(I called them see through mirrors because I don't know what their actual name is)

I have seen a lot of pictures of glass-like materials which reflect light from on side, and from the other side, they transmit light.

What i want to say is - Let side A and side B be the two sides. Side B will reflect all (almost all) the light falling onto it. Side A will allow the light to propagate through the material towards the other side. So in a sense, side B acts like a mirror and side A acts like a transparent glass. This means that if you fit this material into the window of your room, you can see the outside but the people outside can't see you (those people can see their own reflection).

So the question is-

How is this even possible? And more importantly, What are these things made of?


One way mirrors are just semi-transparent mirrors with a little trick.

The laws of thermodynamics prevents a "real" one-way mirrors from existing; if they did exist, then we can put two rooms at the same temperature on the two sides of it. Then the radiation from one side will pass through but the radiation from the other side will be reflected, created a net transfer of heat. This violates the second law of thermodynamics; heat will be transferred from a colder object to a hotter one.

In reality, these are just normal mirrors that reflect 90% (or some proportion) of the light both ways. Suppose you had one person in a dark room and one person in a bright room. If a person is in a dark room, then they see very little reflected light and some of the light from the bright room, so it acts as if it's transparent. If a person is in a bright room, their own reflection overwhelms the small amount of light coming over from the dark room.

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