Undergrad Defining electromagnetic waves

[Andreea007]

TL;DR

Which ones describe electromagnetic waves? Photons or electrons?

Hi! So I'm trying to understand electromagnetic waves but I encountered different definitions: one in terms of electrons and one in terms of photons. Which ones are actually used to produce electromagnetic waves and how?
Also, I saw that alternating current generates electro magnetic waves, but ac is all about accelerated electrons, so how is it possible?
Thank you!

 

[EPR]

Visible light/which is photons/ is an electromagnetic field. In QFT the electron field is what produces electrons. Different situations.

 

[Andreea007]

Visible light/which is photons/ is an electromagnetic field. In QFT the electron field is what produces electrons. Different situations.

Can you be a little more specific? What do you mean by electron field? Isn't it the same as electromagnetic field?

 

[PeroK]

Summary:: Which ones describe electromagnetic waves? Photons or electrons?

Hi! So I'm trying to understand electromagnetic waves but I encountered different definitions: one in terms of electrons and one in terms of photons. Which ones are actually used to produce electromagnetic waves and how?
Also, I saw that alternating current generates electro magnetic waves, but ac is all about accelerated electrons, so how is it possible?
Thank you!

Electromagnetic waves and electromagnetic fields in general are part of classical electromagnetism (EM), governed by Maxwell's equations. The electron is a fundamental charged particle that creates an EM field; and, an accelerated electron produces electromagnetic radiation. There are no photons in classical EM.

The photon is a massless particle in Quantum Electrodynamics (QED), which is a quantum theory of light. The electron remains a fundamental charged particle.

Although EM and QED produce approximately the same results in many cases, in terms of high-energy particle interactions, EM tends to break down and QED is seen to be the more accurate theory.

Many people talk loosely of EM radiation "being made of photons", but this is either sloppy or simply wrong depending on yout point of view.

 

[PeroK]

Can you be a little more specific? What do you mean by electron field? Isn't it the same as electromagnetic field?

In QFT (Quantum Field Theory), there is a quantised EM field (which is a quantum mechanical upgrade to the classical EM field) and an electron field (which has no analogue in classical EM). Photons are the quanta of the EM field and electrons are the quanta of the electron field - and, indeed, particles in QFT generally are the quanta of the appropriate field.

 

[Andreea007]

Electromagnetic waves and electromagnetic fields in general are part of classical electromagnetism (EM), governed by Maxwell's equations. The electron is a fundamental charged particle that creates an EM field; and, an accelerated electron produces electromagnetic radiation. There are no photons in classical EM.

The photon is a massless particle in Quantum Electrodynamics (QED), which is a quantum theory of light. The electron remains a fundamental charged particle.

Although EM and QED produce approximately the same results in many cases, in terms of high-energy particle interactions, EM tends to break down and QED is seen to be the more accurate theory.

Many people talk loosely of EM radiation "being made of photons", but this is either sloppy or simply wrong depending on yout point of view.

I have a question for you. If the electromagnetic waves are made up of accelerated electrons, then what about the vacuum? I mean, the light travels through space, right? Electrons are not massless particles, but there is no mass in the vacuum because there is no substance, so there are no electrons. How do you explain that?

 

[Dale]

Summary:: Which ones describe electromagnetic waves? Photons or electrons?

I encountered different definitions: one in terms of electrons and one in terms of photons. Which ones are actually used to produce electromagnetic waves and how?

It would help if you could link to these two specific definitions that are confusing you. That way we can see if they are genuinely conflicting or not.

An EM wave is just a specific configuration of the EM fields, specifically one in which the fields are oscillating in a wave pattern and energy is being transported. Electrons are sources of the EM field. They are not the EM field itself any more than your faucet (a source of water) is water itself.

 

[PeroK]

I have a question for you. If the electromagnetic waves are made up of accelerated electrons,

I'm not sure where you got that idea from. An electromagnetic wave is the propagation of alternating electric and magentic fields - and is also known as light.

An electron at rest produces a simple electric field. But, an accelerated electron produces an EM wave:

http://labman.phys.utk.edu/phys222core/modules/m6/production_of_em_waves.html

PS note that this is classical EM, not quantum physics.

 

[PeroK]

They are not the EM field itself any more than your faucet (a source of water) is water itself.

Perhaps a stone dropped into a pool that creates water waves would also be a good analogy. The water waves are not made of stones, but are oscillations in the surface of the water.

 

[Andreea007]

I'm not sure where you got that idea from. An electromagnetic wave is the propagation of alternating electric and magentic fields - and is also known as light.

An electron at rest produces a simple electric field. But, an accelerated electron produces an EM wave:

http://labman.phys.utk.edu/phys222core/modules/m6/production_of_em_waves.html

PS note that this is classical EM, not quantum physics.

Yeah I still don't get it. I'm asking you again, how do electromagnetic waves travel through vacuum (void) ? Are there any electrons in the void? Because, if they exists then it means particles exists, and for all we know void is void.

 

[PeroK]

Yeah I still don't get it. I'm asking you again, how do electromagnetic waves travel through vacuum (void) ? Are there any electrons in the void? Because, if they exists then it means particles exists, and for all we know void is void.

The EM field occupies the vacuum. And, therefore, technically it isn't vaccum, but space with EM radiation.

 

[Nugatory]

Yeah I still don't get it. I'm asking you again, how do electromagnetic waves travel through vacuum (void) ?

Electrical and magnetic fields pass through a vacuum just fine. Put a charged particle in a vacuum chamber and its electrical field will affect other particles even though it's in a vacuum.

 

[PeterDonis]

I'm trying to understand electromagnetic waves but I encountered different definitions: one in terms of electrons and one in terms of photons.

Where did you encounter these definitions? Please give specific references.

 

[PeterDonis]

If the electromagnetic waves are made up of accelerated electrons

They aren't. Accelerated electrons produce electromagnetic waves, but that doesn't mean the electromagnetic waves themselves are made of accelerated electrons. They aren't.

 

[vanhees71]

Many people talk loosely of EM radiation "being made of photons", but this is either sloppy or simply wrong depending on yout point of view.

It's simply wrong, particularly if you imply that a photon is just a massless "particle", as if it were in any sense localizable as a small lump of matter. It is almost always better to think in terms of waves when thinking about light.