The principle that the laws of physics are the same for all observers, regardless of their relative motion or orientation. A physical quantity or a set of equations are "Lorentz invariant" if they do not change when subjected to a Lorentz transformation, which accounts for the effects of special relativity at high speeds. This forms the basis of Einstein's [[Theory of Special Relativity]]. It requires the following: * **Universality:** The laws governing gravity, electromagnetism, and other fundamental forces are the same for observers moving at different constant velocities.  * **No preferred reference frame:** There is no single "stationary" frame of reference; instead, all inertial frames (frames moving at a constant velocity) are equally valid for describing physical phenomena.  * **Spacetime:** Lorentz invariance implies a unified spacetime, where time and space are interconnected, and measurements of events are relative to the observer's reference frame.