It is 100 years since Ernest Rutherford published his results proving the existence of the proton. For decades, the proton was considered an elementary particle. But ever since researchers at the SLAC and DESY laboratories began firing electrons into protons, beginning in the 1960s, experiments have revealed that the proton has a complex internal structure, one that depends on how you look at it, or rather on how hard you hit it. A century on, however, much remains to be learnt about the proton. Check out the latest edition of the CERN Courier and read in-depth articles about what we know and don’t know about the proton.

In “Rutherford, transmutation and the proton”, you’ll find an account of the historical events leading to Ernest Rutherford’s discovery of the proton, published in 1919. In “The proton laid bare”, you can read about scientists’ evolving knowledge of the proton, how a deeper understanding may be key to the search for new physics phenomena, and what remains to be learnt – including the origin of the proton’s spin, whether or not the proton decays on long timescales, and the puzzling, although soon-to-be resolved, value of its radius.