The discovery of radioactivity eventually led to the discovery of a new quantum field — the weak field, tucked away in the tiniest nooks of the nucleus. It is this field that causes a neutron to change into a proton while emitting an electron and a neutrino — a process known as beta decay.
The weak field has a mass about 500 times greater that that of the strong field, so its range is about 500 times shorter. Like the strong field, the weak field has charge and comes in three versions, symbolized by W+, W– and Zo. Unlike the strong field, the weak field has spin 1, which puts it in the same family as the EM field; this relationship is called electroweak unification. However, the weak field is the only field that violates the law of parity – that is, its behavior is not left-right symmetric.
Because they have mass and charge, quanta of the strong and weak fields act even more like particles than do photons. In the next chapter we will see that matter fields with half-integral spin narrow the gap even further. The five force fields of nature are summarized in the following table. (Because the Higgs field is so new, I have not assigned a “color” to it.)
|EM||1||Photon (γ)||charged fields||Green|
|Strong*||0||Pion (π+, π–, πo)||baryons||Purple|
|Weak||1||Weakon (W+, W–, Zo)||leptons and baryons||Brown|
*We will see in Chapter 10 that the strong field is made of more basic but “invisible” fields called quarks and gluons.