If light is a wave, what is waving?

[harrylin]

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?

Traditionally in classical physics, light was conceived as either particles in empty space or waves in a medium which got the name "ether". All considered particle models were disproved so that the wave model of light remained, but the medium looked less and less like "ether". In particular, the concept of a kind of thin medium that is pushed away by moving bodies was disproved, leaving as only model that of a "stationary" ether that includes particles as a kind of waves.
However, next the wave description was kept but the medium was considered superfluous by most - even if it doesn't make conceptual sense to have a vibration of nothing. Some people replaced it with the concept of Spacetime (also coined a 4D ether). In recent times medium concepts also came from quantum mechanics but that is out of the scope of this classical forum.
So, if you fancy it then you can use it to satisfy your personal logic, but be prepared to face the fact that a great number of people do not fancy it at all and that it is even dogmatically rejected in influential circles.

 

[harrylin]

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.

Then it may please you to hear that at a certain time even Einstein admitted to a kind of ether of which the "fundamental" difference with the "ether of Lorentz" was that in the new model the state of the ether is affected by matter. However he later promoted the 4D Spacetime concept as hidden reality, which is quite a different philosophy. There are threads on those different interpretations, you may search for them and choose the one that according to your logic is more likely to be close to "hidden reality". So far neither model has been disproved beyond doubt, and it's not sure that this will ever be possible.

 

[PhilDSP]

Dirac also pushed very heavily for a reconsideration of the usefulness of an aether. And he is known to have, more or less, single-handedly defined the modern structural basis of QM. But again, what the "aether" represents is our lack of full recognition of what the rules are for how fluctuations of energy are related to fluctuations of force and what could sponsor those rules.

 

[nikolafmf]

Electromagnetic field has some energy, as has sound. Energy of sound comes from vibrations of molecules of air, say. Where does energy of EM field comes from? One would may be say from the oscillation of the field. But this is conceptually challenging for many people. We can see the molecules under the microscope and know how they look. But we can't see the EM field. So, people keep asking what is that field...?

 

[ZapperZ]

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?

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?

We get question like this rather often, and it is an interesting puzzle for me, as a physicist, on not the question, but why it is asked. Let me explain.

Let's say that you have a charge sitting somewhere, at a fixed location. Now, at a distance r away, you have another charge. This second charge feels a force due to the electrostatic field from the first charge. So far so good?

Now, no one seems to want to ask what MEDIUM that electrostatic field traveled in. Presumably, everyone seems OK with this lack of medium, for some reason, in the case where everything is static. After all, this was never asked in this thread. So I will assume that no one has any conceptual problem with this situation.

Just when things look fine and dandy, I decided to take that first charge, and then wiggle it up and down (or, if you prefer, sideways). What did I just do? I've created an electromagnetic radiation, i.e. "light"! If I look at the second charge, it will detect this oscillating field.

So my question is, if no one seems to find any issue with the electrostatic case, why is the oscillating case any different? Why is there an insistence on a "medium" to satisfy your conceptual understanding when you didn't find it conceptually difficult with the electrostatic situation? It would be malicious of Mother Nature if she doesn't require any medium to transmit electrostatic field, but then suddenly changed the rules of nature and now introduced a medium just because I decided to wiggle that charge! I find THAT to be even more conceptually troubling!

And BTW, if you think I've just made up this example out of thin air, think again. If you visit a synchrotron light source facility, you'll find electron bunches going through insertion devices called "wigglers" or "undulator" that essentially are making these electron bunches wiggle up and down, to generate electromagnetic radiation. In fact, free-electron lasers use this very concept to generate such radiation.

Zz.

 

[nikolafmf]

Let's say that you have a charge sitting somewhere, at a fixed location. Now, at a distance r away, you have another charge. This second charge feels a force due to the electrostatic field from the first charge. So far so good?

Now, no one seems to want to ask what MEDIUM that electrostatic field traveled in. Presumably, everyone seems OK with this lack of medium, for some reason, in the case where everything is static. After all, this was never asked in this thread. So I will assume that no one has any conceptual problem with this situation.

Zz.

Not necessarily. On could ask, how is that that first charge tells the second it is present here. In other words, how is that force transmitted to the second charge? In macroscopic objects, I can push against the wall with my hands, of tight somebody with a rope and pull her to me in that way. There is always direct contact. But how can the second charge feel the force of the first without a direct contact? I have not studied quantum electrodynamics yet, so I want to know if that theory may be gives some answers?

 

[ZapperZ]

Not necessarily. On could ask, how is that that first charge tells the second it is present here. In other words, how is that force transmitted to the second charge? In macroscopic objects, I can push against the wall with my hands, of tight somebody with a rope and pull her to me in that way. There is always direct contact. But how can the second charge feel the force of the first without a direct contact? I have not studied quantum electrodynamics yet, so I want to know if that theory may be gives some answers?

But you didn't ask that. You directly asked about "oscillating" wave. And my point is, why did you ask that and didn't ask why there was a force between them under STATIC condition in the first place? Was that situation understood intuitively already?

BTW, when you push against something, what you say is a "direct contact" is really the electromagnetic interactions of the atoms/molecules of your hand against that of what you're pushing against. That is your "direct contact", which is the same as what I've described earlier in the electrostatic case.

So now what? Do we need to take several steps back and now figure out what exactly gets transmitted between remote objects that do not require a medium? After all, one can make the same argument with gravity as well.

Zz.

 

[jtbell]

There is always direct contact.

Ah, but when you look really closely at the interface between your hand and the wall, at the atomic level, the notion of "direct contact" becomes fuzzy, because you're dealing with "probability clouds" of electrons which are repelling each other via the electrical force.

[Zz beat me to it by a nose.]

 

[nikolafmf]

BTW, when you push against something, what you say is a "direct contact" is really the electromagnetic interactions of the atoms/molecules of your hand against that of what you're pushing against. That is your "direct contact", which is the same as what I've described earlier in the electrostatic case.


Zz.

You are right.

 

[nikolafmf]

So now what? Do we need to take several steps back and now figure out what exact gets transmitted between remote objects that do not require a medium? After all, one can make the same argument with gravity as well.

Zz.

Yeah, that is a good question which could solve many dilemmas. What exact gets transmitted...? And if it is photons, how they make charges to feel force?

 

[harrylin]

[..] no one seems to want to ask what MEDIUM that electrostatic field traveled in. [..]

Surely many people do! It's fascinating to see how the electrostatic force of a plastic pen can deflect "at a distance" the water flow from a tap and as a kid I wondered what "is there" that transmits magnetic force, as we can feel how repulsive forces interact at a distance.

This was also asked by the interviewer in the linked video:

I find Feynman's reply disappointing. In the middle he implied that he didn't know the answer which is OK, but mostly he was just looking for excuses - he spent much time explaining how difficult it is to answer a "why" question and said that he could not explain it in terms familiar to the interviewer.

 

[ZapperZ]

Surely many people do! It's fascinating to see how the electrostatic force of a plastic pen can deflect "at a distance" the water flow from a tap and as a kid I wondered what "is there" that transmits magnetic force, as we can feel how repulsive forces interact at a distance.

Oh, I'm fascinated by it. I'm saying that, especially in THIS thread, this issue NEVER came up. And I've seen many other threads where people dived in right into the more complex situation without bothering to step back and see if they've understood the simpler case.

This was also asked by the interviewer in the linked video - and I find Feynman's reply disappointing. In the middle he admitted that he didn't know the answer which is fine, but mostly he was just looking for excuses: he spent much time explaining how difficult it is to answer a "why" question and he pretended that no explanation is possible using concepts with which the interviewer is familiar.

This "incident" is well-documented, even by the interviewer. Still, at some point, I can understand Feynman's frustration, keeping in mind that this was the SAME guy that captivated the media and the public with his very simple demonstration during the Challenger disaster hearing.

As Einstein was known to say, explain it in simple terms, but not any simpler. One runs the risk to making inaccurate analogies when one tries to do many of these things at the pedestrian level.

Yeah, that is a good question which could solve many dilemmas. What exact gets transmitted...? And if it is photons, how they make charges to feel force?

This gives me the opportunity to kill 2 birds with one stone.

1. It is imperative that, in learning, one starts with the simpler, more basic understanding. This is why I puzzled at the question, because it seems to start with the more complicated time-varying problem of something oscillating. When we teach physics to students, we try to start with something simpler, just so they get an idea and a feel for the physics, before proceeding to more complex physics and situations. That's how one HAS to learn. Really, the cliche that one has to learn how to walk FIRST before attempting to run truly applies here!

2. Many people, especially crackpots, have accused physicists of wanting to stick "within the box", and that we are unwilling to work "outside the box". This is, obviously, utterly false. What happens usually is that we often discover that what we consider to be a "rule" turns out to be only true for a limiting case. For example, we thought we have a conservation rule for energy, and a separate conservation rule for mass. Of course, we KNOW know that the more UNIVERSAL rule is the conservation of mass(energy content)+energy. So we change our concept when that has been shown convincingly to be valid.

Now that last argument applies here with respect to the CLASSICAL FIELD (since this is posted in the Classical Physics forum). We originally thought that all waves must have a medium to propagate in. When Special Relativity came out, and upon further development and experimentation throughout the previous century, we realize that the concept of a medium for EM radiation is superfluous. It is not needed, and more importantly, it is not detected! So we drop the "universal" requirement that all waves must have a medium to propagate. Thus, Maxwell equations, the equations that describe classical EM interactions, no longer require one!

So now, instead of physicists being stuck to thinking only within the box, it now appears that the general public/laymen are the ones who can't go beyond this box. Why? Because it doesn't make sense, or conceptually difficult to accept? That isn't a very strong argument (it isn't a very weak argument either), because having something to "make sense" or conceptually acceptable requires that one is FAMILIAR and understand that something. There are many things that don't make sense but are true, simply because we did not understand it in the beginning.

So the question on "what is waving" cannot be answered other than saying "nothing". This is because asking "what is waving" assume that there's something out there that is waving, and you want to know what it is (other than, presumably, the electric and magnetic fields). One can't answer that question anymore than one can answer "So, when did you stop beating your wife?" Both made an a priori assumption that hasn't been verified.

If you ask "Does EM require a medium to propagate?", then the answer is NO. Once that is established, then the question on what is "waving" doesn't come up anymore, because it becomes moot!

Note that we haven't dealt with quantum field theory, or in particular, quantum electrodynamics. I am extremely hesitant to want to start delving into that, because I can see myself having to take steps backwards at every step along the way to explain the explanation.

I don't know if my response here is sufficient to satisfy the conceptual understanding of this. It may not be satisfying to hear that "nothing" is the answer. However, Mother Nature has no obligation to cater to our feelings or our needs. She does what she does.

Zz.

 

[harrylin]

[..] So the question on "what is waving" cannot be answered other than saying "nothing". [..] One can't answer that question anymore than one can answer "So, when did you stop beating your wife?" Both made an a priori assumption that hasn't been verified. [..]

Following your comparison, your answer on the second question is then that the wife was not beaten because no one knows if she was beaten - because for you answering in the negative is equivalent to not answering?!

 

[ZapperZ]

Following your comparison, your answer on the second question is then that the wife was not beaten because no one knows if she was beaten - because for you answering in the negative is equivalent to not answering?!

Er... no. If you read further, I gave an example in which, apply to this, means that one must FIRST ask "Did you ever beat your wife?". If the answer is "No", then asking "When did you stop beating your wife" is moot and has no answer.

My first answer of "Nothing" to the original question was a demonstration on why many find that answer difficult to understand or accept.

Zz.

 

[nasimrahaman]

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?

In short, the electric and magnetic fields are the ones waving. Their 'waving' is kinda coupled; i.e. a waving electric field induces a waving magnetic field (described by Ampere's corrected circuital law) and a waving magnetic field induces a waving electric field (see Faraday's law of induction).

Think about the pond again. The waves in a pond are very different from electromagnetic waves, but what makes the water 'wave'? You could almost think of it as the periodic vertical translation of the water molecules at every relevant point in space (or just the up and down movement of water molecules on the surface) which makes the wave a wave. ( http://upload.wikimedia.org/wikipedia/commons/7/74/Simple_harmonic_motion_animation.gif )
With light, a vertically waving electric field induces a horizontally waving magnetic field, which in turn induces a vertically waving electric field, the waves propagating in a direction perpendicular to both electric and magnetic field oscillations.

 

[harrylin]

Er... no. If you read further, I gave an example in which, apply to this, means that one must FIRST ask "Did you ever beat your wife?". If the answer is "No", then asking "When did you stop beating your wife" is moot and has no answer.

My first answer of "Nothing" to the original question was a demonstration on why many find that answer difficult to understand or accept.

Zz.

OK, thanks for the clarification!

Still, the OP based his question on an already received answer (or assumption) "[yes], light is a wave". Based on that first answer, his logical next question was: "[well then,] What is waving?".
And you answered: "Nothing is waving" - which means in full, if you were answering the question: "Light is a wave of nothing waving". As I mentioned, I find it logical if many find that a difficult answer to accept!

But it is strange that we rarely hear the question "If a magnet has a magnetic field, what is it made of".

 

[ZapperZ]

OK, thanks for the clarification!

Still, the OP based his question on an already received answer (or assumption) "[yes], light is a wave". Based on that first answer, his logical next question was: "[well then,] What is waving?".
And you answered: "Nothing is waving" - which means in full, if you were answering the question: "Light is a wave of nothing waving". As I mentioned, I find it logical if many find that a difficult answer to accept!

But it is strange that we rarely hear the question "If a magnet has a magnetic field, what is it made of".

But see, that is why I asked why the question of the electrostatic case wasn't asked! If one has no conceptual difficulties in accepting the presence of an electrostatic field in vacuum, with no medium, then why would one has issues accepting a "waving E field"? I'm trying to understand the "flow" of knowledge here of the person who asked the question, because I need to established what is known, and what is accepted by the person asking the question. Jumping in and simply providing an answer, to me, is usually not how I would normally proceed.

Zz.

 

[Studiot]

1. It is imperative that, in learning, one starts with the simpler, more basic understanding. This is why I puzzled at the question, because it seems to start with the more complicated time-varying problem of something oscillating. When we teach physics to students, we try to start with something simpler, just so they get an idea and a feel for the physics, before proceeding to more complex physics and situations. That's how one HAS to learn. Really, the cliche that one has to learn how to walk FIRST before attempting to run truly applies here!

I agree 110%

Which is why I was aghast when I discovered that the modern UK GCSE physics syllabus introduces force by using friction as the example force.

 

[Drakkith]

Thanks for the post ZapperZ! Very well done!

 

[Dale]

Still, the OP based his question on an already received answer (or assumption) "[yes], light is a wave". Based on that first answer, his logical next question was: "[well then,] What is waving?".
And you answered: "Nothing is waving" - which means in full, if you were answering the question: "Light is a wave of nothing waving". As I mentioned, I find it logical if many find that a difficult answer to accept!

This seems reasonable to me. If we say that "X is a wave" then that implies that associated with X is some A such that:
$$\frac{\partial^2 A}{\partial t^2}=k^2 \nabla^2 A$$

Then the question "what is waving" is asking "what is A", so it is a legitimate question which is not assuming anything beyond what is implied by the statement that X is a wave.

So for X=light you can answer the question either A=the electric field or A=the magnetic field, since both are associated with light and both obey the wave equation. That then reduces the problem in understanding to the static case that ZapperZ mentioned. If they are comfortable with electric and magnetic fields, then they should be comfortable with that answer. If not, then they need to get comfortable with static fields first.

 

[PhilDSP]

I'm wondering if what you really mean by "Nothing is waving" is that nothing physical is waving, or at least nothing that we commonly recognize as having physical substance. If you consider the equations for E and B fields, either static or dynamic, that certainly seems the case. But often electromagnetic potentials are placed in the equations along side E or B or even alone. Granted, physical substance is not normally associated with potentials either, even potential energy or gravitational potential. And yet they have a structural place that seems to generate physical effects. So there is a bit of a paradox there.

 

[Boorglar]

What I'm about to say is really only based on something I've read in a vulgarization book so I have absolutely no idea how much of it is true or not (I have never studied Quantum Electrodynamics), but it suggests an answer to the question of "what" is being transferred in the field.

I've read that, basically, there is a bunch of "virtual particles" that get created and destroyed almost momentarily along the whole path between one charged particle and the other charged particle. These "virtual particles" supposedly carry the interaction between the charged particles.

Can someone who is more knowledgeable on the subject explain this more precisely, or tell me if it is absolute nonsense?

 

[Studiot]

Particles of any description are not required for wave theories. Particles are for corpusculer theories, and yes there are corpuscular theories as successful as wave theories that involve 'virtual particles'.

However we are talking about wave theories here and this is the classical mechanics forum.

 

[EskWIRED]

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.

OT, but this is a good place to ask:

If one is interested in the metaphysical aspects of physics, or in any other philosophy of science, is there a good place to discuss it?

By "good", I mean like this place. I mean a forum with well-versed people willing to countenance simple questions and give relevant information. Not a place full of crackpots, but maybe a place where references to more information are routinely given.

 

[EskWIRED]

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.

I share your dissatisfaction with physics. Too often, the answers are to questions of what and how. Too seldom, the answers encompass the question of "why". Too often the answer is "Nobody knows".

But the subject is fascinating nevertheless. And at this point in history, no fault can be laid on our inability to answer the "why' questions. They are hard questions.

But the inability to answer is frustrating to me. Too often, the answers are mere tautologies. For example, I wonder why one can decrease wire gauge when transmitting electricity at higher voltage. I wondered what this voltage thing was. When I found out that voltage is the ability of electricity to overcome resistance, I was disappointed. Higher voltages can carry current through wire with higher resistance because - voltage means the ability to overcome resistance. IOW, increasing the voltage allows the electicity to flow through smaller wires, and that is why increasing the voltage allows...

So much of physics, at the levels that I currently understand, has a tautology at its base.

I find that the more I ask "why', the less satisfied I am. Physics can explain a lot of "how it works", but very little of "Why is it like that".

I have heard that the philosophy of science is of little help in these matters. Some physicists have very disparaging things to say about the current state of the philosophy of science. But IMO, for my taste, I would love to know more "why" to supplement physics' answers to what and how.

 

[jtbell]

OT, but this is a good place to ask:

If one is interested in the metaphysical aspects of physics, or in any other philosophy of science, is there a good place to discuss it?

We do have a Philosophy forum here:

https://www.physicsforums.com/forumdisplay.php?f=112

 

[EskWIRED]

We do have a Philosophy forum here:

https://www.physicsforums.com/forumdisplay.php?f=112

Ack! I should have known!

Thanks.

 

[jtbell]

'Interpretation of quantum mechanics by the double solution theory - Louis de BROGLIE'
http://aflb.ensmp.fr/AFLB-classiques/aflb124p001.pdf

“any particle, even isolated, has to be imagined as in continuous “energetic contact” with a hidden medium”

The hidden medium of de Broglie wave mechanics is the aether. The “energetic contact” is the state of displacement of the aether.

I note that de Broglie himself did not use the term "aether" in that 41-year-old paper. De Broglie-Bohm theory is indeed a currently-researched topic under interpretations of quantum mechanics. We have at least one person who works in this area, and who posts regularly in our Quantum Physics forum. I don't think I've ever seen him refer to the dB-B "quantum potential" as an "aether" or a physical medium in the sense that people usually understand the word "aether".

 

[mikelepore]

I think the answer to the original question is:
It starts out with a charge being accelerated or having a quantum jump.
Then Maxwell's 4th equation says a changing electric field produces a magnetic field.
Then Maxwell's 3rd equation says a changing magnetic field produces an electric field.
Then Maxwell's 4th equation says a changing electric field produces a magnetic field.
Then Maxwell's 3rd equation says a changing magnetic field produces an electric field.
Repeat.
This pattern of a change generating another change is self-perpetuating.
Observers some distance away see sinusoidally changing electric and magnetic fields arriving at their location.
Is this correct? Please criticize. Thanks.

 

[harrylin]

This seems reasonable to me. If we say that "X is a wave" then that implies that associated with X is some A such that:
$$\frac{\partial^2 A}{\partial t^2}=k^2 \nabla^2 A$$

Then the question "what is waving" is asking "what is A", so it is a legitimate question which is not assuming anything beyond what is implied by the statement that X is a wave.

So for X=light you can answer the question either A=the electric field or A=the magnetic field, since both are associated with light and both obey the wave equation. That then reduces the problem in understanding to the static case that ZapperZ mentioned. If they are comfortable with electric and magnetic fields, then they should be comfortable with that answer. If not, then they need to get comfortable with static fields first.

Yes indeed. However an answer like that ignores that those two kinds of "fields" themselves were supposed to be, similarly as the wave description, properties of something and not things on their own - it complicates the original concept behind the equations by replacing the medium with a plurality of media or entities.
So, it's certainly very useful not to ask (or answer) the questions in isolation, as the three questions are related.

 

[harrylin]

[..] If one is interested in the metaphysical aspects of physics, or in any other philosophy of science, is there a good place to discuss it?

By "good", I mean like this place. I mean a forum with well-versed people willing to countenance simple questions and give relevant information. Not a place full of crackpots, but maybe a place where references to more information are routinely given.

We do have a Philosophy forum here:

https://www.physicsforums.com/forumdisplay.php?f=112

That's true. Regretfully it works like a black hole - hardly any physicist looks there. Not even those who make strong philosophical statements elsewhere (I tried it!). So, regretfully it's not a "good place". Perhaps it's too much hidden and far away? And I guess that such a question also needs to be discussed somewhere else.

 

[Dale]

those two kinds of "fields" themselves were supposed to be, similarly as the wave description, properties of something and not things on their own

Huh? Where did you get that from?

 

[harrylin]

Huh? Where did you get that from?

Where did I get what from? That "field" referred to some kind of state of a medium that exercises a force? As far as I know that concept originated with Maxwell and contemporaries.

ADDENDUM: That turns out to be incorrect (imprecise), and interestingly, already Maxwell spoke of "the electromagnetic field" (in singular).
That's in a paper* of 1864, and it sounds as if there he actually invented the term "field" for something that "has to do with the space in the neighbourhood of the electric or magnetic bodies [...] The electromagnetic field is that part of space which contains and surrounds bodies in electric or magnetic conditions". And he argued that this indicated the existence of a medium: "actions which go on in the surrounding medium as well as in the excited bodies".
*A Dynamical Theory of the Electromagnetic Field, 1864

Synonyms for "electromagnetic field" would thus be "electromagnetic area" or ""electromagnetic region".
So, thanks for asking!

 

[Dale]

Where did I get what from? That "field" referred to some kind of state of a medium that exercises a force? As far as I know that concept originated with Maxwell and contemporaries.

ADDENDUM: That turns out to be incorrect (imprecise), and interestingly, already Maxwell spoke of "the electromagnetic field" (in singular).
That's in a paper* of 1864, and it sounds as if there he actually invented the term "field" for something that "has to do with the space in the neighbourhood of the electric or magnetic bodies [...] The electromagnetic field is that part of space which contains and surrounds bodies in electric or magnetic conditions". And he argued that this indicated the existence of a medium: "actions which go on in the surrounding medium as well as in the excited bodies".
*A Dynamical Theory of the Electromagnetic Field, 1864

Synonyms for "electromagnetic field" would thus be "electromagnetic area" or ""electromagnetic region".
So, thanks for asking!

OK, so that is an historically correct "when did you stop beating your wife" question.

 

[PhilDSP]

It seems that the field concept originated with Faraday and Maxwell resisted making it a structural component of his theory in some ways. At least, if Maxwell could identify a non-field component as something else: force, polarization or positional displacement for example, he would prefer that to a field value. That makes sense to me as it seems Maxwell tried to make his theory as physical as possible. (His mentor William Thompson AKA Lord Kelvin didn't really fully approve of Maxwell dabbling with the metaphysics of fields)