| I think I see what you're asking, but I'm not sure I can give a satisfactory (and correct) answer, here but I think you're on the right track: > Why can't the W-'s kinetic energy be smaller... That W- is a virtual particle - it can have any energy (according to some probability distribution) and you're correct that it doesn't _have_ to observe conservation of energy as long as that violation only happens for a very short period of time, which is precisely Heisenberg - there are other numbers it must conserve, such as electric charge. > (b) quantum uncertainty (Heisenberg, tunneling, etc.) should still mean that bound neutrons should still decay once in a while We do see this; this is what beta decay is. > (c) a neutron next to a proton might randomly "swap" places once in a while In general, this is correct. With limitations on what quantum numbers need to be conserved, these events are all constantly happening all the time. When writing out the equations for the system, you don't really have a term describing a proton and a term describing a neutron; you have a complicated mess of _all possible_ interactions and each elementary particle is described as a sort of "mix" of all the things it could be. So, in that sense, a bound neutron and proton is it's own thing - there's plenty of examples of these quasiparticles throughout physics and the definition of "stable" is quite application specific. |