[hilbert42]

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?

[cozzyd]

Generally 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]

A 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]

There 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]

I 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]

Right. 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!

[hilbert42]

For reasons mentioned below, my question was a bit of a facetious throwaway, I would have framed it more precisely had I taken a second or so longer to think about it. Anyway, the question should have been:

Is the total time taken for a neutron to fully complete its decay longer but still comparable to the time taken for the W- boson to decay into an electron and antineutrino or is the latter's decay time much, much shorter than the overall process? That is, is the following statement true or otherwise?

[time (total) for n0 → (p+) + (e-) + (-ve)] >> [time W- → (e-) + (-ve)]

...and if so, then do we know by how much; if not then what is it? Alternatively, if the Feynman diagram for neutron beta decay shown in the following link were to actual scale then what would the scale on the vertical (time) axis be? https://en.wikipedia.org/wiki/Free_neutron_decay

I'm not really trying to be deliberately pedantic or dispute orthodoxy here but my question was in response to these and similar recent stories:

https://scitechdaily.com/zeptoseconds-new-world-record-in-sh...

https://www.quantamagazine.org/quantum-tunnel-shows-particle...

If the info therein is all or in part factual, or if similar measurement methodologies were applicable to other particles, then the ballgame may change, hence the initial reason for my question (similarly so for my first/initial post).

The second (Quanta magazine) link was the subject of a HN story going on about a year ago and it generated many comments (they resolved nothing but many were interesting nonetheless); unfortunately the time for comments was up before discussion had finished (my last, rather prolix comment was still in draft and missed the deadline). In my opinion, controversial topics like this should sometimes be left open to give one time to dwell upon them.

[hilbert42]

Addendum: I should have added that from various sources, Wiki etc., it seems the W- boson does decay very significantly faster than the complete decay but we've still no further info about the timeline of events, as you say, it's likely not possible.

In hindsight, it seems the techniques mentioned in those links to measure a particle's time are unlikely to be applicable or adaptable here. That then begs the question about how did we initially determine that the W- boson's decay is much faster than the overall process.

[wetpaws]

Nobody knows

[dnautics]

is the annoying answer "if it were really that much shorter we probably wouldn't exist"?

[idontwantthis]

https://en.wikipedia.org/wiki/Anthropic_principle

[hilbert42]

I 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. ;-)

[colechristensen]

I’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.

[hilbert42]

"...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.

[kjeetgill]

It's like how every number n has the factors 1 x n. It's always _an answer_, but never the juicy one.

[akomtu]

All 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]

Photons don't, for counterexample

[akomtu]

I'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]

I 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]

OK, 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]

That'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]

Indeed ultra high energy photons "decay" by interacting with the CMB.