# The Naked Scientists Forum

### Author Topic: The Photon as Pure Energy  (Read 8866 times)

#### Emc2

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##### The Photon as Pure Energy
« on: 10/09/2012 09:51:33 »
E2 = m2c4 + p2c2

So in the case of a photon, m=0 so E = pc or p = E/c.

a photon is basically pure energy, that it why it can go from particle to wave and visa versa..

photon
The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge.

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon
« Last Edit: 10/09/2012 09:54:42 by Emc2 »

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #1 on: 10/09/2012 11:18:42 »
E2 = m2c4 + p2c2
So in the case of a photon, m=0 so E = pc or p = E/c.
Ok.
Quote
a photon is basically pure energy, that it why it can go from particle to wave and visa versa..
1. What is "pure energy" and which is the difference with "energy"?
2. Just to be more precise, a photon doesn't "go from particle to wave and vice versa", a photon is a particle; as an electron, a proton, a neutron,  ecc.
But "particle" for a physicist doesn't mean "corpuscle". It actually means (simplistically speaking) "a quantum object which state is found solving the Schroedinger equation" and which has both wave and corpuscolar behaviour depending on the situation.
« Last Edit: 10/09/2012 11:23:06 by lightarrow »

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #2 on: 11/09/2012 07:23:28 »
E2 = m2c4 + p2c2
So in the case of a photon, m=0 so E = pc or p = E/c.
Ok.
Quote
a photon is basically pure energy, that it why it can go from particle to wave and visa versa..
1. What is "pure energy" and which is the difference with "energy"?
2. Just to be more precise, a photon doesn't "go from particle to wave and vice versa", a photon is a particle; as an electron, a proton, a neutron,  ecc.
But "particle" for a physicist doesn't mean "corpuscle". It actually means (simplistically speaking) "a quantum object which state is found solving the Schroedinger equation" and which has both wave and corpuscolar behaviour depending on the situation.

A Photon is energy - and it has been proven that it can act as a wave or a particle

http://en.wikipedia.org/wiki/Double-slit_experiment

Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when its position is measured.

http://en.wikipedia.org/wiki/Photon

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #3 on: 11/09/2012 12:11:28 »
A Photon is energy
A photon "has" energy.
Quote
- and it has been proven that it can act as a wave or a particle
http://en.wikipedia.org/wiki/Double-slit_experiment
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles.
"it can act as a wave or a particle" or "exhibit wave–particle duality" is a better description than the one you wrote in your previous post

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #4 on: 12/09/2012 06:07:34 »
A Photon is energy
A photon "has" energy.
Quote
- and it has been proven that it can act as a wave or a particle
http://en.wikipedia.org/wiki/Double-slit_experiment
Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles.
"it can act as a wave or a particle" or "exhibit wave–particle duality" is a better description than the one you wrote in your previous post

A Photon IS Energy, notice - definition from Goddard Space Center..

( photon
The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge. )

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #5 on: 12/09/2012 20:33:52 »
A Photon IS Energy, notice - definition from Goddard Space Center..
( photon
The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge. )

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon
A photon is not energy, a photon has energy, and wherever you found that idea, sorry, it's wrong...
In the link you gave there isn't written that "photon is energy", at all. Read it well.
Energy is an attribute of objects/systems, it's not an object/system by itself.
Otherwise you should explain (for example) how can a car have kinetic energy and not being a photon, or anything having energy and not having photons to which attribute that energy.

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #6 on: 14/09/2012 06:00:05 »
A Photon IS Energy, notice - definition from Goddard Space Center..
( photon
The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge. )

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon
A photon is not energy, a photon has energy, and wherever you found that idea, sorry, it's wrong...
In the link you gave there isn't written that "photon is energy", at all. Read it well.
Energy is an attribute of objects/systems, it's not an object/system by itself.
Otherwise you should explain (for example) how can a car have kinetic energy and not being a photon, or anything having energy and not having photons to which attribute that energy.

first of all you did not read correctly....

(( photon, The smallest (quantum) unit of light/electromagnetic energy  ) <---this is my quote...

Your are not correct.  Think Again...

A Photon is Energy ( Radiation ), and thereby "has" energy, and it has no mass..  you can accept the facts, or believe what you want to....

http://en.wikipedia.org/wiki/Photon

( A photon is an elementary particle, the quantum of light and all other forms of electromagnetic radiation, and the force carrier for the electromagnetic force, even when static via virtual photons )

http://en.wikipedia.org/wiki/Light

( In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. )

( the photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR )

« Last Edit: 14/09/2012 06:09:40 by Emc2 »

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #7 on: 14/09/2012 13:18:56 »
A Photon IS Energy, notice - definition from Goddard Space Center..
( photon
The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge. )

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon
A photon is not energy, a photon has energy, and wherever you found that idea, sorry, it's wrong...
In the link you gave there isn't written that "photon is energy", at all. Read it well.
Energy is an attribute of objects/systems, it's not an object/system by itself.
Otherwise you should explain (for example) how can a car have kinetic energy and not being a photon, or anything having energy and not having photons to which attribute that energy.
first of all you did not read correctly....

(( photon, The smallest (quantum) unit of light/electromagnetic energy  ) <---this is my quote...
Ok, and then? It's taught in every simple course of qm. Does it mean that a photon is energy? LOL
Quote
Your are not correct.  Think Again...
I don't need it. If you like, ask a professor of physics...
Quote
A Photon is Energy ( Radiation ),
"Is radiation and "is energy" are two different things. Radiation is something and energy is something else.
A photon is a particle. Period. Then you can find that it has some properties, for example energy and spin.
Quote
and thereby "has" energy, and it has no mass..  you can accept the facts, or believe what you want to....
Exactly, but this is what I wrote, you wrote that "a photon is energy".
Quote
http://en.wikipedia.org/wiki/Photon
( A photon is an elementary particle,
Indeed
Quote
the quantum of light and all other forms of electromagnetic radiation, and the force carrier for the electromagnetic force, even when static via virtual photons )
http://en.wikipedia.org/wiki/Light
( In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. )
( the photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR )
In all those quote, and in the links, there is never written that "a photon IS energy".

#### Emc2

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• Posts: 175
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##### Re: The Photon as Pure Energy
« Reply #8 on: 15/09/2012 05:27:02 »
A Photon IS Energy, notice - definition from Goddard Space Center..
( photon
The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge. )

http://imagine.gsfc.nasa.gov/docs/dict_jp.html#photon
A photon is not energy, a photon has energy, and wherever you found that idea, sorry, it's wrong...
In the link you gave there isn't written that "photon is energy", at all. Read it well.
Energy is an attribute of objects/systems, it's not an object/system by itself.
Otherwise you should explain (for example) how can a car have kinetic energy and not being a photon, or anything having energy and not having photons to which attribute that energy.
first of all you did not read correctly....

(( photon, The smallest (quantum) unit of light/electromagnetic energy  ) <---this is my quote...
Ok, and then? It's taught in every simple course of qm. Does it mean that a photon is energy? LOL
Quote
Your are not correct.  Think Again...
I don't need it. If you like, ask a professor of physics...
Quote
A Photon is Energy ( Radiation ),
"Is radiation and "is energy" are two different things. Radiation is something and energy is something else.
A photon is a particle. Period. Then you can find that it has some properties, for example energy and spin.
Quote
and thereby "has" energy, and it has no mass..  you can accept the facts, or believe what you want to....
Exactly, but this is what I wrote, you wrote that "a photon is energy".
Quote
http://en.wikipedia.org/wiki/Photon
( A photon is an elementary particle,
Indeed
Quote
the quantum of light and all other forms of electromagnetic radiation, and the force carrier for the electromagnetic force, even when static via virtual photons )
http://en.wikipedia.org/wiki/Light
( In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. )
( the photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR )
In all those quote, and in the links, there is never written that "a photon IS energy".

It is very complicated to understand, I realize that.....but it is what it is, a mass less piece of energy.....

First of all, everything is "pure energy" thanks to Einstein's famous E=mc^2. Second of all: many elementary particles can decay; in fact, MOST of them! The only ones that don't are the electron, photon, up quark and (possibly) neutrino. The real reason that the photon cannot decay is because it is massless. A counter-example is the Z boson, which is (VERY roughly speaking!!) a "fat photon", which can decay (and does so **VERY** fast - about 10^{-24} seconds!). However, it is just as "elementary" as the photon.

Massless particles can never decay. You can prove this mathematically by just writing down the energies and momenta of the decay products and showing that there are no values of these things that conserve everything. More intuitively: massless particles move at the speed of light. Particles that move at the speed of light do not experience "time" due to Einstein's special theory of relativity (infinite time dilation - they stop aging). Therefore they cannot decay since that would require a clock (the particle has to know how long it has to go before it decays).

BTW, this argument is how they relate neutrino oscillation to neutrino mass: if the neutrinos were truly massless, then they could not oscillate by this argument. Thus, even though we still cannot directly measure the neutrino mass since it's so small, we can still infer that it's not zero since we see the oscillations.

http://www.teachengineering.org/view_lesson.php?url=collection/cub_/lessons/cub_energy2/cub_energy2_lesson03.xml
((  Light is a form of energy  ))

« Last Edit: 15/09/2012 06:36:27 by Emc2 »

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #9 on: 15/09/2012 10:50:03 »
It is very complicated to understand, I realize that
Yes, you are referring to yourself, clearly
Quote
.....but it is what it is, a mass less
Yes.
Quote
piece of energy.....
This is just your personal interpretation, if you want to discuss it, please do it in "New theories" forum.
Quote
First of all, everything is "pure energy"
"pure energy" doesn't exist. Please, ask a physics professor about what is "pure energy" and tell me how long you will have made him laugh...
Quote
thanks to Einstein's famous E=mc^2. Second of all: many elementary particles can decay; in fact, MOST of them! The only ones that don't are the electron, photon, up quark and (possibly) neutrino. The real reason that the photon cannot decay is because it is massless.
And why a non-massless particle as electron doesn't decay?
Quote
A counter-example is the Z boson, which is (VERY roughly speaking!!) a "fat photon", which can decay (and does so **VERY** fast - about 10^{-24} seconds!). However, it is just as "elementary" as the photon.
This is just your personal interpretation, if you want to discuss it, please do it in "New theories" forum.
Quote
Massless particles can never decay.
I have never said the contrary (apart from the fact that I don't know what you mean with "decay": a photon can generate a couple e+ e-, for example)
Quote
You can prove this mathematically by just writing down the energies and momenta of the decay products and showing that there are no values of these things that conserve everything. More intuitively: massless particles move at the speed of light.
Ok. And then? It doesn't mean that a photon IS energy or that something as "pure energy" exists. Why did you forget to define the term "pure energy"?
Quote
Particles that move at the speed of light do not experience "time" due to Einstein's special theory of relativity (infinite time dilation - they stop aging).
Meaningless sentence. You cannot create a frame of reference co-moving with the photon.
« Last Edit: 15/09/2012 11:00:46 by lightarrow »

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #10 on: 15/09/2012 11:57:11 »
It is very complicated to understand, I realize that
Yes, you are referring to yourself, clearly
Quote
.....but it is what it is, a mass less
Yes.
Quote
piece of energy.....
This is just your personal interpretation, if you want to discuss it, please do it in "New theories" forum.
Quote
First of all, everything is "pure energy"
"pure energy" doesn't exist. Please, ask a physics professor about what is "pure energy" and tell me how long you will have made him laugh...
Quote
thanks to Einstein's famous E=mc^2. Second of all: many elementary particles can decay; in fact, MOST of them! The only ones that don't are the electron, photon, up quark and (possibly) neutrino. The real reason that the photon cannot decay is because it is massless.
And why a non-massless particle as electron doesn't decay?
Quote
A counter-example is the Z boson, which is (VERY roughly speaking!!) a "fat photon", which can decay (and does so **VERY** fast - about 10^{-24} seconds!). However, it is just as "elementary" as the photon.
This is just your personal interpretation, if you want to discuss it, please do it in "New theories" forum.
Quote
Massless particles can never decay.
I have never said the contrary (apart from the fact that I don't know what you mean with "decay": a photon can generate a couple e+ e-, for example)
Quote
You can prove this mathematically by just writing down the energies and momenta of the decay products and showing that there are no values of these things that conserve everything. More intuitively: massless particles move at the speed of light.
Ok. And then? It doesn't mean that a photon IS energy or that something as "pure energy" exists. Why did you forget to define the term "pure energy"?
Quote
Particles that move at the speed of light do not experience "time" due to Einstein's special theory of relativity (infinite time dilation - they stop aging).
Meaningless sentence. You cannot create a frame of reference co-moving with the photon.

I realize that you do not understand, that's cool, it is complicated, yet so very simple...

I'm done in this useless conversation anymore....

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #11 on: 15/09/2012 18:35:49 »
If I don't understand, it's not a serious problem, maybe it's me...
Write a document for ArXiv, so that other physicsts can read it.

#### imatfaal

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##### Re: The Photon as Pure Energy
« Reply #12 on: 15/09/2012 22:24:01 »
EMC2 - Lightarrow is completely correct.

One might consider the photon as pure energy, but this is not the best way to think. Energy is a property of waves and particles. Classically you can view waves in the electromagnetic field as being carriers of energy. Energy is a property of the configuration.  A more classical simile would be that sea waves quite clearly transporting energy - but they do not move a lot of water.  You might still claim that waves are energy. But rather say it is more correct that energy is a property of the configuration and that waves transport energy.

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #13 on: 16/09/2012 01:42:58 »
EMC2 - Lightarrow is completely correct.

One might consider the photon as pure energy, but this is not the best way to think. Energy is a property of waves and particles. Classically you can view waves in the electromagnetic field as being carriers of energy. Energy is a property of the configuration.  A more classical simile would be that sea waves quite clearly transporting energy - but they do not move a lot of water.  You might still claim that waves are energy. But rather say it is more correct that energy is a property of the configuration and that waves transport energy.

No, I am sorry he is not correct, you both are not correct.

Light is Energy..  and there nothing left to say about it..

#### JP

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##### Re: The Photon as Pure Energy
« Reply #14 on: 16/09/2012 04:21:01 »
EMC2 - Lightarrow is completely correct.

One might consider the photon as pure energy, but this is not the best way to think. Energy is a property of waves and particles. Classically you can view waves in the electromagnetic field as being carriers of energy. Energy is a property of the configuration.  A more classical simile would be that sea waves quite clearly transporting energy - but they do not move a lot of water.  You might still claim that waves are energy. But rather say it is more correct that energy is a property of the configuration and that waves transport energy.

No, I am sorry he is not correct, you both are not correct.

Light is Energy..  and there nothing left to say about it..

Emc2: Lightarrow and Imatfaal are both correct and trying to point out some subtleties of the photon.  Please remember this is a discussion forum.  Simply telling others they're wrong and you're right without trying to engage in discussion isn't helpful.

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #15 on: 16/09/2012 12:24:31 »
first of all, I am right

http://en.wikipedia.org/wiki/Energy

( In the case of electromagnetic wave these energy states are called quanta of light or photons. )

http://en.wikipedia.org/wiki/Energy_operator

http://en.wikipedia.org/wiki/Photon_polarization

( Einsteins's conclusion from early experiments on the photoelectric effect is that electromagnetic radiation is composed of irreducible packets of energy, known as photons. )

(( packets of energy, known as photons  ))  being a key phrase.

( The connection with quantum mechanics is made through the identification of a minimum packet size, called a photon, for energy in the electromagnetic field.  )

http://en.wikipedia.org/wiki/Photon_dynamics_in_the_double-slit_experiment

( The important conclusion from these early experiments is that electromagnetic radiation is composed of irreducible packets of energy, known as photons )

and this one..

( The photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR )

http://en.wikipedia.org/wiki/Light

It is simple as anything, a photon of light is energy, that is why it has no mass, but momentum

« Last Edit: 16/09/2012 12:35:32 by Emc2 »

#### simplified

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##### Re: The Photon as Pure Energy
« Reply #16 on: 16/09/2012 14:38:16 »
EMC2 - Lightarrow is completely correct.

One might consider the photon as pure energy, but this is not the best way to think. Energy is a property of waves and particles. Classically you can view waves in the electromagnetic field as being carriers of energy. Energy is a property of the configuration.  A more classical simile would be that sea waves quite clearly transporting energy - but they do not move a lot of water.  You might still claim that waves are energy. But rather say it is more correct that energy is a property of the configuration and that waves transport energy.

No, I am sorry he is not correct, you both are not correct.

Light is Energy..  and there nothing left to say about it..

If electron has energy then does the electron have any photon?
« Last Edit: 16/09/2012 14:45:39 by simplified »

#### JP

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##### Re: The Photon as Pure Energy
« Reply #17 on: 16/09/2012 14:56:48 »
first of all, I am right

You'll notice that in those links there's always the important distinction that it is a packet of energy of the electromangetic field.  If you just define a photon as a packet of energy you miss a lot of its important properties that come from the electromangetic field.  As I understood their posts, that's what lightarrow and imatfaal were trying to point out.

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #18 on: 16/09/2012 17:43:00 »
You'll notice that in those links there's always the important distinction that it is a packet of energy of the electromangetic field.  If you just define a photon as a packet of energy you miss a lot of its important properties that come from the electromangetic field.  As I understood their posts, that's what lightarrow and imatfaal were trying to point out.
Yes. Furthermore, that is not the best definition of photon. A better definition is "quantum of electromagnetic field". As such, it has several properties, one of which is energy.

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #19 on: 16/09/2012 22:41:20 »

A Photon is a mass less piece of energy, that can act as a wave and/or a particle.

Of course a Photon has energy,  DOH !!!!  that is because IT IS ENERGY !!

You can not get more clear then that.

If you can not understand that simple concept, you can never understand the complexity of simplicity..  ( get it now ? )

Oh well........

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #20 on: 17/09/2012 18:19:31 »
A Photon is a mass less piece of energy
Wrong. It is a definition used in popular books/documents but it's not the real thing.
Look up in a good book of quantum mechanics or, better, about QFT, quantum field theory (or, at least, which includes QED, quantum electro dynamics).

--
lightarrow
« Last Edit: 17/09/2012 18:24:05 by lightarrow »

#### lean bean

• Guest
##### Re: The Photon as Pure Energy
« Reply #21 on: 17/09/2012 19:06:29 »
Does this help Emc2?
Theoretical Physicist Matt Strassler
Quote
Photons should not be called `energy’, or `pure energy’, or anything similar.  All particles are ripples in fields and have energy; photons are not special in this regard. Photons are stuff; energy is not.
-------
The term “pure energy” is a mix of poetry, shorthand and garbage.   Since photons have no mass, they  have no mass-energy, and that means their energy is “purely motion-energy”.  But that does not mean the same thing, either in physics or intuitively to the non-expert, as saying photons are “pure energy”.

http://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/matter-and-energy-a-false-dichotomy/

#### imatfaal

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##### Re: The Photon as Pure Energy
« Reply #22 on: 17/09/2012 22:13:18 »
Nice find lean bean - I spent some time looking for a nice definitive article like that.

#### Emc2

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##### Re: The Photon as Pure Energy
« Reply #23 on: 19/09/2012 11:04:07 »
A Photon is an energy wave as it travels at C, and a Particle "ONLY" as certain interactions dictate.

It travels at C as a wave of energy ( hence “pure energy ), then as it needs to interact it either changes to a particle ( to interact for example in Human Vision ) to interact, or remains a wave to interact in that form…

so for 99.9 % of it's existence it is a wave of energy

Get it now  ?

#### lightarrow

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##### Re: The Photon as Pure Energy
« Reply #24 on: 20/09/2012 19:19:14 »
if you say so...

#### The Naked Scientists Forum

##### Re: The Photon as Pure Energy
« Reply #24 on: 20/09/2012 19:19:14 »