[HN Gopher] What Is a Particle? (2020)
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What Is a Particle? (2020)
Author : sblank
Score : 77 points
Date : 2024-09-21 19:20 UTC (3 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| AlbertCory wrote:
| 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.
| elashri wrote:
| > 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 wrote:
| > 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.
| deanCommie wrote:
| 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
| danbruc wrote:
| 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 wrote:
| > 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 wrote:
| 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. :-)
| danbruc wrote:
| I have no idea whether or not most physicist think that
| there are actually quantum fields in the universe. The
| Navier-Stokes equations provide a good description of milk
| mixing into my coffee, but should I therefore conclude that
| my coffee mug is filled with density and velocity fields
| and that what coffee really is, is a region in spacetime
| with a nonzero value of the coffee density field?
|
| Quantum fields have gauge symmetries which means that they
| are a redundant description, i.e. any given physical
| situation is represented by an entire equivalence class of
| field configurations which makes me highly suspicious of
| there being real quantum fields. Quantum fields are a nice
| mathematical tool but I do not think we have any good
| reasons to think they are real, but I am not a physicist
| and I am certainly in dangerous half-knowledge territory
| here.
|
| I have been wondering for years whether this might actually
| be a non-issue, could the universe secretly have fixed a
| gauge and just ran with it? Or would this somehow be
| inconsistent?
| bbor wrote:
| 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.
| lisper wrote:
| Richard Feynman gave what I consider to be the best possible
| answer to questions like this:
|
| https://www.youtube.com/watch?v=Q1lL-hXO27Q
| aaa_aaa wrote:
| 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 wrote:
| > he does not have an answer
|
| Well, yeah. That's the whole point.
| divs1210 wrote:
| 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.
| mensetmanusman wrote:
| https://youtu.be/j2oSyAfPzWg?si=bwM2NAsORzkqLQLk
|
| Fun fields discussion on what particles are...
| kayo_20211030 wrote:
| 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.
| prng2021 wrote:
| 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 wrote:
| 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 wrote:
| Do expand. What happened in 2023?
| sfink wrote:
| 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....)
| kayo_20211030 wrote:
| Did you take the time to read the original piece? Even the
| smart people can't agree.
|
| What gives you the faith that a "particle" is not a human
| construct? What on earth does "fundamental" even mean except
| being the bottom turtle we can see on the particular mountain
| of turtles at which we're looking.
|
| "Countless"(?) people around the world are not researching
| particles. They're doing particle physics as they understand
| "particles". That's how it should be and particles _are_
| whatever they say they are. In that field, no measure means
| no reality. *Unless*, of course, you have faith in some
| platonic reality.
|
| Positive materialists will disagree.
| prng2021 wrote:
| When you say particles are whatever we say they are, I
| assume you believe particles are subjective. I'm saying
| particles are objective, like a "wavelength" as opposed to
| subjective, like "morals".
|
| If you are saying even objective things are whatever we say
| they are, then this is a useless discussion. Obviously
| every word is defined with other words and all words are
| human creations. So yea in that sense, literally everything
| we know of is whatever we say it is. That's a pointless
| statement to make in response to this article or really
| ever.
| woopsn wrote:
| What can we see? Vapor trails, patterns burned into a plate,
| etc. The evidence of some "thing" slowing down, perhaps, but
| really the environment that slowed it down necessarily
| changing irreversibly. Irreversible effects cannot be
| arbitrarily small (apparently). We never see a particle, only
| effects such as these -- if we did see anything else, well,
| we couldn't possibly remember. Particles are an attempt to
| explain/theorize evidence that is fundamentally
| observational.
| ithkuil wrote:
| "Things are named before they are understood." -- Matt
| Strassler
| fragmede wrote:
| discovery vs invention is a question in mathematics as well.
| trying to say they're invented isn't clever, it's just a trick
| of language, like how gravity is merely a theory. particles are
| theorized to exist via theoretical physics and math, and then
| tested for experimentally. or as the saying goes, all models
| are wrong, some are useful.
| kayo_20211030 wrote:
| I can't find the reference at the moment. But, I _think_ it
| was about the "creation" of the quark. (I'll find it
| eventually). Either way, a search for reality, no matter how
| far we've progressed thus far, is either a search for a
| platonic reality, or an experimental reality. The former is
| "discovery" and the latter is "invention". It really doesn't
| matter. I don't think, right now, we're quite smart enough to
| pry into the mind of the universe, so we'll keep "inventing"
| things until we actually approach "discovery" asymptotically.
| Maybe we'll get there, but we've never been closer :-)
| geye1234 wrote:
| It's both discovery and experiment (but not invention).
| Forms are real, but not in the way Plato thought. He
| thought they existed in some empyrean realm. In reality,
| they exist in objects themselves. We discover what a
| thing's form is by experimenting with (or on) it. Aristotle
| was largely right.
|
| The big philosophical problem with much of this is that
| people assume that the smallest things are the most
| fundamental. So people think that _stuff_ , whatever that
| stuff is, is fundamentally made up of much smaller stuff,
| and that stuff is fundamentally made of yet smaller stuff,
| and so the smaller you get, the more fundamental you get.
| And so (they think) if you want to work out what is really
| going on at any layer of reality, you need to figure out
| what the smallest possible things are.
|
| Yet this is ultimately a philosophical posit -- it's not
| empirically-informed. There's no good reason for thinking
| it.
|
| To be clear, none of this is about physicists doing
| physics. It's about the philosophy that many people bring
| into, and therefore take away from, these kinds of
| discussions.
| khazhoux wrote:
| 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 wrote:
| 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 wrote:
| Starting with the axiom that what I am experiencing is actually
| representative of reality to begin with.
| michaelsbradley wrote:
| 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
| api wrote:
| The impression this article and many other things like it
| leaves me with is that we are struggling to get language and an
| abstractions out of our way.
|
| We have to use them to talk about things and work with them,
| but they all "leak."
| gpsx wrote:
| 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 wrote:
| Checkout energywavetheory.com. It's essential the Aether, but
| really makes you think.
| skzv wrote:
| Aren't you describing quantum field theory (QFT)?
|
| Anyway, what exactly _is_ a field besides a mathematical
| object? What is it made of?
| gigatexal wrote:
| tangentially: is it consensus at this point that the proton
| decays -- it just does so on a really large timescale?
| elashri wrote:
| 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#Pr...
|
| [2]
| https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.52...
| gigatexal wrote:
| 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 wrote:
| 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.
| ChrisArchitect wrote:
| (2020)
|
| Some discussion then:
| https://news.ycombinator.com/item?id=25091742
| ww520 wrote:
| 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 wrote:
| So, its all gravity, if you turn the sock inside out? Just
| taking different colors and shapes?
| Jabrov wrote:
| What do you mean? How do you reach that conclusion? I wasn't
| aware there was a connection with gravity
| jophj wrote:
| 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
| bbor wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| akira2501 wrote:
| 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.
| interroboink wrote:
| I think there's a useful distinction to be made between "we
| understand it" and "we can make use of it." Certainly the
| latter is true, as you describe in your examples. I don't
| know that it implies the former, though.
|
| I mean heck, even something as mundane as concrete is still
| the subject of active research as to the chemical reactions
| and complexities involved.
|
| I guess it's more a spectrum of understanding than a yes/no
| situation.
|
| For myself, I find it exciting to keep discovering how
| _little_ we understand, despite our abilities. We seem to be
| barely a step removed from alchemy, from some points of view.
| akira2501 wrote:
| I think the distinction is more "we understand it" and "we
| can explain it." Understanding doesn't generally imply
| totality of comprehension.
|
| Going the other way, you most likely cannot explain why
| your body or your brain works, yet, here we are, using and
| understanding them just fine.
|
| Which leads to what I was trying to get at. Perhaps our
| tentative understandings and our means of receiving them
| are what gets in the way of deeper comprehension.
| tambourine_man wrote:
| > yet, here we are, using and understanding them just
| fine.
|
| I think we're failing miserably precisely because we
| don't.
| akira2501 wrote:
| I personally don't think perfection is actually
| achievable, so I'm completely unwilling to accept your
| definition of our present state as "failing miserably."
| That's a rather miserable point of view and I prefer to
| have and encourage hope.
| mensetmanusman wrote:
| We understand _low_ resolution matter.
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