Special relativity

Time dilation and length contraction

Einstein's postulates: the laws of physics are the same in every inertial frame, and the speed of light in a vacuum is the same for all observers. Consequences: moving clocks run slow, $t=\gamma t_0$, and moving lengths shrink, $l=\frac{l_0}\gamma$, where $\gamma=\frac1{\sqrt{1-v^2/c^2}}$. A body's total energy is $E=\gamma m_0c^2$.