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Thread: Can light be trapped?

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    Flashaholic* AlexGT's Avatar
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    Question Can light be trapped?

    Hmmm. While talking to some friends this came up, can a beam of light be trapped? Kind of like inside a sphere where the inner surface is polished to a mirror, would light bounce inside it forever or would it fade away?

    Another one, What part of the atom sheds the photon when exited?

    Thanks!
    AlexGT
    Last edited by AlexGT; 12-25-2008 at 08:23 PM.

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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Can light be trapped?

    The photons get kicked out when an electron returns from an excited state to it's resting state and sheds the excess energy.


    Scientists have come up with a material that can slow down light dramatically (in the mph range) but I havent heard of light actually being trapped.

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    Flashaholic* AlexGT's Avatar
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    Default Re: Can light be trapped?

    So the electron sheds the photon? And would an element that is shedding photons transmutate to a different element?

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    Default Re: Can light be trapped?

    What you describe would theoretically work if the reflection was 100%, and there is no such thing in reality.

    However, I recently saw a science program on TV where a scientist had devised a way to slow light so much that she was able to make it come to a complete stop in a supercooled fluid cloud until released by a triggering laser pulse. The show didn't have much real detail on how the process worked exactly.

    What is happening on the atomic level when a photon is released is that an electron is moving from one orbital path around the nucleus to a lower energy orbit that is closer to the nucleus. This excess energy is released as a photon of light.

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    Flashaholic* AlexGT's Avatar
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    Default Re: Can light be trapped?

    So in theory an atom can emmit light and change elements because its loosing mass (The photon) until it becomes a hydrogen atom then it looses the last electron in the form of light, and dissapears? Correct?

    AlexGT

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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Can light be trapped?

    Yes, the electron releases the excess energy packet as a photon.

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    Default Re: Can light be trapped?

    Quote Originally Posted by AlexGT View Post
    So the electron sheds the photon? And would an element that is shedding photons transmutate to a different element?
    Photons are a release of energy. When an atom gain or sheds an electron, it stays the same element but it becomes an ion with a charge. The element is determined by the number of protons. As long as that doesn't change, it remains the same element. If a neutron is gained or released, it becomes an isotope of the same element.

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    Flashaholic tay's Avatar
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    Default Re: Can light be trapped?

    The electrical charge is dependent on the number of electrons, not their energy.

    Imagine a person driving around the world in a car. That's like being in the ground state (the lowest available energy level). Now imagine a person flying around the world in a spaceship. They're higher up, and going much faster, and have a lot more energy. But either way, there's still only one person travelling around the earth.

    The photon is massless, it is only energy. It's not a part of the element. If you have elements in an excited state (electrons are orbiting high and fast), they will drop down. The excess energy becomes a photon. If you're in the ground state (low and slow), and get hit by a photon, you'll absorb it and bounce up to the excited state.

    The electrical charge doesn't change, nor does the mass. Just the energy.

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    Default Re: Can light be trapped?

    Quote Originally Posted by AlexGT View Post
    So in theory an atom can emmit light and change elements because its loosing mass (The photon) until it becomes a hydrogen atom then it looses the last electron in the form of light, and dissapears? Correct?

    AlexGT
    I think you're confusing photon's with protons

  11. #11

    Default Re: Can light be trapped?

    Quote Originally Posted by AlexGT View Post
    Hmmm. While talking to some friends this came up, can a beam of light be trapped? Kind of like inside a sphere where the inner surface is polished to a mirror, would light bounce inside it forever or would it fade away?

    Another one, What part of the atom sheds the photon when exited?

    Thanks!
    AlexGT
    It's a thought exercise, because there is no such thing as a 100% reflective surface.

    Some energy will always be lost to heat, as the photons collide with atoms that comprise the reflector. Therefore, any light "trapped" inside would rapidly disappear.

    Therefore, as far as I know, there is no current physical framework that would allow the kind of an object that you're describing. Certainly, it would be incredibly useful if it could be developed, due to the ability to store an infinite amount of energy inside. However, our current understanding of the laws of physics does not allow for such an object to exist.

    The only thing that's similar to what you're describing would be an object with sufficient mass concentrated in a small volume, wherefore the curvature of space-time would be completely orthogonal, and thus light would no longer be able to get out. In other words... a black hole.

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    Flashaholic* NA8's Avatar
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    Default Re: Can light be trapped?

    Quote Originally Posted by DonShock View Post
    However, I recently saw a science program on TV where a scientist had devised a way to slow light so much that she was able to make it come to a complete stop in a supercooled fluid cloud until released by a triggering laser pulse. The show didn't have much real detail on how the process worked exactly.
    I saw that show too, It was an episode of The History Channel's The Universe, "Lightspeed". The work was done by Dr Lene Hau at Harvard University. The explanation was very vague. They compared it to teleportation. They are OUT THERE
    Last edited by NA8; 12-26-2008 at 10:26 PM.

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    Default Re: Can light be trapped?

    Nova episode on PBS:

    "Absolute Zero: The Race for Absolute Zero"

    Very cold temp, very close to Aboslute Zero (Zero Kelvin) can be used to slow down light to a standstill, effectively trapping it.
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    Flashaholic* Youfoundnemo's Avatar
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    Default Re: Can light be trapped?

    Actually photons have mass they can be trapped by sufficient gravitational feilds, I cant explain it as well as somebody out of highschool minght be able to but if there is anyone on the forums with a decent understanding of quantum mechanics they would be able to tell you that a photon acts not only as a "massles" particle of energy (or wave) but it can also be a electron which does have mass... like I said its getting into quantum mechanics which I dont quite have a full (or partial ) understanding of....

    Quote Originally Posted by tay View Post
    The photon is massless
    not bad coming from a sophmore right?
    Daniel Coble


    EDIT: the bose einstine condensate is capable of slowing light down to about the speed of a bicycle
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    *Flashaholic* PhotonWrangler's Avatar
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    Default Re: Can light be trapped?

    Quote Originally Posted by Youfoundnemo View Post
    EDIT: the bose einstine condensate is capable of slowing light down to about the speed of a bicycle
    That's what I was thinking of. I was watching that show out of the corner of my eye one day and I remember the part about being able to slow down light to the mph range. Thanks for the memory jog on the name of that custom soup they used.
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    Flashaholic tay's Avatar
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    Default Re: Can light be trapped?

    Quote Originally Posted by Youfoundnemo View Post
    Actually photons have mass they can be trapped by sufficient gravitational feilds, I cant explain it as well as somebody out of highschool minght be able to but if there is anyone on the forums with a decent understanding of quantum mechanics they would be able to tell you that a photon acts not only as a "massles" particle of energy (or wave) but it can also be a electron which does have mass... like I said its getting into quantum mechanics which I dont quite have a full (or partial ) understanding of....



    not bad coming from a sophmore right?
    Daniel Coble


    EDIT: the bose einstine condensate is capable of slowing light down to about the speed of a bicycle
    Frankly, I don't really 'get' the more complicated quantum mechanics, besides the basic Bohr/Heisenberg/Schroedinger tenets like - wave/particle duality, quantized energy levels, distinct quantum numbers (n, l, m, s) with one and only one electron for each number, photoelectric effect: the 'simple' Modern Physics where the photon is in fact a massless particle. We've still got just 3 spatial and 1 temporal dimension, and our subatomic particles are still limited to proton, neutron, electron, positron, and photon. When this simplicity is gone, I am sure I will miss it, and file it with geometrical optics, frictionless surfaces, the small angle theorem, and other fun but ill-fated assumptions.

    My point is simply to dispel the assumption of a previous poster that a photon was a mass particle contained within an atom, and gained or lost during ionization like an electron. We treat the photons as quanta of energy, and an high energy electron can become a photon and a low energy electron, or a photon and a low energy electron can become a high energy electron, photons can be gained or lost without changing the mass of the element - they are not conserved during events like an electron is (they can be spontaneously created or destroyed). Only the energy that they contain is conserved.

    Bose-Einstein condensation? That's when the windows get fogged up in the winter, right? I usually just use my car's defroster.
    Last edited by tay; 12-28-2008 at 10:56 PM.

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    Flashaholic* Youfoundnemo's Avatar
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    Default Re: Can light be trapped?

    Ouch, I think Ive been schooled, you just listed off atleast 10 things that flew over my head (hopefully 12th grade sci will help me figure out some of what you said) I didnt realize that you were trying to help a fellow CPFer out whith the assumption that a photon was part of an atom
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    Default Re: Can light be trapped?

    I'm not sure where people keep getting the incorrect idea that photons have mass. (This claim comes up again and again.)

    Massive particles must always travel at speeds slower than c (the speed of light in a vacuum). Light is made of photons, so if photons had mass, then the conclusion would inevitably be that light cannot travel at the speed of light.
    Andrew

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    Flashaholic* AlexGT's Avatar
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    Default Re: Can light be trapped?

    If a photon doesn't have mass, how is it that it can be affected by gravity?

    AlexGT

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    Flashaholic* LowBat's Avatar
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    Default Re: Can light be trapped?

    I thought that a photon wasn't truly a particle but simply could behave as one.

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    Default Re: Can light be trapped?

    well a photon is both a particle and a wave...their odd little creatures, once you get into the parts of atoms you get into quantum theorum which is very very erratic....

    @ asdalton, photons have mass how else would they be trapped by black holes?
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    Default Re: Can light be trapped?

    Physics classes are years behind me and I was never much interested in this stuff but IIRC, as others mentioned before, photons don't have a mass.

    The way black holes trap light is by "warping space" within their event horizon so much that all the paths fall down further into it and nothing can escape it. Stepping past that dodgy line makes space, time and the known laws of physics all kinds of funky so much that I won't even attempt to understand it.
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    Default Re: Can light be trapped?

    Quote Originally Posted by Youfoundnemo View Post
    @ asdalton, photons have mass how else would they be trapped by black holes?
    What is the mass of a photon?
    Andrew

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    Default Re: Can light be trapped?

    Both of you need a lesson in quantum mechanics, and string theorum. photons are electrons in an excited state, electrons have mass so do photons. the theory that "massless" photons is based on it general relitivity and general relitivity has been proven time and time again to be false when dealing with the extremely small things like atoms and sub atomic particles, Items on the atomic level and sub atomic level are governed by quantum mechanics and string theory @kungfuchicken if photons had no mass they wouldnt be affected by the fabric of space and time
    Last edited by Youfoundnemo; 12-30-2008 at 01:02 AM.
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    Default Re: Can light be trapped?

    It is not known absolutely for sure that photons do not have mass. However, there is an experimental upper limit on what that mass could be; and it's pretty darn small.

    Additionally, if photons had mass, there should be a third possible polarization for light, and electrostatic potentials should fall off as .


    photons "dont have mass because you can not measure its mass, one cant measure a photons mass at rest (how all other objects are measured) becuase once a photon is at rest it is no longer a photon but once again an electron and because a photon isnt always a particle that can be measured (even if it was at rest) sometimes they act as waves , the text book awnser it that no photons have no mass, but im positive that if you were to ask a scientist in the field of sub atomic particles that they would say that they do indeed have mass (in their particulate state) and that if they are acting as a wave they will have no mass. There is no way of saying definitavly that it has or doesnt have mass

    All I have to say is SHEEPLE, come on think for yourself and use reason not wikipedia and other internet sources
    Last edited by Youfoundnemo; 12-30-2008 at 02:13 AM. Reason: Sheeple
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    Default Re: Can light be trapped?

    links are your friend. wiki says photons have no mass

    http://en.wikipedia.org/wiki/Photon

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    Flashaholic tay's Avatar
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    Default Re: Can light be trapped?

    A photon cannot become an electron. What happens is that an electron can absorb or emit a photon in order to change its energy (because a photon is just an energy packet... it's not necessarily visible light).

    The way to slow a photon is running it through a refractive material. Diamond slows it down pretty good, to about a third of it's normal velocity. Or, you can hit an electron with it, which will then absorb the photon.

    But, the photon does not become an electron, and the electron does not become a photon. Atoms emitting light don't lose mass, only energy. Atoms absorbing light don't gain mass, only energy.

    GL with getting this in 12th grade. If you're doing AP Physics, you'll be stuck in Mechanics and Electricity and Magnetism. We like to get that junk out of the way before the fun quantum physics and optics
    We shouldn't get into wave/particle duality.

    Ever heard of young's classic 1801 double slit interference that proved the wave nature of light by creating bright and dark fringe patterns? Even if one photon is run through at a time, so there is no way for it to interfere with another photon, it will still create the fringe patterns. Mindblowing, right?

    Photons will interfere with each other like waves would, and can overlap like waves.
    But, they can be a discrete particle, with a quantized energy, as proven in the photoelectric effect (which Einstein got the Nobel prize for, not for special or general relativity)

    A photon doesn't decide "today ill be a wave", they have some properties of both, and a lot of how they act depends on which properties of them we observe. But the key point is that they're an energy packet, not a distinct piece of mass like an electron. Photons can spontaneously split, combine, be absorbed, or be emitted. They are simply quanta of energy.

    We can extend this to the fact that massive particles like molecules or people behave in a wave manner, but with such a long wavelength that the oscillations are not noticeable.

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    Flashaholic* asdalton's Avatar
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    Default Re: Can light be trapped?

    Youfoundnemo,

    I and other commenters have posted evidence for our position. Please post your own contrary evidence (besides strings of buzzwords and confident assertions) before deciding who "needs a lesson."
    Andrew

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    Default Re: Can light be trapped?

    @Youfoundnemo,
    I'll agree that I could certainly use a lesson in quantum theory, since I've never had one before.

    However, admitting that I ain't the brightest light in the closet, I'm still pretty sure of myself when I think you've got a few things confused with photons and electrons, which are vastly different things as far as we understand them. Some of the simplest equations (even I can understand =P) that you can look up can illustrate how your theory is flawed with the amount of energy required to accelerate a particle up to c0 or the way you calculate the energy carried by photons and electrons for example.

    In any case, inquiring scientists in schools probably won't give you as much of a consensus to your question because, as you mentioned, there are a lot of things that aren't known for sure. At least, it'll give you an idea of how fascinating and unintuitive it really is; in fact, some of the most downright confusing concepts I've ever heard of are in the quantum physics book.

    Also, please don't feel discouraged for finding yourself in an impass; as happy as I am to see you share my skepticism towards wikipedia and its likes, if you plan on going into this field, I advise you to be as open minded as you can be. =)
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    Flashaholic tay's Avatar
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    Default Re: Can light be trapped?

    Well, the rest energy of an electron is equivalent to a photon with a wavelength of about 0.0001 femtometer. That's one seriously energetic photon.

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