Eclipse 1919
In Journal of Scientific Exploration, Vol. 13, No. 2, pp. 271-290, 1999. 892-3310 / 99 is found a very interesting article about the eclipse, which took place May 29, 1919, and which made Einstein worldfamos overnight. It is written by Ian McCausland and the title is: “Anomalies in the History of Relativity”.
Here is briefly, what the article brings to light:
The First World War lasted from 1914 until the end of 1918 and the peace with Germany was signed June 28, 1919 (The Treaty of Versaille). But already in March 1917 the Astronomer Royal of Btitain, Sir Watson Dyson, suggested that the total eclipse of the Sun that was to take place on May 29, 1919, would present an excellent opportunity to test the prediction of The General Theory of Relativity, that light would be bent by a gravitational field. Dyson undertook the organization of the eclipse expeditions, but did not go to observe the eclipse himself. It was Professor Arthur Stanley Eddington who became the leader of the eclipse expeditions. Incidentally he was knighted in 1930. Eddington is said to be a pacifist and that he was deferred from military service in the first world war “with the express stipulation that if the war should end by May 1919, then Eddington should undertake to lead an expedition for the purpose of verifying Einstein’s prediction!”. Eddington happened to lead two expeditions, of which the one went to Brazil, weil the other, in which Eddington himself took part, went to the island Principe in the Gulf of Guinea.
The deflection predicted by Einstein (1916) was very small, being about 1.7 seconds of arc for a ray of light at the edge of the Sun, and inversely proportional to the radial distance from the center of the Sun. Non of those stars, for which measurements were made during the eclipse, were within two solar radii of the center. The largest deflection occurred according to the theory would therefore have been less than 0.8 seconds of arc, which, for the 343-cm focal length of the telescope used by Eddington, would have corresponded to about 0.01 mm on the photograf. In addition, there were other technical difficulties because of having to transport telescopes to remote locations. For example, light from the stars was reflected by a mirror into the telescope, so that the mirror could be rotated to compensate for the rotation of the earth during a time exposure, instead of rotating the telescope, which was not feasible under the conditions of the eclipse expeditions.
Of possible sources of error was named:
1. Refraction of light in the Sun’s corona and/or in the earth’s atmosphere.
2. Distortions in the optical system caused by temperature changes during the eclipse.
3. Changes of scale between the eclipse plates and the comparison plates.
4. Distorsions in the photografic emulsion while drying.
5. Errors in measurement of the images on the plates.
In modern telescopes corresponding to those, present on the eclipse expeditions, but supposedly of a better quality, the possibilities to make accurate observations are estimated like this (MacRobert, 1995): “Viewed at high power from the bottom of our ocean of air, a star is a living thing. It jumps, quivers, and ripples tirelessly, and swells into a ball of steady fuzz. Rare is the night (at most sites) when any telescope, no matter how large its aperture or perfect its optics, can resolve details finer than 1 arc second. More typical at ordinary locations is 2- or 3-arc-second seeing, og worse.”
However, measurements of the actual deflections on the plates may have introduced some errors in view of the extremely small displacements involved. In addition, the weather was cloudy at Principe at the time of the eclipse. And the Astronomer Royal, Sir Frank Dyson, reported at a meeting of the Royal Astronomical Society on July 11, 1919, that he had a letter from Prof. Eddington, that obviously expressed greatly disappointment. Though he had secured 16 photographs, but only for the last six was the sky clear enough to show any stars; and, as the sky was generally only clear on one part of the plate at a time, the stars secured on the plates are badly distributed. From his best plate, however, he has some evidence of deflection in the Einstein sense, but the plate errors have yet to be fully determined.
Eddington’s biographer Professor A. Vibert Douglas (1957), has also descriped his measurement of that plate: From Eddington’s Notebook (June 3) it appears that he spent the whole day measuring, and the one plate measured gave a result agreeing with Einstein.
Douglas’s biography continued with the statement that “This was a moment which Eddington never forgot. On one occation in later years he referred to it as the greatest moment of his life!”
By contrast, the Sobral expedition had expearienced fine wether. It had taken photographs using two telescopes, one similar to the Principe one and another having a different aperture and focal length. Eddington writes (Eddington, 1920, p.117) that the definition of the images on the Sobral photographs has been spoiled. The measures at one of the photographs taken with the telescope similar to the Principe one pointed with all too good agreement to the ‘half-deflection’, that is to say, the Newtonian value which is one-half the amount required by Einstein’s theory.
Eddington (1920) went on to give a reason for preferring the Principe results: the astronomers at Principe had taken “check-plates” of another portion of the sky to check whether there was any effect of the 50-degree difference in temperature between Principe in May and England in January, when the photographs were taken for comparison. No such check-plates were taken by the Sobral expedition.
However, the Sobral expedition had stayed in Brazil for a further two months after the eclipse (Eddington, 1920, p.117) to photograph the same region of the sky before dawn, so it would appear that the large temperature difference would not apply to the comparison of the photagraphs in that case. Although Eddington (1920, p.117) states explicitly that “there were no check-plates taken at Sobral,” the other account (Dyson et al., 1920, p. 298), referring to the Sobral expedition, that “A few check plates of the field near Arcturus were taken, but have not been used.”
A published paper (Dyson et al., 1920) states why it was not feasible for the Principe expedition to make a similar comparison: Unlike the Sobral expedition, we were not able to take comparison Photographs of the eclipse field at Principe, because for us the eclipse occured in the afternoon, and it would be many months before the field could be photographed in the same position in the sky before dawn. The check plates were therefore specially important for us.
A. I. Miller (1996, pp. 88-89) writes: “Although the wether was far better at Sobral, Eddington insisted on emphasizing data from Principe. Clearly, a key part of this experiment is to use the same instruments at same site for comparing data for the apparent and true star positions, but this was not done. The comparison photographs were taken several months later at Oxford”
Campbell (1923) wrote: “Professor Eddington was inclined to assign considerable weight to the African determination, but, as the few images on his small number of astrographic plates were not as good as those on the astrographic plates secured in Brazil, and the results from the latter were given almost negligible weight, the logic of the situation does not seem entirely clear.”
One problem, which has been discussed by von Klüber (1960) and Bertotti, Brill and Krotkov (1962) is, that even after the measurings have been made, there is still the mathematical problem of extrapolating back to the edge of the Sun, since no stars measured were within two solar radii of the center of the Sun and small changes in the observed deflections can cause a much greater change in the computed deflection of the Sun.
Some astronomers deny that the photographs of the eclipse observations, when compared with those taken of the same stars in the absence of the Sun, show deflections approximating the amount or the direction predicted by Professor Einstein. The quantity approximating the predicted one is obtained by averaging a selected few of the observations.
Announcement of the Eclipse Results
The results obtained by the British eclipse expeditions of May 1919 were announced at the famous joint meeting of the Royal Society and the Royal Astronomical Society held on November 6, 1919. In spite of the poor accuracy and the uncertainties surrounding the results, it was announced that the evidence was decisively in favour of the value of displacement that had been predicted by Einstein, and Sir Joseph Thomson, President of the Royal Society and Chair of the meeting, strongly endorsed the results (Thomson, 1919).
The announcement was enthusiastic received at the meeting, and according to a biography of Einstein (Clark, 1971): “Einstein awoke in Berlin on the morning of November 7, 1919, to find himself famous.”
His world-wide fame was a direct result of the announcement. The meeting has also been described in a very interesting way by Abraham Pais (1982), who identified the day of the joint meeting as “the day on wich Einstein was canonized.” Pais compared the meeting to a Congregation of Rites at which a candidate is considered for canonization in the Catholic Church, and, the only one who raised his voice, Ludwik Silberstein, to the advocatus diaboli or Devil’s advocate. Though the likeness was rather limited.
In the first place it is imperative that the arguments of the Devil’s advocate be heard before canonization is pronounced. But a generally accepted account of the meeting (Thomson, 1919) shows that the President of the Royal Society had “pronounced the canonization” before Silberstein had had a chance to speak.
In the second place, it is the responsibility of the Devil’s advocate to ensure that canonization does not occure undeservedly. In order to fulfill that responsibility, he must be given full access to all the relevant information required to make the case for the opposition to canonization. This condition was not fulfilled at the meeting at which the eclipse results were announced, because it was not possible for members of the audience to be sufficiently well-informed about the results that were being announced to make informed criticism of them.
The paper that was eventually published (Dyson et al., 1920), which is 43 pages long. with copious tables of results and mathematical analysis, carries the notation “Received October 30, – Read November 6, 1919.” Also the issue of Nature dated October 30 carried an announcement of the joint meeting, showing that the meeting had been arranged before the paper had been received by the Royal Society. It seems very unlikely, therefore, that the paper had received any critical review by independent referees before presentation, or that its contents were available to the audience early enough to be thoroughly studiet.
Just after the astronomers had presented their results, Thomson rose to call for discussion, but before the discussion actually started he strongly endorced the confirmation of Einstein’s prediction by saying (Tomson, 1919): It is difficult for the audience to weigh fully the meaning of the figures that have been put before us, but the Astronomer Royal and Prof. Eddington have studied the material carefully, and they regard the evidence as decisively in favour of the larger value of the displacement. This is the most important result obtained in connection with the theory of gravitation since Newton’s day, and it is fitting that it should be announced at a meeting of the Society so closely connected with him. ....If it is sustanined that Einstein’s reasoning holds good — and it has survived two very severe tests in connection with the perihelion of Mercury and the present eclipse — then it is the result of one of the highest achievements of human thought.
It was that speech that Pais interpreted as the pronouncement of the canonization of Einstein; the remark about “one of the highest achievements of human thought” has been widely quoted and has obviously contributed enormously to the veneration of Einstein and relativity. If we pursue Pais’s comparison of the joint meeting and a Congregation of Rites, we find another unfortunate feature of the comparison, namely that canonization of a saint by the Pope is infallible and irrevocable, so that subsequent criticism of the process is futile.
The identification of Silberstein as the Devil’s advocate gave the faulty impression, that a critical assesment of the eclipse results had been voiced at the meeting, and that the criticisms had been answered. Although Silberstein (Tomson, 1919) could not find fault in the eclipse observations, for the reasons given above, he did point out the fact the third main prediction of the general theory, the red-shift of light in a strong gravitational field, had not been observed. He said: “There is a deflection of the light rays, but it does not prove Einstein’s theory; it cannot be logically deduced from his theory as a gravitational effect in the absence of the spectroscopic result. And, as far as we know from St. John’s and Evershed’s observations, the predicted shift of the spectrum lines, of the amount exceeding almost 100 times the probable error of the modern spectroscope (as Prof. Fowler has just told us), is not obtained. ...If the shift remains unproved as at present the whole theory collapses, and the phenomenon just observed by the astronomers remains a fact awaiting to be accounted for in a different way.
Although Silberstein, as mentioned, did not have enough information about the eclipse obeservations at the meeting itself, he made the following criticisms of them at a meeting of the Royal Astronomical Society on 12 December, 1919 (Fowler, 1920):
They [the eclipse observations] indicate the presence of other factors modifying the displacement of the stars. These displacements are not radial. The deviations from the radial direction are marked running up to 15o for star No. 6 and to 35o for No.11. Five of the stars near the Sun’s axis show deviations from radial displacement in the same sence; two stars near the Sun’s equatorial plane show angular displacements in the opposite sence. If we had not the prejudice of Einstein’s theory we should not say that the figures strongly indicated a radial law of displacement.
It seems reasonable to suggest that the prestige of Dyson and Eddington led to the arranging of the joint meeting before the paper had even been received, and to the rapid acceptance of the paper when it was received, and it is interesting to note the comment by Wali (1984, p.115), about the influence of prestige on meetings of the Royal Astronomical Society, that “Papers had to be submitted a week before, by the first Friday of the month. Papers submitted by people like Eddington, Jeans and Milne were always read, and they always came first.”
Although it seems obvious that no independent critical assessment of the results was made before the joint meeting, with information still available today it is possible to make some assessment of the results. Other scientists have re-assessed the results of the 1919 and other eclipse results, with a certain amount of variation from the results originally published. For example, Sciama (1969) refers to a table of results of eclipse observations from 1919 to 1952, and comments as follows:
It is hard to assess their significance, since other astronomers have derived different results from a re-discussion of the same material. Moreover, one might suspect that if the observers did not know what value they were “supposed” to obtain, their published results might vary over a greater range than they actually do; there are several cases in stronomy where knowing the “right” answer has led to observed results later shown to be beyond the power of the apparatus to detect.
The Perihelion of Mercury
As already mentioned the general theory of relativity included a formula that correctly matched the variation in the perihelion of the planet Mercury. Pais (1982) has given the following interesting description of Einstein’s excitement on discovering his explanation of that phenomenon:
This discovery was, I believe, by far the strongest emotional experience in Einstein’s scientific life, perhaps in all his life. Nature had spoken to him. He had to be right.
Some commentary:
Collins and Pinch (1993) have commented on the measurements of the redshift pridicted by general relativity as follows:
The experimental observations, conducted both before and after 1919, were even more inconclusive. Yet after the interpretation of the eclipse observations had come firmly down on the side of Einstein, scientists suddently began to see confirmation of the redshift prediction where before they had seen only confusion.
Another unfortunate result of the announcement of the success of the eclipse observations has been an enormous hero-worship of Albert Einstein; Pais statement that he was canonized has now been outmatched by Miller (1996. p.90), who states that he was deified. A result of this deification is that the greatest scorn of the scientific community is reserved for those who would try to criticize either of Einstein’s theories of relativity or to suggest alternative theories, and many mainstream scientific journals reject papers critical of either theory without review.
Because of the euphoric veneration of Einstein and relativity in November 1919, the objectivity with wich science is supposed to act has been compromised, and the search for better theories has been inhibited. Canonization, deification, and claims of personal communication from Nature, should have no place in science. If the findings of the eclipse expeditions had been announced as being inconclusive instead of decisive in 1919, general relativity would have had to compete with other possible theories, such as Gerber’s, to explain certain astronomical observations, and a better theory might eventually have been found. In the author’s opinion, the confident announcement of the decisive confirmation of Einstein’s general theory in November 1919 was not a triumph of science, as it is often portrayed, but one of the most unfortunate events in the history of 20th-century science.
References
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