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Illustration Credit: Jon Han
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This month marks the 100th anniversary of the General Theory of Relativity, the most beautiful theory in the history of science, and in its honor we should take a moment to celebrate the visualized “thought experiments” that were the navigation lights guiding Albert Einstein to his brilliant creation. Einstein relished what he called Gedankenexperimente, ideas that he twirled around in his head rather than in a lab. That’s what teachers call daydreaming, but if you’re Einstein you get to call them Gedankenexperimente.
As these thought experiments remind us, creativity is based on imagination. If we hope to inspire kids to love science, we need to do more than drill them in math and memorized formulas. We should stimulate their minds’ eyes as well. Even let them daydream.
Einstein’s first great thought experiment came when he was about 16. He had run away from his school in Germany, which he hated because it emphasized rote learning rather than visual imagination, and enrolled in a Swiss village school based on the educational philosophy of Johann Heinrich Pestalozzi, who believed in encouraging students to visualize concepts. While there, Einstein tried to picture what it would be like to travel so fast that you caught up with a light beam. If he rode alongside it, he later wrote, “I should observe such a beam of light as an electromagnetic field at rest.” In other words, the wave would seem stationary. But this was not possible according to Maxwell’s equations, which describe the motion and oscillation of electromagnetic fields.
The conflict between his thought experiment and Maxwell’s equations caused Einstein “psychic tension,” he later recalled, and he wandered around nervously, his palms sweating. Some of us can recall what made our palms sweaty as teenagers, and those thoughts didn’t involve Maxwell’s equations. But that’s because we were probably performing less elevated thought experiments.
By the early 1900s, a variety of experiments showed that light traveled at a constant speed, irrespective of the observer’s motion relative to the light source. The physics community was puzzled by this, just as Einstein was still puzzled by his attempts to imagine riding alongside a light beam. So, in 1905, he performed some new thought experiments.
He was then working at the Swiss patent office. Every day, he would attempt to visualize how an invention and its underlying theoretical premises would play out in reality. Among his tasks was examining applications for devices to synchronize distant clocks. The Swiss (being Swiss) had a passion for making sure that clocks throughout the country were precisely in sync. As the Harvard historian of science Peter Galison has found, more than two dozen patents were issued from Einstein’s office between 1901 and 1904 for devices that used electromagnetic signals such as radio and light to synchronize clocks.
What Einstein was able to visualize was that if you sent a light signal from the clocks the instant they struck the hour, a person traveling superfast toward one of the clocks would have a different view of whether they were in sync than someone traveling superfast in the other direction.
He later explained this idea with another thought experiment. Suppose lightning bolts strike a train track at two distant places. Imagine that there’s a man standing on the embankment midpoint between the two strikes. If the light from each bolt reaches him at the same instant, he will say the strikes were simultaneous. Now imagine that there’s a woman in the midpoint of the train just passing him. If the train is moving forward superfast, by the time the light waves arrive she will be slightly closer to the lightning bolt in front. She will declare that it happened first.
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Walter Isaacson, the C.E.O. of the Aspen Institute, is the author of The Innovators and biographies of Einstein, Steve Jobs, Benjamin Franklin and Henry Kissinger