Try a quick experiment: take two flashlights into a dark room and shine them so that their light beams cross. Notice anything peculiar? The rather anticlimactic answer is: probably not. That's because the individual photons that make up light do not interact. Instead, they simply pass each other by, like indifferent spirits in the night. But what if light particles could be made to interact, attracting and repelling each other like atoms in ordinary matter? One tantalizing, albeit sci-fi possibility: lightsabers -- beams of light that can pull and push on each other, making for dazzling, epic confrontations. Or, in a more likely scenario, two beams of light could meet and merge into one single, luminous stream. It may seem like such optical behavior would require bending the rules of physics, but in fact, scientists have now demonstrated that photons can indeed be made to interact -- an accomplishment that could open a path toward using photons in quantum computing, if not in lightsabers.
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