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The first bit is well documented. Einstein (and others) supposed that gravity could bend light. We first observed it around the sun at total solar eclipse, and now it is a tool for astronomers and physicists alike.

But I cannot find anything supposing the reverse. Mechanics aside, if we could bend light, is there anything saying that it would or would not create a gravitational field?

My assumptions are this:

  1. A smaller radius of curvature would create a larger gravitational field

    This makes sense. In gravitational lensing, a larger gravitational field will result in greater bending/curving of a light beam. Hence why we cannot detect light being bent by a mosquito.

  2. A more powerful beam of light - curved/bent with an identical radius of curvature to a weaker beam - would create a larger gravitational field than said weaker beam

    It has been years since my physics days, and so I am unsure of this second assumption. That is to say, I cannot recall if the inverse is true (that a higher energy beam of light will bend/curve less for a given gravitational field). A couple quick searches show no dependency on energy of a beam of light, when calculating deflection due to gravitational lensing.

Thanks in advance.

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Birrel
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    How would you bend the light without a gravitational field? – NoethersOneRing Jan 05 '17 at 19:34
  • Possible duplicates: http://physics.stackexchange.com/q/22876/2451 , http://physics.stackexchange.com/q/6197/2451 and links therein. – Qmechanic Jan 05 '17 at 19:34
  • You could use refraction to bend it. – JMLCarter Jan 05 '17 at 21:30
  • Yes, but the effect is so small that (like with the mosquito) you will never observe it. – Lewis Miller Jan 05 '17 at 21:45
  • Light already creates a gravitational field all by itself, no bending required. – Javier Jan 05 '17 at 21:48
  • Why should bending "create" gravity? In general relativity what "creates" gravity is energy distribution expressed by the stress–energy tensor, so bending would affect curvature only to the extent that it rearranges energy. Your question can also be interpreted as purely mathematical, namely does stronger field bend light more. In that case the answer is yes, but the order of causality is reversed. There is no "creation" there, like fire accompanies smoke but it is not created by it. – Conifold Jan 06 '17 at 03:39
  • @NoethersOneRing did you read the whole post? I, quite literally, mentioned that Mechanics aside.... This is a thought experiment, based on what we know and theorize. – Birrel Jan 08 '17 at 23:31
  • @LewisMiller do you have a link or anything you can point me to? You say yes, others say no. Not very helpful beyond conspiracy. But, to continue on with your answer, why would it be unobservable? The radius of curvature that an entire galaxy can bend light is enormous, so why wouldn't bending light to a smaller (i.e. desktop-sized) radius not produce a greater field? – Birrel Jan 08 '17 at 23:34
  • @Javier Ok, but that isn't the question at hand. A beam of light powerful enough to produce an appreciable amount of gravity (exclusively from photons' inherent gravity) is arguably impossible to create, with all of the energy the universe could muster. What is the total gravitational pull by the sun's photons, assuming that every photon for one second were confined to the same location? – Birrel Jan 08 '17 at 23:37
  • @Conifold No particular reason that it would create gravity. Not all processes (if any) are reversible, but many are very nearly. For instance, the photoelectric effect is essentially a mirror image of an LED producing light. So, perhaps the mechanism between gravity and light bending has a mirror process. – Birrel Jan 08 '17 at 23:40
  • @Qmechanic not a duplicate question. Those deal with individual photons exerting gravity (whether confined to a single point, or allowed to travel). In either case, the light is not curving. I am not interested in the gravitational field due to a single photon at rest or traveling in a straight line, but rather the effect of (somehow...) curving light. – Birrel Jan 08 '17 at 23:42
  • Light, whether bent or not, has energy and will contribute to the stress-energy tensor of GR. But to have an observable effect like that of an astronomical object it would need to have an incredible energy density. – Lewis Miller Jan 09 '17 at 16:46

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