The Hunt for Vulcan

by Thomas Levenson

  In the beginning, most of Watson’s colleagues were prepared to suspend judgment. He was a professional observer and a good one, so the astronomical community was unwilling simply to dismiss his findings. But the sheer weight of all that nothing seen in the other telescopes pointed at the sun at the same time left most astronomers unsure—at best—about what to make of this latest vision of the elusive planet.

  A few flatly refused to defer to reputation. C. F. H. Peters—discoverer of forty-eight asteroids and one of Watson’s avowed rivals in the minor planet game—published a devastating attack on this latest Vulcan candidate. He accused Watson of making a series of elementary errors. Peters questioned Watson’s makeshift system for marking positions. He argued that Watson couldn’t have made a reliable assessment of the brightness of “a.” He offered an explanation for Watson’s description of the unusual ruddy color of the proposed planet. None of the steps in Watson’s procedure survived scrutiny, leading Peters to his blunt, almost brutal conclusion: “It is, therefore quite apparent to every unbiassed mind that Watson observed Theta and Delta Cancri, nothing else.”

  —

  Peters’s report bubbled with scorn, and Watson reacted with a mixture of formal defense and outrage, writing, “Professor Peters’s whole attack upon the integrity of my observations is not of the slightest consequence, since he has created the errors in his own brain,” adding “I do not intend to engage in any controversy about these matters and especially with a person who was, at the time of the observations, more than two thousand miles away.” Publicly, his colleagues gave him tepid support. Commentary in the journal Nature chided Peters for his tone, writing “Throughout Prof. Peters’s criticisms…there is evinced a certain animus which could have been as well avoided.” Fair enough, but for all its seemingly impartial account of the Peters-Watson fight, the Nature piece subtly made its judgment clear. “We will venture to say that the general feeling amongst astronomers when first reading Prof. Watson’s announcement…[is that he] would not risk his whole scientific reputation by putting forth such a statement to the world, unless he was firmly convinced of its truth.” The hammer fell in the next few words: “Otherwise, the fact that there were two known stars on the parallel or nearly so and less than one degree west of the objects supposed to be new, would probably have been felt to be an almost fatal objection to the reality of the discovery.”

  Such delicate language muffled the blow, but the point was plain enough. Peters may have been a rude SOB, but he had said out loud what was rapidly becoming the consensus of astronomical opinion: “a” and “b” were nothing more than “two known stars,” misidentified amid the furor of an eclipse, recklessly trumpeted as discoveries in the adrenaline of the moment and preserved in the heat of desire, the felt urgency to make real what must be there. Watson disagreed, of course. He never retracted his Vulcan in what turned out to be the brief time left to him. In the autumn of 1880, he came down with a sudden infection and on November 23, he died. He was forty-two.

  With Watson silenced, many, and not just the vengeful Peters, felt liberated to say out loud what they had previously only whispered. The old pattern held: Vulcan was to be found only when it was sought in the faith that it had to exist, never when anyone tried to confirm what had persuaded someone else. The astronomical community’s consensus quickly hardened. James Watson had seen what he longed to see. His “Vulcan” was nothing more than a mistake.

  Almost a full two decades earlier, Vulcan had gained entry into the solar system. The eclipse of 1878 signaled its banishment. By the 1880s, the old saw flipped: absence of evidence had finally accumulated to the point where (to almost everyone) it had indeed become evidence of absence.

  —

  July 29, 1878, evening.

  Thomas Edison knew his experiment had failed almost immediately. His tasimeter was not sensitive enough to pick up infrared radiation from the solar corona. That null result couldn’t dent his good mood, though. This western trip, he had told reporters, was the first vacation he’d taken in sixteen years, and he was prepared to enjoy himself, no matter what.

  For their part, his hosts were eager to entertain their famous visitor, but no one let Edison suffer any delusions about his status: he was a tenderfoot. Edison got a taste of western humor a day or so after the eclipse, when he and some companions took a rail excursion up to Separation. Edison packed along his Winchester rifle, on the chance he might bag some local fauna. At the depot, the tourists were greeted by the station agent, John Jackson Clarke. Clarke wasn’t terribly impressed with the outdoor skills of his visitors—“their combined knowledge of game killing,” he wrote, “was about equal to mine of parallaxes and spectrums.” Out went the intrepid hunters anyway, straggling back that evening having bagged between them a grand total of exactly one sparrow hawk.

  Edison returned to the station first, and he asked whether there might be anything else worth shooting nearby. Clarke told him that the surrounding plain enjoyed an abundance of jackrabbits—“what the locals call narrow-gauge mules.” Edison asked where he might find them, and Clarke “pointed west and noticing a rabbit in a clear space in the bushes, said there is one now.”

  Edison picked out a silhouette from the platform, but he wanted to make sure of his kill. He “advanced cautiously to within 150 feet and shot.”

  The animal did not move. He closed to one hundred feet. He fired again.

  The beast wouldn’t jump. He aimed, pulled the trigger once, and then again.

  His target stood its ground.

  Edison glanced over his shoulder and saw that the entire station staff had gathered for the show.

  The penny dropped.

  He’d been set up, played for a dude. His target looked like a desert hare, all right, all ears and legs. It was exactly where one might expect to spy such an exotic creature. And yet…

  Thomas Edison, genius, had just murdered…a stuffed jackrabbit.

  It had seemed so real.

  * * *

  *1 This isn’t terribly impressive as such events go: given all the variables, the relative sizes of the sun and the moon and the variations in both the earth-moon system’s orbit around the sun and the moon’s around Earth, the longest possible eclipse lasts about seven and a half minutes.

  Eclipses won’t be visible forever. The tidal dynamics affecting the earth and moon increase the distance between the earth and the moon—very slowly, by 2.2 centimeters, or less than an inch per year. In approximately 1.4 billion years, the moon will have drifted far enough away so that its apparent size will be too small to block out the sun.

  For a very different kind of take on the fact that the earth and moon are drifting apart, see Italo Calvino’s Cosmicomics.

  *2 Also noteworthy: Wyoming, incorporated in 1868, became in 1869 the first US territory to grant the vote to women.

  *3 Never, never, never look at a partial eclipse with the naked eye or through a telescope or binoculars: eye damage up to and including blindness will result. See NASA’s guide to viewing an eclipse safely: http://​eclipse.​gsfc.​nasa.​gov/​SEhelp/​safety.​html, and in more detail this: http://​eclipse.​gsfc.​nasa.​gov/​SEhelp/​safety2.​html. A nice do-it-yourself guide to eclipse watching can be found here: http://​www.​exploratorium.​edu/​eclipse/​how.​html.

  Interlude

  “A SPECIAL WAY OF FINDING THINGS OUT”

  Vulcan after the eclipse of 1878 became—to steal a twentieth-century trope—something of Schroedinger’s planet. Like the famous cat, as long as no one actually looked for it, an intra-Mercurian mass made such perfect sense that it gained a kind of potential existence. It was there/not there; in and out of sight; logically necessary, yet absent.

  The confounding issue remained, of course. Mercury still misbehaved. Simon Newcomb was the most authoritative student of the solar system in the last years of the nineteenth century. In 1882 he redid Le Verrier’s calculation and showed that Mercury’s excess perihelion advance was
slightly larger than Le Verrier had originally determined. But the drama of the Wyoming eclipse left astronomers with few choices. Vulcan, whether imagined as a single planet or a flock of asteroids, was no longer plausible as the source of Mercury’s anomaly. What to do?

  —

  No-shows are hardly alien to science.

  Theories predict. That’s their job. Ever since Newton and his co-conspirators consummated their revolutionary program of subjecting nature to mathematics, this has come to mean that particular solutions to systems of equations can be interpreted as physical phenomena. If a given mathematical representation hasn’t yet matched up with some phenomenon in the real world, that’s what’s called a prediction. From the theory of Uranus, Neptune; from the theory of Mercury…what, if not Vulcan?

  But what happens when a prediction fails to find its match in nature? This is a constant question in science. Take one recent example: for half a century, there was the mystery of something called the Higgs boson. The Higgs is the quantum, or the smallest possible change in energy, in what is known as the Higgs field. The Higgs concept was first proposed in the mid-1960s as part of what is now called the Standard Model of particle physics, a theory that describes the properties of the elementary particles out of which reality is built.*1 Within the Standard Model, the Higgs boson accounts for how certain of those particles acquired the mass that they have in fact been seen to possess.

  Over the next several decades the Standard Model proved phenomenally successful, its predictions matching experimental results to as many decimal places as any measurement could achieve. But not the Higgs—which stubbornly refused to appear.

  The Higgs was finally captured in in observations made in 2012 and 2013, following the construction of the Large Hadron Collider (LHC), an instrument powerful enough to peer into domains invisible to earlier devices. Up until the machine produced its data it remained an utterly open question as to whether the Higgs would actually show itself at the energies the machine could produce.

  And if the LHC hadn’t found its Higgs? That would have been a direct analogy to the problem Vulcan after 1878 seemed to pose (for all that no one addressed it): the failure to find the result theory anticipated in a context that demanded some solution would raise deep and (for theoretical physicists) very exciting questions.

  —

  The Higgs is no isolated example. Take, for example, the mysteries that remain in the account of what happened as our universe was born. So much has been discovered about that seemingly inaccessible time and process because the Big Bang—the explosive appearance of space and time, matter and energy, essentially out of nothing*2—left a snapshot of itself in a flash of light called the Cosmic Microwave Background, or CMB. Discovered in 1964 as a seemingly uniform hiss of microwaves (the same year that the Higgs idea first emerged), the CMB offered the chance to do something new: to measure detailed properties of the very early universe by extrapolating backward from that microwave glow to the Big Bang process itself.

  In the decades since, the interplay of cosmological theory and ever more refined observations has yielded a series of insights about that nascent universe, along with predictions about what kinds of features should be found in the CMB. For example: just by looking around us, it becomes obvious that the present-day universe is lumpy, with big piles of matter collected into stars and galaxies and clusters of galaxies—and giant, mostly empty spaces in between. What we see now implies that the CMB should clump too, that there should be places in the microwave picture of the universe that shine just a little brighter than other places: hot spots that map the slightly more matter-rich neighborhoods that could ultimately grow into galaxy clusters.

  Early surveys of the microwave sky, though, showed a completely uniform, blank glow. If that were all there was, such a featureless early universe would seem to be incompatible with what we know is out there now—and that in turn would imply that what cosmologists thought they knew about the cosmological evolution was wrong.

  That’s how matters stood for almost three decades until 1989, when a specialized telescope was launched into Earth orbit. By 1993, that instrument had captured enough photons to reveal exactly a broad pattern of light and dark—the first, out-of-focus glimpse of the original “seeds” of galaxy clusters. There was a prediction based on a clearly observed fact in the contemporary universe…and through enormous effort, it was shown to be true.

  Since then, the CMB has been studied at greater and greater resolution to reveal an increasingly detailed picture of the events that turned the infant cosmos into one recognizably like our own. At the same time, theorists have made a series of predictions to be tested when and if observations of the CMB could be improved yet more. One idea first proposed in the 1980s suggests that during its first instants of existence, our universe underwent an episode called inflation, during which space itself expanded at a ferocious rate—the bang of the Big Bang itself, as one of its inventors, Alan Guth, describes it. For more than thirty years, observations have yielded results that are consistent with inflation, but despite that growing body of evidence, open questions remained.

  That seemed set to change in 2014, as researchers closed in on a key expectation of the theory: that inflation’s wild ride would create what are called gravity waves, ripples in the gravitational field that would show themselves in particular (and very subtle) features that might be detectable in the CMB. There are several versions of the idea, each of which predict somewhat different signals. In some of them, those primordial gravitational waves would leave a specific imprint on the CMB as a particular type of polarization within the microwave background—thus revealing the first unequivocal connection between the vast, fast madness of the inflationary universe with our own, more sedate cosmos. If such effects were found, it would be the final rung in the ladder of observations—the smoking gun to confirm that we really do live in an inflated universe.

  That was the mission a research team set for itself with its instrument at the South Pole. The BICEP2 microwave telescope started gathering polarization data in 2010. The team ran it for two years before beginning to study its data in earnest. It was a delicate, difficult analysis, and the stakes in the answer were so high that the researchers took every precaution they could think of to make sure they got it right. The public announcement came on March 17, 2014: B-mode polarization had been observed in the CMB to a 5.9-sigma, which was much better than the 3.5 million–to-one level of certainty required to claim discovery.

  It was a thrilling moment. The result made front pages around the world. It brought one of inflation’s inventors to tears. For scientists and amateurs of science alike it was a gift: something beautiful, strange, and newly intelligible about existence on the largest scale. There was a distant resonance, an echo of what those first few must have felt in 1687, when the earliest copies of Principia came into their hands: a kind of breathlessness, sheer wonder that human minds could penetrate such incredibly deep mysteries. One of the most persuasive readings of inflation is that we dwell not in a singular cosmos, but in just one of uncounted island universes, our little village within a vast Multiverse. What a thought! No wonder that a grown man wept to hear the good news.

  —

  Observing at the ragged edge of technology is always a tricky business. Each Vulcan “discovery” drew informed scrutiny. So did the tiny fluctuations the BICEP team found within their data, the signal they claimed was the signature of inflation’s gravity waves. Questions about their results became doubts within a few weeks, as scientists from outside the team pressed on the issue of foreground dust—perfectly ordinary debris common in galaxies like our own Milky Way. By summer’s end, it had become clear that the filtering of light through such nearby dust might explain all of the effects visible in BICEP data. Planet or sunspot? Multiverse or stellar schmutz?

  Mercury still precesses and by many measures the universe behaves as if inflationary theory is correct, but by early 2015, attempts to check the BICEP2 measur
ement confirmed that it was impossible to distinguish a clear answer, given the confounding role of the galactic dust. As in 1878, the mystery remains open; we still do not know what happened during the birth of the particular cosmos we inhabit. There is one important difference, though, between those searching now for ripples in space-time and those who after the eclipse of 1878 gave up on Vulcan. What is known to date is that BICEP2 results do not contain a reliable observation of inflation’s signature in the CMB. That doesn’t (yet) mean such traces don’t exist. Several attempts are already under way to probe the CMB with yet more precision. Those measurements will likely settle whether the predicted gravity waves really do reveal themselves in the microwave background, and even if the hoped-for polarization effects are not found, there are versions of inflation theory that do not require a gravity wave signature in the ancient glow of the Big Bang.

  Still, even if some form of inflation remains a persuasive candidate to account for the properties we see in the universe right now, it hasn’t closed the deal. The cosmos could see things differently.

  —

  Long gaps between prediction and observation always raise the question: what finally persuades science—scientists—to abandon a once successful idea? When do you take “no” for an answer? There’s a conventional response in science to that question: right away. Or at least as soon as you’re confident of the evidence. In a public talk delivered in 1963, Richard Feynman said that science is simply “a special method of finding things out.” But what makes it special? The way its answers get confirmed or denied: “Observation is the judge”—the only judge, as the catechism goes—“of whether something is so or not.”