Space, Time and Gravitation: An Outline of the General Relativity Theory

by Arthur Stanley Eddington

This classic book is essential reading for all those interested in the development of modern physics. Sir Arthur Eddington's account of the general theory of relativity, 'without,' as he says in his preface, 'introducing anything very technical in the way of mathematics, physics or philosophy', was first published in the exciting days of 1920 soon after the first objective tests of the theory had demonstrated its validity. The book was at once received with acclamation by reviewers and remains today one of the simplest and most straightforward accounts in print. The reviewer in the Athenaeum described it as 'a masterly book. The arrangement, the vigour and ease of the reasoning, the felicity of illustration, the clear, flexible prose and (we must mention it) the wit, make this book one of the most adequate and engaging attempts at the non-technical exposition of a scientific theory that it has ever been our good fortune to encounter.' This reissue includes a foreword by Sir Hermann Bondi, FRS, giving a brief appraisal of the book, and placing it in its historical and scientific context.

Genres: Science, Physics, Nonfiction, Astronomy

232 pages, Paperback

First published January 3, 1920

About the author

Sir Arthur Stanley Eddington, OM, FRS was a British astrophysicist of the early 20th century. The Eddington limit, the natural limit to the luminosity of stars, or the radiation generated by accretion onto a compact object, is named in his honour.

He is famous for his work regarding the Theory of Relativity. Eddington wrote a number of articles which announced and explained Einstein's theory of general relativity to the English-speaking world. World War I severed many lines of scientific communication and new developments in German science were not well known in England. He also conducted an expedition to observe the Solar eclipse of May 29, 1919 that provided one of the earliest confirmations of relativity, and he became known for his popular expositions and interpretations of the theory.

Reviews

[J.D. Steens · Rating 3 out of 5]

The complex concepts in the book (the book’s title) are not, as conveyed by Eddington, easy to understand. I’d say that the book has four overarching themes:

First, everything in the cosmos exists in a field of movement and, therefore, everything is in motion relative to everything else. For physics, which is measurement of intervals between two or more events (points), this is relativity. There is no privileged point (inertial frame) to measure something. Rather, any reference point must be stipulated: “the gravitational field…is not absolute, but always requires that some observer should be specified.” Since everything is in motion relative to each other, any (reference to) reference point, given the vastness of the cosmos, also must be specified in four dimensions: “right-and-left, backwards-and-forwards, up-and-down, sooner-and-later”).

Second, at all cosmological scales (and quantum scales too?), everything exists in a curvature. Mass that is bound energy (congealed energy “which is not yet releasable” or, rest mass as potential energy and motion as expressed energy), curves the fabric of spacetime, creating movement toward itself (subject to the inverse square law: relative size and distance of massive bodies to each other). The drawing of mass-energy together in turn creates greater mass and curvature. This appears to be a predating of Wheeler’s “spacetime tells matter how to move; matter tells spacetime how to curve.”

Third, as the cosmos is curved, mass-energy’s natural straight-line, inertial track, moves around, and turns back to itself. Spacetime, Eddington states, may have “an essential curvature at a great scale,” something he refers to as “the sphericity of the world.” In illustrating this point, Eddington refers to a ray from our sun that, in zillions of years, returns to itself, to a “ghostly” point in space as the sun either no longer exists or because it has moved position. Thus, Eddington says, physics has moved from “a mechanical to a geometric theory of fields of force.”*

Regarding this issue of overall curvature, Eddington states that centrifugal force (outward movement) increases until it reaches the sphere of greatest area and then per gravitation, diminishes to zero in the antipodes. It is not clear if Eddington is writing literally of a centrifugal force as if a rotating singularity pulls in and pushes out mass-energy, or if a big bang sends released mass-energy outward until, per the inverse square law, it reaches its antipode condition (stasis) when, released from gravity, inertial movement continues around, back toward a cosmic starting point, driven by the geometric theory of curvature by an overall, cosmic gravitational center.

Fourth, Eddington’s last chapter, “On the Nature of Things,” per Lucretius I presume, puts his physics into a philosophical framework, though not in a particularly clear way. The world is not governed by stasis. It is governed by movement: Natural, inertial, movement under the presence of curvature. Curvature moves, and movement toward the center creates curvature. There is no absolute beginning. There is no super prime mover agent that got all things rolling. Everything moves between the two antipodal differentials. The mind thinks in terms of linear cause and effect, with absolute points anchoring it all, but that is an illusion,** really, though not the kind of illusion that Plato wrote about in his cave analogy. Yet, in the end, Eddington gets a bit too mystical for me in his theory of “mind-stuff” in which the laws of reality lie in the mind because, it seems to me, the cosmos just is, and the mind encapsulates what is through the formation of laws.*** That’s my best attempt to make sense of what he’s saying here.

This notion of movement back and forth in some great cosmic rhythm without beginning or end is a tough one to grasp.**** We’re about survival. Survival is about, relatively, permanent things (needs and threats) related to survival (Quoting a person named Lodge, Eddington writes “'...our senses were developed by the struggle for existence, not for the purpose of philosophizing the world'”), and their linear cause-effect relationships. Perpetual, causeless, movement means that the cosmos always was. There never was a beginning; there never will be an end.

*The natural track of (inertial) motion is a straight-line - the principle of movement is the the principle of least effort. But in the presence of an all-pervading curvature, straight-line movement’s natural track (though Eddington qualifies it by saying that light is deflected by local gravitation or absorbed by matter) is to curve (be accelerated by large mass-energy bodies) and eventually, to return to itself. Movement through a large gravitational field follows the principle of least action: the shortest length and least time is curved, not straight-line, movement. Also, because straight-line motion is always under curvature, there is rotation, a movement around. “Geodesic structures,” (gravitational centers), he says, “rules all matter.” Eddington writes that the distinction between force as a cause and inertia that is natural movement without a cause “cannot be sustained.” Movement flows from high to low, from low to high, a natural and internal dynamic between states of imbalance and balance. There is nothing that reaches out, grabs and pulls. More specifically, reality is relations. It is a field of movement between the antipodes.

** “Mind,” Eddington writes, “exalts the permanent and ignores the transitory.”

***Nature just is, “but the whole of those laws of nature which have been woven into a unified scheme - mechanics, gravitation, electrodynamics and optics - have their origin, not in any special mechanism of nature, but in the workings of the mind. ‘Give me matter and motion,’ said Descartes, ‘and I will construct the universe.’ The mind reverses this. ‘Give me a world - a world in which there are relations - and I will construct matter and motion.’ Are there then no genuine laws in the external world? Laws inherent in the substratum of events, which break through into the phenomena otherwise regulated by the despotism of the mind? We cannot foretell what the final answer will be; but, at present, we have to admit that there are laws which appear to have their seat in external nature. The most important of these if not the only law, is a law of atomicity…..Action is generally regarded as the most fundamental thing in the real world of physics, although the mind passes it over because of its lack of permanence; and it is vaguely believed that the atomicity of action is the general law, and the appearance of electrons is in some way dependent on this….We have found a strange foot-print on the shores of the unknown. We have devised profound theories, one after another, to account for its origin. At last, we have succeeded in reconstructing the creature that made the foot-print. And, lo, it is our own.”

****Hubble findings, as confirmed, arguably, by others, of an expanding cosmos, at an ever increasing speed, counters this back and forth rhythmic structure. On this point, Eddington seems (I don't really understand it) to offer the possibility of another explanation for that Hubble finding: "The data are not so ample as we should like; but there is no doubt that large receding motions greatly preponderate. This may be a genuine phenomenon in the evolution of the material universe; but it is also possible that the interpretation of spectral displacement as a receding velocity is erroneous; and the effect is really the slowing of atomic vibrations predicted by de Sitter's theory." Given Eddington's leanings to "mind-stuff," his reference to "the material universe" is interesting.

[Riddhiman · Rating 4 out of 5]

To be honest I did not understand most parts of this book when I read it, since it has references to Tensor Calculus, which as a student of 11th standard, I could not grasp (though I was familiar with the basics of calculus). However, I did understand the concepts of general relativity from this book. It also outlines Eddington's account of his famous experiment that established General Relativity firmly.

[Jack · Rating 4 out of 5]

better than I expected.

Eddington was a pretty good writer so this wasn’t too hard to follow. The subject is complicated, so you really have to concentrate and you may find yourself re reading sections. Still, it’s worthwhile hearing from the people who made the discoveries.

[Mukharbek Organokov, PhD · Rating 5 out of 5]

The book about the birth of many fields of Physics.

[Elaine de Jong · Rating 3 out of 5]

An interesting read. I’ll have to go over it many times before I can gain any understanding. One thing I did learn is that “flat earth-ers” have a “homaloidal” view of the earth.

[Yoshimasa Tokioka]

At last, I found the way to how to make a perfect round-trip time machine! Neither the corpuscular theory nor the wave theory, I'm sure!! ......