September 10, 1952
Dear Professor Einstein:
By your answer to my letter you have truly obliged me to think the problem all over again. I have tarried to answer because I did not wish to appear just obstinate; but the problem is permanently on my mind. I have to ask patience, which a Fachman is generally reluctant to accord to an outsider. Without this patience we shall build barriers between sciences, in this caseastronomy and history. I would certainly listen carefully to what you may say on history or psycho- analysis.
You say that the fact of the exact correspondence of the planetary motions with the theory proves this theory as correct: in the celestial motions only two agents participategravitation and inertia. Let us first assume that your statement of exact correspondence between theory and phenomena is rigidly correct. Still the mere fact of a force acting at an inverse square rate would not exclude electricity and magnetism, also acting at the inverse square rate, from participation in celestial motions. But the statement is not rigidly correct, either. Let me illustrate.
Here is the year 1845. Leverrier in France and Adams in England, out of perturbations of Uranus calculated, to the exactness of one degree of arc, the presence of a yet unseen planet. Both of them assumed that a planet of a size not larger than that of Uranus travels on an orbit at a distance dictated by Bodes law. Neptune is actually of the size of Uranus, but the mean distance between their orbits is not ca. 1,750,000,000 miles, as Bodes law required, but only ca. 1,000,000,000 miles; thus the error is equal to ascribing to Neptune a triple mass. The discovery of Pluto did not solve the conflict between the theory and the fact and caused also conflicting estimates of Plutos mass. Thus the finding of the planetary stations in relation to a chart of fixed stars is not enough; if the theory is true the distances must also be correct. And still the discovery of Neptune is regarded as the strongest proof of the Newtonian theory of celestial motions.
Now in the same 1845, the year of this triumph, Leverrier calculated also the anomaly of Mercury, and by this caused to think that the Newtonian law of gravitation may be not precisely true. Leverrier first thought of some planet moving inside the Mercurial orbit or of a possible unequal distribution of the mass in the sun. You have used the fact of the anomaly to prove that the space is curving in the presence of a mass. About the same timein 1913G. E. Hale published his paper on The general magnetic field of the sun (Contr. M. Wilson Obs., #71), in which he estimated the general magnetic field of the sun as of 50 Gauss intensity. At this intensity under certain conditions electromagnetic forces are much stronger than gravitation. (Alfven) The last named author in his cosmical Electro-dynamics (Oxford, 1950, p. 2) shows that a hydrogen atom at the distance of the earth from the sun and moving with the earths orbital velocity, if ionized, is acted upon by the solar magnetic field ten thousand times stronger than by the solar gravitational field.
Now the visible streamers of the sun that conveyed to Hale the idea that the sun is a magnet reach a long way toward Mercury, almost half the way. Was the electromagnetic state of the sun ever considered as the cause of the anomaly? The effect of the e.-m. action must have been reckoned, and possibly excluded, but not disregarded. . . .
The fact that the theory accurately coincided with the observed planetary positions was the main argument for the Ptolemaic system and against the heliocentric system. For more than two generations, until 1600, it was not the Roman Church who opposed the Copernican theory; the scientists opposed it and used as their main argument their ability to predict planetary positions, conjunctions and eclipses. They have actually predicted eclipses that we still have to experience in the future. How could they achieve this degree of accuracy with the sun revolving on one of the orbs around the earth? By a continuous adjustment of their observations to their theories and their theories to observations. Similarly it is today. And when the facts prove to be different from what they were supposed to bethat the sun is charged, or that the cometary tails are electrically glowing, or that planetary positions of Saturn or Jupiter markedly influence our ionosphere,then these facts are left outside of the theory and it covers less and less of the phenomena. No wonder that it agrees with the residual facts in such an arrangement.
Sometimes it seems to me that the hidden psychological cause of the emotional attitude of the scientists to Worlds in Collision is in its reminding a few repressed physical facts. In that book I have not invented new physical laws or new cosmical forces, as cranks usually do; I have also not contradicted any physical law; I came into conflict with a mechanistic theory that completely coincides with a selected group of observations; my book is as strange as the fact that the Earth is a magnet, the cause of which is indeterminate and the consequences of which are not estimated in the Earth-Moon relations.
When over a year ago, Professor Stewart, your neighbor, was invited together with myself by the Presbyterian Society of this town to participate in a debate about my book, and the time became short, I asked my opponent: But you have excluded the existing electromagnetic conditions in the solar system from the celestial mechanics, his answer was: We do not need them: our calculations are perfect without them. Later, when our debate was renewed on the pages of Harpers Magazine, I observed: If the balance sheet of a bank is correct to the last cent, but two large deposits (electricity and magnetism) are omitted, the entire balance may be questioned. . . .