10 ms·

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 thi

• 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
      [dead]
  • 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!