5X5 Episode 69

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5X5 Episode 69
Einstein's Eclipse and General Relativity
5th June 2009

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5X5 68 5X5 70
Skeptical Rogues
S: Steven Novella
R: Rebecca Watson
B: Bob Novella
J: Jay Novella
E: Evan Bernstein
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Einstein's Eclipse and General Relativity[edit]

You're listening to the Skeptics' Guide 5x5, five minutes with five skeptics, with Steve, Jay, Rebecca, Bob and Evan.


S: This is the SGU 5x5 and tonight we're talking about the 90th anniversary of the eclipse that made Albert Einstein famous. Einstein's general theory of relativity, which dealt primarily with gravity, made different predictions as to the degree that the light from distant stars would be bent by the gravitational field of our Sun. This led to the ability to test Einstein's theory of general relativity by observing the degree of the change in the apparent position of stars behind the Sun during an eclipse. Of course it couldn't be tested until there was actually a total eclipse where the observations could be made. That opportunity first occurred on May 29th 1919, and the Royal Astronomical Society sent an expedition to the west African isle of Príncipe to observe the total solar eclipse and it confirmed Einstein's predictions.

E: Yup, that's right. The expedition was led by Sir Arthur Eddington who was a British astronomer who led the expedition and it was interesting if you think about the time line in 1919 they had just got done fighting World War I against the Germans and here was British astronomer going on the expedition to prove, or disprove, the German theorist's theory about the gravitational fields and how it bends light around the Sun.

J: This was really an ironic even because Eddington's confirmation of relativity's predictions made national news headlines all over the world. It made Einstein famous. It wasn't the 1905 special relativity or the 1915 general relativity that made him famous, it took this experiment for everyone in the world to know, pretty much, who Einstein was. But ironically many scientists now doubt that Eddington's equipment was accurate enough to even distinguish between Einstein's relativity prediction compared to Newton's prediction of the effect. It actually took almost a half a century before all doubt was removed when they used radio frequencies to absolutely prove that Einstein was right and Newton was wrong, and it's ironic that it took so long and that the first proof of relativity really wasn't reconfirmed until almost a half a century later. Meanwhile of course, it was confirmed in many other ways. It was just an interesting turn of events I think.

R: There's a common myth actually that Eddington's initial results were fraudulent, but apparently he was aware of a specific defect in the telescopes they were using and he compensated for that apparently. So, yeah his numbers were accurate despite the equipment that he had to use.

J: That technique is actually called gravitational lensing and it's one of the most common ways that they use to study the universe today.

S: interestingly, Newton's theory of gravity also predicts that as light passes by a star like our Sun, that has a heavy gravitational field, that it will be bent. It's not that, it wasn't the difference between the path of the light being bent or not being bent. It was just that Newton's mathematics creates one degree of bending and Einstein's calculations produced a different one. According to general relativity the light should be bent about twice as much as what you would predict from Newton's laws, and again we're still talking about very tiny amounts. It was that number that matched better with Einstein's calculations than with Newton's.

E: And the end result really was a paradigm shift in physics in which it ushered in the age of general relativity and we were able to dispose of, or no longer need, Newtonian mechanics to explain the movements in the universe. It was a more refined, a better theory, it was more complete.

S: Right. It didn't make Newton wrong, it just made his equations an exception to a more general rule that Einstein discovered. And I've always like the fact that Einstein became a world famous science superstar only after his theories were validated by actual observation, not beforehand. To me that's always been a good commentary on the fact that science is based upon testing ideas against reality.


S: SGU 5x5 is a companion podcast to the Skeptics' Guide to the Universe, a weekly science podcast brought to you by the New England Skeptical Society in association with skepchick.org. For more information on this and other episodes, visit our website at www.theskepticsguide.org. Music is provided by Jake Wilson.


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