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I know that we can define electric fields by the influence they have on certain kinds of matter (in particular, the charged kind), and that they store potential energy, but my question is what actually IS an electric field? We understand that a gravitational field is actually the curvature of spacetime (whatever spacetime actually is) in the vicinity of matter, but is there a similar explanation for what an electric field is, or what charge is? Are they just labels we gave to some observed phenomena that stand in a mathematical relationship, or do we understand something more about the physical nature of what the field actually is?

Qmechanic
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The_Mad_Geometer
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    What would it mean to understand the physical nature of something but to understand how they stand in a precise mathematical relationship to the observed phenomena in nature? –  May 31 '19 at 01:07
  • Welcome New contributor The_Mad_Geometer! There are many questions like this here and, mostly, the answers and comments point out that no answer is likely to be satisfactory. Consider an answer like "well, electric charge IS Y". Wouldn't the next question be "but, what IS Y?". Moreover, if to the best of our understanding, X is fundamental, then X cannot be explained in terms of other things (otherwise, it wouldn't be fundamental). – Alfred Centauri May 31 '19 at 02:04
  • Nobody knows exactly what it is because it has no mass for one. But scientists say the EM field is required because light and electric forces traverse a vacuum. There are many properties known about the EM field, basically how light behaves and this provided further proof of its presence .... but nobody can show you a bunch of particle and say here is the EM field. – PhysicsDave May 31 '19 at 02:06
  • I would also look into “force carriers” to understand what we guess about fields in general. The electric field is part of the EM field, which we think is “carried” by photons, but that doesn’t necessarily explain what the field is. https://en.m.wikipedia.org/wiki/Gauge_boson – oeste May 31 '19 at 05:58
  • Thank you all for your excellent replies. I suppose a better way to phrase my question might have been: what is the next most fundamental thing of which the EM field is comprised, and is there a physical interpretation of the EM field similar to the one we have for gravity? Clearly, nothing of experience can be understood in terms of anything except its relationship to other items of our experience. I didn't know if there was some interpretation of the physical nature of the EM field that might give my embodied, primate cognition a "feel" for it, if that makes sense. – The_Mad_Geometer Jun 01 '19 at 12:03

4 Answers4

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The EM field is a physical field created by electrically charged objects. It extends indefinitely through space.

You are asking about the electric field but we talk about EM field, and the electric field and the magnetic field can be observer dependent. A magnetic field can be viewed by one observer as electric field and by another one as magnetic field.

Now you are asking if what it is. The EM field is fundamental, and as you say it is a phenomenon, and in our currently accepted theories, the SM, QM and QFT, we describe this phenomenon with mathematical models, that best fit the data from the experiments.

When we try to describe the EM field as it interacts with something, we use virtual photons. Virtual photons mediate the EM field's interactions. These are not real photons. Virtual photons are just a mathematical model, that best describe the interaction between the EM field and something that it interacts with. In reality we do not know what it is, how it works really, we do not know what really mediates these interaction, we do not really know how they interact. What we do know is the data from experiments, and we built up mathematical models, called virtual photons to best describe these interactions.

Now you are asking whether the EM field can be described as the gravitational field when we use the phrase "gravity bends spacetime".

Yes there is similarity. But, gravity is always:

  1. attractive

  2. interacts with all known particles in the SM

So as per GR, and the SM, all known particles interact with the gravitational field. Thus, we can say that the gravitational field has an effect on spacetime, so that the area of space where the gravitational field exists, will have an effect on all known particles in the SM, so that these particles will have an altered trajectory when they interact with the gravitational field.

Because gravity is always attractive, the particles will always bend one way, towards the center of mass. And because gravity acts on all known particles in the SM, we tend to use this phrase "gravity bends spacetime". In reality we do not know what really bends, we do not know how it bends, and we do not know if anything really bends. All we know is that the particles will have an altered trajectory in all experiments.

Now with the EM field:

  1. sometimes attractive, sometimes repulsive

  2. acts on only some particles in the SM

What we can say, is that the EM field has an effect on spacetime, so that the area of spacetime, where the EM field exists, will have an effect on some particles (that interact electromagnetically) so that these particles will have an altered trajectory when they interact with the EM field.

But because the EM field is sometimes attractive, sometimes repulsive, and it only acts on some particles in the SM, we cannot say that " the EM field bends spacetime". In reality we do not know if anything bends, all we know is that some particles will have altered trajectory in all experiments.

Árpád Szendrei
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  • Great answer! Honest answer! – kpv May 31 '19 at 05:19
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    Can you please clarify what you mean with "When we try to describe the EM field as it interacts with something, we use virtual photons."? This isn't really what we do (also the word "virtual photons" is extremely dangerous as anything can be described without making use of any virtual photon at all). – gented May 31 '19 at 08:45
  • "You are asking about the electric field but we talk about EM field, and the electric field and the magnetic field can be observer dependent. A magnetic field can be viewed by one observer as electric field and by another one as magnetic field."

    Is that because because of special relativity? In other words, because magnetic fields are generated by moving charges and motion is relative, so magnetic fields in one frame of reference seem to be electric fields in others where the moving charge is stationary?

     – The_Mad_Geometer Jun 01 '19 at 12:07
  • Thank you, Arpad. Your answer was what I was looking for -- a "natural philosophy" one. You spelled out the difference between the mathematical relationship used to predict some set of physical properties when a sufficient number of other physical properties are known and how/what a thing actually is whose physical properties we're trying to measure, at least to the depth that asking what something is has meaning for our experience-derived intuition. – The_Mad_Geometer Jun 01 '19 at 12:18
  • @The_Mad_Geometer I am glad you like it. You are correct, as per SR, the relative motion of the charge will decide whether the field generated by it will be viewed by a stationary or moving observer as a magnetic or electric field. – Árpád Szendrei Jun 01 '19 at 16:34
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In biology, animals are divided into species and usually you don't ask what a cat or dog is. But you are able to describe them.
The same is in physics. An electron has a charge and we divide charged subatomic particles into species with exactly two opposite charges.

On the other side it was introduced the electric field. For two electrons the electric field between them and their electric charges are synonyms in the sense, that their charges are defined through the force they exercise on each other. More precisely, our knowledge about charges comes from the effecting electric field between charges. It’s simply avoiding to characterize an electron as “the particle with a negative electric field” instead of the electron is “a negative charge”.

I know that we can define electric fields by the influence they have on certain kinds of matter (in particular, the charged kind)...

is in principle the same what I've explained in so many words.

... but my question is what actually IS an electric field? ... Are they just labels we gave to some observed phenomena that stand in a mathematical relationship, or do we understand something more about the physical nature of what the field actually is?

Good point. The introduction of the field was so successful that so far there was no urge to investigate the consistency of the field. For the gravitational field the constituent of the field was introduced as the graviton. “...the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravity.” For electric fields such an interpretation attempt is missing. We are satisfied with what we have. Our thirst for research in this area is currently too low.

HolgerFiedler
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  • I made an attempt “Are photons composd particles” and very dry written about “Complex one-dimensional structures of space” here https://independent.academia.edu/HolgerFiedler – HolgerFiedler May 31 '19 at 05:37
  • Thank you. Your point about cats and dogs is a good one, and it points out a deficiency in the way I asked the question. My question might have been phrased: "Is there a physical interpretation of the EM field in terms of some more fundamental constituents that would further an understanding of its nature?" Understanding cats and dogs as assemblies of certain types of cells is useful for understanding certain things about them, but wouldn't give a better understanding of the animal's behavior. But knowing gravitational fields are the bending of spacetime toward matter does help intuition. – The_Mad_Geometer Jun 01 '19 at 12:29
  • You rephrased “Is there a physical interpretation of the EM field in terms of some more fundamental constituents that would further an understanding of its nature?”: May be. An approach is in the links above in my first comment. – HolgerFiedler Jun 02 '19 at 05:44
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Electric field is region of space in which if any test charge comes will experience a electrostatic force this defination or hypothesis was given by michael faraday to explain how the charged bodies interact.But this is hypothesis till this date.Nobody knows there really exsists electric field thats why we try to explain it by quantam mechanics that the charged particle exchange photon particle thus exerting a electrostatic force.But electric field allows us to understand and explain certain things very easily thats why we use it.In physics we cannot know always why something happens.eg why F=dp/dt

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The concept of a field (electric, magnetic, gravitational) was put forth to explain observable phenomena in which one body could impose a force on another body, without there being physical contact between the bodies. In particular, the presence of a force without physical contact was described “action at a distance”, a concept that troubled physicists going back to Newton. Newton said

"It is inconceivable that inanimate Matter should, without the Mediation of something else, which is not material, operate upon, and affect other matter without mutual contact".

I believe it was Michael Faraday who suggested that the "something else" that was not "material" that enabled matter to exert a force on other matter without contact was a field.

I'm sure you’ve seen iron filings used to visually demonstrate the presence of the magnetic field of a bar magnet, in which the filings align themselves with the magnetic field.

Hope this helps.

Bob D
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