Thomas Levenson

In his introduction to Vulcan …And How Albert Einstein Destroyed a Planet, Discovered Relativity, and Deciphered the Universe, Thomas Levenson writes, “This book tells Vulcan’s 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” (p. xii). He cautions those who would use historical hindsight to simply write-off the efforts to find Vulcan, writing, “We may – we do – know more than the folks back then. But we are not thus somehow immune to the habits of mind, the leaps of imagination, or the capacity for error that they possessed. Vulcan’s biography is one of the human capacity to both discovery and self-deceive. It offers a glimpse of how hard it is to make sense of the natural world, and how difficult it is for any of us to unlearn the things we think are so, but aren’t” (p. xiv-xv).

The book opens with Newton’s calculus and gravitation, two ideas that played critical roles in the discovery of ice giants Uranus and Neptune by William Herschel and Urbain Le Verrier, Johann Gottfried Galle, and John Couch Adams. Having proved the ability of calculus and Newtonian physics to map and describe the solar system, Le Verrier went on to refine the calculations for other known bodies. His measurements of Mercury revealed a precession of the perihelion in its orbit. Newtonian mechanics suggested that this must result from the gravity of an object between Mercury and the Sun. Le Verrier and other astronomers thus turned their attention toward finding this object, or set of objects if it were an inner asteroid belt (p. 64). Le Verrier’s reputation was enough that it, combined with possible partial sightings, took hold in the public’s imagination. Levenson writes, “Mercury’s perihelion precession was and is real. Newtonian gravitation provides an obvious solution to such a problem” (p. 78). The public dubbed the would-be planet Vulcan due to its proximity to the sun’s fires. Possible sightings continued to trickle in during the mid-nineteenth century, culminating in a search and possible discovery during the American eclipse of 1878. Over time, the theory remained in use but the popular and scientific press slowly petered off in their coverage of possible sightings or rebuttals to those sightings. As Levenson notes, the idea of Vulcan held on because it fit the known facts of Newtonian physics. Historically, Vulcan is no more unusual a hypothesis than the cosmic microwave background radiation, the Higgs boson, or even Neptune itself, all of which scientists eventually found and refined in their understanding of relevant disciplines. Why, then, would Vulcan not reveal itself to determined searchers?

In the twentieth century, Einstein began to explore his theory of relativity, developing an understanding of how gravitation affects space-time. He predicted that the sun’s gravity well should deflect the light from stars appearing near its edge, an experiment made possible during a total eclipse. The eclipse of August 1914 offered just the chance to test Einstein’s hypothesis. Levenson notes, “The symmetry is obvious: Vulcan, of course, had been sought and seen and unseen again in such conditions” (p. 158). Just as a team got underway to Siberia, war broke out. Einstein continued to refine his calculations for relativity and gravitation during the war. He determined that “a ray of light passing through the sun’s gravitational field would deflect by 1.7 arcseconds, double the number his 1913 theory predicted” (p. 170). Continuing to work the numbers, Einstein discovered that “no chunk of matter was required to explain Mercury’s track, no undiscovered planet, no asteroid belt, no dust, no bulging solar belly, nothing at all – except this new, radical conception of gravity. The sun with its great mass creates its dent in space-time. Mercury, so firmly embraced by our star’s gravitational field, lies deep within that solar gravity well” (p. 172).

Levenson concludes, “It was said of Newton that he was a fortunate man, because there was only one universe to discover, and he had done it. It had been said of Le Verrier that he discovered a planet at the tip of his pen. On the 18th of November, 1915, Einstein’s pen destroyed Vulcan – and reimagined the cosmos” (p. 172). Gµv=8πGTµv neatly summarizes Einstein’s theory and ended Vulcan’s place in the solar system. The Eclipse of May 1919 afforded the opportunity to gather photographic evidence of lensing, with careful checks of the data finding it matched Einstein’s prediction. Vulcan was dead, but Levenson returns to his introductory note to point out how the idea of Vulcan over the seventeenth, eighteenth, nineteenth, and early twentieth centuries represents so much of human nature while its ultimate fate represents the best of the scientific method. Levenson’s book manages to capture science in action, placing it in cultural context and weaving a narrative that casual readers will find enthralling.… (mais)

A short but very interesting non-fiction book about the search for an unknown planet postulated to exist closer to the Sun than Mercury. Its existence was proposed in the mid 1800s to explain a very small discrepancy in the orbit of Mercury, specifically how that planet’s orbit precesses over time—that is, how a line drawn between its closest and furthest distance from the sun changes direction in space over centuries.

The discrepancy was first pointed out by the French astronomer Anton Le Verrier. Le Verrier was famous for his earlier prediction that an as-then unknown planet was slightly disturbing the orbit of Uranus. He calculated its position, and then was triumphantly vindicated by the discovery of the planet just where he had predicted it to be. It was later named Neptune.

The discrepancy in Mercury’s orbit was tiny indeed. But Newton’s laws of orbital motion were by then so well established, and the mathematics so clear, that the discrepancy needed explanation. Based on his triumphant discovery of Neptune, it is hardly surprising that Le Verrier proposed another as-yet unseen planet, this time closer to the Sun. The hunt was on! Every solar eclipse was an opportunity for observation, trying to see this world so close to the Sun’s bright disc.

Was the missing planet, dubbed Vulcan, ever discovered? Alas for Star Trek fans, Vulcan does not exist. The true explanation for the discrepancies in Mercury’s orbit was uncovered only with the aid of Einstein’s General Theory of Relativity in 1914 and its revelation of curved space-time.

I love this kind of scientific history. Thomas Levenson makes a fascinating story out of it, and does a great job of explaining the scientific issues involved.… (mais)