# What is the difference between an electron and a photon?

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#### percepts

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##### What is the difference between an electron and a photon?
« on: 11/07/2014 14:15:51 »
I'm trying to visualise this and the both seem to me to be a "disturbance" (for want of a better description) in the electromagnetic field so what differentiates them?

#### chiralSPO

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##### Re: What is the difference between an electron and a photon?
« Reply #1 on: 11/07/2014 16:42:41 »
A photon has no charge--there is an oscillation in the electric field, but it averages out to zero. An electron is negatively charged, always having exactly the same charge. Also, while photons have no rest mass, electrons do. There are other differences too (like spin), but these are the most easily explained.

#### acsinuk

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##### Re: What is the difference between an electron and a photon?
« Reply #2 on: 13/07/2014 15:36:08 »
Photons are a volume of vibrating AC magnetic energy that can helix forward at the speed of light.
Electrons are DC charged particles that move only relatively slowly.
CliveS
A.C.Stevens

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #3 on: 13/07/2014 17:42:34 »
Quote from: percepts
I'm trying to visualise this and the both seem to me to be a "disturbance" (for want of a better description) in the electromagnetic field so what differentiates them?
The difference between particles can be determined as the difference in all the properties that particles have. For example; a particle has a proper mass, proper life time, is either a fermion or a boson defined as follows

Fermion: Any particle characterized by Fermi-Dirac statistics and following the Pauli exclusion principle. Two or more fermions cannot occupy the same quantum state

Boson: Any particle characterized by Bose-Einstein statistics. Two Bosons can occupy the same quantum state.

A photon is a boson whereas an electron is a fermion. An electron has charge whereas a photon has no charge. Since a photon has zero proper mass it can do what all particles with zero mass do, i.e/ travel at the speed of light (although a photon travels at the speed of light by definition).

#### jccc

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##### Re: What is the difference between an electron and a photon?
« Reply #4 on: 15/07/2014 07:48:44 »
Electron is a charged particle, it has mass. Photon is an imaginary particle that has no mass no charge.

When an electron at rest, it produces nothing. When it moves, its force field moves.

The force field movement is light wave/EM wave. Mainstream science call it photon.

If photon is particle, when light passing glass or water slowing down, moving into air again, how it regained original speed?

Glass or water atoms absorb photon and emit another one in the same direction?

What's the mechanism? Sounds like magic not science.

« Last Edit: 15/07/2014 09:27:07 by jccc »

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #5 on: 16/07/2014 05:46:04 »
Quote from: jccc
Photon is an imaginary particle that has no mass no charge.
Since this part of the forum is for main stream science you need to put those kinds of speculations in the New Theories section since mainstream physics considers photons to be absolutely real, imaginary in no sense of the term whatsoever.

Quote from: jccc
When an electron at rest, it produces nothing. When it moves, its force field moves.
That is incorrect. A field does not move. Only the source that produces the field moves. An electromagnetic wave is not a moving EM wave either. It’s merely a time varying field that is the Fourier series of a sum of time varying fields.

It’s a common mistake to think of field lines as moving. The concept of the field was created by Michael Faraday so as to visualize the electric and magnetic field. Field lines don’t really exist although the fields themselves really do exist. Calculation errors can easily arise when one thinks of field lines as moving.

Quote from: jccc
The force field movement is light wave/EM wave. Mainstream science call it photon.
That is incorrect. That is not what a photon is. A photon is a quantum of electromagnetic radiation and easy to detect. In very dim light a very sensitive eye can detect a handful of photons. They’ve been studied for over a hundred years now and have a very solid theoretical basis.
Quote from: jccc
If photon is particle, when light passing glass or water slowing down, moving into air again, how it regained original speed?
Because the last atom that emitted it released it into a vacuum and any photon that moves in a vacuum moves at the speed of light = 3x10^m/s.

Quote from: acsinuk
Photons are a volume of vibrating AC magnetic energy that can helix forward at the speed of light.
That is incorrect. A photon cannot be said to “be” energy (although you phrased it slightly different as ‘photons are a volume of … energy’ so it’s the same thing). Just like electromagnetic fields and waves they “have” energy, i.e. it’s a property of an EM field or EM wave.

Photons also don’t “helix forward.” That notion comes from an elliptical or circularly polarized light. The tip of the field vector of the EM wave moves in a helix but that’s merely a mathematical description. There is no physical reality to it.

It the term AC doesn’t apply here. AC stands for “Alternating Current”. There’s no current to speak of because there’s no charge in motion and just because something alternates with time it can’t be taken to mean that it’s an alternating current.

Quote from: acsinuk
Electrons are DC charged particles that move only relatively slowly.
CliveS
There’s no reason to assert that electrons move “only relatively slowly” since some of them move arbitrarily close to the speed of light in particle accelerator labs.
« Last Edit: 16/07/2014 05:49:30 by PmbPhy »

#### jccc

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##### Re: What is the difference between an electron and a photon?
« Reply #6 on: 16/07/2014 06:22:41 »
Pete, I asked you what's the mechanism of electron emit photon, how electron emit different photons? Why photons travel at c in vacuum? What is energy level?

Mind to give some light? Appreciate.

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #7 on: 16/07/2014 07:01:23 »
Quote from: jccc
Pete, I asked you what's the mechanism of electron emit photon, how electron emit different photons?
Don’t you understand that it’s not the job of physics to find the mechanism to how things work? While at times it’s able to accomplish such a feat it’s not the goal. Too many people make this mistake and then blame the scientist for it when all the time it’s their misunderstanding. That’s why it has such a high Crackpot index. See The Crackpot Index at http://math.ucr.edu/home/baez/crackpot.html
Quote
17. 10 points for arguing that while a current well-established theory predicts phenomena correctly, it doesn't explain "why" they occur, or fails to provide a "mechanism".
An electron cannot emit a photon. If it did that would mean that the proper mass of the electron was greater than it was after it emitted the photon. Since the electron has no internal structure which can be changed to accommodate the increase in internal energy it follows that the proper mass can’t be different so the electron cannot emit a photon.

Quote from: jccc
Why photons travel at c in vacuum?
There’s several ways to look at it

* It’s a postulate – This means that we accept that it’s true and observe that it’s true but we don’t know why it’s true. That’s the second postulate of special relativity. It’s the same thing as saying that the proper mass of a photon is zero.

** Postulate that the rest mass of the photon is zero. It then follows that Maxwell’s equations take their typical form and in a vacuum the electromagnetic wave moves at the speed of light c. https://en.wikipedia.org/wiki/Wave_equation Since photons are the quantum of light it follows that they too must travel at the speed of light.

Quote from: jccc
What is energy level?
The energy level of what?

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #8 on: 16/07/2014 15:37:44 »
An electron cannot emit a photon. If it did that would mean that the proper mass of the electron was greater than it was after it emitted the photon. Since the electron has no internal structure which can be changed to accommodate the increase in internal energy it follows that the proper mass can’t be different so the electron cannot emit a photon.

Electrons emit photons all the time...

They just need enough kinetic energy to emit photon.
In this experiment they have few thousands electron volts kinetic energy:

Free electron is emitting photon 13.6 eV (or sum of photons energies 10.2 eV + 3.4 eV + ....) and is intercepted by free proton.
Ultimate Theory of the Universe
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#### percepts

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##### Re: What is the difference between an electron and a photon?
« Reply #9 on: 16/07/2014 18:58:12 »
Thanks for replies. All being read and absorbed.

#### jccc

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##### Re: What is the difference between an electron and a photon?
« Reply #10 on: 17/07/2014 02:11:19 »
In quantum field theory, fields are things that permeate all space and time.  The "electromagnetic field generated by an electron" is described by the electron coupling to this background electromagnetic field and changing it.  The electron doesn't create the field, but rather creates a disturbance in the field that we call "the electromagnetic field of the electron."

You can think of it loosely like boats on an ocean: the ocean is the background field and would exist even in the absence of boats.  The boats are like particles, which interact with the ocean and can disturb it.  The boats don't generate the ocean, but they do generate particular disturbances on the ocean.

Maybe the above explains the mechanism how electron able to emit photon?

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #11 on: 17/07/2014 05:12:27 »
Quote from: UltimateTheory
Electrons emit photons all the time...
You're either confusing photons with virtual photons, a common misconception or with the photons generated when electrons are accelerating. In the former case QED vertex

$$e^{-} -> e^{-} + \gamma$$

by itself does not represent a possible physical process, the reason being purely kinematical: $$e^{-} -> e^{-} + \gamma$$ would violate conservation of energy. In the center-of-mass frame the electron is initially at rest, so its energy is $$mc^2$$. If the electron was to emit a photon then in that same frame, where we started out with zero energy, there would be the energy of the rest mass of the electron $$mc^2$$ plus the energy of the photon, thus violating  conservation of energy.

In the later case the electron only facilitates the process of creating photons, it doesn't emit them.
Quote from: juccc
Maybe the above explains the mechanism how electron able to emit photon?
You're confusing real photons with real photons.

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #12 on: 17/07/2014 06:01:08 »
Quote from: UltimateTheory
Electrons emit photons all the time...

They just need enough kinetic energy to emit photon.
In this experiment they have few thousands electron volts kinetic energy:

I just looked at the link to that photo. It's a Crooke's tube. You don't understand how it works and your misunderstanding of it has led you to use it to support your flawed idea that electrons emit photons.

Please go to the Wikipedia site and read how a Crook's tube works. You'll see that there is a difference of potential set up between the anode and cathode thus creating an electric field parallel to the axis of the cylinder of the tube. As ions (not electrons) accelerate along the tube's axis they collide with the atoms which make up the gas in the tube. When the atoms de-excite they emit photons.

#### jccc

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##### Re: What is the difference between an electron and a photon?
« Reply #13 on: 17/07/2014 06:22:02 »
Knock rocks in dark, you can see light. Even rub blanket in dark I can see spark/light.

I believe/understand the electrons got exited by the force applied on rock or blanket atoms, produce EM wave in quantum field. light or photon as we call it.

Am I correct so far?

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #14 on: 17/07/2014 06:56:45 »
Knock rocks in dark, you can see light. Even rub blanket in dark I can see spark/light.

I believe/understand the electrons got exited by the force applied on rock or blanket atoms, produce EM wave in quantum field. light or photon as we call it.

Am I correct so far?
No. Each example that you gave emits photons for different reasons but none of them does so because an electron emits a photon.

#### jccc

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##### Re: What is the difference between an electron and a photon?
« Reply #15 on: 17/07/2014 07:23:17 »
So the gas atom hit by the iron in Crook's tube got exited, the electrons bounded by the gas nucleus vibrate in quantum field to emit photon?

Is photon traveling in space or quantum field? After atoms emit photons, do they lose energy equals to e=mc^2?

Thanks Pete, I really should just study auto repair.

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #16 on: 17/07/2014 12:26:23 »
Quote from: jccc
So the gas atom hit by the iron in Crook's tube got exited, the electrons bounded by the gas nucleus vibrate in quantum field to emit photon?
http://en.wikipedia.org/wiki/Crookes_tube#How_a_Crookes_tube_works

Quote from: jccc
Is photon traveling in space or quantum field? After atoms emit photons, do they lose energy equals to e=mc^2?
Photons traveling space, not a quantum field. At least not as far as I know. And yes. They loose energy and thus they loose mass according to $$E = mc^2$$

Quote from: jccc
Thanks Pete, I really should just study auto repair.
Lol! You're welcome.
« Last Edit: 17/07/2014 12:29:54 by PmbPhy »

#### dlorde

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##### Re: What is the difference between an electron and a photon?
« Reply #17 on: 17/07/2014 12:43:15 »
http://en.wikipedia.org/wiki/Crookes_tube#How_a_Crookes_tube_works
Hmm, this article could cause some confusion - it says "When the electrons fall back to their original energy level, they emit light", and you have said "An electron cannot emit a photon", so on the face of it, the article you link to contradicts you.

Perhaps a more detailed or specific explanation would clarify...

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #18 on: 17/07/2014 16:09:49 »
I just looked at the link to that photo. It's a Crooke's tube. You don't understand how it works and your misunderstanding of it has led you to use it to support your flawed idea that electrons emit photons.

Please go to the Wikipedia site and read how a Crook's tube works. You'll see that there is a difference of potential set up between the anode and cathode thus creating an electric field parallel to the axis of the cylinder of the tube. As ions (not electrons) accelerate along the tube's axis they collide with the atoms which make up the gas in the tube. When the atoms de-excite they emit photons.

Quote from Crookes tube description:
"When they strike it, they knock large numbers of electrons out of the surface of the metal, which in turn are repelled by the cathode and attracted to the anode or positive electrode."

Photons emitted by electrons are GREEN on right side of tube, right after cross.
Electrons are going from left to center, then bending path to bottom, and going to anode (positive electrode).

Electron must have ENOUGH kinetic energy to emit photons.
If it's going straight path, it usually must hit something to release its energy.
I am using it to create x-rays in my lab using > 40 kV and then observing ionization made by x-ray in Cloud Chambers..

If in electronic circuit there is U = 2.5 V, it means that each electron has kinetic energy E.K.=2.5 eV
That's why it won't emit f.e. UV photon by UV LED (Light Emitting Diode).

UV photon with 350 nm, needs U > 3.54 V.
UV photon with 400 nm, needs U > 3.1 V.

If kinetic energy of electron is smaller, photon won't be emitted and LED diode won't shine. Energy must be conserved.
« Last Edit: 19/07/2014 10:26:13 by CliffordK »
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#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #19 on: 17/07/2014 21:20:10 »
Quote from: UltimateTheory
Quote from Crookes tube description:
"When they strike it, they knock large numbers of electrons out of the surface of the metal, which in turn are repelled by the cathode and attracted to the anode or positive electrode."
So what?

Quote from: UltimateTheory
Photons emitted by electrons are GREEN on right side of tube, right after cross.
It's impossible for an electron to emit a photon. That's a well known fact that any particle physicist can tell you. Just read Griffiths text on particle physics and he'll explain it to you. For example, from Introduction to Elementary Particles by David Griffiths, page 59
Quote
The Feynman rules enforce conservation of energy and momentum at each vertex, and hence for the  diagram as a whole. It follows that the primitive QED vertex by itself does not represent a possible physical process. We can draw the diagram, but the calculation would assign to it the number zero. The reason is purely kinematical: $$e^{(-)} -> e^{(-)} + \gamma$$ would violate conservation of energy (In the center-of-mass frame the electron is initially at rest, so its energy is $$mc^2$$. It cannot decay into a photon plus a recoiling electron because the later alone would require an energy greater than $$mc^2$$.)
So there you have it. Straight "textbook physics" - An electron ".. cannot decay into a photon plus a recoiling electron ...".

« Last Edit: 20/07/2014 06:07:08 by evan_au »

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #20 on: 17/07/2014 22:06:02 »
In Crookes tube there is not "a single free electron in empty space".
There is beam of electrons, billions of electrons, and they interact with other electrons in beam, colliding each other.
There is electric field, that's not uniform (negative electrode on the left and positive electrode on the bottom).

Any answers in textbooks "can free electron emit photon?" are referring to situation about single particle and nothing else, no electric field, no magnetic field, no other forces, no collisions between multiple particles. Idealized situation in outer space.
« Last Edit: 17/07/2014 22:24:07 by UltimateTheory »
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#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #21 on: 19/07/2014 22:23:25 »
Quote from: UltimateTheory
In Crookes tube there is not "a single free electron in empty space".
Since electrons are point particles, one can zoom in and focus on individual particle/particle interactions. It's not as though electrons are all crammed together in space with no "elbow room".

Quote from: UltimateTheory
There is beam of electrons, billions of electrons, and they interact with other electrons in beam, colliding each other.
There is electric field, that's not uniform (negative electrode on the left and positive electrode on the bottom).

Any answers in textbooks "can free electron emit photon?" are referring to situation about single particle and nothing else, no electric field, no magnetic field, no other forces, no collisions between multiple particles. Idealized situation in outer space.
And still that doesn't mean that an electron can either absorb or emit a real photon. Even the text on particle physics by Griffiths, a highly respected author, is telling this. The only way for an electron to emit a photon is for either the electron or the photon (or was it both?) must be virtual particles. And they cannot be real particles and therefore they can't be observed. When I was talking to Griffiths about this he stressed to me that they're only used as mathematical tools and shouldn't be thought of as real objects. A virtual particle doesn't even lie on its mass shell. They have to go off-shell while in the Feynman diagram. They can't occur on a vertex which connects to outside the Feynman diagram.  They like inside the Feynman diagram.

As Griffith writes
Quote from: David J. Griffiths
Also the Feynman rules enforce conservation of energy and momentum at each vertex, and hence for the diagram as a whole. It follows that the primitive QED vertex by itself does not represent a possible physical process.  We can draw the diagram, but calculation would assign to it the numberzero. The reason is purely kinematical; $$e^{-} -> e^{-} + \gamma$$.
I proved this mathematically in another post above.  So the only way that an electron can emit or absorb a photon is when the photon is a virtual particle at which point it can't be observed.
« Last Edit: 20/07/2014 06:03:03 by evan_au »

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #22 on: 19/07/2014 22:46:51 »
I have devices like Crookes tube in the lab...

If you want to become a real scientist, I suggest you buying or building your own equipment..
http://www.ebay.com/sch/i.html?_nkw=crookes+tube
$70 is cost of Crookes tube + Cockcroft Walton generator producing 40 kV cost$30.
« Last Edit: 20/07/2014 05:58:29 by evan_au »
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#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #23 on: 19/07/2014 23:35:28 »
If you want to see electrons, which loses their kinetic energy while passing through medium (and ionizing its molecules), build Cloud Chamber...

« Last Edit: 20/07/2014 05:54:31 by evan_au »
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#### Ethos_

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##### Re: What is the difference between an electron and a photon?
« Reply #24 on: 20/07/2014 01:29:52 »
Name calling will not advance our scientific knowledge one bit. It's a waste of time to deal with people that are only here to argue!
« Last Edit: 20/07/2014 05:53:28 by evan_au »
"The more things change, the more they remain the same."

#### Ethos_

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##### Re: What is the difference between an electron and a photon?
« Reply #25 on: 20/07/2014 01:38:45 »
http://en.wikipedia.org/wiki/Crookes_tube#How_a_Crookes_tube_works
Hmm, this article could cause some confusion - it says "When the electrons fall back to their original energy level, they emit light", and you have said "An electron cannot emit a photon", so on the face of it, the article you link to contradicts you.

Perhaps a more detailed or specific explanation would clarify...
After examining this link, I would have to agree with you dlorde. Maybe Pete can clarify this for us?
"The more things change, the more they remain the same."

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #26 on: 20/07/2014 03:43:10 »
see the example I gave to describe what the concept of mass-energy equivalence means at
http://home.comcast.net/~peter.m.brown/sr/nuclear_fission.htm

In Eq.5 in equation there should be 931.494 MeV not 952.5 MeV...

[attachment=18997]

And whole equation should give answer:
Uranium-238 -> Thorium-234 + alpha + 4.26992 MeV

Calculation without taking care of the all electrons ionization energies between different isotopes, has large amount of error (from a few eV to few hundred keV difference from actual one).
« Last Edit: 20/07/2014 05:49:26 by evan_au »
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#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #27 on: 20/07/2014 04:33:58 »
There's a proof reading process that ALL scientific literature MUST go through to catch the errors that are in the papers.

I myself love a text called Classical Mechanics which was originally written by Herbert Goldstein. The first and second versions were written by him. It's a very well know text and found on the shelf of nearly all physicists. The latest version is co-authored by Sakfo and Poole. The proof reading process got screwed up on that book. There was tons of errors. I was catching so many of them that I became a proof reader for the author. When the next printing came out the authors placed a thank you in the acknowledgement section of the text. I ended up catching about 250 errors.

I became friends with a man at MIT, Edwin F. Taylor. At the time I met him he was working on writing a text which was called Scouting Black Holes at the time. Later on Edwin's co-author decided he didn't like that name so I suggested calling it Exploring Black Holes and so it's now named. I found many errors in that text too and a few serious misconceptions. It turned out that one of those misconceptions was one which was in ALL GR texts and probably still is. In fact I'm probably the only person in the world who found an error in Gravitation by Misner, Thorne and Wheeler. The author thought that presence of gravitational redshift was evidence of spacetime curvature, which it isn't. So that error does not appear in that text because of me.

The moral of this story is that my website might contain errors. I never said it was error free. The fact is that it's never been proof read.

An Electron CANNOT emit photons.
« Last Edit: 20/07/2014 12:21:06 by evan_au »

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #28 on: 20/07/2014 04:39:14 »
In that equation there should be 931.494061 MeV...
http://en.wikipedia.org/wiki/Atomic_mass_unit

ps3. Uranium-238 decay energy verification:
http://en.wikipedia.org/wiki/Uranium-238
on right side, there is table with value Alpha decay 4.267 MeV...
(the same as mentioned in post #26, and lower by 3% than on your website).
« Last Edit: 20/07/2014 06:08:48 by UltimateTheory »
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#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #29 on: 20/07/2014 04:59:15 »
Physicists don't memorize all physical constants from all fields.
« Last Edit: 20/07/2014 05:40:51 by evan_au »

#### UltimateTheory

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##### Re: What is the difference between an electron and a photon?
« Reply #30 on: 20/07/2014 05:04:47 »
I do remember basic constants that I am using in everyday work.
« Last Edit: 20/07/2014 05:39:52 by evan_au »
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#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #31 on: 20/07/2014 06:37:09 »
Here's an example of errors that creep in conversations like this but wouldn't get past the proof reading process. In Eq. (5) there is a missing $$c^2$$ because what appears as $$\frac{952.5 MeV}{1u}$$ should have been $$\frac{952.5 MeV}{1uc^2}$$.
« Last Edit: 20/07/2014 12:16:43 by evan_au »

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #32 on: 20/07/2014 09:08:18 »
In Crookes tube there is not "a single free electron in empty space".
There is beam of electrons, billions of electrons, and they interact with other electrons in beam, colliding each other.
There is electric field, that's not uniform (negative electrode on the left and positive electrode on the bottom).

Any answers in textbooks "can free electron emit photon?" are referring to situation about single particle and nothing else, no electric field, no magnetic field, no other forces, no collisions between multiple particles. Idealized situation in outer space.
For an electron to emit a photon the proper mass of a photon must change during the process and that simply can't happen. The Griffiths text supports this.
« Last Edit: 20/07/2014 12:20:36 by evan_au »

#### Ethos_

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##### Re: What is the difference between an electron and a photon?
« Reply #33 on: 20/07/2014 13:46:00 »
Thanks for the clarification Pete,..............we are all subject to making errors. It's consistent with the human condition. It's refreshing when we can all learn from each other, makes the world a less lonely place doesn't it.
"The more things change, the more they remain the same."

#### Bill S

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##### Re: What is the difference between an electron and a photon?
« Reply #34 on: 20/07/2014 14:56:30 »
Hi Ultimate Theory,

As a non-scientist I am here to learn.  Sometimes I struggle with Pete’s posts, but if I ask for an explanation, he provides it.  I’m not really qualified to judge who is right or wrong in the matter of electrons emitting photons, so I have to go with what I understand; what seems to make sense to me.

So far, Pete’s explanation makes perfect sense to me, whereas yours leaves me shaking my head and thinking “what’s he saying?”

My usual test of whether or not I understand something is if I can explain it to someone else.  At the point we have reached in this thread I could explain why an electron cannot emit a photon, but not the opposite.

My request would be for less sniping and more explaining.
There never was nothing.

#### PmbPhy

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##### Re: What is the difference between an electron and a photon?
« Reply #35 on: 20/07/2014 15:51:35 »
Thanks for the clarification Pete,..............we are all subject to making errors. It's consistent with the human condition. It's refreshing when we can all learn from each other, makes the world a less lonely place doesn't it.
You're quite welcome. While I'm waiting for Griffiths response (if he chooses to provide one) I'll take a shot at what his response might be like.
Quote from: UT
In Crookes tube there is not "a single free electron in empty space".
There is beam of electrons, billions of electrons, and they interact with other electrons in beam, colliding each other.
There is electric field, that's not uniform (negative electrode on the left and positive electrode on the bottom).

Any answers in textbooks "can free electron emit photon?" are referring to situation about single particle and nothing else, no electric field, no magnetic field, no other forces, no collisions between multiple particles. Idealized situation in outer space.
My proof did not depend on how many electrons were in a region of space and the interaction between them because at that level, i.e. in Feynman diagrams, all those forces are accounted for by the exchange of particles, i.e. everything is particles when one is talking about that kind of thing. Griffiths describes what's going on at a vertex of a Feynman diagram. One doesn't  put in electric fields in Feynman diagrams because their existence in those diagrams are implicit due to virtual particles. So Griffiths argument holds in all situations, i.e. not just isolated particles in free space. Had Griffiths been talking only about the special case of isolated particles in free space and not have stated that as an assumption then that would make.

« Last Edit: 20/07/2014 22:08:05 by evan_au »

#### UltimateTheory

• Sr. Member
• 107
##### Re: What is the difference between an electron and a photon?
« Reply #36 on: 20/07/2014 18:12:31 »
You're using 952.5 MeV instead of proper 931.494 MeV,
and getting incorrect result of decay energy from Uranium-238 4.3815 MeV instead of proper 4.267 MeV.
I didn't bother about c^2. In decay energy calculation we can ignore it completely, and convert mass of isotope directly to energy by multiplying it by 931.494 MeV, then doing the rest of calcs in energy.
« Last Edit: 20/07/2014 22:04:52 by evan_au »
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#### lightarrow

• Neilep Level Member
• 4586
##### Re: What is the difference between an electron and a photon?
« Reply #37 on: 20/07/2014 18:26:55 »
I have devices like Crookes tube in the lab...

http://www.ebay.com/sch/i.html?_nkw=crookes+tube
$70 is cost of Crookes tube + Cockcroft Walton generator producing 40 kV cost$30.

Maybe, but certainly, prior to that, you have to study physics on serious texts or, better, at university, not on popular books.
(The same for jccc).

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lightarrow
« Last Edit: 20/07/2014 22:03:00 by evan_au »

#### UltimateTheory

• Sr. Member
• 107
##### Re: What is the difference between an electron and a photon?
« Reply #38 on: 20/07/2014 18:39:51 »
Imagine we have free proton that has rest mass = 938.272 MeV/c^2 (ion of Hydrogen)
and free electron that has rest mass = 0.510999 MeV/c^2
How can free proton intercept free electron?
Electron must emit photon with E=13.6 eV (that's ionization energy needed for Hydrogen)
It'll be attracted to nucleus and form electric neutral Hydrogen.
http://en.wikipedia.org/wiki/Ionization_energy

Spectral lines are described here: http://en.wikipedia.org/wiki/Spectral_line
Read part "Types of line spectra"
Quote "When a photon has about the right amount of energy to allow a change in the energy state of the system (in the case of an atom this is usually an electron changing orbitals), the photon is absorbed."

Wikipedia says that electron is absorbing or emitting photons...

X-Rays article: http://en.wikipedia.org/wiki/X-ray
Quote: "One common practice is to distinguish between the two types of radiation based on their source: X-rays are emitted by electrons,"
Quote: "A photoabsorbed photon transfers all its energy to the electron with which it interacts, thus ionizing the atom to which the electron was bound and producing a photoelectron that is likely to ionize more atoms in its path."
(photoelectron is highly accelerated electron which absorbed photon)

Video on YouTube showing different photon-electron, and photon-nucleus reactions:

http://en.wikipedia.org/wiki/Emission_spectrum
Quote: "When the electrons in the atom are excited, for example by being heated, the additional energy pushes the electrons to higher energy orbitals. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon."
« Last Edit: 20/07/2014 22:02:23 by evan_au »
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#### PmbPhy

• Neilep Level Member
• 2804
##### Re: What is the difference between an electron and a photon?
« Reply #39 on: 20/07/2014 22:07:24 »
Quote from: UltimateTheory
Electrons emit photons all the time...
I traced this thread back to the point where it bothered me for the first time and this is it. When you said that electrons emit photons all the time that meant ALL the time, even when they're NOT accelerating. While I know that electrons emit radiate when they're accelerating its clear that accelerating electrons generate the production of photons. Claiming they "emit" photons as if it was a process similar to that of an atom emitting photon when it transitions from a higher state of energy to a lower state of energy and the prior state of energy was reflected in a larger state of proper energy is clearly wrong.

However in any case, your claim that electrons emit photons all the time even when they're not accelerating is clearly wrong. If Griffith responds to my e-mail I suspect that he'll refer to accelerating charges such as bremsstrahlung radiation and cyclotron/synchrotron radiation.

Quote from: UltimateTheory
They just need enough kinetic energy to emit photon.
In this experiment they have few thousands electron volts kinetic energy:
Wrong. If you had an electron traveling at constant speed with 100TeV then it still wouldn't emit photons.

What the mechanism is for electrons to generate photons when they're accelerating is something I don't know. What I do know is that the electron does not absorb energy to increase its proper energy where it later releases it.

#### UltimateTheory

• Sr. Member
• 107
##### Re: What is the difference between an electron and a photon?
« Reply #40 on: 20/07/2014 22:30:25 »
You're cutting mine answers to just interesting you part.
The right after I said "electrons emit photons all the time", I wrote:

"They just need enough kinetic energy to emit photon."

Which means that they must be already accelerated.

In Crookes tube case, it's a few thousands volts.

Kinetic energy of electron in electronic circuit with U = 10000 Volts, is at maximum 10 keV energy.
If electron with such huge kinetic energy will hit something, there will be created photon with max 10 keV energy, and electron will be decelerated.
Energy conservation must be obeyed.

When I said "electrons emit photons all the time", I didn't mean that they will emit energy forever and ever. That would obviously violate energy conservation.
If electron emit photon, or other way loses kinetic energy (f.e. resistance of wire), it's decelerated.
It has no longer kinetic energy, and can not give away energy anymore.

« Last Edit: 20/07/2014 23:31:55 by UltimateTheory »
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#### UltimateTheory

• Sr. Member
• 107
##### Re: What is the difference between an electron and a photon?
« Reply #41 on: 20/07/2014 22:47:53 »
While I know that electrons emit radiate when they're accelerating

Acceleration means also change of momentum. Either one are vectors. Change of direction also means acceleration.

When you have electron going straight path, and then there is positive electrode on bottom (attracting them), beam of electrons must change direction, which is equal to acceleration..

However in any case, your claim that electrons emit photons all the time even when they're not accelerating is clearly wrong.

In Crookes tube they are accelerated by two different mechanisms.. High voltage, and electrodes that're not in straight line.

Wrong. If you had an electron traveling at constant speed with 100TeV then it still wouldn't emit photons.

Again, it's not the case for Crookes tube. They're not going inside it in straight path at constant velocity (velocity is vector, btw, while speed is scalar)... They're bended to bottom.

What the mechanism is for electrons to generate photons when they're accelerating is something I don't know. What I do know is that the electron does not absorb energy to increase its proper energy where it later releases it.

You should always mention "free electron in outer space", not "any electron"...
« Last Edit: 20/07/2014 22:54:40 by UltimateTheory »
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#### PmbPhy

• Neilep Level Member
• 2804
##### Re: What is the difference between an electron and a photon?
« Reply #42 on: 21/07/2014 06:21:07 »
Quote from: UltimateTheory
You're cutting mine answers to just interesting you part.
The right after I said "electrons emit photons all the time", I wrote:

"They just need enough kinetic energy to emit photon."

Which means that they must be already accelerated.
It means that you meant to include it while it was moving at constant velocity after it was accelerated. Just because something was at one time accelerated it doesn't mean that it's accelerated now.

Well an electron moving at constant velocity having 1 Tev of kinetic energy surely has enough energy to emit a photon and therefore according to your claim that "electrons emit photons al the time" they must be emitting photons. And that holds for the situation where the observer is at rest in frame S where the electron is at rest and transforms to the frame where the electron has 1 TeV of kinetic energy. When that observer comes to rest neither he nor observers in his initial frame will observe photons (however observers in an accelerating frame would).
« Last Edit: 21/07/2014 10:11:00 by evan_au »

#### lightarrow

• Neilep Level Member
• 4586
##### Re: What is the difference between an electron and a photon?
« Reply #43 on: 21/07/2014 18:10:05 »
If electron emit photon, or other way loses kinetic energy (f.e. resistance of wire), it's decelerated.
It has no longer kinetic energy, and can not give away energy anymore.
An electron goes at constant speed in a circular accelerator.
1. Does it emit synchrotron radiation?
2. Does it lose kinetic energy?
Explain.

--
lightarrow

#### PmbPhy

• Neilep Level Member
• 2804
##### Re: What is the difference between an electron and a photon?
« Reply #44 on: 24/07/2014 05:13:31 »
Quote from: lightarrow
]An electron goes at constant speed in a circular accelerator.
1. Does it emit synchrotron radiation?
2. Does it lose kinetic energy?
Explain.

1 - That depends on the speed. For ultra-relativistic speeds, i.e. v ~ c then it's called synchrotron radiation. Otherwise it's called cyclotron radiation.

2 - Yes.

Particles accelerating in a circle emit synchrotron radiation when v ~ c. All accelerating charges cause radiation. Its the combination of field + particle that does it much like atom + electron can emit photons.

#### lightarrow

• Neilep Level Member
• 4586
##### Re: What is the difference between an electron and a photon?
« Reply #45 on: 24/07/2014 08:33:26 »
Quote from: lightarrow
]An electron goes at constant speed in a circular accelerator.
1. Does it emit synchrotron radiation?
2. Does it lose kinetic energy?
Explain.

1 - That depends on the speed. For ultra-relativistic speeds, i.e. v ~ c then it's called synchrotron radiation. Otherwise it's called cyclotron radiation.
Ok, I didn't know this difference of terminology. Anyway, it emits radiation at every speed.
Quote

2 - Yes.

Particles accelerating in a circle emit synchrotron radiation when v ~ c. All accelerating charges cause radiation. Its the combination of field + particle that does it much like atom + electron can emit photons.
No. I wrote "An electron goes at constant speed, does it lose kinetic energy?" Obviously, it doesn't...

--
lightarrow

#### PmbPhy

• Neilep Level Member
• 2804
##### Re: What is the difference between an electron and a photon?
« Reply #46 on: 24/07/2014 10:34:12 »
Quote from: lightarrow
No. I wrote "An electron goes at constant speed, does it lose kinetic energy?" Obviously, it doesn't...
-
lightarrow
Right. Thanks for pointing out my slip. You're right of course. Work must be done on the particle because work equals change in kinetic energy.

#### JP

• Neilep Level Member
• 3366
##### Re: What is the difference between an electron and a photon?
« Reply #47 on: 29/07/2014 13:13:29 »
This thread is locked since it keeps returning to personal attacks.