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In other methods of concentrating light, the photons are absorbed and then emitted in a direction so that the photons converge upon a point. If we use gravitational lensing to concentrate light, are the photons not being absorbed and re-emitted?

Edit: By the way, another interpretation of Feynman diagrams is that photons are bouncing off of the electrons of the atoms of the lenses, rather than being absorbed and re-emitted. In that case, the question becomes "in gravitational lensing, do photons interact with any discrete particle in order to be concentrated"?

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  • $\begingroup$ How about the two slit experiment? $\endgroup$ – mmesser314 Nov 19 '18 at 4:09
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    $\begingroup$ 1) What 'other methods' are you referring to? 2) How do you differentiate between original and 'non-original' photons? $\endgroup$ – Avantgarde Nov 19 '18 at 4:13
  • $\begingroup$ How about I rephrase the question so that it asks whether gravitational lensing is the only way to concentrate light without involving the absorption and emission of photons? $\endgroup$ – Abdul Moiz Qureshi Nov 19 '18 at 4:34
  • $\begingroup$ As for other methods, we have typical lenses, and also electron lensing. All of these can be classified as lensing due to point charges absorbing and re-emitting photons. $\endgroup$ – Abdul Moiz Qureshi Nov 19 '18 at 4:47
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    $\begingroup$ @HolgerFiedler, in all of these methods, light is concentrated because the photons are being absorbed and re-emitted by the electrons of the atoms of the material lenses being used. $\endgroup$ – Abdul Moiz Qureshi Nov 19 '18 at 6:21
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Any interaction process at all that changes a photon's momentum can be represented by a Feynman diagram with an ingoing and an outgoing photon as external legs. Whether they're "the same photon" is an entirely philosophical question, so your question can't be answered through physical arguments.

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  • $\begingroup$ How about I rephrase the question so that it asks whether gravitational lensing is the only way to concentrate light without involving the absorption and emission of photons? $\endgroup$ – Abdul Moiz Qureshi Nov 19 '18 at 4:34
  • $\begingroup$ Also, since gravity is the curvature of spacetime, can't we say that the photon's momentum is the same, but seems different due to being in curved spacetime? If not, can you draw a Feynman diagram showing the photon being absorbed and re-emitted? $\endgroup$ – Abdul Moiz Qureshi Nov 19 '18 at 4:40
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Lenses also focus light without photons being absorbed and reemitted.

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  • $\begingroup$ Can you explain why? $\endgroup$ – Abdul Moiz Qureshi Nov 19 '18 at 8:34

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