Editing Rotation (section)

=== Cosmological principle ===
The [[laws of physics]] are currently believed to be [[rotational invariance#Application to quantum mechanic|invariant under any fixed rotation]]. (Although they do appear to change when viewed from a rotating viewpoint: see [[rotating frame of reference]].)

In modern physical cosmology, the [[cosmological principle]] is the notion that the distribution of matter in the universe is [[homogeneous]] and [[isotropic]] when viewed on a large enough scale, since the forces are expected to act uniformly throughout the universe and have no preferred direction, and should, therefore, produce no observable irregularities in the large scale structuring over the course of evolution of the matter field that was initially laid down by the Big Bang.

In particular, for a system which behaves the same regardless of how it is oriented in space, its [[Lagrangian mechanics|Lagrangian]] is [[Rotational invariance|rotationally invariant]]. According to [[Noether's theorem]], if the [[Action (physics)|action]] (the [[integral over time]] of its Lagrangian) of a physical system is invariant under rotation, then [[Conservation of angular momentum|angular momentum is conserved]].