Thomas Levenson - The Hunt for Vulcan: . . . And How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe

November 18, 1915, Berlin.

A man is on the move, coming into the center of town from the western suburbs. Usually a bit disheveledhis shock of hair would become almost independently famoustoday hes fully presentable, girded for public performance. He enters Unter den Linden, the grand avenue that pierces the Brandenburg Gate on the way east to the River Spree. He walks up to number 8, the entrance to the Prussian Academy of Sciences, and steps inside.

On this Thursday in the second autumn of what was already being called the Great War, the members of the Academy settle themselves in for a lecture, the third of four in a row by one of their newest colleagues. That still-young man makes his way to the front of the room. He takes up his notesjust a few pagesand begins to speak.

Albert Einsteins talk that day and its sequel, presented the following week, completed the greatest individual intellectual accomplishment of the twentieth century. We now call that idea the general theory of relativity: at once a theory of gravity and the foundation for the science of cosmology, the study of the birth and evolution of the universe as a whole. Einsteins results mark the triumph of a lone thinker, battling the odds, the doubts of his peers, and the most famous scientist in history, Sir Isaac Newton.

For all the grand sweep of his theory, though, when he spoke on the 18th, Einstein focused on something much more parochial: Mercury, the smallest planet then known, andat an even finer grain of detaila tiny, unexplained hitch in its orbit, a wobble, barely measurable, for which there was (until he spoke) no adequate explanation.

By 1915, Mercurys misbehavior had been recognized for over sixty years. Throughout that time, astronomers had gone to greater and greater lengths to come up with some explanation for this errant behavior within the conventional framework of Newtons centuries-old account of gravitythe crowning victory in the Scientific Revolution. The first and seemingly most obvious idea imagined a whole new planet hidden in the glare of the sun, which could provide enough of a gravitational tug to haul Mercury out of its correct orbit.

As a hypothesis, conjuring a planet out of an orbital glitch was perfectly reasonable. Indeed, there was precedent, and at first it seemed not just logical, but right. Almost as soon as Mercurys plight became public knowledge, amateur and professional astronomers alike spotted and identified an object lurking within the concealing glare of the sun. It would be seen again, over and over, more than a dozen times over two decades. Its own orbit would be calculated; its history recovered in old records of unexplained sightings; it would even receive a name.

There was only one problem:

The planet Vulcan was never there.

This book tells Vulcans story: its ancestry, its birth, its odd, twilit journey in and out of the grasp of eager would-be discoverers, its time in purgatory, and finally, on the 18th of November, 1915, its decisive end at the hands of Albert Einstein.

At first blush, this may seem something of a burlesque, a tale of nineteenth-century astronomical follies, Victorian gentlemen chasing a mistake. But theres more here than a comedy of errors. The story of Vulcan suggests something much deeper, an insight that gets to the heart of the way science really advances (as opposed to the way were taught in school).

The enterprise of making sense of the material world turns on a key question: what happens when something observed in nature doesnt fit within the established framework of existing human knowledge? The standard answer is that scientific ideas are supposed to evolve to accommodate new facts. After all, science is a uniquely powerful way of figuring things out precisely because all of its claims, even its most beloved, are subject to the ultimate test of reality. In our common description of the scientific method, any empirical result that refuses to conform to the demands of a theory invalidates that theory, and requires the construction of a new one.

Ideas, though, are hard to relinquish, none more so than those of Isaac Newton. For decades, the old understanding of gravity was so powerful that observers on multiple continents risked their retinas to gaze at the sun in search of Vulcan. And, contrary to the popular picture of science, a mere factMercurys misplaced motionwasnt nearly enough to undermine that sturdy edifice. As Vulcans troublesome history reveals, no one gives up on a powerful, or a beautiful, or perhaps simply a familiar and useful conception of the world without utter compulsionand a real alternative.

Einstein wrote Vulcan out of history on the third Thursday in the second November of the war. It had taken him the better part of a decade to develop what became his radical new picture of gravity: how matter and energy mold space and time; how space and time fix the paths that matter and energy must take. As presented to his colleagues that Thursday afternoon, Einstein showed how Mercurys wobble turned out to be just its natural path, the one it has to take in a universe in which relativity is true. That result emerged at the end of a chain of mathematical reasoning, the inevitable outcome of subjecting matter to number.

In that context, Vulcans fate provided the first test of general relativity, proof that Einstein had managed to capture something true about how our universe works. But to get to that point, to follow the radical strangeness of general relativity all the way to its conclusion took both boldness and exquisitely subtle reasoning: hard labor sustained over the eight years it took Einstein to dispatch the ghost planet. That part of the story shows how powerful a thinker it took to clamber past accepted wisdom to achieve what he, alone of all his peers, was able to do.

Einstein, usually a fairly phlegmatic man, felt this one to the bone. When he completed the calculation of the orbit of Mercury and saw exactly the right number fall out of the long chain of pure reasoning, he told friends that he felt beside himself with excitement. Seeing Mercurys motion simply fall out of his equations pierced him to his heart, he said. He felt palpitations, a sensation as if something had burst within him.