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Book review

How Einstein ended hunt for a planet that never was

You probably have not heard of a planet called Vulcan. That’s because it does not exist. But for a good chunk of the 19th century, leading scientists believed that it did and that it was lurking near Mercury. They had a powerful system of ideas backing them up — Isaac Newton’s theory of gravitation and how it governed the orbits of planets.

Or so it seemed to. “The Hunt for Vulcan” is a short, beautifully produced book that tells a cautionary tale. Thomas Levenson, the head of MIT’s graduate program in science writing, deals in big ideas about the universe — the biggest of all, really, about space, time, and the very ways we perceive the cosmos — and colorfully illustrates the limits of scientific theory as it faces new data and even more persuasive theories.


Levenson is a breezy writer who renders complex ideas in down-to-earth language, though he can be a bit too colloquial at times. (You can explain clearly without saying someone “believed he could simply ramp up his math chops.”)

It all began with Newton. In the 1680s, the renowned British scientist was working out the laws of celestial motion and gave the world one of the most revolutionary theories in intellectual history. Here was “a set of laws that could, deployed properly, describe the how, the where, and the when of every bit of matter on the move anywhere — everywhere — in the cosmos.’’

Plug in a few variables — mass, the square of the distance between two objects — et voilà, the universe was seemingly explained by a beautiful mathematical equation. Newton’s law of gravitation was put to powerful use, showing how the planets of our solar system moved in elliptical orbits. They pointed the way to the discovery of Uranus, then Neptune. Observable data meshed with mathematical reasoning to open up the heavens. The tenets Newton laid down in his “Principia,’’ Levenson writes, enables “anyone to figure out where Mars would be next Tuesday.”


But they would not yield the answer to the Mercury problem. If planets like Mars revolved around the sun in a regular ellipsis, Mercury’s orbit displayed a peculiar anomaly, an irregular path. According to Newtonian logic, there must be another body’s gravitational pull acting on it, causing it to behave the way it did. Was it an asteroid — or an unknown planet?

This was the problem that confronted one of the most intriguing characters in Levenson’s story, the French mathematical astronomer Urbain-Jean-Joseph Le Verrier, who would spend years trying to get to the bottom of why Mercury did what it did. Le Verrier, a brilliant if prickly man, threw everything he had at the problem, endlessly recalibrating and working the numbers. The nearby Venus was ruled out as the cause, but Le Verrier, who published his findings in 1859, contended there was a lurking planet that was exerting itself on Mercury. All that remained was to find this celestial body, which he dubbed Vulcan.

Stargazers and astronomers scanned the skies looking for empirical evidence to back up the conjecture. Reports filtered in, but nothing quite clinched the assertion. No matter. There was enough force to the arguments put forth by Le Verrier to keep the search for Vulcan going. “[A] little scrap of positive evidence overbears an immense amount of negative,’’ The New York Times observed.


The key question, as Levenson puts it,is “what happens when a prediction fails to find its match in nature?” Fast forward several decades to the start of another scientific revolution. It took the powerful mind of Albert Einstein to get to the bottom of the Vulcan problem.

Levenson’s account of Einstein’s journey to the theory of relativity is well-paced and clearly explained. It took Einstein some eight years to formulate his breakthrough. As a way to test it, he applied it to the Mercury question, and it accounted for the eccentric orbit without the existence of a phantom planet. And when he delivered a talk detailing his calculations at the Prussian Academy of Sciences on Nov. 18, 1915 in Berlin, his “pen destroyed Vulcan — and reimagined the cosmos.”

Einstein had brought the very essence of time to bear on the problem, adding a fourth dimension to his model of the universe. Einstein put forth a “new, radical conception of gravity.” Instead of a force that pulls on a body, gravity “is the local curvature of space-time.” It is like a sheet of rubber that gets its shape from the presence and movement of mass and energy. Mercury was merely riding along a curve in the sheet created by the sun. Poor, misbegotten Vulcan was consigned to the dustbin, but our view of the universe was changed forever.


. . . And How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe


By Thomas Levenson

Random House, 229 pp., $26

Matthew Price is a regular contributor to the Globe. He can be reached at mprice68@gmail.com.

Correction: A prior version of this review incorrectly said that Newton’s theories lead the way to the discovery of Jupiter.