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A universality class groups systems with the same long-distance critical behavior, typically because their effective theories approach the same <renormalization-group fixed point>. Shared <critical exponents> and scaling functions can emerge despite different microscopic constituents.

Spatial dimension, symmetry and the nature of interactions help determine the class. A scalar sign-reversal-symmetric transition with short-range interactions can exhibit Ising-type scaling whether its microscopic variable is a spin or another scalar degree of freedom. This does not imply equal critical temperatures or equal amplitudes of every measured response. Those depend on microscopic parameters and normalization. Conservation laws and coupling to slow variables further affect dynamic universality, even when static exponents agree.


 Universality class (source code)