Isotróp

Isotróp is a term used to describe a property that is the same in all directions. In science, a material, space, or physical law is isotróp if its behavior or properties do not depend on orientation; it is invariant under rotations. In physics, isotropy of space is a foundational assumption of the cosmological principle, which states that the universe is the same in all directions on large scales.

In condensed matter and engineering, isotróp describes materials whose mechanical, thermal, electrical, and optical properties are the same in every direction. Many liquids and glasses are intrinsically isotróp; polycrystalline metals and ceramics can be approximated as isotróp when their grains are randomly oriented.

In elasticity theory, an isotróp solid has properties described by two independent elastic constants, such as the bulk modulus and shear modulus (or Young's modulus and Poisson's ratio). This contrasts with anisotropic materials, whose properties vary with direction and require more constants to describe their behavior.

In optics, isotróp materials have the same refractive index in all directions, yielding no birefringence; this simplification breaks down in anisotropic crystals like calcite, which show direction-dependent light propagation.