# What is the electrostatic field?

## Main Question or Discussion Point

What comprises the electrostatic field? Electromagnetic radiation is made of photons, but what about the electrostatic field? Two static charges exert forces on one another, through their E-fields, presumably through photon exchanges. I am having trouble forming an idea of what an electrostatic field is, particular with respect to photons. One question I keep asking myself is "what are the frequencies" of the photons in the exchange between static charges. Hopefully I'm just being dumb and overlooking the simple explanation. I've always thought of QED as the 'quantum theory of light,' but the 'D' in QED makes me think it doesn't deal with this situation. I know very little about QED, btw.

This question is a mixture of classical and quantum which maybe where some misunderstandings are coming from. I had to pick one of the forums, so I picked classical. I guess I'm asking about the quantum nature of a field which I usually think of classically.

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tiny-tim
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hi wuliwong!
What comprises the electrostatic field? Electromagnetic radiation is made of photons, but what about the electrostatic field? Two static charges exert forces on one another, through their E-fields, presumably through photon exchanges. I am having trouble forming an idea of what an electrostatic field is, particular with respect to photons. One question I keep asking myself is "what are the frequencies" of the photons in the exchange between static charges.
the electrostatic field is just one form of electromagnetic field

the electromagnetic field is not "made of photons", it is made of itself

the "photons in the exchange between static charges" are the so-called "virtual photons" which are basically a mathematical trick which helps in the calculations: they exist in the maths (with, incidentally, all possible frequencies and at all possible distances from the charges, both in space and time), but not in the physics

Maybe I'm being sloppy with my terminology. I'm quite certain that it is accurate to say that the quanta of electromagnetic radiation are photons. And electromagnetic radiation is the electromagnetic field produced by accelerating charges. So it seems then that the quanta of the electromagnetic field are photons.

I'd love to hear more about these 'virtual photons.' Does a charged particle only emit virtual photons when there is another charged particle around to 'receive' them? Or, is a static charge constantly emitting virtual photons, similar to an accelerating charge emitting 'real' photons.

hi wuliwong!

the electrostatic field is just one form of electromagnetic field

the electromagnetic field is not "made of photons", it is made of itself

the "photons in the exchange between static charges" are the so-called "virtual photons" which are basically a mathematical trick which helps in the calculations: they exist in the maths (with, incidentally, all possible frequencies and at all possible distances from the charges, both in space and time), but not in the physics

Delta2
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Gold Member
hi wuliwong!

the "photons in the exchange between static charges" are the so-called "virtual photons" which are basically a mathematical trick which helps in the calculations: they exist in the maths (with, incidentally, all possible frequencies and at all possible distances from the charges, both in space and time), but not in the physics
Virtual photons have to exist , otherwise who is the carrier of the electrostatic force??. The force is real. We just cant detect em by the way we detect normal photons for some reason (because they dont exist as an asymptotic state, never fully understood this).

tiny-tim
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Virtual photons have to exist , otherwise who is the carrier of the electrostatic force??.
The field carries the force

do you say the field is isn't real??.

Delta2
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Gold Member
The field carries the force

do you say the field is isn't real??.
Thats in classical physics. In quantum physics force carriers have to be particles.

Thanks guys. I'll continue reading about virtual photons. Any more questions related to this will probably be posted in the Quantum forum.

Hi,

I will ask for tiny-tim. Ok the fields are the "force carriers". Forces make work wich is energy that the field gives to the particle (for example). From where this energy come? I never heard about a field that stoped acting on particles.

The way I understood it, virtual photons are the manifestation of a localized spike in the EM field. The way it was explained to me was like water in the ocean; there are real waves and then there are small "waves" that are small displacements from the ocean's average level. These small "waves" aren't "real" because where you have a small peak, there is another place near it with a valley. In a given area, the net energy is zero, so they aren't "real"

Due to the uncertainty principle, these virtual photons don't have enough energy or live long enough to be detected due to$$\Delta E * \Delta t \geq h / 4 \pi$$. However, the Casimir effect indirectly confirms their existence.

Delta2
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Gold Member
The way I understood it, virtual photons are the manifestation of a localized spike in the EM field. The way it was explained to me was like water in the ocean; there are real waves and then there are small "waves" that are small displacements from the ocean's average level. These small "waves" aren't "real" because where you have a small peak, there is another place near it with a valley. In a given area, the net energy is zero, so they aren't "real"

Due to the uncertainty principle, these virtual photons don't have enough energy or live long enough to be detected due to$$\Delta E * \Delta t \geq h / 4 \pi$$. However, the Casimir effect indirectly confirms their existence.
So you mean that electrostatic field is not in reality static but it has some very small variation with time? How these small variations create a not so small electrostatic force then? Because they happen over an infinite frequency range?

This thread got me searching others about virtual particles. I've found the user 'tom.stoer' to have the most lucid take on the subject. It seems that virtual photons only show up if you approach the problem using perturbation theory. If you use the approach in

Quantum Mechanics of Gauge Fixing
Lenz F., Naus H. W. L., Ohta K. and Thies M.
Annals of Physics
Volume 233, Issue 1, July 1994, Pages 17-50

then you wind up with a theory which does not contain virtual photons. Therefore, virtual photons are something which exists only in a certain mathematical treatment and are not something fundamental to the electrostatic field.

Tom also has a nice explanation here:

https://www.physicsforums.com/showpost.php?p=3022200&postcount=96

GT1
hi wuliwong!

the "photons in the exchange between static charges" are the so-called "virtual photons" which are basically a mathematical trick which helps in the calculations: they exist in the maths (with, incidentally, all possible frequencies and at all possible distances from the charges, both in space and time), but not in the physics
I'm not a physicist, but I read somewhere that effects such as lamb shift, Casimir effect and Z boson mass can be fully explained only if virtual particles are "real".

tiny-tim