8 ms·
How long do neutrons live? Physicists close in on decades-old puzzle
- eruci 8y ago“We’re on the way to pinning this down,” ok, but that can be said about anything we haven't pinned down yet
- posix_me_less 8y agoit's just a figure of speech, it means "we're working on it"
- foxyv 8y agoI think it's kinda like an intermittent bug in some application. You don't even know if it's an actual problem or just a user with a bad internet connection. That is, until you find out that it only happens after a period of inactivity. Suddenly you are "on the way to pinning this down." Instead of "Flailing madly in the dark with wild theories."
- stcredzero 8y agoI think it's kinda like an intermittent bug in some application. Like a "stable" civilization? Sometimes I wonder if clouds of autonomous self replicators, such as our planet and our civilization, aren't viewed as atavistic exponential pests by godlike alien beings who control the entire resources of a civilization in one entity.
- cjohansson 8y agoResearchers need funding so most of them will say this to make it meaningful to ”invest” in their project. I wouldn’t take such statements literally
- phkahler 8y agoHow does one contain neutrons in a "bottle"?
- evanb 8y agoLANL has a lot of high-level description. You can use neutron-reflective material, or magnetic fields. https://lansce.lanl.gov/facilities/ultracold-neutrons/experiments.php https://lansce.lanl.gov/facilities/ultracold-neutrons/experi...
- SiempreViernes 8y agoMagnetic fields and lots of cooling. https://www.nature.com/articles/47444 https://www.nature.com/articles/47444
- taneq 8y agoI definitely understood a few of those words.
- ben509 8y agoAh, but how do you capture a neutral particle with a magnetic field? (As I understand, they're a little bit magnetic because their constituent quarks are charged.)
- convery 8y agoExactly, everything's magnetic if you have a large enough magnet. I'm more interested in how they limit such a field =P
- fsh 8y agoThe magnet inside your compass isn't charged either. Magnetic fields act on magnetic moments, not on charge (unless the charge is moving which gives you a Lorentz force).
- schemathings 8y agoTimely for me - I've been down the rabbit hole lately of understanding how the elements are formed and got as far as stellar nucleosynthesis, s-process which involves neutron capture making a heavier isotope and then apparently the neutron turns into a proton through a process called beta decay. (So I'm all about the lifetime of neutrons right now!) https://en.wikipedia.org/wiki/S-process https://en.wikipedia.org/wiki/S-process
- kwoff 8y agohttp://pdg.lbl.gov/2018/reviews/contents_sports.html http://pdg.lbl.gov/2018/reviews/contents_sports.html
- schemathings 8y agoMaybe next "semester"! :) I love the misleading URL - those particle physicists have a sense of humor.
- kwoff 8y agoIf you haven't seen this series: https://archive.org/details/The_Mechanical_Universe_and_Beyond_51_Atoms_to_Quarks https://archive.org/details/The_Mechanical_Universe_and_Beyo... (it's a bit outdated, but the part around 23 minutes is still mind-blowing to me, especially in the context of the video)
- schemathings 8y agoI haven't, thanks I'll check it out.
- schemathings 8y agoThis was what I was watching most recently .. Nucleosynthesis the origin of elements in our Solar System Jim Connelly University https://www.youtube.com/watch?v=U6tFWA9FyGE https://www.youtube.com/watch?v=U6tFWA9FyGE
- waveforms 8y agoThis made me curious how long a photon lives. "according to the photons frame of reference, Heeck found that its lifetime would be a rather short three years; however, from our frame of reference, light would live about one billion billion (10^18) years" https://futurism.com/science-explained-long-can-photons-live-will-ever-die https://futurism.com/science-explained-long-can-photons-live...
- pdonis 8y agoNote that this article is assuming, for purposes of argument, that photons actually have mass, equal to the current upper limit for possible photon mass based on experiments. But the experiments are all consistent with the current theoretical belief that photons have zero mass; and if they have zero mass, the concept of "lifetime" for a photon (and indeed the concept of "photons frame of reference") is not even well-defined.
- tinus_hn 8y agoIf they are moving with the speed of light no time passes for photons so ‘lifetime’ has no real meaning either.
- pdonis 8y ago> If they are moving with the speed of light no time passes for photons No, the concept of "time passing" for an object moving at the speed of light has no meaning. That's why "lifetime" has no meaning for a photon if it has zero mass.
- omarchowdhury 8y agoWouldn't c have to be infinite for "no time to pass", since light is still traversing space at a finite speed?
- ben_w 8y agoNo, because the rules of Lorenz invariant field theories mean that the infinity you’re (presumably) expecting is mapped, via the joy of hyperbolic geometry, onto the propagation speed of that field. Or, to put it another way, the speed of light is where time dilation and length contraction run into each other and it all goes zero-divided-by-zero.
- not2b 8y agoI've read about this topic before and when I saw the link I hoped that there was news, but there isn't. If you count how many neutrons remain, you get a different answer than if you count how many protons are created, the effect is a good deal larger than the accuracy of the measurements, and it seems the logical answer is that sometimes a neutron decays into ... something else. That would be new physics and would be extremely cool. We still have no idea what dark matter is, it could be the first real lead.
- craftyguy 8y agoWhy do neutrons bound with a proton 'live' substantially longer?
- krastanov 8y agoAn extremely handwavy explanation would be that they do not: the neutron decays into a proton and other stuff. That other stuff is captured by a proton that becomes a neutron. This is borderline metaphoric, but it gives a gist of the physics.
- tim333 8y ago>Spontaneous processes such as neutron decay require that the final state is lower in energy than the initial state. In (stable) nuclei, this is not the case, because the energy you gain from the neutron decay is lower than the energy it costs you to have an additional proton in the core. https://physics.stackexchange.com/questions/9098/how-come-neutrons-in-a-nucleus-dont-decay https://physics.stackexchange.com/questions/9098/how-come-ne...
- davrosthedalek 8y agoBecause that's a lower energy state. The deuteron binding energy is 2.2 MeV, i.e. the mass of a deuteron is 2.2 MeV below the sum of the masses of a proton + neutron. If the neutron inside would decay into a proton, you would have a diproton (^2He). Very unstable, essentially no binding energy, so it's mass is very close to 2 protons, which is still above the deuteron mass. So the neutron can not decay spontaneously. There is not enough energy available.