HOW do radio waves form at the subatomic level?

[taylaron]

Hello,
I've been puzzling over how radio waves and other EMR are formed at the subatomic level. I understand how to produce radio waves using a function generator but I do not understand how an antenna can emit a radio wave (among other types of EMR).
I've asked several people this, but all I've received is "It just does!" Well, that's not good enough for me. How do electrons flowing through a series of atoms produce EMR like radio frequencies? What steps are involved?

Regards,
-Tay

 

[Claude Bile]

Radio waves are typically produced by oscillating free electrons inside conductors. Free electrons, by definition, are not bound to an atomic nucleus and thus do not involve any atomic energy level transitions.

Claude.

 

[Dale]

Except in very specific circumstances* there is really no advantage to thinking of radio waves at the subatomic or quantum level. For one thing, radio waves are much bigger than atoms. Even for Extremely High Frequency (EHF) radio waves, the shortest wavelength radio waves, you are talking about wavelength in the 1-10 mm range. This is so far above the size of an atom that it is just not useful to describe in quantum terms.

You are much better off sticking with a classical (Maxwell's equations) analysis for radio waves.

*EDIT: the very specific circumstances is what is called "hyperfine splitting" which is basically due to the interaction of the nuclear magnetic moment with the magnetic field due to the electrons. The energy difference between a "parallel" and "anti-parallel" is very small and corresponds to a single photon in the RF range (e.g. the famous 21 cm line). This is NOT the way that radio waves are generated in practical applications.

 

[taylaron]

How can one not begin with formation of EMR at the subatomic level? Radio waves can not just appear from nowhere. They must be given birth to.

 

[Theheretic]

How can one not begin with formation of EMR at the subatomic level? Radio waves can not just appear from nowhere. They must be given birth to.

truth is no one here knows the answer so they'll give you the run around. I tried to post an answer but my post was deleted by moderators apparently for being too 'speculative' but in reality your standard definitions are speculative as well because no one knows the real answer so to answer this person's question how else can we do so without being "speculative"?

 

[taylaron]

It see. The situation seems as bad as I feared.

 

[Andy Resnick]

Hello,
I've been puzzling over how radio waves and other EMR are formed at the subatomic level. I understand how to produce radio waves using a function generator but I do not understand how an antenna can emit a radio wave (among other types of EMR).
I've asked several people this, but all I've received is "It just does!" Well, that's not good enough for me. How do electrons flowing through a series of atoms produce EMR like radio frequencies? What steps are involved?

Regards,
-Tay

If I understand your question, then I would answer it this way:

Different portions of the EM spectrum derive from different energy transitions in matter. Starting with x-rays, that involve ionization of inner-shell electrons, through UV (ionization of more loosely-bound electrons), visible (electronic transitions), IR (vibrational and rotational transitions), THz, MMW, radio, all correspond to smaller and smaller energy differences. Most materials emit very little radio-wave energy naturally- the energies are too *small*, but we are able to "synthetically" create radio waveband photons by macroscopic control of a conducting device (as mentioned in another post).

Here's a more interesting question: fluorescent molecules are ~10 nm in size, yet the radiation they emit is 50 times that size. Similarly, radio antennas are a small fraction of the wavelength of emitted light. How can this be? How does the photon 'fit' inside the emitter?

 

[Dale]

How can one not begin with formation of EMR at the subatomic level? Radio waves can not just appear from nowhere.

This is a complete non-sequitir. Just because something cannot just "appear from nowhere" does not in any way imply that it must therefore appear from the subatomic level.

 

[Dale]

truth is no one here knows the answer so they'll give you the run around.

Complete BS. There is no experimental observation in electromagnetism which is not in agreement with modern theory.

 

[Theheretic]

Complete BS. There is no experimental observation in electromagnetism which is not in agreement with modern theory.

That's funny. You've posted about 5 or 6 posts in this thread alone and not a single one of them answers the question. You just proved my point right, i.e. you have no clue what the answer to the thread starter's question is.

 

[Theheretic]

If I understand your question, then I would answer it this way:

Different portions of the EM spectrum derive from different energy transitions in matter. Starting with x-rays, that involve ionization of inner-shell electrons, through UV (ionization of more loosely-bound electrons), visible (electronic transitions), IR (vibrational and rotational transitions), THz, MMW, radio, all correspond to smaller and smaller energy differences. Most materials emit very little radio-wave energy naturally- the energies are too *small*, but we are able to "synthetically" create radio waveband photons by macroscopic control of a conducting device (as mentioned in another post).

Here's a more interesting question: fluorescent molecules are ~10 nm in size, yet the radiation they emit is 50 times that size. Similarly, radio antennas are a small fraction of the wavelength of emitted light. How can this be? How does the photon 'fit' inside the emitter?

Are you asking that last question rhetorically, or in a Socratic way because you know the answer?

I would like to know that as well.

For example ELF waves are a hundred thousand miles in wavelength yet can be emitted by things far smaller. How does that work? The only explanation I've had in that regard is from an electrical engineer who told me that just because a small emitter can emit something of a far huger wave length doesn't mean that it is an efficient transmission. But I have no idea what he meant by the fact that the wave will not be anywhere near as "efficient" as it would be if the emitter was close to the size of the wave.


Anyway, the first portion of your explanation was good and eye opening however it still fails to explain how the actual EM wave is emitted in the most fundamental way possible. Ok so an electron gets ionized and this creates an EM emission according to your theory but how exactly does it do that? Can science explain this process in more detail? Does a EM wave just "magically" fly out of the round shiny electron? This is not a substantial explanation.

 

[Dale]

That's funny. You've posted about 5 or 6 posts in this thread alone and not a single one of them answers the question.

Post 3 answers it at the subatomic level and also mentions that Maxwell's equations are more useful for a practical understanding.

 

[Theheretic]

Post 3 answers it at the subatomic level and also mentions that Maxwell's equations are more useful for a practical understanding.

Yes I noticed you went back and "edited" your post after I called you out on trolling the thread with 5 posts that all failed to even address the actual thread topic.

However after reading your post I don't think it answers the question at all. At least not in a way easily visualized. Which is what I believe thread starter is asking, for a fundamental understanding of how the process occurs not for obscure equations that do nothing but obfuscate the understanding of the fundamental natural process.

Let me try to analyze it with my limited understanding:

"*EDIT: the very specific circumstances is what is called "hyperfine splitting" which is basically due to the interaction of the nuclear magnetic moment with the magnetic field due to the electrons. The energy difference between a "parallel" and "anti-parallel" is very small and corresponds to a single photon in the RF range (e.g. the famous 21 cm line). This is NOT the way that radio waves are generated in practical applications."

Ok so the magnetic moment is the tendency for the nucleus to align with the magnetic field...of what? The electrons or of the nucleus? This part is not clear.
The energy difference between a parallel and anti-parallel "corresponds" to a single photon you said. But where does the actual photon get generated? No where did you mention that. You said it only "corresponds" to a photon. I'm not even sure what that means. It's not very clear.

 

[f95toli]

How can one not begin with formation of EMR at the subatomic level? Radio waves can not just appear from nowhere. They must be given birth to.

We DO have a complete theory for this: quantum electrodynamics (QED).
The "problem" is that it is a very complicated theory and unless you know a fair amount about graduate level quantum mechanics there is no way to explain what is going on (this stuff is so specialized that it is not even covered in "normal" graduate level QM).
Morever, QED is very "abstract" so there really no way to explain it using words, you simply have to use math.

If you want to know more about the physics I would recommend Feynmann's pop-sci book about QED.

 

[Andy Resnick]

<snip>


Anyway, the first portion of your explanation was good and eye opening however it still fails to explain how the actual EM wave is emitted in the most fundamental way possible. Ok so an electron gets ionized and this creates an EM emission according to your theory but how exactly does it do that? Can science explain this process in more detail? Does a EM wave just "magically" fly out of the round shiny electron? This is not a substantial explanation.

Well first off, the photon is emitted when the ionized electron re-joins the atom, not when it is liberated- that's an absorption event. The most fundamental explanation I can think of is 'conservation of energy'.

 

[Theheretic]

Well first off, the photon is emitted when the ionized electron re-joins the atom, not when it is liberated- that's an absorption event. The most fundamental explanation I can think of is 'conservation of energy'.

Surely even you must realize how utterly insufficient this explanation is?

That's like you asking me how does a car brake work at its most fundamental level? And me responding: "it stops the car"

Can anyone here actually explain how a wave is generated without diverting to obscure mathematical equations? For example how about a descriptive diagram of some sort, anything?
For instance, I can quite easily explain the gestalt of how a sound wave works, and how the pressure wave propagates, there are even numerous animated diagrams and such on the internet that can be found. But the same is not true for EM waves.

I'm watching the youtube video on quantum electro-dynamics and even its own creator Richard Feynman said he doesn't understand it so I think we can all admit that while they were able to create accurate equations to predict the exchanges at this subatomic level, NO ONE actually understands the process and no one can explain descriptively how it works.
But I do look forward to someone attempting to prove me wrong.

 

[Dale]

Yes I noticed you went back and "edited" your post after I called you out on trolling the thread with 5 posts that all failed to even address the actual thread topic.

This is completely disingenuous. Look at the timestamps. I edited that before the following post landed and certainly before you started your nonsense. Whenever I edit a post I always make sure that there were not any posts afterwards. If there were then I remove my edits and make a new post.

 

[Theheretic]

This is completely disingenuous. I edited that before the following post and certainly before you started your nonsense.

Please stay on the topic or moderators will be forced to delete your posts. We're discussing EM waves here and how they are formed. Thus far you have failed to explain this phenomenon.

 

[Dale]

I don't think it answers the question at all. At least not in a way easily visualized. Which is what I believe thread starter is asking

That wasn't a stipulation of the OP and if it were I would have said that it is a nonsense stipulation. Being "easy to visualize" is not a requirement of a scientific theory. All we ask of scientific theories is that they accurately predict the results of experiments. Modern theories of electromagnetism (QED at the subatomic level and Maxwell's at the classical scale) accurately predict all EM phenomena encountered thus far.

Ok so the magnetic moment is the tendency for the nucleus to align with the magnetic field...of what? The electrons or of the nucleus?

The electrons.

The energy difference between a parallel and anti-parallel "corresponds" to a single photon you said. But where does the actual photon get generated? No where did you mention that. You said it only "corresponds" to a photon. I'm not even sure what that means. It's not very clear.

By "corresponds" I was referring to the Planck-Einstein equation E=hf. The energy of a photon is proportional to its frequency. So if an atom makes a transition from one energy state to a lower energy state then, by conservation of energy, it must emit a photon with a frequency which corresponds to that energy by the above equation.

 

[Dale]

To the OP, do you understand the generation of a radio wave in the context of Maxwell's equations?

If so, then that is sufficient for all practical "technology" applications. If not, then I would be glad to answer questions about Maxwell's equations, which I think will be much more useful than answering questions about QED.

 

[Theheretic]

By "corresponds" I was referring to the Planck-Einstein equation E=hf. The energy of a photon is proportional to its frequency. So if an atom makes a transition from one energy state to a lower energy state then, by conservation of energy, it must emit a photon with a frequency which corresponds to that energy by the above equation.

Ok so, according to you thus far we have this:

an electron changes its orbital state. This action corresponds to the type of frequency/wave that will be created. Can you expand on this? How does the electron changing its orbital state create a photon?
You said an atom changes state from one energy state to another, did you mean electron not atom?

 

[taylaron]

In my relevant education thus far, I understand basic Newtonian Mechanics and basic electricity and magnetism. I'm sure it is very frustrating for me to tell you that I'm still learning calculus. I apologize for the inconvenience. It is very frustrating to me as well.

I am a very visual learner. Right now I grasp QED and QM at a very conceptual level. I do not yet understand the mathematics inherently associated with both of them.

In reference to post 19, I do understand and grasp the Plank-Einstein equation E=hf. Modern theory however, does not deal with raw units of energy, so to describe a photon in terms of Planks constant multiplied by its frequency seems, well, not as descriptive as it could be. I'm particularly looking for an explanation of QED and QM that deals with raw units of energy that one can visualize. What I'm asking for appears to be very rare in todays scientific community.

 

[Dale]

I understand basic Newtonian Mechanics and basic electricity and magnetism.

OK, that is sufficient. In generating a radio wave in an antenna we simply repeatedly charge and discharge a dipole antenna at a frequency in the RF range. By Gauss' Law charging the dipole antenna sets up an electric field, and by Ampere's law an oscillating electric field sets up a varying magnetic field. These oscillating electric and magnetic fields form the radio wave.

I do understand and grasp the Plank-Einstein equation E=hf. Modern theory however, does not deal with raw units of energy

What do you mean by "raw units of energy"? The E in E=hf is indeed in units of energy, but I don't understand the word "raw" in this context.

 

[Theheretic]

OK, that is sufficient. In generating a radio wave in an antenna we simply repeatedly charge and discharge a dipole antenna at a frequency in the RF range. By Gauss' Law charging the dipole antenna sets up an electric field, and by Ampere's law an oscillating electric field sets up a varying magnetic field. These oscillating electric and magnetic fields form the radio wave.

What do you mean by "raw units of energy"? The E in E=hf is indeed in units of energy, but I don't understand the word "raw" in this context.

If the oscillating electrical/magnetic fields form the radio wave then where does the photon/particle concept come from? If an EM wave is nothing but electric field and magnetic field oscillating at right angles then how can a "particle" magically form out of this?

Unless you view the photon as a wave packet of the burst of oscillations, is that what a "photon" really is then? Just a packet of close frequency oscillations of electric/magnetic fields?

 

[Dale]

an electron changes its orbital state. This action corresponds to the type of frequency/wave that will be created. Can you expand on this? How does the electron changing its orbital state create a photon?
You said an atom changes state from one energy state to another, did you mean electron not atom?

No, the state is the state of the whole atom. As I said in post 3 the hyperfine structure is an "interaction of the nuclear magnetic moment with the magnetic field due to the electrons". So you cannot really localize the energy to the electrons nor to the nucleus, it is an interaction between the two.

When an atom changes state both energy and momentum must be conserved. The parallel and anti-parallel states have different energy, so where should that energy go? You might think that it could simply go into kinetic energy of the atom, but then momentum would not be conserved. So instead it must go into something which can carry both energy and momentum. This is the photon.

 

[taylaron]

OK, that is sufficient. In generating a radio wave in an antenna we simply repeatedly charge and discharge a dipole antenna at a frequency in the RF range. By Gauss' Law charging the dipole antenna sets up an electric field, and by Ampere's law an oscillating electric field sets up a varying magnetic field. These oscillating electric and magnetic fields form the radio wave.

What do you mean by "raw units of energy"? The E in E=hf is indeed in units of energy, but I don't understand the word "raw" in this context.

When I said "raw" energy, I'm referring to the physical manifestation of energy in reality. Photons contain energy, but is not pure energy in itself. In this context, the word "raw" is referring to physical manifestations of energy, not what we recognize its quantity to describe (particles, etc...). An electron has energy, but it is not (to my knowledge) described as a multi-dimensional manifestation of energy. Energy in today's terms seems to exist as a number, not as a 'physical' entity.
When one has a photon of a given frequency, then I would interpret that specific photon to be energy that is physically 'vibrating' at that frequency and it's size and amplitude by Planks Constant.

 

[Dale]

When I said "raw" energy, I'm referring to the physical manifestation of energy in reality. Photons contain energy, but is not pure energy in itself. In this context, the word "raw" is referring to physical manifestations of energy, not what we recognize its quantity to describe (particles, etc...). An electron has energy, but it is not (to my knowledge) described as a multi-dimensional manifestation of energy. Energy in today's terms seems to exist as a number, not as a 'physical' entity.
When one has a photon of a given frequency, then I would interpret that specific photon to be energy that is physically 'vibrating' at that frequency and it's size and amplitude by Planks Constant.

I'm sorry, but I really don't get your point here. Energy is an experimentally measurable quantity, so I don't know in what sense you feel that it is just a number and not physical. Do you similarly think that mass and charge are just numbers and not physical? How about distance or velocity?

Are you drawing a distinction between a particle and all of the quantities (mass, charge, momentum, position, energy, etc.) that we can measure about that particle? Do you believe that some measurements are privileged over others (like energy) or are you talking about some concept where all measurements are not physical?

 

[Born2bwire]

When I said "raw" energy, I'm referring to the physical manifestation of energy in reality. Photons contain energy, but is not pure energy in itself. In this context, the word "raw" is referring to physical manifestations of energy, not what we recognize its quantity to describe (particles, etc...). An electron has energy, but it is not (to my knowledge) described as a multi-dimensional manifestation of energy. Energy in today's terms seems to exist as a number, not as a 'physical' entity.
When one has a photon of a given frequency, then I would interpret that specific photon to be energy that is physically 'vibrating' at that frequency and it's size and amplitude by Planks Constant.

Photons are pure energy. They are packets of discrete amounts of energy and momentum. Dalespam's last post is particularly enlightening in this manner. As he states, in an atomic transition, the energy and momentum of the state changes but the particles the compose the atom do not change. This requires an input or output (depending on if we are increasing or decreasing energy) of a packet of momentum and energy. This is done in the form of a photon.

In the case of the classical theory, the accelerating electrons produce electromagnetic waves. The energy for these waves comes from the energy of the electrons. This is not a simple process to describe because we have to use fields to mediate the change in the electron's energy. That is, if we have an electron that is moving at a constant velocity and wish to decelerate it to a stop so that it emits radiation, a process known as bremsstrahlung radiation, then we have to have the electron pass through an electric field that will apply the braking force. Still, we can see that the change in the electron's energy through this process is equivalent to the energy of the radiation that is emitted.

 

[taylaron]

I'm sorry, but I really don't get your point here. Energy is an experimentally measurable quantity, so I don't know in what sense you feel that it is just a number and not physical. Do you similarly think that mass and charge are just numbers and not physical? How about distance or velocity?Are you drawing a distinction between a particle and all of the quantities (mass, charge, momentum, position, energy, etc.) that we can measure about that particle? Do you believe that some measurements are privileged over others (like energy) or are you talking about some concept where all measurements are not physical?

My perspective and beliefs are very speculative right now. I can not at this moment describe my beliefs because I have not completed my education. In this discussion, I'm simply prodding the possible physical existence of energy in three or more dimensions (let me go on...). If energy found in photons or electrons is (at least) three dimensional, than one would naturally think it would have a "physical" form. This said, It would appear (not necessarily my belief) that everything we see around us exists as multi-dimensional manifestations of pure energy. Mass would appear to be the result of energy arranged in a particular fashion to produce what we perceive as 'mass' and we feel it as weight with the influence of gravity.

My point is: What is mass? What is an electron made of? What is kinetic energy in terms of its physical existence? What is a photon? One should be able to describe all these things using (at least) three dimensional models because they exist in at least these three dimensions. I'm delving into the possibility that all these things that we see and can't see, along with the forces we observe are actually manifestations of arrangement and 'shapes' of different packets of energy and the results of interactions between them in multiple dimensions.

A photon has definite energy and a frequency, correct? How can a photon which exists in (at least) three dimensions exist without the entity physically vibrating? My understanding of physics today describes a photon as a packet of energy with given quantity and (in this case) frequency. For example: "Energy has vibrations, but it doesn't really vibrate in reality" - this doesn't make sense to me. If energy has these characteristics, than it ought to follow those characteristics in reality appearing as a multi-dimensional, vibrating entity.

I hope I'm making myself clear. Try to think outside the box. Take the standard model to the next level. Do not feel limited to what the standard model seems to (in my case) lack in physical description. My current perspective on particle physics tells me that energy is not viewed in this manner. I'm telling you to look at it from a different view. A Quark? What does a quark look like in terms of energy? It exists doesn't it? Then what does it look like?!

 

[jeblack3]

Maxwell's equations are the right answer here. There is a more accurate quantum mechanical theory of electrodynamics, but the quantum corrections are not really relevant.

If you want steps, it goes like this:

At first (assuming we start from zero electromagnetic fields), there is a current \vec{J}, but there is no magnetic field \vec{B}. By

\frac{\partial \vec{E}}{\partial t} = c^2 \nabla \times \vec{B} - \frac{1}{\epsilon_0} \vec{J}

a nonzero electric field is created. Then that electric field will produce a nonzero magnetic field, which in turn produces an electric field even further away from the source, and so on, creating a propagating electromagnetic wave.

You can describe this stuff in terms of photons as well, but that would be more complicated and not really more fundamental; after all, quantum electrodynamics fundamentally describes the world in terms of fields, getting particles as a result, not a postulate.

If the oscillating electrical/magnetic fields form the radio wave then where does the photon/particle concept come from? If an EM wave is nothing but electric field and magnetic field oscillating at right angles then how can a "particle" magically form out of this?

Unless you view the photon as a wave packet of the burst of oscillations, is that what a "photon" really is then? Just a packet of close frequency oscillations of electric/magnetic fields?

In the full quantum theory, one can calculate that an electromagnetic wave, much like an atom, can only have a certain discrete spectrum of energies. But unlike an atom, the energy difference between each possible level is the same: \hbar \nu. If the electromagnetic field is in a state other than its ground state, we say there is one or more photons present.

A comment: Feynman's QED lectures/book is very, very good for giving a conceptual understanding of quantum mechanics. But despite the title, it doesn't do a very good job with QED. He completely skips the treatment of the electromagnetic field and electrons as fields, and launches directly into Feynman diagrams, which are best understood as an calculable approximation scheme to the field theory. So if want to learn QED, you'll need a quantum field theory textbook, and yes, it is hard.