We introduced the ancient Greek concept of atomos, a sort of tiny and indivisible particle from which the universe is made. Though this idea was seriously rekindled in the early nineteenth century, it didn’t take long to show that the particles then believed to be fundamental were actually made up of smaller things. But did this mean we should give up on the atomos idea? Or, could it be that we just hadn’t dug deeply enough?
Today, scientists believe that there is indeed a set of particles that are truly elementary and are not composed of anything else. There are no inner parts or subcomponents waiting to be observed. The fundamental particles, as we call then, are truly indivisible. At least, as far as we can tell.
DEFINITION
An elementary or fundamental particle is the most basic building block in nature. It has no substructure, no physical volume, and no spatial extent, and thus cannot be divided into smaller parts.
We made a big deal of separating particles based on their intrinsic spin. Particles that have half-integer spin are called fermions and those whose spin quantum number is zero or a whole number are called bosons. These two kinds of particles behave completely differently in quantum mechanics, as described by the Pauli exclusion principle. For example, no two electrons in a given system can occupy the exact same quantum state. That’s why atoms have electron structure, chemistry works, and we are all here to know about it in the first place.
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