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Properties of light

  1. Jan 25, 2008 #1
    Has the principal of light emission been discredited?
    If so, is it now considered to be an excitation process?
  2. jcsd
  3. Jan 25, 2008 #2

    Doc Al

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    What do you mean by "the principle of light emission"?
  4. Jan 25, 2008 #3
    Vibration Not substance

    Hi Doc,
    By emission I mean the principal of a physical substance existing a light source.

    I understand that matter and energy are one, but is light effectively energy in the form of vibration?
  5. Jan 25, 2008 #4


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    Er... take a charge particle, and shake it. You have light.

    So what "principle" here that has been "discredited"? You really ought to put some explanation here in your post, because it is rather vague. If you have a specific source that you learned from, that would help.

  6. Jan 25, 2008 #5
    Michelson-Morley looked for the aether but there experiment yeilded negative results.

    Relativity theory requires kinematics which seems to suggest a 'something' that alters the make up and / or dynamics of matter in relation to velocity! (thanks for last night Doc).

    In his book 'RELATIVITY' The Special and the General Theory, Einstein talks about the 'dynamic metric' of space and seems to be suggesting that 'empty' space is somehow capable of affecting change in material objects, that 'empty' space, offers resistance to motion.

    I am having trouble with the idea that 'empty' is equivalent to 'nothing' and that therefore what is being said is that 'nothing' is affecting 'something'?

    I must stress that I am in no way doubting the effects predicted by relativity theory, only trying to understand how those affects take place. The mechanics of the kinematics, if you see what I mean!

    We know that light is affected by gravity. Is it possible that the negative results of the aether detection experiment where due to some form of compressive effect that gravity had on the medium of propagation of light, (If such a thing exists)? That the medium of propagation might not be, as was assumed at the time, a non-inertial subtance with the ability to pass through all things unaffected.

    Is it possible that at the surface of the planet where the test took place, a hypothetical medium for the propagation of light could actually be synchronised with the gravitational field? And, therefore stationary with respect to the planets surface?

    I am trying to make my questions clearer as per the good advise I have recieved.

    The difference between emission and excitation hangs on the existence, or not, of a medium of propagation. Without that medium, then we have only the option of emission and if that is what you think I should accept, then I have another question. I will hold that question until I have a reply to the above.

    Hoping that I have not tested your patience too far already, I very much look forward to your kind reply.

  7. Jan 25, 2008 #6


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    I still don't see in here where you explain what "principal of light emission" that has "been discredited".

    .. and how did "excitation" got into this? You also are confusing the light source with the "medium" or vacuum that light propagates. Just because it requires a "substance" to create it doesn't mean it requires more substance to propagate it. These are different issues. Again, I shake some charges and create light. But that light then propagates in vacuum.

  8. Jan 25, 2008 #7
    OK, I'll try again.

    You shake some charges and create light, what is the light?

    Is the light part of the charge you shook, and does that part of the charge stay as an intrinsically cohesive separate entity that leaves the charge and travels as an individual item through a vacuum. That would be emission!

    Or, does the vibration you impart to the charge by shaking it, transfer to something that is surrounding the charge and then cascade through a medium, that would be excitation!

    which is it?

    By the way, I never stated that emission had been discredited, I asked if it had because of something I had read. I am not in favour one way or the other, merely looking for greater understanding.

  9. Jan 25, 2008 #8
    Ah, there is no aether if that's what you're asking. Light does not travel through a medium.
  10. Jan 25, 2008 #9
    If there is no aether, no medium, then is it fair to say that something leaves the shaken charge and travels across space as a separate thing?
  11. Jan 25, 2008 #10


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    A photon is an individual entity, if that's what you mean.
  12. Jan 25, 2008 #11


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    I really am not sure what you're getting at here, because your question seems to be asking for something beyond what we know. So how can a theory be discredited when it isn't there yet?

    It is well-known from classical E&M that accelerated charges emits light/EM radiation. Period. Now, starting from there, what exactly were you referring to when you say that an emission theory has been discredited? That is what I am seeking clarification for. As far as I can tell, it has been clearly verified that an accelerated charge (as in shaking it, for example) do emit radiation. Synchrotron centers all over the world make use of that in several different ways. What I'm interested in is trying to figure out what exactly such such emission theory that has been "discredited". That was my original question.

    Again, light emission and light propagation are two different issues.

  13. Jan 26, 2008 #12
    John Richard,

    The distinction between an electron's process of atomic energy level transition and its emission [absorption] of a photon may be muddied by quantum uncertainty. In other words, it may be impossible to exactly distinguish between the electrons (as in an atom) and photons (as interacting with an atom).
    Last edited: Jan 26, 2008
  14. Jan 26, 2008 #13


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    Er.. no it isn't!

    Look, I don't have to an "atomic transition" only to have emission and absorption. I have already described how, by simply accelerating charges, you get EM radiation. No "atomic transition" there, and you can very well separate out the photons created and the electrons.

    I can also do absorption that way. Put RF in an accelerating cavity. Then shoot electrons through it. Using a pick-up coil, look at the EM signal in the cavity with and without RF. You'll see a clean signal when there's no electrons, and you'll see a distorted signal with the electrons, because the electrons absorb the RF and use the energy for acceleration.

    Again, no "atomic transition" involved at all, and you can tell very well which is which. This is what is done in a typical accelerator facility, meaning, it is very common. And you need to describe these processes is classical E&M!

  15. Jan 26, 2008 #14
    Due to electrons having a wave nature and photons a particle nature, might measuring actual interactions between the two be indefinite? That is, can one tell whether radial acceleration of electrons takes place in atomic transitions, or where exactly in a cavity photons are absorbed or emitted? Where does the photon end and the electron begin?
  16. Jan 26, 2008 #15
    I am discovering difficulties presented by the relativity of syntax and vernacular!

    A) If by the word 'vacuum' I am to take it that what is meant is a void, an absolute emptiness, a zone containing 'no-thing'. And if light is able to pass through this 'vacuum'. Then the light, which has to be a 'some-thing', must have an intrinsic, encapsulated identity. This identity may be the 'photon', or a vibrating charge, or a zero rest mass particle with spin. But whichever it is, it passes through the 'void' and is at the end, what it was at the beginning. The thing emitted would be like a super tiny vessel that launched from the emitter and passed through the void. The source for such a thing would be an emitter. A launch pad for photons if you like.

    B) If, however, the 'vacuum' is not a 'void' after all. But is in fact populated by, let us say, tiny globes of elastic potential that can receive the vibration from a source, and pass it on from potential to potential via a kind of proximal cascade transfer process. Then the light from the source never actually passes through the vacuum. But the energy inherent in the vibration does. And this vibration brings the tiny globes of potential above the threshold of perception, by whatever method of detection we choose to use, and we call it light or radiation. Then the source for that vibration would be called an excitation device.

    My question regarding the veracity of the principle of light emission stems from a difficulty I am having which is as follows:

    If light is sourced from an emitter, (A above), and if that light source is mounted on a projectile travelling with a randomly variable velocity profile. How is the projectiles velocity communicated to the light so that the light can exactly negated the projectiles velocity and thereby maintain conformance with the rule for the consistency of light speed, (in vacuum).?

    Loren Booda, thank you very much for your link. I am enjoying studying your work and the work of those accessed by your sites links.

    ZappaZ, you have been very patient with me so far and I am grateful, perhaps the most useful point you have made is that I may be asking questions "beyond what we know." I had not considered that possibility!

    John Richard
  17. Jan 27, 2008 #16


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    Please be very careful of what you read on unsanctioned websites. Considering that you are still trying to learn this subject, you also can't tell if you are being given legitimate information or simply some unverified speculation.

  18. Jan 27, 2008 #17
    Yes, John, remember that the link I believe you refer to is part of my signature. My site should be considered speculative and be viewed critically.

    I believe the constancy of light speed in vacuo is one of relativity's two postulates, consistent with the theoretical geometry of relativity and all of its experimental measurements to date.
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