Albert Einstein disproves the existence of Vulcan

Nowadays debate about the number of planets in our solar system revolves around arguing about exactly which of the slightly-larger-than-average icy bodies should be included in the count.  Also, if you talk about the planet Vulcan, it is assumed you are simply a harmless Star Trek nerd referring to the homeworld of a fictional race of emotionless humanoids.

Consider a time when neither of those things were true.  Consider the 19th century.

In the 1840s, French astronomer Urbain Jean Joseph Le Verrier began applying Newtonian dynamics to the problems of planetary orbits.  After noticing a discrepancy between his calculations and the direct observations of Uranus, he predicted that Uranus was being gravitationally affected by another more distant planet.  He was even able to predict where it was in its orbit before it was observed.  In 1846, Neptune was discovered where foreseen, lending credence to both Le Verrier and Newton. 

In the 1850s, feeling emboldened by his historic prediction, Le Verrier turned his sights on the other planets.  Similar to the perturbations he noticed in Uranus's orbit, he also found problems with Mercury, the innermost planet in the solar system.  He concluded that there must be another planet even closer to the sun disturbing Mercury's orbit.  He named it Vulcan (after the Roman God of Fire). 

I won't draw it out here.  For decades he and others searched for Vulcan without success.  Le Verrier and other astronomers who supported the Vulcan theory died convinced it would be found.

So what happened?  Le Verrier had applied Newtons's laws correctly.  If the theory is correct, the outcome must be predictable, yet the prediction in this case ultimately failed.  Had Newton been wrong about gravitational laws? 

Nah.  It just didn't account for everything.  Turns out the inconsistencies between observation and prediction were actually a relativistic effect:

The advance of Mercury's perihelion was brilliantly explained by Albert Einstein in November 1915 at his desk in Berlin -- his general theory of relativity finally exorcised the ghost of Vulcan from the inner solar system. Einstein presented a new theory of gravitation that conceived of it as a warping of the fabric of space-time. According to his theory, Mercury should precess slightly faster than the Newtonian rate -- by 0.1 arcseconds for each orbital revolution of the planet, or 43 arc-seconds per century. This agreed exactly with the observed rate.  Vulcan became redundant.*

Unfortunately Le Verrier didn't know about relativity, and spent a good portion of his professional life trying to work on a problem that demanded its contributions. 

*Excerpted from "Vulcan Chasers" by William Sheehan and Richard Baum, Astronomy, volume 25, issue 12 (December 1997).  Read more of the story there, or the wikipedia article here.

Posted at 06:40PM Jul 25, 2006 by WILSON, JOSHUA in Anecdotes  |  Comments[3]