Presents a lecture of Professor Ramamurti Shankar that introduces four-vector that unifies space-time coordinates x, y, z and t into a single entity whose components get mixed up under Lorentz transformations. The length of this four-vector, called the space-time interval, is shown to be invariant (the same for all observers). Likewise energy and momentum are unified into the energy-momentum four-vectorEducação Superior::Ciências Exatas e da Terra::Física