Photons in a medium

[Bob_for_short]

the frame of a photon is not a valid reference frame. the question makes no sense.

 

The frame of a photon makes sense in a transparent medium where v < c.

[insane_alien]

nope, because the photons always travel at c.

 

the velocity of light propagation is slower because the photons are constantly being absorbed and re emitted.

 

the photon speed doesn't actually change.

[Bob_for_short]

You do not know the basics of physics here. Learn before expressing your guess.

[iNow]

You do not know the basics of physics here. Learn before expressing your guess.

 

Bob,

 

A personal attack is not a valid argument. If you think that insane_alien is wrong, then you need to demonstrate where and why.

 

I will, however, give you a head's up. He is precisely correct. The speed of light is constant, regardless of the medium. What you have mentioned about it "slowing" is only referring to a photons "apparent" speed, not the "actual" speed.

 

I_A rightly informed you that your mention is best described by absorption and re-emission, NOT (as you've suggested) that the speed of light has itself been slowed.

 

 

If you feel otherwise, cool, but you need to prove it.

[Bob_for_short]

I do not need to prove that. Rather, it is you who should learn, pass exams, solve practical problems in order to judge professionally. So far you demonstrated your lack of knowledge and misled the OP author.

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Consecutive posts merged

Have you ever heard of Cherenkov's radiation? Do you understand its physics?

[iNow]

I do not need to prove that. Rather, it is you who should learn, pass exams, solve practical problems in order to judge professionally. So far you demonstrated your lack of knowledge and misled the OP author.

First, you have still failed to support your argument, and you do your credibility here a great disservice by continuing to respond in this manner. You're basic premise is that I'm a big poopoo head and that's why I'm wrong. You're wasting everyone's time with these types of responses, and looking rather foolish as well.

 

 

 

Have you ever heard of Cherenkov's radiation?

Yes, and it is also explained by absorption and re-emission. What exactly is your point?

[D H]

I do not need to prove that. Rather, it is you who should learn, pass exams, solve practical problems in order to judge professionally. So far you demonstrated your lack of knowledge and misled the OP author.

You apparently need to go back to school, then. insane_alien and iNow are correct. Photons always travel at c. Period. You are conflating the group velocity of a stream of photons with velocity of the photons that comprise the stream.

[Bob_for_short]

You are conflating the group velocity of a stream of photons with velocity of the photons that comprise the stream.

 

You forgot to teach me the phase velocity too.

[D H]

Phase velocity can much less than c. Of course, it can also exceed c.

 

You are evading the issue. Are you of the opinion that photons do not always travel at c?

[Bob_for_short]

...Are you of the opinion that photons do not always travel at c?

 

Yes, it is my opinion and it is the experimental fact. Your "explanation" is completely wrong. A transparent medium polarizes and takes part in EMF propagation. There is no absorption and re-emission, like in a fog. On the contrary, there is a collective effect that determines the actual EMF in a medium. The photon velocity in a medium is smaller: v =c/n, where n > 1.

Shame on you.

[insane_alien]

can you provide a source for this. prefferably a peer reviewed paper.

[Bob_for_short]

Read post #4 at http://www.physicsforums.com/showthread.php?t=104715, for beginning.

[D H]

Read post #4 at http://www.physicsforums.com/showthread.php?t=104715, for beginning.

Did you read it?

 

Another post by the same author: http://www.physicsforums.com/showpost.php?p=675711

Yet another: http:// http://www.physicsforums.com/showpost.php?p=865368

 

An interpretation of the post in question: http://www.physicsforums.com/showpost.php?p=1212576

 

More from physics forums:

 

http://www.physicsforums.com/showpost.php?p=856187

Light never travels with a speed that is anything less than c.

 

http://www.physicsforums.com/showpost.php?p=3992497

In fact, photons never travel at any speed other than c.

 

 

We have working physicists at this forum, too:

 

http://www.scienceforums.net/forum/showpost.php?p=508561

photons always travel at c

 

http://www.scienceforums.net/forum/showpost.php?p=179222

So saying that photons always travel at c is correct.

Edited September 20, 2009 by D H

[Bob_for_short]

...So saying that photons always travel at c is correct.[/indent]

 

You references demonstrate a low educational level of those posters.

 

I remind you that in a transparent medium there are bound charges that participate in creation the resulting field. It is impossible to separate (to distinguish) the incident and the induced fields - they both appear in sum in the charge motion equations as a unique force. The resulting field is different from EMF in vacuum, it should be clear. In transparent media there is no dissipation (absorption), do not fool yourself.

[insane_alien]

one of those posters was the same guy you used as evidence for your opinion.

 

now, do you have any peer reviewed source on this? maybe a physics text or university website would do?

[Bob_for_short]

First, it is a common knowledge available in textbooks. Next, why should I make a search for you?

[insane_alien]

i have never seen it in a text book. at all.

 

now, are you going to provide a credible source or not?

[Bob_for_short]

No, I am not going to. It is your interest, not mine, sorry.

[insane_alien]

you seem to be the only one claiming this. i have searched for an article, journal paper or well, anything that says photons move slower when in a material but i can't find one.

 

the burden of proof isn't on me anyway, its on you. you are the one making the claim that photons don't move at c in a material despite everyone else saying they don't(including the guy you linked to to support your claim).

 

so cough up or shut up.

 

EDIT, btw, this thread has gone majorly offtopic. i suggest a mod move this off topic discussion to its own thread.

[Bob_for_short]

Again, speaking of absorption and re-emission as a reason for delay is wrong and it is you burden to learn when you were told so.

[insane_alien]

i can only learn stuff i can find sources for.

[Bob_for_short]

Look in opto-electronics books on propagation of EMF in optical wave guides. You may learn interesting things like acceleration and deceleration of light in non homogeneous media, with variable n.

[insane_alien]

any specific sources though? don't want to have to sift through dozens of books in the university library.

 

also, the only sources i can find something similar to what you are saying is in material dealling with light classically.

 

photons are not in the realm of classical physics.

[Klaynos]

Classical/semi-classical wave theory, and the quantum mechanical explanation of light propagating through media are very different to each other. One has a constant photon speed for single photons, the other has a varying speed of light for an ensemble of photons.

[Bob_for_short]

Classical/semi-classical wave theory, and the quantum mechanical explanation of light propagating through media are very different to each other. One has a constant photon speed for single photons, the other has a varying speed of light for an ensemble of photons.

 

 

If the light propagation depended on number of photons, it would be a non-linear effect. It exists indeed but at very high intensities. So the linear, usual theory of light propagation is valid for any number of photons, even for one.