Invariant (physics)

In mathematics and theoretical physics, an invariant is a property of a system which remains unchanged under some transformation.For example the rule describing Newton's force of gravity between two chunks of matter is the same whether they are in this galaxy or another (translational invariance in space). It is also the same today as it was a million years ago (translational invariance in time). The law does not work differently depending on whether one chunk is east or north of the other one (rotational invariance). Nor does the law have to be changed depending on whether you measure the force between the two chunks in a railroad station, or do the same experiment with the two chunks on a uniformly moving train (principle of relativity). In mathematics and theoretical physics, an invariant is a property of a system which remains unchanged under some transformation. In the current era, the immobility of Polaris (the North Star) under the diurnal motion of the celestial sphere is a classical illustration of physical invariance. Another example of a physical invariant is the speed of light under a Lorentz transformation and time under a Galilean transformation. Such spacetime transformations represent shifts between the reference frames of different observers. By Noether's theorem invariance of the action of a physical system under a continuous symmetry represents a fundamental conservation law. For example, invariance under translation leads to conservation of momentum, and invariance in time leads to conservation of energy.