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by dataflow
1530 days ago
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Thanks a lot for the explanation! I see what you're saying. It raises some follow-up questions for me, if you don't mind: Why can't the W-'s kinetic energy be smaller than whatever the neutron would lose by converting to a proton? There's no quantization preventing that here, right? My guess here is that it would not have (for the lack of a better term) sufficient "escape velocity", meaning that it would fall back into the neutron again, but wouldn't that imply (a) this is more like a dynamic equilibrium than a static one, where neutrons turn into protons and back into neutrons repeatedly, and (b) quantum uncertainty (Heisenberg, tunneling, etc.) should still mean that bound neutrons should still decay once in a while, and perhaps (c) a neutron next to a proton might randomly "swap" places once in a while if a W- from one gets pulled into the other one? (And if any of these is the case, then where do they draw the line to declare that a bound neutron is "stable"?) |
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> 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.