14 ms·

What Is a Particle? (2020)

• AlbertCory 2y ago
  I'm reading "The Big Picture" (Sean Carroll) right now. I'd love to have a real physicist explain this, but: When we think of what a particle IS, we often think as though it were dirt, or a billiard ball, or something. As though there were some other substance of which it's made. At least I do. But the definition is as low as you can go. It's hard to wrap your head around that. Unless you're trained to do so, I guess.
  • deleted 2y ago
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  • elashri 2y ago
    > we often think as though it were dirt, or a billiard ball, or something The problem lies that it is hard to imagine something that does have zero dimensions. You can get the example of ant walking into 2D and it is unaware of third dimension to explain we are have something similar for space-time 4D (although not the same picture exactly as time is different from spatial dimensions). But we don't have an idea how to approximate a mental picture of what a zero dimension could be. So you have something that does not occupy a volume in space (Talking strictly about elementary particles here) in the classical sense. This does not mean they are abstract concept. According to QFT -Quantum field theory- you would think (by training) of particles are excitations or quanta of their respective fields. Fields are there always (vacuum is just filled with fields) and particle appears when they are excited (more complex processes occurs). So you would think of each particle as a manifestation of a quantum field that permeates the universe. What is interesting (and probably confusing to most people) is that these fields are not zero-dimensional, instead, they exist everywhere in space and time. But the quanta (particles themselves) are considered point-like with no spatial extension. In practice physicists will think about particles properties (i.e charge, mass, interactions, spin) ..etc instead of what this particle actually is from that point of view. This is often for practical reasons. You are a working physicist and you learned from your training that you shut up and calculate (or implement if you are doing experimental particle physics as you spend most of your time coding) by this stage.
    • xanderlewis 2y ago
      > The problem lies that it is hard to imagine something that does have zero dimensions. Do you really think so? It’s not hard to picture the real number line, with the point zero (or any other single point) distinguished. Sure — if you draw it in the standard schematic way you have to give it some area, but it still seems quite intuitive that it’s ‘zero-dimensional’. Especially if you play around with converging sequences and open sets and stuff; you quickly develop intuition for what it means to be a point rather than something higher dimensional.
      • mock-possum 2y ago
        I do - specifically, it’s hard to imagine a group of things which collectively constitute mass, but individually constitute no mass. How can something come from nothing?
        • xanderlewis 2y ago
          I thought you were just speaking geometrically. What particles are you talking about exactly? I was under the impression that most particles that constitute things with mass do themselves have mass.
      • dangsux 2y ago
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    • hughesjj 2y ago
      I just think of a zero dimensial object as a ghost. Topological defect. The unpictured thing the contour lines are swirling around. It's influence is only felt by seeing the effects on higher dimensional space, but you can never see the ghost itself.
      • mock-possum 2y ago
        So more like a poltergeist really Or a magnet
    • 2y ago
  • deanCommie 2y ago
    The same is true about the terms "waves" and "fields" when it comes to quantum mechanics. They're analogies. The concepts need names, but I think they do more harm than good because people then start with a mental model of a membrane or a surface - something they have experience seeing waves in. And then after 1 or 2 steps where the analogy helps, it breaks down, and people start being confused. Of course the alternative isn't any better. If they had named it a "Wazoo function" and a "Quantum Flarg" everyone would've just kept asking "OK but what IS a Wazoo? What IS a Flarg" and not been satisfied with a "Yeah, it's a fundamental own thing". Feynman, of course, has a pretty definitive response on the difficulty of this problem: https://www.youtube.com/watch?v=Dp4dpeJVDxs https://www.youtube.com/watch?v=Dp4dpeJVDxs
  • danbruc 2y ago
    I mean I can not speak for you, but I do not think that the problem necessarily is that people think of them as made from some stuff, I think what causes the most trouble is the desire to visualize particles. The trouble is that an electron is an electron and it is nothing like anything you have ever seen in your macroscopic classical world. It shares some aspects with billiard balls and some with water waves but it is not like either. And it does not switch between being a billiard ball and a water wave, it always is the same thing, it always is an electron. It just happens that in certain situations the billiard ball properties are more apparent and in others the water wave properties and in yet other situations neither of the two analogies will help. I think that is what trips people really up, they want to visualize their electron as one thing they know, as something they have an intuition for, but no such thing exists. And electrons being electrons also means that they are not excitations in quantum fields. Those fields are mathematical models that describe the behaviour of electrons, they are not the electrons. Certainly not in the very direct sense of nature is just mathematics because I can differentiate, integrate, and square fields at will but I can not do this to electrons. And even the less direct interpretation, there are real entities in the universe that behave exactly like our mathematical fields, does not seem likely, what would the gauge symmetries mean?
    • criddell 2y ago
      > And electrons being electrons also means that they are not excitations in quantum fields You’re going against the dominant interpretation of QFT here, aren’t you?
      • auntienomen 2y ago
        Yep. Also, ignoring all the ways in which an electron isn't an electron. Electrons can be created and destroyed, and they are both indistinguishable and exchangeable. We can't assign identity to them, thanks to their Fermi statistics. They're just methods of explaining clicks in a detector. I worked in particle physics for years and never once saw an electron. :-)
        • binary132 2y ago
  • bbor 2y ago
    I’m not a physicist, but as an arrogant philosopher of science: isn’t it just field excitation? Like, every particle looks like a circle bouncing around a 2D piece of paper, but if you look reeaaaaally closely it’s just a localized 3D spike of energy in a usually 2D field of energy? So it’s made of the field/paper itself. I must be under-thinking this, but that’s what’s worked pretty convincingly for me.
    • griffzhowl 2y ago
      So what is a field?
      • librasteve 2y ago
        a thing that can have particle-like excitations
        • im3w1l 2y ago
          Historically, electrical and magnetic fields were discovered first. Then em-waves. Then photons. This should tell us that fields are useful in their own right, without referencing particles.
      • FollowingTheDao 2y ago
        A probability.
      • bbor 2y ago
        It’s everything! Idk, I don’t think the universe owes us an answer there. What is a human? Well, it’s a human. You can think of all sorts of mental tools for understanding humans (eg “species”), but ultimately they just are.
        • lottin 2y ago
          No... a field is mathematical representation. The universe is most definitely NOT made of fields.
  • lisper 2y ago
    Richard Feynman gave what I consider to be the best possible answer to questions like this: https://www.youtube.com/watch?v=Q1lL-hXO27Q https://www.youtube.com/watch?v=Q1lL-hXO27Q
    • aaa_aaa 2y ago
      At first I was impressed with that video. Then I felt he does not have an answer and unnecessarily gets edgy with it, because question is valid.
      • lisper 2y ago
        > he does not have an answer Well, yeah. That's the whole point.
        • alok-g 2y ago
          The additional important point, of course, is that there are many more 'Why' questions to be asked (often more interesting, and more important than corner cases like human-scale magnetism) that do not get asked just because of familiarity. Familiarity however is not understanding, and it is the same as simplicity.
        • aaa_aaa 2y ago
          He could simply say so.
          • hydrogen7800 2y ago
            He does repeatedly. And continues to explain why there is no satisfying answer, because we normally stop asking "why" once we reach a level of familiarity. That level of familiarity to the layperson is different between electromagnetism and slippery ice.
        • datavirtue 2y ago
          I see what you did there.
  • divs1210 2y ago
    Particle spin explained: Imagine a ball that’s rotating, Except it’s not a ball, and It’s not rotating. (popular particle physics meme) From what I understand of QFT, the Universe is made of fields of different types, and a “fundamental particle” is just an excitation (wave) in the corresponding field. For example, a photon is a wave in the universal electromagnetic field, A charm quark is a wave in the universal charm quark field, etc. I’m not a trained physicist, so I might be wildly wrong.
    • binary132 2y ago
      I get it but I still think these sorts of concepts are also just another level of mathematical abstraction that isn’t necessarily “really what it is” any more than a rotating ball or a math equation or any of the other ideas are “really what it is”
      • lottin 2y ago
        It's very frustrating. The idea that the universe is made of fields is nonsensical. I don't understand why so many physicists keep saying that.
        • binary132 2y ago
          One of the ultimately epistemological puzzles to me is the question of what math really is. Like, obviously, it is fundamentally descriptive. “Two and two makes four” is pretty straightforwardly talking about something “out there”. And when we’re talking about fields, we are clearly also describing something that is really happening, that is really “out there”; it’s not the math itself that is the real thing, but rather it is a language for accurately describing and analyzing real things. But at some level, the real things it’s describing become so abstract and immaterial that they might as well be magic, or spirit. And it seems to me like our minds also contain and experience such things, too. Very advanced math and physics necessarily start to border on philosophy or theology.
          • travisjungroth 2y ago
  • mensetmanusman 2y ago
    https://youtu.be/j2oSyAfPzWg?si=bwM2NAsORzkqLQLk https://youtu.be/j2oSyAfPzWg?si=bwM2NAsORzkqLQLk Fun fields discussion on what particles are…
    • yahalo 2y ago
      What a trip, the guest speaker was clearly a pseudoscientist, talking about "evolution fields" and "mind fields" and equating fields to souls.
      • mensetmanusman 2y ago
        If anyone that attempts to explain the nature of consciousness in a non-falsifiable is a pseudo-scientist, then yes. I thought it was fun to hear perspectives like this. Also, the soul discussion was pointing more at the history of language and concepts versus a crude equation of the two :)
  • scotty79 2y ago
    Particle is a cloudy, fuzzy thing that can fly and wobble through space. It can be more sharp or more fuzzy and when it overlaps with another fuzzy particle object they might exchange a neat portion of momentum, angular momentum and energy and violently reshape becoming sharper or fuzzier (that's the wave function collapse and expansion) then they go again on their separate merry ways. Sometimes when particles meet or even spontaneously they can split or merge altering other parts of their nature (unrelated momentum, energy and angular momentum). This happens for example when neutron decays into proton and electron. Sometimes they get stuck together because of electromagnetic force and they resonate in interesting harmonies and travel together. That's atoms. Interestingly when they are resonating in those harmonies they become quite fussy about amounts of energy they prefer to exchange and they do it only in a very specific quanta. And there's a class of particles called quarks that travel together all the time as they are always tightly bound with each other and can never get free despite possessing incredible amounts of energy they continuously exchange. That's nucelus. We really don't like this image because fuzziness is actually two dimensional in every point of our already 4 dimensional space-time and described by complex numbers so we prefer to focus on those brief moments when particles interact since if we have a lot of particles that are bound together to form measurement apparatus they are so sharp that the interaction they participate in squash other particles nearly to a point and we can declare that the measure particle collapsed to have some momentum, or location, or spin described by a single vector instead of a cloud. It neatly turns out that the square of complex number fuzziness describes the probability that a fuzzy particle will interact with a sharp one (one of those bound together in measurement apparatus) with a specific outcome.
  • at_a_remove 2y ago
    It's a useful fiction, but the map is not the territory. This sounds blithe but ... it is as close as you will get to the truth. I only got the bachelors' version of physics, though I did take some grad classes, so here is what I will tell you: The human mind learns from experience and it thinks of things in terms of the past experiences it has had. We are big assemblages which exist in a narrow range of temperatures (think in terms of Kelvin). Our experience is classical, in the Newtonian sense: we move at not a particularly notable fraction of c, we are too warm to note the strangenesses which happen below, say, twenty or four or a thousandth of a Kelvin (superfluids and BECs are out), we are too cold to have a great internal experience of plasma, leaving us to be creatures of solid and liquid, with a sort of inferred understanding of gas. We are too large to feel the quantum realm, in the sense that the uncertainty principle is not obvious to us from what we have felt. So, we must make do with abstractions, with fictions, with approximations. Conscious that we are the epitome of the six blind men trying to understand the elephant through touch alone, we try to break our understanding, to search for flaws in our inferences. Yet this does not grant us true experience when we run across, say, the electron. We try to think of it like a billiard ball, but we can say that a billiard ball is this wide, yet we are fairly sure at this time that the electron has no radius, no diameter, that it might as well be a geometric point. Every time we try to measure, we can only establish a smaller and smaller upper bound for the confounded thing's radius. That's not like our lives at all! The reality of this electron is that if we get it going fast enough, it stops getting much faster no matter how hard we smack it. That's not like our reality. If we try to pin down where it is, the more we do it, the harder it is to figure out how fast and in what direction it moves. And as we work to ascertain the velocity (and therefore momentum), we lose sense of this bit of weirdness' position. You eventually have to develop an understanding based not on experience at all. Perhaps this was unique to me, but the first time I understood integration in calculus, I had a brief moment of dizziness as I apprehended this new thing. You know how you are working a math problem and you have a good idea of what the answer is already, a sense of what the magnitude and direction might be? I had ground my way through vector and tensor calculus, and had been working a problem in gravitation and relativity class when I sensed what the resulting tensor would look like, the shape of it, in the sense that I would know if my figures were way off. I nearly fell off the chair, my head spun so. If you care to, you can do this for a particle.
  • __MatrixMan__ 2y ago
    I've only got a physics minor, so hardly an expert, but I felt like quantum mechanics got a lot easier once I started thinking of a particle as merely a situation which has some probability of causing a state change in a detector of some kind.
  • elbasti 2y ago
    This might sound tautological but a particle is, well, a thing that behaves like a particle. Those behaviors are something like: - it has momentum - it's state is uniquely defined by a position in space and a velocity What's not a particle? A wave (well, until 1900 or so ...). Sort of like asking "what is a number?" A number is a thing that obeys certain rules. (You can add them; there's an `identity `, for every number there's a number which if you add together gives zero, etc). That allows things like `(3 + 5i)` to be a number, for example.
    • mr_toad 2y ago
      > a particle is, well, a thing that behaves like a particle Except when they don’t https://en.wikipedia.org/wiki/Electron_diffraction https://en.wikipedia.org/wiki/Electron_diffraction
  • ziofill 2y ago
    Physicist here. You are right that the mental picture we get when we use the term “particle” is a little ball or something like that. It is unfortunately a confusing name… You need to begin with a field, like the electromagnetic field for instance. When you look at its properties like energy, polarization and so on, in order to write down a state of the field you need to specify all of them in a way or another. In quantum mechanics you can associate a vector space to each property, and then (here is the important bit) you need to pick a basis for your vector space in order to write down its vectors. Obviously there is an infinite number of possible choices, and we usually end up choosing what makes things simple, so in the case of energy we pick the basis of eigenvectors of the Hamiltonian, because to evolve them in time you just need to multiply them by a complex number and that’s it. Well, those basis vectors are the “particles“ because when taken individually they share some properties with macroscopic particles, but the analogy really only goes so far. And the thing is that usually the state of the field is not in a single one of these basis vectors unless the conditions are very special, so even saying that the field is “made of particles” is misleading because it’s like saying that the wind is made of air going vertically, horizontally and across, which sure it’s “correct” because you can combine those directions and get any other direction but it’s also not really that…
    • tel 2y ago
      As an amateur, I think I follow most of this, at least at some level, but I don't follow why you'd unify the basis elements and particles. Thinking of a quantum harmonic oscillator, the eigenstates have some kind of localization that feels particle-like, but the oscillating pattern of a coherent solution seems "more particle-like" and arises out of the interference between those eigenstates. In particle-speak, I might try on a sentence like "this classical particle is generated by the interaction between... other... particles" but I'm clearly at a loss there. On basis of that, I'd be more likely to say "QM needs to describe everything as a wave, and sometimes certain kinds of localized 'wave-packets' move around coherently, and that's what we'd call 'particles'". That also seems to gel with less coherent states where it feels like there's not really a particle to be found. So, I'm curious why you'd prefer to relate the eigenstates themselves as particles. Again in the oscillator case, the eigenstates themselves seem less coherent and seem to behave less classically than I'd hope. My best guess is that the property those states have that is not as well replicated by the "particle as a coherent wave packet phenomenon" is that they have well-defined energy quanta. But that's just a bit of a stab in the dark here. It perhaps makes more sense from the perspective of "particles are the things that we're able to measure in detectors" POV, though.
  • csomar 2y ago
    This is essentially the Bohr take on the matter. There is no physicality in the sense that we interact with the world in. There are also no real dimensions as they are just our understanding of what we consider the physical world. If that gets around your head, you’ll throw the physicality and real world away and you’ll come to see everything as information interaction.
  • darby_nine 2y ago
    A metaphor with another physical object will always fall short. Why not just state the number of bits a particle represents? It's much easier to describe going through each dimension (colloqiual, I hate string theory for the same reason of unnecessarily using a physical analogy) and describing how it interacts with other particles. Sure you'll lose a lot of your audience but those that remain will have a much clearer picture than via a comparison to a billiard ball. This also makes the more advanced topics like singularities, entanglement, teleportation, the lack of true vacuum, etc much easier to manage. (I'm aware we don't have an understanding of how quantum physics interacts with singularities, but the whole billiard ball metaphor certainly is incoherent with it)
  • throwaway314155 2y ago
    I truly appreciate the discussion your comment has brought about. Some really great sibling comments. There's also a lot of overlap with the article itself however. From the sibling comments too. At risk of breaking the rules, it's very much worth the read if you haven't read it!
• kayo_20211030 2y ago
  A particle is a thing you can "look" at, and say "that's a particle". It is whatever one says it is. They're not exactly discovered, they're invented. Fundamental in this context is not so much a word as it is an analogy. And, don't get me wrong, that doesn't mean particles don't exist. They do. But, a particle is whatever we say it is.
  • deleted 2y ago
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  • prng2021 2y ago
    We're not asking questions about human constructs like what is moral or what is the ideal form of government. We're trying to understand what the most fundamental building block of reality is, which is something objective. Something independent of whether of not people ever existed. So no, countless people around the world aren't wasting their lives researching particles when the answer is simply, it's whatever we say it is.
    • khazhoux 2y ago
      I'll go even further and point out that in 2003, it was proven that particles are not, in fact, the friends we made along the way.
      • kayo_20211030 2y ago
        Do expand. What happened in 2023?
        • sfink 2y ago
          Yeah, I don't get that, because it seems to me that the friends you make along the way are mathematically indistinguishable from particles being real and having properties. It's a distinction without a difference. Or at least, I'm interpreting "the friends you make along the way" as the sum total of the effects of a particle on the surrounding world. Saying "the particle doesn't exist, but it has effects X, Y, and Z" is the same as "the particle exists and has effects X, Y, and Z". If a distinction is not observable, then it's meaningless to quibble over whether it's "real" or not. (Which all just proves that my interpretation isn't the one you were using....)
• khazhoux 2y ago
  I'm honestly surprised that more people don't go mad in certain fields. If I ponder for 10 minutes the inexplicability of the universe's existence, or the vastness of space, my mind starts to breaks down.
  • fracus 2y ago
    Constantly trying to resolve an incomplete abstraction. They are trying to reverse engineer the Universe. I can usually read half way through these articles before I'm completely lost in the abstractions.
  • seiferteric 2y ago
    Starting with the axiom that what I am experiencing is actually representative of reality to begin with.
  • michaelsbradley 2y ago
    When I consider your heavens, the work of your fingers, the moon and the stars, which you have set in place, what is mankind that you are mindful of them, human beings that you care for them? You have made them a little lower than the angels and crowned them with glory and honor. You made them rulers over the works of your hands; you put everything under their feet: all flocks and herds, and the animals of the wild, the birds in the sky, and the fish in the sea, all that swim the paths of the seas. – Psalm 8:3-8
    • khazhoux 2y ago
      The answer of "the universe was created by a creator" is no more satisfying. It claims to answer everything, by answering nothing (since "a creator always existed" is axiomatic).
      • FollowingTheDao 2y ago
        > It claims to answer everything, by answering nothing. You missed the wisdom in your own statement.
• gpsx 2y ago
  I have another definition, or at least this is how I think of it. I’m not sure many people would buy into it. In the standard model, the fermions are particles, like the electrons, quarks, neutrinos. Electroweak, strong force, gravity are fields. This means the photon is not a particle, but just a field excitation. I know people can think of fermions as fields, I just think of them as particles.
  • arcbyte 2y ago
    Checkout energywavetheory.com. It's essential the Aether, but really makes you think.
    • jiggawatts 2y ago
      I flipped through some of the content. It's very well presented, but unfortunately it is pseudo-science gibberish.
  • skzv 2y ago
    Aren't you describing quantum field theory (QFT)? Anyway, what exactly is a field besides a mathematical object? What is it made of?
    • gpsx 2y ago
      I did study quantum field theory and I have a hard time viewing a fermion as a continuous field, whereas a gauge field I do view as a continuous field. I view a fermion as a true point particle, kind of like it is in a lattice. The fermion still has a wave function of course. It is very different from the wave function of a gauge field. The wave function of an electric field is a wave function over field configurations. The fermion wave function is a wave function of fermion spins. I don't think this is an unreasonable view, but I am not trying to force it on anyone else.
      • dandragona 2y ago
        I'm still new to learning about these things, but is the viewpoint that a particle is a field excitation sort of the thing about starting with a lattice in the ground state with a field defined on the points of the lattice, then some excitations happen which cause the field to enter a particular "mode". This mode is the particle?
• gigatexal 2y ago
  tangentially: is it consensus at this point that the proton decays -- it just does so on a really large timescale?
  • elashri 2y ago
    No it would be very hard to actually have a consensus on proton decay. If it decays then according to the measurements (or the limits on the lack of the measurement) lifetime of such decay will be more than the universe age (Even without all the puzzle about Hubble constant tension and age of universe measurement disagreements). It was predicted first time by SU(5) theory and many other theories since then but the experiments rules out some of them (including original SU(5)) [1] I would be personally interested in proton decay as it could be indirect indication for magnetic monopoles [2]. [1] https://en.wikipedia.org/wiki/Proton_decay?useskin=vector#Projected_proton_lifetimes https://en.wikipedia.org/wiki/Proton_decay?useskin=vector#Pr... [2] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.52.325 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.52...
    • gigatexal 2y ago
      thank you! -- I meant more that is it consensus that those that know or would need to know think it should/does even if it's not been observed or proven to needfully do so (or disproven, if possible) but I get your point. Why are magnetic monopoles interesting to you? I've seen some articles on them but I can't still wrap my head around how they'd work.
• atemerev 2y ago
  A particle is a node in the universal interaction graph. “Space”, however, is a derivative attribute emerging as the “distance” between particles in the graph; there is no “space”, only metrics. Reality does not exist between measurements/interactions; the outcome is calculated on demand.
  • deleted 2y ago
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  • faceloss 2y ago
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  • scotty79 2y ago
    So basically a tree doesn't fall in the forest if there's no one around to see it? There's no forest and there are not trees. It's all spawned as needed when we go for a hike? Kinda arrogant don't you think?
    • atemerev 2y ago
      A tree interacts with many things, not just human observers. We are not special in any way. This discreteness is only relevant and/or observable when we look at individual particles that rarely interact with anything else.
      • scotty79 2y ago
        So we have no idea what's observable in this generic way and what's not.
• ChrisArchitect 2y ago
  (2020) Some discussion then: https://news.ycombinator.com/item?id=25091742 https://news.ycombinator.com/item?id=25091742
• deleted 2y ago
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• ww520 2y ago
  That's why calling Higgs Boson the God particle is not quite right. It's the Higgs field that gives mass to the other particles, not the Boson. A Higgs Boson is just an excitation of the Higgs field; it doesn't give mass to other particles. In fact it's the Higgs field modifying the other fields causing their excitations (particles) to slow down when passing each other, thus gaining masses.
  • ItCouldBeWorse 2y ago
    So, its all gravity, if you turn the sock inside out? Just taking different colors and shapes?
    • Jabrov 2y ago
      What do you mean? How do you reach that conclusion? I wasn’t aware there was a connection with gravity
    • ww520 2y ago
      It’s more like Higgs field gives mass to other particles whose masses warp spacetime that gives gravity.
    • librasteve 2y ago
      best way to reveal a TOE
  • jophj 2y ago
    it was in fact called the "Goddamn Particle" originally, referring to how difficult it was to detect it. The name was changed later to "God Particle" for publishing reasons. https://en.m.wiktionary.org/wiki/God_particle https://en.m.wiktionary.org/wiki/God_particle
    • bbor 2y ago
      The line between whimsy and intellectual negligence seems blurry, in this case… how many people have been tricked by bad-faith gurus using this? Thanks for sharing, TIL and it’s fascinating.
• Biologist123 2y ago
  I feel a curious mix of excitement and disconcerted to discover humans don’t really understand what matter is. Reading the article, I understood so little of it. And I guess it’s because so much of the language is just words chosen through some sort of consensus to represent an abstract idea itself composed of such words-idea-representations which I’ve never encountered before.
  • gosub100 2y ago
    There are about 16 particles in the standard model. We've only mastered the electron, proton, photon, and have dabbled in using neutrons and neutrinos. Imagine the possibilities if we some day are able to use all the remaining particles?
    • interroboink 2y ago
      For some definition of "mastered" (: If I recall correctly, the we can't really solve the equations for anything more complex than a helium atom (or is it hydrogen?). That's not to say there isn't useful work we can do, numerical approximations, etc. But things do get astoundingly complex very quickly, even with the "mastered" bits.
    • jiggawatts 2y ago
      Muons and positrons are used regularly in industry. Neutrinos have been used to image the inside of the Sun.
  • akira2501 2y ago
    We understand matter perfectly well. Look at the size and scope of the engineering marvels that have been constructed on the surface of this planet and in our low orbit. It's astonishing. What we don't understand is the fundamental structure of that matter or of our Universe. I personally feel that the people ostensibly "in charge" of this effort are a little chagrined at their decades of inability to produce not only a cohesive result but even a reasonable intermediate explanation that they intentionally couch these problems in the most arcane and impenetrable language available to them. In any case, you shouldn't feel discontent for humanity, as we've simply discovered all the easy problems, cleverly worked out all the average problems, and now all we're left with is the intractably hard ones. It's very likely that a different type of effort we haven't engaged in yet will be necessary to make progress.
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• graycat 2y ago
  Issues: (1) With Itself: Consider Young's double slit experiment: So, have plane with two slits and some distance away a parallel plane with detectors. (A) Several times, shoot a photon at the slit. Observe that the detection locations form parallel lines, i.e., fringes. (B) Cover one slit, repeat, and observe that the detection locations from a smooth hill without fringes. So, from (A) we conclude that the something about the photon went through both slits and interacted with itself to form the fringes, the ones we didn't see from (B). Q. Between the two planes, where was the energy? (2) Mass and Charge Set aside (1) with its photons and two planes. Now one at a time shoot electrons, i.e., with not just energy but also mass and charge. And shoot the electrons at a beam splitter, i.e., a plane, partially transparent to the electrons, and at 45 degrees to the path of the electrons. Some electrons pass through the plane with no change in direction and some get deflected 90 degrees. On the paths after the plane, have some very sensitive detectors for mass and charge. These detectors are distant enough that what they do cannot affect the electron, i.e., the electron does not know about the detectors. Q. What do the detectors read? For each of the two paths, whole mass and charge, half, or something else?
  • scotty79 2y ago
    You can't detect without affecting. My idea for resolving this is that electron is never a point-like particle. It's always a cloud, just larger or smaller. When it's detected it gets reshaped to be narrower. Mass, energy, momentum and such are a quantities ascribed to the whole cloud and exchanged only on the moment of interaction. Think about diffraction. Photon or electron that passes through a small hole had it's moment messed up proportionally. It becomes large again. Interesting question is where's the gravity in all of this. There are various ideas how to match quantum uncertainty to shape of space-time.
    • graycat 2y ago
      > You can't detect without affecting. "These detectors are distant enough that what they do cannot affect the electron, i.e., the electron does not know about the detectors." We detect gravitational waves without "affecting". The electron mass and charge send out signals. Have the detectors sufficiently far away that they can't affect the particle yet. Get the detection and then know where the particle was and its mass and charge then. Have the particle reflected by some mirrors and then know the current path of the particle and its mass and charge, all without affecting the particle.
• scotty79 2y ago
  This article contains a very neat description of what is energy, momentum and spin and why they there. Energy is just a quantity that's preserved when shifting through time, momentum is a quantity preserved by shifting through space. And spin is a quantity preserved by rotation in space-time. General relativity treats energy and momentum jointly so I guess basically energy-momentum is a quantity preserved in space-time translations and spin is a quantity preserved in space-time rotations. (in flat space-time, I think?) I guess that's why those Poincare symmetries are rarely mentioned when talking about particles. They seem to come more from sheer geometry of space-time than anything else. Particle physicists are mainly interested in all other symmetries (because they were harder to figure out). It also must be bad feeling that while you are trying pull gravity into your framework, more than half of the symmetries that the objects you spent your career observing obey, come from general relativity not from your framework.
• dang 2y ago
  Discussed at the time: What Is a Particle? - https://news.ycombinator.com/item?id=25085286 https://news.ycombinator.com/item?id=25085286 - Nov 2020 (37 comments)
• causality0 2y ago
  But never has physicists’ conception of a particle changed more than it is changing now. A concerning statement for a four year old article. Has anything in it been superseded?
• deleted 2y ago
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• nyc111 2y ago
  As usual comments here are more informative than the article. But no one mentioned that this is not a physics subject. The question “What is a particle?” belongs to philosophy not to physics. The problem for physicists is that they assume the Newtonian worldview that the world is made of indivisible units of matter called particles. [1] This assumption cannot be questioned. It is a dogma of the profession. But their experiments tell physicists again and again that the world is not made of indivisible units of matter. Physicists can either respect their experiments and accept that the world is not made of indivisible units of matter called particles or choose sophistry and try to fit their dogma into nature by wordplay. Physicists chose the latter and instead of dropping their dogma they keep changing the definition of the word “particle”. It does not matter what you call those indivisible units of matter. Physicists used to call them “particle” then “field”, then “excitation” and many other names that can be used case by case to save their sacred Newtonian dogma. Physicists’ dilemma is that they do business under the professional name of “particle” physicists. If there is no particle their profession would be redundant. Obviously they cannot call themselves “excitations of the field physicists”. So they keep the word particle but keep changing the meaning of it and they blame the public for not understanding physics jargon. My advice to physicists: respect the authority of your own experiments and drop the Newtonian dogma of a material world made of indivisible units of matter. [1] "God in the beginning formed matter in solid, massy, hard, impenetrable movable particles." Isaac Newton, Optics, 1704, Book III, page: 375
• m101 2y ago
  One of the biggest problems of a scientific education is the lack of hubris taught. Science has a very clear box it works remarkably well in, but it far too often strays outside of this box. We should have been told that science is about the prediction and description of things. This is very different to what things actually are. If only scientists didn't believe from the very beginning that they were studying what reality of things are, they wouldn't spend so much time unlearning this later in life.
• hwhwhwhhwhwh 2y ago
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• amai 2y ago
  See also Hobson (2012): There are no particles, there are only fields https://arxiv.org/abs/1204.4616 https://arxiv.org/abs/1204.4616
• gweinberg 2y ago
  For some reason this page makes my monitor flicker. Anyone else have this problem? Anyone know why it happens?
  • amai 2y ago
    Do you have an external monitor connected to your Mac Pro Laptop? If so, disable True Tone and disable auto brightness on all screens. That might help.
  • deleted 2y ago
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• jakey_bakey 2y ago
  > "It has been thought of as many things" This makes me remember the time I looked at a random book at my university library, and it happened to be a physics book from 1905. Which was both fascinating and unintentionally hilarious due to it proudly asserting that we knew most of physics now because we knew about atoms, and assuring the plum pudding model as how atoms worked. n.b. Plum Pudding was the old-school idea that atoms were a positively-charged blob with negative electrons embedded. It was refuted when you measure the radiation scattering patterns off gold foil and discover that, actually, there's an extremely dense nucleus.
  • agumonkey 2y ago
    while I often wonder what part of today's knowledge will appear brutally obsolete for those born in the 2100s
    • simpaticoder 2y ago
      As a physics (and SF) enthusiast, I've come to realize that we've discovered most of the physics that exists, and all of what we can use. This is disappointing for those who yearn for FTL or teleportation, but it's good news when you consider that it creates an impregnable defense against interstellar invasion. Within the limits of modern physics, there remains a great deal to understand and apply, especially in QM because to quote Feynman "there's plenty of room at the bottom". Biology and nanotechnology can still revolutionize human existence. The key problem humans must grapple with an solve, if we are to make it long-term, is how to harness greater and greater power without destroying ourselves. Nuclear destruction has been a very real option for 80 years. Biological weapons could do the job, too. And of course, climate change looms. For many years I agreed with the thinkers that wish for a "backup plan" for humanity; however, I don't think Mars will do it simply because its environment is even harsher than a post-nuclear holocaust Earth. The important reality that THIS is our home, and we must protect her even if it's hard. Yearning for advanced physics to solve all our problems has the unfortunate side-effect of undermining motivation to solve the problems we have now with the tech we have now. It underlies an unfortunate "disposable planet" attitude that we'd be better off without.
• spoonfeeder006 2y ago
  > “What is a particle?” > > “An irreducible representation of the Poincaré group,” a precocious classmate answered. Me: Looks up Poincare group Also me: Oooookay, that makes absolute perfect zero sense to me
  • Koshkin 2y ago
    But - again - that is a mathematical construction, which a physical particle is not.
    • spoonfeeder006 2y ago
      I think I'm getting a glimmer of understanding on this now From what I gather, a set of possible transformations is a group in group theory Physical space is a type of group, i.e. a Poincare group, and is described by the set of all transformations on objects, or something (i.e. motion or lack thereof) An irreducible poincare group is a tinest example of physical space, i.e. a 'particle' So although it has no physical space, yet the irreducible Poincare group is intrinsically (but not practically) capable of those same types of transformations within itself as in the larger Poincare group within itself E.g. a larger object (many particles) can undergo shears and strains, i.e. internal motion. In theory an infinitesimal particle can, it just doesn't have the space to undergo those I'm inferring from this that a subset of physical space is also a Poincare group?
      • griffzhowl 2y ago
        The Poincare group is the set of symmetries of spacetime (in special relativity), not spacetime itself. It characterizes the basic geometry of spacetime, so the dynamics of any physical system must be invariant under the action of this group, e.g. a physical system has the same dynamics as a rotated version of itself (as long as you rotate the whole physical system), and a physical system has the same dynamics as a version of itself with the velocities of all its components boosted uniformly in some direction (this is the principle of relativity). So the important things, like the dynamics, are invariant under the Poincare group, and the things that change are just dependent on the perspective of an observer. Where the irreducible representations come in is in quantum mechanics, where physical systems are described by Hilbert spaces. These are spaces in the abstract mathematical sense of a vector space. They're used in quantum mechanics as a way to mathematically describe the fact that there are multiple possible outcomes of an experiment or interaction. The way this is done is by describing a quantum state as a unit vector in Hilbert space, each possible outcome corresponds to a dimension (a basis vector) in this space, and the probability of each outcome corresponds to the projection of the unit vector onto one of these dimensions. You can picture this as an arrow of unit length with its tail at the origin, and evolution of the state makes the arrow rotate about the origin, consequently changing its projection onto the basis vectors. A representation of a group on a vector space is a way of describing the action of that group on the vectors in the space. Any vector space can be decomposed into subspaces which are invariant under the group action, meaning that if a vector starts off in that subspace, then the action of the group will not move it out of that subspace - these subspaces are the irreducible representations of the group. So the irreducible representations of the Poincare group correspond to the components or properties of a physical system that are invariant under the basic symmetries of spacetime, i.e. that are independent of one's perspective, and in that sense they're considered basic or fundamental.
• dionian 2y ago
  This article is fantastic because it makes the subject so accessible