Abstract
As we celebrate the centenary of Einstein's 1905 papers on special relativity, as well as his work on quantum theory and Brownian motion, it is disappointing to read so many confusing reports about what Einstein actually discovered. Sadly Physics World also played a part in creating this confusion by stating that "E=mc2 led to the remarkable conclusion that mass and energy are one and the same" (January p13). According to Einstein's special relativity, mass and energy are not one and the same: mass is a Lorentz scalar, while energy is a component of a Lorentz 4-vector.