![]() But somehow, strangely, when you stick a detector in the scene and measure the electron’s location, its wave function suddenly “collapses” to a point, and the particle clicks at that position in the detector. The wave function representing an electron, say, is spatially spread out, so that the electron has possible locations rather than a definite one. Quantum mechanics revealed to its discoverers in the 1920s that photons and other quantum objects are best described not as particles or waves but by abstract “wave functions” - evolving mathematical functions that indicate a particle’s probability of having various properties. Wave-particle duality turned out to be a symptom of a deep strangeness. The discovery of quantum mechanics some 250 years after that proved both luminaries right: Light comes in individual packets of energy known as photons, which behave as both particles and waves. Two millennia later, Isaac Newton and Christiaan Huygens debated whether light is made of particles or waves. The quest to understand nature’s fundamental building blocks began with the ancient Greek philosopher Democritus’s assertion that such things exist. I should not say there’s a unified point of view, but there’s several different points of view, and all look interesting.” A Particle Is a ‘Collapsed Wave Function’ 1 “Nowadays there is progress in this direction. “‘What is a particle?’ indeed is a very interesting question,” said Wen. They also described two major research thrusts in fundamental physics today that are pursuing a more satisfying, all-encompassing picture of particles. They emphasized that their answers don’t conflict so much as capture different facets of the truth. When I recently asked a dozen particle physicists what a particle is, they gave remarkably diverse descriptions. As points of contact between mathematics and reality, particles straddle both worlds with an uncertain footing. But those particles’ properties derive not from constituents of their own but from mathematical patterns. With any other object, the object’s properties depend on its physical makeup - ultimately, its constituent particles. “But that’s just a to students, ‘Don’t ask! I don’t know the answer. “We say they are ‘fundamental,’” said Xiao-Gang Wen, a theoretical physicist at the Massachusetts Institute of Technology. How can a dimensionless point bear weight? And yet particles have distinct traits, such as charge and mass. “We basically think of a particle as a pointlike object,” said Mary Gaillard, a particle theorist at the University of California, Berkeley who predicted the masses of two types of quarks in the 1970s. Namely, electrons, photons, quarks and other “fundamental” particles supposedly lack substructure or physical extent. ![]() The easy answer quickly shows itself to be unsatisfying. Given that everything in the universe reduces to particles, a question presents itself: What are particles?
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