
#REDIRECT Wave-particle_duality
#REDIRECT Talk:Wave-particle_duality
In physics, wave-particle duality holds that light and matter can exhibit property of both waves and of particles. This concept is a key part of quantum mechanics. In the usual formulations of classical mechanics a given object ''is'' either a particle or a wave. For example, an electron is a particle (because they are observed to behave in particle-like ways), and light is a wave (because it behaves in wave-like ways, such as interference: see below). This categorisation was applied even to objects below the scale of direct observation, essentially by analogy with macroscopic phenomena. However, problems emerge with the viewpoint: electrons too can be made to interfere and thus appear wave-like; light (especially in the photoelectric effect, as analysed in 1905 by Albert Einstein) can possess particle-like properties. Quantum mechanics emphasises the primacy of measurement and not attributing properties to objects beyond what can be measured. Hence the concept of wave-particle duality arose: it is not necessary, or useful, to say that an electron ''is'' a particle - or a wave - just that in certain circumstances it behaves like a wave, and in others like a particle. == Fresnel, Maxwell, and Young == In the early 1800s, the double-slit experiments by Thomas Young (scientist) and Augustin-Jean Fresnel provided evidence for Christian Huygens theories: these experiments showed that when light is sent through a grid, a characteristic interference pattern is observation, very similar to the pattern resulting from the interference of water waves; the wavelength of light can be computation from such patterns. James Clerk Maxwell, during the late-1800s, explained light as the propagation of electromagnetic waves with the Maxwells equations. These equations were verified by experiment, and Huygens' view became widely accepted. ==Einstein and photons== In 1905, Albert Einstein reconciled Huygens' view with that of Isaac Newton; he explained the photoelectric effect (an effect in which light did not seem to act as a wave) by postulating the existence of photons, quantum of energy with particulate quality. Einstein axiom that light's frequency, ''ν'', is related to the energy, ''E'', of its photons: :, where ''h'' is Planck's constant (6.626 x 10-34 J seconds). ==De Broglie== In 1924, Louis-Victor de Broglie claimed that ''all'' matter has a wave-like nature; he related wavelength, λ, and momentum, ''p'': :. This is a generalization of Einstein's equation above since the momentum of a photon is given by ''p'' = ''E'' / ''c'' where ''c'' is the speed of light in vacuum, and ''λ'' = ''c'' / ''ν''. De Broglie's formula was confirmed three years later by Clinton Joseph Davisson and Lester Halbert Germer, by guiding a beam of electrons (which have rest mass) through a crystalline grid and observing the predicted interference patterns. Similar experiments have since been conducted with neutrons and protons. Authors of similar recent experiments with atoms and molecules claim that these larger particles also act like waves. The most famous experiments are those of Estermann and Otto Stern in 1929, and the diffraction of fullerene C60 by researchers from the University of Vienna in 1999; in the later case, the wavelength of de Broglie is 2.5 picometer whereas the diameter of the molecule is about 1 nanometer, i.e. about 400 times larger. This is still a controversial subject because these experimenters have assumed arguments of wave-particle duality and have assumed the validity of deBroglie's equation in their argument. The Planck constant ''h'' is extremely small and that explains why we don't perceive a wave-like quality of everyday objects: their wavelengths are exceedingly small. The fact that matter can have very short wavelengths is exploited in electron microscopy. In quantum mechanics, the wave-particle duality is explained as follows: every system and particle is described by state functions which encode the probability distributions of all measurable variables. The position of the particle is one such variable. Before an observation is made the position of the particle is described in terms of probability waves which can interfere with each other. In quantum electrodynamics, Richard Feynman shows the wave-particle duality of photons and electrons is an illusion. In his view, photons and electrons obey rules that share some qualities of both particles and waves. They are neither particle nor wave, but some generalized object with no direct macroscopic analog. An intriguingly simple experiment, the double-slit experiment, summarizes the duality: aim an electron gun at a screen with two slits and record their positions of detection at a detector behind the screen. You will observe an interference pattern just like the one produced by diffraction of a light or water wave at two slits. This pattern will even appear if you slow down the electron source so that only one electron's worth of charge per second comes through. "Classically speaking", every electron is a point particle and must either travel through the first or through the second slit. So we should be able to produce the same interference pattern if we ran the experiment twice as long, closing slit number one for the first half, then closing slit number two for the second half. But the same pattern does not emerge. Furthermore, if we build detectors around the slits in order to determine which path a particular electron takes, this very measurement destroys the interference pattern as well. But this is a classical explanation and something much more profound is taking place. The interference pattern can be explained as a result of the charge wave being diffracted by ''both'' slits and interfering with itself. In quantum mechanics, the state function is a complex-valued function (mathematics) of space and time. The square of the magnitude (mathematics) of this function describes the probability of finding the electron at a given location at a given time. Interference is due to the fact that the square of the magnitude of the sum of two complex number may be different from the sum of the squares of their magnitudes. The experiment also illustrates an interesting feature of quantum mechanics. Until an observation is made the position of a particle is described in terms of probability waves, but after the particle is observed, it is described as a fixed value. How to conceptualize the process of measurement is one of the great unresolved questions of quantum mechanics. The standard interpretation is the Copenhagen interpretation which leads to interesting thought experiments such as Schrödinger's cat. Due to this confusion, some theorists (including Stephen Hawking and Murray Gell-Mann) believe the many-worlds interpretation is true. However, there is currently some doubt over the validity of both the Copenhagen interpretation and the many-worlds interpretation, due to the controversial Afshar_experiment [http://www.irims.org/quant-ph/030503/], a variation of the two-pin-hole \"which way\" experiment. Notes ''Wave-particle duality of C60'', M. Arndt , O. Nairz, J. Voss-Andreae, C. Keller, G. van der Zouw, A. Zeilinger, ''Nature'' 401, 680-682, 14 October 1999 ==See also== * Niels Bohr * Louis de Broglie ** De Broglie hypothesis * diffraction * double-slit experiment * Albert Einstein * electromagnetism * electron * photoelectric effect * Max Planck * quantum mechanics * Erwin Schrödinger * x-rays ==External links== * Shahriar S. Afshar, [http://www.irims.org/quant-ph/030503/ Afshar Experiment Preprint] * Nave, R., "''[http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Wave-Particle Duality]''". HyperPhysics, Quantum Physics. * [http://www.quantum.univie.ac.at/research/matterwave/c60/index.html Diffraction and Interference with Fullerenes: Wave-particle duality of C60] (University of Vienna) Quantum mechanics Electromagnetism
---- ==Flaws== In texts that talk about detecting light by means of either a "particle detector" or a "wave detector" no information is given as to the suitability of these objects to the tasks to which they are put. Why is the "particle detector" believed to be detecting a particle and not high tide. Conversely why is the "wave detector" detecting a wave-type light and not just showing it's own distortion from being collided with a particle-like light. Furthermore, no explanation is given as for how they know one and only one photon is emitted. User:hackwrenchRobert Claypool ==misleading or wrong== [The stuff below this line is misleading or wrong, I would recomend deleting it. The measurement problem is far more general then what is touched on here, and the ``rule of thumb'' is just plain wrong.] Mathematically, electrons and other such creatures are modelled as waves. The question is, then, why they appear to be particles in certain experiments. This is called the measurement problem, and is solved differently in different interpretations of quantum mechanics. An extremely simple (and possibly overgeneralised) layman's rule of thumb is that when fast and small, think "wave". When slow and big, think "matter". ---- ---- ==Why is the rule of thumb wrong== Why is the rule of thumb wrong? Are there situations where it is advantageous to model, say, a cow as a wave? --AxelBoldt ----- There are a number of problems with the rule of thumb. The big problem is that the key difference between what we normal think of "matter" and "energy" has nothing to do with particle/wave duality but rather the difference between fermions and bosons and the pauli exclusion principle. Also the rule just doesn't work. A standing radio wave is big and slow but you can think of it as a wave. A beam of X rays is fast and small, but is best conceptualized as a stream of particles. -- User:Chenyu ---- ==explanation of what Wave-Particle duality means== I'd like to see more explanation of what Wave-Particle duality means and less incomprehensible history of how it was discovered by physicists. What is it supposed to mean that wavefunctions exhibit ''some properties'' of waves and ''some properties'' particles? For that matter, what does it mean for something to be a wave or a particle? Key terms I'm looking for are: ''soliton'' and ''non-linear wave''. And given that we're talking about non-linear waves, terms like "frequency" should be avoided or explained; non-linear waves don't ''have'' an exact frequency or wavelength! (I'd prefer if it were explained since that would make explaining the Heisenberg "uncertainty" principle easier.) Oh, and I'd like the first paragraph to explain that "duality" is a misnomer since the wave and particle theories of light are not equivalent. That's just a term tacked on by some loser who wanted to sell a mind-bender to a bunch of stuffy conservative physicists. And "probability wave" is seriously misleading. Probability is not what most people think it is; mathematical probability has no relation to the everyday concept of probability. And since "probability" adds nothing to "wave" or "wavefunction", it should be junked. Other misleading things: the ever popular misconception that quantum mechanics has anything to do with the travesty called Copenhagen. The impression that quantum mechanics recognizes a pre-observation and post-observation domain is seriously wrong and should be avoided at all cost. And as long as we're explaining the history, why is Huygens left out of the picture? IF YOU'RE GOING TO TALK.....BE SPECIFIC....YOU CAN'T JUST STATE WHY SOMETHING IS WRONG WITHOUT STATING YOUR REASONING. ISN'T THAT WHAT A PHYSICIST DOES? JUSTIFY WHY. THINK ABOUT IT == Rule of thumb == Wouldn't the ratio of mass to kinetic energy make for a better rule of thumb? Photons: No mass, zero ratio = very wave-like Electrons: Low mass, low ratio = quite wave-like ... Deep-frozen chicken: Enormous mass, enormous ratio (compared with the others) = no measurable interference when shot through double-slit ;-) ---- ---- ==understanding of QM POV== I'm made to recall Willis Lamb's statement that appeals to a "wave-particle duality" (among other things) reveal an individual's misunderstanding of QM...the historical discussion in this article is nice (and deserves expansion) but the physics needs serious updates. (Whoever wrote the above comment that ended in all caps needs to brush up on his physics...) For starters, regarding the article, there is a glaring error, namely, that the "wave function" encodes all knowable information about a physical system. In relativistinc QM we have no "wavefuctions"--half-integer spin systems, for example, can't be described by a wavefunction. Wavefunction itself is somewhat of an anachronistic term--it's used either as a colloquialism for "state" or "state vector" or as the technical term for a continuous-basis (usually position or momentum) representation of a state vector. The latter usage probably merits an entry of its own, but I digress. The "duality" is at best an historical paradox which was resolved by the development of quantum mechanics, although good resolution of the classical problem involving light interference (polarization filtering effects were more problematic and actually resulted in the earliest developments in quantum-mechanics--in 1804!) came from Maxwell's equations and Fourier analysis--the problem really arose when interference was observed for "matter" particles as opposed to the EM force field. "Particle" refers to spatial localization and treatment of some problems to good approximation using classical or semiclassical collision theory; "wave" is a code-word for linearity which can yield interference effects such as fringes and nodes, as observed in the Young slit experiment, for example. A few comments on above statements: The person who apparently started this thread seems mostly on the right track. The "rule of thumb" is wrong in part because comparing photons and electrons is like comparing apples and oranges. Photons aren't "particles" per se--they're not localized in free space. Some have taken the position that photons "do not exist" except as mathematical tools (either bases for a Fourier or mode decomposition or the extension of this in QED, etc.) and I have to say that I agree, although I qualify that agreement. It is certainly more proper unless you're in a quantum cavity to talk about excitation quanta--I may be being a pedant here, but this non-abuse of terminology does avoid much (especially popular) confusion. "Probability wave" is less misleading if one clears up what it means--that by definition its square yields a position or momentum-space probability distribution function, which does correspond to the everyday usage--the PDF is just a continuous version of the histograms that would arise when one talks of chances of winning the Lottery (equally likely for each number) or landing on Boardwalk as opposed to Illinois Ave in monopoly (not equally likely) Why is the angry guy looking for discussion of solitons in this context?, and what the heck is a nonlinear wave? And why so mad about the use of duality?--the Huygens type wave theories and the corpuscular theories of light both turned out to be wrong--both were replaced by Maxwell's theory of light which (until quantization of the field became apparent from observations of line spectra and the photoelectric effect, and Planck's successful theoretical treatment of black-body radiation) resolved the "duality" for light. Regarding Copenhagen (and I'm a many-worlds guy, although I have reservations about the term), there is no credible interpretation of quantum mechanics which doesn't from some angle "look" exactly like Copenhagen, probabilities and all. What does the interpretation of QM have to do with this article, anyway? Coming back to "nonlinear waves," QM is a linear theory. All solutions are linear. Observable operators are linear. Show me a soliton arising directly from the Schrodinger or Heisenberg equation of motion and I'll show you either an error. State vectors add like, well, vectors. The deBroglie frequency of matter particles is, again, an old approximation, and a theoretical tool which pops out of free-space treatments. In a potential it's meaningless. Physicists recognize this. We use mode-decomposition, which is related, as a theoretical tool and these modes can take on physical meaning in certain situations. Are you objecting to the mathematics? Does the Fourier transform (linear!) bother you? I don't understand what your objection is. You can't do a mode-decomposition of a "wavefunction" that's a soliton like a wave rolling onto a beach, but that would be like doing heart surgery--neither exist in the real world. Wave-particle duality, historically, refers to observation of interference effects (linearity) such as fringes and nodes in experimental and theoretical treatments of matter particles such as electrons. It's not a concept considered to be accurate or enlightening by today's physicists and isn't referred to except as a metaphor used in teaching beginners. It is obfuscatory, but I don't understand your (the angry guy) side objections. --- ==Planck== We need to add something about Planck! It looks as though E = hv is attributed entirely to Einstein so far... User:Dgrant 01:14, Mar 25, 2004 (UTC) ==Doubt== I've added a bit to the section on Doubt, noting that while complementarity [has been conceptually violated], the mathematics have not been. However, it is the first use of the term ''complementarity'' in the article on wave-particle duality. I don't think that's right. ''Complementarity'' should either be mentioned in the introduction, or have its own subheading. --User:ErikStewart I am moving the entire section from the article to here, on the grounds that the result has not been peer-reviewed and so counts as unpublished research which is inappropriate for an encyclopedia. If and when it is published in a peer-reviewed journal, it can be moved back to the article. — User:Miguel 05:33, 2004 Nov 22 (UTC) === Doubt over wave-particle duality === There is currently (August 2004) some doubt over complementarity, the current description of Wave-particle duality, due to Double-slit_experiment#Shahriar_Afshar.27s_2004_contradictory_result using a variation on the double-slit experiment, which also appears to invalidate the Copenhagen interpretation. (See also: [http://www.spaceandmotion.com/Haselhurst-Biography.htm Geoff Haselhurst Biography]) So far this revised experiment has only been carried out with photons, not electrons, neutrons or protons, and the results have yet to be peer-reviewed. However, this experiment does not invalidate the Heisenberg equations on which the concept of complementarity was based. So similar experiments with other particles would almost certainly be successful. It seems that complementarity was an overly simple conceptual attempt to describe the mathematics, and will need to be revised. Peer review is still required to confirm this. == details == can we have more details about the electron gun experiment? what kind of detector is used? is this inside a vacuum tube? how do you specify that one electron per second is being output? is the interference pattern seen all at once, or is it an average of the pattern over time? etc. - User:Omegatron 02:09, Feb 4, 2005 (UTC) ==orbits== when i first heard bohrs model of the hydrogen atom, it included electrons "snapping" to each energy level because they were forming a "standing wave", and there was a drawing of a wave going around the atom, and showing how it fit together at some radii, but interfered with itself at others. but then later in chemstry i learned about the lobe-things and the "probability clouds", so the older standing wave thing sounds like BS to me now. how does this fit in? - User:Omegatron 02:09, Feb 4, 2005 (UTC) something like this: http://www.wonderquest.com/images/2003-04-25-atom.jpg http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod/ewav3.gif == Request for comments: popularized part == Hello, I (User:Cdang) made a popularized explaination that was removed by user:Afshar the 28 Jan 2005 at 15:28 with the comment: ''Removed oversimplistic and inaccurate "popularized" section.'' Of course, I do not support this deletion. First of all, the text itself: ---- ---- ''To spare room, I put the last version before removal(i.e. 21:54, 14 Mar 2005) instead of the original version and not besides, which should imho not alter the unterstanding of the discussion'' — User:Cdang|User talk:Cdang 09:29, 25 Mar 2005 (UTC) ---- == Popularised explanation: metaphor of the whirlpools in swift water == ''The original text of this part was published in French on the usenet forum news:fr.sci.physique the 13 September 2003, and is translated here under GFDL license with the author's consent.'' {| class="disputeabout" style="background: beige; border: 1px solid #aaa; padding: .2em; margin-bottom: 3px; font-size: 95%; width: auto;" | style="padding-right: 4px; padding-left: 4px;" | |Warning: the following section is not a scientific presentation. Its aim is to make understand that it ''is'' possible for an object to have both wave ''and'' particle properties, but the physical behaviour of a whirlpool is very different from an elementary particle.
Students are warned that this point of view should not be presented in tests, homework or examination. However, it can help them accepting the "odd" facts of the quantum physics such as the diffraction of fullerene or the diffraction of photons or electrons sent one by one. |} === Introduction === One of the main problem with quantum physics is to give images. Indeed, the human being needs images to think, memorise (see the article ''Cognitive psychology''). In the case of quantum physics, two different notions are required to represent the objects (elementary particles): waves and solid particles. The images are necessary built by analogy with what we know, our everyday experience. Thus, when we think about a sound wave, we think about the waves on the surface of the water; when we think about a particle, we think about a ball. These two concepts are different and exclusive: {| border="1" |+ Macroscopic properties of waves and particles |- ! Particle !! Wave |- |localised, finite extension |not localised (a sound can be heard everywhere in a room) |- |creation and destruction impossible1 |creation and destruction easy (pinch or stop a guitar string) |- |separated, impossible to merge1 |addition easy (interferences) |}
Note : # impossible means in the « classical » physics ; the mass creation phenomena (creation of a electron/positron par from a γ photon), of mass annihilation (disintegration) and nuclear fusion require precisely quantum physics This causes a great trouble, a misunderstanding, which often leads to a mental block, especially when asking: "if a particle is localised during an interaction, why isn't it also localised between interactions?" We will propose here an image, the whirlpools in swift water, to give a macroscopic illustration of this phenomenon. === The metaphor === Let us imagine a river with a rock in its middle. When the stream meets the rock, this gives birth to whirlpools. While the whirlpool moves away from the rock, it expands and vanishes. The object that is observed is the whirlpool, but is it itself an object, or is it just the interaction between two objects? It is possible to study the whirlpool itself: define its position, size, speed etc. but the whirlpool cannot exist alone, it is the result of the interaction between the stream and the rock. Let us now imagine two rocks placed in a straight line in the stream. We can see a whirlpool after the upstream rock, and a whirlpool after the downstream rock. Can we say that it is the same whirlpool that travelled from a rock to the other? Certainly not, nor can we say that the whirlpool comes from the source of the river. The whirlpool forms locally by the interaction between the stream and the obstacle, but it has no existence between two obstacles. === Comparison with the photon === The photon is like the whirlpool: * both appear randomly; the frequency and the size of the whirlpool is determined by the strength of the stream and the size of the rock, the energy of the photon and the frequency of appearance is determined by the wavelength and the flow of energy of the electromagnetic (EM) wave; * if there is no rock, there is no whirlpool; if the EM wave travels in vacuum, there is no wave packet; * as well as the whirlpool vanishes, the photon, when it is scattered (i.e. when it is not absorbed), is only localised on a short distance after the interaction (the wave packet spreads). This comparison can also be done with any elementary particle, just replace "electromagnetic wave" by "wavefunction". === Limits of the metaphor === But comparison is not reason. The metaphor does not reflect the wave packet reduction/collapse. In the case of the whirlpool, there is just a local concentration of kinetic energy, but the stream keeps its strength besides the rock. In the case of the photon, all the ''h''·ν energy is concentrated in the wave packet. Thus, if the photon is absorbed by an atom, there can be no other wave packet reduction further; in case of a low energy flow (photons emitted one by one), if a photon "appears" on a metal plate with a slit, "a given amount" of time is required before a photon can appear on the photographic plate behind the slit (the higher the energy stream, the shorter the time). Additionally, the whirlpool always follow the stream; the photon can be scattered in all directions (Rayleigh scattering). The metaphor only presents the "wave point of view" of the duality, i.e. how a particle can arise from a wave. It does not present the "particle point of view", i.e. the wave function associated to particle, and the relationship between the particle momentum and the de Broglie wavelength. ---- == Discussion == I noticed in my personnal and professional experience that many "science users" — engineers, but even some physics teachers — felt "uncomfortable" with this notion, and even did not accept it! And this notion is sometimes used for pseudo-sciences, to explain "bilocalization" (ethereal, extra-corporal experiences and such craps). For these reasons, I think it is important to help the conceptualization for everybody. Additionally, I think that if a non-physicist reads the text, he should retain a little bit more than a few dates. This is why I wrote this text. Now, I am aware that it has flaws that must be corrected, but I do not see the deletion as a correction. Afshar, please let me know what is wrong in this text, so I can improve it — or improve it yourself. User:Cdang|User talk:Cdang 11:10, 7 Feb 2005 (UTC) :No news after 10 days... I put the section back, but let the
just remove the
right !! Statement !! wrong or
right |- | photons appear randomly
the probability is determined by the EM field (and other parameters) || | whirlpools appear randomly
the probability is determined by the strength of the flow (and other parameters) || |- | the wave packet is well localised only during the interaction and a short moment after || | the whirlpool only exist during the interaction and a short moment after || |- | the wave packet dispersion after the interaction || | the whirlpool spreads after the rock || |} ==== Quiz answers ==== == New mode of discussion? == Set up a quiz. Marrant. C'est un piège ça?User:CSTAR 17:19, 23 Feb 2005 (UTC) :No trap. This is a scientific article so we should discuss about facts. :Well if you answer wrong to any of the topic, we can then talk about the accuracy of the exposed facts. As facts are facts, it will be easy to point out my errors. :If we all agree that the facts that are presented are right, we will then discuss about pedagogy, whether the presentation is relevant or not, which is ''completly'' different. :User:Cdang|User talk:Cdang 11:03, 24 Feb 2005 (UTC) == Possible compromise == OK here is a possible compromise: 1. The thing you propose is neither a metaphor nor an analogy. Please label the section soem other way. For instance visualization (to which you could add ''for some aspects of wave particle duality'') 2. Remove the psychobabble at the beginning. ::e.g ''One of the main problem with quantum physics is to give images. Indeed, the human being needs images to think, memorise (see the article Cognitive psychology).'' 3. Retain the contrast table, prefixing with some such thing as ::''Waves and particles are ordinarily thought of as being radically different kinds of entities; these differences are illustrated by entries in the following table'' 4. AFter the table make a comments such as :: ''However, it is possible for some aspects of particle behavior to be displayed in a wave-like medium (ed. remark: I'm not sure what a wave-like medium is other than a continuous medium which supports wave propagation)'' 5. Please get another picture. It's too big, it's not clear to focus on. If you tell me what to draw, I'll draw it myself. 6. What does this mean? ::''if there is no rock, there is no whirlpool; if the EM wave travels in vacuum, there is no wave packet;'' I assume you mean some aspect of wave propagation in free space; 7. State the limitations of the visual picture ''right away'', not in another section and without making any idle speculations. e.g., remove ''But comparison is not reason.'' User:CSTAR 16:38, 24 Feb 2005 (UTC) :# if you like, but if you could explain me in why it is not a metaphor nor an analogy, it would be nice :# OK, that's not the point here; it is just a way to justify why it is imho important to visualise things... The brain builds anyway pictures (a basis of pedagogy). :# I agree that the contrast table is more general and could be in another section :# If the table clearly states that it is a macroscopic and not quantic vision, then it is useless. :# try thenbetween the springs. You can imagine that this will modify the probability of apparition of the concentrates, and that it may stabilise a concentrate (i.e. there will always be a concentrate near this object). And if you have several foreign objects, you will see concentrates travelling between the objects, if they are close enough. If they are far away, you will see a concentrate disappearing randomly from one object, appearing randomly next to the other, but no concentrate between (the concentrates spread between the stabilising objects).
:The concentrates can also interact with each other. This explains that the thermal conductivity evolves with the temperature: the phonons, which "carry" the heat, interact with each other, thus the number of phonons (i.e. the temperature) influences their movement. They also interact with electrons (waves of course), explaining that good thermal conductors are good electric conductors too, and that the electric conductivity changes with temperature.
:Do the clouds clear a little bit ?
:User:Cdang|User talk:Cdang 19:17, 2 Mar 2005 (UTC)
::A tiny bit. This doesn't seem right to me, though. So it's really just waves adding on each other and bouncing off boundaries and such that happen to look kind of like particles every once in a while? This mesh could be simulated on the computer pretty easily. I'd like to see it. Something like this http://www.falstad.com/ripple/ . I don't understand how the "particles" are anything important in this example. - User:Omegatron 18:06, Mar 5, 2005 (UTC)
:Well, the particle aspect of the thing is that the energy is quantified, e.g. a concentrate of elastic deformation carries a given amount of energy. User:Cdang|User talk:Cdang 13:38, 8 Mar 2005 (UTC)
::??? How is it quantized? Aren't there also multiple particles taking up the same space? Sorry this is losing me more and more. I guess this discussion helps to come up with a way to explain this so that everyone can understand, though... - User:Omegatron 15:03, Mar 8, 2005 (UTC)
: Sorry, I'm not sure I understand what you mean; several particles can take the same place as long as they are bosons (and if you imagine it as wave, it is obvious: interferences), but the energy of each particle stays quantified. Of course, if this energy is too small to be detected individually, you will see a continuum, it will be apparently unquantified (that's the difference between long wavelength electromagnetic waves such as radio waves, and the short wavelength such as light or X-rays).
:I'm not sure there is a ''how'': the quanitfication ''is'' a fact, and that's all. It was discovered with the photoelectric effect (the electrons are taken away only by ultraviolet and not by red light, so the energy comes in packets) and the black body (the energy spectrum ''must be'' discontinuous otherwise the radiative energy of a black body would be infinite).
: That's where the representation of the phenomenon as a wave reaches its limit. There is nothing to understand because facts are not to be understood, they are to be accepted. You can go deeper and deeper in the explanation (i.e. description), you will always meet somewhere a fact that must simply be accepted — e.g. you know that you fall down, you know how (the cinetic law), you can tell that the same phenomenon make the planets turn around the sun, you can imagine gravitons, but still you just have to admit that you fall...
:Sorry if I answered the wrong question.
:User:Cdang|User talk:Cdang 19:29, 9 Mar 2005 (UTC)
== My edits ==
(User:William M. Connolley 15:57, 5 Mar 2005 (UTC)) I came to this page via RFC expecting constant dispute but the page appears quiet for a week or more. I've added a new intro that is how I see it; and I've moved the popular exposee down to the bottom. I'm not really sure I like the analogy stuff at all, but I really didn't like it being right at the top, and very long, so that the casual reader might never get beyond it to the actual science.
== Removed ==
Whether correct or not, the "popularised explanation" is a piece of essaying and therefore not appropriate for Wikipedia. Having it there with the warning messages is just ridiculous. There are many places on the web more suitable for things like this. User:Fredrik | User talk:Fredrik 02:27, 20 Mar 2005 (UTC)
: Agree. User:CSTAR 04:02, 20 Mar 2005 (UTC)
::Disagree: User:Fredrik, you didn't give any argument proving the text is wrong.
::A "piece of essaying", well, what do you mean? If all the facts are true (nobody ever pointed a false fact in this text, i.e. nobodyever put a ''wrong'' in the quizz), how can you say it is inappropriate?
::If someone wrote the hydraulic/electricity analogy (you know, voltage~pressure and intensity~flow), would you also say it is an essay? If not what is the difference between both cases?
::User:Cdang|User talk:Cdang 13:37, 23 Mar 2005 (UTC)
:::I thought "''the following section is not a scientific presentation''" would be sufficient. The question is, is this metaphor used in any physics textbooks? If so, references should be cited and the discussion of whether it is scientific should be integrated into its description, not presented in the meta-text. If the best reference is an anonymous Usenet post, the metaphor certainly fails the no original research policy. In either case, the text is also inappropriately worded. It does not present facts; it attempts to have a dialog with the reader. This might be more appropriate for Wikibooks, if really correct. User:Fredrik | User talk:Fredrik 17:57, 23 Mar 2005 (UTC)
::the "''the following section is not a scientific presentation''" is just a precaution; it means that it does not add any fact (it just repeats the facts presented above) but present them in another way. I can change the sentence if it is the problem.
::The reference to the Usenet post is just to avoid copyrights problems (I am the author of the post). The other references are all the physics books because all the facts presented in the section are in the general consensus. It is just the fact to put besides hydraulics and quantum mechanics that is unusual.
::User:Cdang|User talk:Cdang 08:02, 24 Mar 2005 (UTC)
: I agree that it should be removed, but I think an article on the water/electric current analogy would be a good thing. I might start that... :-) I think this "popularization" is more misleading than helpful, though. - User:Omegatron 15:39, Mar 23, 2005 (UTC)
::Well you judge ''this'' popularisation is good and ''that one'' is misleading… Great, we have a referee for pair review.
::Come on, Wikipedia has a deletion policy, if you delete this section, you have to do it according to this policy:
::* Wikipedia:What Wikipedia is not? Sorry, the article as it is is imho as useful as a blank page: people who know quantum physics already know this (it is ''the'' basis of QP), and people who do not know QP can't catch a word.
::* Wikipedia:No original research? Certainly not, nothing new, only consensual facts.
::* Wikipedia:Vanity page?
::* Copyright infringement? No copyright infringement.
::* Wikipedia:Wikipedia is not a dictionary?
::* Wikipedia:Patent nonsense?
::* Wikipedia:Vandalism?
::So which point(s) of the policy does the section violate?
::User:Cdang|User talk:Cdang 08:02, 24 Mar 2005 (UTC)
:::For me? Non-encyclopedic original research. It's very large and all it attempts to say is "some things behave like waves and particles at the same time". That's where the analogy ends, though. It's a ''very'' loose analogy. I am one of the aforementioned people who doesn't know QP, but I have read enough in trying to learn this concept that I know yours is more misleading than helpful. - User:Omegatron 17:54, Mar 24, 2005 (UTC)
(User:William M. Connolley 10:09, 24 Mar 2005 (UTC)) For myself, I simply found it unhelpful: too long, too vague, well I never really finished reading it. I didn't remove it, but I'm happier with it removed. IMHO the new text I added at the start is far clearer and far more helpful for people to understand what is going on.
:For User:Omegatron : unencyclopedic, well, it is a very vague thing, an information about a fictitious video game character such as Dark Force (Phantasy Star) has its place on Wikipedia, but not an attempt to make understand to the non-physicists one of the main concept that governs the electronics that fills their pockets… Original research certainly not, as I pointed out all the facts are known since more than 50 years, but the Double-slit_experiment#Shahriar_Afshar.27s_experiment which is refered to in the article is original research. Do Wikipedia considers two different types of contributors?
::''I just noticed that Afshar's experiment has been removed from the Double slit experiment article, sorry for this User:Cdang|User talk:Cdang 09:23, 25 Mar 2005 (UTC)''
:Additionally, you said "this "popularization" is more misleading than helpful", could you tell me in which way it is misleading so I can improve it (not necesserily for Wikipedia)? Which false idea came to your mind when you read this?
:For User:William M. Connolley, OK, you find it annoying and vague, but you did not try anything to improve it. Yes the text you added is far clearer and far more helpful and I thank you for that, but it does not clear all the clouds for the novices.
:Now, let's try to be constructive: a student comes to you and asks (as it happened to me): "uh, I didn't understand one thing: how can you say a particle is not localised? For the double slit experiment, if I put a photographic plate, I can see the photon, if I move it a few millimeters away, I can still see it, thus little by little I can track the photon; the photon ''has'' a trajectory and thus does ''not'' go through the ''both'' slits".
:What would you answer to him/her? Propose an answer and put it on the article, then the article will be more useful than a blank page…
:User:Cdang|User talk:Cdang 08:59, 25 Mar 2005 (UTC)
:: (User:William M. Connolley 15:57, 25 Mar 2005 (UTC)) I think you have to tell them that only things that can be observed really make sense; thus to speak of a trajectory (for an individual photon) when you don't observe that trajectory is dubious; and of course the results of the double split expt don't make sense if you believe in trajectories.
::* Why was Ashfar's experiment removed? It looks interesting...
::* Un-encyclopedic
::: By this, I simply mean "not accurate". You asked which of those categories it belonged to, so I picked the closest. A whirlpool can move through the water in a straight line and collide with and interact with other whirlpools, but this is not the same thing as the effects seen in the double-slit experiments. The whirlpool probably has more in common with things like solitons. It's really just a special type of wave...
::* Original research
::: Well, yes, of course whirlpools really do exist, and really do travel in straight lines, but your essay on using that "duality" to make an analogy to quantum wave/particle duality is original, no? Do others use the same analogy to teach this?
::* The article as it currently exists is as useless as a blank page? I disagree. I would like a better "popularized" explanation, though. - User:Omegatron 15:22, Mar 25, 2005 (UTC)
:To User:William M. Connolley :
:''when you don't observe that trajectory is dubious;'' → but they do see a trajectory when putting a photographic plate; you see, the student ''could not'' imagine why the photon would act differently with or without a photo plate. That's why I imagined this metaphor, to show him an object can exist when there is an interaction and not exist when there is no interaction.
:: (User:William M. Connolley 09:43, 30 Mar 2005 (UTC)) No they don't see a trajectory: they see a measurement of a photon at a point. If they think they are seeing a trajectory, then here is where you can explain the difference to them.
:''and of course the results of the double split expt don't make sense if you believe in trajectories'' → of course, but that's what you already told during the lesson: "the result of the double slits experiments proves that you must forget etc."; if the message did not work the first time, I doubt it will work by just repeating it. The reason why I tried to find a different way (and I think it worked).
:To User:Omegatron :
:''A whirlpool can move through the water in a straight line'' → yes, that's precisely why the last section points out the flaws of the metaphor.
:''and collide with and interact with other whirlpools'' → interact yes, not colide (just like quantic particles)
:''but this is not the same thing as the effects seen in the double-slit experiments.'' → of course not, that's why it is called "metaphor" or "analogy"; if my student doesn't know the difference between a fact and an analogy, I just send him to read a dictionary.
:''your essay [...] is original, no?'' → when you teach, you have to adapt your message to your public; a teacher ''must'' be original, i.e. find new solutions when new difficulties of understanding arise (and mind that you are always at least 10 years older than the students and it never decreases, so the generation discrepancies come one day or another).
:''The article as it currently exists is as useless as a blank page? I disagree.'' → well, just ask a young science student (e.g. first year of university) what he/she can do with it; and just ask a curious person who did not follow science studies. We will never write "Quantum physics for dummies", but we can try anyway to make some concepts as reachable as possible, can't we?
:''I would like a better "popularized" explanation, though.'' → I would be happy too, but for the moment, I didn't see any other try. You think that nothing is better, I think not.
:User:Cdang|User talk:Cdang 17:23, 26 Mar 2005 (UTC)
----
==Reader's comments==
Consider me as an intelligent non-physicist, someone who would look up an encyclopedia to understand Wave Particle Duality. In this light, I believe my first impressions would be useful in updating the article. I expected the first section of the article to introduce the idea, the next to give a brief history and the last to explain the prevailing consensual model and explanation. I also expected the last section to tell me what I should already know to understand the explanation being presented.
That said, I found the article dense with information but disorienting. The external link [http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Nave, R.,Wave-Particle Duality. HyperPhysics, Quantum Physics] was more useful. Presently, the article headings are anchored around scientists (Fresnel, Einstein, Broglie). I would find it more meaningful to see section headings based on the conceptual history that underpin Wave-Particle Duality than on physicists.
For now, I would suggest folks above to skip the Whirlpool argument. The overall format of the article needs revision and the current argument above is moot till the article takes better shape. I'll stick around and work with anyone who responds. -User:Selva 15:01, 16 Apr 2005 (UTC)
:I like your ideas. - User:Omegatron 17:12, Apr 16, 2005 (UTC)
== help me someone ==
all i want to know is WHAT IS wave/particle duality and de broglie hypothesis. ive being bugging on understanding this for months. if anyone knows any books/sites/mag that gives a easy AND detailed introduction to them PLEASE tell me (just not too hard please)
- thanks for your time
edit: for the probability wave of a particle, does it really exist in phyiscal terms? like electromagnetic waves? because i really don't know why they call it a 'wave'
See other meanings of words starting from letter:
Words begining with Wave-particle_duality:
Wave-Particle_duality
Wave-Particle_duality
Wave-particle_duality
Wave-particle_duality
Wave-Particle duality
#REDIRECT Wave-particle_duality
Wave-Particle duality
#REDIRECT Talk:Wave-particle_duality
Wave-particle duality
In physics, wave-particle duality holds that light and matter can exhibit property of both waves and of particles. This concept is a key part of quantum mechanics. In the usual formulations of classical mechanics a given object ''is'' either a particle or a wave. For example, an electron is a particle (because they are observed to behave in particle-like ways), and light is a wave (because it behaves in wave-like ways, such as interference: see below). This categorisation was applied even to objects below the scale of direct observation, essentially by analogy with macroscopic phenomena. However, problems emerge with the viewpoint: electrons too can be made to interfere and thus appear wave-like; light (especially in the photoelectric effect, as analysed in 1905 by Albert Einstein) can possess particle-like properties. Quantum mechanics emphasises the primacy of measurement and not attributing properties to objects beyond what can be measured. Hence the concept of wave-particle duality arose: it is not necessary, or useful, to say that an electron ''is'' a particle - or a wave - just that in certain circumstances it behaves like a wave, and in others like a particle. == Fresnel, Maxwell, and Young == In the early 1800s, the double-slit experiments by Thomas Young (scientist) and Augustin-Jean Fresnel provided evidence for Christian Huygens theories: these experiments showed that when light is sent through a grid, a characteristic interference pattern is observation, very similar to the pattern resulting from the interference of water waves; the wavelength of light can be computation from such patterns. James Clerk Maxwell, during the late-1800s, explained light as the propagation of electromagnetic waves with the Maxwells equations. These equations were verified by experiment, and Huygens' view became widely accepted. ==Einstein and photons== In 1905, Albert Einstein reconciled Huygens' view with that of Isaac Newton; he explained the photoelectric effect (an effect in which light did not seem to act as a wave) by postulating the existence of photons, quantum of energy with particulate quality. Einstein axiom that light's frequency, ''ν'', is related to the energy, ''E'', of its photons: :, where ''h'' is Planck's constant (6.626 x 10-34 J seconds). ==De Broglie== In 1924, Louis-Victor de Broglie claimed that ''all'' matter has a wave-like nature; he related wavelength, λ, and momentum, ''p'': :. This is a generalization of Einstein's equation above since the momentum of a photon is given by ''p'' = ''E'' / ''c'' where ''c'' is the speed of light in vacuum, and ''λ'' = ''c'' / ''ν''. De Broglie's formula was confirmed three years later by Clinton Joseph Davisson and Lester Halbert Germer, by guiding a beam of electrons (which have rest mass) through a crystalline grid and observing the predicted interference patterns. Similar experiments have since been conducted with neutrons and protons. Authors of similar recent experiments with atoms and molecules claim that these larger particles also act like waves. The most famous experiments are those of Estermann and Otto Stern in 1929, and the diffraction of fullerene C60 by researchers from the University of Vienna in 1999; in the later case, the wavelength of de Broglie is 2.5 picometer whereas the diameter of the molecule is about 1 nanometer, i.e. about 400 times larger. This is still a controversial subject because these experimenters have assumed arguments of wave-particle duality and have assumed the validity of deBroglie's equation in their argument. The Planck constant ''h'' is extremely small and that explains why we don't perceive a wave-like quality of everyday objects: their wavelengths are exceedingly small. The fact that matter can have very short wavelengths is exploited in electron microscopy. In quantum mechanics, the wave-particle duality is explained as follows: every system and particle is described by state functions which encode the probability distributions of all measurable variables. The position of the particle is one such variable. Before an observation is made the position of the particle is described in terms of probability waves which can interfere with each other. In quantum electrodynamics, Richard Feynman shows the wave-particle duality of photons and electrons is an illusion. In his view, photons and electrons obey rules that share some qualities of both particles and waves. They are neither particle nor wave, but some generalized object with no direct macroscopic analog. An intriguingly simple experiment, the double-slit experiment, summarizes the duality: aim an electron gun at a screen with two slits and record their positions of detection at a detector behind the screen. You will observe an interference pattern just like the one produced by diffraction of a light or water wave at two slits. This pattern will even appear if you slow down the electron source so that only one electron's worth of charge per second comes through. "Classically speaking", every electron is a point particle and must either travel through the first or through the second slit. So we should be able to produce the same interference pattern if we ran the experiment twice as long, closing slit number one for the first half, then closing slit number two for the second half. But the same pattern does not emerge. Furthermore, if we build detectors around the slits in order to determine which path a particular electron takes, this very measurement destroys the interference pattern as well. But this is a classical explanation and something much more profound is taking place. The interference pattern can be explained as a result of the charge wave being diffracted by ''both'' slits and interfering with itself. In quantum mechanics, the state function is a complex-valued function (mathematics) of space and time. The square of the magnitude (mathematics) of this function describes the probability of finding the electron at a given location at a given time. Interference is due to the fact that the square of the magnitude of the sum of two complex number may be different from the sum of the squares of their magnitudes. The experiment also illustrates an interesting feature of quantum mechanics. Until an observation is made the position of a particle is described in terms of probability waves, but after the particle is observed, it is described as a fixed value. How to conceptualize the process of measurement is one of the great unresolved questions of quantum mechanics. The standard interpretation is the Copenhagen interpretation which leads to interesting thought experiments such as Schrödinger's cat. Due to this confusion, some theorists (including Stephen Hawking and Murray Gell-Mann) believe the many-worlds interpretation is true. However, there is currently some doubt over the validity of both the Copenhagen interpretation and the many-worlds interpretation, due to the controversial Afshar_experiment [http://www.irims.org/quant-ph/030503/], a variation of the two-pin-hole \"which way\" experiment. Notes ''Wave-particle duality of C60'', M. Arndt , O. Nairz, J. Voss-Andreae, C. Keller, G. van der Zouw, A. Zeilinger, ''Nature'' 401, 680-682, 14 October 1999 ==See also== * Niels Bohr * Louis de Broglie ** De Broglie hypothesis * diffraction * double-slit experiment * Albert Einstein * electromagnetism * electron * photoelectric effect * Max Planck * quantum mechanics * Erwin Schrödinger * x-rays ==External links== * Shahriar S. Afshar, [http://www.irims.org/quant-ph/030503/ Afshar Experiment Preprint] * Nave, R., "''[http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Wave-Particle Duality]''". HyperPhysics, Quantum Physics. * [http://www.quantum.univie.ac.at/research/matterwave/c60/index.html Diffraction and Interference with Fullerenes: Wave-particle duality of C60] (University of Vienna) Quantum mechanics Electromagnetism
Wave-particle duality
---- ==Flaws== In texts that talk about detecting light by means of either a "particle detector" or a "wave detector" no information is given as to the suitability of these objects to the tasks to which they are put. Why is the "particle detector" believed to be detecting a particle and not high tide. Conversely why is the "wave detector" detecting a wave-type light and not just showing it's own distortion from being collided with a particle-like light. Furthermore, no explanation is given as for how they know one and only one photon is emitted. User:hackwrenchRobert Claypool ==misleading or wrong== [The stuff below this line is misleading or wrong, I would recomend deleting it. The measurement problem is far more general then what is touched on here, and the ``rule of thumb'' is just plain wrong.] Mathematically, electrons and other such creatures are modelled as waves. The question is, then, why they appear to be particles in certain experiments. This is called the measurement problem, and is solved differently in different interpretations of quantum mechanics. An extremely simple (and possibly overgeneralised) layman's rule of thumb is that when fast and small, think "wave". When slow and big, think "matter". ---- ---- ==Why is the rule of thumb wrong== Why is the rule of thumb wrong? Are there situations where it is advantageous to model, say, a cow as a wave? --AxelBoldt ----- There are a number of problems with the rule of thumb. The big problem is that the key difference between what we normal think of "matter" and "energy" has nothing to do with particle/wave duality but rather the difference between fermions and bosons and the pauli exclusion principle. Also the rule just doesn't work. A standing radio wave is big and slow but you can think of it as a wave. A beam of X rays is fast and small, but is best conceptualized as a stream of particles. -- User:Chenyu ---- ==explanation of what Wave-Particle duality means== I'd like to see more explanation of what Wave-Particle duality means and less incomprehensible history of how it was discovered by physicists. What is it supposed to mean that wavefunctions exhibit ''some properties'' of waves and ''some properties'' particles? For that matter, what does it mean for something to be a wave or a particle? Key terms I'm looking for are: ''soliton'' and ''non-linear wave''. And given that we're talking about non-linear waves, terms like "frequency" should be avoided or explained; non-linear waves don't ''have'' an exact frequency or wavelength! (I'd prefer if it were explained since that would make explaining the Heisenberg "uncertainty" principle easier.) Oh, and I'd like the first paragraph to explain that "duality" is a misnomer since the wave and particle theories of light are not equivalent. That's just a term tacked on by some loser who wanted to sell a mind-bender to a bunch of stuffy conservative physicists. And "probability wave" is seriously misleading. Probability is not what most people think it is; mathematical probability has no relation to the everyday concept of probability. And since "probability" adds nothing to "wave" or "wavefunction", it should be junked. Other misleading things: the ever popular misconception that quantum mechanics has anything to do with the travesty called Copenhagen. The impression that quantum mechanics recognizes a pre-observation and post-observation domain is seriously wrong and should be avoided at all cost. And as long as we're explaining the history, why is Huygens left out of the picture? IF YOU'RE GOING TO TALK.....BE SPECIFIC....YOU CAN'T JUST STATE WHY SOMETHING IS WRONG WITHOUT STATING YOUR REASONING. ISN'T THAT WHAT A PHYSICIST DOES? JUSTIFY WHY. THINK ABOUT IT == Rule of thumb == Wouldn't the ratio of mass to kinetic energy make for a better rule of thumb? Photons: No mass, zero ratio = very wave-like Electrons: Low mass, low ratio = quite wave-like ... Deep-frozen chicken: Enormous mass, enormous ratio (compared with the others) = no measurable interference when shot through double-slit ;-) ---- ---- ==understanding of QM POV== I'm made to recall Willis Lamb's statement that appeals to a "wave-particle duality" (among other things) reveal an individual's misunderstanding of QM...the historical discussion in this article is nice (and deserves expansion) but the physics needs serious updates. (Whoever wrote the above comment that ended in all caps needs to brush up on his physics...) For starters, regarding the article, there is a glaring error, namely, that the "wave function" encodes all knowable information about a physical system. In relativistinc QM we have no "wavefuctions"--half-integer spin systems, for example, can't be described by a wavefunction. Wavefunction itself is somewhat of an anachronistic term--it's used either as a colloquialism for "state" or "state vector" or as the technical term for a continuous-basis (usually position or momentum) representation of a state vector. The latter usage probably merits an entry of its own, but I digress. The "duality" is at best an historical paradox which was resolved by the development of quantum mechanics, although good resolution of the classical problem involving light interference (polarization filtering effects were more problematic and actually resulted in the earliest developments in quantum-mechanics--in 1804!) came from Maxwell's equations and Fourier analysis--the problem really arose when interference was observed for "matter" particles as opposed to the EM force field. "Particle" refers to spatial localization and treatment of some problems to good approximation using classical or semiclassical collision theory; "wave" is a code-word for linearity which can yield interference effects such as fringes and nodes, as observed in the Young slit experiment, for example. A few comments on above statements: The person who apparently started this thread seems mostly on the right track. The "rule of thumb" is wrong in part because comparing photons and electrons is like comparing apples and oranges. Photons aren't "particles" per se--they're not localized in free space. Some have taken the position that photons "do not exist" except as mathematical tools (either bases for a Fourier or mode decomposition or the extension of this in QED, etc.) and I have to say that I agree, although I qualify that agreement. It is certainly more proper unless you're in a quantum cavity to talk about excitation quanta--I may be being a pedant here, but this non-abuse of terminology does avoid much (especially popular) confusion. "Probability wave" is less misleading if one clears up what it means--that by definition its square yields a position or momentum-space probability distribution function, which does correspond to the everyday usage--the PDF is just a continuous version of the histograms that would arise when one talks of chances of winning the Lottery (equally likely for each number) or landing on Boardwalk as opposed to Illinois Ave in monopoly (not equally likely) Why is the angry guy looking for discussion of solitons in this context?, and what the heck is a nonlinear wave? And why so mad about the use of duality?--the Huygens type wave theories and the corpuscular theories of light both turned out to be wrong--both were replaced by Maxwell's theory of light which (until quantization of the field became apparent from observations of line spectra and the photoelectric effect, and Planck's successful theoretical treatment of black-body radiation) resolved the "duality" for light. Regarding Copenhagen (and I'm a many-worlds guy, although I have reservations about the term), there is no credible interpretation of quantum mechanics which doesn't from some angle "look" exactly like Copenhagen, probabilities and all. What does the interpretation of QM have to do with this article, anyway? Coming back to "nonlinear waves," QM is a linear theory. All solutions are linear. Observable operators are linear. Show me a soliton arising directly from the Schrodinger or Heisenberg equation of motion and I'll show you either an error. State vectors add like, well, vectors. The deBroglie frequency of matter particles is, again, an old approximation, and a theoretical tool which pops out of free-space treatments. In a potential it's meaningless. Physicists recognize this. We use mode-decomposition, which is related, as a theoretical tool and these modes can take on physical meaning in certain situations. Are you objecting to the mathematics? Does the Fourier transform (linear!) bother you? I don't understand what your objection is. You can't do a mode-decomposition of a "wavefunction" that's a soliton like a wave rolling onto a beach, but that would be like doing heart surgery--neither exist in the real world. Wave-particle duality, historically, refers to observation of interference effects (linearity) such as fringes and nodes in experimental and theoretical treatments of matter particles such as electrons. It's not a concept considered to be accurate or enlightening by today's physicists and isn't referred to except as a metaphor used in teaching beginners. It is obfuscatory, but I don't understand your (the angry guy) side objections. --- ==Planck== We need to add something about Planck! It looks as though E = hv is attributed entirely to Einstein so far... User:Dgrant 01:14, Mar 25, 2004 (UTC) ==Doubt== I've added a bit to the section on Doubt, noting that while complementarity [has been conceptually violated], the mathematics have not been. However, it is the first use of the term ''complementarity'' in the article on wave-particle duality. I don't think that's right. ''Complementarity'' should either be mentioned in the introduction, or have its own subheading. --User:ErikStewart I am moving the entire section from the article to here, on the grounds that the result has not been peer-reviewed and so counts as unpublished research which is inappropriate for an encyclopedia. If and when it is published in a peer-reviewed journal, it can be moved back to the article. — User:Miguel 05:33, 2004 Nov 22 (UTC) === Doubt over wave-particle duality === There is currently (August 2004) some doubt over complementarity, the current description of Wave-particle duality, due to Double-slit_experiment#Shahriar_Afshar.27s_2004_contradictory_result using a variation on the double-slit experiment, which also appears to invalidate the Copenhagen interpretation. (See also: [http://www.spaceandmotion.com/Haselhurst-Biography.htm Geoff Haselhurst Biography]) So far this revised experiment has only been carried out with photons, not electrons, neutrons or protons, and the results have yet to be peer-reviewed. However, this experiment does not invalidate the Heisenberg equations on which the concept of complementarity was based. So similar experiments with other particles would almost certainly be successful. It seems that complementarity was an overly simple conceptual attempt to describe the mathematics, and will need to be revised. Peer review is still required to confirm this. == details == can we have more details about the electron gun experiment? what kind of detector is used? is this inside a vacuum tube? how do you specify that one electron per second is being output? is the interference pattern seen all at once, or is it an average of the pattern over time? etc. - User:Omegatron 02:09, Feb 4, 2005 (UTC) ==orbits== when i first heard bohrs model of the hydrogen atom, it included electrons "snapping" to each energy level because they were forming a "standing wave", and there was a drawing of a wave going around the atom, and showing how it fit together at some radii, but interfered with itself at others. but then later in chemstry i learned about the lobe-things and the "probability clouds", so the older standing wave thing sounds like BS to me now. how does this fit in? - User:Omegatron 02:09, Feb 4, 2005 (UTC) something like this: http://www.wonderquest.com/images/2003-04-25-atom.jpg http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod/ewav3.gif == Request for comments: popularized part == Hello, I (User:Cdang) made a popularized explaination that was removed by user:Afshar the 28 Jan 2005 at 15:28 with the comment: ''Removed oversimplistic and inaccurate "popularized" section.'' Of course, I do not support this deletion. First of all, the text itself: ---- ---- ''To spare room, I put the last version before removal(i.e. 21:54, 14 Mar 2005) instead of the original version and not besides, which should imho not alter the unterstanding of the discussion'' — User:Cdang|User talk:Cdang 09:29, 25 Mar 2005 (UTC) ---- == Popularised explanation: metaphor of the whirlpools in swift water == ''The original text of this part was published in French on the usenet forum news:fr.sci.physique the 13 September 2003, and is translated here under GFDL license with the author's consent.'' {| class="disputeabout" style="background: beige; border: 1px solid #aaa; padding: .2em; margin-bottom: 3px; font-size: 95%; width: auto;" | style="padding-right: 4px; padding-left: 4px;" | |Warning: the following section is not a scientific presentation. Its aim is to make understand that it ''is'' possible for an object to have both wave ''and'' particle properties, but the physical behaviour of a whirlpool is very different from an elementary particle.
Students are warned that this point of view should not be presented in tests, homework or examination. However, it can help them accepting the "odd" facts of the quantum physics such as the diffraction of fullerene or the diffraction of photons or electrons sent one by one. |} === Introduction === One of the main problem with quantum physics is to give images. Indeed, the human being needs images to think, memorise (see the article ''Cognitive psychology''). In the case of quantum physics, two different notions are required to represent the objects (elementary particles): waves and solid particles. The images are necessary built by analogy with what we know, our everyday experience. Thus, when we think about a sound wave, we think about the waves on the surface of the water; when we think about a particle, we think about a ball. These two concepts are different and exclusive: {| border="1" |+ Macroscopic properties of waves and particles |- ! Particle !! Wave |- |localised, finite extension |not localised (a sound can be heard everywhere in a room) |- |creation and destruction impossible1 |creation and destruction easy (pinch or stop a guitar string) |- |separated, impossible to merge1 |addition easy (interferences) |}
Note : # impossible means in the « classical » physics ; the mass creation phenomena (creation of a electron/positron par from a γ photon), of mass annihilation (disintegration) and nuclear fusion require precisely quantum physics This causes a great trouble, a misunderstanding, which often leads to a mental block, especially when asking: "if a particle is localised during an interaction, why isn't it also localised between interactions?" We will propose here an image, the whirlpools in swift water, to give a macroscopic illustration of this phenomenon. === The metaphor === Let us imagine a river with a rock in its middle. When the stream meets the rock, this gives birth to whirlpools. While the whirlpool moves away from the rock, it expands and vanishes. The object that is observed is the whirlpool, but is it itself an object, or is it just the interaction between two objects? It is possible to study the whirlpool itself: define its position, size, speed etc. but the whirlpool cannot exist alone, it is the result of the interaction between the stream and the rock. Let us now imagine two rocks placed in a straight line in the stream. We can see a whirlpool after the upstream rock, and a whirlpool after the downstream rock. Can we say that it is the same whirlpool that travelled from a rock to the other? Certainly not, nor can we say that the whirlpool comes from the source of the river. The whirlpool forms locally by the interaction between the stream and the obstacle, but it has no existence between two obstacles. === Comparison with the photon === The photon is like the whirlpool: * both appear randomly; the frequency and the size of the whirlpool is determined by the strength of the stream and the size of the rock, the energy of the photon and the frequency of appearance is determined by the wavelength and the flow of energy of the electromagnetic (EM) wave; * if there is no rock, there is no whirlpool; if the EM wave travels in vacuum, there is no wave packet; * as well as the whirlpool vanishes, the photon, when it is scattered (i.e. when it is not absorbed), is only localised on a short distance after the interaction (the wave packet spreads). This comparison can also be done with any elementary particle, just replace "electromagnetic wave" by "wavefunction". === Limits of the metaphor === But comparison is not reason. The metaphor does not reflect the wave packet reduction/collapse. In the case of the whirlpool, there is just a local concentration of kinetic energy, but the stream keeps its strength besides the rock. In the case of the photon, all the ''h''·ν energy is concentrated in the wave packet. Thus, if the photon is absorbed by an atom, there can be no other wave packet reduction further; in case of a low energy flow (photons emitted one by one), if a photon "appears" on a metal plate with a slit, "a given amount" of time is required before a photon can appear on the photographic plate behind the slit (the higher the energy stream, the shorter the time). Additionally, the whirlpool always follow the stream; the photon can be scattered in all directions (Rayleigh scattering). The metaphor only presents the "wave point of view" of the duality, i.e. how a particle can arise from a wave. It does not present the "particle point of view", i.e. the wave function associated to particle, and the relationship between the particle momentum and the de Broglie wavelength. ---- == Discussion == I noticed in my personnal and professional experience that many "science users" — engineers, but even some physics teachers — felt "uncomfortable" with this notion, and even did not accept it! And this notion is sometimes used for pseudo-sciences, to explain "bilocalization" (ethereal, extra-corporal experiences and such craps). For these reasons, I think it is important to help the conceptualization for everybody. Additionally, I think that if a non-physicist reads the text, he should retain a little bit more than a few dates. This is why I wrote this text. Now, I am aware that it has flaws that must be corrected, but I do not see the deletion as a correction. Afshar, please let me know what is wrong in this text, so I can improve it — or improve it yourself. User:Cdang|User talk:Cdang 11:10, 7 Feb 2005 (UTC) :No news after 10 days... I put the section back, but let the
<!--'''wrong'' ''right'' --> just remove the
<!-- and --> and let your answer to the statement
* please sign your quiz by putting four tilde ~~~~ right !! Statement !! wrong or
right |- | photons appear randomly
the probability is determined by the EM field (and other parameters) || | whirlpools appear randomly
the probability is determined by the strength of the flow (and other parameters) || |- | the wave packet is well localised only during the interaction and a short moment after || | the whirlpool only exist during the interaction and a short moment after || |- | the wave packet dispersion after the interaction || | the whirlpool spreads after the rock || |} ==== Quiz answers ==== == New mode of discussion? == Set up a quiz. Marrant. C'est un piège ça?User:CSTAR 17:19, 23 Feb 2005 (UTC) :No trap. This is a scientific article so we should discuss about facts. :Well if you answer wrong to any of the topic, we can then talk about the accuracy of the exposed facts. As facts are facts, it will be easy to point out my errors. :If we all agree that the facts that are presented are right, we will then discuss about pedagogy, whether the presentation is relevant or not, which is ''completly'' different. :User:Cdang|User talk:Cdang 11:03, 24 Feb 2005 (UTC) == Possible compromise == OK here is a possible compromise: 1. The thing you propose is neither a metaphor nor an analogy. Please label the section soem other way. For instance visualization (to which you could add ''for some aspects of wave particle duality'') 2. Remove the psychobabble at the beginning. ::e.g ''One of the main problem with quantum physics is to give images. Indeed, the human being needs images to think, memorise (see the article Cognitive psychology).'' 3. Retain the contrast table, prefixing with some such thing as ::''Waves and particles are ordinarily thought of as being radically different kinds of entities; these differences are illustrated by entries in the following table'' 4. AFter the table make a comments such as :: ''However, it is possible for some aspects of particle behavior to be displayed in a wave-like medium (ed. remark: I'm not sure what a wave-like medium is other than a continuous medium which supports wave propagation)'' 5. Please get another picture. It's too big, it's not clear to focus on. If you tell me what to draw, I'll draw it myself. 6. What does this mean? ::''if there is no rock, there is no whirlpool; if the EM wave travels in vacuum, there is no wave packet;'' I assume you mean some aspect of wave propagation in free space; 7. State the limitations of the visual picture ''right away'', not in another section and without making any idle speculations. e.g., remove ''But comparison is not reason.'' User:CSTAR 16:38, 24 Feb 2005 (UTC) :# if you like, but if you could explain me in why it is not a metaphor nor an analogy, it would be nice :# OK, that's not the point here; it is just a way to justify why it is imho important to visualise things... The brain builds anyway pictures (a basis of pedagogy). :# I agree that the contrast table is more general and could be in another section :# If the table clearly states that it is a macroscopic and not quantic vision, then it is useless. :# try the
|thumb See other meanings of words starting from letter:
W
WA | WB | WC | WD | WE | WF | WG | WH | WI | WJ | WK | WL | WM | WN | WO | WP | WR | WS | WT | WU | WX | WY | WZ |Words begining with Wave-particle_duality:
Wave-Particle_duality
Wave-Particle_duality
Wave-particle_duality
Wave-particle_duality
These materials are based on Wikipedia and licensed under the GNU FDL
YouTube.com videos better site than Turbo Tax 2007
