3 ms·
Half-lives that long really begs the question to me - does every heavy nucleus (i.e. heavier than Iron-56) have a half-life? Does Gold-197 which is 'stable' act
by NeoTar 3y ago
Half-lives that long really begs the question to me - does every heavy nucleus (i.e. heavier than Iron-56) have a half-life? Does Gold-197 which is 'stable' actually just have a half-life of 10^50, or 10^100 years?
- fsh 3y agoThere are nuclides heavier than 56Fe, for which no decay mode is energetically allowed. 197Au is not one of them, because it could in principle do alpha decay. Wikipedia has a long list of theoretically stable nuclides (no decay mode possible), and observationally stable nuclides (at least one decay mode possible, but not observed): https://en.wikipedia.org/wiki/List_of_nuclides https://en.wikipedia.org/wiki/List_of_nuclides
- jychang 3y agoAlso, proton decay is a thing. At a certain point, if the proton is unstable, the half life of the nucleus is longer than the proton itself.
- fsh 3y agoNo, it isn't. According to the Standard Model, the proton is stable at every time scale. And no proton decay has ever been observed.
- MichaelZuo 3y agoThe Standard Model that is known to be, at best, incomplete?
- jfengel 3y agoOnly in that it doesn't incorporate gravity. And given the extremely low energy scale of gravity, it's unlikely to make a difference here. There are extensions to the Standard Model being used to search for dark matter, but until one of those is actually found experimentally, you can't say that it makes the Standard Model incomplete. It's sound within its domain -- aggravatingly so, since that makes it really hard to figure out what's next.
- wiml 3y agoProton decay may be a thing but it's not predicted by current models. But similar to your example, neutron decay is a thing (a free neutron has a halflife of about 10 minutes), and yet many nuclei are stable for much longer.
- ISL 3y agoProton decay is predicted by many models -- it's the reason the first huge water-Cherenkov detectors were built. The surprising thing is that, for some reason, they've never been observed to decay.
- mensetmanusman 3y agoIf they can’t decay then time can’t stop.
- jacquesm 3y agoThe theory is that everything, even subatomic particles has a half life. But these are so long that we are not able to perceive them with present day technology. Eventually the whole universe will fall apart into degenerate matter and then much later even the remnants will decay. But such decay is happening all the time, just not fast enough to result in measurable effects (fortunately!).
- dilyevsky 3y agoNot true. neutrons decay within minutes, protons and electrons dont decay within SM Also to nitpick - “half life” is not applicable to subatomic particles
- jacquesm 3y agoFree neutrons do, but bound ones do not afaik, and electrons and protons do decay but we do not know how long it takes, but there is some lower bound. And yes, you're correct, I should not have used the term 'half life' because that implies a different kind of event. Lifetime would have been a better term to use.
- fsh 3y agoProtons and electrons do not decay according to the Standard Model.
- jacquesm 3y agoI'm familiar with the theory but: it's technically an open problem, isn't it? Whether it lives forever or has some average life-span or not. At least, that's what I got from reading about this. It is very well possible that I'm wildly out of date but from memory: there are some subtle problems with the present day theory that could be fixed but they would require for proton and electron decay to be possible. But all that has happened so far is that we've established a (very high) lower bound to how long these particles live, but there is no hard rule that says they can't decay, it's just that if they do (as in: we find experimental proof that they do) then the Standard Model will be ripe for an upgrade. And that in turn might get us one step closer to a UFT.