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The Hunt for Vulcan, the Planet ThatWasnʼt ThereEveryone thought the gravitational pull of anundiscovered planet made Mercury wobble. Theywere wrong. Albert Einstein explained why.November 4, 2015

One hundred years ago today at the Prussian Academy of Sciences, AlbertEinstein gave the first in a series of lectures that rewrote Newtonʼs laws ofgravity and changed the world. In The Hunt For Vulcan: … And How AlbertEinstein Destroyed A Planet, Discovered Relativity, And Deciphered TheUniverse, Tom Levenson reveals how this revolution could not have happenedwithout disproving an obscure astronomical calculation.

According to Newton, Mercuryʼs wobble was caused by the gravitational pullof some other planet. Enter Vulcan—the so-called “other” planet—firstobserved in 1859; confirmed by the greatest astronomer of the day, Urbain LeVerrier; and hailed by The New York Times as one of the great discoveries ofthe century. Trouble was, it didnʼt exist.

Speaking from the Massachusetts Institute of Technology, where he isProfessor of Science Writing, the author explains how a provincial doctor inFrance triggered “Vulcan-mania”; how Einsteinʼs theory of relativity offered atotally new explanation of the universe; and why Vulcan still has lessons toteach about the nature of truth and illusion.

Today, the story of the ‘planetʼ Vulcan barely registers as a footnote inthe history of science. Why did you decide to pluck it from obscurity?

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I came to Vulcan from Einsteinʼs perspective. Thereʼs this marvelous storyabout Einstein, as heʼs just at the point of the single greatest breakthrough ofhis career, the Theory of General Relativity. Heʼs preparing the third of fourpapers he delivers to the Prussian academy, and he does a calculation to seewhat his new theory predicts for the orbit of Mercury.

Vulcan is remarkable because the idea of this littlebody inside the orbit of Mercury makes perfectsense.

Tom Levenson

His new theory correctly provides what astronomers call the table for Mercury,accurately describing how it moves around the Sun. Einstein tells friends aboutthis in the most extraordinary language. He said he felt actual palpitations ofhis heart and that he was so excited he couldnʼt work for three days, he was soovercome with joy. So, this grand theory that would explain the universe in anew way rested on this almost forgotten issue of what causes Mercury towobble. And that made me curious.

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Disproving Vulcanʼs existence was central to the Theory of Relativity, which Einstein, pictured here at the Mount Wilson

Observatory, unveiled 100 years ago.

Photograph by Alamy

You say, “Vulcanʼs biography is one of the human capacity to bothdiscover and self-deceive.” Explain.

Vulcan is remarkable because the idea of this little body inside the orbit ofMercury makes perfect sense. If you believe Isaac Newtonʼs theory of gravity,which everyone does at that time, the discovery of a slight wobble in themiddle of Mercuryʼs orbit that canʼt be explained by the tug of Venus or Earthhas only one interpretation: there has to be an undiscovered planet or flock ofasteroids that we canʼt see because itʼs too close to the sun but must beexerting some gravitational influence on Mercury.

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Facts on their own don’t mean anything unless youhave a framework to put them in. And theframework was Newton’s laws.

Tom Levenson

Not only does that make absolute sense within the mathematical framework ofNewtonʼs theory, itʼs how scientists managed to figure out that Neptune had tobe there based on the wobbles of the orbit of Uranus just a few years before.

The self-deception comes in that over the next 20 years, people believed theysaw specks of light that corresponded to what they thought Vulcan shouldlook during an eclipse: round objects crossing the face of the sun, which wereinterpreted as transits of Vulcan.

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The “wobble” in the orbit of Mercury (seen here) was thought to be the result of the gravitational tug of an

undiscovered planet called Vulcan, which didnʼt exist.

Photograph by Messenger, NASA

These were not just amateurs, but men like Urbain Joseph Le Verrier, the mostfamous astronomer in the world and director of the Paris Observatory. Only afew years earlier Le Verrier had discovered Neptune “at the tip of his pen,” byanalyzing the wobbles in Uranusʼ orbit. He had done a similar analysis ofMercury, so there was utterly convincing logic that Vulcan had to be real.

The first sighting of Vulcan was by amateur French astronomer EdmondModeste Lescarbault. Put us inside his stone barn in the village ofOrgeres-En-Beauce on March 26, 1859.

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French astronomer, Urbain Joseph Le Verrier, was one ofthe worldʼs leading authorities

… Read More Photograph by Alamy

Edmond Lescarbault, a young doctor in love with astronomy, had built anobservatory in a stone barn with a little dome on top of it. On that day in 1859,he sees a patient then goes across the backyard to his stone barn, climbs upand looks through his telescope.

As he trains his telescope on the sun,he sees a round object on the face ofthe Sun. He times it as it moves steadilyacross the sun, records the data, thenanother patient arrives, so he checksout that patient, then comes back to thebarn. This round dot is still crossing theSun. He tracks it continuously, takingnotes on its path until it finally goes overthe other edge of the Sun.

He sits on that result and says nothing.At this point he doesnʼt know anythingabout Le Verrierʼs work on Mercury.Finally, he learns about this in a popularaccount Le Verrier had published andsends a letter to Le Verrier.

Le Verrier is at a New Yearʼs Eve partywhen he gets the letter and treks out to Lescarbaultʼs house, which involves atrain ride and then a 12-mile walk, to interrogate him. Le Verrier becomesconvinced that Lescarbault really did see what he claims to have seen and thatthe proper interpretation is that this is a transit of a planet. Itʼs not clear whofirst named it, but it quickly became known as Vulcan.

You quote a contemporary as saying, “Everyone with a telescope was

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looking for Vulcan. Some found it.” Give us a picture of Vulcan-mania asit swept the world.

Two things: You have in Le Verrier the ultimate authority on the solar system. Ifhe says Vulcan not only has to be there, but Vulcan has been found, then foralmost everyone that makes it real. Astronomers go poring through oldrecords, just as they had when Uranus was discovered, to see if it had beenpreviously seen. If one amateur could find it, anybody with a telescope could.Suddenly, there was another object in the solar system, another confirmationof Newtonʼs theory of gravity.

Even Thomas Edison got in on the act. Put us on the ground in Rawlins,Wyoming in 1878.

The great eclipse of 1878 followed a track that started in Siberia, crossed overCanada, and then went all the way down the United States through Wyoming.This was such a major event that the U.S. government funded observationstations up and down the track of totality. Other astronomers who werenʼt partof the official parties flocked to places regarded as the most likely to give agood view.

Disproving Vulcan’s existence was central toEinstein because it showed that this radical, bizarrenew picture of his … was actually the right way tosee the universe.

Tom Levenson

One of the prime locations was Rawlins, Wyoming, a small town with a raildepot and a hotel. Thomas Edison was mostly there for some hunting and

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The great solar eclipse of July 29th 1878, pictured here inSnake River Pass, Colorado

… Read More Photograph by Alamy

fishing. But he brings with him a new invention, the Tasimeter, which measuresinfrared radiation or heat. Edison wants to test it during the eclipse, to see if itwill detect the heat of a solar corona.

On the day of the eclipse, Edison trieshis instrument, which actually doesnʼtwork. He then goes up the rail trackabout ten miles from Rawlins to the nowcompletely vanished outpost ofSeparation, Wyoming, where the twomost famous Vulcan hunters of the dayhad set up their telescopes.

One of them, Simon Newcomb, hadmissed it. The other, James Watson,director of the Ann Arbor observatory,saw a little bright star where there wasno star on his chart and said, thatʼsVulcan. News of this discovery wasreported all around the world withindays.

Why was there such a powerfuldesire to believe in Vulcan that even

the “newspaper of record,” The New York Times, jumped on thebandwagon?

There were two reasons. The first is scientific. Over the previous hundredyears, the greatest mathematical minds in Europe and America had worked outmore and more sophisticated models of the solar system using Newtonʼs laws,and they had always been right.

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According to Newtonʼs laws, Mercuryʼs wobble has to be caused by somesource of gravitational energy. There was no other way to think about it. Factson their own donʼt mean anything unless you have a framework to put them in.And the framework was Newtonʼs laws.

There is also a populist aspect. Why does the New York Times teaseprofessional astronomers over their doubts about Vulcan? The answer is thatthere is a human impulse to say, ‘look at you smart guys, you donʼt actuallyknow everything, thereʼs stuff out there that maybe even you canʼt handle.̓

How was disproving Vulcanʼs existence central to Einsteinʼs GeneralTheory of Relativity?

Einsteinʼs theory of relativity explains the same phenomenon, but does so witha completely different kind of structure or picture than Isaac Newton. InNewtonʼs theory, gravity is a property that leaps across space between twobodies; a force that pulls on you. Einstein didnʼt just say, my numbers arebetter. He said, you have to fundamentally change that picture of gravity, thatunderstanding of what the properties of reality are.

The core of General Relativity is that space and time are not static, butdynamic and can change. The way they change is by the presence and motionof matter and energy. A vast mass like the sun creates curves in spacetime,which means that things donʼt go straight. A ray of light passing close to thesun will travel a curving path.

Disproving Vulcanʼs existence was central to Einstein because it showed thatthis radical, bizarre new picture of his, that spacetime is flowing, was actuallythe right way to see the universe. Mercury wobbles because thatʼs the shortestpath it can take through the curved spacetime created by that huge dentimposed by the mass of the Sun. Without curved spacetime you need someother mass to pull on it. With curved spacetime, Mercury behaves exactly how

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Canadian-American astronomer, Simon Newcomb, wasone of the many Vulcan-hunters

… Read More Photograph by Alamy

Einsteinʼs theory says it should.

You call the story of Vulcan “acautionary tale.” What lessons doesit hold for us?

Vulcan teaches us how hard it is tounderstand what nature is telling us,how hard it is to understand whennature says no. Thereʼs this famousphrase that a single brute fact canundermine the most beautiful theory.But thatʼs not how it worked for Vulcan,and itʼs still not how it works. Until youhave a framework that allows you to seethat thereʼs an alternative to what youthought before, you canʼt easilyassimilate new facts.

People kept discovering Vulcanbecause the way they saw the worldrequired Vulcan to be there. It tookAlbert Einstein to provide theframework in which Vulcan became not only non-existent, but unnecessary.

Simon Worrall curates Book Talk. Follow him on Twitter or atsimonworrallauthor.com.