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Does Slow Light Respond to Gravity

  1. Mar 13, 2013 #1
    Does "Slow" Light Respond to Gravity

    "Lene Vestergaard Hau (born in Vejle, Denmark, on November 13, 1959) is a Danish physicist. In 1999, she led a Harvard University team who, by use of a superfluid, succeeded in slowing a beam of light to about 17 metres per second, and, in 2001, was able to stop a beam completely." --wikipaedia
    Does anyone know if this beam of light would be able to be seen to drop towards the earth because of the effect of gravity?
     
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  3. Mar 13, 2013 #2

    ZapperZ

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    Why would it do such a thing?

    Zz.
     
  4. Mar 13, 2013 #3
    Does "Slow" Light Respond to Gravity

    Light in a vacuum traveling near a massive object will be deflected towards the mass because gravity acts on light just as it does on matter. No? I'm asking if this same thing occurs in a medium that slows light enough to measure visually.
     
    Last edited: Mar 13, 2013
  5. Mar 13, 2013 #4
  6. Mar 13, 2013 #5

    ZapperZ

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    Not in the way that a particle with a mass would. Read our FAQ!

    Furthermore, one should really read the actual paper here. If you have the impression that there are these photons sitting still doing nothing, you are very mistaken.

    Zz.
     
  7. Mar 13, 2013 #6

    DrClaude

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  8. Mar 13, 2013 #7
    Does "Slow" Light Respond to Gravity

    Terrific reference and lead for further reading, Dr. Claude. Thank you.
     
  9. Mar 13, 2013 #8
    No, I don’t think that.

    Fine, now you are saying not in the way that a particle with mass would, but you do admit that light is affected by gravity. But that’s not what you indicated in post #2.

    The OP had a legitimate question, and you proceeded to give a glib and antagonist reply like you often do. It seems like you get more pleasure out of trying to derail someone’s post than trying to help them. It’s sad really. You are very intelligent, and your FAQ’s (and posts) are very helpful.
     
  10. Mar 13, 2013 #9

    ZapperZ

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    You got it all wrong.

    When a question like this pops up, I have to figure out what causes such a question, meaning I want to know what the OP knows. That why I want to know why he/she thinks that a "stopped light" in this case would be affected by gravity. Is it simply due to GR?

    Furthermore, would that apply to this case? After all, no one seems to care when light gets absorbed by a lot of surfaces. No one seems to want to know about the gravitational effects in those cases. Why is that? Light is stopped when it gets absorbed there.

    One simply cannot give out any answers one likes at any level without figuring out the context and what the OP can understand.

    Zz.
     
  11. Mar 14, 2013 #10
    Ok. Fair enough.

    I am only a student of physics myself, and I learn by the reference material as well as the forum posters.

    What I think I know about the current discussion is that a photon has no rest mass, and therefore is not affected by gravity in the usual way of thinking.

    However, if I have this correct, relativity shows that mass is described with the energy-momentum tensor. Therefore, although the photon has no rest mass, it certainly has energy/momentum, and in that way (using the mathematical methods of relativity) participates under the influence of gravity. The effects are of course small compared to the amount of energy of objects with mass, even small ones like electrons.

    Am I on the right track?

    BTW, that is an excellent point about considering the gravitational influence of light after it is absorbed. Gravity doesn't stop its influence after absorption, nor does it suddenly start when a photon is emitted.
     
  12. Mar 14, 2013 #11
    Something I may have missed. If the original question is indicating that there might be something about "slow light" per se that causes its influence by gravity to change, I believe the answer to that question is no.

    Subtract out all the factors causing the light to be slow, and what remains is the same gravitational influence that normal speed light experiences, at least with respect to the vector component in the direction of the gravitational source.
     
  13. Mar 15, 2013 #12

    DrDu

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    In general the reduced speed of light in media is due to the energy being partly present in the form of photons and partly in the form of electronic excitons (or phonons in the IR) or some other exitation of the medium. In slow light, the energy is most of the time stored in exitations of the medium. So I would guess that the gravitational deflection of slow light is qualitatively not different from the deflection of exitons or phonons in a gravitational potential, i.e. completely negligible.
     
  14. Mar 15, 2013 #13

    ZapperZ

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    Remember the original post:

    So this is not a "slow light" issue but also a "stopped light" issue.

    Now of course there is a difference between shinning light onto a black piece of paper versus what is done in these stopped light experiments. In the former, you cannot "replay" that light. It is lost via heat, etc. The in the latter, both the energy and all the information that was in that light can be recreated on demand! It was why I was emphasizing that this is not simply a bunch of photons frozen and waiting to get out, and why I said that one should actually read the paper (or newer ones that have done the experiments in novel ways). As DrDu has stated, the light has been absorbed into the media - it literary no longer exists in its original form. All the information about that light has been "recorded" in the atomic gas in Hau's experiment, and waiting to be replayed.

    In other words, not that much different than shinning a light onto a black paper. This is why I wanted to know in the beginning why the OP thinks that gravity plays a role here. Why is gravity suddenly important in this experiment, but not when light is absorbed under everyday occurrences.

    And just in case people missed it, just this week, PRL published TWO papers on this "catch and release" of photons.

    http://physics.aps.org/articles/v6/25

    The two papers do this using different mechanisms. And if you click on that link, you also get free access to the actual papers. So for people who only depend on that rumor mill called Wikipedia for your primary source of information, here's your chance to get to read the actual sources.

    Zz.
     
  15. Apr 5, 2013 #14
    Does "Slow Light" Respond to Gravity--continued.

    In regards to Zz's reply--Zz states: In other words, not that much different than shinning a light onto a black paper. This is why I wanted to know in the beginning why the OP thinks that gravity plays a role here. Why is gravity suddenly important in this experiment, but not when light is absorbed under everyday occurrences.

    To answer your question, Zz, as to why I ask if gravity could play a role is because photons or the their energy/ information content are not simply absorbed by the atoms of a medium but are also conveyed atom to atom and/ or through intervening space. There would seem to be a component Of this energy that interacts with the atoms of the medium but also a component that moves between electrons, either as a resonance or as a classical wave or by some other mechanism. As long as there is directionality, my question is, "Is this directionality effected by spacetime curvature near a mass?" It would appear, at least as a naive first approximation, that it could.

    There is no "suddenly" about it, Zz. Gravity, as curvature of spacetime, is omnipresent. The path of light whether in vacuo or through a medium could be thought, at least naively, to be deflected in the presence of mass. Whether true or not is not known a priori. Only after testing.
    Furthermore, light through a medium shares similarity to light absorbed by a black body only with respect to the absorption aspect of the process. What happens to the energy or information dynamics after that initial absorption is a totally different issue. The potential effect of gravity on these dynamics was at the heart of my question. For example, photon energy absorbed by black paper and later released is released omnidirectionally. It is totally undirected and random. In a medium, at least for the most part, the energy flows in the same direction as the original beam. This is quite different from the former mentioned process.
    I hope that gives you an idea of why I asked the question in the first place. I apologize for not being clearer. But the question should also give you an idea of what level my understanding of physics might be. That's what questions do.
    And, yes, I have read your FAQs. I understand the predicament you guys are in when trying to answer questions from a large group of people with very diverse backgrounds and very different levels of knowledge, understanding and thinking. It must be very frustating. It must be just as frustrating as when I hear a response such as "why would you think such a thing?" from an expert in a field instead of the more gracious, "I (the expert) don't understand why gravity might effect the transmission of light through a medium."
    Your FAQs bring out valid points especially as to why all questions may not be entertained equally. This make sense. But your FAQs also betray an underlying inconsistency because I am of the opinion that it is totally irrelevant from whom a question originates, or her background, or her level of education or anything else about her. The question itself will give you all you need to know about the asker. These background questions are really designed to function as are defenses to protect wounded egos. On one hand, when it is clear the questioner is at a lower level of education, the expert can play the doting or patronizing pedagog who can garner great satisfaction from imparting his great knowledge to the novice and therefore display proudly his insight into how the world works. Very satisfying indeed.
    On the otherhand, when it is clear the questioner is as advanced or more advance than the expert, precautions are taken with the manner of response to protect his conceit from being immediately smashed to pieces by the more powerful adversary.
    Ego, my friend, is a terrible betrayer. It would do anyone well to temper their reactions to any questions with as much or even more reflection and research one gives to the weighty matters of his field, as you so thoughtfully encourage others to do. Please regard well your own advice but in the shoes of others.
    I apologize for the belated response in this forum, but I have to perform a deal work to generate funds and taxes to send to school the eager-to-learn to be edicated by the eager-to-teach.

    Massimo.
     
  16. Apr 5, 2013 #15

    ZapperZ

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    If this is true, then you've invented a new phenomenon, because you are arguing that you can detect gravitational effects on phonons. After all, this is what has become of the absorbed photons in solids. However, to quote someone, "... Whether true or not is not known a priori. Only after testing.... " So where is the "test" here to show the validity of what you just guessed to be true?

    Back up a bit. You have experimental evidence that photons absorbed by black paper can be later released omnidirectionally? I'd like to read it.

    A "black paper" is a "medium". So is glass, wax, water, etc. I can get "directional" transmission, scatter/diffused transmission, etc.. etc. from all these different types of medium. Not only that, for the same type of medium, say typical glass, I can get transmission of visible spectrum and a complete absorption of the UV/higher frequency spectrum. Where is the "energy flow in the same direction as the original beam" there?

    You are asking that we GUESS and make assumptions on what you know and don't know. Do you really want us to do this?

    On second thought, maybe I should have made such assumption. The "explanation" that you have provided in this post have created even more confusion on the question as you can see from my response here. There are simply a lot of very confusing things being said, some even contradictory to not only with each other, but also with what we know in Solid State physics.

    I find it rather strange that while you asked the question, you somehow already have the answer that you want because what you wrote here is essentially an type of answer that I am assuming that you are looking for. You somehow are already convinced that yes, light IS affected by gravity, no matter under what situation and conditions. So since you already have an answer, and especially an answer that you like, regardless of what you have been presented with, why are you then asking it here?

    Zz.
     
  17. Apr 7, 2013 #16
    Massimo.
     
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