The little crystal, Iceland spar, baffled Isaac Newton and others by splitting light into two beams. The spar and its anomalies ultimately led to the downfall of Newton’s particle theory of light. Credit: Bruce Watson.
It may not be sunny where you are reading this, but you’ll need sunglasses to continue. Dark shades in hand, study the screen in front of you, whether laptop, desktop, or mobile. Now put on your sunglasses. Whoa, where did the light go? Try it again. Without the glasses, you can read these words. With the glasses, the screen dims or, depending on how much you paid for those glasses, goes dark. What is happening? The puzzle of “polarized light” owes its solution to a dapper French captain in Napoleon’s army, a contest of cutting-edge physics, and little crystal found on the coast of Iceland.
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