4 ms·
The question I want answered is not why a neutron takes so long to decay - that seems understandable as it's mitigated by the weak force - but why is that time
by hilbert42 5y ago
The question I want answered is not why a neutron takes so long to decay - that seems understandable as it's mitigated by the weak force - but why is that time of ~14.63 minutes the actual time it is?
When the W- boson decays into an electron and antineutrino it happens millions of times faster than the life of the neutron itself. What makes that trigger point happen when it does?
- wetpaws 5y agoNobody knows
- dnautics 5y agois the annoying answer "if it were really that much shorter we probably wouldn't exist"?
- idontwantthis 5y agohttps://en.wikipedia.org/wiki/Anthropic_principle https://en.wikipedia.org/wiki/Anthropic_principle
- hilbert42 5y agoI actually heard Frank Tipler give a long talk of about 40 minutes on radio about the Anthropic principle several—perhaps even three—decades ago. At the time it was an exciting notion (and he was very animated when discussing the matter which made it all the more interesting). Then I thought his notion likely balmy or eccentric, now I've no opinion as my brain tends to overheat whenever I think about it. ;-)
- kjeetgill 5y agoIt's like how every number n has the factors 1 x n. It's always _an answer_, but never the juicy one.
- hilbert42 5y ago"...much shorter we probably wouldn't exist" Reckon that stands to reason, same goes for the physical constants, c, µ, ε, α, etc. But why remains the question.
- colechristensen 5y agoI’m always a bit dissatisfied with this way of thinking, if parameters were different it’s pretty easy to believe that there would still likely be a sweet spot for complexity that enabled life, it would just be somewhere else.
- cozzyd 5y agoGenerally decay rates scale with the energy release (Q) which is relatively small here compared to the W decay. Decay is a tunneling process so less Q generally means a slower decay since there are fewer final states available (but the details are complicated). Fermi's Golden Rule in principle allows you to calculate the decay rate. In practice we dont know how to calculate all the relevant quantities since QCD is hard.
- hilbert42 5y agoA question I've never given much thought about until now. When the neutron begins to decay [i.e. at or around ~14.63 min] then is the duration of that decay process essentially equivalent to the time taken for the W- boson to decay into an electron and antineutrino?
- adrian_b 5y agoThere is no way to measure the "duration of the decay process". When you look for it, you either find a neutron that has not decayed yet, or you find the decay products. The quoted decay time is just the average time. A free neutron might decay after 1 millisecond or after 5 hours. Like for any other decay process, it is unpredictable when an individual neutron will decay. Nevertheless the decay probability in a time interval is predictable so if you start with a large number of free neutrons, you can predict very accurately how many will remain after 1 minute or after 10 minutes or after an hour, because the number will decrease exponentially with a known time constant, which was measured more precisely in this new experiment.
- cozzyd 5y agoI think parent was asking about how long the virtual W "exists" for in the decay, but the virtual W is virtual so I don't think it has a "lifetime," but maybe I'm not thinking about this correctly.
- hilbert42 5y agoRight. Hopefully, I've clarified my question in my reply to adrian_b. I don't claim to have cutting-edge knowledge on this topic but it seems that not all descriptions I've read are consistent, nor for that matter is the nomenclature. In my opinion the word 'virtual' doesn't help as it's a catch-all word for when we've no clearer description. That's certainly not a criticism of you for using it, it's just a bit vague or general when we also apply the name in connection with Zero Point Energy/Quantum Vacuum, Casimir and static electric/magnetic fields etc. My point is that a 'virtual W' is significantly different to the others I've mentioned. That said, you'll note in my reply to adrian_b that I'm no angel in such matters either in that I've postulated somewhat by repurposing a Feynman diagram as a graph. But then, Wiki led the way by providing the axis!
- akomtu 5y agoAll things decay and have half life time. I don't get what's so mysterious about it. Neutrons have some not well understood structure and that structure is unstable in the dangerous waters of quantum turbulence.
- beebmam 5y agoPhotons don't, for counterexample
- akomtu 5y agoI'm wary of such absolute statements. I'd put photons near protons in terms of stability: they just don't show signs of decaying.
- ben_w 5y agoI understand the wariness. However, in relativity a photon cannot decay: because it travels at the speed of light and has infinite time dilation, it does not subjectively experience the passage of time in which the possibly of decay could exist.
- hilbert42 5y agoOK, fair enough. But what happens in a homogeneous lossless dielectric with say a velocity factor of about say 0.6? And what would happen in some theoretical meta material where say, values for say µ and ε were lower than their vacuum counterparts? OK, it's a red herring, but interesting to contemplate.
- akomtu 5y agoThat's the model of photon, not the photon itself. A mathematical photon cannot decay. What prevents a photon from hitting a quantum bump on its way between galaxies and become an electron?
- cozzyd 5y ago