### Einstein and Action-at-a-distance

By Johny Jagannath

I recently stumbled on an address that Einstein gave in 1920, at Leiden about his theories in which Einstein talks about action-at-a-distance [in the Newton's Bucket experiment]. I found this puzzlingly interesting as it demonstrates a fundamental misunderstanding of the simple mechanics that are at work in the Newton's Bucket experiment.

This fundamental misunderstanding first began when a philosopher made certain incorrect remarks about the Newton's Bucket experiment. Einstein took these incorrect remarks and elevated them to a Principle that is now known as: The Mach's Principle. Wikipedia summarizes the Principle or the conjecture in the following manner:
You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?
Of course the answer to the above question is: Centrifugal forces. And the origin of centrifugal forces lie in the fact that someone physically applied a force on you which caused you to rotate. Rotations give rise to Centrifugal forces [that push your arms outwards]. So there is nothing unusual about the Mach's conjecture. This is very simple mechanics. But let us see what Einstein thought of this, but in the context of the Newton's Bucket experiment, where water gives itself a concave surface because of centrifugal forces. Read on...
Albert Einstein gave an address on 5 May 1920 at the University of Leiden. He chose as his topic Ether and the Theory of Relativity. He lectured in German but we present an English translation below. The lecture was published by Methuen & Co. Ltd, London, in 1922.

http://www-groups.dcs.st-and.ac.uk/~history/Extras/Einstein_ether.html
From the above 1920 address Einstein explains why there were centrifugal forces in the Newton's Bucket experiment when the bucket/water was rotated relative to the universe [distant masses, stars etc]. See below ...
But inertial resistance opposed to relative acceleration of distant masses presupposes action at a distance;
Please note the term: action-at-a-distance. What Einstein is saying above is that when a Bucket/water is rotated, relative to the universe [distant masses, stars etc] the resistance offered by the water/bucket to rotate [which manifests itself as centrifugal forces] presupposes action-at-a-distance! This is totally wrong. This is like saying, when I physically try to move a large object, the resistance it provides [which I need to overcome to have the large object move] is due to action-at-a-distance! This makes no sense at all because I am making physical contact to move an object. There is no question of action-at-a-distance when I physically move an object [to rotate it]. When I move an object, I physically touch it.

By definition, action-at-a-distance means to move [or deform] an object without physically touching it.

Therefore, why did Einstein think that there is action-at-a-distance when one spins around [that causes your arms to fly out]? In my opinion, Einstein was probably unaware of centrifugal forces, and therefore watching the arm fly out without an external agent acting on the arms misled Einstein into believing that the arms do fly out because of action-at-a-distance. That is, stars pulling on them from a distance! LOL.

Therefore, the suggestion that there is action-at-a-distance in the Newton's Bucket experiment [Mach's Principle or conjecture] is a catastrophic misunderstanding of the laws of mechanics.

Einstein goes on to say, that he is going to re-explain inertia [and gravity] via an ether that he calls, spacetime. Of course this is totally unwarranted without any mechanical basis whatsoever, as outlined here. Einstein does not realize that his botched up redefinition [or understanding] of inertia [centrifugal forces and gravity] is taking him right back to action-at-a-distance, which he appears to dislike very much as seen in the following quote from the 1920 address at Leiden.
and as the modern physicist does not believe that he may accept this action at a distance, he comes back once more, if he follows Mach, to the ether, which has to serve as medium for the effects of inertia.
Yet, Einstein sees no reason why his own theory is action-at-a-distance. Ether, prior to Einstein was assumed to freely penetrate through matter. Now Einstein turns the medium on its head. He gives it properties, such as elasticity because it can now curve in the presence of matter. It can transmit or render the effects of "inertia" on an object [when I push it]. The problem in all of this is he has provided absolutely no [relevant] mechanics to back his claims.
It was Newton's theory of gravitation that first assigned a cause for gravity by interpreting it as action at a distance, proceeding from masses. Newton's theory is probably the greatest stride ever made in the effort towards the causal nexus of natural phenomena. And yet this theory evoked a lively sense of discomfort among Newton's contemporaries, because it seemed to be in conflict with the principle springing from the rest of experience, that there can be reciprocal action only through contact, and not through immediate action at a distance.
The introduction of a medium and giving it properties is hardly a mechanism. To know more about Einstein's assertions [on centrifugal forces and gravity] and why it has no mechanical basis, please click here.