Electrons as Particles and Atomic Orbitals

[MrMuse]

I am curious about an issue raised in another thread of this forum: namely, that of the interpretation of atomic orbitals in light of the fact that electrons are particles, not waves. In most organic chemistry textbooks, the atomic orbitals are shown to be standing waves, with regions of positive amplitude and regions of negative amplitude (the 2p atomic orbital, for example). If wave/particle duality is obsolete, then how is one to interpret these pictures in textbooks? Are they merely mathematical functions that have no physical relevance? What I mean is, rather than talk about atomic orbitals (ψ(r,θ,φ)), which contain positive and negative phases, would it be more physically meaningful/relevant to talk about probability distributions (|ψ(r,θ,φ)|²)? If electrons are not waves, then what are we to make of the negative spatial components of atomic orbitals? Further, if electrons are not waves, then in what way should we modify these observations:

1. The electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves. The lowest possible energy an electron can take is therefore analogous to the fundamental frequency of a wave on a string. Higher energy states are then similar to harmonics of the fundamental frequency.
2. The electrons are never in a single point location, although the probability of interacting with the electron at a single point can be found from the wave function of the electron.

Thanks for your help!

 

 

 

[mathematic]

"I am curious about an issue raised in another thread of this forum: namely, that of the interpretation of atomic orbitals in light of the fact that electrons are particles, not waves. "

 

 

 

Fact??? Electrons have wave and particle properties.

 

 

 

http://en.wikipedia.org/wiki/Electron_configuration

[MrMuse]

"I am curious about an issue raised in another thread of this forum: namely, that of the interpretation of atomic orbitals in light of the fact that electrons are particles, not waves. "

 

 

 

Fact??? Electrons have wave and particle properties.

 

 

 

http://en.wikipedia....n_configuration

 

You're right. "Fact" is a loaded word. How about, the observation that electrons are particles, not waves. It was mentioned in another thread that wave/particle duality is obsolete and that particle physicists now believe that electrons are quantum particles, not particles and waves, as was previously thought. A wavefunction can't be experimentally measured (none of the supposed "wave" properties can), but particle properties are experimentally measured all the time, i.e. mass, charge, density, etc. Further, it was suggested that there are quantum systems that can not be described by wave mechanics and that modern Dirac formalism does not use wavefunctions. In this sense, (if I understand the argument correctly) it may be correct to regard the electrons as quantum particles all of the time and that wave mechanics may just be a mathematical tool and not representative of physical reality. This is what I meant.

Edited May 28, 2012 by MrMuse

[MigL]

And what physical reality do 'quantum particles' represent ??

 

I'm not saying you are wrong, I just don't think its fair to say that one is more 'realistic' than the other. They are both mathematical models of a reality which may actually be neither .

What you should say is that one has a more complete mathematical model than the other, but then again most applied quantum mechanics is not done with QED, but rather good, old-fashioned wave mechanics.

Edited May 29, 2012 by MigL

[swansont]

You're right. "Fact" is a loaded word. How about, the observation that electrons are particles, not waves. It was mentioned in another thread that wave/particle duality is obsolete and that particle physicists now believe that electrons are quantum particles, not particles and waves, as was previously thought.

emphasis added.

 

I don't want to recreate that discussion, but particle physicists ≠ all physicists. If you operate in a regime where the particle properties dominate, you'll treat them as particles. Meanwhile, other physicists still talk of wave properties and atomic electrons have orbitals, not orbits.

[MrMuse]

OK. Let me further clarify. Before oxygen was discovered, there was a competing theory called the phlogiston theory. The phlogiston theory seemed to explain the same phenomena as the competing theory of oxygen, but in a different way. To explain combustion, it was postulated that some substances contain phlogiston and when burned in a closed atmosphere, the air becomes saturated with phlogiston and so combustion stops. Rather, we know what is happening is that the oxygen runs out and that is what stops combustion. Not the overabundance of one substance, but the lack of another. One theory was confirmed in the physical world and the other was not. Surely there was a time when both theories were accepted as different views of the way the world worked, but since they were mutually exclusive, they could not both be true. I see this as the same with particle versus wave/particle duality. Theories that postulate that electrons are particles are mutually exclusive from theories that postulate that electrons are particles and waves. Both theories can not be true. Certainly wave mechanics can be used to describe particles, but are they really waves? Incredibly complex epicycles were used by Ptolemy to accurately describe the mathematical motion of the heavens to support his Earth-centered galaxy, but that does not mean that his system was just as physically relevant as Galileo's sun-centered system even though the math was the same, does it? One theory was physically meaningful, the other was only mathematically meaningful, even though both seemed to accurately describe the motion of the heavens. In a similar fashion, the modern math that is being used to describe electrons as only particles, while completely ignoring their wavefunctions, is much simpler and is currently the most promising area of molecular computation (density functional theory). Wave/particle duality (Psi) describes the atomic orbitals with spatial coordinates that result in standing waves, with areas of positive amplitude and areas of negative amplitude. How are we to physically think of "negative amplitude space"? Rather, if we take the absolute value of the square of psi, then we will obtain the probability density of the electron (in fact, one can also obtain the probability density of the electron without reference to the wavefunction). The shape of the probability density is nearly identical to the shape of the atomic orbitals and it has physical meaning. We could design an experiment to measure the probability density, but we couldn't design an experiment to measure the wavefunction.

 

emphasis added.

 

I don't want to recreate that discussion, but particle physicists ≠ all physicists. If you operate in a regime where the particle properties dominate, you'll treat them as particles. Meanwhile, other physicists still talk of wave properties and atomic electrons have orbitals, not orbits.

 

PS. I'm not a particle physicist, I'm an organic chemist.

Edited May 29, 2012 by MrMuse

[swansont]

The problem with asking "are they really waves" is that physics is an attempt to describe how nature behaves, not what it's true nature really is. Things exhibit wave behavior. That's as far as physics is going to take you.

[mathematic]

Electrons have wave properties. For example, the double slit experiment using electrons gives the same kind of pattern one gets from using light.

[juanrga]

I am curious about an issue raised in another thread of this forum: namely, that of the interpretation of atomic orbitals in light of the fact that electrons are particles, not waves. In most organic chemistry textbooks, the atomic orbitals are shown to be standing waves, with regions of positive amplitude and regions of negative amplitude (the 2p atomic orbital, for example). If wave/particle duality is obsolete, then how is one to interpret these pictures in textbooks? Are they merely mathematical functions that have no physical relevance? What I mean is, rather than talk about atomic orbitals (ψ(r,θ,φ)), which contain positive and negative phases, would it be more physically meaningful/relevant to talk about probability distributions (|ψ(r,θ,φ)|²)? If electrons are not waves, then what are we to make of the negative spatial components of atomic orbitals? Further, if electrons are not waves, then in what way should we modify these observations:

1. The electrons do not orbit the nucleus in the sense of a planet orbiting the sun, but instead exist as standing waves. The lowest possible energy an electron can take is therefore analogous to the fundamental frequency of a wave on a string. Higher energy states are then similar to harmonics of the fundamental frequency.
2. The electrons are never in a single point location, although the probability of interacting with the electron at a single point can be found from the wave function of the electron.

Thanks for your help!

 

As you know chemists define the electron as a particle. For instance the IUPAC officially defines an electron as:

 

Elementary particle not affected by the strong force having a spin quantum number , a negative elementary charge and a rest mass of .

 

I remark this because some people here pretends again that only particle physicists consider the electron a particle, which is just untrue. Electrons are always particles. They are particles in atoms, in big accelerators, in solids conductors, in electrolytes, in stars, in living cells...

 

The above definition of electron by the IUPAC is valid for any branch of chemistry, from electroweak quantum chemistry to astrochemistry and cosmochemistry, passing by any other branch: biochemistry, chemistry of solid state, nuclear chemistry, incorganic chemistry, analytic chemistry, organic chemistry, chemical thermodynamics, molecular spectroscopy, electrochemistry...

 

Now your questions.

 

Atomic orbitals are not standing waves, but stationary wavefunctions. A wave (e.g. an electromagnetic wave) is a physical system a wavefunction is a mathematical function.

 

As emphasized in any quantum chemistry textbook, wavefunctions are merely mathematical functions that describe the quantum state of a particle or system under certain approximations. In fact, any decent textbook in quantum chemistry explains that atomic orbitals are only approximations when one ignores electron-electron correlation, spin, and other corrections.

 

If you want study the quantum state of an electron in a given molecule immersed in a fluid, you cannot use a wavefunction ψ.

 

Wavefunctions ψ describe the quantum state of the particle only in some special cases. However |ψ|² never describe the state, but the amplitude of probability associated to the reduction of the wavefunction during a measurement. If you are measuring the position of an electron and ψ=ψ(r,θ,φ) is an atomic orbital that describe the state of the particle before the measurement, then |ψ|² gives the probability that you will find the particle in position (r,θ,φ) when measuring.

 

There is no need to modify the observations that you report. They are 100% compatible with the electron being a quantum particle. That is the reason which IUPAC defines the electron as a particle. Recall that "particle" is not a synonym for small-billiard-ball-following-Newtonian-laws.

 

Only two comments about the observations. First, electrons in the atom do not "exist as standing waves" they exists as particles and its quantum state can be approximated by a wavefunction (at least as a first crude approximation). Second, it is not true that "electrons are never in a single point location". When the electron is in state ψ which is an eigenstate of the position operator, the electron has a position.

 

Yes, the so-named wave-particle duality is an outdated viewpoint very similar to the phlogiston theory. Phlogiston theory is today a historical curiosity and forgotten by physicists/chemists. Any modern and rigorous textbook in quantum physics or quantum chemistry discusses wave-particle duality only in the introductory chapter about the history of the subject and then immediately avoids duality when presents the subject in rigorous and complete form.

Edited May 30, 2012 by juanrga

[StringJunky]

The problem with asking "are they really waves" is that physics is an attempt to describe how nature behaves, not what it's true nature really is. Things exhibit wave behavior. That's as far as physics is going to take you.

 

Is Juangra trying to impose a substantial description or reality upon something which it is not possible to verify either way? As very much a noob on physics, he has left me somewhat confused with regard to the current position on wave-particle duality in the physics community as a whole.

[swansont]

Recall that "particle" is not a synonym for small-billiard-ball-following-Newtonian-laws.

 

I think this sums things up quite well. You can call everything a particle if you redefine what you mean by particle and adopt the position of "by particle we mean quantum particle".

 

As with many issues, it's a matter of defining your terms. However, it's a bit tiresome to leverage this into a matter of equivocation. Scientists calling electrons particles is an issue, in part, of convenience. I think most scientists understand what is implied by quantum particle, i.e. that it means you can have effects like interference and diffraction, which are wavelike properties.

[juanrga]

Is Juangra trying to impose a substantial description or reality upon something which it is not possible to verify either way? As very much a noob on physics, he has left me somewhat confused with regard to the current position on wave-particle duality in the physics community as a whole.

 

In the other thread alluded by the OP, about 30 references to general dictionaries, scientific encyclopedias, textbooks and academic websites, including the CERN website and similar international research centres were given. All the references state that the electron is a particle.

 

A Wikipedia talk page was also added in the other thread. In that page several Wikipedians stated that wave-particle duality is a misnomer and that "wave-particle duality" is not used in modern treatises on quantum mechanics.

 

In this thread I have given a link to the official definition of electron promoted by chemists. The IUPAC defines the electron as a particle, because this definition is perfectly compatible with the quantum states of a particle being given by atomic orbitals.

 

I am aware that most if not all of the popular physics literature is plain wrong and surely you can find many popular presentations of quantum mechanics that still allude to a supposed wave-particle duality, which does not exist. Being a real scientist I am not obligated to repeat those errors, even if are relatively common.

 

Recall that "particle" is not a synonym for small-billiard-ball-following-Newtonian-laws.

I think this sums things up quite well. You can call everything a particle if you redefine what you mean by particle and adopt the position of "by particle we mean quantum particle".

 

As with many issues, it's a matter of defining your terms. However, it's a bit tiresome to leverage this into a matter of equivocation. Scientists calling electrons particles is an issue, in part, of convenience. I think most scientists understand what is implied by quantum particle, i.e. that it means you can have effects like interference and diffraction, which are wavelike properties.

 

The term particle was never defined by "small-billiard-ball-following-Newtonian-laws". The electron was also considered a particle in Maxwell electrodynamics, where Newtonian laws are not valid in general.

 

If you redefine particle to mean "small-billiard-ball-following-Newtonian-laws" then you will have to invent new terms for all those experimental situations where electrons do not behave as "small-billiard-ball-following-Newtonian-laws". Then you will be forced to invent new terms such as "wave-particle duality".

 

The term "quantum particle" is redundant. That is the reason which IUPAC defines electron simply as a "particle" not as "quantum particle". An electron can behave as "classical particle" described by the laws of Maxwell electrodynamics in some situations.

 

I also find a mistake to talk about "wavelike properties". This non-rigorous terminology is at the source of many misconceptions about quantum mechanics. Those "interference and diffraction effects" are not the interference and diffraction effects of a real wave as described by electromagnetic theory, but have a completely different physical interpretation. Recall that the wavefunction is not a real wave but a mathematical function.

Edited May 30, 2012 by juanrga

[swansont]

Recall that the wavefunction is not a real wave but a mathematical function.

 

Nothing that needs recalling, since I don't think I stated that they were. deBroglie waves are not synonymous with wave functions.

[MrMuse]

I also find a mistake to talk about "wavelike properties". This non-rigorous terminology is at the source of many misconceptions about quantum mechanics. Those "interference and diffraction effects" are not the interference and diffraction effects of a real wave as described by electromagnetic theory, but have a completely different physical interpretation. Recall that the wavefunction is not a real wave but a mathematical function.

 

Thanks for your response, Juangra. I'm wondering, then, what IS the physical interpretation of the interference patterns that are created from particles even as large as buckyballs (C60) in the double slit experiment?

 

Why does the interference pattern from a particle (electron or buckyball) look so similar to the interference pattern from a wave?

 

Further, why does the interference pattern disappear when one tries to observe which slit the particle passed through?

[juanrga]

Thanks for your response, Juangra. I'm wondering, then, what IS the physical interpretation of the interference patterns that are created from particles even as large as buckyballs (C60) in the double slit experiment?

 

Why does the interference pattern from a particle (electron or buckyball) look so similar to the interference pattern from a wave?

 

Further, why does the interference pattern disappear when one tries to observe which slit the particle passed through?

 

Let me first ask the next questions: If you observe wave motion on a piece of water, do you claim that water is sometimes a substance sometimes a wave? I claim that water is never a wave.

 

If you observe a satellite moving in an ellipse around the Earth, do you claim that it is sometimes a satellite sometimes an ellipse? I claim that satellites are never ellipses.

 

Let us imagine by an instant that it is correct to say that a particle (electron or buckyball) moves as a wave, do you claim that the particle is sometimes a particle sometimes a wave? I claim that electron or buckyball are never a wave.

 

Do you believe that IUPAC do not know the existence of the double slit experiment when they define the electron as a particle or the buckyball as a molecule?

 

And the last question: Do you know what is the system observed and what is being measured and how in the double slit experiment? I recall this this because after reading your "Why does the interference pattern from a particle..." I am not sure if you know how the pattern is obtained.

Edited May 30, 2012 by juanrga

[MigL]

Since Juanrga is more interested in discussing terminology and definitions, let me try to answer your question MrMuse.

 

Quantum Mechanichs is very dependant on observation for the result. In the typical double slit experiment, an electron or similar particle ( ? ) is emitted on one side and allowed to pass through to the other side. Now if the observer sets up an experiment to detect particles, he will be able to determine which slit the electron passed through. If he sets up an experiment to detect waves, he will see the usual interference pattern from interfering wave fronts.

 

What is even stranger is that the observer can wait until the electron has already passed through the slit (s) before deciding which experiment ( particle or wave ) to perform, and the results will still be the same. I forget the name of this experiment, delayed choice or something like it, but it has all sorts of strange implications,

[MrMuse]

Let me first ask the next questions: If you observe wave motion on a piece of water, do you claim that water is sometimes a substance sometimes a wave? I claim that water is never a wave.

 

If you observe a satellite moving in an ellipse around the Earth, do you claim that it is sometimes a satellite sometimes an ellipse? I claim that satellites are never ellipses.

 

Let us imagine by an instant that it is correct to say that a particle (electron or buckyball) moves as a wave, do you claim that the particle is sometimes a particle sometimes a wave? I claim that electron or buckyball are never a wave.

 

Do you believe that IUPAC do not know the existence of the double slit experiment when they define the electron as a particle or the buckyball as a molecule?

 

And the last question: Do you know what is the system observed and what is being measured and how in the double slit experiment? I recall this this because after reading your "Why does the interference pattern from a particle..." I am not sure if you know how the pattern is obtained.

 

I do not know how the pattern is obtained; that is why I asked the question. I suppose I understand what you're referring to: that I said "the interference pattern from a particle" rather than "the interference pattern from thousands of particles." This was merely a typo on my part. I understand how the experiment is performed. I understand that there is a source of electrons that fires electrons, one at a time, through two slits. I understand why we might see a pattern that consists of two lines that lie directly behind the two slits. What I'm asking is, what is responsible for the non-parallel trajectories of the electrons that DON'T strike the surface directly behind the slits? Are some of the electrons somehow bouncing off the edges of the slits, as was previously suggested in another thread? But, in this case, why does the interference pattern disappear? Does modern physics believe the interpretation that the particle goes through both slits at the same time and interferes with itself? You are right that a wave of water does not mean that a water molecule is a wave, however, a wave of water consists of many molecules moving together. The experiment we are referring to consists of one electron fired at a time, not many electrons moving together, so your analogy is not accurate.

Edited May 31, 2012 by MrMuse

[juanrga]

Since Juanrga is more interested in discussing terminology and definitions, let me try to answer your question MrMuse.

 

It makes no sense to discuss something if each poster uses different terminology and definitions. Why do you think that there are international bodies devoted to define and spread a set of common terminology and definitions? To avoid confusions...

 

Quantum Mechanichs is very dependant on observation for the result. In the typical double slit experiment, an electron or similar particle ( ? ) is emitted on one side and allowed to pass through to the other side. Now if the observer sets up an experiment to detect particles, he will be able to determine which slit the electron passed through. If he sets up an experiment to detect waves, he will see the usual interference pattern from interfering wave fronts.

 

This is completely wrong. The electron in the double slit experiment is always a particle. And no wave is "detected" because there is none therein.

 

I do not know how the pattern is obtained; that is why I asked the question. I suppose I understand what you're referring to: that I said "the interference pattern from a particle" rather than "the interference pattern from thousands of particles." This was merely a typo on my part. I understand how the experiment is performed. I understand that there is a source of electrons that fires electrons, one at a time, through two slits. I understand why we might see a pattern that consists of two lines that lie directly behind the two slits. What I'm asking is, what is responsible for the non-parallel trajectories of the electrons that DON'T strike the surface directly behind the slits? Are some of the electrons somehow bouncing off the edges of the slits, as was previously suggested in another thread? But, in this case, why does the interference pattern disappear? Does modern physics believe the interpretation that the particle goes through both slits at the same time and interferes with itself? You are right that a wave of water does not mean that a water molecule is a wave, however, a wave of water consists of many molecules moving together. The experiment we are referring to consists of one electron fired at a time, not many electrons moving together, so your analogy is not accurate.

 

Therefore I assume that your answer to the questions is "water is never a wave" and "satellites are never ellipses". Now the key question is if you are able to differentiate between the system (water, satellite) and the motion of the system "oscillatory motion, elliptical motion", why you cannot differentiate between an electron and its motion?

 

As you say the interference patter is obtained when the experiment is repeated with thousands of electrons. One electron does not generate an interference pattern. Why then you believe that an electron is a wave?

 

A wave is a physical system. E.g. a wave in water is a system, an electromagnetic wave is a system. In an approximated formulation of quantum mechanics, the state of particles as electrons is given by a wavefunction. A wavefunction is not a wave, but a mathematical function. A wavefunction is not observable. A wavefunction is not the particle. A wavefunction only describes approximatedly the state of the particle. There are situations where the state of a particle is not given by a wavefunction but by a more general formalism.

 

The wave-particle duality myth is based in the next misunderstandings:

1. Suppose that a wavefunction always exists.
2. Confound a wavefunction with a wave.
3. Confound the system with one of the possible states of the system
4. Suppose that particle is a synonym for "small-billiard-ball-following-Newtonian-laws"

You ask "what is responsible for the non-parallel trajectories of the electrons that DON'T strike the surface directly behind the slits?"

 

Sorry, but there are not trajectories in quantum mechanics. In quantum mechanics, position x and momentum p do not commute. The electron does not move classically following a trajectory as in Newtonian physics, but moves according to quantum mechanics rules, where there are not trajectories. Therefore your question makes no sense. Your question is so weird like if I was to as ask you "what is responsible for the polarization in the oxygen atoms in benzene molecule" (you would reply me that there is not oxygen atoms in that molecule!).

 

"Are some of the electrons somehow bouncing off the edges of the slits, as was previously suggested in another thread?" The poster who said that merely wrote nonsense.

Edited May 31, 2012 by juanrga

[swansont]

Therefore I assume that your answer to the questions is "water is never a wave" and "satellites are never ellipses".

 

This is a non sequitur. The notion of the wave-particle duality is that you will observe classical particle-like and wave-like behavior. You're answering a different question, but also claiming that the other answers are wrong.

 

Does water exhibit wave behavior? Yes. Do satellites travel in ellipses? Yes.

[juanrga]

This is a non sequitur. The notion of the wave-particle duality is that you will observe classical particle-like and wave-like behavior.

 

In this same thread you can find several posters claiming that wave-particle duality means that "electrons are particles and waves", which is not right.

 

Neither your version is still acceptable, because the wave-particle duality is always formulated within the scope of the wavefunction formulation of QM and this formulation cannot provide "classical particle-like" behaviour.

 

In any case, I was trying to explain the difference between a system and the state of the system. I also tried to explain that a wavefunction is not a wave but a function.

Edited May 31, 2012 by juanrga

[swansont]

In this same thread you can find several posters claiming that wave-particle duality means that "electrons are particles and waves", which is not right.

 

And you can find pretty much an equal number of corrections to those statements, saying that they exhibit that behavior, not that they are these things.

[pmb]

And you can find pretty much an equal number of corrections to those statements, saying that they exhibit that behavior, not that they are these things.

This is the most basic, and thus first, thing one learns when studying quantum theory. Nobody is more correct on this point than Feynman. From his lectures V-III page 1-1

... 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 billiar balls, or weights on springs, or anything that you have ever seen.

Newton thoughtthat light was made up of particles, but then discovered that it behaves like a wave. Later, however (in the beginning of the twentieth century), it was found that light did indeed sometimes behaves like a particle. Historically, the electron, for example, was thought to behave like a particle, and then it was found that in many repects it behaved like a wave. So it really behaves like neither. Now we have given up. We say: "It behaves like neither."

Never try to say it better then this I say.

[mississippichem]

This is the most basic, and thus first, thing one learns when studying quantum theory. Nobody is more correct on this point than Feynman. From his lectures V-III page 1-1

 

Never try to say it better then this I say.

 

Feynman conveys the pedagogy of quantum theory quite plainly and succintly in FLP III in my opinion. I'm no physicist but this has been my understanding of quantum "objects" for some time. I agree with you and Feynman. Well placed reference. Cheers.

 

 

The "shut-up and calculate" paradigm may be unsatisfying but it almost never lets us down or leads us astray.

Edited May 31, 2012 by mississippichem

[MigL]

Don't put words in my posts Juan, I did not say a wave is detected. What I said was that an experiment to detect wave behaviour will get the usual interference pattern on the screen, ie wave behaviour is manifested. Particle behaviour is also manifested in other cases, but I've never said electrons are both particles and waves as you imply I've said.

As a matter of fact I was one of the first to state that wave and particle behaviour are mathematical models which don't describe the actual reality, ie electrons may be neither. We have one group touching the trunk of an elephant and saying its snakelike and another group holding the elephant's ear and saying its thin, flat and floppy. The elephant is neither, but it does exibit those qualities.

[juanrga]

And you can find pretty much an equal number of corrections to those statements, saying that they exhibit that behavior, not that they are these things.

 

But the statement that electrons exhibit both particle-like and wave-like behaviour is the reason which many people believes that an electron is not a particle but another thing; indeed, many posters write in this forum that they believe that an electron is a wave. This same people is very confused when read that physicists and chemists consider that the electron is a particle.

 

I completely agree with most of my colleagues and I also define the electron as a particle (I agree 100% with the IUPAC definition given above). A logical consequence is that it makes no sense to claim that a particle exhibits wave-like behaviour because all the observables are those of a particle.

 

Of course, others may dislike this.

 

This is the most basic, and thus first, thing one learns when studying quantum theory. Nobody is more correct on this point than Feynman. From his lectures V-III page 1-1

 

Never try to say it better then this I say.

 

In his book "QED : The strange theory of Light and Matter" Feynman wrote:

 

You had to know which experiment you were analyzing in order to tell if light was waves or particles. This state of confusion was called the "wave-particle duality" of light, and it was jokingly said by someone that light was waves on Mondays, Wednesdays, and Fridays; it was particles on Tuesdays, Thursdays, and Saturdays, and on Sundays, we think about it! It is the purpose of these lectures to tell you how this puzzle was finally resolved.

 

[...]

 

the wave theory cannot explain how the detector makes equally loud clicks as the light gets dimmer. Quantum electrodynamics "resolves" this wave-particle duality by saying that light is made of particles (as Newton originally thought), but the price of this great advancement of science is a retreat by physics to the position of being able to calculate only the probability that a photon will hit a detector, without offering a good model of how it actually happens.

 

I find delicious his joke about the days of the week. I only disagree with him on a point. Quantum electrodynamics was not the first theory that introduced a probabilistic description of particles.

 

Don't put words in my posts Juan, I did not say a wave is detected. What I said was that an experiment to detect wave behaviour

 

Sorry but you said wave and I replied to what you wrote:

 

If he sets up an experiment to detect waves, he will see...

Edited June 1, 2012 by juanrga