12 ms·
Exotic four-neutron no-proton particle confirmed
- zw123456 11y agoI know this is probably dumb on my part but am I the only one that had "dark matter" pop into my mind?
- cgs1019 11y agoNeutrons are electrically neutral but they still interact electromagnetically (they're composed of charged quarks). They have a magnetic moment, for instance [1]. So they wouldn't be dark the way "dark matter" appears (heh) to be. [1] - https://en.wikipedia.org/wiki/Neutron_magnetic_moment https://en.wikipedia.org/wiki/Neutron_magnetic_moment
- drjesusphd 11y agoIf dark matter particles had a magnetic moment, how would we know?
- gliese1337 11y agoThey would interact with photons, allowing us to see some effects of concentrations of dark matter against background light sources.
- Kronopath 11y agoDark matter isn't made of protons, neutrons, or anything as pedestrian as that. It's a sort of "placeholder name" for an effect seen in situations like the collision of galaxies, where there seems to be more gravitational attraction between the two of them than there should be given the matter observed in them. It's as if they had a whole bunch more mass to them, but for some reason that mass is interacting gravitationally, and not in any other way or through any other forces. Scientists can model this by assuming that this type of gravitational-only matter is real, calling it "dark matter", because we don't have a better sense of what it really is. The stuff made in this experiment, on the other hand, has more to do with what you find in something like a neutron star—clumps of neutrons (which are regular, non-dark matter) packed closely together—albeit in an extremely small scale compared to the star.
- deleted 11y ago[deleted]
- akiselev 11y agoThere aren't any known arrangements of neutrons that are stable without protons. Solo neutrons don't exist for longer than 10-20 minutes before decaying into protons and I doubt these tetraneutrons exist for longer than a few seconds unless they're moving at relativistic speeds (and even then, for not much longer). Unless there is something drastically different going on in the interstellar medium, neutrons as dark matter is extremely unlikely.
- noobermin 11y ago>Solo neutrons don't exist for longer than 10-20 minutes Don't equate the bound states with the unbound states.
- ars 11y ago"If a four-neutron nucleus did occur it lasted about a billionth of a trillionth of a second before decaying into other particles."
- noobermin 11y agoSure, but his reasoning of "single neutron is unstable implies a bound state containing neutrons is also unstable" is not necessarily sound.
- akiselev 11y agoWhy is this reasoning unsound? The fact that, after centuries of theoretical and experimental physics, we have yet to see stables neutrons in any configuration other than with protons in an atomic nucleus? We know pretty accurately the decay rates of single neutrons and now we know that all the way up to a tetraneutron that the particles are unstable on the order of minutes and seconds. What evidence is there that we are wrong?
- caf 11y agoThe number of centuries for which we've even known of the neutron's existence is 1, and that's rounding up!
- deciplex 11y agoDark matter is probably popping into and out of all our minds, all the time, and we just don't notice it.
- ars 11y agoI know it's the title of the article, but this is NOT confirmed! There is a paper about it, and some hints it exists, but it has not risen to the level of accepted particle.
- ch8230 11y agoAgreed. Until they eliminate other possibilities then it is not confirmed.
- blahDeeBlahBlah 11y agoExcept neutrons are protons bound to electrons, so that's really just 4 of each, so maybe this is just some exotic Beryllium, or a clump of degenerate neutron gas as might escape from a dead-ish star.
- leni536 11y ago> neutrons are protons bound to electrons No, they are not.
- logfromblammo 11y agoTo be more specific, you can turn a proton into a neutron by electron capture or beta+ decay, but that's not what a neutron is. A neutron is 2 down (-1/3 charge) quarks and 1 up (+2/3 charge) quark, whereas a proton is 2 up and 1 down quark. Electron (-1 charge) capture changes an up to a down and emits an electron neutrino (0 charge). Beta decay is when a neutron changes to a proton and emits an electron and an electron antineutrino (beta-), or when a proton changes to a neutron and emits a positron and electron neutrino (beta+). Even if you wanted to be generous, the grandparent post left out the electron antineutrino.
- winter_blue 11y agoA proton is neutron bound by an electron? Where did you get that from? Beta decay goes both ways[1]. In β+ decay, a proton decays into a neutron and positron, and in β− decay, a neutron decays into proton and electron. (I don't know much physics, but I suppose there's a limit to them decaying from one to another, and I suppose each proton/neutron is unique in terms of its mass/energy content.) [1] See https://en.wikipedia.org/wiki/Beta_decay https://en.wikipedia.org/wiki/Beta_decay
- raattgift 11y agoLet's add "at rest" to the end of your question: "I suppose each proton/neutron is unique in terms of its mass/energy content" Oh boy, so there's a can of worms. "Unique" would need to be nailed down to test that statement, and runs into some observational problems in that atoms exist and can be found in things like monatomic gasses in enormous enough quantities that you can wash out any contributions from other matter. These gas clouds can be measured and manipulated, and have been. The results limit the variation from proton to proton (and climbing the periodic table of elements, from nucleus to nucleus) to be entirely negligible. Theory depends on where you look. Protons are usually taken to be indistinguishable particles (each proton obeys the same particle statistics at low energy). Additionally, there are good reasons to believe that any distinguishability -- however small -- leads to observables (an example is elucidated and generalized in the "Bosonic Birthday Paradox" http://arxiv.org/abs/1106.0849 http://arxiv.org/abs/1106.0849 ). Those observables are not seen. Proton distinguishability also goes to the question of the mechanisms by which the Pauli Exclusion Principle manifests. It does manifest among protons in atomic nuclei, which is important. Retaining that and introducing actual distinguishability at small scales is a challenge. If protons are (barely) distinguishable to us in experiments, they'll be (barely) distinguishable in decays and in electron interactions too. But if you think of a proton as "a mess"[1] and look at it at, say, the QCD scale, your question might be better put as,"how do confinement (and asymptotic freedom) and colour exchange work?". Peering into the structure of a proton at that scale is certainly interesting, but any information in there can only escape in ways permitted by confinement. [1] http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-structure-of-matter/protons-and-neutrons/ http://profmattstrassler.com/articles-and-posts/particle-phy...
- Animats 11y agoPaywall. Is this stable for some reasonable length of time, or is it one of those "particles" with a lifetime in nanoseconds?
- ars 11y ago"If a four-neutron nucleus did occur it lasted about a billionth of a trillionth of a second before decaying into other particles."
- pif 11y agoHello, why writing "particles" with the quotes? Do you consider the reality of a particle to be proportional to its lifetime? By the way, a nanosecond is a very long time when you compare it to the lifetimes of some particles (with no quotes)!
- tfgg 11y agoParticles are sort of mathematically more poorly defined the shorter their lifetime. But yes, a nanosecond is a long time in this context :)
- pif 11y ago> Particles are sort of mathematically more poorly defined the shorter their lifetime. This sentence doesn't make any sense to me. Could you please elaborate?
- pc86 11y agoNot the person to whom you're replying, but my lay understanding of it was that it's much more difficult to model mathematically those particles which exist for incredibly small spans of time.
- Benjamin_Dobell 11y agoI know nothing about the mathematics. But I think it's fair to say that in general people tend think of particles as being a _stable_ unit of some sort. So the term "particle" becomes less appropriate the less stable something is, and time is often a factor when thinking about stability. If someone were simply to slam 4 neutrons together, for how long would they need to stay together for this to be deemed a real particle? I think it's for this reason the original commenter quoted the use of the term "particle".
- friendzis 11y agoMay be dumb, but first thing that popped into my mind reading the title was "Whoa, element 0 discovered!"
- diskcat 11y agovoidium
- T-zex 11y agoHoarium, to honor null refs! /s
- tosseraccount 11y agoHe may not play dice, but He does program in ansi C.
- logfromblammo 11y agoBy current standards, it should be provisionally named nilium-4.
- HalcyonicStorm 11y agoJust need to find the mass effect relays and then fight the Reapers
- rm_-rf_slash 11y agoMaybe if we lay low for a while we can skip this extinction event and mop up after the Reapers are through, which I assume is roughly how the Protheans got started.
- Manishearth 11y agohttps://en.wikipedia.org/wiki/Onium https://en.wikipedia.org/wiki/Onium (Positronium is often called the zeroeth element in pop sci)
- SideburnsOfDoom 11y agoThey make no mention of how long the tetraneutron might stay around for. Are we looking at whole seconds, or 10^-10 seconds of stability, or what?
- sp332 11y agoIt's short enough that it doesn't even touch the detector. The evidence is that the energy from the four neutrons all shows up at once, instead of being split among four individual neutrons. http://arstechnica.com/science/2016/02/no-protons-needed-possible-discovery-of-a-four-neutron-particle/ http://arstechnica.com/science/2016/02/no-protons-needed-pos...