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Photonic vacuum and atomic stability

  1. Mar 5, 2015 #1
    Hi friends, this is my third post of my curiosity. :woot:
    First of all a photonic vacuum (as defined by me) is a region of space where there doesn't exist any type of photons or EM radiations ( those too which are beyond the detection of our present tech..... i.e. including each and every radiation of EM spectrum).
    Now my first question is does there exist any place like this?
    If not then is it possible to create one? (My hypothesis= not possible at least now)

    We know that every region in space (at least on earth) is full of some sort of radiation (like microwaves which are detectable or also some of them beyond our detection like hypothetical cosmic radiations which we are not aware of).
    Now according to our modern atomic model electrons revolves in certain stationary orbitals which are quantised. All of these atoms exist in space along with other radiations, continuously continuously emitting and absorbing radiations of particular frequency (as they show spectral lines) while maintaining their equilibrium in respective orbitals.

    Now consider the following thought experiment....
    Assume there exist a photonic vacuum in your lab. Now you have picked up a single atom of any type and placed in that photonic vaccum. My questions are:
    Will atom be able to maintain its stability?
    Will its stationary states remain at the same levels or will they change?
    As there are no photons for electrons to maintain their orbits won't they lose their energy and fall into the nucleus destabilising the whole atom? ( here I am not stating Rutherford's drawbacks but I asked this question assuming that atoms exist in reality because of continuous supply of radiation energy to them to maintain the electrons in their stationary orbits. I hypothesized that electrons in their stationary states maintain equilibrium by opposing the electro static force of attraction of nucleus with the energy from photons. Since they continuously show dark lines in absorption spectrum I think this is that energy that electrons are using. Also it may also be using energy from other region of spectrum which are available to maintain their stability.)

    Also my question is will a particular atom show different line spectrum for different regions of EM spectrum. For e.g I know only about visible light line spectrum of atoms. What will happen to pattern of line spectrum if we only passed say gamma rays through them and observe the gamma ray line spectrum? Will some pattern or line spectrum even exist in gamma region as in the visible region?

    #To summarise, my overall question is will atoms ever exist in photonic vacuum? Why or why not?

    (Note: I am still young in physics so I may not know if some modern theories have already discarded or proved the above questions. So please do tell me more, I want to learn. also if I was not able to ask my question properly please do tell me. I will elaborate as much as I could. Thanks in advance:-p)
    Last edited: Mar 5, 2015
  2. jcsd
  3. Mar 5, 2015 #2
    According to quantum mechanics it is not possible to have a region of space without any photon.
    If you want a region of space without photons you can detect, probably you can have it between two metal plates, separated by a length which is smaller than half of the smallest measurable wavelength. See Casimir effect.

    Atoms show spectral lines only if the absorb/emit a photon. Some atoms stay without absorbing/emitting photons for extremely long times.

    See Purcell effect.
    The "stationary states" probably change with/without radiation, see dressed states in quantum mechanics.
    However electrons do not maintain their orbits because they are absorbing/emitting photons, but because otherwise they would violate Heisenberg's uncertainty principle.

    Electronic transitions happens in a large range of frequencies, from ~ GHz to the frequency associated to the ionization energy.
    If you "probe" an atom with higher frequencies, e.g. gamma, ..., what you are going to see is probably an absorption spectrum for the excitations of the nucleus. See. nuclear gamma spectroscopy.
  4. Mar 5, 2015 #3

    Simon Bridge

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    What you are calling a photonic vacuum sounds like a classical vacuum. i.e. a volume of space with nothing in it - except what we put there.
    Quantum mechanics shows that what we are used to calling "nothing" is better thought of as a kind of foamy mess of virtual particles - including virtual photons.
    But I think it is possible to answer your questions in terms of the classical vaccuum - if I have understood you properly.


    They remain the same. The stationary states you read about are actually calculated on the assumption there are no outside influences on the atom.

    No. Photons from the surrounding volume are not required to maintain stability.

    This idea is simply wrong - you can safely discard it.

    The spectral lines of atoms continue throughout the electromagnetic spectrum, not just the visible part. Electronic transitions may be very small, giving infra-red lines, or very large, giving ultra-violet. The frequency of the emitted light depends on the energy of the transition so there is a limit to how high in frequency you can get.

    Short answer: Yes - because that is what they already do.
  5. Mar 5, 2015 #4
    Thank you very much sir Simon.
    OK, after safely discarding my false hypothesis of electrons maintaining stationary States using photons, I still have one more doubt.
    When we illuminate an atom with visible light(or any other region of EM spectrum) we see spectral lines in absorption spectrum, right!, and that too continuously (means without any time lags in between).
    So if they are neither using this absorbed energy for maintaining stationary states nor there is a time lag in between (time lag in the sense they are returning to their original level {after exciting to higher level due to absorption} and emits photons instead of absorbing one in this time interval), then where is this energy used? Or where is this energy going?
    Also as there is no time lag and no use of energy for maintaining stationary states then wouldn't the electrons go on absorbing energy and will keep on rising their levels until they are ionised? Wouldn't this make atom unstable? ( this is just an opposite of Rutherford's drawback)

    Also can anybody please explain why my above hypothesis( which I was told to dicard safely) is false? Please elaborate deeply, please,please! I am very curious!
    Last edited: Mar 5, 2015
  6. Mar 6, 2015 #5

    Simon Bridge

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    Once a photon is absorbed, the atom may be in a new stable state that is not the ground state, and stays there.

    It need not return to the ground state at all, nor does it have to do this directly. There may be a delay between absorption and emission.
    For example, phosphorous absorbs light from a wide range of wavelengths but predominantly radiates in a narrow range in the visible spectrum and after a long delay - which is why it glows in the dark.

    The hypothesis could be discarded safely because it is not supported by experiment. It is so completely demolished by experiment that it would be tedious to go into it - you should look through pretty much any introductory text book on physics instead.
  7. Mar 6, 2015 #6


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    It is perfectly possibly to engineer environments where there are no (real) photons that can interact with your atom/system. You could e.g. take a small metallic box and cool it down to millikelvin temperatures. Due to the low temperature the only black body photons around will have quite long wavelengths (several mm) and if your box is small enough there are no modes to support them.
    This is routinely done in experiments where we want to protect sensitive devices from the environment (although it is rarely done for atoms, there is no real need).
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