Relativity Lite

14 | Relativity Lite Figure 7. Invariant mass distribution in the H → γγ analysis for data (7 TeV and 8 TeV samples combined), showing weighted data points with errors, and the result of the simultaneous fit to all categories. The fitted signal plus background is shown, along with the background-only component of this fit. The different categories are summed together with a weight given by the s/b ratio in each category. The bottom plot shows the difference between the summed weights and the background component of the fit. Figure 4 of G. Aad et al. (ATLAS Collaboration), Phys. Rev. D 90, 052004, reproduced under the terms of the Creative Commons Attribution 3.0 License. The idea that mass increases with velocity was introduced by Hendrick Lorentz * in 1899 so that he could use the low-speed expression for momentum, m v , for relativistically high veloci- ties. When Einstein introduced relativity six years later, the idea of mass increasing with velocity became unnecessary, but unfortunately, it has retained a very long life. This puts you, the reader, in the nasty position of having to decide between two “authorities.” Since the explanation for the upper limit on rocket speeds given on the previous page does not need tomentionmass, changing or otherwise, Occam’s razor † would dictate that we choose it over an explanation that includes the idea of varying mass. I would recommend that you discard the latter idea as outdated. After * H. Lorentz, Proc. R. Acad. Sci. Amsterdam 1 , 247 (1899); 6 , 809 (1904). † William of Occam (c. 1280) said that when there are several explanations of a phenomenon, the simplest is most likely to be correct.