>There is a room >Every wall, the cieling and floor are

>>8241422
After 90 seconds aliens from outer our universe will pop into existence to turn off the light switch because fuck you for not being green.

>>8241422
The room will heat up

>>8241422
what kind of light source

>>8241422
everything becomes a solid color room, depending on the lights color.

>>8241422
Is the light on?

If the light source is constantly inputting energy then the room will heat up and get very bright. 100% reflection is not possible tho

>>8241859
>heat up
why? 100% reflection of the walls + nothing in the room therefore pure vacuum so nothing there to heat up

>>8241863
Assuming 100% reflection and vacuum, the light would experience a redshift (an increase in its wavelength) after a lot of years.

>>8241863
That's a physical non-sence though. 100% reflection can't exist. As the photons bump into your perfect mirrors they will put some energy into the mirror. The act of bumping a particle into another particle is impossible the ignore. The room will heat up. No matter how I look at it, there is no way some energy won't be lost and transformed either into motion or heat.

But I do like the redshift answer, in a perfect hypothetical world that's probably what would happen...
and in that world the photons would also exist forever (as no energy would ever be lost) and since even photons have mass I wonder if they could eventually form some kind of substance as the room fills and there is no more space for them to move at... But light also always moves at the speed of light... now my head hurts

>>8241422
Assuming that no energy is absorbed by any body in the room but the light source, the light source would eventually heat up and just fucking break.

And then you would have a massive photon orgy. That's about it.

>>8244090
>no energy will be lost
The expansion of the universe does not preserve energy. For any given amount of photons trapped that undergo redshift, the total energy will decrease over time.

>>8241422
If it was truly 100% reflection, the photon count in the reflective cavity would eventually get so high, that the flux through your light source would cause a population inversion and the light source would begin to lase.

Not long after that, the light source (it doesnt reflect 100% you never mentioned that) would become so hot that it would ionize into a plasma and light production would cease.

Because you have a magic box that cannot absorb energy, the temperature of the plasma/photon soup would never drop, and the system would remain like this until spacetime itself began to manifest significant changes.