What We Cannot Know: Explorations at the Edge of Knowledge. Marcus Sautoy du

strong nuclear force to a proton and a pion. In contrast, a Sigma baryon ∑ decays via the weak nuclear force.

      So why did the Delta baryon find a way over the easy hill while the Sigma baryon went the long way? This seemed rather strange. There appeared to be certain particles that encountered a barrier (represented in the figure by a broken line) that prevented them from crossing via the easy route to the lower valley.

       THERE IS NO EXQUISITE BEAUTY WITHOUT STRANGENESS

      The physicists Abraham Pais, Murray Gell-Mann and Kazuhiko Nishijima came up with a cunning strategy to solve this puzzle. They proposed a new property like charge that mediated the way these particles interacted or didn’t interact with the strong nuclear force. This new property, called strangeness, gave physicists a new way to classify all these new particles. Each new particle was given a measure of strangeness according to whether or not its decay would have to take the long route.