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A common misunderstanding about wave-particle duality
- Jun8 2y agoGood article. If you want to delve in more have a look at the answers to this Physics SE question: https://physics.stackexchange.com/questions/46237/is-the-wave-particle-duality-a-real-duality?rq=1 https://physics.stackexchange.com/questions/46237/is-the-wav.... One unfortunate effect of the presenting it as "wave-particle duality" to the laymen audience is that it's as if physicists don't have a good understanding of what's going on and are puzzled by the behavior, whereas QFT is well-established.
- gipp 2y agoTl;Dr: "Wave-particle duality" is not the notion that matter is "sometimes" a particle and "sometimes" a wave. It is, at all times, its own separate category of thing, for which "particle" and "wave" are just metaphors that approximate its behavior. One metaphor usually comes closer than the other depending on what system you're looking at, but it's never changing back and forth between some "particle state" and "wave state".
- andoando 2y agoMy understanding is that what we consider as particles can be described as waves of smaller particles. For example, atoms are fluctuating electrons, neutrons and protons, all of which are fluctuating subatomic particles and so on. And what we describe as particles are essentially the maxima of these fluctuations.
- ajkjk 2y agoNot really. Electrons are as far as we know not composed of smaller particles, and there's good reason to think they are elementary. Basically because smashing them with things reveals no smaller structure. Whereas when you smash things into a proton it is very clear that there are smaller localized objects inside it (there is a great blog post with pictures of what a proton looks like at different energies that I can't seem to find now...)
- ajkjk 2y agoThis article seems to get it backwards? > This doesn’t mean that the atoms themselves are smeared out like waves; rather, what spreads is the probability distribution of them being found subsequently in a given location No, it really does mean they're smeared out like waves. Prior to the measurement they are in superposition, relative to you. When your experiment images the atoms, that's a measurement that entangles you with the atoms. If the observable value takes values in (A,B) then when you get entangled you end up in a state (A, measured A) + (B, measured B), each of which perceives a definite value of the measurement. The whole system would still be (to an outside, non-entangled observer, if you could pull such a thing off) in a superposition which could continue to interfere with itself, but the observer who's inside the superposition will never be able to tell. Afaik this is the standard interpretation nowadays. Particles are waves (well, in the sense that what we call a particle is usually a momentum eigenstate that evolves in space like a wave), but the measurement process that entangles us to the causes them to come in quantized packets which we call particles. Maybe I'm missing the point of the article somehow though...
- notfed 2y ago> Afaik this is the standard interpretation nowadays You've described the Everett interpretation. It should be the standard. There's still a surprising amount of resistance for some reason.
- ajkjk 2y agoI feel like there isn't really, not anymore, and most of the semblance of a debate is people reporting on historical debates. Although hard to be sure without, like, a survey. At least in what I read it seems like the remaining debate is over how literally to interpret the words "many worlds", rather than whether the basic idea is correct. Ideas like entangling with the experiment and the decoherence of quantum states are very well-established.
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- csours 2y agoTo me, Wave/Particle means that we have observations consistent with waves and observations consistent with particles. I don't think you really have to go beyond that - except that is not how things behave in the macro world. The problem is trying to map Wave/Particles to the macro scale. Just don't do it.
- wry_discontent 2y agoThis is exactly what I learned in a philosophy of science course in college. Not this specific topic, but that approach. Science is a model, and as soon as you're generalizing past experiments and observations, you're outside of where you should be.
- lijok 2y agoWhat I always wondered as a layman with no background in physics is - couldn’t the observed particle-like properties of waves be an emergent property?
- burnished 2y agoYou can observe the effect even when there is only one particle moving at a time.
- Maxatar 2y agoI think this needs to be qualified a bit. You can make numerous observations of a single electron over a period of time and see a wave like pattern emerge, or you can take a single observation of numerous electrons and see a wave like pattern emerge, but you can never take a single observation of one electron and see a wave like pattern.
- richardw 2y ago> You can make numerous observations of a single electron over a period of time and see a wave like pattern emerge I thought measurement along the path collapses the wave, removing the wave pattern over the full source to destination that would be displayed if there was no observation? Eg in dual slit if you observe at one of the slits, the pattern disappears. Wave-like behaviour only exists between observations.
- pjs_ 2y agoWhy is the bicycle self stable? https://www.science.org/doi/10.1126/science.1201959 https://www.science.org/doi/10.1126/science.1201959 We can't say, in any satisfying way. The mathematics is uncontroversial, but all of the simple natural-language explanations fail under scrutiny. Where is the electron in the double slit experiment? Is it a particle or a wave? Similarly, we can't say. We don't have a good way of talking about this by analogy, or using natural language. As with the bicycle, the mathematics is bulletproof and boring. This is not to say that quantum mechanics is unmysterious - I think it is very mysterious. However, the bicycle example shows how this characteristic, frustrating elusiveness of good natural-language descriptions is not limited to exotic quantum systems.
- TheBlight 2y agoI think a significant aspect of this specific problem is that a notion of a "field" is very difficult to translate to everyday language no matter how easy it is for a physicist to conceptualize and model with math. Similar to coming up with a good analogy for a hash function in computer science world. These are largely very foreign concepts for everyday human life experiencers.
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- amelius 2y agoWould it be possible to remote-control a bicycle like you can remote-control a drone?
- dahart 2y agoAbsolutely! This is on my bucket list of home robotics projects. A stretch goal is to get steering during a wheelie, but I think this will be extra difficult. I’m guessing a well tuned PID controller will handle counter-steering just fine, but we’ll see.
- itishappy 2y agoJust strap a drone to it! Only somewhat facetious. :)
- layer8 2y agoThe article completely ignores quantum field theory, which forms the basis of the standard model of particle physics, and in which particles are emergent (rather than fundamental) features of the respective underlying field, which is described by wave equations.
- criddell 2y agoIf a particle is an excitation of a quantum field, what is a wave?
- itishappy 2y agoThe same thing. A wave is just something that obeys the wave equation by wiggling in a certain way.
- oneshtein 2y agoIn some mathematical models, a particle is an excitation of a field, e.g. a mountain is an excitation of a height field. It makes calculations much easier. In those models, waves can be represented in many different ways. In the real world, a particle can be a lot of different things, but usually we use this word to describe small parts of larger objects. There is no much physical difference between a small grain of sand and a planet, but we use different words for them, while we use the same word for small things, which can be different by many orders of magnitude. In the real world, a wave, is just a form of group behavior of particles, i.e. many particles are doing the same thing at once because of an interaction between them and some energy in a system. For example, merging of black holes makes waves in a galaxy, so we can watch that in super slow motion.
- criddell 2y ago> In the real world, a particle can be a lot of different things I thought the idea that a particle is an excitation of a quantum field was broadly accepted.
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- DavidHull 2y agoAs an interested amateur, I recommend the book "Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime" by Sean Carroll as a good overview of quantum fundamentals. The book discusses several interpretations of the reality of matter at the quantum level. Dr. Carroll himself believes that everything is waves/fields at the lowest level, and a many-worlds interpretation of why matter appears to be particles when we observe it, but also discusses de Broglie–Bohm pilot wave theory and spontaneous collapse theory. https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec...
- mech422 2y agoseems to be my day for stupid questions... Do quantum effects make solar sails work ? My High School physics said F=MA and photons have zero mass.. so where does the force come from ? Thanks!
- bandrami 2y agoZero rest mass
- mech422 2y agoSorry - again, only HS physics - does that imply they have mass when moving ? (hmm - can you even have a photon at rest?) thanks!
- itishappy 2y agoSorry, we're leaving HS physics with this one... Objects in motion have kinetic energy, and Einstein says mass and energy are equivalent. This means in a very real sense objects in motion have additional "relativistic mass". When you annihilate that photon it's energy is transferred to whatever absorbed it. Confused? You're not alone! Physicists are trying to move away from the terms "rest mass" and "relativistic mass" for reasons including one you've already identified: what does it even mean for a photon to be "at rest"? https://en.wikipedia.org/wiki/Mass_in_special_relativity https://en.wikipedia.org/wiki/Mass_in_special_relativity
- zokier 2y agoThis whole article and discussion reminds me of the key idea that physics is a model and map is not the territory. Reality is just its own thing, to me it seems pointless to debate if something is really wave or particle or quubaz, the question should be what insights and predictions you can get. Conversely just because you can model things with waves/particles/x doesn't mean that they are waves/particles/x.
- tetris11 2y agoIf you fire a single particle between two slits repeatedly, the cumulative places it hits form a wave-like interference pattern, of course. If you fire a single particle between two slits just once and it still forms a wave-like interference pattern, then surely what is being observed is more than just a probability distribution?
- breck 2y ago> If you fire a single particle between two slits just once Can you ever be sure you only fired a single particle?
- itishappy 2y agoYup! Photons are tough, it's a lot easier with electrons.
- dahart 2y agoWhere did you read about a single particle forming an interference pattern? “The atoms themselves are only ever observed in a given experimental run as particles – just as quantum mechanics says they should be. The wavelike behaviour – which is to say, the smeared-out probability distribution – is reconstructed from many particle-like observations.”
- epgui 2y agoA single particle is never observed as a wave afaik (not my area of expertise).
- crazygringo 2y ago> just once and it still forms a wave-like interference pattern That's not a thing. There's no pattern to observe from a single particle. The situation you're describing doesn't exist. Wave behavior and interference patterns can only be observed in statistically significant collections of particle interactions. Not single interactions.
- itishappy 2y ago
- breck 2y agoA question for any physicists on here: is Wave/Particle duality analogous to Lisp/Binary duality? In other words, 2 different languages/models but 1 underlying reality that neither perfectly represents?
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- scotty79 2y ago> there is no reason to say that quantum entities are ever really waves I'm on the completely opposite end of the spectrum. I see no reason to say that quantum entities are ever really pointlike particles. I'd rather see them as smeared wave-like entities that occasionally rapidly reshape while exchanging energy and momentum through fields as if the were two small billiard balls bouncing. There's really nothing particle-like about those quantum objects apart from this momentum and energy exchanges (and even that is weird because it's quantized) and that evolution of their center of mass in time seems like a thing flying in space according to Newtonian dynamics. We draw our simplest intuitions from macroscopic objects that are built of huge number of actual elemental material objects so tightly bound with one another that they are barely smeared. It's not an accident that macroscopic object obeys the same equations that a tight quantum objects obey. But it's a huge mistake to think that those equations that we wrote for this very bizarre state of matter that are macroscopic objects is anything primary just because the math describing them is as simple as it goes. Take a look at ideal gas equations about pressure volume and temperature. They are childishly simple when compared to the math you'd need to accurately describe what actually happens in a gas. Framing quantum mechanics in terms of "observation" instead of "instance of momentum and energy exchange" might be a very computationally convenient interpretation of what happens but I don't think it's real in any sense of the word. In broader context we have very many interpretations in physics l that are the simplest possible interpretations of the mathematical abstractions of our models. With complete disregard for how sensible they seem. Even though there are completely reasonable alternative interpretations of the same math available. Physics educators seem to delight in the quirkiness of the interpretations that theoretical physicists love because they are just their equations narrated, nothing more, nothing less, instead of exploring more reasonable interpretations or even mention that they exist. In absence of new math, bringing new insights to our fundamental knowledge, one of the goals of physics should be to get real. New, or old but rekindled, more plausible interpretations might inspire new generations of young physicists to visit avenues less explored. Because abstract narratives we globally adopted failed to do that for many decades already.
- jiggawatts 2y agoSomething that I've been wondering about is whether the original development of quantum mechanics involved a simple "mixup" due to the duality of the mathematics involved in wave mechanics. Imagine implementing a QED simulator: some EM source emitting billions of photons, each with a vector clock rotating to indicate the wavelength. You could code this up as an array tracking each photon. Alternatively, at very large numbers of photons, you'd notice that each pixel on your screen would have so many (maybe millions!) that you could just simulate the aggregate behaviour of each little square patch of space instead of individual particles. Ta-da... it's a continuum. No particles. You can simulate waves in space either using a Monte Carlo particle simulation or by subdividing the space into finite elements and tracking exchanges over their boundaries. Superficially the maths looks different, but the result is the same, and the finite element method has locality and makes the speed of light limit manifest. Why do we keep insisting on covering only the particle model in text books?
- lupire 2y agoThe article clouds more than it illuminates. I don't think the author knows what he is trying to say. This is common in strawman "mythbusting" articles, but even more fraught when the topic is quantum mechanics. Saying that an electron "isn't a wave" when it is in motion, because the wave is probability, not the electron, is equivalent to saying the electron doesn't exist between emissions and absorption. This is a valid interpretation, but even more conunterintuitive to novice, and raises more questions. Ultimately, arguing over vocabulary as interpretation is a distraction. What the thing does is what the thing is. Interpretations are intuitive guides.