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Thread: Do photons have mass?

  1. #1 Do photons have mass? 
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    Do photons have mass? If so will their speed through space be restricted by dark matter?


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    Not in the usual sense of the word. People usually assume that mass is "rest mass", though sometimes they talk about "invariant mass" or "intrinsic mass" or "proper mass". See http://en.wikipedia.org/wiki/Invariant_mass . There's also "inertial mass" which is subtlely different for moving bodies, though for non-moving bodies inertial mass is the same as rest mass. Imagine a brick just sitting there, at rest. It's inertial mass is telling you how tough it is to move it and accelerate it to some velocity.

    You can't do this kind of thing to a photon. You can't make a photon go faster than it's already going, and you can't make it go slower either. So inertial mass doesn't apply. Or you could say that rest mass doesn't apply, because the photon isn't at rest.

    You will hear people say that the photon has "relativistic mass". That's usually considered to be a measure of energy rather than mass though. In similar vein a photon has "active gravitational mass". And you can change the velocity of a photon. That's what's happening in Compton scattering. So things get a bit fuzzy, and overall, people argue about this sort of thing because "mass" is rather ambiguous.


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  4. #3 Re: Do photons have mass? 
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    Quote Originally Posted by des.red35
    Do photons have mass? If so will their speed through space be restricted by dark matter?
    In the vacuum ?
    In the water ?
    In the glass ?
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  5. #4 Do photons have mass? 
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    Then what is a photon made of?
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  6. #5 Re: Do photons have mass? 
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    Quote Originally Posted by des.red35
    Then what is a photon made of?
    A photon is the successfull electromagnetic transaction between an absorber and an emitter. It begins by a handshake emerging form the ambiant broglian and chaotic noise, it continues by a synchroneous transfer (momentum and energy), and ends by a disconnecting when a whole quantum of action is transferrred, and return to the chaotic usual noise, for both the emitter and the receiver.

    Well, the above sentence is oversimplified, as it has omitted a third partner in the transaction : the vacuum and/or the matter in the middle, mirrors or lenses for instance, sometimes gravitational lenses at the astronomical scale, gratings, other synchroneous photons, etc.

    The Maxwell equations remain valid at the scale of a photon, at least in the vacuum.

    At the surface of the metals, there is also a coupling between the conduction electrons and each photon, but it may be enough for today.

    Each one of these couplings with the electronic clouds of matter, temporarily confers a mass to the photon. As far as I know, there is no photonic mass in the vacuum.



    Edit : spelling and grammar.
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    So is the transfer of energy restricted in space? I ask this because we are led to believe that space mainly consists of dark matter so I assume that dark matter must either absorb the energy or halt the transfer process.
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    Quote Originally Posted by des.red35
    So is the transfer of energy restricted in space? I ask this because we are led to believe that space mainly consists of dark matter so I assume that dark matter must either absorb the energy or halt the transfer process.
    How old are you ?
    What is your background ?
    What is your motivation ?
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  9. #8 Re: Do photons have mass? 
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    Quote Originally Posted by des.red35
    Do photons have mass? If so will their speed through space be restricted by dark matter?
    Photons have no rest mass. They do have energy.

    The macroscopic speed of a photon is always c, as is the speed of a classical electromagnetic wave in a vacuum.

    The speed of an electromagnetic wave through a medium (matter) is less than c and the ratio of c to that speed is known as the index of refraction.

    Very little is known about dark matter. The general notion is that most of it, non-baryonic dark matter, does not intereact with electromagnetic waves, and therefore would not affect the speed of propagation.

    See this thread for a discussion of mass.

    http://www.thescienceforum.com/What-...ass-31248t.php

    Please ignore Farsight. He is a well-known internet crank.


    http://www.toequest.com/forum/physic...verything.html


    Be cautious of Lavau. He has revealed himself as a psychologist posing as a scientist with a hidden agenda in this thread.

    http://www.thescienceforum.com/viewt...31111&start=60

    http://jacques.lavau.perso.sfr.fr/
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  10. #9 Re: Do photons have mass? 
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    Quote Originally Posted by DrRocket
    He has revealed himself as a psychologist posing as a scientist with a hidden agenda in this thread.
    Do not hesitate to support your allegations, by exhibiting solid proofs.

    Such a brillant man should find the proofs he wills, even by swimming up to the Moon if necessary.
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  11. #10 Re: Do photons have mass? 
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    Quote Originally Posted by J.C. Lavau
    Quote Originally Posted by DrRocket
    He has revealed himself as a psychologist posing as a scientist with a hidden agenda in this thread.
    Do not hesitate to support your allegations, by exhibiting solid proofs.

    Such a brillant man should find the proofs he wills, even by swimming up to the Moon if necessary.
    I think everyone but you has already read that proof, and nothing we say will prove it to you anyway. :?
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  12. #11 Re: Do photons have mass? 
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    Quote Originally Posted by MagiMaster
    Quote Originally Posted by J.C. Lavau
    Quote Originally Posted by DrRocket
    He has revealed himself as a psychologist posing as a scientist with a hidden agenda in this thread.
    Do not hesitate to support your allegations, by exhibiting solid proofs.

    Such a brillant man should find the proofs he wills, even by swimming up to the Moon if necessary.
    I think everyone but you has already read that proof, and nothing we say will prove it to you anyway. :?
    And about the subject of the thread, the eventual mass of photons ? What is your position ?
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  13. #12 Re: Do photons have mass? 
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    Quote Originally Posted by des.red35
    Then what is a photon made of?
    Recall Einstein's . All particles, the photon included are manifestations of energy.

    The photon is an "elementary" particle, which means that in the best available theory, in this case the quantum field theory of the electromagnetic and weak interactions, it is not composed of any other particles.

    This picture, like all of physics, is subject to revision as we learn more. String theory treats the photon a bit differently, but that theory is not fully formulated or supported by experiment and remains speculative.

    For a treatment of the theory of the photon, by a master of the subject, at a level accessible to a layman, read Richard Feynman's QED, or use the links in the "sticky" thread in this forum that lead to videos of the Robb Lectures on which that book is based.
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    So can the path or direction of a photon be altered by a strong enough magnetic field? Can light be curved? If so, could the positions of stars and galaxies as we see them be completely different.
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    Quote Originally Posted by des.red35
    So can the path or direction of a photon be altered by a strong enough magnetic field? Can light be curved? If so, could the positions of stars and galaxies as we see them be completely different.
    Photons carry no electric charge so they do not feel the electromagnetic force. Photons carry the electromagnetic force, so this statement means that photonsdo not directly interact with one another. ( There is a subtle process involving very high energy electrons and the strong force that is a sort of photon-photon interaction, but that is not relevant here.)

    However, photons are affected by gravity, the curvature of spacetime. Photons have worldlines that are geodesics in spacetime. That effect was one of the first experimental tests of general relativity. The image of distant galaxies can be affected by gravitational lensing.

    http://imagine.gsfc.nasa.gov/docs/fe...grav_lens.html
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    Does that mean that photons reaching us from very distant galaxies could have had their path altered many times so the distance from their source to us seems greater than what it actuallly is?
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    Quote Originally Posted by des.red35
    Does that mean that photons reaching us from very distant galaxies could have had their path altered many times so the distance from their source to us seems greater than what it actuallly is?
    Your question is overly broad. Read the links and try to be more specific with regard to what you are thinking.

    Also do a search and read the articles on the debunking of "tired light' theories.
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    Please excuse my ignorance on this subject. I just have a keen interest on this subject and you have been very helpful in pointing me in the right direction to finding the answers. My first thought was that the speed of a photon(light) may have been affected by the resistance of particles(dark matter) it encountered on its journey through space.
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    The thing is, any such effects have already been calculated into the stated size of the visible universe, and those numbers are updated as we learn more details. In general though, such effect wouldn't be very large.
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  20. #19  
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    Quote Originally Posted by des.red35
    Please excuse my ignorance on this subject. I just have a keen interest on this subject and you have been very helpful in pointing me in the right direction to finding the answers. My first thought was that the speed of a photon(light) may have been affected by the resistance of particles(dark matter) it encountered on its journey through space.
    Any interaction between light and matter in space that could increase the travel time would also result in scattering of the light. This scattering would result in a blurring or smearing of images we see from deep space. The fact that we can see crisp, clear images of distant galaxies is evidence that the light has undergone an insignificant amount of interaction with matter on its way to us.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
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  21. #20  
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    Quote Originally Posted by des.red35
    Does that mean that photons reaching us from very distant galaxies could have had their path altered many times so the distance from their source to us seems greater than what it actuallly is?
    There's nothing to prevent this in theory. Gravity can change the path of a beam of light. There are a number of black holes that act as though they were lenses, refracting the light that passes near them.

    However, it's unlikely that this would happen to a very large degree with most of the light sources in space. It takes a lot of gravity to have a substantial effect.

    Quote Originally Posted by des.red35
    Please excuse my ignorance on this subject. I just have a keen interest on this subject and you have been very helpful in pointing me in the right direction to finding the answers. My first thought was that the speed of a photon(light) may have been affected by the resistance of particles(dark matter) it encountered on its journey through space.
    Nothing can change the speed of a photon in a vacuum. It slows down when it passes through a medium such as glass, but immediately after exiting the glass and entering a vacuum again it will resume its previous speed as though it had never encountered any glass at all.
    Some clocks are only right twice a day, but they are still right when they are right.
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  22. #21  
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    Quote Originally Posted by kojax
    Quote Originally Posted by des.red35
    Does that mean that photons reaching us from very distant galaxies could have had their path altered many times so the distance from their source to us seems greater than what it actuallly is?
    There's nothing to prevent this in theory. Gravity can change the path of a beam of light. There are a number of black holes that act as though they were lenses, refracting the light that passes near them.

    .
    In addition to galaxy clusters, galaxies, stars, planets, and other flotsam of the Universe.

    People always assign magical powers to black holes. They are just x amount of mass in a very small space.
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    Could a photon encountering a particle of anti-matter on it's jouney be neutalised by the anti-matter particle? By which I mean would the photons energy be absorbed by the anti-matter or would it be deflected in another direction without any loss of energy or velocity?
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    You are not aware how much your scenario fits in scifi, and not in astrophysics.
    Real world astrophysics is very different of what you imagine on the basis of the scifi fairy tales.
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  25. #24  
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    Quote Originally Posted by des.red35
    Could a photon encountering a particle of anti-matter on it's jouney be neutalised by the anti-matter particle? By which I mean would the photons energy be absorbed by the anti-matter or would it be deflected in another direction without any loss of energy or velocity?
    Please ignore Lavau. He is a troll with a (warped) personal agenda.

    A photon is its own anti-particle. There is nothing to "neutralize".

    There is not very much anti-matter so interaction with anti-matter is not a major factor. A photon would be expected to interact with anti-matter in the same way that it interacts with ordinary matter -- which brings you back to the post by Janus.
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  26. #25 Do photons have mass? 
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    Yes, photons do have masses,since they are made up of packets of radiations with each nucleus of the radiation having respective masses. But as they move in free space, they tend to loose most of thier kinetic energy to the surronding bodies,thus they can be easily absorbed.
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  27. #26 Re: Do photons have mass? 
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    Quote Originally Posted by Oche
    Yes, photons do have masses,since they are made up of packets of radiations with each nucleus of the radiation having respective masses. But as they move in free space, they tend to loose most of thier kinetic energy to the surronding bodies,thus they can be easily absorbed.
    Complete rubbish.
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  28. #27 Re: Do photons have mass? 
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    Quote Originally Posted by Oche
    Yes, photons do have masses,since they are made up of packets of radiations with each nucleus of the radiation having respective masses. But as they move in free space, they tend to loose most of thier kinetic energy to the surronding bodies,thus they can be easily absorbed.
    Oche, I do believe you are going to have to think again on this one!
    Have you got the knowledge, or ability, to properly understand the physics of photons.
    I was quite upset when one of my many friends told me that my aptitude for literary work did not match a certain verbal ability what I possess.
    We can't have it all altho' I have had more than my fair share of red wine.
    Corporal Billy.
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  29. #28  
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    Quote Originally Posted by des.red35
    Please excuse my ignorance on this subject. I just have a keen interest on this subject and you have been very helpful in pointing me in the right direction to finding the answers. My first thought was that the speed of a photon(light) may have been affected by the resistance of particles(dark matter) it encountered on its journey through space.
    You're right to be interested in this. But you shouldn't think in terms of "particles of dark matter". They're hypothetical, not proven, Take a look instead at the Shapiro Delay

    "The time delay effect was first noticed in 1964, by Irwin I. Shapiro. Shapiro proposed an observational test of his prediction: bounce radar beams off the surface of Venus and Mercury, and measure the round trip travel time. When the Earth, Sun, and Venus are most favorably aligned, Shapiro showed that the expected time delay, due to the presence of the Sun, of a radar signal traveling from the Earth to Venus and back, would be about 200 microseconds..."

    Light is affected by the space it's travelling through. People often say it's because of "curved spacetime", and downplay what's called "the coordinate speed of light", which varies. The Shapiro delay isn't caused by the light curving, instead it's the other way around. This article by Professor Ned Wright at UCLA tells you a bit more about it. Note where it says: In a very real sense, the delay experienced by light passing a massive object is responsible for the deflection of the light.

    NB: Magnetic fields do affect light, see the Faraday Effect.
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  30. #29  
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    Quote Originally Posted by Farsight
    Quote Originally Posted by des.red35
    Please excuse my ignorance on this subject. I just have a keen interest on this subject and you have been very helpful in pointing me in the right direction to finding the answers. My first thought was that the speed of a photon(light) may have been affected by the resistance of particles(dark matter) it encountered on its journey through space.
    You're right to be interested in this. But you shouldn't think in terms of "particles of dark matter". They're hypothetical, not proven, Take a look instead at the Shapiro Delay

    "The time delay effect was first noticed in 1964, by Irwin I. Shapiro. Shapiro proposed an observational test of his prediction: bounce radar beams off the surface of Venus and Mercury, and measure the round trip travel time. When the Earth, Sun, and Venus are most favorably aligned, Shapiro showed that the expected time delay, due to the presence of the Sun, of a radar signal traveling from the Earth to Venus and back, would be about 200 microseconds..."

    Light is affected by the space it's travelling through. People often say it's because of "curved spacetime", and downplay what's called "the coordinate speed of light", which varies. The Shapiro delay isn't caused by the light curving, instead it's the other way around. This article by Professor Ned Wright at UCLA tells you a bit more about it. Note where it says: In a very real sense, the delay experienced by light passing a massive object is responsible for the deflection of the light.

    NB: Magnetic fields do affect light, see the Faraday Effect.
    As ever, you are merely posting links the content of which you do not understand.

    Shapiro delay is nothing more and nothing less than a manifestation of the curvature of spacetime, like "gravitational time dilation" of which it is a special case. It is indeed an effect on "coordinate time" which is not proper time, and proper time is what clocks measure, and the only thing that clocks measure.

    Light does not curve. Spacetime (not just space) curves and light follows a geodesic in spacetime. Thus you misunderstand Ned Wright's comment. It is curvature of spacetime that accounts for the Shapiro delay.

    Finally, the Faraday effect has to do with propagation of light through a material medium and in no way has anything to do with a direct interaction among photons, or equivalently an interaction between the electromagnetic field and a photon.
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  31. #30 Reasoning by insults... 
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    Posted: Wed Jun 15, 2011 10:48 pm Post subject:

    Quote Originally Posted by DrRocket
    Quote Originally Posted by des.red35
    ...
    Please ignore Lavau. He is a troll with a (warped) personal agenda.
    Are reasoning by insults and harassing the others, scientific methods ?
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  32. #31 Re: Reasoning by insults... 
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    Quote Originally Posted by J.C. Lavau
    Posted: Wed Jun 15, 2011 10:48 pm Post subject:

    Quote Originally Posted by DrRocket
    Quote Originally Posted by des.red35
    ...
    Please ignore Lavau. He is a troll with a (warped) personal agenda.
    Are reasoning by insults and harassing the others, scientific methods ?
    You are a menace to neophytes on the board, and deserve to be clearly labeled.

    Clear identification is indeed scientific.
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  33. #32 Re: Reasoning by insults... 
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by J.C. Lavau
    Posted: Wed Jun 15, 2011 10:48 pm Post subject:

    Quote Originally Posted by DrRocket
    Quote Originally Posted by des.red35
    ...
    Please ignore Lavau. He is a troll with a (warped) personal agenda.
    Are reasoning by insults and harassing the others, scientific methods ?
    You are a menace to neophytes on the board, and deserve to be clearly labeled.

    Clear identification is indeed scientific.
    Congratulations ! You have won your place in the Museum of Science-Faking Frauds :
    http://deonto-ethics.org/impostures/...pic,281.0.html

    You are in company with Florian N., who fakes to have a tectonic theory of bloating Earth, with radiesthesists, with "kinesiologists" who pretend to have hold a colloquium on Quantic Mechanics and Kinesiology (the food was good), with creationists as Jean Staune, financed by the John Templeton Foundation, with Jol Sternheimer who pretends to play the right melody to tomatoes, scientology, inventors of perpetual motors, and so on....

    Just by your quotes. It is enough.
    Thank you for your generous contribution to the Museum of howlers.
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  34. #33 Re: Reasoning by insults... 
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    Quote Originally Posted by J.C. Lavau
    Quote Originally Posted by DrRocket
    Quote Originally Posted by J.C. Lavau
    Posted: Wed Jun 15, 2011 10:48 pm Post subject:

    Quote Originally Posted by DrRocket
    Quote Originally Posted by des.red35
    ...
    Please ignore Lavau. He is a troll with a (warped) personal agenda.
    Are reasoning by insults and harassing the others, scientific methods ?
    You are a menace to neophytes on the board, and deserve to be clearly labeled.

    Clear identification is indeed scientific.
    Congratulations ! You have won your place in the Museum of Science-Faking Frauds :
    http://deonto-ethics.org/impostures/...pic,281.0.html

    You are in company with Florian N., who fakes to have a tectonic theory of bloating Earth, with radiesthesists, with "kinesiologists" who pretend to have hold a colloquium on Quantic Mechanics and Kinesiology (the food was good), with creationists as Jean Staune, financed by the John Templeton Foundation, with Jol Sternheimer who pretends to play the right melody to tomatoes, scientology, inventors of perpetual motors, and so on....

    Just by your quotes. It is enough.
    Thank you for your generous contribution to the Museum of howlers.
    Wrong. Troll.
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  35. #34 Re: Do photons have mass? 
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    Quote Originally Posted by DrRocket

    Photons have no rest mass. They do have energy.

    The macroscopic speed of a photon is always c, as is the speed of a classical electromagnetic wave in a vacuum.
    No, the speed of a photon is NOT "always c."

    If it were, prisms would not work, eyeglasses would not work, telescopes would not work. In fact, not even your eyes would work, since light must be bent, i.e. slowed down, from its prior speed and path. Refractive index is a measure of the material's ability to slow down light.

    Lau wrote: A photon is the successfull (sic) electromagnetic transaction between an absorber and an emitter.
    No, no "absorber" is necessary. Light can travel across the universe forever, without ever being absorbed by anything. We see light 15,000,000,000 years old, never before absorbed. Other light continues on past us.
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  36. #35 Re: Do photons have mass? 
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    Quote Originally Posted by IsaacNewton
    Quote Originally Posted by DrRocket

    Photons have no rest mass. They do have energy.

    The macroscopic speed of a photon is always c, as is the speed of a classical electromagnetic wave in a vacuum.
    No, the speed of a photon is NOT "always c."

    If it were, prisms would not work, eyeglasses would not work, telescopes would not work. In fact, not even your eyes would work, since light must be bent, i.e. slowed down, from its prior speed and path. Refractive index is a measure of the material's ability to slow down light.

    Lau wrote: A photon is the successfull (sic) electromagnetic transaction between an absorber and an emitter.
    No, no "absorber" is necessary. Light can travel across the universe forever, without ever being absorbed by anything. We see light 15,000,000,000 years old, never before absorbed. Other light continues on past us.
    Wrong.

    The speed of an electromagnetic wave in a medium can be less than c, but the speed of a photon is c. The speed of light in a medium accounts for the refraction of light in lenses. They work just fine, thank you very much, even though photons travel at c.

    The process of propagation in a medium involves interactions between photons and electrons and those interactions account for the difference in propagation speed of electromagnetic waves in the medium as opposed to a vacuum., but photons always travel at c.

    You should refrain from contradicting people when you don't know what you are talking about.
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  37. #36 Re: Reasoning by insults... 
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    Quote Originally Posted by J.C. Lavau
    Congratulations ! You have won your place in the Museum of Science-Faking Frauds :
    http://deonto-ethics.org/impostures/...pic,281.0.html
    Free advertising for this site? Awesome.
    "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." ~ Douglas Adams
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