Why can't we have a wave of particles?

Question

I understand the nature of light can be complex and has extensive theories/experimental data. We hear light can be both a wave and particle, so why can't it be both, a wave of particles?

What is a wave of particles? Do you mean a wave composed of particles? — jinawee, Mar 18 '14 at 18:03
I think the reason we can't have a "wave of particles", whatever that means, is because there's no experimental data supporting that interpretation. — nitro2k01, Mar 19 '14 at 04:40
I think there is a bit of a misunderstanding of the concept on your side. It is not both wave and particle or sometimes particle, sometimes wave. It is just what it is all the time. This wave-particle interpretation is merely a model which makes our understanding more clear, since it is expressed in terms known to us. We say it sometimes behaves like particle, sometimes like wave, but actually all the time it just behaves like itself and it is described by some complex equation, which sometimes can be approximated by a simple particle or a wave. — sashkello, Mar 19 '14 at 05:30

score 17 · Answer 1 · answered Mar 18 '14 at 12:28

17

The problem is that light is not a wave and it's not a particle. Light is a quantum field, or at least that's our current best description of it.

Quantum fields can behave in ways that appear to be wave like, and they can also behave in ways that appear to be particle like, and this the origin of the claim that light is both a wave and a particle. It's more accurate to say that light can behave like both a wave and a particle.

Anyhow, as far as I know quantum fields can't behave like a wave and like a particle at the same time. Generally speaking they behave like waves when propagating and like particles when exchanging energy. So we can't have a wave of particles or a particle of waves. It's one or the other.

Incidentally, this applies to all particles and not just light.

answered Mar 18 '14 at 12:28

John Rennie

355,118

Isn't specular reflection a nice case that's explained by both light-as-a-particle and light-as-a-wave? Also, the "it's not either" nature seems to me to be neatly illustrated by diffraction mirrors and similar technology; if it were a particle, it should have a randomness in the angle of reflection (did the particle hit the ridge or the valley?). And really, the same would apply for a wave, wouldn't it? The fact that you can shine a laser (or send an atom) and have it reflect at a given angle IMO isn't explained be neither the particle nor the wave approximation. Or am I missing something? – Luaan Mar 19 '14 at 10:37
@Luaan: A particle explanation of specular reflection strikes me as hard. After all, a surface is lumpy because it's made up of a collection of electrons and nuclei, and it's not obvious why light particles interacting with all those other particles would give rise to specular reflection. With a wave model specular reflection is easy to explain. I'm not sure what you're asking about diffraction mirrors. Maybe it's worth asking as a separate question? – John Rennie Mar 19 '14 at 10:46
I was thinking about specular reflection in metals. Doesn't the "electron cloud" produce a relatively flat surface (compared to the "size" of the "particles" involved)? I'll see if I can form a good question out of the diffraction mirrors / gratings thing :) – Luaan Mar 19 '14 at 10:58
compared to the "size" of the "particles" involved - and what would the size of the photon be? – John Rennie Mar 19 '14 at 13:54
Well, that's part of the issue of photons as particles, isn't it? In the context, I'd say a reasonable definition of that might be the size of a slit that no longer produces a (significant) diffraction pattern for a particular photon wave-length. The fact that photons aren't little balls does make this a bit complicated, but this sounds reasonable to me if you subscribe to the particle definition - in a way, it's the diameter, at which the photon no longer seems to throw away particle-like characteristics in favour of wave-like ones. Now, what is the wave-length of the metallic surface? :D – Luaan Mar 19 '14 at 14:24

score 5 · Answer 2 · answered Mar 18 '14 at 17:06

5

In the non-quantum sense, most waves we experience in the everyday world are waves of particles. Ocean waves and sound waves are the transmission of energy through a bunch of particles/the medium

answered Mar 18 '14 at 17:06

Hoffmaniacal

61

score 0 · Answer 3 · answered Mar 18 '14 at 12:55

If the wave function was a wave of particles, then you wouldn't get an interference pattern if you did a double slit experiment with one particle at a time going through the apparatus. But there are many experiments in which an interference pattern is observed when particles are sent through double slits one at a time.

The only satisfactory explanation of single particle interference that I am aware of is the many worlds interpretation of quantum mechanics as described by David Deutsch, see Chapter 2 of his book "The Fabric of Reality".

score 0 · Answer 4 · answered Mar 18 '14 at 15:17

IT seems that wave phenomena (properties) can possibly be applied to atoms, and then molecules - ie. a bunch of particles (properties) in coherent form, here:

The quantum superchemistry of the out-coupled hybrid matter waves is studied by using the powerful tool of positive-P representation in quantum optics. We identify the stimulated eﬀects of the molecular output step and atomic revivals by steering the rf output couplings. The coherent conversion of atoms to molecules is robust, with the noise-induced molecular damping occurring near the total conversion. If these eﬀects are typical, then the quantum superchemistry in an atom laser can be tunable and potentially useful for, e.g., making a continuous molecule laser.

Also here: An article (not copy/pastable) regarding interferometry of molecules -only 9 pages, worth a read.

score 0 · Answer 5 · answered Mar 18 '14 at 17:45

0

I think you need to read de broglies Noble lecture:

I thus arrived at the following overall concept which guided my studies: for both matter and radiations, light in particular, it is necessary to introduce the corpuscle concept and the wave concept at the same time. In other words the existence of corpuscles accompanied by waves has to be assumed in all cases. However, since corpuscles and waves cannot be independent because, according to Bohr’s expression, they constitute two complementary forces of reality, it must be possible to establish a certain parallelism between the motion of a corpuscle and the propagation of the associated wave. The first objective to achieve had, therefore, to be to establish this correspondence.

From this I believe you are right in saying that at the same time, each photon is accompained by waves.

answered Mar 18 '14 at 17:45

Sensebe

5,769

That was in 1929, quantum mechanics has evolved since then. – jinawee Mar 18 '14 at 17:47
I will be happy to know, if any article source is provided which proves this to be false i.e photons are associated with waves. – Sensebe Mar 18 '14 at 17:51
1

See this question: http://physics.stackexchange.com/questions/103196/quantum-wave-mechanics. The "wave" associated to matter is not a wave in the classical sense. And there are other formulations which don't use the concept of wave at all. – jinawee Mar 18 '14 at 18:01
Would you like to say de broglies hypothesis has been proved false? – Sensebe Mar 18 '14 at 18:04
1

You could say it has been reformulated. – jinawee Mar 18 '14 at 18:05
Light energy is carried by photons, I don't think in between this energy would be vanishing during propagation. It (photons) will be there, but this property is observed only when there is interaction between matter. If not would you like to say that light energy is not carried by photons and it is carried by those "waves"? – Sensebe Mar 18 '14 at 18:14
let us continue this discussion in chat – jinawee Mar 18 '14 at 18:16

score 0 · Answer 6 · answered Mar 18 '14 at 17:49

Light is neither particle nor wave. It's something different we haven't fully understood. When we try to find behavior of light assuming it's particle, light says affirmative. When we try to find behavior of light assuming it's wave, light says affirmative again. Means, light is behaving like particle and wave at the same time.

But, here your problem starts: Why can't we accept from behavior that light is both? Ok, natures of particle and wave are different, but why can't it be a wave of particles?

Answer:

A wave of particles is disturbance in the medium. When you fire sound waves, you actually fire disturbance not air molecules. So, if light is reaching a dark place from a distance, it'd be dumb to assume Photons are already there. And, if there aren't any Photons already, a Wave of Photon isn't possible.
Even if you fire one Photon, it'd spread out like wave (which you shouldn't accept with one particle) and make interference patterns with other one Photon.

score -1 · Answer 7 · answered Mar 18 '14 at 14:18

A simple question about light is, "where is it?"

The wave model says that there's no single precise answer. It's spread out.

The particle model says that each photon has a place in space.

A model that assumes both at the same time doesn't have a good answer to this.

Modern physics of course has much more complicated models, but they are made possible through math. And then it turns out there are rather identical models for other types of waves and particles, so much that De Broglie assumed that all those waves were particles and vice versa, i.e. that you could use the same unified mathematical model. (Which still didn't answer exactly what that model should be, though)

Why can't we have a wave of particles?

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