Can light be trapped forever between two perfect mirrors?

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Discussion Overview

The discussion revolves around the theoretical implications of light behavior between two perfect mirrors and the effects of gravitational changes, particularly in the context of a collapsing sun. It includes speculative scenarios regarding the speed of gravity and the persistence of light in a vacuum.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether a beam of light could continue to bounce indefinitely between two perfect mirrors if the light is aimed correctly and the mirrors reflect 100% of the light.
  • Another participant asserts that if the sun collapsed into a black hole, the gravitational effects would not change, and thus, there would be no immediate pull towards the black hole.
  • A different viewpoint suggests that if the sun were replaced by a black hole of the same volume but greater mass, it raises questions about the speed of gravity and its implications.
  • One participant clarifies that it is changes in gravity that propagate at the speed of light, not gravity itself, and that any significant change would take time to be felt on Earth.
  • Another participant acknowledges the impossibility of the scenario but agrees that under the assumption of perfect mirrors, the light could theoretically continue bouncing without loss.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gravity and its propagation, as well as the theoretical scenario of light between mirrors. No consensus is reached regarding the implications of a collapsing sun or the behavior of light in this context.

Contextual Notes

Participants acknowledge limitations in their scenarios, such as the impossibility of certain conditions (e.g., perfect mirrors) and the assumptions made about gravitational changes.

maniaciswicke
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1. If gravity waves travel at the speed of light and it take about 8.5 minutes for to reach Earth from the sun, If the sun suddenly collapsed into a black hole would it take 8.5 minutes for us to start being pulled in?


2. If you could somehow set up 2 mirrors facing each other than reflected 100% of light. And if you could aim a laser pointer beam into one of the mirrors and take it away before the light bounced back to it,could the beam of light keep going back and forwards at the speed of light between the mirrors and maintain a beam of light in the air?

just couple of random things i was thinking about :)
 
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1. If the sun suddenly collapsed into a black hole, nothing would happen except that we would stop seeing the sun. The mass of the sun does not change whether it is a black hole or not, so there is nothing that can pull us in more than the sun is doing right now already.
 
i know its a bad example because extra matter can't just appear in the sun

maybe if the sun was instantly replaced by a black hole of the same volume (with much larger mass)
i know its impossible but just interested with the speed of gravity as such
 
It's not gravity that travels at the speed of light (gravity is just there, it does not travel), but rather changes in gravity. So yes, if the sun would suddenly get twice as massive, it would take us 8 minutes to notice that. Likewise, if the sun would suddenly disappear, it would take us 8 minutes to realize it had gone (visually and 'gravitationally').
 
kk yeah that's wat i meant lol
thanks :)
 
2. Obviously impossible, but if you want to make the assumption that you have perfect mirrors, then yes. However, unless the laser beam interacts with the air (which invariably reduces the strength of the beam), it will remain invisible (unless you stick your eye in the reflecting path).
 

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