The special theory of relativity is an extension of classical mechanics that more accurately describes the motion and dynamics of objects moving at significant fractions of the speed of light.

In Einstein's original 1905 formulation, The postulates of Special Relativity are that

*The Principle of Relativity* is that the laws of physics are the same in every inertial reference frame.
*The Speed of Light* is the same in every reference frame.
In Special Relativity, the Galilean transformations are replaced with the Lorentz transformations, which form the Lorentz group.

An alternative formulation of Special Relativity is that of Minkoswski, which sort - of "unifies" space and time into spacetime, and the Lorentz transformations are derived from insisting the invariance of $\mathrm{d}s^2$