One way sphere

Here’s a question I first thought of way back in high school physics class:

Say you were able to create a sphere that was made of a perfect one-way mirror (I realize such a thing doesn’t exist). The inside of the ball would be the reflective part. Any light that struck the ball would be trapped inside - it would just keep bouncing back and forth. I’d think that lots of heat energy would get trapped too - plus who knows what else (radio waves, etc ?).

What do you think would happen if such an object was constructed ? Would it explode in the same way as an unopened tin can would if you threw it in a fire ?

If you were able to keep it from exploding do you think you could use such an object to “store” light or other waves ?

Well, your reflective substance is theoretical, so it has the properties you decide it has.

You need to decide whether it only reflects visible light, or the entire electromagnetic spectrum (or something else).

You also need to decide what range of electomagnetic radiation is projected towards the sphere from outside.

What’s in the sphere? Is it a vacuum? If not, what?

I think you answered your own question. Such a thing cannot exist because if it did, it will violate the laws of thermodynamics. Such a sphere will absorb energy and get hotter than the environment, which means entropy is decreasing. Use the temperature difference to drive a generator and you get free energy, which we believe is impossible.

The one thing I forgot was saying the inside was a vacuum.

Yes, it would blow up; light does exert pressure, and would, in the absence of other effects, overpressurize your container.

If your box (it doesn’t have to be a sphere, after all) isn’t a perfect reflector it will inevitably absorb some of the energy. It gets hot. As a perfect reflector it starts to emit its own photons from blackbody radiation, so it radiates (probably farther to the infrared than in incoming light, so it doesn’t look like the light energy is escaping). Eventually you end up in equilibrium with your surroundings.

If the box doesn’t absorb but still isn’t a perfect reflector, then some of your light energy escapes anyway. Again, you eventually end up in equilibrium.

I don’t know what happens in the perfect reflector case. Eventually, I suppose, the heat energy inside starts to degrade your coatings or whatever and it ceases to be a perfect radiator.

In any case, it seems to me that your energy will probably leak out by some mechanism long before your box explodes.

It’s too bad such a thing isn’t possible. If you had a ball made out of a fragile material that would soak up all the light that hit it and then release it all in a big flash when broken, you could leave one out in the sun for several years to make a weapon of mass destruction that would make the environmentalists happy: a solar-powered bomb!

I always thought it was kind of a cool concept to think about. If such a thing was possible you could have fields filled up these glass globes instead of windmills for power.

The globes would look completely black because they would reflect no light, yet inside would be utterly brilliant.

I thought it was a cool concept to think about - there’s lots of different aspects to consider.

Just for fun, I believe sf author Theodore Sturgeon described such a device in a “throwaway” section of his short story “Microcosmic God” (anthologized several times, including in The Science Fiction Hall of Fame Vol. I), where he calls it a “light pump”. He claimed (well, his character claimed) that it reduced the amount of light in a room by a measurable amount. But it seems to me that once it reaches equilibrium, you might as well have a piece of black cardboard in the room for all the difference it would make.

I’ve never been the best at entropy-related things, but I believe that if you left it out in the Sun, Thermo Law 2 would only restrict temperatures above 5800 K. Right?

I’ve never been the best at entropy-related things, but I believe that if you left it out in the Sun, Thermo Law 2 would only restrict temperatures above 5800 K. Right?

I’ve never been the best at entropy-related things, but I believe that if you left it out in the Sun, Thermo Law 2 would only restrict temperatures above 5800 K. Right?