servation of charge. This particle was called a B-meson. So on the one hand we have a particle called a T, which disintegrates into three T-mesons, and aa, which disintegrates into two T-mesons. Now it was soon discovered that the T and the are almost equal in mass; in fact, within the experimental error, they are equal Next, the length of time it took for them to disintegrate into three T's and two T's was found to be almost exactly the same; they live the same length of time Next, whenever they were made, they were made in the same proportions, say 14 percent T's to 86 percent as Anyone in his right mind realizes immediately that they must be the same particle, that we merely produce an object which has two different ways of dis- integrating-not two different particles. This object that can disintegrate in two different ways has, therefore, the same lifetime and the same production ratio (because this is simply the ratio of the odds with which it disintegrates into these A schematic diagram However, it was possible to prove(and we cannot here explain at all how ),fromthe ation of a t+andaθ the principle of reflection symmetry in quantum mechanics, that it was impossible particle to have these both come from the same particle-the same particle could not disintegrate in both of these ways. The conservation law corresponding to the principle of reflection symmetry is something which has no classical analog, and so this kind of quantum-mechanical conservation was called the conservation of parity. So, it was a result of the conservation of parity or, more precisely, from the symmetry of the quantum-mechanical equations of the weak decays under reflec tion, that the same particle could not go into both, so it must be some kind of incidence of masses lifetimes and so on but the more it was studied the more remarkable the coincidence, and the suspicion gradually grew that possibly the deep law of the reflection symmetry of nature may be false. As a result of this apparent failure, the physicists Lee and Yang suggested that ther experiments be done in related decays to try to test whether the law was correct in other cases. The first such experiment was carried out by Miss wu fro Columbia, and was done as follows. Using a very strong magnet at a very low temperature, it turns out that a certain isotope of cobalt, which disintegrates by emitting an electron, is magnetic, and if the temperature is low enough that the thermal oscillations do not jiggle the atomic magnets about too much, they line up in the magnetic field. So the cobalt atoms will all line up in this strong field They then disintegrate, emitting an electron, and it was discovered that when the atoms were lined up in a field whose b vector points upward, most of the electrons were emitted in a downward direction If one is not really"hep"to the world, such a remark does not sound like anything of significance, but if one appreciates the problems and interesting things in the world, then he sees that it is a most dramatic discovery: when we put cobalt atoms in an extremely strong magnetic field more disintegration electrons go down than up. Therefore if we were to put it in a corresponding experiment in a"mirror, in which the cobalt atoms would be lined up in the opposite direction, they would spit their electrons up, not down; the action is unsymmetrical. The magnet has grown the electrons in a B integration tend to go away from it that distinguishes, in a physical way, the north pole from the south pole After this, a lot of other experiments were done: the disintegration of the T into u and v; u into an electron and two neutrinos; nowadays, the a into proton and T; disintegration of 2's; and many other disintegrations. In fact, in almost all cases where it could be expected, all have been found not to obey reflection symmetry! Fundamentally, the law of reflection symmetry, at this level in physics, incorrect In short, we can tell a martian where to put the heart: we say, " Listen, build yourself a magnet, and put the coils in, and put the current on, and then take some cobalt and lower the temperature. Arrange the experiment so the electrons go from foot to the head, then the direction in which the current goes through the coils is the direction that goes in on what we call the right and comes out on the left So it is possible to define right and left, now, by doing an experiment of this kind 52-9