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They do it with mirrors (Posted on 2006-04-26) Difficulty: 3 of 5
If I stand in front of a mirror, the light takes a finite, albeit small, amount of time to reach my eye.

So I am seeing myself as I looked some small fraction of time in the past.

Now if I stand with a second mirror behind me, I can see an infinite number of images of myself, each slightly older.

If I had my arm raised, and then I lowered it, can I still see an image of myself with raised arm?

No Solution Yet Submitted by goFish    
Rating: 3.7500 (4 votes)

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Solution I think it's... (fully opinionated solution) | Comment 4 of 8 |

I think it's impossible.

Although you will indeed have an image of yourself with your arm raised at that moment:

a) You will not be able to make out the image because due to light refraction in air, the image will be much, much, much smaller than it was originally, and therefore impossible to detect by the human eye, and also;

b) You're in the way!!!  If you're standing in the middle of the mirror, looking forward, the image of you with your hand in the air would be behind your torso, away from your plain view.  If you don't believe me, try going to a barber shop where both walls are mirrored, and try to see the back of your head by looking forward.  What do you see?  Your face, of course!  Your image exists, sure.  Everyone else can see it.  You know it exists, but it will be out of your sight no matter how hard you try.  This also explains why barbers use an additional mirror to show you the work they did behind your head... otherwise they wouldn't bother... the customer could see the work himself on the back mirror. 

In fact, the only way you'd be able to access that image with your eyes is if they were as sharp as an eagle's or more, and you'd have to have an invisible body... but then again you wouldn't be able to see the image because your body is invisible.  Unless you were able to disappear at will so you could see your image before it refracted.

See?  Even barbers need to know physics!

Edited on May 18, 2006, 5:45 am
  Posted by Alexis on 2006-05-18 05:43:18

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