Quanta Magazine examines a deceptively fundamental question in physics: how many elementary particles actually exist? The Standard Model identifies about 17 fundamental particles — quarks, electrons, photons, and the rest. But venture into beyond-Standard-Model physics, and the number explodes. When physicists account for theories involving dark matter, extra dimensions, and other extensions, plausible counts reach nearly a thousand — with the oddly specific ceiling of 995.5 particles. The fact that physicists can legitimately disagree by that margin suggests our understanding of reality's building blocks remains incomplete.

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