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Is light fundamentally a wave or a particle?
- deleted 6y ago[deleted]
- SideburnsOfDoom 6y agoThis was linked recently: https://www.lesswrong.com/posts/hc9Eg6erp6hk9bWhn/the-quantum-physics-sequence https://www.lesswrong.com/posts/hc9Eg6erp6hk9bWhn/the-quantu... > An electron is not a billiard ball, and it’s not a crest and trough moving through a pool of water. An electron is a mathematically different sort of entity, all the time and under all circumstances, and it has to be accepted on its own terms. > The universe is not wavering between using particles and waves, unable to make up its mind. It’s only human intuitions about quantum mechanics that swap back and forth. The intuitions we have for billiard balls, and the intuitions we have for crests and troughs in a pool of water, both look sort of like they’re applicable to electrons, at different times and under different circumstances. But the truth is that both intuitions simply aren’t applicable. > If you try to think of an electron as being like a billiard ball on some days, and like an ocean wave on other days, you will confuse the living daylights out of yourself. > Yet it’s your eyes that are wobbling and unstable, not the world. This also applies to light. IMHO, light is light. When we view it as a particle, we are wrong. When we view it as a wave we are also wrong, but in a different way.
- vanderZwan 6y agoWhy not say "when solving problem X, we can approximate it as a particle" or "when solving problem Y, we can approximate it as a wave"?
- amelius 6y agoBecause someone might come up with a problem that is a bit like X and a bit like Y.
- the_other 6y agoThat sounds like an excellent opportunity to test both the models, and perhaps to develop a third.
- maxnoe 6y agoWe already have, its called QED and is the most preise physical theory ever created and tested. Theoretical predictions agree with experiment inside the statistical uncertainties which are now at the 15th or so decimal digit. The problem is, people still want to map the mathematical description of how light and particles behave of QED to common sense analogies and that just does not work. There is no commonly known and understood thing that lends itself as a working analogy.
- el_don_almighty 6y agoThe French called this the "le principe Donny et Marie," based on some research from the mid 70's for some reason. Oooh la la, those hot pants!
- lurquer 6y agoHmmm... that post was a little bit HackerNews-ish, and a little bit Reddit-ish. I’m going to simultaneously upvote and downvote you.
- vanderZwan 6y agoHow is that different from saying "this problem cannot be approximated these ways"?
- andreareina 6y agoHow do you know a priori which kind of problem it is? Wave or particle are interpretations we attach to the results of applying the Schrodinger equation.
- vanderZwan 6y agoSo if I understand your point correctly, approximations are a priori simplifications of problems, while we are talking about after-the-fact interpretations here, and therefore they are not the same? That sounds logical, thank you.
- abdullahkhalids 6y agoImagine talking to an ancient philosopher who strongly believed that the everything in the world was made of Earth, Air, Water and Fire. Explain electromagnetic waves to them. They might end up saying, "so EM waves are invisible like Air, but they move around like Water waves, so really EM waves display Air-Water duality?" That's how stupid the idea of wave-particle duality is. When you upgrade to a better model of the world, you have to drop the old concepts, and start anew with new concepts.
- coolgeek 6y agoI hope that this is as amazing (complete, consistent and coherent) as it initially looks. But I don't see your quote in the link. Did it come from another source, or did the linked sequence change in the interim, or something else?
- witherk 6y agoWave particle duality used to stress me out before I read Feynman talk about it. "Things on a very small scale behave like nothing that you have any direct experience about. They do not behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen..... There is one lucky break, however—electrons behave just like light. The quantum behavior of atomic objects (electrons, protons, neutrons, photons, and so on) is the same for all, they are all “particle waves,” or whatever you want to call them. So what we learn about the properties of electrons (which we shall use for our examples) will apply also to all “particles,” including photons of light."
- effie 6y agoSingle beam of electrons diffracts like single beam of light, but otherwise electrons behave very differently than light: two electron beams interfere with each other, while two light beams do not.
- beojan 6y agoTwo coherent beams of light will absolutely interfere.
- danbruc 6y agoI think that was meant to mean that the two beams interact. Two crossing light beams will pass right through each other without much happening while two electron beams will interact. But this is because electrons are charged and photons are not. On careful inspection and with high energy photons one would also notice an interaction between two light beams due to photon photon scattering [1]. But one could reasonably call this a kind of distraction due to different charges of different particles. Ignoring those makes photons and electrons behave identical in respect to the phenomena discussed in the article. [1] https://en.wikipedia.org/wiki/Two-photon_physics https://en.wikipedia.org/wiki/Two-photon_physics
- ahartmetz 6y agoElectron beams interfere in ways that light beams don't, though. If they cross in vacuum, they deflect each other due to the electric charge carried by electrons. Light beams can only deflect each other in media with non-linear response to electromagnetic fields, i.e. the response to one beam modifies the response to the other beam.
- tsjq 6y agoYes
- FooHentai 6y agoThis is the answer I came here to make/find. Thank you.
- quietbritishjim 6y agoFunnily enough, I would give a one word answer too: No
- Razengan 6y agoI think the tendency to see everything as discrete units is a very human thing. Would love to see how alien species with fundamentally different perceptions approach these concepts.
- misja111 6y agoI'm not so sure that other intelligent life could have evolved without having the same way of reducing complexity as we do. It is the essence of modelling: when you are interested only in certain aspects of an environment you try to categorise and classify your subject accordingly.
- danbruc 6y agoWhich was helpful till now but there is no a priori reason that this must always be the case. And we might actually have reached to bottom in this regard with quantum physics where splitting things into pieces, studying them separately, and putting them together again does not really work anymore. A system of two or more quantum particles is not just the sum of those particles, the combined system can be in states that are not decomposable, i.e. the particles can be entangled. Splitting the universe into galaxies, those into star systems, things in them into cells and molecules and then atoms and eventually elementary particles and all the success we had with this might give the impression that reductionism, that decomposing and reassembling things, is the only way that the world can be and that this will always work, but this is not true. And there is no a priori reason that the universe should be easily decomposable all the way down.
- robertlagrant 6y agoIt is decomposable; this doesn't affect that. It just means what we've decomposed it to cannot be modelled sufficiently with the current metaphors.
- danbruc 6y agoWhat do you mean with it? The quantum state of a two particle system? In that case I am pretty sure - even though I am not a physicist - that you are wrong. The quantum state of a two particle system can not be decomposed into two states, one state for each particle, in the general case. You can find the density matrix for each particle which will tell you how each corresponding particle will behave in isolation but you will lose information about the system by doing so in the general case.
- bhaak 6y agoWhy not both?
- danbruc 6y agoIt is both, or probably even better neither. Elementary particles are not classical particles and they are not classical waves. They are things that behave similar to classical particles in some circumstances and similar to classical waves in others, but they are neither. But as humans have no experience with such things in the macroscopic world, as we lack intuition for them, we desperately want them to be either or the other in order to comprehend them. Ironically this desire is probably what makes them actually more incomprehensible.
- bhaak 6y agoIt might be some kind of an uncanny valley situation. Because they share behavior with two very distinct objects we have macroscopic experience with, we try to categorize them as such.
- aliceryhl 6y agoNo.
- atomack 6y agoIn quantum mechanics, it's a wave function. Wavelike, but not a wave; particle-like, but not a particle.
- cycomanic 6y agoI found Scott Aaronson's explanation very helpful (and I'm a physicist, I think it might make even more sense to computer scientists and engineers). https://www.scottaaronson.com/democritus/lec9.html https://www.scottaaronson.com/democritus/lec9.html
- im3w1l 6y agoIn each of the many-worlds it is a particle. The wave behavior is caused by the interaction of the many-worlds.
- 2038AD 6y agoWhat a fun interpretation
- mhh__ 6y agoI'm not sure that's how MWI works?
- quietbritishjim 6y agoDoes that explain the two slit experiment, with a single particle inferring with its own wave function? If you consider it to be a particle, then you probably need to make the interact of the many-worlds be wavelike. At that point you probably have a more complex model than admitting the photon was not a particle.
- im3w1l 6y ago> you probably need to make the interact of the many-worlds be wavelike. Yes > At that point you probably have a more complex model than admitting the photon was not a particle. Yes again. But then why a more complex model? To be able to deal with interference of complex systems of entangled particles.
- noiv 6y agoStrange question, how about: Are wave or particle appropiate concepts to describe light at any scale? Even I might behave like a wave, it's just extremely unlikely :)
- chrisweekly 6y agoAnswer: Yes.
- tiborsaas 6y agoI feel like this question is like asking a hexagon if it's a circle or a square. Let me summon the annoying physicist take on this by Sabine: https://youtu.be/kSG4Rfc9YIw?t=179 https://youtu.be/kSG4Rfc9YIw?t=179
- mhh__ 6y agoI assume it's ultimately in good humour but some of the things she does seem quite "out" for a physicist e.g. the annoying physicist things looks like position yourself towards outsiders. I'm still a mere trainee so I'm basically neutral on her opinion of HEP and Accelerators, but I know enough that it looks a little weird for an academic.
- tiborsaas 6y agoI dig her style, but don't subscribe to all her views either. I linked this part in the video because it points out that it's quite common to try to categorize things in one box or another while it should really be given a new box even if that box contains one item only.
- at_a_remove 6y agoYour undergraduate physics education is a series of approximations. Every so often, you will go to a new class and the professor will say, "Okay, that was nice, but that was an approximation. You were wading in the shallow end of the pool. Let's go a little deeper. Throw away what you thought you knew and how you previously modeled things, it isn't as accurate as this ..." and then you're on to the next thing. QM is one of those transitions and the jump bothers many.
- deleted 6y ago[deleted]
- lilgreenland 6y agoIs nature made of waves or particles? The annoying answer is neither. The wave model and the particle model are approximations of nature that are each accurate for different conditions. Quantum field theory describes reality with wave functions. In this theory there is a field for each type of fundamental particle spread across all of space and time. Regions of a field can evolve into a localized excited state. Particles are a useful mathematical approximation of these excited states. For example, an electron is a region where the electron field has more amplitude, or bigger ripples. The electron field exists everywhere, but electrons are more likely to be measured where the field amplitude is larger. Fields interact with other fields, and with themselves. These interactions can be approximated with a Feynman diagram, which treats everything as particles. Using Feynman diagrams electron field interactions generally model well as particles. This is because the most complex electron interactions are weak enough to be mathematically canceled out. Quarks, the particles inside protons and neutrons, interact through the "strong force". This force has frequent complex interactions that don't cancel out, making the particle model less useful for calculations.
- emrah 6y agoWatch this TED talk by Aaron O'Conell's experiment if you haven't seen it. Even objects large enough to be seen can exhibit quantum effects. It's not the size of the object that matters but the condition of its environment. Of course the smaller the object, the easier it gets to create those conditions https://ed.ted.com/lessons/making-sense-of-a-visible-quantum-object-aaron-o-connell https://ed.ted.com/lessons/making-sense-of-a-visible-quantum...
- Viliam1234 6y agoI watched, and was disappointed. First I had to listen to the debunked psychological theory of two brains, which anyway was unrelated to the topic. The they brought the thing... and it was a tiny dot that did nothing. Then he excitedly talked about how cool it is. Okay, I get that the theory is cool. But what's the point of showing audience an object, where they can't see anything interesting anyway? And perhaps, if you are quantum physicist, stick to quantum physics and don't meddle in psychology. You should know best how annoying it is when psychologists start meddling in quantum physics, so don't do the same thing in reverse.
- SpaceLawnmower 6y agoOne of my physics professors liked to say that a photon is an event. The particle we know as a photon is a point in spacetime where there is some sort of interaction, but the electromagnetic field is closer to a wave.
- gpsx 6y agoMost people with exposure to any physics learn some basics about electrons, light and quantum mechanics, but I think it is tough to put these different ideas together. The hard part about quantum mechanics for physicists is not the rules for quantum mechanics but how that manifests itself in the real world. This is how I have understand it. I'll talk about electrons first. An electron is a point particle. The position of the electron is governed by a wave (wave function). The wave is not made out of "electron". It is made out of something else, kind of like "probability". The wave tells you where you find the electron. But when you do find the electron, it is always a point particle. You will never detect the electron smeared out over space. (As an aside, for those who think about field theory, I still see the electron as point in field theory, though some might see it differently.) Light is a field/wave made of the electric field. And it has a wave function too. The wave function again is made of probability. But it is probability for different electric field configurations, rather than photon locations, so it might be harder to picture. Why does a light behave like a particle at all? Though the light has spatial extent it does come in discrete chunks, specific quanta of energy. When light is absorbed it can only be absorbed in these discrete quanta. In most detectors (like photographic paper) the light is absorbed by an electron. Since the electron is a point particle, the photon absorption happens at a single point. This might make it look as if a "particle" of light hit the detector.
- jfengel 6y agoBetteridge's Law applies nicely here. The answer is "no". Light is neither a wave nor a particle. It is a quantum thing whose formula can be simplified to either wavelike or particlelike under certain assumptions, but not in the general case. Experiments that force those assumptions will reliably turn up wavelike and particlelike behavior, while more general experiments reveal the harder case where the assumptions don't hold. This really isn't a hard thing. This has been known for pretty much a century. People keep insisting that quantum mechanics is really just classical mechanics with an extra bag on the side, and that approach will always fail in some limit case. When you accept that it's the reverse -- that classical mechanics is a special case of quantum mechanics -- you can work with QM in a very straightforward way. It's just not the straightforward way you're used to.
- deleted 6y ago[deleted]
- jiggawatts 6y agoThese discussions always frustrate me, because for the ten thousandth time the same conversation plays out like a needle stuck on a record: "So what is a particle?" "Well, it acts like a wave but is not a wave." "Aha..." "It also acts like a particle but is not a particle." "Okay, but then what is it?" "I just told you! It's neither a particle, nor a wave, it's something else entirely!" "I accept that it isn't either of those two things, but then describe the thing that it is!" "I can't do that! You have to study a pile of textbooks this high to understand what it is!" "Why? I understand relativity without having to have read a pile of textbooks! That's also an unintuitive physical concept with no classical analogy with which we are familiar with in every day life. Despite this it has intuitive visualisations to aid understanding! [1] Why can't you do something similar for quantum mechanics?" "Wave-particle duality just has to be understood through the mathematics, there is no simpler way" "Okay, okay, never mind. Now what about Spin?" "Go away." [1] https://www.youtube.com/watch?v=DYq774z4dws https://www.youtube.com/watch?v=DYq774z4dws
- zkmon 6y agoBy the way, light has no speed. Light is not a "thing" that "moves" through space, even if it is a particle. Source and target of light incidence simply exchange their excitations through entanglement, symmetrically. There is no direction of movement. And there is no movement.
- zkmon 6y agoAnd time is a product of causality chain established by light incidence, thus making up reality.
- thelightthat 6y agoWhere can I read more about this? Thank you in advance
- zkmon 6y agoI haven't read this somewhere. I was just consolidating my thoughts through reasoning. The first abnormality I observed was light propagation having a direction that is asymmetric between source and target. There is no room for that asymmetry. Next is, assumption that time, space and causality exist independent of light, and movement of light being described in terms of those concepts. This can't be true, because all these (light, time, space, change, causality, direction etc) only have mutual existence but not independent or absolute existence. So, light can't be described in terms of others as if others already exist. For more discussion, you can ping me at vrpbkp_at_gmail.
- pontifier 6y agoI believe you're right. While I'm not a physicist by profession, I took enough high level physics to be dangerous. The way I interpret lorentz contraction and time dilation, there will always be a possible observer for which the photon does not need to exist because the interacting particles collided. This is in much the same way that there is always a possible observer that sees only electrical interactions when magnetic fields are involved for other observers.
- ta1234567890 6y ago> we can swap one type of detector for another at the very last instant, implying that the photon was “always a wave” or “always a particle” in order to produce the result that we see. Can't help but think that whatever supposedly "happened" is not that relevant, what matters is the measurement. Clearly "the photon" is only the effect of the interaction between light and the act of measuring it. You just can't remove the measurement from the phenomenon. In our reality ("to us"), light doesn't make sense if it's not measured, and the result of that measurement is not light itself, but the product or outcome of the interaction of the measuring device/method and whatever "light is" (when not being measured), if light can even exist without being measured (which is unknowable).