Re: Can you explain weak nuclear force?

Greetings!

You are confused by the fact that everybody talks about the four fundamental forces, but that one of them seems to be special in the sense that it it responsible for some decay processes. The others seem to be forces in the usual sense of the word.

Actually, on a microscopic level, all four forces are no forces in the usual sense of the word. The way that physics today explains the forces of nature is by exchange of gauge particles. Gauge particles are particles which are exchanged between other particles that form the genuine constituents of matter (quarks and leptons). So when an electron repels or attracts another electron or positron, what happens is that there is a `force-carrying field' between them. In that particular case, it is actually a field composed of photons! Photons are the mediators of the electromagnetic interaction, and particles interacting electromagnetically constantly exchange photons between them (those photons can not be `seen' in the usual sense, but that is another story). Now when an electron emits or absorbs a photon, it more or less stays the same, only its momentum and spin might change.

On the other hand, when a particle interacts via the weak interaction, its character can change: Take, for instance, the beta decay of a neutron in a nucleus. For the experimentor, it looks as if the neutron turns into a proton, emitting an electron and an anti-neutrino. This is how beta decay was described before the true nature of the weak interaction and the inner structure of the neutron was discovered. In fact, it is a certain quark inside the neutron which emits a gauge particle (a W^- in this case) and turns into another type of quark, which converts the neutron into a proton. The emitted W^- particle later decays into the electron and the anti-neutrino. You see that this is not how a `force' is usually conceived, but it is completely in agreement with the microscopic picture of the fundamental forces that I have sketched in the previous paragraph: A gauge particle is emitted. The fact that there is no other particle to absorb it does not matter. The point is that the weak interaction can change some of the features of the interacting particles that we consider important for the determination of the particle `type'. The electromagnetic interaction does not do that.

Of course, the whole phenomenology of particle interactions is too large to be explained in detail here, so I advise you to go to the standard place where those kinds of questions are treated: The Particle Adventure.

Hope that helps,
Georg.