Magnetic field is made of virtual photons?

In summary: So, if we have a closed surface, with no outside input, and we want to know the magnetic field ( induced by the electric field ) that is present, we can use Maxwell's equations. However, note that this is just a theoretical calculation - the magnetic field actually does not exist until there is an electric field present to create it.
  • #1
taylaron
Gold Member
397
1
magnetic field is made of photons?

i've been researching photons and i discovered on
http://http://van.physics.uiuc.edu/qa/listing.php?id=414"
and
http://en.wikipedia.org/wiki/Photon"

both resources state that all mangetic fields are made of photons. soooooo, this brings up a lot of questions... first, why (when I am in the presence of a mangetic field) don't i see light? (because light is mad of photons):cry:
I am sure if i get a simple understanding of this concept, it will probably rule out most of my questions, so i'll wait for a reply to continue.


SO WHAT ARE PHOTONS MADE OF? -obviously they're charged (hence mangetic fields)
 
Last edited by a moderator:
  • Like
Likes Alan Tomazin
Physics news on Phys.org
  • #2
Photons aren't "particles" in the sense that they're made of anything. You seem to have a somewhat naive understanding of what a photon is, so I'd recommend reading a little more about them from credible sources before moving on.
 
  • Like
Likes Symmetry777
  • #3
The photons in a magnetic or electric field that doesn't transport energy from one place to another are virtual photons, not real ones. Some people consider virtual photons to be simply a name for a mathematical construct that pops up in calculations in quantum electrodynamics. Others consider them to have some degree of "reality" but not as much as real photons.

And even real photons are pretty strange things. Don't think of them as little tiny balls flying around!
 
  • Like
Likes Symmetry777
  • #4
"both resources state that all mangetic fields are made of photons"
I couldn't get to the first website. The Wikipedia was confusing as usual, but I didn't see that it said "all magnetic fields are made of photons".
A static magnetic field is not made of photons. EM waves are quantized in packets called photons.
 
  • #5
Then is a static magnetic field made of virtual photons?
 
  • #6
petm1 said:
Then is a static magnetic field made of virtual photons?
No. That simple answer was too short for the forum.
 
  • #7
If Photons are light waves and you’re able you reflect them with a mirror, and some are saying magnetic waves are virtual photons so can you reflect magnetic waves.

And how could you reflect a magnetic wave “flux”, is it possible, a mirror will probably not work.
 
  • #8
A static magnetic field being made of virtual photons is too simple and short for the forum, if not the particle part of a light wave, would it be more appropriate to call it a potentional wave of photons?
 
  • #9
Can you tell me, what must I do to be able to reflect magnetic wave from a permanent magnet?
 
  • #10
Can you tell me, what must I do to be able to reflect magnetic wave from a permanent magnet?

I would think that you must spin the magnetic within reach of a coil of wire. I do not believe you will be reflecting the complete wave but just parts of all the waves in the field, or am I just trying to over simplify.
 
  • #11
Can you tell me, what must I do to be able to reflect magnetic wave from a permanent magnet?

I would think that you must spin the magnetic within reach of a coil of wire. I do not believe you will be reflecting the complete wave but just parts of all the waves in the field, or am I just trying to over simplify.
 
  • #12
I’ve got no idea, I would really be nice if somebody knows how to built a camera to see magnetic waves just like you can see IR light with a video cam after you take the IR filter out.

Or maybe just add a magnetic filter :-)
 
  • #13
I don't know how this concept of "magnetic waves" got started here.
To be a wave in the usual sense requires a specific combination of both electric and magnetic fields. There is no purely magnetic wave.
 
  • #14
There's some confusion about the nature of electromagnetic fields here. The electromagnetic field is mediated by the photon as part of the standard model. Changing electromagnetic fields are propagated by real photons that we can detect. Charged particles exchange virtual photons presenting the behavior of an electrostatic field. See here for a discussion of deriving Coulomb's law from virtual photon exchanges. Charged particles in motion similarly account for magnetic fields.
For more information, see texts on quantum electrodynamics (QED), ie., https://www.amazon.com/dp/0471184330/?tag=pfamazon01-20.
 
Last edited by a moderator:
  • Like
Likes Spinnor
  • #15
Didn't we have this discussion a month a go? Oh well, here is my take now:


If we take a look at Maxwell's Equations, what do we get? We get something like this if we digest them in a semi-mathematical manner:

1. Electrical Flux through a closed surface = net charge inside closed surface / constant

2. Magnetic field through a closed surface = 0

3. Circulation of electrical flux around a curve = d(magnetic field through the surface that the curve, on the left side, encloses)/dt
Note(d/dt is just the rate of change of the value in ())

4. Constant times the circulation of magnetic flux around a curve = d(electric field through the surface that the curve, on the left side, encloses)/dt + flux of electric current through the surface /constant.

#1 tells us that if we have a charged particle, we have an electric field.
#2 tells us that we can't have a static magnetic field (no monopole)
#3 tells us that the change of the magnetic flux, creates electric flux
#4 tells us that the change of the electric flux creates magnetic flux and a current also creates an electric flux.

Because the current is made of moving charged particles, it has electric fields associated with it (see #1) and therefore #4 is a restatement of #2: Magnetic fields are ALWAYS associated with moving electric fields. And what do you get when you have an electric wave and a magnetic wave. Yea! Photons!

Of course you have photons associated with magnetic fields. Of course the energy is carried by the photons. What else would it be? Little green men?

A magnetic field is a mathematic construct to describe what we are seeing when the associated photons are at low frequency. In other words, the photons are big enough to study with our instruments. At higher frequencies (like visible light), the magnetic field can't be teased out by itself because the photons are too small, but we would be able to pick out the magnetic field in photons in the same manner if our instruments were small enough (I think!)
 
  • #16
That's very nice, Interested Learner. A question -
the electric field from a point charge extends
to infinity in the absence of other charges. How is the electric field in a photon confined to a smaller region ?
 
  • #17
An electric field is an abstact concept. It is model to describe what we observe at a macroscopic level. It is really not fundamental in any sense.

While a photon is something that is fundamental in the sense that it is an actual particle. It is what mediates the forces in electromagnetic fields. Electromagnetic fields are made up of photons. So the field is what we see at a macroscopic level with our instruments (at least at low frequency), but photons are what we get when we drill down and look at what is really going on.

And don't take that stuff about electric fields extending to infinity too seriously. It is a model. Nothing else. Of course in real life, charged particles don't exist in isolation and we haven't checked to see if the field of that nonexistant isolated particle really does extend to infinity. (Since it is nonexistant, that would be difficult even if we could get out to infinity [which we can't] to measure the field).
 
  • #18
Thank you, IL. I have seen exactly the opposite view expressed, but I lean towards
the photon, which seems to have a lot of experimental support now.
M
 
  • #19
interested_learner said:
An electric field is an abstact concept. It is model to describe what we observe at a macroscopic level. It is really not fundamental in any sense.
Why is it not fundamental ?

While a photon is something that is fundamental in the sense that it is an actual particle.
What do you mean by "actual particle" ? A particle like an electron ?

It is what mediates the forces in electromagnetic fields.
Forces IN EM fields ? What is that supposed to mean ? Can you give me an example of a force IN an EM field ?

No, photons are the force carriers of the EM INTERACTION. They mediate all forces between electrically charged particles, magnetic dipoles, quadropoles etc etc etc...So all the "EM stuff"

So the field is what we see at a macroscopic level with our instruments (at least at low frequency), but photons are what we get when we drill down and look at what is really going on.
Really ? So how come i detect and E field at the metal high k interface in a MOSFET transistor. When i study such an interface, i study a crystallographic cell. This cell contains maybe 30 atoms (which is far from being macroscopic, no ?) and still i can detect an E field if i plot the electrostatic potential.

No, we already discussed this "E field is made up of photons stuff" and the picture is not that clear-cut. You should certainly not be making any conclusions from such a vague model.
https://www.physicsforums.com/showthread.php?t=139763&page=2
Of course in real life, charged particles don't exist in isolation
How can you be so sure of that ?

marlon
 
Last edited:
  • #20
Thanks Marlan. When I read the question, the first impression was to send you an email to try to ask you to answer it. That is what I should have done. I did my best but it was obviously short of good. I am after all just an engineer and not a phyisicist. Or maybe I should just ignored the question and stopped when I was winning...

But still, I am going to blow back a bit, not to say you are wrong (you seldom are wrong), but for my own education. I will start at the top.

1) Bad use of the word fundamental. I really didn't know what to say. I have a gut level feeling for fields from the math, but it is sort of hard to put that into English... I guess I was trying to say what the difference is between a field and a photon. My take on a field is that it is a mathematical model (of vectors) of something that we can measure at a macroscopic level. It really isn't what is going on at the lowest level. I think? Oh well...

2) A force would be on a charged particle. You place a charge particle in a field and there is a force exerted on it. Right? I mean F = q1 E? Right? It is a photon that mediates that Force. Right?

3) You are right about the bad use of English again. Saying that fields are made up of photon stuff is not accurate. I was kind of struggling for words. What is actually going on? I just do the math and it comes out right. I don't really know what a field really is beyond the mathematical models I use. Does anyone?

4) Of course, I didn't mean that fields don't exist at high frequency. What I mean is that we normally use fields to describe what we see at low frequency and optics at high frequency. It is the old wave particle duality thing. When the "particles" are large we study them as fields and when they are small they study them as particles. It is a practical thing that has nothing to do with reality.


5) Ok, an isolated charged particle might exist somewhere in the universe. However, what I meant was a charged particle that we could experimentally study. Our bodies and our tools are full of particles. There is no way we could get close enough to study an isolated particle without affecting the particle. In that sense, an isolated particle is a mathematical model. They really don't exist in a practical sense.

I guess I try to make it simple so the person reading the answer can understand. But I can't get it right. How come what is so clear and beautiful in the math comes out so rotton in the English?
 
Last edited:
  • #21
Are there anyway of using this invisible photons, and generate electricity out of theme, in a solid state setup, no moving parts
 
  • #22
Photons, the existence and putative properties of, is a fruitful topic, so I'd like to add -

It seems that light only gets localised when it interacts with matter. We want the interaction to take place where the matter is to avoid action-at-a-distance so the field or part of it must be localised. The exchange of energy takes place in quanta. Einstein won a prize for his photo-electric effect theory, but he stressed that the 'photon' was merely a convenience and did not necessarily have true independent existence.

Before I mention Hong-Ou-Mandel, the above begs the question - how big is a photon ? It it is interacting with an atom, so one might guess at a similar scale, but the quantised theory of the interaction, the Jaynes-Cummings model, assumes that the electric field has a much larger spatial extent than the atomic dipole.

The HOM single-photon interferometry experiments are the best evidence for photons we have. Non-locality on a grand scale. But whether a very weak beam of light can be thought of as containing a single photon is still moot for some.

I believe in the photon because when I shine a focused laser beam across the room I can see how tight and localised the light is, and I know that strong electric and magnetics 'fields?' are contained in the beam.


We need to know more about photons - what are their internal dynamics, and how on Earth they can become matter and anti-matter.
 
Last edited:
  • Like
Likes Spinnor
  • #23
I guess I just assumed that photons with longer wavelengths would be larger than the photons with shorter wavelengths. I assumed this for several reasons:

1) Well, the wavelengths are longer so shouldn't the photon be longer? Of course quanta mechanics never work the way we think it should...

2) You would expect photons with less momentum (lower frequency) to smear over a large area due to the uncertainy principle.

3) Experimentally, if you take a faraday cage and make the mesh smaller than the wavelength of a radio frequency EM wave, then it will stop the wave, but you can still take a laser and shoot the beam right through the mesh. So it stops the "larger" radio wave and doesn't stop the "small" visible light wave.
 
Last edited:
  • Like
Likes Spinnor
  • #24
That seems intuitive and entirely feasible. And we do tune antennae to the wavelength we want to receive. In QM, of course, things are different. There's no way to localise the photon because the momentum can be determined near exactly.

But when an atom in a cavity say, absorbs energy from the field, it's always quantised. If the photon existed during this exchange it must be smaller than the atom. Of course, one does not need photons, and there's no scale problem if the ineraction is betwen a small dipole and a large field. So the quantum model is not really about photons but
assumes the energy is quantised.Anyhow, I may getting off topic so I'll stop.

Do you know where I might find the problem of a magnetic and/or electric dipole in an oscillating field, worked out ?
 
  • #25
So my #2 is wrong. All photons seemed to be smeared since their momentum can be found very closely.

However, with #3 you bring up an interesting question:

My faraday experiment seems to indicate a large photon and your cavity experiment seems to indicate a small photon. What is it? Or is that the wrong question?
 
  • #26
An overview of the description of E-M wave phenomena

Warning, this is super long.

jtbell said:
The photons in a magnetic or electric field that doesn't transport energy from one place to another are virtual photons, not real ones. Some people consider virtual photons to be simply a name for a mathematical construct that pops up in calculations in quantum electrodynamics. Others consider them to have some degree of "reality" but not as much as real photons.

And even real photons are pretty strange things. Don't think of them as little tiny balls flying around!

Ok, to clarify. Electromagnetic phenomena occur in different distance scales, namely the classical and the quantum. Magnetic fields do not exist in isolation from electric fields because there exist no magnetic monopoles (point sources of magnetism) observable in today's universe, as stated by Maxwell's equation div(B)=0. Classically, a moving electric charge will produce a changing electric field, thereby inducing a magnetic field because a time-varying electric field creates a magnetic field: curl(E)=-1/c dB/dt , curl(B)= 1/c dE/dt +4Pi J /c [E=electric field, B=magnetic field, J=current density, c=speed of light, all this in vacuum with Gaussian units]. A charge moving at constant velocity will produce a constant B field, because curl(B) is directly proportional to the first derivative of E (gradient); so if that first derivative is constant B is constant. Now if the charge is accelerating, the dE/dt will not be constant, and B will change. This means that as the disturbance caused by an accelerated charge on the electric field travels through space in time, there is a corresponding disturbance in the magnetic field that will accompany it. This is what is called an *electromagnetic wave.*

What, you might ask, are these fields exactly, and therefore what is this wave I speak of? An electric field is simply a description of what will happen to a charged particle if I place it inside that field. A magnetic field similarly describes what force arises if I have a moving charge (remember magnetic fields come into play classically only with *changing* electric fields). Ok, fine. But if these fields are only descriptions, then how can an E-M wave be a physical entity when it is a propagating disturbance in a 'description' of something I measure?

The answer relies on a closer look at the phenomenology. We are only measuring interactions between particles. E-M fields are defined by what we measure to happen on charged particles: how other charges cause them to move through space in time. A disturbance in these fields, namely an E-M wave, will exist in that it will change the effect we measure on charged particles. But how exactly do fields and their disturbances affect said particles? Classically, the fields exert forces, or accelerations on the particles that can be measured via the time-dependence of their spatial location. This is why charge is defined by the action it effects as can be measured in space and time. But on small scales, there are other strange effects. Enter quantum theory.

When we deal with really tiny distance scales, quantum effects alter how physics behaves. I don't want to get into the heart of it, but quantum mechanics is based on the fact that on tiny scales (larger scales too, but not noticeably) particles of matter are also to some degree waves (matter waves!). de Broglie showed that each particle has an associated wavelength indicated by lambda=h/p [lambda=wavelength, h=Planck's constant, p=particle's momentum]. Associated with this property is Heisenberg's Uncertainty principle, which means that if you measure a particle, the product of the uncertainty in its position by that in its momentum must always be greater than a particular constant. In other words, you can never measure exactly both where it is and where (and how fast) it is traveling. Exactly equivalently but in a different form, the same result holds for the energy of the system and its location in time (more abstract, but will describe soon). You cannot measure its energy exactly without being uncertain about when the hell that energy state existed, and if you know exactly when a particle passed a certain place you can't be sure of how much energy it was carrying.

Because of particle/wave duality, this means that with a particle you have a choice of how to measure it: you can figure out where it is or where it is going, at what time it passed or how much energy it was carrying. If you measure location very precisely, you will be measuring the system as a single unit of information about location (a particle). If you measure momentum very precisely, you will be measuring how it travels but not exactly where it is (a wave). For an overly simplified analogy, think of a rope that is suspended in midair. If you give it one jerk, there will be a pulse traveling on the rope and you can say, "hey, my 'thing' is right there, I can see its location"; but can you determine the wavelength from one pulse? It's not so well-defined to say what its wavelength is because it's not measured to be undulating (and remember that wavelength is directly related to momentum via de Broglie's formula). Conversely, if you start moving the end of the rope up and down you'll get a regular wave pattern, but you can't ask where your 'thing' is anymore, it's all along the rope. You can say, "my 'thing' has a wavelength that looks to be lambda, say, but it's kind of everywhere, it's not located at anyone point."

Ok. That was a little much, but we understand conceptually what the uncertainty principle means between wave-like and particle-like behavior. But now we are talking about the E-M waves. How do we measure *them*? We measure them by their effect on charged particles, but this means that they are subject to the Rules of Quantum Mechanics (quantum electrodynamics, to be precise)! E-M waves can be measured as either pointlike or wavelike depending on how we measure them. If we use atomic transitions to measure them, they are particles. If we use crystals and slits and things they appear to behave like waves. The electron is most familiar as a particle, but it also has an associated wave. *It is not one or the other.* Likewise with E-M waves, they are both particles and waves, depending on what scale of interactions you are looking at. Light is a particular example of an electromagnetic wave, and generally the energy determines how it will
act; a highly energetic gamma ray will act like a particle because it has such a high energy that it will allow a large uncertainty in the momentum and thus a small uncertainty in the position, whereas low-energy radio waves are always dealt with and measured as waves, or undulating E-M forces on antennae and such (actually undulations acting on the quantum fields of the constituent atoms, causing resonances). Einstein showed that Energy=hf=hc/lambda. Light 'particles' are called *photons*.

But when we get down to it, most of the matter we are concerned with are electrons, nuclei, and atoms, and we are interested in how light affects them. These are quantum mechanical systems involving tiny constituents. Electrons can certainly affect one another, because they are both electrically charged. If one accelerates, it will generate a changing E-M field and thus a photon/EM-wave, which will then move in space as time increases and then affect the other one by causing an acceleration. This is an *electromagnetic interaction,* one where one electron emitted light and the other one absorbed it (more or less, this is not very precise language). The acceleration in one caused an acceleration of another, or also the change in momentum of one caused the change of momentum in the other (Newton's 3rd law). But since energy is conserved here (can you find any energy loss in the process?), what happened to the energy after the electron emitted the E-M disturbance but before the other electron received it? The energy was carried by the E-M disturbance itself! This is one way (potential theory is another) to argue that the E-M field itself carries energy. Also, look at the conservation of momentum--the first accelerated electron has changed its momentum but the other one hasn't been affected yet. The photon/E-M wave carried that momentum! [Note, this is why lasers can actually suspend small spheres of quartz by pushing light on them against the force of gravity!] This is a most remarkable property of the E-M field and its disturbances.

Ok, now remember the Heisenberg Uncertainty Principle, that because a photon is a physical entity (it carries energy and momentum!) it is subject to uncertainty based on its momentum (or equivalently energy). If two electrons are close enough, the light will take very very little time to travel from one to the other (it *is* traveling at the speed of light, after all). This means that the time frame involved is tiny, and thus we can have a very large uncertainty of the energy. Actually, the conservation of energy can be violated for very small time windows: a 'virtual' photon can be emitted by one and received by the other and not even preserve energy--the photon energy plus the electron energies can be greater than the total initial energy--so long as it occurs for a really really short time. For a quaint analogy, this like a magician saying, "Ok, now don't blink... Did you notice anything? I just created a rabbit out of thin air and then made it disappear, but it was so fast that you couldn't see it." The argument is that energy will be transmitted from one system to another system by a virtual particle that for a very short time can have more energy than both systems combined, provided that the time is short enough for it not to be directly measurable (observable by
any other system). This means that it doesn't actually exist on its own, and thus it doesn't actually carry energy around with it as do 'real' particles.

Thus, photons on the most fundamental level are what causes charges to interact (exchange force). But there is a difference between real and virtual photons; 'real' photons can be seen (and philosophically thence they exist) *on their own,* whereas virtual photons do not exist by themselves. But here is where the philosophy of science becomes unclear, because then we have all these photons and what exactly are they but quantizations of some action? The modern viewpoint is what I said, that light is really made of particles that on large time scales can be measured as waves; the Coulomb force and Lorentz force are described by E-M fields, which are quantized to interact by virtual photons (not able to be seen individually), and E-M field disturbances are energy described by photons/E-M waves.

So, that is it. I am sure I missed some subtleties here and there, but that is the best way I can see to introduce a beginner to the idea of light. Some very good introductory texts from which I have borrowed some examples include Electricity and Magnetism by Edward M. Purcell, Optics by Eugene Hecht, and Quantum Mechanics by David J. Griffiths.
 
  • Like
Likes Spinnor
  • #27
Mentz114 said:
That seems intuitive and entirely feasible. And we do tune antennae to the wavelength we want to receive. In QM, of course, things are different. There's no way to localise the photon because the momentum can be determined near exactly.

But when an atom in a cavity say, absorbs energy from the field, it's always quantised. If the photon existed during this exchange it must be smaller than the atom. Of course, one does not need photons, and there's no scale problem if the ineraction is betwen a small dipole and a large field. So the quantum model is not really about photons but
assumes the energy is quantised.Anyhow, I may getting off topic so I'll stop.

Do you know where I might find the problem of a magnetic and/or electric dipole in an oscillating field, worked out ?

Yes, this is exactly right. E=hf, so any measurement determining the frequency exactly will yield the momentum exactly, making localization unfeasible. As to your question about the oscillating dipole field, Hecht describes it in Optics and I believe it is solved more thoroughly in Jackson's book on electrodynamics.
 
  • #28
Thank you, Cesar. I will check those references.
M
 
  • #29
I hate talking about what is or is not 'fundamental'. Its philosophy more so than science.

The local fields 'E' and the fields 'M' are not relativistic invariants, you can say boost your frame and arrange it so that they swap places.

Moreover they appear in quantum mechanics as sort of a derived concept, as combinations of the electromagnetic field strength potentials.

In fact, in general the entire field formalism is redundant, what is or is not fundamental is of course only true up to 'field redefinition'.

Its far worse w.r.t the point of view of particles being fundamental. In fact, you cannot make quantum mechanics consistent with special relativity without insisting that operators are built out of fields. So already you have particles relegated to being 'excitations of some field' or built out of 'lumps of energy and momentum'.

In general I find convincing arguments against just about any ontology I can place on what is or is not fundamental and no good a priori bet (probably an indictment of my intellect, but I suspect I am in good company)

If you are still interested in thinking about this, try
http://plato.stanford.edu/entries/quantum-field-theory/#Ont
 
Last edited:
  • #30
interested_learner said:
1I guess I was trying to say what the difference is between a field and a photon. My take on a field is that it is a mathematical model (of vectors) of something that we can measure at a macroscopic level. It really isn't what is going on at the lowest level. I think? Oh well...

First of all, fields DO arise at the microscopic level. To explain how a field and a particle are connected we need to look at the basic QFT picture. Consider a mattress consisting of a 1000 springs. If you push that mattress, it will vibrate. Now the mattress can be seen as the field. The vibration of tha mattress has a certain energy. We also know that energy and mass are the same thing. So this vibrating field has some energy that can also be seen as a particle with certain mass m. This is the intuitive concept behind quantum field theory, explained in very easy terms. Again, don't try to visualise the field versus the particle because it does NOT work like that. Keep in mind that we are dealing with a mathematical concept that explains reality very well. That is all that physics is supposed to do.


2) A force would be on a charged particle. You place a charge particle in a field and there is a force exerted on it. Right? I mean F = q1 E? Right?
Correct if there is only an electrical field. If you include a magnetic field you get the entire Lorentz force equation.

It is a photon that mediates that Force. Right?
Yes

What is actually going on? I just do the math and it comes out right. I don't really know what a field really is beyond the mathematical models I use. Does anyone?
I refer to the mattress analogy.

When the "particles" are large we study them as fields and when they are small they study them as particles. It is a practical thing that has nothing to do with reality.
I don't get the "when particles are large" part. What is a large particle ? If you refer to a car or a tennis ball, we use classical physics to describe the behaviour.

At the atomic scale, we use QM and there we get the particle wave duality stuff.

5) Ok, an isolated charged particle might exist somewhere in the universe. However, what I meant was a charged particle that we could experimentally study. Our bodies and our tools are full of particles. There is no way we could get close enough to study an isolated particle without affecting the particle. In that sense, an isolated particle is a mathematical model. They really don't exist in a practical sense.
No, we CAN study isolated particles. Just look at the equation you gave above !

In the case of QM, we can also study isolated particles but we indeed get a spread on the position and momentum if we repeat the same measurement.


marlon
 
  • #31
Haelfix said:
I hate talking about what is or is not 'fundamental'. Its philosophy more so than science.

Fine, fine. I agree, I fell prey, after such a long post, to laziness in my language. I did not mean 'fundamental' as in a fundamental entity of ontological existence, but rather that on the femtoscale the fields are quantized. I wanted to illucidate that, relevant to the post that started this thread asking about whether magnetic fields were made of photons (which was really the question I wanted to address in a fashion suitable to the class of question itself), the aforementioned virtual particles do not 'make' magnetic fields, but rather they do play a 'fundamental' role as quantizations of the quantum electromagnetic field. Please note that I did try to make a quick note to the philosophical uncertainty of the ontology:
cesar314 said:
But here is where the philosophy of science becomes unclear, because then we have all these photons and what exactly are they but quantizations of some action?

Haelfix said:
The local fields 'E' and the fields 'M' are not relativistic invariants, you can say boost your frame and arrange it so that they swap places.
You are of course right about the lack of invariance, especially considering the magnetic field itself even classically arises due to changes in reference frame.

In fact, in general the entire field formalism is redundant, what is or is not fundamental is of course only true up to 'field redefinition'.
Ah, philosophy.

Moreover they appear in quantum mechanics as sort of a derived concept, as combinations of the electromagnetic field strength potentials.
Its far worse w.r.t the point of view of particles being fundamental. In fact, you cannot make quantum mechanics consistent with special relativity without insisting that operators are built out of fields. So already you have particles relegated to being 'excitations of some field' or built out of 'lumps of energy and momentum'.
(addressed above) Though perhaps my language did delegate an unfair bias toward the particle interpretation of QFT, I wanted to clarify the concept that photons are not little elements of magnetic force.

In general I find convincing arguments against just about any ontology I can place on what is or is not fundamental and no good a priori bet (probably an indictment of my intellect, but I suspect I am in good company)
I totally agree with you. Perhaps this philosophical issue of ontology will never go away; with the current paradigms, I can see no plausible way to argue about what is 'fundamental' except within the confines of specific theories or mechanisms for computation. That is what I loosely meant about 'fundamental' in the sentence you commented upon, though obviously there are problems with photons as fundamental even within the well-established paradigm of QED. I do not suspect superstring theories will much remedy the situation, if indeed anything more philosophically 'fundamental' can be 'discovered' :devil: . It's all about falsifiability, really.

Thanks for the excellent link, by the way! It contains a most lucid discussion, thank you.
 
  • #32


I think the reason we can't see magnetic fields is because the magnet is stationary.
Its not waving.

A photon is a name for a waving magnetic field.
A photon is a name for a waving electric field.
A moving magnetic field creates an electric field.

I postulate that If we could spin a magnet at 10^14 rpm we could generate light.

What do you think about that?
 
  • #33


Mentz114 said:
That's very nice, Interested Learner. A question -
the electric field from a point charge extends
to infinity in the absence of other charges. How is the electric field in a photon confined to a smaller region ?

Because a photon does not have charge. Also, even in the presence of other charges the electric fields still extend to infinity.
 
  • #34


When a permanent magnet attracts an iron coin, there are only "virtual photons" involved in this process?

If the coin is on a table, and the permanent magnet is positioned a few centimeters above the coin, what about Earth's gravity attracting the coin? Why the virtual photons are "stronger" than the gravitons and make the coin "fly", defying Earth's gravity?
 
  • #35


We don't have a generally accepted theory that "explains" both electromagnetism and gravity, so we can't say why one is stronger than the other.
 

Similar threads

  • Quantum Physics
Replies
29
Views
2K
  • High Energy, Nuclear, Particle Physics
Replies
3
Views
2K
  • High Energy, Nuclear, Particle Physics
2
Replies
42
Views
29K
Replies
3
Views
850
  • High Energy, Nuclear, Particle Physics
Replies
2
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
5
Views
2K
  • Electromagnetism
Replies
5
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
2
Views
1K
  • Electromagnetism
Replies
7
Views
12K
  • Quantum Physics
Replies
10
Views
1K
Back
Top