of Maxwell’s laws of the electro-magnetic field.

The laws were clear and simple, the mechanical interpretations clumsy and contradictory.

They were influenced by the electro-dynamical investigations of Heinrich Hertz.

Before Hertz, the conclusive theory only demanded mechanics-concepts (e.g. densities, velocities, deformations, stresses).

They gradually admitted electric and magnetic force as fundamental concepts side by side with those of mechanics, without requiring a mechanical interpretation for them.

Thus the purely mechanical view of nature was gradually abandoned.

This led to a fundamental dualism which was insupportable in the long-run. The strict validity of Newton’s mechanics was shaken by the experiments with β-rays and rapid cathode rays.

In the theory of Hertz, matter is:

• the bearer of velocities, kinetic energy, and mechanical pressures, and
• electromagnetic fields which also occur in vacuo (in free ether)

This means that the ether also bears electromagnetic fields. It is thus indistinguishable in its functions from ordinary matter*.

Within matter, it takes part in the motion of matter. In empty space, it has a velocity everywhere*.

In this way, it has a definite velocity throughout space. There is no fundamental difference between Hertz’s ether and ponderable matter (which in part subsists in the ether).

The Hertz theory was wrong in ascribing mechanical states and electrical states to matter and ether because I think they have no relation to each other. It was also at variance with Fizeau’s experiment on the speed of light in moving fluids.

Then, H. A. Lorentz entered the scene and simplified the theory.

He harmonized the ether theory with experience through a wonderful simplification of theoretical principles.

• This was the most important advance in the theory of electricity since Maxwell.

He achieved this by taking from ether its mechanical qualities, and from matter its electromagnetic qualities.

The ether in empty space and inside matter was exclusively the seat of electromagnetic fields*.

According to Lorentz, only the quantum particles of matter can carry out movements. Their electromagnetic activity is entirely confined to the carrying of electric charges*.

Thus, Lorentz reduced all electromagnetic happenings to Maxwell’s equations for free space.

The only mechanical nature of the Lorentzian ether is its immobility. Special Relativity removed this immobility.