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  • Writer's pictureKristjan Salev

What Happens to the Reflection in the Mirror When Everyone Leaves the Room?

Updated: May 28

What Happens to the Reflection in the Mirror When Everyone Leaves the Room

While reading a book, I came across an interesting question that I hadn't thought of myself. The question is as follows: 'Is there an image of the room in the mirror in a room empty of people? In other words, does the mirror in the room reflect the room's image even when everybody is left, and nobody is looking into the mirror?

Suppose you are sitting in your room and looking at the view of the room reflected in the mirror on the wall. You move to another spot in the room and look into the mirror again: the picture looks completely different. But no matter where you are in the room, the mirror always shows some view of the room. But what happens if you leave the room? Will the mirror still show an image of the room? And if it does, what will it show?

Surprisingly, it turns out that in an empty room, there is actually no image of the room in the mirror.

A mirror in the room is generally a plane mirror, which means it does not converge light rays but disperses them, and they do not form an image anywhere. An image is created only when light rays coming from an object converge after passing through some optical system (for example, our eye). If we have a converging lens, for instance, then the Sun's rays intersect at the lens's focus and create an image of the Sun there.

Human eye as lens

If the Sun's rays are directed at a plane mirror, the reflected light creates a spot on the wall or somewhere else that is the size of the mirror but not an image of the Sun. However, if we look at the light reflected from the mirror with our eyes, we see the Sun. Naturally, one should not look directly at the Sun but use sunglasses, for example. Therefore, it can be concluded that a plane mirror does not create an image of an object, but if we look at the reflected light, we see the light source. This is because the eye has a lens that converges the light rays. Similarly, a camera has a lens that converges light.

A magnifying glass converges light rays

From the above, it can be concluded that there is no image of the room in a mirror in an empty room. However, this cannot be verified, because to see something, we need to use systems that converge light rays, such as our eyes or camera lens.

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