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adrianN
Is there a physicist in the audience who can tell us what happens at sharp corners? I would assume things happen as the distance between the two mirrors becomes comparable to the light's wavelength.
Ono-Sendai
You get diffraction - the wave spreads out in a range of directions, like a water wave bending around a harbour barrier.
lmm
Presumably the light must reflect properly, otherwise corner reflectors wouldn't work.
danbruc
That is not the only issue, mirrors don't really work the way one naively imagines. See for example this video [1], mirrors have their appearance between about 10 and 15 minutes into the video. Reality won't match the simple mathematical model even ignoring the corners and having a door is the correct solution in practice.

[1] https://www.youtube.com/watch?v=NumSE2LvSmQ

adrianN
That's a really cool video. Thanks!
spacehome
The Feynman lectures on physics has a great explanation, too.
empath75
It's really a question about geometry, and uses light to illustrate it. What actually happens with light isn't that important.
lubujackson
I feel like this problem is sitting on some big important concept, kind of like how topology expanded into a rich area of mathematics.
stuxnet79
I agree. But I have only a superficial and rough understanding of the big ideas that underpin topology. What practical applications does it have?