Point particle
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A point particle is an idealized object heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space. A point particle is an appropriate representation of any object whose size, shape, and structure is irrelevant in a given context. For example, from far away an object of any shape will look and behave as a point-like object.
Sometimes due to specific combinations of properties extended objects behave as point-like even in their immediate vicinity. For example, spherical objects interacting in 3-dimensional space in a particular manner called the inverse square law behave in such a way as if all their matter were concentrated in the geometric centers of their spherical shapes. In Newtonian gravitation and classical electromagnetism, for example, the respective fields outside of a spherical object are identical to those of a point particle of equal charge/mass located at the center of the sphere.
In general relativity a point particle with mass only "exists" in the sense of a "test particle", inasmuch as its influence on the curvature of spacetime must be ignored. (Otherwise it would be a black hole instead.)
In particle physics, whose theoretical framework is relativistic quantum mechanics (a.k.a. quantum field theory), "point particle" is synonymous with "elementary particle", which is defined as a particle without structure or, equivalently, as a particle lacking component parts, or a particle whose compositional details are too small to be detected by current experiments. According to the Standard Model (of fundamental particles and forces), quarks, electrons and other leptons are point particles in this sense.
