There are a lot of other features that were predicted. For example, it turns that the spin, the angular momentum, of the cobalt nucleus before disintegration is 5 units of h, and after disintegration it is 4 units. The electron carries spin angular momentum, and there is also a neutrino involved. It is easy to see from this that the electron must carry its spin angular momentum aligned along its direction of motion, the neutrino likewise. So it looks as though the electron is spinning to the left, and that was also checked. In fact, it was checked right here at Caltech by Boehm and Wapstra, that the electrons spin mostly to the left. (There were some other experiments that gave the opposite answer, but they were wrong!) The next problem, of course, was to find the law of the failure of parity con- servation. What is the rule that tells us how strong the failure is going to be? The rule is this it occurs only in these very slow reactions, called weak decays, and when it occurs, the rule is that the particles which carry spin, like the electron neutrino,and so on, come out with a spin tending to the left. That is a lopsided ule;it connects a polar vector velocity and an axial vector angular momentum and says that the angular momentum is more likely to be opposite to the velocity than along it. Now that is the rule, but today we do not really understand the whys and wherefores of it. Why is this the right rule, what is the fundamental reason for it, and how is it connected to anything else? At the moment we have been so shocked by the fact that this thing is unsymmetrical that we have not been able to recover enough to understand what it means with regard to all the other rules. however the subject is interesting, modern, and still unsolved, so it seems appropriate that we discuss some of the questions associated with it 52-8 Antimatte The first thing to do when one of the symmetries is lost is to immediately go back over the list of known or assumed symmetries and ask whether any of the others are lost. Now we did not mention one operation on our list, which must necessarily be questioned and that is the relation between matter and antimatter Dirac predicted that in addition to electrons there must be another particle, called the positron(discovered at Caltech by Anderson), that is necessarily related to the electron. All the properties of these two particles obey certain rules of corre- spondence: the energies are equal; the masses are equal the charges are reversed but, more important than anything, the two of them, when they come together can annihilate each other and liberate their entire mass in the form of energy, say Y-rays. The positron is called an antiparticle to the electron, and these are the characteristics of a particle and its antiparticle. It was clear from Dirac's argument hat all the rest of the particles in the world should also have corresponding anti- particles. For instance, for the proton there should be an antiproton, which is now ymbolized by a p. The p would have a negative electrical charge and the same mass as a proton, and so on. The most important feature, however, is that a proton and an antiproton coming together can annihilate each other. The reason w emphasize this is that people do not understand it when we say there is a neutron and also an antineutron, because they say, "A neutron is neutral, so how can it have the opposite charge? "" The rule of the"anti""is not just that it has the opposite charge, it has a certain set of properties, the whole lot of which are opposite.The antineutron is distinguished from the neutron in this way: if we bring two neutrons together, they just stay as two neutrons, but if we bring a neutron and an anti neutron together, they annihilate each other with a great explosion of energy being liberated, with various T-mesons, y-rays, and whatnot ow if we have antineutrons, antiprotons, and antielectrons, we can make antiatoms, in principle. They have not been made yet, but it is possible in principle For instance, a hydrogen atom has a proton in the center with an electron going around outside Now imagine that somewhere we can make an antiproton with a positron going around, would it go around? Well, first of all, the antiproton is electrically negative and the antielectron is electrically positive so they attract each other in a corresponding manner-the masses are all the same; everything is the