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No Shadow of a Doubt: The 1919 Eclipse That Confirmed Einstein's Theory of Relativity
On their 100th anniversary, the story of the extraordinary scientific expeditions that ushered in the era of relativity
In 1919, British scientists led extraordinary expeditions to Brazil and Africa to test Albert Einstein's revolutionary new theory of general relativity in what became the century's most celebrated scientific experiment. The result ushered in a new era and made Einstein a global celebrity by confirming his dramatic prediction that the path of light rays would be bent by gravity. Today, Einstein's theory is scientific fact. Yet the effort to "weigh light" by measuring the gravitational deflection of starlight during the May 29, 1919, solar eclipse has become clouded by myth and skepticism. Could Arthur Eddington and Frank Dyson have gotten the results they claimed? Did the pacifist Eddington falsify evidence to foster peace after a horrific war by validating the theory of a German antiwar campaigner? In No Shadow of a Doubt, Daniel Kennefick provides definitive answers by offering the most comprehensive and authoritative account of how expedition scientists overcame war, bad weather, and equipment problems to make the experiment a triumphant success.
The reader follows Eddington on his voyage to Africa through his letters home, and delves with Dyson into how the complex experiment was accomplished, through his notes. Other characters include Howard Grubb, the brilliant Irishman who made the instruments; William Campbell, the American astronomer who confirmed the result; and Erwin Findlay-Freundlich, the German whose attempts to perform the test in Crimea were foiled by clouds and his arrest.
By chronicling the expeditions and their enormous impact in greater detail than ever before, No Shadow of a Doubt reveals a story that is even richer and more exciting than previously known.
In 1919, British scientists led extraordinary expeditions to Brazil and Africa to test Albert Einstein's revolutionary new theory of general relativity in what became the century's most celebrated scientific experiment. The result ushered in a new era and made Einstein a global celebrity by confirming his dramatic prediction that the path of light rays would be bent by gravity. Today, Einstein's theory is scientific fact. Yet the effort to "weigh light" by measuring the gravitational deflection of starlight during the May 29, 1919, solar eclipse has become clouded by myth and skepticism. Could Arthur Eddington and Frank Dyson have gotten the results they claimed? Did the pacifist Eddington falsify evidence to foster peace after a horrific war by validating the theory of a German antiwar campaigner? In No Shadow of a Doubt, Daniel Kennefick provides definitive answers by offering the most comprehensive and authoritative account of how expedition scientists overcame war, bad weather, and equipment problems to make the experiment a triumphant success.
The reader follows Eddington on his voyage to Africa through his letters home, and delves with Dyson into how the complex experiment was accomplished, through his notes. Other characters include Howard Grubb, the brilliant Irishman who made the instruments; William Campbell, the American astronomer who confirmed the result; and Erwin Findlay-Freundlich, the German whose attempts to perform the test in Crimea were foiled by clouds and his arrest.
By chronicling the expeditions and their enormous impact in greater detail than ever before, No Shadow of a Doubt reveals a story that is even richer and more exciting than previously known.
416 pages, Hardcover
Published April 30, 2019
About the author
Daniel Kennefick
5 books2 followersDaniel Kennefick is associate professor of physics at the University of Arkansas, Fayetteville. He is the author of Traveling at the Speed of Thought: Einstein and the Quest for Gravitational Waves and a coauthor of An Einstein Encyclopedia (both Princeton).
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Displaying 1 - 7 of 7 reviews
May 15, 2020
If you know a little scientific history you know that in 1919 Arthur Eddington found empirical confirmation for Albert Einstein's theory of general relativity by measuring the deflection of light from distant stars by the gravitational force of the sun as measured by the shifting apparent positions of stars in an eclipse. The magnitude of the effect matched Einstein's predictions and were the first out-of-sample test of his theory (explaining the perihelion of Mercury was also explained by the theory, but was not a proper out of sample test). The result catapulted Einstein from publicly unknown (his name had not appeared in the newspapers before) to global fame, with my favorite New York Times headline of all time: "Lights All Askew in the Heavens ; Men of Science More or Less Agog Over Eclipse Observations; Einstein Theory Triumphs; Stars Not Where They Seemed or Were Calculated to be, but Nobody Need Worry."
If you know a medium amount of scientific history you know that Eddington was a biased partisan who was out to find for Einstein (possibly because he was a pacifist who opposed World War I and either liked his fellow pacifist Einstein or wanted to re-establish global ties by vindicating a German scientist over the most famous English one, Isaac Newton), that his instruments had huge error bands, that he dropped some of the data that disagreed with Einstein, that his work was not reproducible, and in sum his experimental "proof" was just cooked up to prove what he set out to prove.
If you read this impressive and meticulous scholarly work by someone who has studied this question for decades you learn that the "know a little" happy folktale version is actually much closer to the truth than the "know a medium amount" sophisticated and cycnical version. In particular, Daniel Kennefick makes many arguments, the two most important of which are:
--Eddington co-did the work with Frank Dyson (no relation to Freeman). In fact, Dyson largely organized and led the work and did the data analysis. Importantly, Dyson appears to have been skeptical of General Relativity (and a key researcher on the project was outright hostile to it).
--The biggest argument against Eddington was that one of the three sets of data was discarded (there were two sets of plates from observations from Brazil and one set of plates from observations in Principe). Kennefick shows that before any analysis was done the researchers thought something had gone wrong with the observations in that data so the decision to discard it does not seem to have been based on the results. Moreover, by their own measures, including those data would have resulted in an average result across all the data sets even closer to the Einstein prediction. Finally, modern re-analysis of the discarded data show that even by itself it agreed with general relativity if measured properly.
--Eddington's ex ante theoretical framing of the "Newton" prediction and the "Einstein prediction" made it easier to establish a pro-Newton result by generously interpreting his theory to predict some deflection of light (half the Einstein prediction) when it probably predicted none.
As I read it, I did sometimes worry that Kennefick was like the Eddington of the cynical myth--someone who was out to prove a thesis (vindicating Eddington's vindication of Einstein) and had access to vastly more data on the question than anyone so was able to sort it to make his argument. That said, it was a "sometimes worry" because the argument did seem compelling and much of the "medium knowledge" darker version does seem to have come from people who approached the issue much more superficially and casually.
This vindication of Eddington is only a part of the book. The book is also a meticulous history of Eddington, eclipse astronomy and its difficulties, rise and subsequent fall, and more that I had never read in a scientific history or popularization and was particularly fascinating.
Most interesting, however, was he extensive and thoughtful discussion of what all of this tells you about the scientific method, Popper's version of falsification, whether theory should guide evidence, how scientists pick the null hypotheses they test, when you should stop tinkering with an experiment, how scientific bias does and does not help. Some of these questions were fleshed out further in his discussion of the Michelson and Morley experiment that came up with the surprising results of overturning the ether and the successors to it that tried to prove the original experiment wrong and re-establish the ether.
The bottom line of this discussion is that Kennefick shows the simple Popper version of science is wrong because you never really know whether you've falsified a theory or run a false experiment, that experimenters are better when they bring biases and hypotheses generated by theory to bear, that science has an important social and cultural aspect to it at least for prolonged periods of time, and that our knowledge advances by a combination of theory, evidence, and other types of evidence, not just simple crisp tests. Ultimately this is a much richer and more exciting and more realistic vision of science than either the simple ("Einstein proved right") or medium ("Einstein proof was fraudulent") versions of the story.
If you know a medium amount of scientific history you know that Eddington was a biased partisan who was out to find for Einstein (possibly because he was a pacifist who opposed World War I and either liked his fellow pacifist Einstein or wanted to re-establish global ties by vindicating a German scientist over the most famous English one, Isaac Newton), that his instruments had huge error bands, that he dropped some of the data that disagreed with Einstein, that his work was not reproducible, and in sum his experimental "proof" was just cooked up to prove what he set out to prove.
If you read this impressive and meticulous scholarly work by someone who has studied this question for decades you learn that the "know a little" happy folktale version is actually much closer to the truth than the "know a medium amount" sophisticated and cycnical version. In particular, Daniel Kennefick makes many arguments, the two most important of which are:
--Eddington co-did the work with Frank Dyson (no relation to Freeman). In fact, Dyson largely organized and led the work and did the data analysis. Importantly, Dyson appears to have been skeptical of General Relativity (and a key researcher on the project was outright hostile to it).
--The biggest argument against Eddington was that one of the three sets of data was discarded (there were two sets of plates from observations from Brazil and one set of plates from observations in Principe). Kennefick shows that before any analysis was done the researchers thought something had gone wrong with the observations in that data so the decision to discard it does not seem to have been based on the results. Moreover, by their own measures, including those data would have resulted in an average result across all the data sets even closer to the Einstein prediction. Finally, modern re-analysis of the discarded data show that even by itself it agreed with general relativity if measured properly.
--Eddington's ex ante theoretical framing of the "Newton" prediction and the "Einstein prediction" made it easier to establish a pro-Newton result by generously interpreting his theory to predict some deflection of light (half the Einstein prediction) when it probably predicted none.
As I read it, I did sometimes worry that Kennefick was like the Eddington of the cynical myth--someone who was out to prove a thesis (vindicating Eddington's vindication of Einstein) and had access to vastly more data on the question than anyone so was able to sort it to make his argument. That said, it was a "sometimes worry" because the argument did seem compelling and much of the "medium knowledge" darker version does seem to have come from people who approached the issue much more superficially and casually.
This vindication of Eddington is only a part of the book. The book is also a meticulous history of Eddington, eclipse astronomy and its difficulties, rise and subsequent fall, and more that I had never read in a scientific history or popularization and was particularly fascinating.
Most interesting, however, was he extensive and thoughtful discussion of what all of this tells you about the scientific method, Popper's version of falsification, whether theory should guide evidence, how scientists pick the null hypotheses they test, when you should stop tinkering with an experiment, how scientific bias does and does not help. Some of these questions were fleshed out further in his discussion of the Michelson and Morley experiment that came up with the surprising results of overturning the ether and the successors to it that tried to prove the original experiment wrong and re-establish the ether.
The bottom line of this discussion is that Kennefick shows the simple Popper version of science is wrong because you never really know whether you've falsified a theory or run a false experiment, that experimenters are better when they bring biases and hypotheses generated by theory to bear, that science has an important social and cultural aspect to it at least for prolonged periods of time, and that our knowledge advances by a combination of theory, evidence, and other types of evidence, not just simple crisp tests. Ultimately this is a much richer and more exciting and more realistic vision of science than either the simple ("Einstein proved right") or medium ("Einstein proof was fraudulent") versions of the story.
May 20, 2019
I remember hearing a report on NPR about how scientific articles were more likely to be shared and cited if they were written in a story-like fashion. The reason: humans are natural storytellers who delight in narratives with compelling characters, struggles, and resolutions. This is why I'm giving 'No Shadow of a Doubt' five stars and applauding Daniel Kennefick's approach to the subject. It is precisely the type of writing we need more of in academia.
This book depicts a fascinating page from history—the scientific expeditions that tested Einstein's theory of general relativity during the solar eclipse of May 29, 1919—with as much drama as if it were an Academy Award-winning movie. Key players in the expeditions are vividly illustrated, their methods and materials finely detailed, and the echos of the First World War rumble like a distant thunderstorm throughout the work. I found this fascinating and wonderfully refreshing as someone whose limited education in the sciences (Astronomy and Newtonian Mechanics) never featured such engaging readings. It is something I have always tried to emulate in historical fiction and which I was overjoyed to read.
I consider this book a model for those interested in how otherwise exhaustive research can be presented in a way accessible and enjoyable to the public, those with anything from a professional to casual interest in the cosmos, and those shopping for ideas from history that would make a damn good screenplay.
This book depicts a fascinating page from history—the scientific expeditions that tested Einstein's theory of general relativity during the solar eclipse of May 29, 1919—with as much drama as if it were an Academy Award-winning movie. Key players in the expeditions are vividly illustrated, their methods and materials finely detailed, and the echos of the First World War rumble like a distant thunderstorm throughout the work. I found this fascinating and wonderfully refreshing as someone whose limited education in the sciences (Astronomy and Newtonian Mechanics) never featured such engaging readings. It is something I have always tried to emulate in historical fiction and which I was overjoyed to read.
I consider this book a model for those interested in how otherwise exhaustive research can be presented in a way accessible and enjoyable to the public, those with anything from a professional to casual interest in the cosmos, and those shopping for ideas from history that would make a damn good screenplay.
May 7, 2019
It's something of a truism that science tends to go through stages, where each new stage can be typified as 'It's more complicated than we thought.' This book demonstrates that this assertion is also true of history of science. It examines the 1919 eclipse expeditions and their conclusions used to bolster Einstein's general theory of relativity, and how those results have been treated.
This is a very tightly focussed subject for a whole book, and there is a distinct danger here of the material of an article being stretched out to book length - it often did feel that Daniel Kennefick was dragging out a handful of conclusions by repeating the same assertions over and over in subtly different ways. However, this isn't entirely fair as he does give exhaustive detail of the two expeditions which wouldn't have fit in an article, covering how their results were produced and how the controversy (if it could really be called that) arose.
Like many physics professors, Kennefick struggles to explain the details of physics in a way that's accessible to the general reader, but this is only a very small part of the book, which is far more about the history and its implications, and here he is significantly more readable. Though the points may be made rather too often, they are indeed fascinating if you are interested in the way experimental support for scientific theories - and the history of science - develops.
Arguably, as Kennefick points out, eclipse science is an oddball field, as it's very difficult to repeat experiments successfully, particularly as there is only a few-minute window in which to undertake them. This is the context in which we see the developing story of the 1919 eclipse expeditions. From their results being announced through to the 1970s they were generally presented as a triumphant demonstration of Einstein's prediction of the amount the mass of the Sun should warp space, causing stars appearing near it in the sky to be shifted in position. From the seventies onwards - and it's largely how I've seen it presented - it was more seen as a bit of a fudge by English astrophysicist Arthur Eddington, taking results which couldn't really demonstrate anything and making them show what he wanted: that Einstein was correct. Kennefick demonstrates at length that this view is also wildly over-simplistic.
One reason for this is that the myth of Eddington's bias omits the fact that he was only responsible for one of the two expeditions - the other was under the aegis of the Astronomer Royal Frank Dyson (apparently no relation to, but an inspiration for Freeman Dyson). Dyson had no axe to grind and was responsible for the decision, usually blamed on Eddington, of ignoring the data that disagreed with Einstein's predictions. Dyson did this not to cherry pick, but because there were technical problems with the device used that produced these photographic plates, making them difficult to interpret. (Apparently Eddington's only influence was to stop Dyson using the dubious data averaged with the other rather overshot data of Dyson's, which would have brought the results closer to the Einstein prediction.)
Interestingly, and again not revealed in the myth, the remaining 1919 plates were re-measured in the 70s and in fact showed that the ignored data, if measured properly, would also have confirmed the general theory's predictions.
Of course it's entirely possible that Eddington was biassed anyway and was over-confident about the way the results were presented - but after reading this book, this early effort to test Einstein's theory (which would be verified many times over later by far better tests than the always tricky observation of eclipses) does not seem as flawed as it has repeatedly been presented to be.
An interesting book, then - but it does rather labour the point.
This is a very tightly focussed subject for a whole book, and there is a distinct danger here of the material of an article being stretched out to book length - it often did feel that Daniel Kennefick was dragging out a handful of conclusions by repeating the same assertions over and over in subtly different ways. However, this isn't entirely fair as he does give exhaustive detail of the two expeditions which wouldn't have fit in an article, covering how their results were produced and how the controversy (if it could really be called that) arose.
Like many physics professors, Kennefick struggles to explain the details of physics in a way that's accessible to the general reader, but this is only a very small part of the book, which is far more about the history and its implications, and here he is significantly more readable. Though the points may be made rather too often, they are indeed fascinating if you are interested in the way experimental support for scientific theories - and the history of science - develops.
Arguably, as Kennefick points out, eclipse science is an oddball field, as it's very difficult to repeat experiments successfully, particularly as there is only a few-minute window in which to undertake them. This is the context in which we see the developing story of the 1919 eclipse expeditions. From their results being announced through to the 1970s they were generally presented as a triumphant demonstration of Einstein's prediction of the amount the mass of the Sun should warp space, causing stars appearing near it in the sky to be shifted in position. From the seventies onwards - and it's largely how I've seen it presented - it was more seen as a bit of a fudge by English astrophysicist Arthur Eddington, taking results which couldn't really demonstrate anything and making them show what he wanted: that Einstein was correct. Kennefick demonstrates at length that this view is also wildly over-simplistic.
One reason for this is that the myth of Eddington's bias omits the fact that he was only responsible for one of the two expeditions - the other was under the aegis of the Astronomer Royal Frank Dyson (apparently no relation to, but an inspiration for Freeman Dyson). Dyson had no axe to grind and was responsible for the decision, usually blamed on Eddington, of ignoring the data that disagreed with Einstein's predictions. Dyson did this not to cherry pick, but because there were technical problems with the device used that produced these photographic plates, making them difficult to interpret. (Apparently Eddington's only influence was to stop Dyson using the dubious data averaged with the other rather overshot data of Dyson's, which would have brought the results closer to the Einstein prediction.)
Interestingly, and again not revealed in the myth, the remaining 1919 plates were re-measured in the 70s and in fact showed that the ignored data, if measured properly, would also have confirmed the general theory's predictions.
Of course it's entirely possible that Eddington was biassed anyway and was over-confident about the way the results were presented - but after reading this book, this early effort to test Einstein's theory (which would be verified many times over later by far better tests than the always tricky observation of eclipses) does not seem as flawed as it has repeatedly been presented to be.
An interesting book, then - but it does rather labour the point.
November 8, 2022
I always have a hard time giving five stars to non fiction because it can depend so much on your interest in the topic but this really is a very well researched and written account of the Eddington and Dyson eclipse expeditions. In addition to the logistics of the expeditions, it covers the history and politics of the time around the war and gives a nice, approachable background on the science of general relativity. It's pretty amazing the effort astronomers would put into observing a eclipse, dedicating months to preparation and travel when so many things could go wrong in the only 5 minutes that mattered. As well as the challenges and ambiguities with the subsequent data analysis. The author also provides a good account and general rebuke, of some of the criticisms that have arisen in recent years regarding the Eddington measurements. Highly recommend if you're interested in the topic of 20th century science in general.
June 9, 2019
I thought a really good read. Cogently written, anyone with a moderate understanding of the scientific process will find a lot in this book: theory vs. experiment, nature of science, history. Really good nature of science here.
May 12, 2024
First two-thirds of the book were very fascinating and compelling discussion of the various characters involved in the science of gravity during ther early 20th century, and the work that went into mounting eclipse expeditions to potentially prove or refute the competing theories. I did feel like the later part of the book did bog down a little bit in too detailed of examination of the potential biases of the different players - but the author still made some very compelling points about how scientists are human and our biases are an integral part of the scientific process.
March 17, 2024
Interesting and well-written account of the first major tests of Einstein's theories. Four stars for general readers, five stars for physics nerds.
Displaying 1 - 7 of 7 reviews