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Thread: The Speed of Light Paradox

  1. #1 The Speed of Light Paradox 
    Forum Freshman sp1der's Avatar
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    I recently had a very in-depth conversation with a dear friend of mine where we discussed the chances of humans ever achieving light speed.
    Over the course of this discussion we also realized that this entire concept is an utter paradox.

    Speed of Light = 299, 792, 458 m/s
    The Length of the Universe = Theoretically infinite

    So, what's the point in traveling such speed if we will never be able to truly utilize it? Now, I do realize the scientific breakthrough it would be
    and the concept is just so interesting to me I would love to see that discovery within my lifetime. (which most likely won't occur)

    But, here's the real point of my discussion and where the actually paradox comes into play:
    Scientists say that the speed of light is so fast that if we were to travel anywhere we would
    get there instantaneously. Makes sense, right? But, how can that be true if the Universe is infinite?

    So, my question is if such events were possible, would humans feel the journey across the Universe or would it feel instant?
    Would it all be one big blur?
    What would it feel like if the human body could survive such high G's?


     

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  3. #2  
    KJW
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    Humans will never be able to directly travel at the speed of light. In principle, we could travel arbitrarily close to the speed of light, but regardless of how close to the speed of light we do travel, the speed of light will always be faster than us by the same amount as it is now.


    There are no paradoxes in relativity, just people's misunderstandings of it.
     

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    Brassica oleracea Strange's Avatar
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    Firstly, it isn't possible to travel at the speed of light, so some of your conclusions are moot.

    So, what's the point in traveling such speed if we will never be able to truly utilize it?
    If we could travel at near the speed of light, it would still be useful. For example, we could get to the nearest star in a few years rather than decades.

    Scientists say that the speed of light is so fast that if we were to travel anywhere we would
    get there instantaneously. Makes sense, right?
    No, it doesn't make sense. At best, you are mixing up frames of reference. If you were to travel to the nearest star (about 4 light years away) it would take you just over 4 years at almost-the-speed-of-light - as measured by someone on earth.

    Form "your" point of view, the distance would appear to be less and so it would take less time.

    What would it feel like if the human body could survive such high G's?
    You haven't mentioned acceleration so it is not possible to know what sort of Gs you are talking about.
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    Quote Originally Posted by Strange View Post
    If you were to travel to the nearest star (about 4 light years away) it would take you just over 4 years at almost-the-speed-of-light - as measured by someone on earth.

    Form "your" point of view, the distance would appear to be less and so it would take less time.
    If you traveled at 90%c how long would that journey take for you by your onboard clock?

    Quote Originally Posted by KJW View Post
    Humans will never be able to directly travel at the speed of light. In principle, we could travel arbitrarily close to the speed of light, but regardless of how close to the speed of light we do travel, the speed of light will always be faster than us by the same amount as it is now.
    Is there such a thing as a source of light that moves wrt an observer at c? (I imagine not ;any source would have mass and so be unable to travel at c )
     

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    Quote Originally Posted by geordief View Post
    If you traveled at 90%c how long would that journey take for you by your onboard clock?
    In that case, you would see the distance reduced by a factor of 2.29 (1) and so it would be 4/2.29 light years at 0.9c = 1.94 years.

    (1) RELATIVITY CALCULATOR

    Is there such a thing as a source of light that moves wrt an observer at c? (I imagine not ;any source would have mass and so be unable to travel at c )
    I think you are right.
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by geordief View Post
    If you traveled at 90%c how long would that journey take for you by your onboard clock?
    In that case, you would see the distance reduced by a factor of 2.29 (1) and so it would be 4/2.29 light years at 0.9c = 1.94 years.
    If the answer is 2.15 light years ,it will be the first time I have got one of those questions right
    (1) RELATIVITY CALCULATOR
    Suppose he skimmed the Earth at the same moment an observer on Earth was judging the star in question to be 4 light years away ,what distance would the astronaut judge the star to be as he sped past?

    If the answer is 2.15 ly's then it will be the first time I will have got one of those questions right

    So not confident....at all!
     

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    Not sure where you get 2.15. If an observer on the Earth measure the distance to be 4 ly, then the person passing at 0.9c will measure it as 4/2.29 = 1.75 ly. (Unless I have got it wrong, which is entirely possible. I am going to double check ...)

    ... no. seems to be correct.

    Your answer would be correct if the person were passing at 0.843c
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    Quote Originally Posted by Strange View Post
    Not sure where you get 2.15. If an observer on the Earth measure the distance to be 4 ly, then the person passing at 0.9c will measure it as 4/2.29 = 1.75 ly. (Unless I have got it wrong, which is entirely possible. I am going to double check ...)

    ... no. seems to be correct.

    Your answer would be correct if the person were passing at 0.843c
    Oh well (I divided 1.94 by 0.9)

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  10. #9  
    Brassica oleracea Strange's Avatar
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    You had me worried/confused for a moment there!

    speed = distance / time
    So distance = speed x time = 1.94 x 0.9 = 1.746
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
     

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    Quote Originally Posted by Strange View Post
    You had me worried/confused for a moment there!

    speed = distance / time
    So distance = speed x time = 1.94 x 0.9 = 1.746
    So,I was almost there?(I just divided instead of multiplying?)
     

  12. #11  
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    Quote Originally Posted by geordief View Post
    Quote Originally Posted by Strange View Post
    You had me worried/confused for a moment there!

    speed = distance / time
    So distance = speed x time = 1.94 x 0.9 = 1.746
    So,I was almost there?(I just divided instead of multiplying?)
    Exactly. Don't worry, I always have to double-check these basic things myself! (But that could just be age...)
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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by geordief View Post
    Quote Originally Posted by Strange View Post
    You had me worried/confused for a moment there!

    speed = distance / time
    So distance = speed x time = 1.94 x 0.9 = 1.746
    So,I was almost there?(I just divided instead of multiplying?)
    Exactly. Don't worry, I always have to double-check these basic things myself! (But that could just be age...)
    I sometimes wonder if time doesn't also dilate as we get older
     

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    No, it doesn't make sense. At best, you are mixing up frames of reference. If you were to travel to the nearest star (about 4 light years away) it would take you just over 4 years at almost-the-speed-of-light - as measured by someone on earth.

    Form "your" point of view, the distance would appear to be less and so it would take less time.

    This makes incredible sense. I never thought of it from such perspective.

    You haven't mentioned acceleration so it is not possible to know what sort of Gs you are talking about.

    I was just adding some additional thoughts sorry if it was confusing.
    By the way is there any way to calculate how many G's the speed of light has?

    Last edited by sp1der; October 27th, 2017 at 08:40 AM. Reason: formatted text incorrectly
     

  15. #14  
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    Quote Originally Posted by sp1der View Post
    By the way is there any way to calculate how many G's the speed of light has?[/COLOR]
    G is used to measure acceleration not speed. (Imagine sitting in a car: you are pressed back into your seat by the "g-force" as the car accelerates. When it is moving at a steady speed, you feel no pressure.)

    Light doesn't accelerate so, none.
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    Quote Originally Posted by Strange View Post

    Light doesn't accelerate so, none.
    If it was moving through a continuously "transparency decreasing" medium could it be said to accelerate?
     

  17. #16  
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    could it be said to accelerate?

    Once light photons are created they are already traveling at light speed. Thus, the acceleration simply isn't there. I feel like this '"transparency decreasing" medium' would have no affect. But I'm not sure you may need to be more specific.
     

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    Well light travels slower than c depending on the medium.For instance photons take hundreds(?) of years to make their way out from the centre of the Sun.

    Their speed must vary as they encounter different regions,I imagine.
     

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    Quote Originally Posted by geordief View Post
    Well light travels slower than c depending on the medium.
    Nah.

    Their speed must vary as they encounter different regions,I imagine.
    Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
    There's a difference between the speed of light (a constant) and the speed at which it propagates.
    As light it's always at c. It's the absorption and emission which "slows it down" (but it's not "travelling light" per se while it's doing that bit).
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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by geordief View Post
    Well light travels slower than c depending on the medium.
    Nah.

    Their speed must vary as they encounter different regions,I imagine.
    Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
    There's a difference between the speed of light (a constant) and the speed at which it propagates.
    As light it's always at c. It's the absorption and emission which "slows it down" (but it's not "travelling light" per se while it's doing that bit).
    Thanks
    That is the "phase velocity" of light that I was confusing with the speed of individual photons,perhaps.
     

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    Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
    There's a difference between the speed of light (a constant) and the speed at which it propagates.
    As light it's always at c. It's the absorption and emission which "slows it down" (but it's not "travelling light" per se while it's doing that bit).
    Very interesting..and explained extremely well I might add
    Last edited by sp1der; October 27th, 2017 at 11:01 AM. Reason: numerous typos
     

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    Quote Originally Posted by Dywyddyr View Post
    Quote Originally Posted by geordief View Post
    Well light travels slower than c depending on the medium.
    Nah.

    Their speed must vary as they encounter different regions,I imagine.
    Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
    There's a difference between the speed of light (a constant) and the speed at which it propagates.
    As light it's always at c. It's the absorption and emission which "slows it down" (but it's not "travelling light" per se while it's doing that bit).
    That's incorrect.

    https://youtu.be/CiHN0ZWE5bk?t=4m53s
     

  23. #22  
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    Yes I was wondering whether someone would draw attention to that.

    As I understand it, it can't really be described as true absorption and re-emission, since if it were, there would be scattering, which there isn't. The explanation I have been given is that the electric vector of the radiation couples to the medium via its polarisability, and this slows down the phase velocity, though not, I think, the front velocity, which determines the rate of transmission of information.

    But this area is fraught with scope for misunderstanding, so I'd be very happy to hear from a real physicist.
     

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    Quote Originally Posted by exchemist View Post
    Yes I was wondering whether someone would draw attention to that.

    As I understand it, it can't really be described as true absorption and re-emission, since if it were, there would be scattering, which there isn't. The explanation I have been given is that the electric vector of the radiation couples to the medium via its polarisability, and this slows down the phase velocity, though not, I think, the front velocity, which determines the rate of transmission of information.

    But this area is fraught with scope for misunderstanding, so I'd be very happy to hear from a real physicist.
    I always end up talking to you about this and you never seem to remember. Very bizarre!

    https://en.wikipedia.org/wiki/Refrac...ic_explanation
     

  25. #24  
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    Quote Originally Posted by Secular Sanity View Post
    Quote Originally Posted by exchemist View Post
    Yes I was wondering whether someone would draw attention to that.

    As I understand it, it can't really be described as true absorption and re-emission, since if it were, there would be scattering, which there isn't. The explanation I have been given is that the electric vector of the radiation couples to the medium via its polarisability, and this slows down the phase velocity, though not, I think, the front velocity, which determines the rate of transmission of information.

    But this area is fraught with scope for misunderstanding, so I'd be very happy to hear from a real physicist.
    I always end up talking to you about this and you never seem to remember. Very bizarre!

    https://en.wikipedia.org/wiki/Refrac...ic_explanation
    Haha, indeed! It's my old age I think. But it is a topic that comes round quite often.
     

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    Quote Originally Posted by exchemist View Post
    Haha, indeed! It's my old age I think. But it is a topic that comes round quite often.
    My first time around . I hope I can keep up.
     

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    The human body is only restricted by skeletal frame to be able to condense its body mass into a small frame,w

    eight and ability to condense to say humans will never travel the speed of light by terms of laws present could
    be false. Due to the fact travel might not be based by

    speed but other means. Currently no,
    future why not.
     

  28. #27  
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    Quote Originally Posted by Mastema View Post
    The human body is only restricted by skeletal frame to be able to condense its body mass into a small frame,weight and ability to condense to say humans will never travel the speed of light by terms of laws present could
    be false. Due to the fact travel might not be based by speed but other means. Currently no, future why not.
    This is nonsense.
    Do NOT post in the hard sciences sub fora in future.
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    Quote Originally Posted by Dywyddyr View Post
    Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
    There's a difference between the speed of light (a constant) and the speed at which it propagates.
    As light it's always at c. It's the absorption and emission which "slows it down" (but it's not "travelling light" per se while it's doing that bit).
    This is nonsense.

    Do NOT post in the hard sciences sub fora in future.
     

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    Quote Originally Posted by Secular Sanity View Post
    Quote Originally Posted by Dywyddyr View Post
    Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted.
    There's a difference between the speed of light (a constant) and the speed at which it propagates.
    As light it's always at c. It's the absorption and emission which "slows it down" (but it's not "travelling light" per se while it's doing that bit).
    This is nonsense.

    Do NOT post in the hard sciences sub fora in future.
    I'm not sure what the objection is -- the description is rigorously correct. Someone (maybe you) linked to a youtube earlier, and I didn't hear the professor deny the correctness of the above description.

    Forget about propagation through a dielectric medium for the moment and consider instead how a metallic mirror works. It is by re-radiation, which is why mobile electrons are so useful in making good mirrors.

    If you've taken physics at uni, you've undoubtedly encountered the notion of images in solving certain boundary problems in E&M. The success of this method in describing the radiation behaviour of, say, a monopole antenna tells us that induction and re-radiation are happening. The familiar wedge-shaped aerials of yore (the so-called Yagi or Yagi-Uda antenna) consist of connected and unconnected elements. Re-radiation by the latter of incident energy from the former makes such antennas work.

    In QED, the description of photons propagating through a medium has those photons always traveling at c. Re-emission superposes with the incident energy to produce the slowdown in propagation. Even if one takes the view that QED doesn't "really" describe what is going on -- that it is merely a calculational aid whose intermediate pictures are fictions that nonetheless lead to correct outcomes -- the fact that one gets the right answer means that it is perfectly proper to invoke its language.
     

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    Quote Originally Posted by tk421 View Post
    I'm not sure what the objection is -- the description is rigorously correct. Someone (maybe you) linked to a youtube earlier, and I didn't hear the professor deny the correctness of the above description.
    Note that theyíre discussing transparency and that Dywyddyrís link is referring to a transparent material like from air to glass.

    Iím not sure why you didnít hear the objection. I linked the video at the exact spot where Professor Merrifield explains the problems with that explanation.

    Dywyddyr is smart enough to realize that his answer is incorrect and Iím sure he knows that my last reply was just me being a smartass.

    Hereís another one from Professor Moriarty.

    https://youtu.be/YW8KuMtVpug
     

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    Quote Originally Posted by Secular Sanity View Post
    Quote Originally Posted by tk421 View Post
    I'm not sure what the objection is -- the description is rigorously correct. Someone (maybe you) linked to a youtube earlier, and I didn't hear the professor deny the correctness of the above description.
    Note that theyíre discussing transparency and that Dywyddyrís link is referring to a transparent material like from air to glass.

    Iím not sure why you didnít hear the objection. I linked the video at the exact spot where Professor Merrifield explains the problems with that explanation.

    Dywyddyr is smart enough to realize that his answer is incorrect and Iím sure he knows that my last reply was just me being a smartass.

    Hereís another one from Professor Moriarty.

    https://youtu.be/YW8KuMtVpug
    Watching the snippets doesn't reveal anything other than expressions of taste. You are talking about right and wrong. Very different. The videos all explicitly acknowledge that reradiation (and superpositions thereof with the incident energy) is fundamental, so that's all good.

    What the speaker(s) shy away from for reasons of personal taste is the fact that the Feynman diagram for a photon in a dielectric medium has the photon always traveling at c.

    The only valid objection I could possibly see in Dywyddyr's wording is the use of "absorption," which to some could sound like the promotion of an electron in an atom to a higher-energy orbital. But that is a minor matter of semantics. It is completely rigorous to describe the action of a dielectric medium the way he expressed it. One might quibble about the explanatory power of that approach in a given circumstance -- de gustibus non disputandum est and all that -- but that's different to saying that such a description is wrong.
     

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    Quote Originally Posted by tk421 View Post
    Watching the snippets doesn't reveal anything other than expressions of taste. You are talking about right and wrong. Very different. The videos all explicitly acknowledge that reradiation (and superpositions thereof with the incident energy) is fundamental, so that's all good.

    What the speaker(s) shy away from for reasons of personal taste is the fact that the Feynman diagram for a photon in a dielectric medium has the photon always traveling at c.

    The only valid objection I could possibly see in Dywyddyr's wording is the use of "absorption," which to some could sound like the promotion of an electron in an atom to a higher-energy orbital. But that is a minor matter of semantics. It is completely rigorous to describe the action of a dielectric medium the way he expressed it. One might quibble about the explanatory power of that approach in a given circumstance -- de gustibus non disputandum est and all that -- but that's different to saying that such a description is wrong.
    Are you sure about that, tk421?

    Is that your final answer or would you like to call a friend? Perhaps, Dywyddyr?
     

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    Quote Originally Posted by Secular Sanity View Post

    Are you sure about that, tk421?

    Is that your final answer or would you like to call a friend? Perhaps, Dywyddyr?
    Very sure, thanks. As to "final answer", I subscribe to the scientific method, but to the extent that "my" answer is nothing other than what QED says when taken literally, it is final in the same sense that QED is final. If you have a quibble with QED, then please present your alternative formulation here. I'm sure that it would be edifying.

    From your behaviour, I infer that you aren't familiar with QED. I recommend reading de Grooth, "Why is the propagation velocity in a transparent medium reduced?", Am. J. Phys 65 (12), 1997. I just took a fresh look at it after many years, and I'd forgotten (or perhaps never noticed) that he presents a nice series expansion in which each term corresponds to propagation at c. It is only after summing over all paths that one finds the classical result of c/n. One may then interpret the result as saying, effectively, that the collective effect of propagation along all possible paths is to lengthen the distance over which the photon travels.

    To be clear, I am not saying that the classical textbook presentation, to which you apparently cleave with religious fervour, is wrong. I am, however, objecting very strongly to your charge that an interpretation from QED is incorrect. Just because someone expresses his dislike of QED's explanation in a youtube impresses me very little.
    Last edited by tk421; November 29th, 2017 at 12:35 AM.
     

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    Quote Originally Posted by Secular Sanity View Post
    Quote Originally Posted by tk421 View Post
    Watching the snippets doesn't reveal anything other than expressions of taste. You are talking about right and wrong. Very different. The videos all explicitly acknowledge that reradiation (and superpositions thereof with the incident energy) is fundamental, so that's all good.

    What the speaker(s) shy away from for reasons of personal taste is the fact that the Feynman diagram for a photon in a dielectric medium has the photon always traveling at c.

    The only valid objection I could possibly see in Dywyddyr's wording is the use of "absorption," which to some could sound like the promotion of an electron in an atom to a higher-energy orbital. But that is a minor matter of semantics. It is completely rigorous to describe the action of a dielectric medium the way he expressed it. One might quibble about the explanatory power of that approach in a given circumstance -- de gustibus non disputandum est and all that -- but that's different to saying that such a description is wrong.
    Are you sure about that, tk421?

    Is that your final answer or would you like to call a friend? Perhaps, Dywyddyr?
    This was a surprise to me as well. I wonder if the two descriptions may be reconcilable if one keeps in mind that what tk21 said is that the behaviour can be treated as a superposition of the light being transmitted and it being absorbed and re-emitted. If the re-emission component is stimulated emission, rather than spontaneous, then I presume it would continue to be in the direction and phase of the transmitted radiation.

    The bit that escapes me though is how the distinction between phase and signal velocity is treated.
     

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    Quote Originally Posted by tk421 View Post

    Very sure, thanks. As to "final answer", I subscribe to the scientific method, but to the extent that "my" answer is nothing other than what QED says when taken literally, it is final in the same sense that QED is final. If you have a quibble with QED, then please present your alternative formulation here. I'm sure that it would be edifying.

    From your behaviour, I infer that you aren't familiar with QED. I recommend reading de Grooth, "Why is the propagation velocity in a transparent medium reduced?", Am. J. Phys 65 (12), 1997. I just took a fresh look at it after many years, and I'd forgotten (or perhaps never noticed) that he presents a nice series expansion in which each term corresponds to propagation at c. It is only after summing over all paths that one finds the classical result of c/n. One may then interpret the result as saying, effectively, that the collective effect of propagation along all possible paths is to lengthen the distance over which the photon travels.

    To be clear, I am not saying that the classical textbook presentation, to which you apparently cleave with religious fervour, is wrong. I am, however, objecting very strongly to your charge that an interpretation from QED is incorrect. Just because someone expresses his dislike of QED's explanation in a youtube impresses me very little.
    Itís not just a matter of semantics. The duckís explanation is wrong. Photons are not absorbed and re-emitted by the atoms in the glass. The electrons in glass canít absorb any wavelengths of visible light to jump to higher energy levels. Thatís why itís transparent.

    Here is his answer...

    "Each time the light bumps into a particle of the medium, the light gets absorbed which causes the particle to vibrate a little and then the light gets re-emitted. This process causes a time delay in the light's movement so the more particles there are (the more dense the medium), then the more the light will be slowed down."

    https://ris.utwente.nl/ws/portalfiles/portal/6710958

    I read Bart G. de Groothís paper and reviewed Feynmanís lectures on it. Now, letís see if you can explain how any of this proves that the duckís answer is correct.

    Or perhaps, Dywyddyr himself would like to explain it.
     

  37. #36  
    Forum Freshman Secular Sanity's Avatar
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    Quote Originally Posted by tk421 View Post
    I am, however, objecting very strongly to your charge that an interpretation from QED is incorrect. Just because someone expresses his dislike of QED's explanation in a youtube impresses me very little.
    BTW, where in hell did I make the claim that an interpretation from QED was incorrect? And where in the video does he express his dislike for QED’s explanation? He pulls Feynman’s lectures from his shelf and goes straight to Chapter 31, for Christ’s sake.
    The Feynman Lectures on Physics Vol. I Ch. 31: The Origin of the Refractive Index

    Oh, well, you must have just skimmed Dywyddyr’s answer because it’s clear that what he’s describing is an atomic transition. No worries, though.

    Hey…would you like to join a few of us at a more casual discussion science forum? You never know, this place may crash again. The owner of the other one is always around, easy to get ahold of, and there’s no fussy little moderators. In fact, there’s no moderators at all. We could use a few more sciencey types.

    Would love to have you. You, too, Dywyddyr and how 'bout you Exchemist? It sure beats Sciforums.

    https://www.scivillage.com/index.php

    Cheers!
     

  38. #37  
    Genius Duck Moderator Dywyddyr's Avatar
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    So...
    When the electric field of the source acts on these atoms it drives the electrons up and down, because it exerts a force on the electrons. And moving electrons generate a fieldóthey constitute new radiators. These new radiators are related to the source S, because they are driven by the field of the source.
    Essentially, then, the light gets "absorbed" by the electrons of the material and those electrons then re-radiate.

    With regard to the other (linked) forum: I'm already a member, but it's not somewhere I frequent much (nor particularly wish to given certain posters and what utter crap they manage to get away with). FYI, it was suggested at one point that I be made a mod there - I turned it down flat, the forum's (IMO) too far gone for that.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
     

  39. #38  
    Forum Freshman Secular Sanity's Avatar
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    Quote Originally Posted by Dywyddyr View Post

    So...
    When the electric field of the source acts on these atoms it drives the electrons up and down, because it exerts a force on the electrons. And moving electrons generate a fieldóthey constitute new radiators. These new radiators are related to the source S, because they are driven by the field of the source.
    Essentially, then, the light gets "absorbed" by the electrons of the material and those electrons then re-radiate.
    Nope. The photons do not get "absorbed" by the electrons. If it was absorbed by the electron, it would have to give up its energy to get that electron transition to happen, which isnít the case in transparent material. If itís absorbed, it doesnít make it through the glass, and it would be opaque.

    When the light comes into contact with the glass it causes the electrons to start vibrating. The vibrations are passed to neighboring atoms, which in turn cause the electrons to emit their own light, but most of this light gets canceled out in all other directions with the exception of the forward direction.

    These vibrational modes can absorb a photon, though, and convert it to heat, but the solid is then opaque to that particular photon. This absorption process has to be distinguished from the fundamental absorption process that youíre describing, because what youíre describing is a very different effect, and it is wrong. You should read 31-4 the section on absorption.

    Quote Originally Posted by Dywyddyr
    With regard to the other (linked) forum: I'm already a member, but it's not somewhere I frequent much (nor particularly wish to given certain posters and what utter crap they manage to get away with). FYI, it was suggested at one point that I be made a mod there - I turned it down flat, the forum's (IMO) too far gone for that.
    Suit yourself. You canít blame a girl for trying.

    FYI, I was the one that suggested it because you seemed intelligent. Silly me.
     

  40. #39  
    Genius Duck Moderator Dywyddyr's Avatar
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    Quote Originally Posted by Secular Sanity View Post
    Nope. The photons do not get "absorbed" by the electrons.
    Hence the scare quotes...

    If itís absorbed, it doesnít make it through the glass, and it would be opaque.
    Apart from the electron re-radiating, of course.

    FYI, I was the one that suggested it because you seemed intelligent.
    Well yeah. But that forum doesn't manage to be. Too many inane posters.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
     

  41. #40  
    Forum Freshman Secular Sanity's Avatar
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    Quote Originally Posted by Dywyddyr View Post
    Apart from the electron re-radiating, of course.
    You canít just admit that you were wrong, eh?

    Quote Originally Posted by Secular Sanity
    because you seemed intelligent
    "seemed"

    Quote Originally Posted by Dywyddyr
    Well yeah. But that forum doesn't manage to be. Too many inane posters.
    In other words, your high-caliber posters need babysitting.

    I like Scivillage because it is the one place where everyone is welcome.

    Some of the members think of it as an online coffee shop. A place where somebody might drop an interesting tidbit or a topic to chat about. I think of it as pub where you can enjoy an occasional brawl without having to tip toe around an overly defensive moderator prone to binge banning. Werenít you even banned from here at one time?

    Who owns this place? Do you even know?

    Well, anyhow, if you need my help with any future misconceptions that you may have, you know where to find me.

    See you later, little ducky.
     

  42. #41  
    Bullshit Intolerant PhDemon's Avatar
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    This guy is just trolling, ignore or ban but stop feeding...
     

  43. #42  
    Genius Duck Moderator Dywyddyr's Avatar
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    Quote Originally Posted by Secular Sanity View Post
    [You canít just admit that you were wrong, eh?
    According to Feynman (your own link), I'm not wrong.

    In other words, your high-caliber posters need babysitting.
    It's funny how you manage to get that from what I actually wrote.

    I like Scivillage because it is the one place where everyone is welcome.
    Including the morons who can't, or won't, approach things scientifically.

    Some of the members think of it as an online coffee shop. A place where somebody might drop an interesting tidbit or a topic to chat about. I think of it as pub where you can enjoy an occasional brawl without having to tip toe around an overly defensive moderator prone to binge banning.
    So not a science forum then?

    Werenít you even banned from here at one time?
    Nope.

    Who owns this place? Do you even know?
    Yup.

    Well, anyhow, if you need my help with any future misconceptions that you may have, you know where to find me.
    No thanks.
    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
     

  44. #43  
    Forum Freshman Secular Sanity's Avatar
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    Quote Originally Posted by Dywyddyr View Post
    According to Feynman (your own link), I'm not wrong.
    Read all of it.

    Quote Originally Posted by Dywyddyr
    It's the absorption and emission which slows it down.
    When a light wave strikes the surface of glass, it sets the electrons vibrating at a certain frequency. This frequency is not the resonant frequency of the glass. The vibrations pass from the surfacing atoms to the neighboring atoms and then on to more atoms through the bulk of the glass. The frequency doesnít change when the vibration passes from one atom to another. Once this energy gets to the other side of the glass it is then re-emitted from the opposite surface. The light is not absorbed because the frequencies do not match the natural frequencies in the glass. That's why it is transparent. It is transmitted. If it strikes a material with the same frequencies, those electrons will absorb the energy and transform it into vibrational motion, which also interacts with neighboring atoms by converting its vibrational energy into thermal energy. Never again to be released in the form of light. Capisce?

    https://en.wikipedia.org/wiki/Refrac...ic_explanation


    Quote Originally Posted by Dywyddyr View Post
    Including the morons who can't, or won't, approach things scientifically.
    Oh, like this one here, who obviously doesnít have the ability to add anything other than an ad hominem.

    Quote Originally Posted by PhDemon View Post
    This guy is just trolling, ignore or ban but stop feeding...
    Quote Originally Posted by Secular Sanity
    Werenít you even banned from here at one time?
    Quote Originally Posted by Dywyddyr
    Nope.
    Oh, right, you were demoted. My bad, sorry.
     

  45. #44  
    Forum Radioactive Isotope Paleoichneum's Avatar
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    No, He actually wasn't. He was inappropriately banned by a former Admin in a fit of spite, who's posts were rightly (per the forum members) moderated by Dywyddyr. That same admin then went on to essentially crash the forum and it wasnt until a site reset months later by the owners did the other mods and admins get access back.

    So please stop making false assertions.
    If more of us valued food and cheer and song above hoarded gold, it would be a merrier world. -Thorin Oakenshield

    The needs of the many outweigh the need of the few - Spock of Vulcan & Sentinel Prime of Cybertron ---proof that "the needs" are in the eye of the beholder.
     

  46. #45  
    exchemist
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    Quote Originally Posted by Secular Sanity View Post
    Quote Originally Posted by Dywyddyr View Post
    Apart from the electron re-radiating, of course.
    You can’t just admit that you were wrong, eh?

    Quote Originally Posted by Secular Sanity
    because you seemed intelligent
    "seemed"

    Quote Originally Posted by Dywyddyr
    Well yeah. But that forum doesn't manage to be. Too many inane posters.
    In other words, your high-caliber posters need babysitting.

    I like Scivillage because it is the one place where everyone is welcome.

    Some of the members think of it as an online coffee shop. A place where somebody might drop an interesting tidbit or a topic to chat about. I think of it as pub where you can enjoy an occasional brawl without having to tip toe around an overly defensive moderator prone to binge banning. Weren’t you even banned from here at one time?

    Who owns this place? Do you even know?

    Well, anyhow, if you need my help with any future misconceptions that you may have, you know where to find me.

    See you later, little ducky.
    Is this needling and patronising tone your habitual mode of interaction? If it is, I'm less sure that joining you on this other site would be to my taste. I prefer to debate these issues in such a way that the participants feel encouraged, rather than discouraged, in continuing.
     

  47. #46  
    Forum Freshman Secular Sanity's Avatar
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    Quote Originally Posted by Paleoichneum View Post
    He was inappropriately banned by a former Admin in a fit of spite.
    My bad, but he just said that he was never banned.

    I only asked about the problems with the forum because of what Markus said.

    http://www.thescienceforum.com/announcements/46833-forum-back.html#post608056


    Quote Originally Posted by Exchemist
    Is this needling and patronising tone your habitual mode of interaction? If it is, I'm less sure that joining you on this other site would be to my taste. I prefer to debate these issues in such a way that the participants feel encouraged, rather than discouraged, in continuing.
    Patronizing? Itís Dywyddyr for Christ's sake.

    If calling you lazy is patronizing...then yes, I'm a little bit of a smart-ass.

    Remain dry underwater | Page 2 | Sciforums

    Well, fuck me for inviting you guys, right?

    Good day to you, Exchemist.
     

  48. #47  
    Forum Radioactive Isotope Paleoichneum's Avatar
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    Given the situation surrounding the ex admins implosion and subsequent tanking of the forum as a whole, it doesnt count, in my opinion, as it was done by someone actively trying to destroy and not help.
    If more of us valued food and cheer and song above hoarded gold, it would be a merrier world. -Thorin Oakenshield

    The needs of the many outweigh the need of the few - Spock of Vulcan & Sentinel Prime of Cybertron ---proof that "the needs" are in the eye of the beholder.
     

  49. #48  
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    Quote Originally Posted by Paleoichneum View Post
    Given the situation surrounding the ex admins implosion and subsequent tanking of the forum as a whole, it doesnt count, in my opinion, as it was done by someone actively trying to destroy and not help.
    And don't forget the Admin who demoted the Duck also locked out the other Admin(Kalster) and then absented himself from the forum

    Secular Sanity go fuck yourself and do us all a favour.
     

  50. #49  
    Bullshit Intolerant PhDemon's Avatar
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    ^ Like.
     

  51. #50  
    exchemist
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    Quote Originally Posted by Secular Sanity View Post
    Quote Originally Posted by Paleoichneum View Post
    He was inappropriately banned by a former Admin in a fit of spite.
    My bad, but he just said that he was never banned.

    I only asked about the problems with the forum because of what Markus said.

    http://www.thescienceforum.com/announcements/46833-forum-back.html#post608056


    Quote Originally Posted by Exchemist
    Is this needling and patronising tone your habitual mode of interaction? If it is, I'm less sure that joining you on this other site would be to my taste. I prefer to debate these issues in such a way that the participants feel encouraged, rather than discouraged, in continuing.
    Patronizing? It’s Dywyddyr for Christ's sake.

    If calling you lazy is patronizing...then yes, I'm a little bit of a smart-ass.

    Remain dry underwater | Page 2 | Sciforums

    Well, fuck me for inviting you guys, right?

    Good day to you, Exchemist.
    Ah yes, an obsessive, point-scoring cunt, indeed. Just the sort of person we admire on this forum. Bye. [click]
     

  52. #51  
    Moderator Moderator Markus Hanke's Avatar
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    MOD NOTE: Enough of this, I donĎt like the tone of this thread. Locked.
     

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