[HN Gopher] Rare oxygen isotope detected
___________________________________________________________________
Rare oxygen isotope detected
Author : Brajeshwar
Score : 108 points
Date : 2023-08-31 17:14 UTC (5 hours ago)
(HTM) web link (www.nature.com)
(TXT) w3m dump (www.nature.com)
| ftxbro wrote:
| Can we not simulate even one atom of oxygen well enough to
| determine if it's stable or not. What if they used a big computer
| like the ones they keep building at national labs or the ones
| they used for training GPT.
| tsimionescu wrote:
| This is one of the tasks for which a functional quantum
| computer is needed. Simulating quantum systems with classical
| computers is (as far as it is known today) exponentially hard.
| Even simulating a hydrogen nucleus (which has a single proton
| made out of 3 quarks) is actually too complex for even the
| biggest classical computer we can build. An oxygen atom is FAR
| beyond what we could ever simulate with any known algorithm.
|
| Note: it's not currently proven that it's impossible for
| classical algorithms to simulate quantum systems in polynomial
| time, but it is strongly believed to be the case.
| semi-extrinsic wrote:
| Do we know any quantum algorithm by which a quantum computer
| would be able to simulate nuclear physics better than a
| classical one?
|
| The interactions inside a nucleus are completely different
| from regular quantum mechanics with electrons etc. like in a
| quantum computer.
| btilly wrote:
| https://www.pnas.org/doi/10.1073/pnas.0808245105 shows them
| winning on multi-body atom problems.
|
| https://www.nature.com/articles/s41598-023-39263-7 shows
| them winning on simulating a nucleus.
| bsder wrote:
| _IF_ you can build a scalable quantum computer, it can do
| this.
|
| Note that "if"--it's a big, unsolved problem right now.
|
| The problem right now is that once you start adding
| qubits the noise in the system grows faster than your
| signal.
| btilly wrote:
| The question is whether the algorithm was known, and not
| whether we have the technology to actually implement the
| algorithm.
| ars wrote:
| No, we can not. We can't even simulate a hydrogen atom, which
| is far simpler.
|
| For that matter we can't simulate a single proton either. See:
| https://www.quantamagazine.org/inside-the-proton-the-most-co...
|
| (Unrelated but this is why I don't believe singularities exist
| in the universe - we don't know enough about quark degeneracy
| pressure to know if it's actually possible for a star to
| collapse - it's possible the quark pressure keeps the matter
| from compressing.)
| addaon wrote:
| > it's possible the quark pressure keeps the matter from
| compressing
|
| Why are you more comfortable with infinite pressure forces
| than infinite densities?
| AnimalMuppet wrote:
| It wouldn't have to be an infinite pressure force - just
| enough to keep a finitely-sized collection of quarks from
| collapsing further.
| addaon wrote:
| Finite, but bounded only by the mass of the visible
| universe.
| codethief wrote:
| You don't need fermions to form a black hole. Bosons (in
| particular: photons) work, too [0, 1, 3], as do gravitational
| waves [2], so Pauli pressure is not a convincing argument
| against singularities.
|
| [0]:
| https://en.m.wikipedia.org/wiki/Kugelblitz_(astrophysics)
|
| [1]: https://arxiv.org/abs/1408.2778
|
| [2]: https://arxiv.org/abs/0805.3880
|
| [3]: https://arxiv.org/abs/1105.5898 (building on [2])
| ars wrote:
| It's pretty unlikely that any exist though. Which was my
| point.
|
| Although I have a side question: Imagine three streams of
| light, each 1/3 the density needed to make a black hole,
| traveling at a slight angle from each other, and then
| meeting.
|
| The moment they meet they are a black hole. How fast is
| that black hole moving afterward in order to concerve both
| momentum and energy? You'll find the answer is: The speed
| of light.
|
| There are clearly unsolved issues with Kugelblitze.
| samus wrote:
| The plural of "Kugelblitz" is "Kugelblitze".
| btilly wrote:
| Do you have a source?
|
| When I do a naive version of the calculation I find it is
| slightly below the speed of light, with the amount below
| depending on the angles between the beams. The full
| calculation is beyond my skills.
| ars wrote:
| Yah, I errored in thinking 3 beams would negate that, but
| it wouldn't, it would be just below, as you say.
|
| But you have another issue: Even if you are just below
| the speed of light, most of the mass would become
| relativistic mass (and relativistic momentum), with
| almost no rest mass.
|
| But there's a postulate that only rest mass can make a
| black hole, and relativistic mass doesn't count. (Because
| otherwise you could travel fast and see inside the black
| hole.)
|
| So we are left with a contradiction.
| namibj wrote:
| There's also the continuous collapse theory that assumes you
| start with a mostly classical gravity system and then just
| reach a runaway where the internal pressure can't keep up
| anymore, followed by the space time well getting rapidly
| stretched towards beyond an event horizon, making it so that
| due to finite propagation speed of this concentric ripple in
| space time, the further in you start, the sooner the distance
| left to the first spacetime outside for a fresh photon
| increases with time passing instead of decreasing, because
| the space time between the photon and outside continues to
| stretch fast enough to cause "beyond-infinite" red shift.
| AtlasBarfed wrote:
| They're just quark stars with an event horizon?
| ars wrote:
| No event horizon, just incredibly powerful gravity.
| rich_sasha wrote:
| I was once told simulating N quantum particles interacting with
| each other is exponentially hard in N. I wouldn't know myself.
|
| But if it's true, that's why you can do your hydrogen atom in
| Quantum 101, and why this is not merely O(28^2) harder (or do
| you need the electrons too?).
| db48x wrote:
| Exponential means 2^N, not N^2. Also, notice that every
| proton and neutron is really three quarks, so its at least
| 2^84 times harder than a hydrogen atom.
| shwaj wrote:
| I think they intended to say quadratic. For N classical
| objects interacting, each of them can interact with each of
| the N-1 others, hence O(N^2). The GP is saying that the
| quantum interactions don't follow this rule, hence "not
| merely O(28^2)", but in fact much bigger.
| btilly wrote:
| No, they meant exponential because that is what they
| heard. That is correct, it is exponential.
|
| They were just apparently confused about what exponential
| means.
| shwaj wrote:
| Not to make a big thing about it, but you're wrong. Try
| read it again, slowly.
|
| Edit: hint: focus on "if that's true" and "merely".
| db48x wrote:
| I disagree too. He asks "If it is truly exponential, why
| is it not just 28^2x (aka 784x) harder than hydrogen?".
| The answer is that he misunderstood exponential growth,
| and thus it is at least 19342813113834066795298816x
| harder than hydrogen.
| moelf wrote:
| simulating atom is hard because the interaction between protons
| and neutrons are described by not only EM force but also Strong
| force, and in particular, Strong force at this low energy (as
| oppose to what happens at the LHC) is hard, partly because
| https://en.wikipedia.org/wiki/Asymptotic_freedom , basically
| our usual physics tricks of "perturbation approximation"
| doesn't work because the Strong force diverge at lower energy
| bazzargh wrote:
| Speaking as someone whose PhD was simulating the nuclear
| structure of nuclei like this... yes, we probably could, now.
|
| Back then (like, 30 years ago, and I stopped doing physics
| after this so my memory of this is fuzzy) we were looking at
| simulations of nuclei like O16. I say 'we' - nuclear theorists
| were _very_ thin on the ground, we were the only remaining
| group in the UK. Most particle physicists are of the kind
| looking at subatomic particles, not nuclei. Anyway, we were
| attempting to port the code to run on parallel processors (a 96
| transputer rack at the time), and then diagonalise the matrices
| of the interactions to get out a spectrum of energy levels.
| IIRC the matrices worked out as ~20m x 20m, and the technique
| used was the https://en.wikipedia.org/wiki/Lanczos_algorithm
| ... the problem we had was that the state space explodes
| combinatorically with increasing numbers of nucleons; and the
| computation time scaled something like n^1.1 for n states, due
| to inter-processor communication.
|
| In the end that was what killed the project - it became clear
| that with moores law we were about 10 years from having
| affordable access to a computer that could do the calculation
| for larger shells (including O28, which was well out of our
| range).
|
| That was the state for _exact_ calculations, but there were
| alternative approaches - I recall VAMPYR being a German Monte-
| Carlo simulator for shell models that performed really well,
| and could extract properties even for quite heavy nuclei.
|
| Looking back a lot of the problems were just a lack of memory,
| even more so than compute. The matrix elements weren't stored
| explicitly but recalculated on the fly because we lacked
| memory, this led to us not using off-the-shelf matrix code and
| the whole thing had numerical stability issues and used lanczos
| because we could fit that into the memory on board the
| processors. These days I use servers in AWS with ungodly
| amounts of memory and extremely fast cpus, I'm pretty sure they
| could simulate this for a couple of hundred bucks.
| jacquesm wrote:
| Can you give an indication of the amount of precision
| required for the initial conditions to be able to perform
| such a simulation? Fascinating stuff this, thank you for your
| comment.
| sjtgraham wrote:
| This is the kind of HN comment I live for.
| jacquesm wrote:
| To help give a way to grip _why_ this is a hard problem:
| computers work with quantized values so you get quantization
| noise (or you get thermal noise in the analog domain), and that
| means that every datum that you want to ingest, compute and
| spit out again as a result is going to be _about_ right, but
| not quite right. You then take it through a few million cycles
| to see how it behaves and as you do so with every iteration you
| are further and further away from how it really would behave.
| And that 's just that one aspect: quantization noise.
|
| Then there is the uncertainty principle to deal with which may
| preclude one or more parameters from being known exactly in the
| first place. And so on. In the end you find that no matter how
| much computing power you throw at it _even just a simplest
| atom_ is beyond your capability of simulation for as much as a
| tiny fraction of a second.
|
| What we do in almost every simulation is to take a shortcut:
| instead of simulating the individuals atoms we simulate their
| observed properties and usually in larger numbers. This allows
| for useful work to be done in a timespan not measured in aeons.
| But it's an approximation at best, never a simulation accurate
| enough to make definitive statements about how any individual
| atom behaves and what its future state will be given some set
| of initial conditions with any accuracy.
| Angostura wrote:
| We did simulate it - using our models. The model said 'stable'.
| Reality said 'nope'
| ftxbro wrote:
| The simple shell model said 'stable' but we can calculate
| with more detailed models than that one.
| coder543 wrote:
| From the article: "Oxygen-28 might prompt physicists to revamp
| theories of how atomic nuclei are structured."
|
| If the theories are incomplete or wrong, how could we
| accurately simulate things we don't yet understand? It doesn't
| matter how powerful the computer is.
| rcme wrote:
| Isn't that the point of simulation? To gain understanding of
| something? I think the underlying point is that, if our
| understanding is so incomplete that we can't simulate a
| single atom, how can we trust all of our other physical
| understanding?
| ars wrote:
| No, that's not the point of simulation. You gain no
| understand from simulation because what you put into it is
| what you get out of it. Simulation can help you verify what
| you already know, and point to areas to examine, but you
| can't actually directly learn anything from it.
|
| We trust our physical understanding by experimentation, not
| simulation.
|
| You can use simulations in areas that are fully understood
| to run calculation on new arrangements of those those
| things, without having to make the physical object. But it
| only works when you already understand the thing, you can't
| gain that original understanding from the simulation.
| nomel wrote:
| I think there's an assumption that the "unit" of
| simulation is much smaller than the oxygen atom, allowing
| these "emergent" behaviors to arise.
| Retric wrote:
| We don't actually know the laws of physics, we just have
| some decent approximations.
|
| So sure run a simulation at whatever level of granularity
| you want that doesn't mean it's correct.
| jacquesm wrote:
| Because just like statistics don't say anything about an
| individual person they are quite useful when applying them
| to larger populations and we usually deal with larger
| populations of atoms. Gas simulations work well because the
| noise more or less cancels out and then your macroscopic
| gas laws emerge and allow you to say useful things about
| how a gas will behave. Even if under the hood it is a
| completely stochastic process that gives rise to these
| laws. The laws themselves are simply our best description
| of observed reality, they are not laws that any particular
| atom needs to obey!
| ChuckMcM wrote:
| Yes and no. A simulation can test your model, which you
| then compare with empirical results to validate both the
| model and the simulation of it. When those results do not
| match, you have to figure out if your simulation is wrong
| or the model is wrong. The model said that O28 would be
| doubly magic and thus stable, and yet when they managed to
| make it, it was exceptionally short lived. As a result the
| model they have is missing something.
|
| On the plus side, now that they have an empirical result,
| they can tweak the model such that it continues to
| accurately describe what it currently describes, and
| describes a short lived O28. Once they have those tweaks,
| they can find another experiment to see if their updated
| model accurately _predicts_ what the experiment would
| produce. If it does, they gain more confidence in the
| model, if it does not, they go back to tweaking the model.
|
| This is the essential core of scientific research, for
| science to be believable it needs to predict things that
| will happen given conditions, and then experimentalists
| establish those conditions and look for confirmation of the
| prediction. It is the only way to know if what we think we
| know is in fact worth knowing!
| at_a_remove wrote:
| You have this backward.
|
| So imagine you have a simulation, and you get an answer
| out. Yay.
|
| How do you know it is correct? You don't. You must compare
| against reality. Reality always wins.
|
| This is not a "single atom," you might as well say "a
| single person." Each one of those protons is composed of
| two up quarks and one down quark. Each one of the neutrons
| is composed of two down quarks and one up quark. Each
| nucleon is therefore three quarks, held together by the
| exchange of virtual quarks. The nucleons themselves
| interact via a stepped-down approximation of that called
| the strong nuclear force. And you're not allowed to forget
| the electromagnetic force, either. And then there's self-
| interaction ...
|
| There's a lot going inside of a nucleus.
|
| Simulations are only useful for testing your _models_.
| cwillu wrote:
| Also, the "composed of two up quarks and one down quark"
| is a dramatic simplification, kinda sorta like saying
| that the valence electrons of an atom are the only
| electrons.
|
| https://i0.wp.com/profmattstrassler.com/wp-
| content/uploads/2...
|
| "Fig. 3: A more realistic, though still imperfect, image
| of protons and neutrons as full of quarks, anti-quarks
| and gluons, moving around at high speed. More precisely,
| a proton consists of two up quarks and a down quark plus
| many gluons (g) plus many quark/anti-quark pairs (u, d, s
| stand for up, down and strange quarks; anti-quarks are
| marked with a bar.) The edge of a proton or neutron is
| not sharp. Ignore the color-coding for now; it will
| become clearer in future articles."
|
| -- https://profmattstrassler.com/articles-and-
| posts/particle-ph...
| at_a_remove wrote:
| Sorry, I meant to type "virtual gluons" instead of
| "virtual quarks."
| wheelerof4te wrote:
| "Each one of those protons is composed of two up quarks
| and one down quark. Each one of the neutrons is composed
| of two down quarks and one up quark."
|
| And we know this, how? Using magic?
|
| Has anyone ever seen a quark? We could barely detect
| atoms, now we're detecting something even smaller?
| at_a_remove wrote:
| ... "we could barely detect atoms." You're a few decades
| out of date on the science. Almost a century, really.
|
| Atom detection has been ... quite a while. The parts of
| the atom: electron, proton, neutron (all somethings even
| smaller) started with the electron in 1897. Neutrons
| lagged until the 1930s. Quarks were hypothesized in 1964.
| Now, you'll never find free quarks (due to something
| called color confinement) but we started detecting that
| the nucleons (protons and neutrons) must have something
| even smaller inside via scattering experiments around
| 1968. We were producing charm quarks in 1974. 1977 we
| observed the bottom quark, and in 1995 we got the
| heaviest of the bunch, the top quark.
|
| The current year is 2023.
| ftxbro wrote:
| They found them by blasting protons at each other and
| seeing what happened when they collided like this
| https://en.wikipedia.org/wiki/Quark#/media/File:Charmed-
| dia-... and then using detective skills to figure out
| what could have been inside them to make those spirals
| jacquesm wrote:
| Quarks are a very useful construct because even if we
| can't perceive them directly theories based on quarks
| appear to work. That makes them a useful tool and even if
| we will never be able to 'observe' (for whatever that
| means: you can't observe an electron directly either but
| you _can_ observe electricity) quarks directly we can
| create theories that hold true if quarks exist and see
| whether the interaction between particle beams is such
| that it experimentally confirms those theories. This has
| been done countless times by now and the various
| properties of quarks and combinations of quarks have been
| determined to the point that it would be very surprising
| if quarks were a completely wrong way of describing the
| fundamentals of matter.
|
| But: it's a theory and it may well be displaced by
| something else at some point, but that something else
| would have to be _even better_ at describing reality as
| observed than quarks are. Maybe a unified field theory
| will do away with the 'zoo' of subatomic particles but
| that would in itself be a very surprising result. But it
| could definitely happen.
| addaon wrote:
| There's multiple levels of "theory" here. We have reasonable
| confidence that an ab initio simulation of a O28 nucleus
| would match experiment, but such a simulation is outrageously
| hard. We simplify things by creating an abstraction of the
| strong nuclear force, the residual force of the strong force
| at the scale of nucleons; there's plenty of room for
| improvement here. Then, we have a further abstraction of
| "magic numbers," a rule-of-thumb level theory that reduces
| the calculations of the strong nuclear force to a lookup
| table. While this last step is a pretty good approximation
| when applied to the EM force and electron orbitals, it's no
| surprise that it's a mediocre-at-best approximation for
| nuclear structure. Even so, finding cases where it doesn't
| apply is useful for developing a refined version of this
| third-level rule-of-thumb -- and a more accurate, more
| grounded rule of thumb here would be useful for refining
| speculations about the possible island of stability, where ab
| initial simulation is even less practical.
| eikenberry wrote:
| All theories are incomplete and wrong, that is a core
| principle of science. When and how simulations might be
| useful in testing that theory are context dependent. In other
| words.. it depends.
| semi-extrinsic wrote:
| The strong and weak nuclear forces are insanely hard to
| simulate directly. You might have a look at e.g. this paper for
| some fairly current modelling:
| https://journals.aps.org/prc/abstract/10.1103/PhysRevC.103.0...
|
| Just to be clear, simulating the atomic nucleus isotope
| stability (like here) is something entirely completely
| different than simulating the quantum mechanics of electrons in
| one or more atoms (like we do in DFT), or simulating molecules
| (like we do e.g. in molecular dynamics). The latter two are
| comparably much easier.
| ftxbro wrote:
| it's paywalled
| awesome_dude wrote:
| Um, so I took the papers title and list of authors "Unbound
| spectra of neutron-rich oxygen isotopes predicted by the
| Gamow shell model J. G. Li, N. Michel, W. Zuo, and F. R.
| Xu"
|
| Threw that into Google Scholar and the only hit had a link
| to the pdf of the paper
|
| https://link.aps.org/accepted/10.1103/PhysRevC.103.034305
| AnimalMuppet wrote:
| [flagged]
| moelf wrote:
| https://arxiv.org/pdf/2103.01478.pdf
| foota wrote:
| Iirc the simulation is more difficult the more components there
| are in an atom, and oxygen 28 has a lot of them.
| segfaultbuserr wrote:
| My favorite isotope story is the detection of tungsten-180's
| decay. W-180 has a half life of 10^18 years. It was
| observationally stable, until its theoretical radioactivity was
| confirmed in 2009 by _Cryogenic Rare Event Search with
| Superconducting Thermometers_ - an experiment meant to search for
| dark matter. Tungsten was used inside the detector, and the
| sensitivity of the instrument enabled the detection of W-180 's
| alpha decay with confidence [0]. Dark matter was nowhere to be
| seen, but at least they still got an interesting minor result.
|
| > _All naturally occurring tungsten isotopes are expected to
| alpha decay into hafnium, but with extremely long lifetimes.
| Since the decay energies for all these decays are in the same
| energy range as beta and gamma backgrounds from the natural decay
| chains, their observation is a difficult task. Yet with cryogenic
| scintillator experiments, these backgrounds can be discriminated
| from the alpha signal, leading to a basically background free
| measurement of such alpha decays, see figure 13. Hence, the
| natural decay of W-180 was observed unambiguously for the first
| time._
|
| Update: Apparently it was not the only rare decay detected during
| a dark matter experiment, in fact dark matter searches are a
| major source of rare decay detection. Previously in 2003,
| Bismuth-209's radioactivity was also detected as a bonus result
| of a dark matter search, with a half life of 10^19 years. [1] In
| 2019, the XENON1T experiment detected the radioactivity of
| Xenon-124 (again, because Xe was used inside the detector), with
| a half life of 10^22 years. By far it's the rarest radioactive
| decay ever directly observed by physicists [2].
|
| [0]
| https://en.wikipedia.org/wiki/Cryogenic_Rare_Event_Search_wi...
|
| [1] https://physicsworld.com/a/bismuth-breaks-half-life-
| record-f...
|
| [2] https://en.wikipedia.org/wiki/Isotopes_of_xenon#Xenon-124
| jacquesm wrote:
| That's super impressive. How many discrete events did they
| observe?
|
| The Tungsten isotope page lists two alpha decays per year per
| gram, that must have been quite the mass of Tungsten if they
| got a usable signal out of that. Amazing result, if you think
| about it: your measurement is so accurate that you can measure
| you measuring gear falling apart.
| knodi123 wrote:
| Does this suggest that over long enough timescales, everything
| is radioactive?
| kevinventullo wrote:
| If the half-life is 10^22 years, doesn't that mean after one
| year you'd expect a proportion of (0.5)^(10^-22) of the atoms
| to be the same? This is very close to 1-A^-1 where A is
| Avogadro's number. I think this means that with a mol of this
| stuff, you'd expect about one atom to decay after a year.
|
| If I have that right, it does seem mind blowing that they were
| able to detect it.
| xhrpost wrote:
| At 10^22 years, where do we draw the line between what we
| consider stable and what is "radioactive" or "decays"? If the
| heat death theory of the universe is true, then isn't
| everything above iron eventually going to "decay"?
| segfaultbuserr wrote:
| If proton decay is real, all atoms will eventually cease to
| exist, but it is still an open question. More than one
| experiments are still waiting for an event.
| [deleted]
| NeoTar wrote:
| 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 wrote:
| There 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
| jychang wrote:
| Also, 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 wrote:
| No, it isn't. According to the Standard Model, the proton
| is stable at every time scale. And no proton decay has
| ever been observed.
| jacquesm wrote:
| The 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 wrote:
| Not true. neutrons decay within minutes, protons and
| electrons dont decay within SM
|
| Also to nitpick - "half life" is not applicable to
| subatomic particles
| jacquesm wrote:
| Free 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 wrote:
| Protons and electrons do not decay according to the
| Standard Model.
| jacquesm wrote:
| I'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.
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