Reference: The Book of Physics
Note: The original text is provided below.
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Summary
Eddington says that some people are skeptical about the contraction of measuring rods. There exists deep conditioning about location in space. When we sense objects and their locations in space, we have a frame of space. But this frame of space changes when we are in motion at high speeds.
This shows that “right” location in space cannot be nearly so important and fundamental as it is made out to be in the Newtonian scheme of things. The Newtonian idea of location contains some truth and some padding.
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Comments
What actually is missing in Newtonian scheme of things is the relationship between inertia and motion. The frame of space does not depend on the relative speed of the observer. It depends on the acceleration of the object with resulting change in its inertia.
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Original Text
Before going further I must answer the critic who objects in the name of common sense. Space—his space—is so vivid to him. “This object is obviously here; that object is just there. I know it; and I am not going to be shaken by any amount of scientific obscurantism about contraction of measuring rods.”
We have certain preconceived ideas (about location in space) which have come down to us from ape-like ancestors. They are deeply rooted in our mode of thought, so that it is very difficult to criticize them impartially and to realise the very insecure foundation on which they rest. We commonly suppose that each of the objects surrounding us has a definite location in space and that we are aware of the right location. The objects in my study are actually in the positions where I am “aware” that they are; and if an observer (on another star) surveying the room with measuring rods, etc., makes out a different arrangement of location, he is merely spinning a scientific paradox which does not shake the real facts of location obvious to any man of common sense. This attitude rejects with contempt the question, “How am I aware of the location?” If the location is determined by scientific measurements with elaborate precautions, we are ready enough to suggest all sorts of ways in which the apparatus might have misbehaved; but if the knowledge of location is obtained with no precautions, if it just comes into our heads unsought, then it is obviously true and to doubt it would be flying in the face of common sense! We have a sort of impression (although we do not like to acknowledge it) that the mind puts out a feeler into space to ascertain directly where each familiar object is. That is nonsense; our common sense knowledge of location is not obtained that way. Strictly it is sense knowledge, not common sense knowledge. It is partly obtained by touch and locomotion; such and such an object is at arm’s length or a few steps away. Is there any essential difference (other than its crudity) between this method and scientific measurements with a scale? It is partly obtained by vision—a crude version of scientific measurement with a theodolite. Our common knowledge of “where things are” is not a miraculous revelation of unquestionable authority; it is inference from observations of the same kind as, but cruder than, those made in a scientific survey. Within its own limits of accuracy the scheme of location of objects that I am instinctively “aware” of is the same as my scientific scheme of location, or frame of space.
When we use a carefully made telescope lens and a sensitized plate instead of the crystalline lens and retina of the eye we increase the accuracy but do not alter the character of our survey of space. It is by this increase of refinement that we have become “aware” of certain characteristics of space which were not known to our ape-like ancestor when he instituted the common ideas that have come down to us. His scheme of location works consistently so long as there is no important change in his motion (a few miles a second makes no appreciable difference); but a large change involves a transition to a different system of location which is likewise self-consistent, although it is inconsistent with the original one. Having any number of these systems of location, or frames of space, we can no longer pretend that each of them indicates “just where things are”. Location is not something supernaturally revealed to the mind; it is a kind of conventional summary of those properties or relations of objects which condition certain visual and tactual sensations.
Does not this show that “right” location in space cannot be nearly so important and fundamental as it is made out to be in the Newtonian scheme of things? The different observers are able to play fast and loose with it without ill effects.
Suppose that location is, I will not say, entirely a myth, but not quite the definite thing it is made out to be in classical physics; that the Newtonian idea of location contains some truth and some padding, and it is not the truth but the padding that our observers are quarrelling over. That would explain a great deal. It would explain, for instance, why all the forces of Nature seem to have entered into a conspiracy to prevent our discovering the definite location of any object (its position in the “right” frame of space); naturally they cannot reveal it, if it does not exist.
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