Can you get glass which is opaque one side and transparent on the other side?

Question

Can you get glass which is opaque one side and transparent on the other side?

Answer 1

Yes is that not what they use for police identification when the witness looks through the glass and can see the identification line up but they cant see you.

Answer 2

No. Definitely not. If you could, it would be a violation of the laws of thermodynamics and you would be able to make a perpetual motion machine.

So called "One way Mirrors" are glass with a semi-reflective coating. If you stand in a darkened room, you can see through to a brightly lit exterior, but the people outside cannot see in because of the high level of reflected light. However the glass itself is just as good passing light through one way as it is the other way.

If you had glass that preferentially transmitted in one direction, you could use it to get a radiative thermal equilibrium between two warm bodies at different temperatures. This would be a violation of the zeroth law of thermodynamics that says that bodies in thermal equilibrium are at the same temperature. This in turn could be used to violate the second law of thermodynamics and allow you to convert heat at equilibrium into useful work. You would have then solved the world's energy problems and be a hero and fabulously wealthy.

Answer 3

Yes, if you coat it with a thin layer of metal, which will give it semi-reflective properties. If the light on one side is stronger than the other, people from the lighter side will see their own reflection instead of seeing through the glass.

Answer 4

Yeah, they have it in airports too, to watch for smugglers, see how people act.

Answer 5

Input "Window film" into your search bar.

There are a lot of companies that produce and sell different kinds of obscure films that allow one way vision. Most of them are varieties of mirror film. As long as the light is stronger on the mirrored side, no-one on that side can see through it. It is in common use in police stattions and airports, as well as other security situations, and is not too difficult to apply to most windows.