December marked the 100th anniversary of Albert Einstein’s development of the General Theory of Relativity, a revolutionary theory that gave scientists the mathematical tools to analyze the universe and inaugurated the modern era of cosmology.
As science journalist Natalie Angier has written, “No longer could space be seen as a featureless void, the nothingness between the somethingness of galaxies and stars. Einsteinian space has heft, shape and a sense of place. It bends around giant suns and plunges down the throats of black holes. It expands restlessly in all directions and drags us along for the ride.”
Just as he had with his 1905 Special Theory of Relativity, Einstein began with a thought experiment that he would later call “the happiest thought in my life.”
To do the thought experiment, imagine a man in an elevator that is falling. The man has no way to tell if the elevator is falling at an accelerated rate or if it is floating in a gravity-free region of space.
Conversely, if the elevator is being pulled up at an accelerated rate the man cannot distinguish between the pull of gravity and the force of acceleration.
From this thought experiment, Einstein concluded the effects of gravity and acceleration are equivalent.
Instead of a separate space through which objects move, Einstein envisioned space itself warping to create the effect of gravity. Physicist John Wheeler described it, “Space-time tells matter how to move; matter tells space-time how to curve.”
Going back to the elevator example, Einstein realized that if one shined a light through a pinhole on one side of the elevator toward a pinhole on the other side, the acceleration of the elevator would cause the light to be slightly lower on that other side. By his equivalence principle, gravity should bend light. And just such an effect was seen in a famous astronomical observation made by Arthur Eddington in 1919. Today, astronomers use this gravitational lensing as one tool to observe distant objects in space.
Interesting ideas we might agree, but of what practical value? Or, as Ronald Reagan once remarked, we shouldn’t be “subsidizing intellectual curiosity.”
Nineteenth-century physicist Michael Faraday, whose intellectual curiosity laid the foundations for our modern electrified world, said when questioned by a politician about the practical value of electricity, “One day, sir, you may tax it.”
It turns out that Einstein’s theory does have a direct impact on our lives. The theory predicts that clocks close to a massive object (like the Earth) where space-time is more curved run slower than those farther away (such as on a GPS satellite).
If not corrected, such clock errors could add up to global positioning errors of about 10 kilometers (6 miles) per day. Fortunately, on board each GPS satellite there is a microcomputer that performs the necessary timing calculations to correct for such relativistic effects.
So, the next time you use your GPS, remember the man who, over a hundred years ago, was curious about gravity. And to hold off the gathering darkness of anti-intellectualism, continue to support intellectual curiosity.
Gary L. Bennett of Emmett is a physicist who has worked in the space program.