Date: 29 November 2002
Subject: Physics

There's weird, very weird, and then there's physics!

Half the Nobel prize for physics for 2002 went jointly to Raymond Davies Jnr formerly of the Brookhaven National Laboratory and Masatoshi Koshiba of Tokyo University for work on Neutrinos.

The history of theory and work on neutrinos is one of the most fascinating in physics. it reflects basic ways in which actual science differs greatly from some of the popular misconceptions of it as a ?purely observational? activity where all one needs is a lack of preconception. The story begins soon after the new ?uncertainty principle? physics of 1928, in which the physicist, as Sir Arthur Eddington wrote, ?no longer ?borrowed the raw material of his world from the familiar world.? Concepts in physics were no longer expected to be ?even explicable in terms of common experience.? (The Nature of the Physical World, 1928).

On 4th December 1930 Physics Professor Wolfgang Pauli (1900-58) wrote of his theories on beta-decay in radium:

I have hit upon a desperate remedy to save the "exchange theorem" of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spin 1/2 and obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass and in any event not larger than 0.01 proton masses. The continuous beta spectrum would then become understandable…

Pauli was a scientific genius, proposed in 1945 by Einstein for his Nobel Prize - but he spent much time in the last 15 years of his life exploring the philosophy and history of science, and its relationship with religion. Like Einstein, Planck, Eddington, and so many other 20th century physicists, he was by no means dismissive of religion. The popular image of the "hard-nosed" physicist is as mistaken for the 20th as for earlier centuries where most pioneers in physics were unusually religious.

It was Fermi who, in 1934, proposed the name "neutrino" for this mysterious particle, by then believed to have a mass much lower than the electron and invented basically to preserve the law of conservation of mass-energy from apparent refutation. By then it was also recognised that the particle reacted so weakly with matter that it could pass right through the earth without effect.

So how to demonstrate it experimentally?

Fredrick Reines was a professor of physics who in the 1950's was looking for evidence of neutrino emission from nuclear reactors. The anti-neutrino coming from the nuclear reactor interacts with a proton of the target matter (a large tank of water and cadmium chloride), giving a positron and a neutron, In 1956, at the new Savannah River reactor in South Carolina, the electron antineutrino was detected. Reines continued work on the particle, and still led the team that in 1987 detected neutrinos emitted from Supernova SN1987A demonstrating conclusively for the first time the theoretically postulated role of the neutrino in stellar collapse. Reines received a half Nobel Prize "for work on the neutrino" in 1995.

Meantime, however, interest mounted in the possible emission of neutrinos by the sun. Ray Davis had been working on neutrinos since the 1950's, and from 1964-68 organised construction of a tank containing 100,000 gallons of perchloroethylene (cleaning fluid!) 3-4000 underground in Homestake mine. The confirmed 1969 results showed about a 3x lower rate of solar neutrino emission than expected from theory - though theory and observation continued to interact.

Masatoshi Koshiba and his team constructed the Kamiokande detector - a huge tank filled with pure water deep underground in Japan. When neutrinos pass through this tank, they may interact with atomic nuclei in the water. This reaction leads to the release of an electron, creating small flashes of light Photomultipliers surrounding the tank capture these flashes. Unlike Davis's, Koshiba's experiments could register the time and direction of events - proving definitely that neutrinos came from the Sun. In 1995 a bigger "Super-Kamiokande" tank was built, and in June 1998 this demonstrated oscillation in atmospheric neutrinos, showing that actually neutrinos have non-zero mass.

For Christians the continuing neutrino story is fascinating for several reasons. Firstly, it shows that science is far from a simple process of generalising from observation. Neutrino work has involved a complex interaction of theory and experiment - each affecting the other. Neutrino work also has odd implications for the meaning of "observation" - it would not occur to most people that the best way to examine the inside of the sun was to go down a mine! A second implication, then, is that the heart of matter in our universe contains a number of mysterious and far from "common sense" concepts. This is not obscurantism or any kind of anti-science, but as someone who works in a university department of physics astronomy and mathematics, I have been known to remark to colleagues that after struggling with comprehending some of the (non-mathematical) concepts in modern physics, believing in the trinity is a doddle. All credit to those who can achieve Nobel prizes in any such area!

NB: Some pictures courtesy of Kamioka Observatory, ICRR and Brookhaven National Laboratory