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Mirror mirror…

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Why does a mirror reverse left and right, but not up and down? Discuss 🙂

Written by CGF

June 30, 02012 at 14:22

Posted in Puzzles

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5 Responses

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  1. A matter of how your brain interprets left and right?

    Normally left and right are transposed when you look at something directly (your right is my left), if you look at something in the mirror it’s not transposed.

    If you place a mirror on a page of text the text will appear upside down but not back to front. If you rotate the page so it faces away from you it will appear back to front but not upside down.

    Stephen Nelson

    July 1, 02012 at 08:24

    • Mmmm interesting… I don’t quite understand what you mean by how it’s transposed when you look at something directly though?

      Christo Fogelberg

      July 1, 02012 at 09:56

  2. Here’s my thinking on this one…

    1) Observation: Mirrors don’t reverse left and right, in the same way that they don’t reverse up and down (as verified by tilting my head to one side and looking in a mirror).

    2) But mirrors do reverse something – the scar above my right eye is on the left hand side of my face in the mirror, albeit on the right hand side of the mirror (but it’s still actually on the right hand side, as verified by lifting my right arm and touching above my right eye)

    3) Conclusion: Mirrors are reversing forwards and backwards. Since left and right swap sides when you turn 180 degrees around this is why they seem to swap in a mirror.

    A diagram showing how the mirror suggests projected locations of objects “behind the mirror”, making it look like they go from LHS to RHS, would probably make this a *lot* clearer, but I don’t know how to add a picture to a WP comment…

    Christo Fogelberg

    July 11, 02012 at 14:36

    • I think it’s all to do with our interpretation of a symmetrical object. Humans (as with most living things due a to our gravitational environment) have a vertical line of symmetry, our brain interprets the mirror image as being spun 180 degrees on a vertical axis. By turning your head on its side, you could argue that top and bottom parts of the image have swapped (or likewise for any other object with a horizontal line of symmetry) but we dont interpret it that way as due to gravity we very rarely rotate on that axis.


      July 25, 02012 at 09:31

      • Interesting…! I’m immediately wondering what happens with astronauts trying to shave in orbit, but Google seems short on facts on this one. I suspect that despite “lack of gravity” mirror would still reverse left and right though, relative to observer?

        Christo Fogelberg

        July 25, 02012 at 14:12

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