When looking in a mirror why does left become right?

08 January 2012

Question

When looking in a mirror why does left become right not top become bottom?

Answer

Dominic - That's quite a good brain teaser. In fact, when you look at yourself in a mirror, nothing is inverted at all. When you look at where the left side of your face is in the mirror, it's on the left hand side exactly where you might expect it to be. But if I turn around and look at Dave then I've had to swing myself around and invert my definition of left and right by swinging myself around and in doing that, my definition of left and right is the opposite to Dave's, so I see his right side on my left side. Dave - So does that mean that if you turned around, instead of turning around left or right, you you just did a forward roll and turn yourself up - so you turned around to look at me by inverting yourself - Would up and down be swapped instead of of left and right being swapped? Dominic - That's absolutely right. I don't think I'll try from the studio, but if I were to stand on my head to look at you, I'd see up and down inverted rather than left and right. Chris - Is this important in your field of space science when you're looking in telescopes and things like that? Dominic - Yes. Certainly, with telescopes, different sides, left and right, top and bottom will be inverted in different kinds of optical system and you do have to worry about that, yes.

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