# Flaw in the measurements of light deflection confirming General Relativity **URL:** \ **Category:** Factual Questions\ **Created:** [August 28, 2015, 2:42pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175 "2015-08-28T14:42:39Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [August 28, 2015, 2:42pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/1 "2015-08-28T14:42:39Z")
I’m in no way disputing the validity of general relativity, but just curious about one small aspect: the putative confirmation of the bending of light around the sun during the West African eclipse of 1919. Everyone who writes popular science articles on GR mentions how pictures of the stars near the sun taken during this eclipse showed the light bending. Heck, in the current issue of SciAm, devoted to the 100th anniversary of GR, it’s trotted out umpteen times. But in _A Brief History of Time_, Hawking makes the point: > [@](#): > > It is ironic, therefore, that later examination of the photographs taken on that expedition showed the errors were as great as the effect they were trying to measure. Their measurement had been sheer luck, or a case of knowing the result they wanted to get, not an uncommon occurrence in science. I’ve read a fair share of lay writing on general relativity, and I’ve never seen anyone else make this point. So - the general question: Is Hawking correct? And if so, is this common knowledge among physicists? And yes, I fully realize that even if this experiment turned out to be flawed, that the gravitational bending of light has been unequivocally established in further experiments since then. ---
**Author:** ![dolphinboy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dolphinboy/32/330_2.png) [@dolphinboy](https://boards.straightdope.com/u/dolphinboy)\ **Post date:** [August 28, 2015, 2:47pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/2 "2015-08-28T14:47:22Z")
1. Who are we to argue with Stephen Hawking 2. Yes, I think Hawking’s comments are fairly well known to most physicists but reporters tend to focus on the “oh wow” factor versus the “they just got lucky this time” factor ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [August 28, 2015, 3:12pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/3 "2015-08-28T15:12:56Z")
Thank you! 1. I’ll take Hawking on in an argument on Bach any day he wants his ass whipped! 2. My google-fu is weak, and when I tried to look up more details on the flaw in this experiment I keep getting yet another regurgitation of the fact that it confirmed it. Can you point me to any more details on the issue? I hear you about run of the mill reporters. But just in this issue of SciAm alone, the story is repeated by both Brian Greene and Lawrence Krause. I just find it disingenuous for people who should know better to keep referencing a flawed experiment when writing about GR. It would be a marvelous opportunity to show how real science works. But that’s a topic for another thread in another forum! 😉 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 28, 2015, 4:39pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/4 "2015-08-28T16:39:07Z")
To be clear, both Newton’s and Einstein’s theories predict the bending of starlight around the Sun. But Einstein’s theory predicts more, twice as much in fact. The original experiment was good enough to verify that there was bending, but it wasn’t good enough to verify how much. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 28, 2015, 5:16pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/5 "2015-08-28T17:16:48Z")
I’ve read a lot of popular physics and the flaws in the measurements are trotted out continually in modern books. I’m sure each of us are reading a subset of all the books published, but I’d be surprised if any treatment longer than a magazine article didn’t mention it. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [August 28, 2015, 5:19pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/6 "2015-08-28T17:19:03Z")
> [@Chronos](#): > > To be clear, both Newton’s and Einstein’s theories predict the bending of starlight around the Sun. But Einstein’s theory predicts more, twice as much in fact. The original experiment was good enough to verify that there was bending, but it wasn’t good enough to verify how much. Did Newton predict based on his corpuscular theory of light? For it is hard to see how gravitational bending of light would be predicted if light was just a wave. In general relativity there is no actual bending, just light following a geodesic in the local geometry. Has there ever been another case where a successful prediction vaulted its predictor into instant fame like that? How well was Newton known to his contemporaries, for example? ---
**Author:** ![Nelson\_Pike](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Nelson\_Pike](https://boards.straightdope.com/u/Nelson_Pike)\ **Post date:** [August 28, 2015, 5:32pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/7 "2015-08-28T17:32:42Z")
Surely there have been numerous empirical tests of General Relativity since 1919 which employ observation of solar eclipses. At least there should have been- I mean, all we are talking about is the standard replication of results, aren’t we? What I have always found astounding is that these presumed replications never receive prominent media attention. That is as much the fault of experts like Hawking and Krause, who are both passing up a great chance to draw attention to scientific success. Instead, Hawking draws undivided attention to a correctable error, and even worse, Krause joins the throng of those who pass off the error as an accurate observation. Can anyone here point me in the direction of an online report for any replication of Eddington’s 1919 original study? ---
**Author:** ![Nelson\_Pike](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Nelson\_Pike](https://boards.straightdope.com/u/Nelson_Pike)\ **Post date:** [August 28, 2015, 5:44pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/8 "2015-08-28T17:44:10Z")
> [@Hari\_Seldon](#): > > Has there ever been another case where a successful prediction vaulted its predictor into instant fame like that? How well was Newton known to his contemporaries, for example? As of publication of Principia (1787), a great scientific _tour de force_ of the ages, Newton’s name became universally known to all educated Europeans, and he was recognized as one of the greatest geniuses of all time. ---
**Author:** ![D18](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@D18](https://boards.straightdope.com/u/D18)\ **Post date:** [August 28, 2015, 5:56pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/9 "2015-08-28T17:56:05Z")
**Exapno** , I’m not doubting you, but I’d be curious who you’ve read that has discussed the problem with the Eddington study? I will admit that I read several pop-science books on the topic several years ago (Hawking, Greene, a a few others) and stopped because they were just starting to repeat themselves. So I haven’t seen what is being communicated lately. **Nelson** , to be fair to Hawking, the next sentence after what I quoted was; > [@](#): > > The light deflection has, however, been accurately confirmed by a number of later observations So he didn’t just leave it as negatively as you may be thinking. (No citations, however, so I can’t answer your query about later replication. **Hari** , as an interesting counter example of how long it can take for breakthrough ideas to be embraced, SciAm had an interesting [article a few issues ago](http://www.scientificamerican.com/article/the-case-against-copernicus/) about how long even scientists resisted Copernicus’s idea of the Earth revolving around the sun. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [August 28, 2015, 6:11pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/10 "2015-08-28T18:11:57Z")
That Eddington’s result has been questioned is extremely well-known amongst physicists. What tends to be less well known is that others have revisited his raw data and in turn questioned that reassessment. So there was [this study from 1979](http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1979Obs....99..195H&db_key=AST&page_ind=0&data_type=GIF&type=SCREEN_VIEW&classic=YES), then [this one in 2007](http://arxiv.org/abs/0709.0685). It’s worth noting that there was a lot of effort in the late Seventies and Eighties to digitally scan old sky survey plates and questions of estimating distortions in such plates was a live issue for a while, so these attempts didn’t happen in a methodological vacuum. Daniel Kennefick, the author of the second study, surveyed the issue at a less technical level in a [_Physics Today_ article](http://w.astro.berkeley.edu/~kalas/labs/documents/kennefick_phystoday_09.pdf). (For an example of another oft-reprinted popular science - well, kind of - book arguing that Eddington was wrong, see Collins and Pinch’s _The Golem_.) ---
**Author:** ![Nelson\_Pike](https://avatars.discourse-cdn.com/v4/letter/n/c6cbf5/32.png) [@Nelson\_Pike](https://boards.straightdope.com/u/Nelson_Pike)\ **Post date:** [August 28, 2015, 7:33pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/11 "2015-08-28T19:33:19Z")
> [@Nelson\_Pike](#): > > As of publication of Principia (1787), a great scientific _tour de force_ of the ages, Newton’s name became universally known to all educated Europeans, and he was recognized as one of the greatest geniuses of all time. Pardon me- I was only off by a century on Principia’s publication date, which was 1 **6** 87. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 28, 2015, 9:16pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/12 "2015-08-28T21:16:28Z")
> [@D18](#): > > **Exapno** , I’m not doubting you, but I’d be curious who you’ve read that has discussed the problem with the Eddington study? I’m not coming up with specific names, although I’ll bet Simon Singh was one of them since I found an account on his [site](http://simonsingh.net/media/articles/maths-and-science/1919-eclipse-and-general-relativity/). There were a lot of books about relativity in 2005, at the centennial. I remember one book in particular that took us through the entire expedition and how and why the plates were near unusable. Probably took it out from the library, though. ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [August 28, 2015, 11:45pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/13 "2015-08-28T23:45:02Z")
It was in [Australia, 1922,](http://www.powerhousemuseum.com/insidethecollection/2012/08/einsteins-theory-of-relativity-proven-in-australia-1922/) that all doubt was swept away. > [@D18](#): > > But in _A Brief History of Time_ … I started this but when Hawkings got into the heavy mathematical derivations I set it aside, just wasn’t in the mood. ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [August 29, 2015, 12:25pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/14 "2015-08-29T12:25:09Z")
> [@watchwolf49](#): > > I started this but when Hawkings got into the heavy mathematical derivations I set it aside, just wasn’t in the mood. Are you joking? In it, Hawking complains that his publisher said that every equation would cut sales in half, so he grudgingly omitted them all. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 29, 2015, 1:20pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/15 "2015-08-29T13:20:00Z")
Not quite. He included E = mc[sup]2[/sup], because he just couldn’t bring himself to get rid of that one. But he cut all the others. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 29, 2015, 1:39pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/16 "2015-08-29T13:39:52Z")
What does the experiment involve? Does it measure how long the star is behind the sun, or the time that the star becomes visible? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 29, 2015, 2:22pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/17 "2015-08-29T14:22:03Z")
It’s the position of the star relative to other stars while it’s visible near the limb of the Sun. Basically, you take a picture of the stars near the Sun during the eclipse (when they’re visible despite being near the Sun), and then you take a picture of the same patch of sky months later or earlier when the Sun is nowhere around. The picture with the Sun in it should show the other stars sort of smooshed out of the way, as if they’re trying to make room for the Sun. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 29, 2015, 2:26pm UTC](https://boards.straightdope.com/t/flaw-in-the-measurements-of-light-deflection-confirming-general-relativity/729175/18 "2015-08-29T14:26:34Z")
Thanks, Chronos.