Mirrors switch left/right, but not up/down

chris malcolm

chris malcolm

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This is the next silly Xmas mirror question. Why this oddly asymmetric behaviour? Why do mirrors reverse left and right, but not up and down?
 
Because left and right are abstract concepts while up and down are defined by gravity (try describing left or right without pointing so that anyone can understand - no point saying "the hand you write with" or "the side of the road you drive on" since they both vary).
 
Try getting a piece of paper and marking the top, bottom and each side with a different colour. If you hold the paper in front of you with the colours facing away and then turn to face the mirror you will see the top & bottom colours where they should be and the side colours have apparently swapped!!
Now hold the paper with the colours facing you and flip the paper on a horizontal axis, you will find that the top & bottom colours have apparently swapped and the side colours stay where they should be.

It is a bit harder to do it with your own reflection.
Stand with your back to the mirror, left and right, top and bottom do not change. Turn on a vertical axis to face the mirror and left and right appear to have changed.
Return to the starting position with your back to the mirror and then turn on a horizontal axis, i.e. stand on your head, and top and bottom have changed while left and right stay the same.
 
It is because they reflect what is in front of them - they don't reverse or flip it.
 
Exactly ^

Stand in front of a mirror and wave your right hand. That odd looking bloke in the mirror will wave his hand on your right as well. Likewise, his head is at the top and his feet at at the bottom just like yours.

Now lie on the floor in front of a mirror. Your head will be on the same side as your reflection's head - no left/right reversal.


Steve.
 
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chris malcolm said:
This is the next silly Xmas mirror question. Why this oddly asymmetric behaviour? Why do mirrors reverse left and right, but not up and down?
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Try looking at your reflection in a spoon. And then turn it around and look at the back ;)
 
Mirrors don't switch left and right; they switch front and back. To visualise this better think compass points instead of "left and right". If you stand facing north with a mirror in front of you, everything to your east is still east in the mirror, and everything to the west is still west in the mirror - it's NORTH and SOUTH that have been "flipped". The light hitting the mirror has been "flipped" perpendicular to the axis of the mirror; the light that was travelling north is now travelling south.
 
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2 first surface mirrors (silvered on the side closest to the viewer) will be more efficient at reflecting to almost infinity but there will still be tiny losses at each "bounce" of the photons which will eventually take their toll. Normal mirrors lose more light at each bounce since the light has to go through the carrier medium as well as bouncing off the reflecting surface.
 
Raptor Mike said:
Put a mirror in front of a mirror. Does it go on for infinity?
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Only if you align the mirrors absolutely perfectly parallel, AND the mirrors are perfectly optically flawless, AND the mirrors reflect 100% of the light. Since none of those three essentials are possible in this imperfect world, no. You'll be lucky to get more reflections than your camera's sensor has stops of dynamic range.
 
hollis_f said:
They don't.

When I look in my rear-view mirror and see the car behind me indicating by using the flashers on the left hand side then it normally means that it will be turning left.
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If standing in front of a Mirror you raise your Left arm than the Reflection lifts the arm on the Left of the Reflection, which appears to our minds Logic as being the Right arm but its not.
Take a Photo of yourself with your Left arm raised and look at it and the arm on Right of the Photo will be raised and which your mind will tell you raised your Left arm although it apperars on the Right of the Photo.

Try telling some one that they have a spot on the Left side of their face by pointing to your Left Cheek and they will try to remove the Spot from their Right Cheek, surely the same principal!!
 
hollis_f said:
They don't.

When I look in my rear-view mirror and see the car behind me indicating by using the flashers on the left hand side then it normally means that it will be turning left.
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You don't live in Athens, do you? :)
 
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