Sir Arthur Stanley Eddington, OM (28 December, 1882 – 22 November, 1944) was Plumian Professor of Astronomy at the University of Cambridge. He was arguably the most important astrophysicist of the early 20th century, and was also a successful populariser. He became world-famous in 1919, when his observations of the bending of starlight near the eclipsed sun proved the correctness of Albert Einstein's General Theory of Relativity.

Sourced

• We have found a strange footprint on the shores of the unknown. We have devised profound theories, one after another, to account for its origins. At last, we have succeeded in reconstructing the creature that made the footprint. And lo! It is our own.
  • Space, Time and Gravitation (1920)

• Physics has in the main contented itself with studying the abridged edition of the book of nature.
  • "A Generalization of Weyl's Theory of the Electromagnetic and Gravitational Fields" in Proceedings of the Royal Society of London A99 (1921), p. 108

• At terrestrial temperatures matter has complex properties which are likely to prove most difficult to unravel; but it is reasonable to hope that in the not too distant future we shall be competent to understand so simple a thing as a star.
  • The Internal Constitution of Stars, Cambridge. (1926). ISBN 0521337089
  • Paraphrased variants: It is sound judgment to hope that in the not too distant future we shall be competent to understand so simple a thing as a star.
    It is not too much to hope that in the not too distant future we shall be competent to understand so simple a thing as a star.

• I think that science would never have achieved much progress if it had always imagined unknown obstacles hidden round every corner. At least we may peer gingerly round the corner, and perhaps we shall find there is nothing very formidable after all.
  • Stars and Atoms (1927); lecture 1

• To the pure geometer the radius of curvature is an incidental characteristic — like the grin of the Cheshire cat. To the physicist it is an indispensable characteristic. It would be going too far to say that to the physicist the cat is merely incidental to the grin. Physics is concerned with interrelatedness such as the interrelatedness of cats and grins. In this case the "cat without a grin" and the "grin without a cat" are equally set aside as purely mathematical phantasies.
  • The Expanding Universe. (1933) Ch. IV The Universe and the Atom

• There once was a brainy baboon,
  Who always breathed down a bassoon,
  For he said, "It appears
  That in billions of years
  I shall certainly hit on a tune".
  • New Pathways in Science (1939)

• It is also a good rule not to put overmuch confidence in the observational results that are put forward until they are confirmed by theory.
  • As quoted in "Annals of Science II-DNA" by Horace Freeland Judson in The New Yorker (4 December 1978), p. 132

• We used to think that if we knew one, we knew two, because one and one are two. We are finding that we must learn a great deal more about 'and'.
  • As quoted in A Dictionary of Scientific Quotations (1991) by Alan L. Mackay, p. 79

The Nature of the Physical World (1928)

Published versions of his Gifford Lectures delivered in the University of Edinburgh (January - March 1927)

• The idealistic tinge in my conception of the physical world arose out of mathematical researches on the relativity theory. In so far as I had any earlier philosophical views, they were of an entirely different complexion.
  From the beginning I have been doubtful whether it was desirable for a scientist to venture so far into extra-scientific territory. The primary justification for such an expedition is that it may afford a better view of his own scientific domain.
  • Preface

• Science aims at constructing a world which shall be symbolic of the world of commonplace experience. It is not at all necessary that every individual symbol that is used should represent something in common experience or even something explicable in terms of common experience. The man in the street is always making this demand for concrete explanation of the things referred to in science; but of necessity he must be disappointed. It is like our experience in learning to read. That which is written in a book is symbolic of a story in real life. The whole intention of the book is that ultimately a reader will identify some symbol, say BREAD, with one of the conceptions of familiar life. But it is mischievous to attempt such identifications prematurely, before the letters are strung into words and the words into sentences. The symbol A is not the counterpart of anything in familiar life.
  • Introduction

• The external world of physics has thus become a world of shadows. In removing our illusions we have removed the substance, for indeed we have seen that substance is one of the greatest of our illusions.
  • Introduction

• In the world of physics we watch a shadowgraph performance of the drama of familiar life. The shadow of my elbow rests on the shadow table as the shadow ink flows over the shadow paper. It is all symbolic, and as a symbol the physicist leaves it. Then comes the alchemist Mind who transmutes the symbols. The sparsely spread nuclei of electric force become a tangible solid; their restless agitation becomes the warmth of summer; the octave of aethereal vibrations becomes a gorgeous rainbow. Nor does the alchemy stop here. In the transmuted world new significances arise which are scarcely to be traced in the world of symbols; so that it becomes a world of beauty and purpose — and, alas, suffering and evil.
  The frank realisation that physical science is concerned with a world of shadows is one of the most significant of recent advances.
  • Introduction

• The quest of the absolute leads into the four-dimensional world.
  • Ch. 2 Relativity

• Motion with respect to the universal ocean of aether eludes us. We say, "Let V be the velocity of a body through the aether", and form the various electromagnetic equations in which V is scattered liberally. Then we insert the observed values, and try to eliminate everything which is unknown except V. The solution goes on famously; but just as we have got rid of all the other unknowns, behold! V disappears as well, and we are left with the indisputable but irritating conclusion —

0 = 0

This is a favourite device that mathematical equations resort to, when we propound stupid questions.

• • Ch. 2 Relativity

• Shuffling is the only thing which Nature cannot undo.
  • Ch. 4 The Running-Down of the Universe

• If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.
  • Ch. 4 The Running-Down of the Universe

• Never mind what two tons refers to. What is it? How has it entered in so definite a way into our exprerience? Two tons is the reading of the pointer when the elephant was placed on a weighing machine. Let us pass on. ... And so we see that the poetry fades out of the problem, and by the time the serious application of exact science begins we are left only with pointer readings.
  • Ch. 7 Pointer Readings

• Schrödinger's wave-mechanics is not a physical theory, but a dodge — and a very good dodge too.
  • Ch. 10 The New Quantum Theory

• The universe is of the nature of a thought or sensation in a universal Mind... To put the conclusion crudely — the stuff of the world is mind-stuff. As is often the way with crude statements, I shall have to explain that by "mind" I do not exactly mean mind and by "stuff" I do not at all mean stuff. Still that is about as near as we can get to the idea in a simple phrase. The mind-stuff of the world is something more general than our individual conscious minds; but we may think of its nature as not altogether foreign to feelings in our consciousness... Having granted this, the mental activity of the part of world constituting ourselves occasions no great surprise; it is known to us by direct self-knowledge, and we do not explain it away as something other than we know it to be — or rather, it knows itself to be.
  • Ch. 13 Reality

• The mind-stuff is not spread in space and time. But we must presume that in some other way or aspect it can be differentiated into parts. Only here and there does it arise to the level of consciousness, but from such islands proceeds all knowledge. The latter includes our knowledge of the physical world.
  • Ch. 13 Reality

• Consciousness is not sharply defined, but fades into sub-consciousness; and beyond that we must postulate something indefinite but yet continuous with our mental nature. This I take it be the world-stuff.

• It is difficult for the matter-of-fact physicist to accept the view that the substratum of everything is of mental character. But no one can deny that mind is the first and most direct thing in our experience, and all else is remote inference — inference either intuitive or deliberate.
  • Ch. 13 Reality

• Proof is the idol before whom the pure mathematician tortures himself.
  • Ch. 15 Science and Mysticism

The Philosophy of Physical Science (1938)

• For the truth of the conclusions of physical science, observation is the supreme Court of Appeal. It does not follow that every item which we confidently accept as physical knowledge has actually been certified by the Court; our confidence is that it would be certified by the Court if it were submitted. But it does follow that every item of physical knowledge is of a form which might be submitted to the Court. It must be such that we can specify (although it may be impracticable to carry out) an observational procedure which would decide whether it is true or not. Clearly a statement cannot be tested by observation unless it is an assertion about the results of observation. Every item of physical knowledge must therefore be an assertion of what has been or would be the result of carrying out a specified observational procedure.

• Let us suppose that an ichthyologist is exploring the life of the ocean. He casts a net into the water and brings up a fishy assortment. Surveying his catch, he proceeds in the usual manner of a scientist to systematise what it reveals. He arrives at two generalisations: No sea-creature is less than two inches long. (2) All sea-creatures have gills. These are both true of his catch, and he assumes tentatively that they will remain true however often he repeats it.
  In applying this analogy, the catch stands for the body of knowledge which constitutes physical science, and the net for the sensory and intellectual equipment which we use in obtaining it. The casting of the net corresponds to observation; for knowledge which has not been or could not be obtained by observation is not admitted into physical science.
  An onlooker may object that the first generalisation is wrong. "There are plenty of sea-creatures under two inches long, only your net is not adapted to catch them." The icthyologist dismisses this objection contemptuously. "Anything uncatchable by my net is ipso facto outside the scope of icthyological knowledge. In short, "what my net can't catch isn't fish." Or — to translate the analogy — "If you are not simply guessing, you are claiming a knowledge of the physical universe discovered in some other way than by the methods of physical science, and admittedly unverifiable by such methods. You are a metaphysician. Bah!"

• The mathematics is not there till we put it there.

Misattributed

• Not only is the universe stranger than we imagine, it is stranger than we can imagine.
  • Though sometimes attributed to Eddington without citation, this seems to be derived from a statement by J. B. S. Haldane, in Possible Worlds and Other Papers (1927), p. 286: The Universe is not only queerer than we suppose, but queerer than we can suppose.
  • Variants: The universe is not only stranger than we imagine, it is stranger than we can imagine.
    The world is not only stranger than we imagine, it is stranger than we can imagine.