Einstein’s Postulates

About the lecture

In this mini-lecture, we introduce Einstein’s two postulates of Special Relativity: the principle of relativity and the universal speed of light. In particular, we consider: (i) a thought experiment for the principle of relativity to help us understand that it only applies to systems moving at constant velocity; (ii) the universal speed of light, which is 3×10⁸ m/s; (ii) Galileo’s velocity addition rule and how it contradicts Einstein’s postulate of the universality of the speed of light; (iii) Einstein’s velocity addition rule, which corrects that of Galileo; and (iv) the reasoning behind why Galileo’s velocity addition rule is a very good estimate for velocities at everyday speeds.

About the lecturer

David Griffiths is an Emeritus Professor from Reed College in Portland, Oregon in the United States. He is known for his highly regarded undergraduate physics textbooks, including Introduction to Elementary Particles (published in 1987, second edition published 2008), Introduction to Quantum Mechanics (published in 1995, third edition published 2018), and Introduction to Electrodynamics (published in 1981, fourth edition published in 2012). He was also the 1997 recipient of the Robert. A Millikan award (renamed the Lillian McDermott Medal in 2021), an American Association of Physics Teachers (AAPT) award that recognises those who have made notable and intellectually creative contributions to the teaching of physics.