Lecture 4 YouTube

The video titled Lecture 2-3 comes after Lecture 7.

We continue on with Lorentz transformations, and define space-time separation.

This allows us to define proper time and proper length, which are invariant quantities and contrast with coordinate variables, which aren't the same in all reference frames.

We look at consequences of these definitions, describing the relativistic effects of time dilation and length contraction.