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This description is missing a key part which explains why it appears to reverse left and right. Mirrors reverse something: the direction perpendicular to the mi
by tgb 10y ago
This description is missing a key part which explains why it appears to reverse left and right. Mirrors reverse something: the direction perpendicular to the mirror. Mirrors can also reverse up-and-down just as easily as left-and-right. Imagine holding text printed on a clear sheet up before so that you can read it. Now look in a mirror that's behind the sheet. The text in the mirror is so readable, since it's reversed in the one dimension it has symmetry in (the thickness of the sheet). But now if the sheet were opaque, you'd only see the back of the page in the mirror and no text. So you flip the page around to read it. Now you've rotated AND mirrored the text and it looks swapped left to right instead of by the mirror's perpendicular direction: the rotation changes which axis was mirrored. Start again with the text facing you ready for reading, but now rotate the text to face the mirror again but this time do so in the 'unusual' manner of flipping it head over heel. Now the text in the mirror is mirrored upside down! Which rotation you apply changes which axis is apparently inverted. We're just so used to rotating things about their vertical axis that everything looks mirrored left and right.
Also there are mirrors which do reverse specifically left and right in the manner that you debunk above, but they are nonsymmetrically concave.
- roywiggins 10y agoThe way I try to explain it is in absolute (ish) coordinates: If you face north, your image faces south. Your left hand is on your west side. The reflection of your left hand is also on the west side. If you grab the mirror and turn so you face west, your reflection faces east and both your left hand and the reflection are on the south side. If you reset the mirror and then stand sideways (facing east, mirror to your north), your left hand is to the north and right hand is to the south. In the mirror, the image of your left hand is to the south and right hand, to the north. But your reflection is facing east, just like you are.
- tgb 10y agoI think this is good too, but it leaves the reader with the original question "Okay, if the mirror doesn't reverse left-and-right, then why does it appear to do so?" A question which left me scratching my head for a while and frustrated that explanations given in otherwise excellent sources like Martin Gardner's The Ambidextrous Universe never actually addressed.
- roywiggins 10y agoThis is a good question and I think it's the perception that the person you see as a reflection is actually a clone turned around to face you. When you raise your left hand, your "clone" (if it is a clone) raises their right hand. If you imagine stepping through the mirror and turning around to stand next to your reflection you really will be reversed laterally compared to your reflection-twin.