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How can light absorbing material absorb forever?

  1. Mar 4, 2015 #1
    It is my understanding that a photon is absorbed when the photon's energy is sufficient to excite an electron into a higher energy state.

    So if I shine a light unto a light absorbing material, let's say a thin black metal, then why the surface never reaches a saturated state?

    I mean, if we keep the light pointing continuously on the black surface for years, the color never varies. To put it in another way. If the light excites every available electron on that surface, what happens when there are no more electrons to excite? Shouldn't the light be then 100% reflected or the light simply goes through the material like a glass?

    Moreover, if photons do not stay at an excited energy level for more than a nanosecond, where does all that photon energy go? Is it lost as kinetic energy? Or radiated as another form of energy?

    This makes me think that the current understanding of photon interaction with atoms is partially wrong. The frequency (energy level) of the photons DOES have a direct relation to the electron's energy transition.

    This electron "exciting" and "emission" cannot be true. I am thinking that the behavior of photons striking a surface is more akin to the behavior of radio waves as they strike surfaces. Which is better described as kinetic interactions. After all, light is an EM wave.

    I think that light is absorbed by the atoms acquiring more momentum, thus the material gets hotter. Not this explanation of electron absorption.
    Last edited: Mar 4, 2015
  2. jcsd
  3. Mar 4, 2015 #2


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    It depends on the frequency of the light and the material. Some photons will only excite vibrations in the material.

    Because the excitation is very short lived.

    Depends on the material. Haven't you ever seen fabric with faded colors from being in the sun? How about yellowed newspaper?

    Fire. You don't even need that much "excitation" before something will start burning.

    It becomes thermal energy, and yes, some of that energy will be radiated back, look up blackbody radiation.

    I guess you haven't studied the subject, because you would be amazed at how well the subject of atom-photon interactions is well understood. Also, materials can't be seen as behaving as a collection of individual atoms. For example, fabrics are better seen as collections of molecules, and solids display collective behaviors on a big scale.

    Who said it doesn't?

    Again, you can't see a solid as made up of independent atoms. For metals in particular, you get electrons that move around.

    For starters, you can look at the FAQ https://www.physicsforums.com/threads/do-photons-move-slower-in-a-solid-medium.511177/ [Broken]
    Last edited by a moderator: May 7, 2017
  4. Mar 5, 2015 #3
    I apologize for being slow. I still don't get the big picture. We shine a light onto the thin black metal. It is black because it "absorbs" the photons. The theory is that the photons got absorbed as electrons are exited into higher orbits, which almost instantly the electrons bounce back into their preferred orbit, thus radiating an equal amount of photons. That would mean that the surface can never be black. To my simple mind, black means that the photons got absorbed. That is, the photons do not come out of the material. Therefore, that photon energy has to be transformed into something else. I will read up on blackbody radiation.
  5. Mar 5, 2015 #4


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    The photons that come out are not at the same frequency that those that were absorbed. After absorption, the energy gets redistributed into many different degrees of freedom, and mostly vibrations. These vibrations then relax by emitting photons in the infra-red part of the spectrum. That's why thermal imaging is done by IR cameras.
  6. Mar 5, 2015 #5
    That is the ticket!! Many thanks.
  7. Mar 5, 2015 #6
    Dr. Claude, I want to start a discussion thread on light double slit experiment. It got denied by the forum because it needs to connect that to an existing accepted interpretation of quantum mechanics before it is suitable for discussion. It's not a specific question. It is a new interpretation of the nature of photons (does not follow existing theories). The closest theory I've found is "quantum gravity". I really don't know how to get it into the forum to get feedback.

    I am still trying to wrap my head around this experiment. A photon has properties such as frequency and intensity and momentum and direction, even when the observer instrument has "collapsed" the wave function. So a free photon is definitely always a wave (not a particle). The detector's measurements tell us that both the "collapsed" photon and the "wave" photon are identical. Same frequency, same intensity, same momentum. The only thing that changes is its direction of travel. Moreover, the placement of the detector whether in front or back or at the slits causes the wave to "collapse". It this some trick of time dilation or projection? Not really.

    What all of this means is that the detector is not collapsing the photon itself. Rather, it is collapsing a "space field" that existed at the moment the photon was released. The photon rides this preexisting wave to determine its movement through space. This preexisting wave (space field or quantum field) was centered at the point when the photon was originally released. This wave is, in my opinion, a space density pulse. The photon is simply following its space field's tiny differences in density as it travels until it strikes the detector. When the observer "collapses" the wave function, what we really see is that the photon did not follow its space field to determine its trajectory, but went in a straight line. The photon is uniquely tuned to this space field but is be aware of other photon's space field as they pass by. All photons of the same frequency and intensity are identical. See how lasers work. This space field center instantly relocates to the photon's new location when the photon's energy is joined with a larger particle. I believe that all subatomic particles have a space field as well. This "space field" could also explain spooky action at a distance. There are more things about this "space field" idea I am still thinking about. Comments welcomed. Please no formulas. This is a thought experiment using simple logic.

    I think Lord Kelvin and Carl Anton Bjerknes were on the right track..

    Quantum gravity? Or whatever name we give it, is a theory in the right direction.
    Right now no one has come up with a good explanation of what is gravity. We can describe how it works. There are plenty of formulas out there.
    If we talk about gravity, we also have to talk about space and time. The traditional explanation as described by Einstein is that gravity, space, and time - is a "space-time" fabric where particles live. In my mind, space is another force of energy. Time, gravity, dark energy (anti-gravity), and inertia are effects of space. Particles (as expressed in Quantum theory) should not be seen as separate from the environment in which they exist. The assumption that a particle's influence is localized to its immediate vicinity is true for most of the forces. But not all.

    Composition of the universe
    70% expanding force (aka "dark energy", not explained with traditional gravitational equations)
    25% contracting force (aka "dark matter", not explained with traditional gravitational equations)
    5% contracting force (particle mass, gravity explained with traditional gravitational equations)
  8. Mar 5, 2015 #7


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    Thread closed for Moderation...
  9. Mar 5, 2015 #8


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    Discussions of personal theories or theories that do not follow mainstream science are not allowed here on PF. Our mission here at PF is to teach people about current, mainstream science as it is understood and practiced by the scientific community. Discussing personal theories runs counter to that goal and attracts far too many crackpots and other people who know little to nothing of mainstream science and do not care to learn about it. This thread shall remain locked.
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