# Question regarding wave/particle duality

#### jimmylegss

Regarding to wave/particle duality. Are there places in the universe without magnetic fields or where magnetic fields are too weak for light to be able to behave as a wave (since they travel in the magnetic field as a wave right?).

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#### bhobba

Mentor
Its got nothing to do with that.

Classically the wave nature of light is simply its the solution to Maxwell's equations.

Regarding wave/particle duality its basically a myth:
http://arxiv.org/abs/quant-ph/0609163

Thanks
Bill

#### ZapperZ

Staff Emeritus
2018 Award
Regarding to wave/particle duality. Are there places in the universe without magnetic fields or where magnetic fields are too weak for light to be able to behave as a wave (since they travel in the magnetic field as a wave right?).

You really shouldn't try to climb a tree before you are able to even stand up.

As bhobba implied, you need to first understand the classical EM wave picture, because what you asked here makes no sense. There is a reason why light is called an "electroMAGNETIC" wave. Without the "magnetic" component, it is no longer "light" as we know it!

This also has nothing to do with "wave-particle" duality. I suggest you start by reading the FAQs in the STEM Learning Materials forum.

Zz.

#### maline

"the magnetic field" isn't something that a region needs to "have". If there's nothing going on, the electric and magnetic fields will have the value zero (vector). A field by definition gives numbers for every point in space.

As for "duality": light doesn't "choose" between two types of "behaviour". It is absorbed as particles that are distributed according to patterns determined by a wave equation.

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#### carllooper

"the magnetic field" isn't something that a region needs to "have". If there's nothing going on, the electric and magnetic fields will have the value zero (vector). A field by definition gives numbers for every point in space.

As for "duality": light doesn't "choose" between two types of "behaviour". It is absorbed as particles that are distributed according to patterns determined by a wave equation.
Hmmm. If a field gives numbers for every point in space (as it does) then any region within such a space will have such a field. A value of zero is still a value given by the field. Without a field the value wouldn't be zero as such: rather it would be better to say the value is undefined or unspecified or ungiven.

C

#### bhobba

Mentor
Hmmm. If a field gives numbers for every point in space (as it does) then any region within such a space will have such a field. A value of zero is still a value given by the field. Without a field the value wouldn't be zero as such
Without a field, by DEFINITION, its value is zero.

Zero means - no field.

Thanks
Bill

#### carllooper

Without a field, by DEFINITION, its value is zero.

Zero means - no field.

Thanks
Bill
Without a field how would we know if it's zero or otherwise in any particular region? To say there is "no field" where the field otherwise gives us a zero value, is certainly a way of speaking, but it's a bit messy I'd suggest - especially if we start from the proposition (or DEFINITION) that a field gives us values (including zero) for every point in space. It follows from this proposition/definition that without a field we wouldn't have any values at all (zero or otherwise) for any point in space.

C

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#### bhobba

Mentor
I wouldn't call it a myth as such. It's a model.
It's not a model because its incorrect - as the paper I linked to explained.

Or if it is a myth it's no less mythological than the suggestion that "theoretical and interpretational ambiguities"
Ambiguity - doubtfulness or uncertainty of meaning or intention.

There is no known ambiguity in QM. People who think so don't understand it.

Without a field how do you know it's zero?
Because by definition that's what zero means - no field - its assigned value zero. Its similar to many things - no money - you have 0 dollars.

Thanks
Bill

#### carllooper

It's not a model because its incorrect - as the paper I linked to explained.

Ambiguity - doubtfulness or uncertainty of meaning or intention.

There is no known ambiguity in QM. People who think so don't understand it.

Because by definition that's what zero means - no field - its assigned value zero. Its similar to many things - no money - you have 0 dollars.

Thanks
Bill
We can certainly say that a particular region of a field gives us what might be called "no field" there, but it would be far less awkward to say there is a zero value there rather than "no field" there.

A zero value for a field doesn't mean no field. The field is there but it has a zero value. Likewise we can speak of our savings account being empty (without any money) without in anyway suggesting that the savings account itself is not there. Indeed, if we did not have access to our savings account we wouldn't know if it was empty or not.

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#### carllooper

It's not a model because its incorrect - as the paper I linked to explained.

Ambiguity - doubtfulness or uncertainty of meaning or intention.

There is no known ambiguity in QM. People who think so don't understand it.

Thanks
Bill
The paper refers to the "existence of various theoretical and interpretational ambiguities", not in QM, but underlying certain myths. And I quote:

The fact is that the existence of various theoretical and interpretational ambiguities underlying these myths does not yet allow us to accept them as proven facts. I review the main arguments and counterarguments lying behind these myths and conclude that QM is still a not-yet-completely-understood theory open to further fundamental research.

These ambiguities (as proposed here) do not belong to QM, but nor is the conclusion. Both are, at this juncture, mythological. ie. both the premise and the conclusion are mythological.

A model doesn't need to be correct to be a model. It can be an incorrect model.

C

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#### maline

There is some confusion here b/c the word field is being used in two ways. Technically, a "field" is simply a function on space, so it's defined everywhere. When we say "the EM field is the medium for light waves", we mean it in that sense. But when we say "there is an electric field in this region", we mean that a charge will experience a force; i.e. a nonzero field. This is what confused the OP.

#### carllooper

In introductory texts one speaks of a "wave/particle" duality in order to steer the student away from any overly hasty conclusion that light can be described exclusively by a wave model, or exclusively by a particle model, as it had been prior to QM. The author of the paper himself goes on to elaborate what could easily be called a "wave/particle duality" model even if the author himself finds such words are too "deep" and "mysterious".

They are not. To suggest otherwise is to invite the very thing the author is trying to avoid: mythologisation.

C

#### vanhees71

Gold Member
There is no wave-particle duality. It's an old-fashioned concept, given up almost 90 years ago. Further photons are as far from classical particles as anything can be. It's a certain excitation of the quantized electromagnetic field, described by a one-particle Fock state. Unfortunately this highly abstract construct contains the word "particle" in its name, but that's just convenient convention.

#### carllooper

The author of the paper isn't entirely against the words "wave-particle duality":

one may conclude that the notion of “wave-particle duality” should be completely removed from a modern talk on QM. However, this is not necessarily so. Such a concept may still make sense if interpreted in a significantly different way. One way is purely linguistic; it is actually common to say that electrons and photons are “particles”, having in mind that the word “particle” has a very different meaning than the same word in classical physics. In this sense, electrons and photons are both “particles” (because we call them so) and “waves” (because that is what, according to the usual interpretation, they really are).

Another meaningful way of retaining the notion of “wave-particle duality” is to understand it as a quantum-classical duality, becuse each classical theory has the corresponding quantum theory, and vice versa. However, the word “duality” is not the best word for this correspondence, because the corresponding quantum and classical theories do not enjoy the same rights. Instead, the classical theories are merely approximations of the quantum ones.

#### carllooper

Some form of duality is required if one wants to explore not just light in itself (which a wave model might usefully be all that's required), but the effect light has within an observable world. There are particle-like effects that light produces, and can be exploited, eg. in photography and the cinema. There are also wave-like effects (visible interference patterns) that can also be exploited (in holography).

This is not necessarily important in physics but it is in science/technology of which physics plays a part. There is nothing to suggest that attention to waves and particles on an equal basis leads to any mythologicalisation of such - although certainly it's not ruled out. Particle-like effects are quite real - they're certainly not in the same category as unicorns.

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#### craigi

It's worth noting that wave-particle duality is still a very relevant concept in the de Broglie-Bohm interpretation of quantum mechanics. The wave being the pilot wave for the counterfactual definite particle. So, the concept isn't as out of date as other posters in this thread might lead you to believe.

#### vanhees71

Gold Member
"Light" is described by QED, and it is in the sense of QED that light has wave and particle like properties, but it's neither a classical particle nor a classical field.

#### jimmylegss

Im sorry, I phrased it poorly. The question is 2 fold, do magnetic fields go on forever, or to the edge of the universe? I think gravity is something that goes on forever right? The gravity of our earth affects the entire universe, allthough very very weakly, is it the same with magnetic fields?

And the second part is, the fact that light can behave as a wave is very strange. Because it would imply it travels (and somehow interacts) through a surface (like the case for sound and water waves). And since vaccuums are empty, I thought the explanation was that light travels through magnetic waves (of for example the earth's). And that explains how light can behave as a wave. Or at least it is explained that way in Asimov's book on physics (which i guess is somewhat outdated now).

This is the one:
https://www.amazon.com/dp/0880292512/?tag=pfamazon01-20

So if magnetic fields would not be able to reach all over across the universe that would mean there are places where light can only behave as a particle (or better said, where no interference patterns can be seen with regards to light?).

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#### bhobba

Mentor
Im sorry, I phrased it poorly. The question is 2 fold, do magnetic fields go on forever, or to the edge of the universe?
Yes. According to Quantum Field Theory (QFT), the quantum EM field, which is the field of the photon, and the magnetic field is part of, pervades all of space-time.

Thanks
Bill

#### jimmylegss

Shouldn't you get different looking wave functions then in different area's of the universe? So let's say you do the exact same experiment far into space where the magnetic field is weaker, you would then get a different result? Has this been seen yet?

#### bhobba

Mentor
Shouldn't you get different looking wave functions then in different area's of the universe? So let's say you do the exact same experiment far into space where the magnetic field is weaker, you would then get a different result? Has this been seen yet?
The laws of physics governing magnetic fields are the same regardless of its strength. Why you would think otherwise has me beat.

Of course it hasn't been tested on the other side of the universe - but as far as we can tell the same laws of physics hold everywhere.

Thanks
Bill

#### jimmylegss

No I mean they are weaker, the further out no? As the field lines are spread out more. So does that affect what kind of interference pattern you would get on the screen, if you would do a double slit experiment much further out from earth.

#### bhobba

Mentor
So does that affect what kind of interference pattern you would get on the screen.
I am having difficulty following your reasoning. Are you talking about if you move the screen a long way from the source?

Thanks
Bill

#### jimmylegss

yeah, doing an experiment where the magnetic field is considerably weaker then on earth. Would you get different results in any way.

So I guess really waht I am asking is, does the strength of the magnetic field affect what happens in the double slit experiment.

#### craigi

yeah, doing an experiment where the magnetic field is considerably weaker then on earth. Would you get different results in any way.

So I guess really waht I am asking is, does the strength of the magnetic field affect what happens in the double slit experiment.
One thing that you're still missing is that light is electromagnetic radiation. That means that wherever there is light, there is a varying electric and a magnetic field.

We're not talking about the Earth's magnetic field or a magnetic field created by magnets. The light bulb or laser (or whatever light source) is what creates the light (electromagnetic radiation). This is what causes fluctuations in the electric and magnetic fields.

Does the Earth's magnetic field affect light or the double slit experiement? No.

Does the strength of the electric and magnetic field fluctuations affect the light or the double slight experiement? Yes. They affect the how bright the light and the interference patttern are.

Perhaps, your next question is, why does light (electomagnetic radiation) not appear to affect metal objects (iron). The answer is that the fluctuations of visible light are of too high frequency for the iron to respond to in the way that a magnet might affect iron.

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