How a solar eclipse first proved Einstein right (Synopsis)

"Eddington had needed to make significant corrections to some of the measurements, for various technical reasons, and in the end decided to leave some of the Sobral data out of the calculation entirely. Many scientists were suspicious that he had cooked the books. Although the suspicion lingered for years in some quarters, in the end the results were confirmed at eclipse after eclipse with higher and higher precision." -Peter Coles

If ever you attempt to come out with a new scientific theory, there are three criteria you must fulfill:

  1. You must reproduce all the successes of the old theory, the one you're looking to replace.
  2. You must explain at least one observation or measurement, successfully, that the old theory failed to explain.
  3. You must make a new prediction, different from the old theory's prediction, that you can go out and test.

When Einstein's General Relativity first came out, it met those first two criteria, but the third proved exceedingly difficult.

During a total eclipse, stars would appear to be in a different position than their actual locations, due to the bending of light from an intervening mass: the Sun. Image credit: E. Siegel / Beyond the Galaxy.

The only practical test that people could come up with involved measuring the position of distant stars during the day: very close to the Sun. According to Einstein, the curved space around a large mass would bend the starlight, causing its position to shift in a measurable way. While VLBI radio observations can do this today, there was no such technology a century ago. And yet, a total solar eclipse made exactly those critical observations possible.

Actual negative and positive photographic plates from the 1919 Eddington Expedition, showing (with lines) the positions of the identified stars that would be used for measuring the light deflection due to the Sun's presence. Image credit: Eddington and Sobral, 1919.

Come get the story on exactly how that works, and learn how you can see the same evidence for yourself this August!

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Events 1919 - Einstein's theory of general relativity is tested (later confirmed) by Arthur Eddington's observation of a total solar eclipse in Principe and by Andrew Crommelin in Sobral, Ceará, Brazil. Births 1675 - Humphry Ditton, English mathematician 1716 - Louis-Jean-Marie Daubenton, French…
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Even fanatic Einsteinians (Sabine Hossenfelder, Brian Greene, Stephen Hawking) admit that Eddington's 1919 results were inconclusive and even fraudulent:

Sabine Hossenfelder: "His measurements had huge error bars due to bad weather and he also might have cherry-picked his data because he liked Einstein's theory a little too much. Shame on him."

People outside Einsteiniana are much franker:

Frederick Soddy (1921 Nobel Prize in chemistry for his research in radioactive decay and particularly for his formulation of the theory of isotopes): "Incidentally the attempt to verify this during a recent solar eclipse, provided the world with the most disgusting spectacle perhaps ever witnessed of the lengths to which a preconceived notion can bias what was supposed to be an impartial scientific inquiry. For Eddington, who was one of the party, and ought to have been excluded as an ardent supporter of the theory that was under examination, in his description spoke of the feeling of dismay which ran through the expedition when it appeared at one time that Einstein might be wrong! Remembering that in this particular astronomical investigation, the corrections for the normal errors of observation - due to diffraction, temperature changes, and the like - exceeded by many times the magnitude of the predicted deflection of the star's ray being looked for, one wonders exactly what this sort of "science" is really worth."

By Pentcho Valev (not verified) on 04 Jul 2017 #permalink

In 1919 Arthur Eddington was a solitary fraudster but a few years later he was already a gang boss:

Quote: "Consider the case of astronomer Walter Adams. In 1925 he tested Einstein's theory of relativity by measuring the red shift of the binary companion of Sirius, brightest star in the sky. Einstein's theory predicted a red shift of six parts in a hundred thousand; Adams found just such an effect. A triumph for relativity. However, in 1971, with updated estimates of the mass and radius of Sirius, it was found that the predicted red shift should have been much larger – 28 parts in a hundred thousand. Later observations of the red shift did indeed measure this amount, showing that Adams' observations were flawed. He "saw" what he had expected to see."

Quote: "In January 1924 Arthur Eddington wrote to Walter S. Adams at the Mt. Wilson Observatory suggesting a measurement of the "Einstein shift" in Sirius B and providing an estimate of its magnitude. Adams' 1925 published results agreed remarkably well with Eddington's estimate. Initially this achievement was hailed as the third empirical test of General Relativity (after Mercury's anomalous perihelion advance and the 1919 measurement of the deflection of starlight). It has been known for some time that both Eddington's estimate and Adams' measurement underestimated the true Sirius B gravitational redshift by a factor of four."

Quote: "...Eddington asked Adams to attempt the measurement. [...] ...Adams reported an average differential redshift of nineteen kilometers per second, very nearly the predicted gravitational redshift. Eddington was delighted with the result... [...] In 1928 Joseph Moore at the Lick Observatory measured differences between the redshifts of Sirius and Sirius B... [...] ...the average was nineteen kilometers per second, precisely what Adams had reported. [...] More seriously damaging to the reputation of Adams and Moore is the measurement in the 1960s at Mount Wilson by Jesse Greenstein, J.Oke, and H.Shipman. They found a differential redshift for Sirius B of roughly eighty kilometers per second."

By Pentcho Valev (not verified) on 04 Jul 2017 #permalink

Pentcho - It's fairly easy to find scientists from the era 1915 - 1923 who denigrated Einstein and his theories. There was an active group that fought a long hard battle to deny the Nobel prize to Einstein. They were motivated partly from anti-semitism and partly from reluctance to embrace a strange theory that many simply didn't understand. In quoting these old sources, there's an obligation to recognize the biases held by the speaker. By the time of the quote above, Soddy had left active scientific work and was engaged in somewhat strange political pursuits, and wrote several papers expressing anti-semitic views.

Anti-semitism is irrelevant here. I have also quoted Sabine Hossenfelder - she is not an anti-Semite but essentially confirms Soddy's words. Actually Soddy is the only "old source" I quote. Here are new sources:

Discover: "The eclipse experiment finally happened in 1919. Eminent British physicist Arthur Eddington declared general relativity a success, catapulting Einstein into fame and onto coffee mugs. In retrospect, it seems that Eddington fudged the results, throwing out photos that showed the wrong outcome. No wonder nobody noticed: At the time of Einstein's death in 1955, scientists still had almost no evidence of general relativity in action."

New Scientist: "Enter another piece of luck for Einstein. We now know that the light-bending effect was actually too small for Eddington to have discerned at that time. Had Eddington not been so receptive to Einstein's theory, he might not have reached such strong conclusions so soon, and the world would have had to wait for more accurate eclipse measurements to confirm general relativity."

Stephen Hawking: "Einsteins prediction of light deflection could not be tested immediately in 1915, because the First World War was in progress, and it was not until 1919 that a British expedition, observing an eclipse from West Africa, showed that light was indeed deflected by the sun, just as predicted by the theory. This proof of a German theory by British scientists was hailed as a great act of reconciliation between the two countries after the war. It is ionic, 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."

By Pentcho Valev (not verified) on 04 Jul 2017 #permalink

Another piece by Ethan in praise of Einstein. (Thanks, P. V. for the reality check... obviously not welcome here.)

Ethan: " According to Einstein, the curved space around a large mass would bend the starlight, causing its
position to shift in a measurable way."

There is another explanation for light being bent as it travels past massive objects: "The Force of Gravity," which Einstein denied as he applied Minkowski's geometrical MODEL, malleable spacetime... since he could not believe that gravity is a force reaching across "empty space"... that unbelievable "spooky action at a distance."

The model was an improvement (over Newtonian physics) as a math concept for predicting trajectories, but nobody dares to say what space or time or spacetime actually IS (as a malleable entity in the real world.... What real world?!)

There is no ontology of "spacetime," not that physics ever cares about "what it IS" if there is no real world independent of variations in observation.

Ps: They say that light has no "resting mass." Maybe that's because it never "rests!" It's kinetic energy (as momentum) equals mass and can push on solar sails... and be deflected by THE FORCE OF GRAVITY without "curved space" as an ironclad Einsteinian doctrine/ invention.

But the indoctrinated keep chanting in praise of Einstein.

By Michael Mooney (not verified) on 04 Jul 2017 #permalink

“According to Einstein, the curved space around a large mass would bend the starlight, causing its position to shift in a measurable way.”

Why was this considered so special?
Isn’t space curving around a large mass like water or air curving around a mass?
Space isn’t really empty, is it?

Well, Einstein did produce a theory that does agree with observation and experiment. Every test of the theory to date so far has been successful. You rely on it every day whenever you use GPS to navigate. If GPS didn't take Einstein's prediction of gravitational time dilation into account then the positions calculated by GPS would be wrong and the system would be completely unworkable.

Where's your competing theory that does all those the three things that Ethan has succinctly laid out for us?

By Anonymous Coward (not verified) on 04 Jul 2017 #permalink

@skl:
"Isn’t space curving around a large mass like water or air curving around a mass?"

Realize if that was true objects would bend spacetime outward, instead of inward which is what really happens.
So the sign of curvature would be reversed and so the nature of the lens effect. (I think the observed star that is near sun during a solar eclipse, would get closer to sun instead of getting farther away like actually happens.)

Anonymous Coward wrote: "Well, Einstein did produce a theory that does agree with observation and experiment. Every test of the theory to date so far has been successful. You rely on it every day whenever you use GPS to navigate. If GPS didn’t take Einstein’s prediction of gravitational time dilation into account then the positions calculated by GPS would be wrong and the system would be completely unworkable."

Not true. Alleged confirmations of Einstein's relativity are either fraudulent or inconclusive. The GPS fraud: One calculates the distance between the satellite and the receiver by multiplying the time by Einstein's constant speed of light, obtains a wrong value (because the speed of light is variable, not constant), "adjusts the time" in order to fix the wrongness, and finally Einsteinians inform the gullible world that Einstein's relativity (time dilation) is gloriously confirmed:

Quote: "Your GPS unit registers the exact time at which it receives that information from each satellite and then calculates how long it took for the individual signals to arrive. By multiplying the elapsed time by the speed of light, it can figure out how far it is from each satellite, compare those distances, and calculate its own position. [...] According to Einstein's special theory of relativity, a clock that's traveling fast will appear to run slowly from the perspective of someone standing still. Satellites move at about 9,000 mph - enough to make their onboard clocks slow down by 8 microseconds per day from the perspective of a GPS gadget and totally screw up the location data. To counter this effect, the GPS system adjusts the time it gets from the satellites by using the equation here."

By Pentcho Valev (not verified) on 04 Jul 2017 #permalink

Blatantly lying Einsteinians: Einstein was able to predict, WITHOUT ANY ADJUSTMENTS WHATSOEVER, that the orbit of Mercury should precess by an extra 43 seconds of arc per century:

Jose Wudka, UC Riverside: "This discrepancy cannot be accounted for using Newton's formalism. Many ad-hoc fixes were devised (such as assuming there was a certain amount of dust between the Sun and Mercury) but none were consistent with other observations (for example, no evidence of dust was found when the region between Mercury and the Sun was carefully scrutinized). In contrast, Einstein was able to predict, WITHOUT ANY ADJUSTMENTS WHATSOEVER, that the orbit of Mercury should precess by an extra 43 seconds of arc per century should the General Theory of Relativity be correct."

However Michel Janssen (honest in this case) describes endless empirical adjustment (groping, fudging, fitting) until "excellent agreement with observation" was reached:

Michel Janssen: "But - as we know from a letter to his friend Conrad Habicht of December 24, 1907 - one of the goals that Einstein set himself early on, was to use his new theory of gravity, whatever it might turn out to be, to explain the discrepancy between the observed motion of the perihelion of the planet Mercury and the motion predicted on the basis of Newtonian gravitational theory. [...] The Einstein-Grossmann theory - also known as the "Entwurf" ("outline") theory after the title of Einstein and Grossmann's paper - is, in fact, already very close to the version of general relativity published in November 1915 and constitutes an enormous advance over Einstein's first attempt at a generalized theory of relativity and theory of gravitation published in 1912. The crucial breakthrough had been that Einstein had recognized that the gravitational field - or, as we would now say, the inertio-gravitational field - should not be described by a variable speed of light as he had attempted in 1912, but by the so-called metric tensor field. The metric tensor is a mathematical object of 16 components, 10 of which independent, that characterizes the geometry of space and time. In this way, gravity is no longer a force in space and time, but part of the fabric of space and time itself: gravity is part of the inertio-gravitational field. Einstein had turned to Grossmann for help with the difficult and unfamiliar mathematics needed to formulate a theory along these lines. [...] Einstein did not give up the Einstein-Grossmann theory once he had established that it could not fully explain the Mercury anomaly. He continued to work on the theory and never even mentioned the disappointing result of his work with Besso in print. So Einstein did not do what the influential philosopher Sir Karl Popper claimed all good scientists do: once they have found an empirical refutation of their theory, they abandon that theory and go back to the drawing board. [...] On November 4, 1915, he presented a paper to the Berlin Academy officially retracting the Einstein-Grossmann equations and replacing them with new ones. On November 11, a short addendum to this paper followed, once again changing his field equations. A week later, on November 18, Einstein presented the paper containing his celebrated explanation of the perihelion motion of Mercury on the basis of this new theory. Another week later he changed the field equations once more. These are the equations still used today. This last change did not affect the result for the perihelion of Mercury. Besso is not acknowledged in Einstein's paper on the perihelion problem. Apparently, Besso's help with this technical problem had not been as valuable to Einstein as his role as sounding board that had earned Besso the famous acknowledgment in the special relativity paper of 1905. Still, an acknowledgment would have been appropriate. After all, what Einstein had done that week in November, was simply to redo the calculation he had done with Besso in June 1913, using his new field equations instead of the Einstein-Grossmann equations. It is not hard to imagine Einstein's excitement when he inserted the numbers for Mercury into the new expression he found and the result was 43", in excellent agreement with observation."

By Pentcho Valev (not verified) on 04 Jul 2017 #permalink

Ethan, you wouldn't be baiting the resident anti relativity nuts with a post like this now, would you? ;)

PV and MM, by all means if you guys have the theories/math all worked out to show that the "Einsteinians" are wrong, by all means just follow the procedure that Ethan nicely laid out for you and show the rest of us. Just remember there are a bunch of really smart people"(Sabine Hossenfelder, Brian Greene, Stephen Hawking)" who HAVE DONE THE HARD WORK TO ACTUALLY UNDERSTAND THE THEORY OF RELATIVITY! Or any other commonly accepted theory currently under fire.

I know someone will say don't feed the trolls, and you are right...but this makes me feel better for a while.

rich r wrote: "Ethan, you wouldn’t be baiting the resident anti relativity nuts with a post like this now, would you?"

Why not? I expect him to start a discussion about other important experiments - e.g. Michelson-Morley and Pound-Rebka. Both confirm Newton's emission theory of light and refute Einstein's relativity (mythology says the opposite of course).

By Pentcho Valev (not verified) on 05 Jul 2017 #permalink

The Eddington observation actually was insufficiently precise enough to eliminate the Brans/Dicke theory of relativity. However, experiments performed in the 1970s using one of the early Mars probes showed that Einstein's prediction was within the two standard deviation experimental error while the Brans/Dicke prediction was not. Further refinements have eliminated Brans/Dicke as an explanation for the light deflection.

Of course, the B/D theory was in hot water from the getgo as it required that the interior of the Sun was rotating 10 times as fast as the atmosphere in order to produce a quadrupole moment sufficient to account for a significant fraction of the observed discrepancy of 43 seconds of arc/century which has been attributed to GR.

By colnago80 (not verified) on 06 Jul 2017 #permalink

Ummm, Pentcho, the emission theory of light is conclusively DISPROVEN by a variety of observations. For instance consider binary star systems. When a binary is on one side of its orbit, it's moving toward the earth, on the other side it's moving away. If emission theory were correct, light emitted on one side of the orbit should travel faster with respect to us than the light emitted on the other side. We can now measure light speed quite precisely, precisely enough to observe such differences. When the speed of light emitted by binary star systems is measured, there is no noticeable variation, thus ruling out emission theory. The consistency of emission theory with the MM experiment (or any other experiment) is irrelevant; emission theory is ruled out.

Sean T wrote: "The consistency of emission theory with the MM experiment (or any other experiment) is irrelevant; emission theory is ruled out."

Even brothers Einsteinians would find this not very clever.

Besides, you have not understood de Sitter's (Brecher's) argument. Study it more diligently!

By Pentcho Valev (not verified) on 07 Jul 2017 #permalink

Again, either you're ignorant or dishonest. DeSitter and Brecher both argued AGAINST emission theory. Both argued that the overtaking of "slow" light by "fast" light over long enough distances would lead to observed anomalies in the dynamics of binary systems. No such anomalies were observed. Brecher's results constrained the independence of the speed of light upon source velocity to within 2 parts per billion. Emission theory is indeed dead.

@Sean T #16

Ah, now you know something about de Sitter's and Brecher's argument. Quick learner! Bravo!

By Pentcho Valev (not verified) on 07 Jul 2017 #permalink

"Not true. Alleged confirmations of Einstein’s relativity are either fraudulent or inconclusive. "

Bravo. The usual science deniers on ethan's blog (mooney, cft, the aptly named denier) haven't been brave enough to so boldly assert their one denial.

However dicey Eddingtons photographs and measurements were, subsequent tests of light bending around the Sun show that Einstein's theory is spot on.

By Robert J Kolker (not verified) on 12 Jul 2017 #permalink