How any sub-atomic particles are there?
I ask because currently I’m reading a book by John Gribbin called “In Search Of Schrödinger’s Cat” and subtitled “Quantum Physics And Reality”.
When my parents went to school in the 1930s, they were taught that the smallest particle was the atom, although the electron was discovered in 1897, the proton was discovered in 1918, and the neutron was discovered in 1932. When I was at school in the 1960s, I was taught about electrons, protons and neutrons but no other sub-atomic particles were mentioned, even though many others were then known.
What about today? In his book “A Short History Of Nearly Everything” [my review here], Bill Bryson writes: “Today the particle count is well over 150, with a further 100 or so suspected”.
So, what are these other sub-atomic particles. Well to start with, protons and neutrons are both composite particles, consisting of smaller particles called quarks. A proton contains two ‘up’ quarks and one ‘down’ quark, while a neutron consists of one ‘up’ quark and two ‘down’ quarks. The quarks are held together in the nucleus by other particles called gluons.
And so it goes on. Most of the particles that have been discovered are not encountered under normal earth conditions but are found in cosmic rays and are produced by scattering processes in particle accelerators. We seem to be a long way from identifying all the sub-atomic particles and even further from understanding how they all relate to one another.
Currently the nearest thing we have to a comprehensive explanation is the Standard Model which consists of six quarks, six leptons, five known bosons and a speculated sixth called the Higgs boson (after the Scottish scientist Peter Higgs). As Bryson put it: “Physics is really nothing more than a search for ultimate simplicity, but so far all we have is a kind of elegant messiness”.