The Hunt for Vulcan: Wonderful exploration of the search of the hidden planet

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

With recently-demoted-from-the-planetary-ranks Pluto in the news lately thanks to the New Horizons probe, it’s a good time to recall when the solar system, rather than shrinking, used to be larger by one planet. That would be the planet Vulcan, which for decades was listed as lying just inside the orbit of Mercury. Why did people think Vulcan existed? More interestingly perhaps, why did so many people think they actually saw it? And what eventually convinced the scientific community that it wasn’t there? That’s the story of The Hunt for Vulcan by Thomas Levenson, and the answer to that third question lies in the book’s subtitle: How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe. Fully engaging, wholly compelling, always smooth and fast-paced, The Hunt for Vulcan is an excellent bit of non-fiction.

Levenson opens with a quick overview of how observations of Mercury’s orbit led to a need to explain some stranger perturbations. That explanation could either be found by questioning Newton’s theory of gravity — almost holy script by then — or using those same laws, which seemed to predict the existence of an entirely new planet, as yet unseen, whose mass and gravity could cause the mysterious orbital wanderings. It comes as no surprise the latter solution won out, but Levenson is more interested in how long that “solution” lasted, despite observational evidence to the contrary, and what that reluctance to question Newton says about the scientific method (especially in contrast to what we’re taught about the scientific method).

The first part after the preface takes us from Newton to Neptune, sketching out in quick fashion Newton development of his theory of gravity after Edmond Halley had asked for some help in celestial mechanics, then showing how Pierre Laplace and Urbain Le Verrier built on Newton to more thoroughly lay out the solar system’s workings. It was Le Verrier in fact who used Newton’s theory to perform a series of crushingly difficult calculations that led to his prediction of another planet beyond Neptune. When Uranus (the not-so-humble Le Verrier tried for a time to call it, yes, Le Verrier), was discovered it not only confirmed Newton’s glory, but moved Le Verrier into the limelight.

Part II, Neptune to Vulcan, follows Le Verrier’s attempt to comprehensively detail the solar system’s mechanics. Doing so eventually led to his prediction that there must be an inner planet causing Mercury’s odd orbital pattern, after a detour to deal with the question of where the asteroid belt came from. Here enters country doctor and amateur astronomer Edmond Lescarbault, who was the first to report to Le Verrier that he had “seen” his new predicted planet. From there it’s a long stretch of such “observations,” none of them ever confirmed. Even Thomas Edison worked himself into the mix, heading out to Rawlins, Wyoming during a solar eclipse. Though he was there to test his own invention, he was surrounded by fellow scientists who had come to look for Vulcan.

Finally, in Part Three, From Vulcan to Einstein, Levenson details in quick-paced fashion Einstein’s first few papers during his “miracle year” and then in more detail his work on both special then general relativity. It was the latter that finally put paid to Vulcan, as Einstein showed that his new formulation of space-time’s warping was enough to explain Mercury’s discrepancy from Newton’s predictions — no extra planet need apply.

It’s all wonderfully, lucidly, interestingly laid out. As mentioned, the pace of The Hunt for Vulcan is fast moving, but one never has the sense that Levenson is leaving out material or dumbing things down. His explanations of the theories are clear and his analogies and visuals — some probably familiar to lay readers of physics while others are wholly original — greatly enhance understanding. Nor does he stint on the people, bringing them to life in a few deft sentences for some or longer passages of time (as with Le Verrier) over pages.

Even better is the way the underlying theme of the scientific method is woven through, adding context to the particular events. Here he is early on how the ideal — hypotheses are tested and then discarded if observations do not match — is harder than it seems:

In our common description of the scientific method, any empirical result that refuses to conform to the demands of 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… No one gives up on a powerful, or beautiful, or perhaps simply a familiar and useful conception of the world without utter compulsion — and a real alternative.

He’s careful as well to make sure we don’t think we’re beyond this in our more “enlightened” era.

Levenson also shows a deft hand in the more lyrical moments, which are very rare but so well done that one almost wishes for more of them, as when he describes a solar eclipse:

The persistence of the ordinary slips as totality approaches… Colors shifts, then drain from the landscape. There are none of the cues of a sunset. Rather, the effect of pulling sunlight from the sky in the fullness of the day is just odd enough to make it seem as if reality itself has cracked… When the moon’s disc slides past the face of the sun, the world jumps. It feels unfair, as if one’s been granted a moment’s glimpse of an utterly different reality — that rectangle of Narnian forest through the open doors of a wardrobe, or a sudden vision of the train on Platform Nine and Three-Quarters. Then a crescent of sunlight appears and the normal, increasingly day-lit world returns. 

Sharp in its details of people and place and time, thoroughly clear and informative in its handling of the science, thoughtful in the ways it raises larger issues beyond the particular scientific discoveries and connects past science to our own hunt for knowledge (bringing the Higgs, gravity waves, and the like), The Hunt for Vulcan is an excellent work of popular science and highly recommended.