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A question about mirrors

ZeeGerman

Graduate Poster
ZeeGerman
Joined
Jan 16, 2003
Messages
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Location
Nuremberg area
AUP's son's question about the magnets reminded me of a question I once had to face (and failed to answer in a simple and sufficient way):

Since mirrors swap left and right, why don't they swap top and bottom?

Zee
 
ZeeGerman said:
AUP's son's question about the magnets reminded me of a question I once had to face (and failed to answer in a simple and sufficient way):

Since mirrors swap left and right, why don't they swap top and bottom?

Zee
Click to expand...
They don't swap left and right, you're just looking "through" the things seen in a mirror.

Quick way to see what I mean, print something on a piece of thin paper and hold it up very close to a mirror. Slowly back it away and observe that the reflection would have to reverse the image IF it was still readable. Things on the right side of the paper will be on the right side of the reflection, and vice versa.
 
ZeeGerman said:
AUP's son's question about the magnets reminded me of a question I once had to face (and failed to answer in a simple and sufficient way):

Since mirrors swap left and right, why don't they swap top and bottom?

Zee
Click to expand...
Short answer: No.
 
Swapping left and right is exactly what they DO NOT do. Nor up and down. If you look in the mirror, you see your right side to the right, and your left side to your left. No swapping. It is when you face another person that left and right is swapped. Imagine the other person standing in front of you, but with his back turned to you. His right is to your right. Now he turns to face you, and his right and left are swapped as he turns, he now faces you and his left is at your right.

What the mirror swaps, however, is FRONT and BACK. As compared to the person standing in front of you, but facing the same way as you (so you see his back), your mirror image faces you, but without having turned in any way: Front and back are swapped.

Hans :cool:
 
depth inversion

They don't swap left and right, they swap front and back. You THINK of them swaping left and right because you would rotate your body about a vertical axis in order to walk around a mirror and stand where your image is. But that choice of rotation axis is arbitrary in a geometric sense. Imagine instead rotating about a horizontal axis - that is, think of climbing OVER the mirror and down the back side, so that your head is where the image's feet are. Now you've vertically inverted, again because of an arbitrary choice of which axis to rotate around. The only non-arbitrary inversion is depth - walk through the mirror (no assumptions about orientation involved) then invert front-to-back. It sometimes helps to think of the problem if you imagine a mirror lying on the ground, and you stand on top of the mirror.
 
Simple explanation: because when we walk around we turn around left to right, not upside-down. So when you see another persons face or text on his t-shirt it's swapped left to right.

The mirror does NOT swap left to right, but we're used to see everything swapped left to right.
 
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