Editors: Rahul Krishnakumar, Anuprita Kulkarni, Goutham Vinjamuri, Vatsala Nema, Shamika Tapasvi, Vedant Bhutra

In today’s world, one would hardly find anyone who has not heard of Albert Einstein, a famous physicist of modern times. His work completely reformed the perspective of physicists, leading to a paradigm shift in the field. While it is common to publish papers and get recognition in terms of awards and appreciation from elite groups in the research community, the kind of appreciation Einstein got was phenomenal. Pioneers like Erwin Schrodinger, Paul Dirac, Richard Feynman, and many others made immense contributions to the field of physics but none of them have received the legendary status enjoyed by Einstein. This article aims to shed light on the series of events that set Einstein apart from his contemporaries, and how they were embroiled in controversy.

A Brief History of Relativity

As a researcher, Einstein was very much involved in his work. He spent a lot of his time thinking about electricity and magnetism. In the year 1905, which is termed as the “miracle year” of his life, he published four papers in various fields of physics, one of which fetched him a Nobel prize sixteen years later. He also worked on formulating the General Theory of Relativity, which was an effort to incorporate gravity to (what is now termed as) the special theory of relativity. This took him almost ten years, and stands as a perfect example of collaborative efforts of physicists and mathematicians like Grossman, Lorentz, Planck, Hilbert, Noether, and others.

In 1916, Albert Einstein published his complete theory in full mathematical detail. It was so complex in nature that hardly anyone dared to undertake the Herculean task of going through the paper, and those who did didn’t have any references or anyone to discuss it with. Another factor that compelled many researchers to not look into the theory was that it was so revolutionary that, if proven correct, it would completely wash out the Newtonian theory of physics prevalent at that time. Along with introducing the ideas of a combined spacetime that could warp, Einstein had made some suggestions for experiments (in the scientific community’s parlance - predictions) to verify his theory. All that was left was to get these predictions verified.

Many expeditions launched by Einstein’s colleagues were unsuccessful due to the ongoing World War I. Meanwhile, Einstein’s ideas travelled across the English channel, buoyed by his Dutch colleagues, de Sitter and Lorentz. Fortunately, one of de Sitter’s letters was received by the famous astronomer, Arthur Stanley Eddington of the Royal Astronomical Society of Cambridge University.

Enter Arthur Stanley Eddington

When Eddington received Einstein’s thesis report on relativity, he found it very intriguing. Being a good mathematician, he quickly familiarized himself with the ideas presented. He recognized that this was a brand new area to be explored in the field of astronomy and astrophysics. Although at the time other elite scientist groups of Britain were involved in the war, Eddington, as a conscientious objector, was exempted from war with a promise to the military of doing work of national importance.

Immediately after understanding the theory, Eddington went to match the results of Mercury’s precession calculated by Einstein with the experimental value. It matched with very high accuracy! The experimental value obtained was 45±5 arc-seconds and with Einstein’ theory they got 43. This was a ground-breaking discovery as the existing Newtonian theory could not explain the precession in Mercury’s orbit, an anomaly for a very long time. Eddington was now convinced that Einstein's theory must somehow be correct. He persuaded Dyson, Chairperson of the Royal Astronomical Society to plan an expedition to verify the second prediction, which was about deflection of light around a massive object. This could be observed by measuring stars’ position in the presence of the sun, which can only be done during an eclipse. Dyson and Eddington planned to go for expeditions at two different sites, Principe in Africa and Sobral in Brazil, with two different groups, led by Eddington and his colleague Cottingham from Cambridge University in the former group and Andrew Crommelin and Charles Davison from Greenwich Laboratory in the latter, on 29th May 1919, the day of the next solar eclipse.

The day prior to the eclipse was filled with rampant thunderstorms. As eclipses can’t be observed in cloudy weather, Eddington found himself in a helpless condition. Fortunately, the weather cleared up just prior to taking the measurements, and both teams at Principe and Sobral were able to record the positions of the stars.

One Thing is Certain and the Rest Debate

Once both the teams returned to Britain, Dyson decided to extract the results from them separately, in order to avoid getting unconsciously biased. As the astrographic plates were a bit hazy, Eddington used his vast field experience to manually calculate the results. He used a micrometer to measure the displacement and finally ended up with a value very close to Einstein’s prediction i.e. 1.65. On the other hand, measurements from Sobral’s data gave a variety of results matching both Newtonian and Einstenian predictions. The results of Sobral from the four-inch lenses were 1.61 and 1.98, whereas from the astrographic plates was 0.93. Einstein's and Newton’s predictions were 1.75 and 0.87 respectively. The mean of Sobral’s four-inch lenses’ results was very close to Einstein’s prediction. Moreover the Principe results calculated by Eddington were also directing towards Einstein’s theory to be correct. In the end, after analyzing all the plates and lens, Dyson and Eddington decided to only consider the results obtained from the astrographic plates of Principe and the four-inch lens of Sobral. On the basis of these results, Dyson and Eddington verified that Einstein’s theory was correct with a very high accuracy. 

In late 1919, results obtained from the expedition were discussed in the scientific society and were presented at the Royal Astronomical Society (RAS) by Eddington and Dyson. Showing his light-hearted side, Eddington composed the following verse while addressing a dinner held at the society:

Oh leave the Wise our measures to collate

One thing at least is certain, light has weight

One thing is certain and the rest debate

Light rays, when near the Sun, do not go straight.

Newspapers started printing this news with headlines such as, “Einstein theory triumphs”, “New theory of the universe”, “Revolution in science”, and “Newtonian ideas overthrown.”

Unlike other theories, general relativity gained importance from a nationalisitic view too. At the end of World War I, even though this theory was proposed by a scientist from the enemy’s country, Germany, it was proven by a British researcher. It acted as a reconciliation between the two countries through science. Researchers across the world realized that science is much more than mere borders – science is international and it should be kept away from the political motives of any country. The war which took science from rationalism to nationalism was again brought back to rationalism by science.

Deeper Motives

When World War I began between Germany and Britain in 1914, it was all politically motivated. As the war kept on raging, heavy casualties were reported from both sides. As a result, demand for soldiers was high, which meant that anyone who was fit to hold a gun was forced to go to war and safeguard their nation. There was a heavy shortage of daily requirements like food and clothes in Germany due to the sea route being blockaded by Britain. Einstein, being from a Jewish family, suffered heavily due to all of this and survived with the help of his Dutch friends. He was against the war and participated in many peaceful movements. Similarly, Eddington believed in peace and non-violence. He was also against the war and didn’t participate in it in order to prevent harm to his moral values. Both were passionate proponents of pacifism and internationalism in politics. Eddington earnestly sought postwar reconciliation between scientists in Britain and Germany, and saw the confirmation of the theory of Germany’s leading physicist by a British expedition, as a heaven-sent opportunity to further this goal. He wanted the expedition to shatter nationalism and celebrate what could be achieved across borders. The relations between the two countries started improving and the science community once again opened communication channels, journals and started collaborating with each other. In some way, the science of relativity triumphed over the great war.

Aftermath

In 1921, Einstein and Eddington finally met for the first time at a conference at the Royal Astronomical Society. From then onwards, Einstein received a lot of fame and people started seeing him as a new pioneer of physics, replacing Newton. Einstein became so famous that wherever he went, the media waited for him to give interviews. At one point of time he was so fed up with this fame that he complained to his friend Max Born that the publicity was “so bad that I can hardly breathe”. In 1919, Eddington had freely admitted that additional observations were needed to more accurately confirm Einstein’s predictions of light bending. So astronomers traveled to southern Australia in 1922 for the next major solar eclipse opportunity, observing the event from a sheep farm. This time the skies were clear, and images revealed the apparent displacement of many more stars due to their light bending. The three tests suggested by Einstein himself, namely, the precession of Mercury’s orbit, light bending, and the gravitational redshift of light emitted by the Sun, were all verified by this point. In the decades during which visible light tests of Einstein’s theory languished, radio astronomy came to the forefront. By combining the acuity of several radio telescopes, astronomers could determine with great precision the positions of quasars — celestial objects that emit powerful, highly collimated beams of radio waves. Astronomers compared the positions of the radio sources when the Sun was and was not present in that part of the sky, and measured deflections that were in agreement with Einstein’s prediction.

The Controversy - Critiques of the 1919 expedition

The results of the 1919 experiment were considered spectacular news and made the front page of most newspapers, making Einstein world-famous. But in recent years, scientists have been sceptical about the accuracy of Eddington’s methods and results. It has been argued by some that the experiment was plagued by systematic error and conformational bias.

Arthur Eddington, who was the best known astronomer involved in the expedition, had major reasons why he wanted Einstein’s theory to be proven. He was one of the first people to understand the theory and its significance. He was convinced, even before the experiment was performed, that the prediction of light-bending had to be correct. Going into the expedition with a strong belief in the theory coupled with his motivation to stop the war, it is possible that he ‘over-interpreted’ the data to favour Einstein’s theory.

The Greenwich Observatory’s astrographic lens at Sobral produced dubious-looking plates, with stars that looked slightly more like smidges than circles. These plates, however, produced a result closer to the Newtonian calculation. Apparently, Eddington made a decision to throw the plates out, instead relying on the data he manually took under cloud cover at Principe and the four-inch lens at Sobral with a smaller field of view to confirm the theory, making some historians wonder if the Dyson-Eddington pair was so hopeful to prove Einstein right that they improperly threw out that portion of the data because it didn’t agree. Eddington also convinced scientists and the general public about the accuracy of his findings through a brilliant public relations campaign in an effort to replace Newton’s worldview with Einstein’s.

The physicist C.W.F. Everitt went so far as to completely reject the 1919 results. He wrote that “this was a model of how not to do an experiment.” On “cooler reflection” from sixty years’ distance it seemed that the data did not support Einstein at all. Perhaps, Eddington, Dyson, and Davidson had always intended to prove Einstein right and manipulated the results to that end. Everitt disputed the idea that there was anything reliable on those photographic plates. “Only Eddington’s disarming way of spinning a yarn could convince anyone that there was a good check of General Relativity.”

Even Stephen Hawking casually dismissed the 1919 results. The errors were, he said, “as large as the effect they were trying to measure (like saying you’re sure it is Tuesday, but that it might be Monday or Wednesday)”. His book, A Brief History of Time concluded that “their measurement had been sheer luck, or a case of knowing the result they wanted to get, not an uncommon occurrence in science”.

Re-Analysis

Did the photographic plates show what Eddington said they did? A scientist’s reflex in a situation like this is to go check again. So in 1979 (for the centenary of Einstein’s birth), the original photographs were pulled from the Royal Astronomical Society’s archives and checked with modern methods. The Royal Greenwich Observatory staff reanalyzed the Sobral plates with computerized measuring equipment and checked whether the 1919 analyses had been done properly. For the four-inch telescope, Dyson had reported 1.98 ±0.18. The modern computer reported 1.90 ±0.11. For the astrographic plates, Dyson had reported the uncorrected value of 0.93, even though if he applied likely corrections for the distorted mirror he would have had 1.52. The computer, though, could apply those corrections much more reliably, getting 1.55 ±0.34. The new analysis gave a combined result of 1.87±0.13, solidly close to Einstein’s 1.75 prediction. It seemed that Dyson’s original analysis had been pretty good, and certainly did not show evidence of tampering in favor of Einstein.

Through the Philosopher’s Lens

The reanalysis of the plates, though, left out a critical part of the events of 1919. Eddington and Dyson had made the case that the Sobral astrographic results should not be taken seriously because of the coelostat (rotating mirror) problems. These results had been worryingly close to the Newtonian half-deflection; if they had been included it would have been difficult to claim a confirmation for Einstein. In 1980, two philosophers, John Earman and Clark Glymour, argued that the Sobral astrographic results should not have been excluded. If those results were dropped, then the Principe results (which were far from perfect) should have been dropped as well. Since Eddington did not do that, he must have been biased. Earman and Glymour conclude that Eddington only won the debates because he ended up writing the textbooks afterward. They reassured their readers that, while this might cause “despair on the part of those who see in science a model of objectivity and rationality,” it was not a deep problem because we had other reasons to think relativity is true. Indeed, today we have a dizzying number of different experiments confirming relativity—it is one of the best-supported theories of all time. The gravitational redshift can now be seen in any laboratory. The deflection of light is so well established today that it is used as a basic tool for exploring the universe (in the form of “gravitational lensing”). From the movements of galaxies to spinning spheres in orbit to the GPS system in your pocket, physicists keep looking for failures of relativity’s predictions and find none.

On the other hand, physicist Daniel Kennefick has stressed that even though Eddington and Dyson made important decisions about what data to accept and what to reject, that does not mean those decisions were wrong. Context, he writes, is crucial for understanding any experimental result. The astronomers in 1919 had good reasons for attributing systematic error to the Sobral astrographic plate but not to the Principe one—and they presented those reasons publicly. They understood that recognizing the difference between good and bad data was hardly a controversial or suspicious thing. It was an ordinary part of doing science.

“It is not always easy to tell the difference between good and bad data. Generally you need lots of experience producing and looking at specific kinds of data. In 1919, it was good to trust people who knew telescopes very well.”

Einstein and relativity’s victory involved good science, bad science, politics, and personal authority. Any episode in science does. None of those mean relativity is wrong (it has been confirmed many, many times since then) or that Eddington fudged the numbers (there were good reasons to trust the 1919 results). Science is done by people. That means it will be inherently complicated and often confusing. People will make mistakes, equipment will break, poor decisions will be made because of political or personal bias. But people will also have flashes of insight, they will have friends who make crucial suggestions, they will take up a cause because of political or personal beliefs.

Beyond data points and error analyses, mostly everyone agrees about the broader historical importance of the 1919 expeditions. They were a great victory for the higher values of science. They showed that scientists could rise above petty nationalism, that science could help one escape the shackles of nationalism and war. We saw how Eddington and Einstein intentionally spread this interpretation; they wanted to use the moment to change the way scientists were behaving.

Even those who attacked the expeditions’ scientific value acknowledged its importance for the postwar world. Hawking called them a triumph of international reconciliation in the same sentence in which he rejected their data. Physicist Clifford Will in 1986 described the expeditions as something to strive for in his own era

“when cold-war politics sometimes

obstructs the free flow of scientific information and interaction,

we would do to remember this example: a British government

permitting a pacifist scientist to avoid wartime military duty so

he could go off and try to verify a theory produced by an enemy

scientist.”

References:

1. The Golem: What Everyone Should Know About Science by Harry Collins and Trevor Pinch
2. Gravity’s Century From Einstein’s Eclipse to Images of Black Holes by Ron Cowen
3. Not Only Because of Theory: Dyson, Eddington and the Competing Myths of the 1919 Eclipse Expedition
4. Eddington, Einstein, Matthew

Einstein's war: how relativity triumphed amid the vicious nationalism of World War I

1. The Sociology of Scientific Knowledge