[HN Gopher] What Is a Particle? (2020)
___________________________________________________________________
What Is a Particle? (2020)
Author : sblank
Score : 173 points
Date : 2024-09-21 19:20 UTC (1 days 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.
| hughesjj wrote:
| 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.
| Traubenfuchs wrote:
| So we have the three spatial dimensions, + time as 4.
| dimensions and at any of those 4-part coordinates there are
| additional properties like mass/spin/etc., some of much
| always come together or at least strongely correlate, and
| those values not being zero means there is a particle there
| and every value corresponds to a certain ,,field" and it not
| being zero means the field is excited?
| 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. :-)
| binary132 wrote:
| Joke: "birds aren't real"
|
| Woke: "electrons aren't real"
| 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?
| pgotibojgg wrote:
| Do you think photons are real?
|
| Because according to QFT they only exist because of the
| gauge symmetries. Photons are the solution to the
| redundant symmetries. Remove those redundant symmetries
| and you also need to remove the photons.
|
| Universe "fixing a gauge" means no photons and no
| electromagnetic field, because the electromagnetic field
| IS the gauge symmetry.
| binary132 wrote:
| I think this is why "shut up and calculate" is popular
| User23 wrote:
| Or as Newton more eloquently put it _hypothesis non
| fingo_.
| raattgift wrote:
| > I am not a physicist and I am certainly in dangerous
| half-knowledge territory here.
|
| Gauging is just dealing with the fact that there is no
| absolute universal fixed value against which can compare
| a value at some point in a field; but we still want to
| consider values at one or more points in the field.
|
| Let's do a really simple _static_ model of the
| atmosphere, with a single scalar value: air pressure at
| each point. Let 's use a simple device: an air pressure
| gauge which reports some fraction of a pressure measured
| when we push a "calibrate now" button. We'll call this a
| calibrated barometer. We can then recover the full air
| pressure field by measuring at every point in space (not
| space-time, the staticity means there is no time-
| dependence to the measurements; we can do them in any
| order and not have to worry about time of day or season).
|
| Where do we push the "calibrate now" button? At some
| point on the surface? At mean sea level? At the top of
| the atmosphere? The choice of any of these will provide
| different readings on our gauge (i.e., it reports some
| fraction of the calibrated pressure, will differ when the
| calibration point is 101 kPa vs some fraction of the
| value actually measured at a specific point on the
| surface). But with a bit of care in choices of units,
| whatever we use as the calibration point, the difference
| between two different points in space will be the same.
|
| A good choice of gauge lets use our calibrated barometer
| as an altimeter. In aviation, aircraft pressure
| altimeters have a calibration knob, which is used to
| recalibrate during different stages of a flight. Common
| calibration points are: QFE, field elevation, which lets
| one know how far above an airfield one is if separated
| only vertically from it, at the cost of being unable to
| simply compare the vertical separation between two
| aircraft above two different airfields; SPS (the pressure
| of the standard atmospheric pressure, 1013.25 hPa) is a
| global setting useful for quickly determining the
| vertical separation between two reasonably nearby
| aircraft, at the cost of not being able to quickly
| determine height above terrain, or even the height above
| mean sea level; QNH is another local setting which lets
| one compare how high above mean sea level the aircraft
| is, at the cost of needing to know the height above mean
| sea level of local terrain, and not being able to easily
| compare vertical distances with aircraft using one of the
| other two calibrations.
|
| All three settings are "redundant descriptions" of the
| aviator's atmosphere. They describe the same column of
| air, but each makes it easier to pinpoint different
| hazards scattered through that column (the ground, other
| aircraft in level flight, the aircraft's operating
| ceiling).
|
| We could complicate the atmosphere by introducing time
| dependency (at night in cold dry winter a QNH altitude
| will be fewer RADAR-measured metres above the same patch
| of ground), and atmospheric interactions (atmospheric
| waves, Bernouilli effects from winds). Each complication
| can be made to vanish via a careful choice of gauge,
| although it gets harder and harder to write down such a
| gauge as complications increase. (As a result, in
| aviation they allow for a certain amount of measurement
| error and safety margin, and comparisons with different
| means of measuring altitude like radio altimeters and
| satellite multilateration.)
|
| In a quantum field theory (QFT), one might choose a gauge
| in which some particles vanish. A sibling comment pointed
| out that very commonly one wants to choose a gauge in
| which gauge bosons like photons don't need to be counted,
| rather than a gauge in which there is a sea of an
| enormous number of low-energy gauge bosons. Choosing the
| gauge does not eliminate the low-energy gauge bosons; in
| general QFT field values are time-dependent (and usually
| gauged to admit only "relevant" fluctuations). Low-energy
| fluctuations can be _boosted_ into "real particles" by
| relativistic observers, and strongly accelerated
| observers can count more particles than a weakly
| accelerated one. Therefore the choice of a gauge for one
| observer might make calculations for another observer
| more difficult.
|
| In QED there are several well-known and frequently-used
| gauges roughly analogous to SPS/QFE/QNH, and one often
| chooses one of them for convenience. Each of tehse gauges
| breaks the gauge freedom.
|
| Gauge freedom means simply an uncalibrated system waiting
| to be calibrated. A common illustration of this is to
| choose a non-rotating sphere and setting down
| latitude/longitude. A less-gauge-symmetrical rotating
| sphere naturally picks out latitudes (the poles and the
| equator, notably), but there's still gauge freedom in
| longitude that we can fix by choosing a prime meridian,
| and gauge freedom in picking out one of the primary
| compass directions. These choices do not change the
| sphere or its rotation (or non-rotation), and of course
| one can choose any other set of coordinates one wants.
|
| Once one has fixed the gauge on the sphere, though, one
| can more easily compare positions on the surface: is
| point A in the northern hemisphere, is point B in the
| eastern hemisphere? Just asking if point B is North-East
| of point A requires us to at least choose a north pole --
| that can be one of two places on a rotating sphere, and
| it can be anywhere at all on a non-rotating one. The
| "right hand rule" is the conventional "gauge" for
| rotating astronomical bodies: anticlockwise rotation
| around the north pole (right hand: thumb up, fingers
| curled). But we don't _have_ to use that convention as
| our "gauge". (We also have a problem for a truly non-
| rotating spherical object: where's the north pole? We
| might solve that by using an imagnariy axis parallel to
| the axis of a relevant body like the local star or the
| parent galaxy).
|
| Finally, in many gauge theories there are gauge invariant
| quantities. On our spheres the geodesic intervals between
| two points are gauge invariant. The gauge tells us
| something about _direction_. In practice, fixing a gauge
| also usually involves choosing (and scaling) units: on
| our geodesic which might run south-east to north-west
| (gauge problem), the length might be measured in metres
| or light seconds (units problem) or kilometres and light-
| years (scaling problem). We might want to label different
| points along the geodesic in latitude /longitude
| (coordinate problem) rather than adapted Cartesian
| sphere-centred/sphere-fixed ("ECEF" on Earth) or
| tangential ("Local East-North[-Up]", "LENU") ones.
| 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.
| griffzhowl wrote:
| So what is a field?
| librasteve wrote:
| a thing that can have particle-like excitations
| FollowingTheDao wrote:
| A probability.
| bbor wrote:
| 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 wrote:
| No... a field is mathematical representation. The
| universe is most definitely NOT made of fields.
| dgoodell wrote:
| Are you saying that the universe cannot be represented by
| mathematics?
|
| I imagine you could use that argument to shoot down
| pretty much any explanation.
| lottin wrote:
| I'm saying that a mathematical representation of a
| physical phenomenon isn't the physical phenomenon.
| bbor wrote:
| Ok fair: they're _things_ that right now are best
| understood using the term Field. I don 't understand what
| kind of answer you're hoping for that would be better
| than this -- what kind of answer to "what is a particle"
| wouldn't be describable by mathematics?
|
| By saying "the universe is fields", I'm saying "it's
| distributions of energy across spacetime". That's
| seemingly a consensus. Why demand that that energy must
| also form into strings or even tinier spheres or spheres
| in an alternate dimension or something? We have described
| fields in detail, I say _Mission Accomplished_
| lottin wrote:
| Let's say we describe a particle as being an excitation
| of a field. Can't we describe _any_ physical phenomenon
| in the same way? For example, describe a football as an
| excitation of the football field. I think we all agree
| that this description does a terrible job of actually
| describing a football. In fact, I don 't think it can be
| called a description at all. Likewise, I find describing
| a particle as an excitation of a field to be equally
| unsatisfactory.
| im3w1l wrote:
| A function that takes a point in space as input. The output
| can be various things, e.g. a scalar field gives a
| (possibly complex) number as output.
| contravariant wrote:
| That's a bit too simple, not all functions work well as
| fields (differentiability is quite desirable) and you
| have no way to interact with the fields that way.
|
| I think principal bundles come closest to what physicists
| call fields. Though I'm holding open the option that
| _really_ the things in most equations are more like
| elements of the corresponding Lie-algebra.
| 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.
| alok-g wrote:
| 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 wrote:
| He could simply say so.
| hydrogen7800 wrote:
| 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 wrote:
| I see what you did there.
| AlbertCory wrote:
| I just watched it. I don't think he's edgy.
|
| You can't explain it in terms of anything else, which was
| sorta my original point. Maybe he could have been more
| touchy-feely in his answer, but that wasn't his nature.
| johndhi wrote:
| Hmm I think he's merely explaining what physics is and is
| not. Physics isn't really answering "why" questions, at
| least not ones with infinite scope.
| vertnerd wrote:
| Feynman grapples with the question the same way we would
| grapple with a question from a child: "why is the sky
| blue?" If you drill down into the explanation, you
| ultimately reach a statement that everyone just accepts as
| true, or you simply end with, "no one knows".
| mewpmewp2 wrote:
| The way Feynman answered it looked extremely
| condescending and anti curiousity. Being pedantic for no
| reason. When answering you should try to guesstimate what
| the asker who is not an expert in your field is looking
| for and then start explanation relative from there.
|
| At certain point, yes, you do have to say that either you
| don't know or humans haven't figured it out yet.
| kstrauser wrote:
| Having read some of his lectures, and his autobiography,
| he was anything but anti-curiosity in him or in others.
| Watch that through the lens of someone who valued nothing
| more than asking questions and it might come across
| differently.
| passion__desire wrote:
| In similar vein, the following question is very apt. Please
| read the question because it captures all of our intuition
| when we try to understand something.
|
| https://physics.stackexchange.com/questions/46573/what-
| are-t...
|
| What are strings made of?
|
| One answer is that it is only meaningful to answer this
| question if the answer has physical consequences. Popularly
| speaking, string theory is supposed to be the innermost
| Russian doll of modern physics, and there are no more dolls
| inside that we can explain it in terms. However, we may be
| able to find equivalent formulations.
| 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.
| binary132 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| One way of viewing it is that math is games. Not in the
| winner sense, but in the activities with rules sense.
| Addition is a game.
|
| Some games make you better at other activities. Like,
| playing chess could make you better at logistics because
| you're practicing planning and managing losses.
|
| Some games match some real world situations so tightly
| that we can go through them step by step and solve the
| real world situation in the game. You can play addition
| to figure out two apples and two more makes four apples.
|
| Whether the game is "real" or not is immaterial. It just
| needs to be internally consistent and matched to the
| right thing.
|
| There's also the idea that math is another world that we
| can visit, similar to the dream world. But that's a whole
| other thing.
| fasa99 wrote:
| The idea that it's an abstraction is 100% accurate. That
| physics is a discrete set of fields with field rules and
| interaction rules, and what we observe is a scaffold on
| top of that. It's like okay, let's say the math is right
| and we have a set of fields, what are they and where are
| they from, how do we manipulate them. Then the
| physicists, often driven by ego, is want for an
| explanation and points to vibrating strings and such, and
| finally they knock on the door of the empiric physicist
| and say "can you do an experiment to show that I'm right"
| "sure, build a machine the size of the universe and I
| could test that" and that's the state of physics the last
| gorillion years
|
| https://www.youtube.com/watch?v=FYJ1dbyDcrI
| jerf wrote:
| The Universe May Do As It Damned Well Pleases.
|
| Maybe it is "made of fields", maybe it isn't, but "I
| think that's nonsense", which is just a gussied up way of
| saying "my intuition rejects that", is not a valid
| judgment method. The universe does not check with our
| intuition before doing what it Damned Well Pleases.
| lottin wrote:
| So you think the universe might be made of, say,
| subordinate clauses?
| jerf wrote:
| Whether or is or it isn't, it does it without consulting
| you or me or our intuitions.
|
| I assume you meant that as an obvious absurdity, but if
| you were going for that you probably should have avoided
| the concept of "language", which can be Turing Complete.
| Still, the main point is, whatever it is, it is, and it
| isn't asking us for permission to be what it is.
| lottin wrote:
| My point is that physical reality cannot be made of
| something that doesn't exist physically, such as
| mathematical objects, abstract concepts or more generally
| ideas of any kind. Do you not agree that this must be
| true?
| Koshkin wrote:
| It is true, but also kind of trivial. More subtly, one
| can say that we tend to call what is real using the same
| words that we use for mathematical objects that model
| them.
| antonvs wrote:
| If you don't invest the statement "the universe is made
| of fields" with more meaning than necessary, then it
| makes more sense.
|
| A quantum field is just a mathematical construct that
| models an aspect of what can happen at every point in
| spacetime. The fields follow rules for how they interact,
| and fluctuations in the fields and interactions between
| them, according to their respective rules, provide a good
| model for the universe we observe.
|
| If you consider this purely mathematically, it's hard to
| argue with. The models in question make very accurate
| predictions, can correctly model the vast majority of
| observations we know how to make, and don't predict many
| things that we don't observe. In other words, all the
| evidence is that it's a very good model - a very good fit
| for the universe we observe.
|
| From this perspective, one way to interpret the statement
| that "the universe is made of fields" is simply that the
| universe conforms to the quantum field model. Again, this
| claim is hard to argue with - it seems to me like a true
| statement, and there's a lot of evidence for it.
|
| Hawking & Mlodinow explored this in their description of
| what they called "model-dependent realism" - see:
| https://en.wikipedia.org/wiki/Model-dependent_realism
|
| If perspectives like these don't satisfy you, and you
| want to try to develop an understanding beyond
| mathematical models, then you have a tough problem to
| solve: how to go beyond the models that we know how to
| construct, to something that somehow gives you some sort
| of more fundamental insight. But what would that even
| look like? How would you test it? What would make this
| approach more true than existing theories?
|
| In short, an answer that satisfies the criteria that you
| want it to satisfy may simply not be possible.
| Koshkin wrote:
| "It's very frustrating. The idea that Earth revolves
| around the Sun is nonsensical. I don't understand why so
| many astronomers keep saying that."
| jiggawatts wrote:
| Spin is easy as long as you avoid trying to draw a direct
| analogy with ordinary rotation.
|
| It's just the statement that the object spinning is attached
| to its surroundings in a smooth and continuous fashion. Less
| rigid object, more a patch of space-time fabric spinning.
|
| There's a video here:
| https://youtu.be/LLw3BaliDUQ?feature=shared
| im3w1l wrote:
| It's worth keeping in mind that we don't yet have the sought-
| after Theory of Everything. We have a bunch of theories that
| mostly work in their domain of validity. These field theories
| are supposedly very accurate we don't actually know if they
| are the final word.
| mensetmanusman wrote:
| https://youtu.be/j2oSyAfPzWg?si=bwM2NAsORzkqLQLk
|
| Fun fields discussion on what particles are...
| yahalo wrote:
| What a trip, the guest speaker was clearly a pseudoscientist,
| talking about "evolution fields" and "mind fields" and
| equating fields to souls.
| mensetmanusman wrote:
| 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 wrote:
| 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 wrote:
| 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.
| librasteve wrote:
| this
| heresie-dabord wrote:
| Thank you for this post. Given the limitations of human
| understanding and experience, one could safely use one
| metaphor or another for casual description. But at a deeper
| level of understanding, we do understand that our common
| experience does not apply, and that human language is too
| imprecise.
| __MatrixMan__ wrote:
| 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 wrote:
| 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.
| ziofill wrote:
| 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 wrote:
| 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.
| ziofill wrote:
| You are exactly right at the end when you say that
| particles are what makes a detector go click. Let me try to
| clarify further. The "particleness" is not about
| localization, but about energy quantization. In fact, a
| single photon can be very non-localized, because spatial
| position is a different Hilbert space and it can be
| entirely independent of the energy. So the packets you are
| referring to are particles only if in their energy Hilbert
| space they correspond to a well-defined photon numbers, and
| that's why the analogy with classical particles only goes
| so far. To add to the confusion, one can speak of packets
| localized in phase space (e.g. coherent states, like the
| light produced by a laser) and packets localized in
| physical space like a short pulse, and these refer to
| different Hilbert spaces.
| evanb wrote:
| Also a physicist.
|
| It's not quite right to call basis vectors particles, even in
| a free field theory. The particles correspond better to the
| creation / ladder operators that take you from one
| Hamiltonian eigenstate to another.
|
| In a perturbative interacting case, people still think of
| particles as these same ladder operators, but they don't
| connect eigenstates so simply (the interactions generically
| mix all the states with the same quantum numbers).
|
| In a strongly interacting case the story is even more subtle,
| because composite operators may be closer to the ladder
| operators between the asymptotic states, even though they're
| built of other... particles? Language isn't great in this
| instance.
| ziofill wrote:
| Yeah it's hard to use everyday language to exactly describe
| these things... And even more difficult to decide where to
| draw the line where some hand waving is acceptable.
| csomar wrote:
| 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 wrote:
| 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)
| 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.
| kayo_20211030 wrote:
| I was saying that I don't know what a particle is, and
| neither does anyone else, but subjective isn't quite the
| correct word.
|
| What I am sayings is that there are _many_ useful
| interpretations of what a particle "is" that allows
| science to progress. The theoreticians and the
| experimentalists use, sometimes even form, those
| interpretations to help them along in their work. I'm
| saying that they yet remain interpretations, even
| analogies; and it really doesn't matter whether those
| folks believe in an objective reality or not, good work
| still gets done. Maybe it's subjective in that sense, but
| a particle is whatever they say it is; and _nothing_ more
| can be said with certainty unless you dive into
| philosophy.
|
| You can measure a perturbation in a field, or a track in
| a bubble chamber, and call it a particle. Then you can
| work backwards to an "objective" representation, and a
| particle still becomes whatever you say it is. It's still
| scientific, consistent, mathematically rigorous, and in
| line with theory and observation, but it remains a human
| construct. You can't escape that. Ultimately, one is free
| to believe that there is some fundamental thing; and,
| maybe there is and maybe there isn't.
|
| > literally everything we know of is whatever we say it
| is
|
| Of course "literally everything we know of is whatever we
| say it is". That, precisely, is my point. It most
| certainly _does not_ mean that we can just state anything
| as true unless it is sensible, consistent, observable and
| verifiable; and expect not to be challenged.
| prng2021 wrote:
| Is the first law of thermodynamics whatever we say it is?
| If that's how you want to phrase it, then again, this is
| a useless discussion. All you're really saying is that
| the literal English words and sentences we use to define
| something are human constructs. That's so obviously true.
| 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
| heresie-dabord wrote:
| Further: Things are named, then the linguistic burden
| actually comes to limit understanding.
| 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.
| kayo_20211030 wrote:
| I found the reference. It was an interview with Freeman
| Dyson where he said "quarks were invented", and I don't
| think it's a slip of the tongue.
|
| It's at 3:17 in this video of an interview with him
| https://www.youtube.com/watch?v=hV41QEKiMlM
|
| It's representative of a view that there's a thing (a
| particle) that explains another thing (a force) that was
| consistent with both theory and experiment. Thus, a quark
| could be a particle, and it was whatever the
| experimentalists and theorists said it was, however it
| was measured or contemplated.
|
| For a deeper meaning it becomes an exercise in
| hermeneutics i.e what does it mean when we say
| "particle"? That was the point of the original piece -
| there is no uncontested view of a particle's form, should
| one even exist. Each field, in order to advance, finds it
| useful to interpret it, or think about it, in different
| ways.
| 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
| khazhoux wrote:
| 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 wrote:
| > It claims to answer everything, by answering nothing.
|
| You missed the wisdom in your own statement.
| 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."
| scotty79 wrote:
| It's just a puzzle and should be taken as such.
| khazhoux wrote:
| The universe is a puzzle?
| scotty79 wrote:
| If you try to understand things about it, yes.
| UncleSlacky wrote:
| As someone once said, "There is no requirement on the
| Universe to make sense".
| disambiguation wrote:
| 1.1 INTRODUCTION: THERMODYNAMICS AND STATISTICAL MECHANICS OF
| THE PERFECT GAS Ludwig Boltzmann, who spent much
| of his life studying statistical mechanics, died in 1906, by
| his own hand. Paul Ehrenfest, carrying on the work, died
| similarly in 1933. Now it is our turn to study statistical
| mechanics.
| 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.
| jiggawatts wrote:
| I flipped through some of the content. It's very well
| presented, but unfortunately it is pseudo-science gibberish.
| 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?
| gpsx wrote:
| 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 wrote:
| 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 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.
| scotty79 wrote:
| 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 wrote:
| 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 wrote:
| So we have no idea what's observable in this generic way
| and what's not.
| 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
| ww520 wrote:
| It's more like Higgs field gives mass to other particles
| whose masses warp spacetime that gives gravity.
| librasteve wrote:
| best way to reveal a TOE
| 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.
| scotty79 wrote:
| Actually it doesn't seem to be that simple. Higgs Boson seems
| to contribute mainly to masses of leptons (mostly electrons)
| and bosons W and Z. And that influence goes to zero at high
| energies of the measures system making W and Z weightless and
| merging electrostatic and weak interactions into a singular
| electroweak interaction.
|
| Quarks get most of their mass from QCD with very minor
| contribution from Higgs Boson. And nobody has any idea where
| the mass of neutrinos comes from.
|
| It also has no influence on photons and gluons.
|
| Higgs seems to be very peculiar and not very universal
| mechanism. I wonder if one of the potential future approaches
| won't do away with Highs Boson (together with virtual
| particles) as artifacts of specific math approach and
| interpretation without any physical manifestation.
|
| Higgs was detected, sure, but it was detected through an
| interpretation of the data through the best available
| mathematical model which some postulate might contain some
| purely mathematical constructions along the way to the ultimate
| real world result.
| 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.
| jiggawatts wrote:
| Muons and positrons are used regularly in industry. Neutrinos
| have been used to image the inside of the Sun.
| 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.
| graycat wrote:
| 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 wrote:
| 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 wrote:
| > 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 wrote:
| > The electron mass and charge send out signals.
|
| This affects them.
| graycat wrote:
| So LIGO detects a gravitational wave. Optical telescope
| data indicates that the wave was generated 10 billion
| light years away from two neutron stars. So, then, LIGO
| today affected the two neutron stars 10 billion years
| ago? Affected them today?
| oezi wrote:
| Absolutely. But this not a causal effect, but it
| collapses the probabilities of what has occurred.
| evanb wrote:
| You're very close to understanding to quantum eraser experiment
| / the even more upsetting delayed-choice quantum eraser.
|
| Even though it _sounds_ as though your arguments are gotchas
| that prove quantum mechanics to be nonsense, it turns out the
| world really is that way.
|
| https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser
| graycat wrote:
| Gee, I'm not the first to make this mistake about quantum
| mechanics!
| scotty79 wrote:
| 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 wrote:
| Discussed at the time:
|
| _What Is a Particle?_ -
| https://news.ycombinator.com/item?id=25085286 - Nov 2020 (37
| comments)
| causality0 wrote:
| _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?
| nyc111 wrote:
| 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 wrote:
| 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.
| amai wrote:
| See also
|
| Hobson (2012): There are no particles, there are only fields
|
| https://arxiv.org/abs/1204.4616
| gweinberg wrote:
| For some reason this page makes my monitor flicker. Anyone else
| have this problem? Anyone know why it happens?
| amai wrote:
| 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.
| jakey_bakey wrote:
| > "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 wrote:
| while I often wonder what part of today's knowledge will appear
| brutally obsolete for those born in the 2100s
| spoonfeeder006 wrote:
| > "What is a particle?" > > "An irreducible representation of the
| Poincare group," a precocious classmate answered.
|
| Me: Looks up Poincare group
|
| Also me: Oooookay, that makes absolute perfect zero sense to me
| Koshkin wrote:
| But - again - that is a mathematical construction, which a
| physical particle is not.
| spoonfeeder006 wrote:
| 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?
| spoonfeeder006 wrote:
| Yes, mathematical constructions are merely a model of reality
|
| It is interesting to note that (correct me if I'm wrong)
| perhaps our mathematical constructs are based on a classical
| intuition and perception of the universe?
|
| And here we are trying to fit that classical intuition into
| the quantum realm
|
| Perhaps that can be related to why shit gets complicated with
| particle physics?
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