6 ms·

Can wave-particle duality be considered as part of the riddle?

jonquark 5y ago
Not really in the same way. The Standard Model is built out of quantum field theories that take as a given our experiment results that matter on quantum scales is unlike the "large scale" matter we see around us. The problems described in the articles are unexpected results that we see in our experiments compared to the Standard Model, "weird/nonintuitive" aspects of modern particle physics would be a separate article.
mikhailfranco 5y ago
No, it's quite clear in QFT that elementary entities: - travel as unitary time-reversible non-local waves (propagate, interfere, entangle) - interact as non-unitary time-irreversible local particle events (position, time, exchange, create, destroy) Your interpretation of quantum mechanics will determine how you imagine the two views connect (Born Law, Many Worlds, ...)
- ajkjk 5y ago
  I don't think it's correct to say that they interact as particle events, because off-shell interactions are a thing, and interacting strictly as particles would prohibit that, no?
casparvitch 5y ago
No, physicists are pretty comfortable with that one. It isn't immediately intuitive, but the models we have are powerful and predictive. There is of course a somewhat open question as to the interpretation of quantum mechanics. That question is almost metaphysics, whereas the problems quoted in the article are more holes in our present theory.
- hdjjhhvvhga 5y ago
  Well, they're comfortable because the phenomenon is well-studied, we have very good models and can with good accuracy predict what will happen. What we don't know is why exactly it behaves in this way.
  - andrewgleave 5y ago
    One explanation is the "Many-Worlds" interpretation of quantum mechanics: https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation
  - khafra 5y ago
    The word "why" (and other references to causation) don't work in a normal way when you're talking about fundamental physics, because fundamental physics is the lowest-level model within which causation takes place. To ask "why" some part of the standard model is the way it is, you either invoke some rubric for comparing models, like Occam's Razor; or you indulge in metaphysics and speculate on the nature of whomever is running the Simulation. Either of these is a different meaning than the "why" of "why do rockets work in space."
    - hdjjhhvvhga 5y ago
      Well, you made quiet a few assumptions here. We don't yet know how much fundamental quarks are and what (if anything) hides in the subquark level. Given the lack of adequate instruments, our minds and unconventional approaches are our most powerful tools at this point. For example, we generally consider the space between particles as void. We can't see anything, we can't detect anything, so we assume there's nothing there. But for what it's worth, there could be trillions of unknown particles that don't interact with matter. So why would it matter, you ask? Because it's not impossible that under certain conditions some of these might cluster into matter or interact with it in unobvious ways. The existence of dark matter and energy (or the related phenomena) indicates this is not impossible. But yes, I see your point. However, I hope we get deeper into understanding this phenomenon before I die. Who knows, maybe it's because of some yet-undiscovered aspect of photons, and metaphysical speculation is not necessary?
- DangitBobby 5y ago
  I thought the most surprising thing about wave/particle duality is that the act of observation itself is what causes the waveform of particles to collapse. Do we know of a mechanism for that? Are we not still surprised that you change the outcome of events by changing where you look?
  - FeepingCreature 5y ago
    As I understand it, collapse is an artifact of the necessity to derive classical results from an experiment. You can think of it as "at a certain scale, calculating this as a quantum system as opposed to classical is no longer worth it." But it's of course still a quantum system, because everything is quantum all the time.
    - DangitBobby 5y ago
      I don't think so. The double-slit experiment demonstrates light acting as a wave in some circumstances and as individual photons in others [1]. > the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate.[5][6] The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles.[5][7] However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen.[8] Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave).[9][10][11][12][13] However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. These results demonstrate the principle of wave–particle duality.[14][15] This is the part I'm talking about, mainly. > However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. Once they are measured, you know where they are and they stop acting like a wave. 1. https://en.m.wikipedia.org/wiki/Double-slit_experiment https://en.m.wikipedia.org/wiki/Double-slit_experiment
immmmmm 5y ago
no the SM is a quantum field theory: particles are excitations of quantum fields, so wave-particle duality is implicit. these fields, at the classical level are function that take a space time coordinate as an argument (space time filling) and typically yields a vector in some vector space (except the higgs field which is a scalar). this vector space in turn is a representation of some symmetry group. the symmetry group of SM is U(1)xSU(2)xSU(3).
mabbo 5y ago
Many years ago, a friend (who is far smarter than I am) said something to me that made wave-particle duality click: "It's not that it's sometimes a particle and sometimes a wave. It's that very small things have a bunch of properties: some are shared with waves, and some are shared with small solid objects." We're duck-typing what we see and going "aha! It's a particle! No wait, now it's a wave!" but the class simply has both sets of methods on it and does not care how we classify it.
- Angostura 5y ago
  That doesn't really help me understand how a single 'thing' interferes with itself when travelling through a double slit, unfortunately.
  - danielheath 5y ago
    I always struggled with that too - I found this Veritasium video helpful https://www.youtube.com/watch?v=WIyTZDHuarQ&ab_channel=Veritasium https://www.youtube.com/watch?v=WIyTZDHuarQ&ab_channel=Verit...
    - __s 5y ago
      Never heard of this, looked up whether there was some gap in the theory the video failed to mention, found a discussion on why this model isn't more pervasive: https://physics.stackexchange.com/questions/341400/why-would-pilot-wave-be-wrong https://physics.stackexchange.com/questions/341400/why-would... & one comment which specifically separates pilot waves from the bouncing droplet demo https://old.reddit.com/r/quantum/comments/7crdz6/whats_wrong_with_pilot_wave_theory/dpuw6h5/ https://old.reddit.com/r/quantum/comments/7crdz6/whats_wrong...
  - __s 5y ago
    If you view a body of water as a single thing, would you think it odd that its wave interferes with itself in the double slit? The issue isn't unintuitive phenomena (intuitive being patterns in microscopic/macroscopic scale which match by analogy to patterns you've learnt all your life from phenomena at your scale), but inadequately modeled phenomena https://youtu.be/citY6G8ePJw?t=223 https://youtu.be/citY6G8ePJw?t=223 > But what can I call it? I can say they behave like a particle-wave or they behave in a typical quantum mechanical manner. There isn't any word for it, if I say they behave like particles, I give the wrong impression if I say they behave like waves. They behave in their own inimitable way. Which, technically, could be called the quantum mechanical way. They behave in a way that is nothing like anything you have seen before. Your experience with things you have seen before is inadequate, is incomplete. The behavior of things on a very tiny scale is simply different ... Well, there's at least one simplification, at least electrons behave exactly in this respect as photons, that is they're both screwy, but in exactly the same way ... But the difficulty really is psychological, and exists in the perpetual torment that exists from your saying to yourself "But how can it be like that?" which really is a reflection of an uncontrolled by say an utterly vain desire to see it in terms of some analogy with something familiar. I will not describe it in terms of an analogy with something familiar. I'll simply describe it
littlestymaar 5y ago
The wave/particle duality is just an illusion, a feature of how we model physical objects, and ultimately how we teach physics. Neither waves or particles exist in the real world, but we do model some features of the world through them. Particles and waves are just the solutions to the differential equations found in classical mechanics, and electromagnetism (which, interestingly enough, rely on the same mathematical framework). Then when teaching about them, we use analogies from the perceptible world. (And those analogies are wrong btw, waves in the sea don't really behave like physics “waves”). In quantum mechanics, the equations are completely different ones, based on a completely different branch of mathematics. Then unsurprisingly their solutions have little in common with those above.
f154hfds 5y ago
I have a particle physicist friend I asked this very question to last year. He laughed and told me that this is not something that keeps physicists up at night. After doing a fair bit of my own research and watching a lot of PBS Spacetime it does make more sense to me. Someone with more knowledge please check my understanding: Quantum Field Theory treats everything as a wave and 'particles' arise as a result of a 'collapse' of that more fundamental wave (probability distribution) as we decide to probe our uncertainty budget by getting specificity on the locality of the particle. It can also collapse of course by interacting with a combinatorial explosion of other particles (such as the back wall of the double slit experiment). If the above is accurate I still think the collapse is a strange phenomenon that we shouldn't just take on faith (without probing deeper of course) - the disagreement between Copenhagen and Many Worlds (and the lack of a testable hypothesis) seems to indicate the collapse itself isn't well understood [1]. Many Worlds seems to have an elegant solution but it needs experiment and wasn't (and probably still isn't) 'accepted' by the overall community. [1] https://en.wikipedia.org/wiki/Wave_function_collapse#History_and_context https://en.wikipedia.org/wiki/Wave_function_collapse#History...
- FeepingCreature 5y ago
  There is no experiment that can settle this - collapse can be shown to exist, but it cannot be shown to not exist, just not for a particular system at a particular scale. In other words, experimenters can push the possible size of a quantum superposition upwards, but they will never be able to disprove the claim "if it were but a bit bigger, it would collapse."
  - rocqua 5y ago
    I remember a Physics PhD who thought that 'waveform collapse' was not a transition from 'waveform' to measurement. Instead, he felt that 'measurement' was just becoming entangled with the wider world, which causes the waveform to converge to a dirac-delta distribution. Are there reasons to assume that 'random' entanglements cause the waveform to 'concentrate'? it would need to be that the probability of concentration at a given 'point' is proportional to the square magnitude of the waveform? Has this been studied?
akomtu 5y ago
Afaik, the many worlds interpretation (MWI) trivially explains all these "duality mysteries", but people don't like it for philosophical reasons. A one-world with randomness is a much more cozy place to live in than a cold super deterministic " matrix" that doesn't even leave room for "free will".

Not really in the same way. The Standard Model is built out of quantum field theories that take as a given our experiment results that matter on quantum scales is unlike the "large scale" matter we see around us. The problems described in the articles are unexpected results that we see in our experiments compared to the Standard Model, "weird/nonintuitive" aspects of modern particle physics would be a separate article.

mikhailfranco 5y ago

No, it's quite clear in QFT that elementary entities: - travel as unitary time-reversible non-local waves (propagate, interfere, entangle) - interact as non-unitary time-irreversible local particle events (position, time, exchange, create, destroy) Your interpretation of quantum mechanics will determine how you imagine the two views connect (Born Law, Many Worlds, ...)

ajkjk 5y ago
I don't think it's correct to say that they interact as particle events, because off-shell interactions are a thing, and interacting strictly as particles would prohibit that, no?

casparvitch 5y ago

No, physicists are pretty comfortable with that one. It isn't immediately intuitive, but the models we have are powerful and predictive. There is of course a somewhat open question as to the interpretation of quantum mechanics. That question is almost metaphysics, whereas the problems quoted in the article are more holes in our present theory.

hdjjhhvvhga 5y ago
Well, they're comfortable because the phenomenon is well-studied, we have very good models and can with good accuracy predict what will happen. What we don't know is why exactly it behaves in this way.
- andrewgleave 5y ago
  One explanation is the "Many-Worlds" interpretation of quantum mechanics: https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation
- khafra 5y ago
  The word "why" (and other references to causation) don't work in a normal way when you're talking about fundamental physics, because fundamental physics is the lowest-level model within which causation takes place. To ask "why" some part of the standard model is the way it is, you either invoke some rubric for comparing models, like Occam's Razor; or you indulge in metaphysics and speculate on the nature of whomever is running the Simulation. Either of these is a different meaning than the "why" of "why do rockets work in space."
  - hdjjhhvvhga 5y ago
    Well, you made quiet a few assumptions here. We don't yet know how much fundamental quarks are and what (if anything) hides in the subquark level. Given the lack of adequate instruments, our minds and unconventional approaches are our most powerful tools at this point. For example, we generally consider the space between particles as void. We can't see anything, we can't detect anything, so we assume there's nothing there. But for what it's worth, there could be trillions of unknown particles that don't interact with matter. So why would it matter, you ask? Because it's not impossible that under certain conditions some of these might cluster into matter or interact with it in unobvious ways. The existence of dark matter and energy (or the related phenomena) indicates this is not impossible. But yes, I see your point. However, I hope we get deeper into understanding this phenomenon before I die. Who knows, maybe it's because of some yet-undiscovered aspect of photons, and metaphysical speculation is not necessary?
DangitBobby 5y ago
I thought the most surprising thing about wave/particle duality is that the act of observation itself is what causes the waveform of particles to collapse. Do we know of a mechanism for that? Are we not still surprised that you change the outcome of events by changing where you look?
- FeepingCreature 5y ago
  As I understand it, collapse is an artifact of the necessity to derive classical results from an experiment. You can think of it as "at a certain scale, calculating this as a quantum system as opposed to classical is no longer worth it." But it's of course still a quantum system, because everything is quantum all the time.
  - DangitBobby 5y ago
    I don't think so. The double-slit experiment demonstrates light acting as a wave in some circumstances and as individual photons in others [1]. > the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate.[5][6] The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles.[5][7] However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen.[8] Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave).[9][10][11][12][13] However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. These results demonstrate the principle of wave–particle duality.[14][15] This is the part I'm talking about, mainly. > However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. Once they are measured, you know where they are and they stop acting like a wave. 1. https://en.m.wikipedia.org/wiki/Double-slit_experiment https://en.m.wikipedia.org/wiki/Double-slit_experiment

immmmmm 5y ago

no the SM is a quantum field theory: particles are excitations of quantum fields, so wave-particle duality is implicit. these fields, at the classical level are function that take a space time coordinate as an argument (space time filling) and typically yields a vector in some vector space (except the higgs field which is a scalar). this vector space in turn is a representation of some symmetry group. the symmetry group of SM is U(1)xSU(2)xSU(3).

mabbo 5y ago

Many years ago, a friend (who is far smarter than I am) said something to me that made wave-particle duality click: "It's not that it's sometimes a particle and sometimes a wave. It's that very small things have a bunch of properties: some are shared with waves, and some are shared with small solid objects." We're duck-typing what we see and going "aha! It's a particle! No wait, now it's a wave!" but the class simply has both sets of methods on it and does not care how we classify it.

Angostura 5y ago
That doesn't really help me understand how a single 'thing' interferes with itself when travelling through a double slit, unfortunately.
- danielheath 5y ago
  I always struggled with that too - I found this Veritasium video helpful https://www.youtube.com/watch?v=WIyTZDHuarQ&ab_channel=Veritasium https://www.youtube.com/watch?v=WIyTZDHuarQ&ab_channel=Verit...
  - __s 5y ago
    Never heard of this, looked up whether there was some gap in the theory the video failed to mention, found a discussion on why this model isn't more pervasive: https://physics.stackexchange.com/questions/341400/why-would-pilot-wave-be-wrong https://physics.stackexchange.com/questions/341400/why-would... & one comment which specifically separates pilot waves from the bouncing droplet demo https://old.reddit.com/r/quantum/comments/7crdz6/whats_wrong_with_pilot_wave_theory/dpuw6h5/ https://old.reddit.com/r/quantum/comments/7crdz6/whats_wrong...
- __s 5y ago
  If you view a body of water as a single thing, would you think it odd that its wave interferes with itself in the double slit? The issue isn't unintuitive phenomena (intuitive being patterns in microscopic/macroscopic scale which match by analogy to patterns you've learnt all your life from phenomena at your scale), but inadequately modeled phenomena https://youtu.be/citY6G8ePJw?t=223 https://youtu.be/citY6G8ePJw?t=223 > But what can I call it? I can say they behave like a particle-wave or they behave in a typical quantum mechanical manner. There isn't any word for it, if I say they behave like particles, I give the wrong impression if I say they behave like waves. They behave in their own inimitable way. Which, technically, could be called the quantum mechanical way. They behave in a way that is nothing like anything you have seen before. Your experience with things you have seen before is inadequate, is incomplete. The behavior of things on a very tiny scale is simply different ... Well, there's at least one simplification, at least electrons behave exactly in this respect as photons, that is they're both screwy, but in exactly the same way ... But the difficulty really is psychological, and exists in the perpetual torment that exists from your saying to yourself "But how can it be like that?" which really is a reflection of an uncontrolled by say an utterly vain desire to see it in terms of some analogy with something familiar. I will not describe it in terms of an analogy with something familiar. I'll simply describe it

littlestymaar 5y ago

The wave/particle duality is just an illusion, a feature of how we model physical objects, and ultimately how we teach physics. Neither waves or particles exist in the real world, but we do model some features of the world through them. Particles and waves are just the solutions to the differential equations found in classical mechanics, and electromagnetism (which, interestingly enough, rely on the same mathematical framework). Then when teaching about them, we use analogies from the perceptible world. (And those analogies are wrong btw, waves in the sea don't really behave like physics “waves”). In quantum mechanics, the equations are completely different ones, based on a completely different branch of mathematics. Then unsurprisingly their solutions have little in common with those above.

f154hfds 5y ago

I have a particle physicist friend I asked this very question to last year. He laughed and told me that this is not something that keeps physicists up at night. After doing a fair bit of my own research and watching a lot of PBS Spacetime it does make more sense to me. Someone with more knowledge please check my understanding: Quantum Field Theory treats everything as a wave and 'particles' arise as a result of a 'collapse' of that more fundamental wave (probability distribution) as we decide to probe our uncertainty budget by getting specificity on the locality of the particle. It can also collapse of course by interacting with a combinatorial explosion of other particles (such as the back wall of the double slit experiment). If the above is accurate I still think the collapse is a strange phenomenon that we shouldn't just take on faith (without probing deeper of course) - the disagreement between Copenhagen and Many Worlds (and the lack of a testable hypothesis) seems to indicate the collapse itself isn't well understood [1]. Many Worlds seems to have an elegant solution but it needs experiment and wasn't (and probably still isn't) 'accepted' by the overall community. [1] https://en.wikipedia.org/wiki/Wave_function_collapse#History_and_context https://en.wikipedia.org/wiki/Wave_function_collapse#History...

FeepingCreature 5y ago
There is no experiment that can settle this - collapse can be shown to exist, but it cannot be shown to not exist, just not for a particular system at a particular scale. In other words, experimenters can push the possible size of a quantum superposition upwards, but they will never be able to disprove the claim "if it were but a bit bigger, it would collapse."
- rocqua 5y ago
  I remember a Physics PhD who thought that 'waveform collapse' was not a transition from 'waveform' to measurement. Instead, he felt that 'measurement' was just becoming entangled with the wider world, which causes the waveform to converge to a dirac-delta distribution. Are there reasons to assume that 'random' entanglements cause the waveform to 'concentrate'? it would need to be that the probability of concentration at a given 'point' is proportional to the square magnitude of the waveform? Has this been studied?

akomtu 5y ago

Afaik, the many worlds interpretation (MWI) trivially explains all these "duality mysteries", but people don't like it for philosophical reasons. A one-world with randomness is a much more cozy place to live in than a cold super deterministic " matrix" that doesn't even leave room for "free will".