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Offline PmbPhy

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Electrons emitting radiation
« on: 11/10/2014 23:30:45 »
I spoke to the Physicist Ralph F Baierlein about the "electron emits a photon" subject that we discussed a while back. Since he knows electrodynamics much better than I do I thought I'd post his answer to my questions in this forum.

What bothered me about this notion was that if we were to take this notion literally such as in the same way we think of an atom emitting photons then just like an atom's proper mass decreases when it emits a photon that one might be led to think that a photon's proper mass might decrease when it emits radiation. However I knew this was true. And it turns out that the other Ralph agrees with me. Here is his response
Quote
Electrons that run around a circular track, as in a betatron or a synchrotron, do radiate light.  The electrons are being accelerated radially inwards, and accelerated charges emit radiation (at least usually so).

The proper mass of the electron remains a constant.  The energy for the light comes, I suppose, from the force that pushes the electron radially inward (or maybe pushes at an angle slightly off radial)--though I suspect that a purely classical analysis is highly difficult, if not impossible.  (One would need to handle "radiation reaction," which is notoriously difficult.)

To return to your original question, an electron free of external forces and in vacuum does not radiate.  Such an electron moves at constant velocity.  The rest frame of the electron is an inertial frame.  In that frame, the electron just sits in place and, of course, does not radiate.

Beware, however, that an electron moving at constant velocity through a medium like air or water may radiate.  That's Cherenkov radiation--a well-established fact.

You can find these topics discussed in Classical Electricity and Magnetism, by Wolfgang Panofsky and Melba Phillips.  I'm confident that J. D. Jackson treats the topics in depth in his fat book on electromagnetism.

Ralph
The reference he spoke of is in the 1955 edition of Panofsky & Phillips, the material lies in chapters 19 and 20, that is, pages 297-321.

We have to keep in mind here that the electron by itself cannot emit radiation. It must be interacting with an EM field to do this and that's where the energy of the radiation comes from.




 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #1 on: 12/10/2014 00:17:01 »
I have a feeling that the problem is in semantics, i.e. how its described and the words used to describe it. For example; if we say that the EM field accelerates an electron in such a manner so as to generate an electromagnetic field which is composed of photons. This way someone who is studying this phenomena won't erroneously conclude that the energy from the photons generated came from the mass of the electrons proper mass since that's both invariant and constant.
 

Offline Bored chemist

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Re: Electrons emitting radiation
« Reply #2 on: 12/10/2014 10:15:56 »
The electron slows down when it emits a photon.
 

Offline jeffreyH

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Re: Electrons emitting radiation
« Reply #3 on: 12/10/2014 10:49:42 »
The electron slows down when it emits a photon.

Which follows from the fact that the electron assumes a lower energy state. The question is where does the photon come from? Is it a lower energy photon that interacts with the field and then itself gains energy and a change in wavelength? The photon must already exist. Rather than emission shouldn't we be talking this change in wavelength?
 

Offline chiralSPO

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Re: Electrons emitting radiation
« Reply #4 on: 12/10/2014 14:07:37 »
Given the narrow emission bands, and general lack of dependence on irradiation of the frequencies associated with electronic transitions in atoms and molecules, I am skeptical of the notion of changing wavelengths of existing photons. Presumably the final energy pf the photon would have to be the sum of the original energy and that imparted by the state change. Unless you want to say there is a huge universal flux of photons that have zero energy (which is another interesting subject), I'm not sure that we can say there is a conservation of photons.
 

Offline jeffreyH

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Re: Electrons emitting radiation
« Reply #5 on: 12/10/2014 18:58:43 »
Given the narrow emission bands, and general lack of dependence on irradiation of the frequencies associated with electronic transitions in atoms and molecules, I am skeptical of the notion of changing wavelengths of existing photons. Presumably the final energy pf the photon would have to be the sum of the original energy and that imparted by the state change. Unless you want to say there is a huge universal flux of photons that have zero energy (which is another interesting subject), I'm not sure that we can say there is a conservation of photons.

It all depends upon how photons are viewed. They are massless and therefore entirely composed of energy in the form of momentum. Are they a disturbance in some other medium and virtual? If so then it is not a universal photon flux but a universal flux of some other field. The effect of gravity on light raises serious problems in this regard. The gravitational field echoes the photon field in its inverse square nature and is a candidate for this universal flux. However, the distribution of field lines makes no sense for a photon leaving the source of a gravitational field. The decrease in time dilation just doesn't add up for the virtual photon being a field disturbance. Its motion through spacetime cannot be virtual in my view. This may all be completely wrong thinking of course.
 

Offline Zarathustra

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Re: Electrons emitting radiation
« Reply #6 on: 13/10/2014 01:11:08 »
I agree with Jeffrey H...." I am skeptical of the notion of changing wavelengths of existing photons." However for a different reason. You see I see and here all of you grabbing at valid information from multiple directions and I feel that Cherenkov working within the universe of rigid accepted science could not perceive the obvious. A basic fundamental of the resonance principle (new to all) sets forth all matter as Orbs containing changeable amounts of a universal singular energy named resonance. The amount contained within an Orb is relative to velocity, weight and more. Resonance is gained or lost most commonly from collision with other Orbs. It may appear that electrons (or aren't they photon Orbs ) are emitting radiation or as recorded travel at slower than pristine photon speed and "cause blue light radiation?" - OR rather glow at a lower energy level - "blue" - as they collide with H2O molecules in the water surrounding the reaction chamber and transfer resonance to the H2O molecules. In the principle the only time any orb like an electron emits energy is when it establishing parity with orbs and resonance in close proximity. Oh well, I suppose you will all think I'm a fool but I have given up on models that produce skewed discussion rather than logical consensus. The new principle allows for data to piled onto a heap that always produces the same practical conclusion. feel free to google The Resonance Principle by Marc Rubin but be prepared for an animated simple over view of the entire concept.
 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #7 on: 13/10/2014 03:15:17 »
Quote from: jeffreyH
It all depends upon how photons are viewed. They are massless and therefore entirely composed of energy in the form of momentum.
Momentum is not a form of energy. A photon is composed entirely of kinetic energy.

Quote from: jeffreyH
Are they a disturbance in some other medium and virtual?
No. Virtual photons can't be observed.

Quote from: jeffreyH
However, the distribution of field lines makes no sense for a photon leaving the source of a gravitational field.
Why?

Quote from: jeffreyH
The decrease in time dilation just doesn't add up for the virtual photon being a field disturbance. Its motion through spacetime cannot be virtual in my view. This may all be completely wrong thinking of course.
Forget virtual photons. They have nothing to do with this, at least for the most part.
 

Offline lightarrow

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Re: Electrons emitting radiation
« Reply #8 on: 13/10/2014 12:47:48 »
I agree with Jeffrey H...." I am skeptical of the notion of changing wavelengths of existing photons."
Did you mean that you agree with ChiralISPO?

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Offline lightarrow

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Re: Electrons emitting radiation
« Reply #9 on: 13/10/2014 12:54:11 »
...
What bothered me about this notion was that if we were to take this notion literally such as in the same way we think of an atom emitting photons then just like an atom's proper mass decreases when it emits a photon that one might be led to think that a photon's proper mass might decrease when it emits radiation.
Maybe you intended "that an electron's proper mass might decrease"?
However, there is no difference: it's the mass of particle+field which is conserved.
 

Offline jeffreyH

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Re: Electrons emitting radiation
« Reply #10 on: 14/10/2014 00:06:07 »
Quote from: jeffreyH
It all depends upon how photons are viewed. They are massless and therefore entirely composed of energy in the form of momentum.
Momentum is not a form of energy. A photon is composed entirely of kinetic energy.

Quote from: jeffreyH
Are they a disturbance in some other medium and virtual?
No. Virtual photons can't be observed.

Quote from: jeffreyH
However, the distribution of field lines makes no sense for a photon leaving the source of a gravitational field.
Why?

Quote from: jeffreyH
The decrease in time dilation just doesn't add up for the virtual photon being a field disturbance. Its motion through spacetime cannot be virtual in my view. This may all be completely wrong thinking of course.
Forget virtual photons. They have nothing to do with this, at least for the most part.

I was arguing against virtual photons but badly. I did mean kinetic energy BTW.
 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #11 on: 14/10/2014 04:04:58 »
Quote from: lightarrow
Maybe you intended "that an electron's proper mass might decrease"?
Yes. That's correct. Thanks.

Quote from: lightarrow
However, there is no difference: it's the mass of particle+field which is conserved.
How is that relevant to what I said or this discussion? The notion that an electron emits a photon implies that the energy of the photon came from the electron. I was confused about Ralphs explanation so I asked him
Quote
I don't understand this. If an electron emits photons then doesn't that mean that mean that the proper mass of the electron prior to the emission of the photon was greater than its proper mass after emission the emission of the photon?

Perhaps the electron doesn't really emit photons but it generates an electromagnetic field when in the presence of an EM field?
He responded as follows
Quote from: Ralph
"Emitting photons" is merely the quantum description of what a classical physicist would call "generating an electromagnetic field."

In both descriptions, an electron is merely an intermediary in a process of energy transfer.  Whatever force causes the acceleration of the electron is the original source of energy (by doing "work").  The radiation--described QM-ly or classically--is the new entity that possesses the transferred energy.

The electron per se does not change; only its trajectory changes.  Hence the electron retains the original value of its proper mass.

Here's another way to see things. 

An atom has many internal states: the ground state and numerous excited states.  So an atom in an excited state can emit a photon and lose internal energy; consequently, its proper mass changes. 

An electron, however, has no internal excited states.   So an electron's proper mass is always the same.


Ralph
Now that makes a lot of sense.
 

Offline JohnDuffield

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Re: Electrons emitting radiation
« Reply #12 on: 16/10/2014 17:26:34 »
...He responded as follows
Quote from: Ralph
...An electron, however, has no internal excited states. So an electron's proper mass is always the same.
Now that makes a lot of sense.
Pity it's wrong. The electron's mass is reduced when it combines with a proton to form a hydrogen atom. It's also reduced when it falls down, wherein "gravitational potential energy" is converted into kinetic energy. This gravitational potential energy isn't in the system or the field, it's in the electron. You do work on the electron when you lift it up. You add energy to it. You increase its mass. Check out the mass deficit and binding energy:

"In bound systems, if the binding energy is removed from the system, it must be subtracted from the mass of the unbound system, simply because this energy has mass."

You might want to check that with Ralph. 
 

Offline jeffreyH

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Re: Electrons emitting radiation
« Reply #13 on: 18/10/2014 00:02:29 »
In my view the electron's proper mass is always the same and Pete and Ralph are right.
 

Online Ethos_

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Re: Electrons emitting radiation
« Reply #14 on: 18/10/2014 00:26:27 »
In my view the electron's proper mass is always the same and Pete and Ralph are right.
I also agree. Adding energy to the electron will add mass but will not change it's proper mass. The same thing happens to Protons in the LHC, kinetic energy will add mass to any particle but it's proper mass will remain the same.
 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #15 on: 18/10/2014 08:30:31 »
Quote from: JohnDuffield
Pity it's wrong. The electron's mass is reduced when it combines with a proton to form a hydrogen atom. It's also reduced when it falls down, wherein "gravitational potential energy" is converted into kinetic energy. This gravitational potential energy isn't in the system or the field, it's in the electron. You do work on the electron when you lift it up. You add energy to it. You increase its mass. Check out the mass deficit and binding energy:

"In bound systems, if the binding energy is removed from the system, it must be subtracted from the mass of the unbound system, simply because this energy has mass."

You might want to check that with Ralph.
I'll respond point by point:

1) Pity it's wrong.

Actually it's quite right.

2) The electron's mass is reduced when it combines with a proton to form a hydrogen atom.

This too is wrong and based on a lack of understanding of atomic physics and mass-energy equivalence. The proper mass of the proton and the proper mass of the electron remain invariant when combined to form a hydrogen atom. It's the system whose  mass has changed and that is a result of the potential energy. A bound system, in this case the hydrogen atom, typically has a lower potential energy than the sum of its constituent parts. It is an error to think that the proper mass of the electron and proton changes when they are combined to form the hydrogen atom whereas its the mass associated with the potential energy that causes the decrease in the potential energy of the system. Since the potential energy of the bound system is less than the unbound system the mass of the system decreases.

3) It's also reduced when it falls down, wherein "gravitational potential energy" is converted into kinetic energy.

When an electron falls in a gravitational field the proper mass if the electron remains unchanged. There's no reason whatsoever to believe that the proper mass of an electron changes as it moves through a gravitational field.

4) You do work on the electron when you lift it up. You add energy to it. You increase its mass.

That's a mistake to assume that mass-energy equivalence applies to potential energy of position. E.g. if an electron was moving in an electric field and its potential energy changed then both it's relativistic mass and its proper mass remains unchanged. In Wolfgang Rindler's text Relativity; Special, General and Cosmological, Rindler clearly states that this is far from the truth. I.e. Rindler explicitly states that the energy associated with the position of a particle will not change its relativistic mass (and of course there's nothing in nature what we know of  which could change its proper mass). This can be demonstrated if you know the math and physics and how to apply them correctly.
« Last Edit: 20/10/2014 21:43:41 by evan_au »
 

Offline JohnDuffield

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Re: Electrons emitting radiation
« Reply #16 on: 18/10/2014 14:05:50 »
In my view the electron's proper mass is always the same and Pete and Ralph are right.
I also agree. Adding energy to the electron will add mass but will not change it's proper mass. The same thing happens to Protons in the LHC, kinetic energy will add mass to any particle but it's proper mass will remain the same.
Pete's wrong. I can't be sure about Ralph. Accelerating an electron doesn't increase its proper mass, but lifting it does. You start with an electron at rest. Then you do work on it* by lifting it, then it's at rest again. Conservation of energy applies, its proper mass has increased. This is the flip side of the mass deficit. Have a look at the Wikipedia Binding energy article:

"The "mass deficit" from binding energy is therefore removed mass that corresponds with removed energy, according to Einstein's equation E = mc˛. "

Also see Mass in general relativity on Wikipedia:

"In special relativity, the invariant mass of a single particle is always Lorentz invariant. Can the same thing be said for the mass of a system of particles in general relativity?

Surprisingly, the answer is no."


As for hydrogen, the mass of one hydrogen atom is less than the mass of a free proton plus the mass of a free electron. What part of the system is comprised of negative energy? no part of the system. Because the system consists of a proton and an electron. And its mass is less than that of a free proton plus a free electron. 


* strictly speaking you also do some work on the Earth, wherein conservation of momentum applies, and momentum is equal and opposite. But the Earth is so massive it hardly moves, and the smaller object which moves aplenty gets the lion's share of the added energy. Check out sleds and collisions for this sort of stuff. 
« Last Edit: 20/10/2014 21:37:55 by evan_au »
 

Offline yor_on

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Re: Electrons emitting radiation
« Reply #17 on: 18/10/2014 15:56:54 »
How about looking at as 'emergences'? Not about anything 'really existing' but as of expressions from a new definition? As if it was not 'things' but instead 'states'?
 

Offline alancalverd

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Re: Electrons emitting radiation
« Reply #18 on: 18/10/2014 23:49:34 »
Intriguing. Some weeks ago, on another thread, I pointed out that electrons do not emit photons. PmbPhy asked around to confirm that statement and repeated it at the top of this thread. Since then, there have been 17 further contributions discussing, with varying degrees of erudition, heat and misunderstanding, the meaning of the word "no".

The mind boggles at what might have evolved if the answer had been "yes". 
 

Offline jeffreyH

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Re: Electrons emitting radiation
« Reply #19 on: 19/10/2014 01:31:34 »
Intriguing. Some weeks ago, on another thread, I pointed out that electrons do not emit photons. PmbPhy asked around to confirm that statement and repeated it at the top of this thread. Since then, there have been 17 further contributions discussing, with varying degrees of erudition, heat and misunderstanding, the meaning of the word "no".

The mind boggles at what might have evolved if the answer had been "yes".

It passes the time and stops us from being bored. No is such a short answer and it's no fun.
 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #20 on: 19/10/2014 14:09:26 »
Quote from: JohnDuffield
I'm not wrong. I back up what I say with references. The mass deficit is not something I've made up. Nor is conservation of energy.
Please post your references. You made the mistake of thinking that proper mass of a particle changes when its part of a hydrogen atom. E.g. you made the mistake of thinking that because there is a mass defect that it means that proper mass changes whereas, as I explained, that mass defect comes from the mass equivalence of potential energy. Since that potential energy is negative the mass of the system decreases.
I created a webpage to describe something similar to this which is at http://home.comcast.net/~peter.m.brown/sr/nuclear_fission.htm
« Last Edit: 20/10/2014 21:29:20 by evan_au »
 

Offline lightarrow

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Re: Electrons emitting radiation
« Reply #21 on: 19/10/2014 16:27:57 »
Quote from: lightarrow
However, there is no difference: it's the mass of particle+field which is conserved.
How is that relevant to what I said or this discussion? The notion that an electron emits a photon implies that the energy of the photon came from the electron. I was confused about Ralphs explanation so I asked him
You wrote:
"What bothered me about this notion was that if we were to take this notion literally such as in the same way we think of an atom emitting photons then just like an atom's proper mass decreases when it emits a photon that one might be led to think that an electron's proper mass might decrease when it emits radiation"
But why we say "an atom's proper mass" here and not "the system's proper mass" where the system is an electron in the force field of an ion+ the force field itself? Just because it' simpler. But the description is the same, if you already know that an electron doesn't have internal states; if you don't know it, you cannot say that is "the atom" which changes its proper mass and not the electron itself.
But we already know that the electron itself doesn' have such states; it wouldn't be an elementary particle, if it had.

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Offline lightarrow

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Re: Electrons emitting radiation
« Reply #22 on: 19/10/2014 16:48:24 »
...
As for hydrogen, the mass of one hydrogen atom is less than the mass of a free proton plus the mass of a free electron.  Which part of the system has negative energy? no part of the system. Because the system consists of a proton and an electron. And its mass is less than that of a free proton plus a free electron.   
Wrong, the system is not only proton+free electron.
Fields in a fixed region of space have mass too (and I mean proper = invariant, mass). A simple static electric field HAS mass.
About gravitation, I cannot answer: according to GR, there is no field, just space-time curvature, so I cannot say that bodies proper masses don't vary when they interact gravitationally.

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« Last Edit: 20/10/2014 21:25:30 by evan_au »
 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #23 on: 19/10/2014 20:46:40 »
Quote from: lightarrow
But why we say "an atom's proper mass" here and not "the system's proper mass" where the system is an electron in the force field of an ion+ the force field itself? Just because it' simpler.
It makes no difference since they're the same thing. The proton + electron = Hydrogen atom.

Quote from: lightarrow
But the description is the same, if you already know that an electron doesn't have internal states; if you don't know it, you cannot say that is "the atom" which changes its proper mass and not the electron itself.
But we already know that the electron itself doesn' have such states; it wouldn't be an elementary particle, if it had.
Exactly.
« Last Edit: 20/10/2014 21:18:53 by evan_au »
 

Offline PmbPhy

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Re: Electrons emitting radiation
« Reply #24 on: 19/10/2014 22:26:02 »
Quote from: lightarrow
Wrong, the system is not only proton+free electron.
Beautiful response. He's ignoring the mass due to potential energy.

For future reference when I, myself, speak of particles such as electrons and protons then since an electric field is part of those particles they don't need to be mentioned explicitly.

I recently came across a good explanation of this from an authority on the subject, i.e. Sheldon Glashow. I found it in his text From Alchemy to Quarks. On pages 581-582 the author discusses this subject in terms of quantum electrodynamics
Quote
The next most complicated diagrams, shown in Figure 14.3, portray the six fundamental acts by which particles interact with one another:
1.   An electron may emit a photon.
2.   An electron may absorb a photon.
3.   A positron may emit a photon.
4.   A positron may absorb a photon.
5.   An electron and positron may annihilate into a photon.
6.   A photon may create an electron-positron pair.
     Energy and momentum conservation imply that none of these acts can take place as real physical processes. An electron cannot simply emit a photon: The invariant mass of the electron and photon necessarily exceeds that of the initial electron, and the invariant mass of an isolated system cannot change. Similarly, an electron or positron cannot simply absorb a photon. Nor can electron-positron annihilate into or be created by a single photon. The fundamental acts of QED are forbidden!
« Last Edit: 20/10/2014 21:20:31 by evan_au »
 

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Re: Electrons emitting radiation
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