It is a masterpiece worthy of hype and celebration, for sure. Equating gravity with geometry, the theory posited that a massive object, like the Sun, would warp the fabric of space-time around it. The hackneyed, and imprecise, analogy is of a bowling ball sagging the fabric of a trampoline. Stunning vindication came four years later, in 1919, when photographs of a solar eclipse, taken by intrepid English scientists who traveled to Brazil and to the African island of Principe, revealed a tiny deflection of starlight matching Einstein’s prediction. The findings caused a media commotion, propelling Einstein’s name into the stratosphere of fame. The legend of the superstar scientist was born.
Since then, general relativity has survived every conceivable scientific test, as well as endless crackpot assaults, for a hundred years. That ain’t no mean feat.
Those who challenged the theory haven’t fared so well. Take the case of the astronomer Thomas Jefferson Jackson See, a renowned telescopic observer and a charismatic public speaker (the naval captain’s uniform adorning his six-foot-four figure didn’t hurt). While much of the world toasted the eclipse result, See accused Einstein of plagiarism and worse. He denounced general relativity as “a crazy vagary, a disgrace to our age!” The poor chap didn’t seem to grasp what he was up against: Made a virtual pariah by the scientific community, he spent the rest of his quarrelsome life at a navy yard in California. Today See is remembered for little beside the controversies he wrought in his heyday, while public adulation of Einstein continues unabated.
General relativity is not only elegant and successful as a theory. It is also surprisingly handy. Astronomers use it to “weigh” the dark matter that dominates distant galaxy clusters and to discover alien planets through a technique known as “microlensing.”
At this point, you might say: Sure, Einstein was one smart fellow, but what good has his highfalutin theory done for the rest of us? In fact, general relativity underpins a multibillion-dollar industry right here on planet Earth. And, you might want to thank the secular saint of science the next time your plane lands safely in bad weather.
That’s because the global positioning system would not work properly without relativistic corrections: Internal clocks of GPS satellites would tick at different rates depending on their location in the Earth’s gravitational field. If these offsets weren’t accounted for, you might drive into a corner café, or worse, a pilot might miss the ground by miles. Perhaps Einstein wasn’t that smart after all: Imagine the windfall his heirs would inherit had he found a way to patent this particular application of relativity.
Despite the countless verifications of general relativity over the years, in the celestial realm and closer to home, scientists are not done with testing the theory yet. I, for one, am grateful for their insatiable, almost desperate, hankering to look for cracks in this grand edifice. It gave me a good excuse to do somersaults in zero gravity, on a parabolic flight operated by the European Space Agency, as a team of French physicists fine-tuned their apparatus (and a few unfortunate souls, with strained faces, were strapped in their seats, bravely resisting the overwhelming urge to puke). Their aim is to test whether rubidium and potassium atoms fall at exactly the same rate, as required by general relativity. The so-called equivalence principle has been tested already to a precision of one part in ten trillion. That may seem plenty good enough for most people, but most people are not scientists.