4 upvotes, 1 direct replies (showing 1)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
Say you have a closed room. Inside is perfectly reflective. No light cam escape this room. You turn on a light, and then turn it off. Does the room still go dark if the light has no where to be absorbed?
Comment by gnex30 at 06/12/2023 at 17:05 UTC
15 upvotes, 2 direct replies
Inside is perfectly reflective.
Light can reflect, refract, or absorb. It's implicit in the question that there is no absorption, so the light will continue bouncing forever.
But what's really interesting is this: What happens when you accelerate the box?
The light that's moving in the forward direction gets blue-shifted in wavelength to higher energy during the bounce off the back wall, while the light that's moving against the direction gets red shifted to lower energy. The result is there is more pressure on the rear surface and that acts as a resistance to accelerating it. That "resistance" is exactly the mass equivalence of light by E=mc^2 which gives the box the same inertia as any other equal mass.