system
Given the following post, respond as if you're commenting on Reddit:
human
Can you refract light in a circle with the right materials?
gpt
No.

One way to see this is because the equations that describe the motion light can be reversed in time.  If you have a setup that somehow causes light to travel in an un-ending cycle, you should be able to reverse time and watch the light going in an un-ending backwards cycle.  And that right there is the conflict: "un-ending cycle".  If you have a perfect loop such that light can never get _out_ when the system is run backwards in time, it means that light will never be able to get _in_ to a perfect loop when the system is run forwards in time.

It can't be done.

You can build a perfect loop (use mirrors, it's easier), but you can't insert any light into it.