Thanks to Steven Mosher on Twitter, I came across an article that discusses Arthur Eddington’s attempt to test Einstein’s Theory of General Relativity. The basic story is that Newton’s Theory of Universal Gravitation assumed that gravity was a force that acted between two masses and that this force acted instantaneously. In 1915, however, Albert Einstein proposed that rather than gravity being a force that acts instantaneously across distance, what actually happens is that masses curve spacetime and that this then influences the behaviour of all other masses in the universe; gravity is then a manifestation of this curvature of spacetime
One consequences of General Relativity is that if light passes close to a massive body, it will be deflected. The massive body will essentially act like a lense and, hence, this is often referred to as gravitational lensing, an example of which is shown in the image on the right. The bright orange object in the centre of the image is a massive elliptical galaxy. The blue horseshoe is an image of a much more distant galaxy that has passed almost directly behind the elliptical galaxy and the light from which has been deflected to produce a horseshoe-like image.
When Einstein first proposed his theory of General Relativity it was not easy to test, as the large telescopes we have today didn’t exist at that time. One way to do so, however, was to observe stars close to the limb of the Sun. The light from these stars would pass very close to the Sun and be deflected. Doing this, however, required making observations during a Solar eclipse and then making comparison observations at a different time to see if the light from the these stars did indeed deflect when it passed close to the limb of the Sun. To be clear, if you treat light as a particle, Newtonian gravity would also predict a deflection, but it is smaller than that predicted by General Relativity.
In 1919, two groups went to try and test General Relativity during a solar eclipse. One, including Arthur Eddington, went to Principe off the coast of Africa, and another went to Sobral, in Brazil. The story of these expeditions, and the results of their observations, is what the article I mentioned earlier is about. What makes it interesting is that the claim is that Arthur Eddington was a supporter of General Relativity and essentially massaged the analysis so as to produce a result that was consistent with General Relativity. The suggestion is that if he was being honest he would have presented an inconclusive result, rather than one that was seen as confirming Einstein’s theory.
I had heard something like this before, so seeing this made me think this might be an interesting thing to discuss. How do you judge someone in such a circumstance? It’s a long time ago, and they’ve been proven correct, but they potentially fiddled their results so as to appear to have confirmed what is now clearly one of the greatest scientific breakthrough’s of the 20th century. They were just lucky that their intuition turned out to be correct. However, before doing so I thought I would just look into this a bit more, and came across a paper called Not Only Because of Theory: Dyson, Eddington and the Competing Myths of the 1919 Eclipse Expedition. It argues that
a close examination of the views of the expedition’s organizers, and of their data analysis, suggests that they had good grounds for acting as they did, and that the key people involved, in particular the astronomer Frank Watson Dyson, were not biased in favor of Einstein.
Dyson, the Astronomer Royal at the time, being principal organiser and director of the two expeditions.
The claims against Eddington include that the results from his observations taken in Africa – which were consistent with General Relativity – were biased, and that he unjustifiably argued against some of the results obtained using the observations from Brazil, which were more consistent with the Newtonian prediction than the prediction from General Relativity. It turns out, however, that in 1979 (60 years after the original expeditions) some of the observations were reanalysed, the results of which were published in this paper. All of the observations that were reanalysed produced results consistent with General Relativity, even those that originally were more consistent with the Newtonian predicition, and produced an average that was within one standard deviation of the General Relativity prediction.
So, it seems that maybe the analyses that produced results consistent with General Relativity were not necessarily biased and that there was some justification for discounting some of those that were not consistent with General Relativity. Of course, I don’t know if there are valid criticisms of the 1919 analysis, or not, but I think the big picture issue here is more subtle than simply completely right, versus flawed and wrong. I think it’s worth bearing in mind that any form of cutting edge research is difficult. Researchers may be using methods that are new and not fully tested. They may have to make decisions about the analysis that will require some amount of subjective judgement. It’s particularly difficult when dealing with a primarily observational area, like astronomy, where there may be factors that will be beyond their control, and so even very careful planning doesn’t guarantee that they won’t later encounter unexpected problems.
It’s possible that it may later become clear that some of the judgements were poor, or that the analysis method wasn’t optimal. However, it’s far easier to recognise this in retrospect, than in advance. Science is a process in which we learn both from our mistakes and from our successes, and in which we develop our understanding over time; we don’t regard something as confirmed after a single study, even if it is by some of the leading researchers of the time. Of course there are some things, like outright fraud and plagiarism, that are clear indicators of scientific misconduct; making a judgement that others might later disagree with doesn’t, however, typically qualify.
So, it seems to me that the main message in this story is how messy science can be. It can involve making risky measurements/observations to test new hypotheses. It can involve making somewhat subjective judgements by people who cannot be completely free from bias. It can involve developing new, or modifying old, methods in order to carry out observations, or to analyse what is observed. It’s not perfect, and probably can’t be. However, over time, we can develop an ever increasing confidence in our understanding of something, even if not all steps in the process are perfect. We don’t trust Einstein’s Theory of General Relativity because of what Eddington did in 1919; we trust it because it has continued to pass tests, the most recent of which was the first detection of gravitational waves. That doesn’t mean, however, that the work done in 1919 didn’t make a significant contribution to the overall process.
Update: I originally credited the highlighting of the article to Willard, but it was actually Steven Mosher. Now corrected.