Let's imagine this kind of experiment.

We have ideal optical fiber circle (or ideal ring laser cavity without any losses, i.e. all the mirrors have 100% reflection rate) where light can go infinitely without losses. We put this ring on the scales and let's say it shows the mass 1 gram. Then we pump to this ring a lot of energy, for example, according to $E=mc^2$ 1 gram is $9*10^{13}$ J. It is just 25 hours of 1 GW power station work :) (25 Gw*h).

My question is: After we finished our energy pumping, will the scales show 2 gram or not? Or if we take 2 rings like this, will we see gravitational force between these 2 rings? Maybe someone already did similar experiments?

  • $\begingroup$ My first idea is that this energy will be transformed in a huge pressure against the external border of the core of the fiber optic ring, thus causing this one to heat a lot. There won't be any transformation of energy into mater. $\endgroup$ – dan Mar 3 '17 at 9:48
  • $\begingroup$ Of course, in real life, optical fiber will be melted and evaporates. I am asking about the ideal case where optical fiber can handle any energy density or laser cavity with ideal 100% reflecting mirrors which can reflect GigaWatts of power without damaging. $\endgroup$ – Zlelik Mar 3 '17 at 10:02
  • $\begingroup$ With such a theoretical fiber optic, I imagine it will heat without melting and will heat the environment. A 1GW heater :). $\endgroup$ – dan Mar 3 '17 at 10:17
  • $\begingroup$ The answer is yes, it will have mass greater than 1 gram, and I think it must be exactly 2, but I'm not confident enough of that to put it as an answer (someone will say 'oh, you need to consider the x effect'). It will also have lots of angular momentum. $\endgroup$ – tfb Mar 3 '17 at 10:22
  • $\begingroup$ @tfb Thanks! The angular momentum, you mean, if I put this fiber in free space, it will be rotating to the opposite side of light direction? If I send all light clockwise, fiber itself will be rotating counterclockwise? $\endgroup$ – Zlelik Mar 3 '17 at 14:02

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