# If light is a wave, what is waving?

• timmyteapot
In summary, the conversation discusses the concept of a displacement medium for waves, specifically in relation to light as an electromagnetic/magnetic wave. The expert explains that the displacement medium for light is the electromagnetic field itself, and clarifies that the field does not physically travel but is present everywhere. The conversation also touches on the distinction between mathematics and physics in understanding the concept of a field, and the expert notes that our current understanding of electromagnetic radiation is supported by experimental evidence. The conversation ends with a comparison to the evolution of our understanding of gravity, with the expert suggesting that field theory may also evolve in the future.
timmyteapot
We are all familiar with the description of a wave as being the ripples on a pond with water being the displacement medium for the wave. I understand that light is a electromagnetic/magnetic wave but in reality there has to be a displacement medium for the wave to transmit, what is it?

timmyteapot said:
but in reality there has to be a displacement medium for the wave to transmit
Why do you think that?

Any mathematical model used to describe waves, is just that, a model, and is not reality. I see, therefore I am receiving information, how is it possible to receive information ie light without there being a transfer of information from the subject to the receiver? There has to be a disturbance in some form along the path between the two? What is the displacement or disturbed medium?

The information is carried by the E&M field itself. It's not a disturbance of some medium (as is the case with sound, for example).

timmyteapot said:
We are all familiar with the description of a wave as being the ripples on a pond with water being the displacement medium for the wave. I understand that light is a electromagnetic/magnetic wave but in reality there has to be a displacement medium for the wave to transmit, what is it?
Yes, light is a wave (or ripple) in the electro-magnetic field. That is the "displacement medium".

If light is transmitted via E&M fields, then how does the field manifest itself in reality, if information is "carried" there has to be a transmittance through the field as you state so what is the mechanism for the transmittance?

Haven't we gone through this already at the beginning of the 20th Century?

Zz.

timmyteapot said:
If light is transmitted via E&M fields

I would say, light is a disturbance of the E&M field.

timmyteapot said:
, then how does the field manifest itself in reality,

By the light that you see. Or by the cellphone you are using. Or the lightning that burns down your house.

timmyteapot said:
if information is "carried" there has to be a transmittance through the field as you state so what is the mechanism for the transmittance?

The mechanism is waves.

The explanation of "a field" or "wave" is a mathematical description of a disturbance of a physical something. Light travels through a vacuum so by your definition so does the field, so if you prefer the question could be, what in reality is a field and what is being disturbed to transmit the information through that field? There has to be a physical reality and not just a mathematical concept of a field or wave? So what is it?

ZapperZ said:
Haven't we gone through this already at the beginning of the 20th Century?

Zz.

Sounds like you don't think that the E&M field is 'real'.

timmyteapot said:
The explanation of "a field" or "wave" is a mathematical description of a disturbance of a physical something.

Are we talking about mathematics or physics? In physics, the physical something you talk about IS the field. That physical something is modeled using the mathematical concept of a field. So a field can be real or imaginary in a sense. But it's all just semantics of the language we use.

We could maybe just say that a field is real. Like a corn field or an E&M field. We then invent an abstract mathematical concept that we call the fieldotronicoid and use that to model real fields... It just happens that the word field is overloaded. That's all.

timmyteapot said:
Light travels through a vacuum so by your definition so does the field, so if you prefer the question could be, what in reality is a field and what is being disturbed to transmit the information through that field? There has to be a physical reality and not just a mathematical concept of a field or wave? So what is it?

First of all the field doesn't travel. It's just there, everywhere, including the vacuum. In reality the field is made up of quantized harmonic oscilators. Does that help? We know the field is there because we can measure it. That's all. What more do you want?

timmyteapot said:

Actually, it has, per Special Relativity!

The problem here is that you have made an a priori assumption that ANY wave needs a medium of transmission. So now you're asking for what that medium is for EM radiation. That's like asking someone "when was the last time you bashed your wife?". The question can't be answered within the framework that it was asked!

We have seen, in physics, where our "prejudice" needs to be revised in light of (i) experimental evidence and (ii) new formalism to describe something. So far, your question is based on a matter of "taste" ("there has to be some disturbance of something") without pointing out experiments in which such a thing is supported. On the other hand, a whole zoo of experiments have indicated that our current understanding of EM radiation is valid, that light requires NO medium for transmission.

Zz.

FredericGos said:
Are we talking about mathematics or physics?
I am talking about the physical reality, in Schrodingers equation for quantum harmonic oscillation the wave form is a function of kinetics and angular frequency which may describe reality but is in truth a mathematical interpretation of a reality. If we interpret a measurement, or series thereof, as being the evidence of a force or field as reality, surely we have only supplied a plausible interpretation of that measurement. For example Newton "discovered gravity" (I assume we all floated round before he did so (joke)) anyway he saw the apple fall and offered an interpretation to the best of his knowledge and dutifully quantified that experience and numerically was able to predict the behaviour of or movement of objects. Many years later along came other thinking and we now visualise gravity in terms of space time.

The reality of field theory seems to be at the same stage as Newton. If a field is "just there" or "real" because we have measured something the question remains through what physical medium, in reality does it function?

timmyteapot said:
Any mathematical model used to describe waves, is just that, a model, and is not reality.
This is a pretty common complaint of crackpots everywhere. Unfortunately, it doesn't hold water in the context of science. This is not just an arbitrary mathematical model, it has been experimentally validated to incredible precision. So although math is a construct of human logic, in this case it is a model which does in fact accurately describe reality.

timmyteapot said:
I am talking about the physical reality, in Schrodingers equation for quantum harmonic oscillation the wave form is a function of kinetics and angular frequency which may describe reality but is in truth a mathematical interpretation of a reality. If we interpret a measurement, or series thereof, as being the evidence of a force or field as reality, surely we have only supplied a plausible interpretation of that measurement. For example Newton "discovered gravity" (I assume we all floated round before he did so (joke)) anyway he saw the apple fall and offered an interpretation to the best of his knowledge and dutifully quantified that experience and numerically was able to predict the behaviour of or movement of objects.

So, you just want a non mathematical explanation. Fine, but that's not physics.

timmyteapot said:
Many years later along came other thinking and we now visualise gravity in terms of space time.

How do you think that happened? I suppose you think that someone just had a better idea and was able to convince the others that he was right?

What happened was that MEASUREMENTS at some point started to conflict with existing theory and assumptions. So, some people thought long about how that could be. those person ended by proposing a refinement of the existing theory which encompassed both. Since then no experiment has been able to falsify that. In fact it keeps coinciding with reality to an absurd level of precision, everyday.

Your question is one of philosophy. In which language do you expect the answer to be?

I assume the term crackpot was not to be taken personally, even though you may have been a little exasperated when you wrote it. If questioning interpretation of experimental evidence is crackpot then you would have to add Galileo and Einstein to your collection. I can accept the existence of waves and all the experimental evidence for them, but in every graphical representation of those waves amplitude is shown as well as a wave length. I believe my original question was asked of Einstein who coined the term photon after Hertz demonstrated with his plate experiment that waves were inadequate explanation of light. It is also known that waves are transmitted through vacuum yet there is no obvious explanation offered other than “a field”. So assuming EM wave or field is a widely accepted term for a light field what in reality is the amplitude of the wave (other than brilliance), something physical must change in the field so what is it? I really hope I am not exasperating you over this but my searching question is genuine.

FredericGos said:
Your question is one of philosophy. In which language do you expect the answer to be?

The question is one of reality which is neither mathematical or philosophical

I think http://www.physicsclub.net/images/wave_anim.gif" is a decent animation of the physical interpretation of an electromagnetic wave in classical electromagnetism. One of the colors represents the electric field and the other color represents the magnetic field. You probably understand electric and magnetic fields as being fields of vectors, well in that picture the arrows are electric and magnetic vectors. That wave can be created from an accelerating charge. In order to conserve energy the charge radiates away some of it's energy in the form of that oscillating electric and magnetic field shown in the link. That oscillating electric and magnetic field is an electromagnetic wave. The wave continues to propagate in order to satisfy Maxwell's equations.

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timmyteapot said:
The question is one of reality which is neither mathematical or philosophical

If we found "reality," how would we know it? (That is a philosophical question, is it not?)

timmyteapot said:
I assume the term crackpot was not to be taken personally, even though you may have been a little exasperated when you wrote it. If questioning interpretation of experimental evidence is crackpot then you would have to add Galileo and Einstein to your collection. I can accept the existence of waves and all the experimental evidence for them, but in every graphical representation of those waves amplitude is shown as well as a wave length. I believe my original question was asked of Einstein who coined the term photon after Hertz demonstrated with his plate experiment that waves were inadequate explanation of light. It is also known that waves are transmitted through vacuum yet there is no obvious explanation offered other than “a field”. So assuming EM wave or field is a widely accepted term for a light field what in reality is the amplitude of the wave (other than brilliance), something physical must change in the field so what is it? I really hope I am not exasperating you over this but my searching question is genuine.

But here is where it becomes very puzzling. Consider the following:

I have a charge sitting at some origin that I define. Now, at a distance r away, I can measure an electric field at that point. This is all simple electrostatics. How come you don't have an issue with this? After all, what is the origin of that field at that point, since technically, it requires NO medium for that field to exist? We have nothing oscillating here, no "wave" of any kind. You didn't ask about this, so I presume that you have no issue with such a thing.

But the question is, why not? You see, I can now take that charge, and then jiggle it up and down, and voila, I get your EM wave! No different than before other than, now, I have an oscillating E and B field, per Maxwell equation.

So how come you have a problem with the latter, but not the former?

Zz.

jtbell said:
If we found "reality," how would we know it? (That is a philosophical question, is it not?)

Good point but I am asking for at least some suggestion of a reality

timmyteapot said:
I assume the term crackpot was not to be taken personally, even though you may have been a little exasperated when you wrote it. If questioning interpretation of experimental evidence is crackpot then you would have to add Galileo and Einstein to your collection.
It is up to you if you want to take it personally or not. I was simply identifying your argument as a very common one used by crackpots. Incidentally, comparing yourself to Einstein is also a very common tactic by crackpots. If you are not one then you should be aware that you are unintentionally casting yourself in a very unfavorable light.

timmyteapot said:
I can accept the existence of waves and all the experimental evidence for them, but in every graphical representation of those waves amplitude is shown as well as a wave length. ... So assuming EM wave or field is a widely accepted term for a light field what in reality is the amplitude of the wave (other than brilliance), something physical must change in the field so what is it?
The amplitude is the field strength, i.e. the force that would be exerted on a stationary test charge at that location due to the EM wave.

ZapperZ said:
But here is where it becomes very puzzling. Consider the following:

I have a charge sitting at some origin that I define. Now, at a distance r away, I can measure an electric field at that point. This is all simple electrostatics. How come you don't have an issue with this? After all, what is the origin of that field at that point, since technically, it requires NO medium for that field to exist? We have nothing oscillating here, no "wave" of any kind. You didn't ask about this, so I presume that you have no issue with such a thing.

But the question is, why not? You see, I can now take that charge, and then jiggle it up and down, and voila, I get your EM wave! No different than before other than, now, I have an oscillating E and B field, per Maxwell equation.

So how come you have a problem with the latter, but not the former?

Zz.

I do have issue with it. Why should one particle, or even subatomic particle have influence over its surroundings for no explanation other than a field. What attribute could nature possibly impose on one fundamental particle (quark) and yet not on another when they are both fundamental. If one quark is different to another because of charge then where is the charge "kept" if both are fundamental.

timmyteapot said:
If one quark is different to another because of charge then where is the charge "kept" if both are fundamental.

That is certainly a question of meta physics. I don't believe anyone really knows what charge is exactly, it's just a property of some particles. It's just something you have to accept for now. You could classify charge as having to do with the particles interactions with photons. Neutral particles don't interact with photons (the fact that they don't interact is what causes the particle to have no charge).

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timmyteapot said:
I do have issue with it. Why should one particle, or even subatomic particle have influence over its surroundings for no explanation other than a field. What attribute could nature possibly impose on one fundamental particle (quark) and yet not on another when they are both fundamental. If one quark is different to another because of charge then where is the charge "kept" if both are fundamental.

Ah, then go back even further. Why would nature impose translational/rotational symmetry on empty space to give us conservation of linear and angular momentum? What could possibly cause such a symmetry to exist?

And why would nature impose a CPT symmetry?

Etc.. etc.

Your question has nothing to do with "If light is a wave, what is waving?", does it? In fact, this is beginning to sound like a philosophy question, which doesn't belong here.

Zz.

DaleSpam said:
Incidentally, comparing yourself to Einstein is also a very common tactic by crackpots. If you are not one then you should be aware that you are unintentionally casting yourself in a very unfavorable light.

The amplitude is the field strength, i.e. the force that would be exerted on a stationary test charge at that location due to the EM wave.

I didn't compare myself with anyone, they were the first people to come to mind. I am sorry if you find my probing questions unfavourable, I guess that is the nature of probing questions, but for a number of years I have been questioning our understanding of EM waves and remain unconvinced that anyone truly understands the reality of the nature.

timmyteapot said:
I didn't compare myself with anyone, they were the first people to come to mind. I am sorry if you find my probing questions unfavourable, I guess that is the nature of probing questions, but for a number of years I have been questioning our understanding of EM waves and remain unconvinced that anyone truly understands the reality of the nature.

What exactly is "reality of the nature"? How do you know when you find it? Tell me ONE example where you think you've understood the reality of ANYTHING.

This is one of those phrases that gets tossed around and people using it think they know what it is, when in reality, you haven't defined what it is and have no clue what it is.

Zz.

timmyteapot said:
I didn't compare myself with anyone, they were the first people to come to mind.
Sure you did. You were clearly saying that if I were going to classify you as a crackpot that I would have to also classify Einstein and Galileo as crackpots since they were also "questioning interpretation of experimental evidence".

timmyteapot said:
I am sorry if you find my probing questions unfavourable, I guess that is the nature of probing questions
On the contrary, I answered your questions directly. What is unacceptable is not your "probing" questions but rather your position that any mathematical model is automatically unrealistic simply by virtue of being mathematical, regardless of how well-validated it may be.

timmyteapot said:
for a number of years I have been questioning our understanding of EM waves and remain unconvinced that anyone truly understands the reality of the nature.
We understand EM waves completely. There is not even one single observed behavior of EM waves that isn't predicted by QED with amazing accuracy. If you disagree, then please cite the experimental EM phenomenon that you believe is not consistent with theory.

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The field model (and it is a model) is imperfect like every model, the only perfect model being the thing itself.

I commend to you the excellent essay by Shahn Majid (Professor of Mathematics at edit: London University) in the book he edited 'On Space and Time'.
The essay is entitled Quantum Spacetime and Physical Reality.

go well

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timmyteapot said:
Good point but I am asking for at least some suggestion of a reality

The situation has much to do with the tendency for informal terms to develop formal scientific meaning.

The ancients would see 'wave', and use that word or its equivalent in other languages, to describe a mass of water seemingly moving as a mound over the surface. At some level they recognized, no doubt, that the water wasn't actually going anywhere.

Then the formal treatment of wave behaviour required careful analysis to resolve the cyclical motion of particles of water.

This is a crucial first step in the formation of 'wave' as an abstraction. But the ancient idea of a substance that waved hung onto the definition of light, especially since some medium, especially one that is so viscerally tangible as water, and only slightly less so air (to the modern) is essentially attached to the specification list of the term 'wave'.

The final shift in abstraction came when, for light, even the idea of a medium was dispensed with. All of the vestigial waving that remains is the oscillating and self-generating magnetic and electric fields. The direction of propagation is fixed by the conservation of the momentum that gave birth to the 'wave'.

Likewise the idea of 'spin' has been applied to a property of elementary particles, but it no longer carries the least amount of its original macroscopic force, except for a bright high-school physics student. The man on the street scratches his head at the idea of 'angular momentum' with reference to 'spin', it vaguely makes sense to myself, but it speaks very much of spin to the physics major.

I think waves are just mathematical concept we use to describe behaving of some physical objects, as quantum mechanics does that. So, similar should be with light: there are photons who travel here and there. They sometimes show particle nature, sometimes wave nature. Why is this so, I think no one knows, but it works in description of many phenomena. So, my answer to the question would be: at this moment it is not answerable.

That is my opinion, not necessarily true.

nikolafmf said:
I think waves are just mathematical concept we use to describe behaving of some physical objects, as quantum mechanics does that.

Everything could be described like this. What makes a wave any different? I could claim a particle is just a concept describing something.

timmyteapot said:
We are all familiar with the description of a wave as being the ripples on a pond with water being the displacement medium for the wave. I understand that light is a electromagnetic/magnetic wave but in reality there has to be a displacement medium for the wave to transmit, what is it?

What is waving? In one simple word: energy.

EM fields might be considered conceptual crutches that allow us to determine the relationships between energy and force. (Maxwell regarded what we now call the E field as a force). More recently, the field idea replaced Maxwell's force in a consistent manner. EM fields are not directly observable and depend on the concept of having an artificial "test charge" to determine their values by observing the motion of a charge or set of charges that can be compared with that "test charge" by determining the force needed to move the mass associated with the charged particle(s) in such a manner.

If we assume that Poynting theory is correct then all fluctuations of EM fields can be reduced (or translated) to fluctuations of energy.

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