At a more technical level, some particle physicists like to glibly answer the question “What’s a particle?” by saying, “It’s an element of an irreducible representation of the symmetry group of the Lagrangian.” That’s quite a mouthful, and enough to stop most budding conversations dead in their tracks, but it’s a completely mathematical thing, just a bit more general than the concept of a set of numbers. And yes, sure, string theory or a competitor may deepen our understanding of what particles really are, but all the leading theories out there simply replace one mathematical entity with
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