# Particle wave duality

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LIGHT

We do know that photons behave like a wave and a particle both, that's what particle wave duality tells us..

1)So which source of light behave likes a particle and which one like a wave, How do we know that??

2)If a particle has larger wavelength it behaves like a wave and the one which has smaller wavelength behaves like a photon?

3)Photons have momentum, p=hv/c, do wave have some momentum?

Electrons

Electrons are present around the nucleus of an atom(we all know that)

4) Are they present there as particles, standing frequency, clouds or on orbits(which is the least i would prefer) ??

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In a lot of instances it's easier to see wave behavior as the wavelength increases. The momentum of EM radiation is also E/c, as it must.

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Can you please tell me a bit more in detail??

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LIGHT

We do know that photons behave like a wave and a particle both, that's what particle wave duality tells us..

1)So which source of light behave likes a particle and which one like a wave, How do we know that??

It's not the source which determines what it behaves like, its the circumstanes. Young's Double Slit Experiment is nice way to explain the wave paticle duality. A beam of photons hits a screen where there are two parallel slits, closely spaced together. An array of photon detectors is placed behind the screen. On the array there forms an interference pattern. That's the wave aspect of photons. If the intensity of the beam is decreased so that only one photon hits the screen at the time then the array will detect only one click at a time indicating that only one photon has hit the screen. If we record where the photons land and let the experiement run for a long time then the interference pattern will appear. That's what the wave-particle duality means.

2)If a particle has larger wavelength it behaves like a wave and the one which has smaller wavelength behaves like a photon?

No.

3)Photons have momentum, p=hv/c, do wave have some momentum?

Yes. If L is the wavelength associated with a particle and p its momentum then L = h/p.

Electrons

Electrons are present around the nucleus of an atom(we all know that)

4) Are they present there as particles, standing frequency, clouds or on orbits(which is the least i would prefer) ??

That can't be answered. Whether a electron is a partical or a wave depends on how you measure it.

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I have heard about the double split experiments, but performed with waves..

Why can't the question related to electrons be answered?

Taking electrons on orbits might be wrong, because they are present in quantum number or energy states..

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Why can't the question related to electrons be answered?

Sorry qft123. I intended that to show the nature of the wave-particel duality. In principle the double slit experiment doesn't work just for photons. Theoretically you can defract electrons through a double slit too. It's just way too impractical. However, in 1928 Davisson and Germer did a similar experiment whereby electrons were scattered from the surface of nick crystals and a diffraction pattern was formed. The wonderous thing about this is that they discovered this phenomena by an accident. Cool, huh?

Edited by pmb
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"Wave-particle duality" is often a misleading name. Electrons and photons are quantum mechanical particles. They do not behave in the same way that classical particles do, and indeed can't really be explained in terms of anything familiar to you. The particles have an associated "wave function," which is essentially a wave of probability. The wave function gives the probability of finding the particle in a given region of space, and it exhibits normal wave characteristics (i.e. it can interfere, etc.). Asking whether or not it is a particle or a wave is nonsensical.

1)So which source of light behave likes a particle and which one like a wave, How do we know that??

2)If a particle has larger wavelength it behaves like a wave and the one which has smaller wavelength behaves like a photon?

Whether or not it behaves more like a classical particle or a wave depends on its energy. The more energetic the photon, the more it will exhibit "particle-like" behavior, and vice versa.

3)Photons have momentum, p=hv/c, do wave have some momentum?

You pretty much answered your own question, didn't you? But yes, a de Broglie wave has momentum $\vec{p}=\hbar \vec{k}$ where k is its wave vector ($|\vec{k}|=2 \pi /\lambda$), and ħ is the reduced Planck constant, h/2π.

Electrons are present around the nucleus of an atom(we all know that)

4) Are they present there as particles, standing frequency, clouds or on orbits(which is the least i would prefer) ??

It is a particle whose associated wave function is a standing wave.

Edited by elfmotat
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Hello qft, I see you are interested in chemistry as well as physics.

I don't know why wave/particle duality evokes such strong feelings and reactions.

We do not find it suprising and readily accept schizophrenic behaviour in other physical phenomena.

The short answer is that the behaviour depends upon the circumstances ie what we do to the subject or what we want from it.

As a for instance or two

Aluminium compounds are often amphoteric depending upon whether their environment is more acid or more basic.

I have a piece of black plastic on the end of my DVD controller that I can regard as opaque if I look at it (visible light) or transparent (infra red) from the point of view of the internal transmitter.

So it is with quantum theory.

If we look for particulate effects, we will find them eg the photoelectric effect.

If we look for wave effects we can find those too eg diffraction.

Edited by studiot
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Double slit experiment conducted with single electrons building up a pattern expected if the electrons were waves:

http://www.hitachi.com/rd/research/em/doubleslit.html

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LIGHT

We do know that photons behave like a wave and a particle both, that's what particle wave duality tells us..

1)So which source of light behave likes a particle and which one like a wave, How do we know that??

2)If a particle has larger wavelength it behaves like a wave and the one which has smaller wavelength behaves like a photon?

3)Photons have momentum, p=hv/c, do wave have some momentum?

Electrons

Electrons are present around the nucleus of an atom(we all know that)

4) Are they present there as particles, standing frequency, clouds or on orbits(which is the least i would prefer) ??

Particle wave duality is a myth, which arose in the early times of quantum mechanics when only classical particles or classical waves were known and the myth was born to try to explain the experiments where the objects under study did not behave as classical particles or classical waves. The idea that photons sometimes behave as waves and sometimes behave as particles is a recurrent, but completely incorrect, claim. A well-known joke about this is

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!

In modern physics the photon is defined as a particle, always. Everything around us is made of particles as CERN remarks:

http://public.web.ce...rdModel-en.html

An electron or a photon are always particles and all particles behave as particles. Danger! Particle does not mean "little-hard-sphere-following-Newtonian-laws".

Are particles and waves somewhat related? Yes. An electromagnetic wave is a large collection of photons. Therefore a wave has momentum and energy. Note, however that the description of a collection of photons as a electromagnetic wave is only an approximation. Quantum optics is more general and requires a photon treatment.

Edited by juanrga
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Thanks Juangra.

But is electron present as a standing wave or as a particle in the atom??

I have read in some book, that it is still a mystery and we can't figure out what goes inside the atom..

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Thanks Juangra.

But is electron present as a standing wave or as a particle in the atom??

I have read in some book, that it is still a mystery and we can't figure out what goes inside the atom..

The thing about quantum mechanics is that you can't talk about what a system is doing until you make a measurement. Asking about an electron is doing when it hasn't been observed is a meaningless question in QM. There are states in the atom which stationary states. Once you measure owhat state its in then you can make a statement about it.

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Particle wave duality is a myth, which arose in the early times of quantum mechanics when only classical particles or classical waves were known and the myth was born to try to explain the experiments where the objects under study did not behave as classical particles or classical waves. The idea that photons sometimes behave as waves and sometimes behave as particles is a recurrent, but completely incorrect, claim. A well-known joke about this is

In modern physics the photon is defined as a particle, always. Everything around us is made of particles as CERN remarks:

http://public.web.ce...rdModel-en.html

An electron or a photon are always particles and all particles behave as particles. Danger! Particle does not mean "little-hard-sphere-following-Newtonian-laws".

Are particles and waves somewhat related? Yes. An electromagnetic wave is a large collection of photons. Therefore a wave has momentum and energy. Note, however that the description of a collection of photons as a electromagnetic wave is only an approximation. Quantum optics is more general and requires a photon treatment.

Have you ever heard of the quantum resonator Juangra???

If not could you please look it up, and once you have, can you still tell me the wave function is a myth?

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Thanks Juangra.

But is electron present as a standing wave or as a particle in the atom??

I have read in some book, that it is still a mystery and we can't figure out what goes inside the atom..

Let us see. The above link to the CERN starts with the following quote (bold from mine):

The theories and discoveries of thousands of physicists over the past century have resulted in a remarkable insight into the fundamental structure of matter: everything in the Universe is found to be made from twelve basic building blocks called fundamental particles, governed by four fundamental force.

"Everything" includes atoms. Indeed atoms are made of particles such as the electron. The electron is a particle of the kind fermion. The electron is mentioned in the CERN link in the section "matter particles", third paragraph.

What does happen in an atom? Consider an isolated atom (not an atom in a molecule nor in a solid), but a solitary atom.

If we ignore nuclear structure and treat the nucleus as a classical point, if we assume that this atom is in a stable pure quantum state, and if we ignore spin and relativity, then the state of the atom can be described by a wavefunction, sometimes named electronic wavefunction because it only depends on electrons coordinates. Recall that the atom continues being made of particles!

Assume that this same atom is in some stationary state (i.e., its physical properties do not change with time). Then its wavefunction will not depend on time.

If further we consider that electrons in this atom are not-interacting (which is not true because electrons are electrically charged {*} and repeal between them) then that wavefunction can be split into a product of wavefunctions for each electron. The whole wavefunction is defined in a generalized space (not in ordinary space!). Only the wavefunction for each electron-j is defined in ordinary space $\Psi_j=\Psi_j(x,y,z)$.

This $\Psi_j$ is what you call "standing wave", but notice that it is not a wave (i.e. it is not a physical system with energy and momentum), but a mathematical function. The correct technical name is stationary wavefunction. This $\Psi_j$ only describes the quantum state of the electron approximatedly. In fact they are a very crude approximation to real atom. Moreover, the electron continues being a particle.

In more advanced quantum treatments the electron continues being a particle, but its state is not more given by a wavefunction $\Psi_j$ but by a more general and complex formalism.

{*} An exception is the Hydrogen atom because has only one electron.

Edited by juanrga
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Here... I found you a link. One of the most direct experiments we have confirming the quantum behaviour

http://news.bbc.co.uk/1/hi/8570836.stm

I can tell you without a shadow of a doubt, that not only is the wave function real, but it is also physical.

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"Wave-particle duality" is often a misleading name. Electrons and photons are quantum mechanical particles. They do not behave in the same way that classical particles do, and indeed can't really be explained in terms of anything familiar to you. The particles have an associated "wave function," which is essentially a wave of probability. The wave function gives the probability of finding the particle in a given region of space, and it exhibits normal wave characteristics (i.e. it can interfere, etc.). Asking whether or not it is a particle or a wave is nonsensical.

I love the way Feynman explains it in his Lectures. In V-II page 1-1

"Quantum mechanics" is the description of the behavior of matter and light in all details and, in particular, of the happenings on an atomic scale. Things on an atomic scale behave like nothing that you have any direct experience about. Thet dot behave like waves, they do not behave like particles, they do not behave like clouds, or billiard balls, or weights on springs, or like anything that you have ever seen.

Newton thought that ligt was made up of particles, but then it was discovered that it behaves like a wave. Later, however (in the beginning of the twentieth century), t was found thalight did indeed sometimes behave like a particle, and then it was found that in many respects it behaved like a wave. So it really behaves like neither. Now we have given up. We say: "It i like neither."

Someone once coined the term wavicle (http://en.wiktionary.org/wiki/wavicle) as a comprimise but it never really took. Today physicists ue the term "particle" not because they behave like particles, but because there is no other term and its good enough since nobody ever gets confused by it and actually thinks that photons and electrons are "really" particles. Although I'm sure there are a lot of people who are confused on this point.

The wave function, like any mathematical quantity in physics, is a quantity that has the physical meaning that the square of the magnitude is related to probability. For a continuous wave the square of the magnitude is a probability density.

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Yes, I do often write a lot of physics, but you know... the word wavicle had never really caught onto me. Of course, the entity was indeed a wave and a particle simultaneously, but for some reason a name adopted towards this nature never really caught on for me... maybe somewhere embedded in my psyche my brain still likes the idea of thinking it as two distinct forms... who knows eh?

Nice quote

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

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.

Yes Feynman agrees, as virtually everyone else, that light is made of particles. Of course, as emphasized above by at least two posters, particle does not mean classical particle. The transition "classical particle" --> "quantum particle" is firmly rooted to the transition classical physics --> quantum physics.

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

Yes Feynman agrees, as virtually everyone else, that light is made of particles. Of course, as emphasized above by at least two posters, particle does not mean classical particle. The transition "classical particle" --> "quantum particle" is firmly rooted to the transition classical physics --> quantum physics.

It's ok to wrong, I've been wrong quite a few times in my lifetime.

The wave function is certainly not a myth. Quantum mechanics has been built from such things, and as you know, quantum mechanics is all about experimental evidence.

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It's ok to wrong, I've been wrong quite a few times in my lifetime.

The wave function is certainly not a myth. Quantum mechanics has been built from such things, and as you know, quantum mechanics is all about experimental evidence.

Consider a large number of Young's Double Slit experiment. Allow just one photon to go through the slit. It will be detected on the screen behind it by the "click" of one photon detector. If you were to look at the ensemble of all those experimental setups you'd see that there is an interference phenomena present. Its for this reason that its said that there is a wave-particle duality and why Feynman said "It's like neither.'

Note: The quote from Feynman's QED only addresses light/photons. It makes no mention of electrons. I have the check the context. What page is that on?

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everything in the Universe is found to be made from twelve basic building blocks called fundamental particles, governed by four fundamental force.

And just how many times in the past have scientists and thinkers made this claim that they know everything?

Mendelev and his mates were wrong about the number of elements

Kelvin was wrong about the cooling of the earth....

I suggest that anyone making such an extravagant claim is suffering from a severe case of bloaty head.

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And just how many times in the past have scientists and thinkers made this claim that they know everything?

Mendelev and his mates were wrong about the number of elements

Kelvin was wrong about the cooling of the earth....

I suggest that anyone making such an extravagant claim is suffering from a severe case of bloaty head.

I think that its a fair way to speak though. It would become cumbersome to keep repeating according to the laws of physics as they are presently known ..... I always take that as a given and that the scientist who says those things understands that.

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Consider a large number of Young's Double Slit experiment. Allow just one photon to go through the slit. It will be detected on the screen behind it by the "click" of one photon detector. If you were to look at the ensemble of all those experimental setups you'd see that there is an interference phenomena present. Its for this reason that its said that there is a wave-particle duality and why Feynman said "It's like neither.'

Note: The quote from Feynman's QED only addresses light/photons. It makes no mention of electrons. I have the check the context. What page is that on?

yes quite right though. Feynman was right I think personally to say it was neither, but then, he said these things because the objective world is so obscure, that how can anyone even say there is an electron?

Wasn't it Feynman who said an electron didn't even exist, in its manifestly probabilistic form? I could be wrong here, very wrong... ??

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One of the silliest things about this argument is that there is no need for a case of 'either....... or' as presented.

How about the bicarbonate ion in solution in the presence of HCl?

Answer both at the same time.

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One of the silliest things about this argument is that there is no need for a case of 'either....... or' as presented.

How about the bicarbonate ion in solution in the presence of HCl?

Answer both at the same time.

My chemistry is a bit vague, but I think you are making a good point with what I know. It's been several years since my diploma in the subject.

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