The Search for Vulcan
Uranus and Mercury, Verrier and Einstein
The first thing I look at on the internet every morning—before email, before the news—is the Astronomy Photo of the Day. (A pastor friend of mine once called this habit “a form of daily prayer.”) A few weeks ago, APoD featured a new Webb telescope image of my dark-horse favorite planet, Neptune. In visible light, the planet is an oceanic blue, but in infrared, it becomes luminous—its normally invisible rings glowing concentric halos, reflective clouds in the upper atmosphere brilliant as aurorae, the whole globe enveloped in a hazy aureole of light, and its nitrogen ice moon Triton looks like a Christmas star, with dramatic diffraction spikes. I clicked on a link in the caption, then clicked on a link from that—you know how this goes—and eventually found myself reading about the man who discovered Neptune, and thought he’d discovered another planet as well, but never found it. He’d come, though he never knew it, to the edge of human understanding.
In the nineteenth century Urbain le Verrier, a French astronomer and mathematician, noted some irregularities in the orbit of Uranus, the outermost known planet. But they were periodic irregularities. Predictable. He hypothesized that these irregularities could be explained by the presence of an eighth planet outside the orbit of Uranus, exerting a gravitational pull that perturbed its orbit. He calculated exactly where such a theoretical planet would be, and sent his calculations to an observational astronomer, Johann Gottfried Galle, in Berlin. On the same day that Galle received Verrier’s letter, he pointed his telescope at the predicted spot in the night sky, and there it was: Neptune. A new world.
Later in his career, Verrier detected the same sorts of irregularities in the orbit of Mercury, the innermost planet, and again posited—reasonably enough, given his previous experience—that they could be explained by the presence of a hitherto undiscovered planet, this one inside Mercury’s orbit, so close to the sun it had never been observed. They even named this theoretical planet: Vulcan. (No relation to the fictional homeworld of Mr. Spock et al, which canonically orbits the star 40 Eridani A, 17 light years away.) Over the following decades, various observers claimed to have sighted this planet, either near the sun or in transit across its disk. A doctor using homemade equipment even convinced Verrier he’d found it, and was awarded the Legion of Honor for his “discovery.” But none of these observations ever agreed with each other, and none were repeatable.
It turns out that this was because Vulcan doesn’t exist. Mercury’s orbit wasn’t being perturbed for the same reason as Uranus’; its orbit is deformed by the warping of spacetime by the colossal mass of the sun. This was conceptually unimaginable within the framework of Newtonian physics; it had to wait to be described by Einsteinian physics. Mercury’s orbit was ultimately being distorted by the same force as Uranus’—gravity—but gravity was stranger than 19th-century physicists understood. The deviations couldn’t be explained by classical orbital mechanics, but by the theory of general relativity. Einstein’s equations described Mercury’s observed deviations precisely, and experimental observations of the deflecting of starlight during an eclipse in 1919 empirically confirmed the theory.1 (Later, more powerful space-based telescopes were able to observe more obvious and spectacular instances of this phenomenon in “gravitational lensing,” in which the images of distant galaxies are elongated into arcs or doubled or quadrupled by the mass of galaxies in the foreground.)
The two problems seemed identical, but required radically different solutions, and entirely different conceptual frameworks. Some problems are Uranian problems, solvable within the current model; others are Mercurian problems, which prove to be insoluble within the existing model, and challenge it, requiring a new perspective, a revolution in thought—what Thomas Kuhn called a paradigm shift. A Uranian solution lets you see at a higher resolution, like the Hubble telescope, revealing new features; a Mercurian one is like seeing in a different wavelength, as the Webb does, the old world transfigured. It takes time, thought, and repeated, confounding failures to distinguish which problem is which kind.
It's a handy metaphor; you can preface a relationship talk by saying, “Look, this is a Uranus problem, not a Mercury problem.” My partner and I are still reading that Barbara Tuchman history of the 14th century: during the Papal schism most people were confronted with the Uranian problem of deciding which pope to follow; John Wycliffe advanced the Mercurial proposition that maybe we didn’t need a pope, or any other intermediary between man and God. You can apply it to all sorts of issues: disciplining and re-training police officers is a Uranian solution; reconsidering what exactly police are for is Mercurian. To paraphrase a meme, saving an orphan from the Orphan-Crushing Machine that is our society is Uranian; asking why such a machine should exist (let alone advocating dismantling it) Mercurian.
Uranian problems require ingenuity, even brilliance to solve; the Mercurian call for imagination, vision, even a kind of courage—valuing truth over certitude, a readiness to see the world upended. It’s hard to bring yourself to reconsider fundamental assumptions, the ones that have gotten you this far, that always worked perfectly well right up until now, except for this one niggling little discrepancy that won’t go away. A Uranian solution may resolve contradictions or discrepancies, even reveal a whole new world; but a Mercurian solution can displace you from the world you thought you knew, render your old reality obsolete and open an alien new universe.
The new insight may require forfeiting more of your old worldview than you can afford to lose. I saw Jupiter brilliant and high in the night sky last night, and looked through binoculars to see its pinpoint moons, jiggling wildly in my unsteady hands. This same sight caused another revolution, five hundred years ago. That anyone refused to look through Galileo’s telescope is probably apocryphal, but other astronomers were certainly incredulous at his discovery, which discredited the Aristotelian model of the solar system. He was eventually forced to deny the implications of what he had seen, so that we could remain comfortably ensconced at the center of the universe, secure in our understanding.
We have arrived at a point in our own time and society when the Uranian solutions aren’t working. We seem to be encountering a Mercurian problem, one that can’t be resolved within the current paradigm. The numbers aren’t adding up; there’s a pattern here, pointing to something. We keep searching and searching—occasionally there’s a premature eureka—but Vulcan just doesn’t seem to be there. What is it we’re not seeing?
Historical aside: in order to make the observations that would confirm Einstein’s predictions from a West African island during the eclipse, astronomer Arthur Stanley Eddington had to wrangle an exemption from the draft from the British government, which felt he would better serve the national interest by feeding his carcass into the pointless slaughter of the First World War.
Fantastic.
I too observed Jupiter through my binoculars, and I wasn't sure I'd actually seen the Jovian moons until I heard others report the same. Incredible!
Great piece Tim. I appreciate you writing here on Substack.