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From: rlr@pyuxn.UUCP (Rich Rosen)
Newsgroups: net.philosophy
Subject: Re: Why do mirrors reverse left & right, not up & down?
Message-ID: <450@pyuxn.UUCP>
Date: Tue, 7-Feb-84 13:47:07 EST
Article-I.D.: pyuxn.450
Posted: Tue Feb  7 13:47:07 1984
Date-Received: Fri, 10-Feb-84 07:38:11 EST
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I haven't seen such an anthropocentric discussion (outside of net.religion)
in my life!  Mirrors reversing left to right because of OUR binocular
vision?  If it wasn't a person in the mirror it wouldn't be reversed?

O.K.  Picture yourself and your Rubik's cube (assume each side of the cube
has been made uniform in color) walking in a three dimensional grid.
(Assume x axis is the horizontal left-right line in front of you, y axis
is the vertical line in front of you, and the z axis is passing through you
from front to back; actually, assume that your cube is standing on the
y = 0 plane at a location x = 0, y = 0 [actually ranging from 0 to the height of
the cube], and z = 3).  Now suddenly a "mirror image" of your cube appears
at x =0, y = 0, z = -3 (on the other side of the z = 0 plane that we will
consider to be the "mirror").  You walk over to the other side of the
"mirror" to meet your cube's doppelganger, and you discover (aha!) that
the top and bottom sides of the cube (red and blue, respectively---I don't
have a cube handy so please forgive any cubic inaccuracies) are on the top and
bottom (as expected---after all, mirrors don't reverse up and down, do they?),
the front and back sides (assume front to be that which faces the "mirror")
are yellow and green respectively, on both sides of the "mirror", also as
expected.  But, look, if you assume the side facing the mirror on both
sides to be the front, then there's a reversal of the left and right sides
(again as expected)---in the original, the left side is white and the right
side purple, but if you make the above assumptions, in the doppelganger the
left side is purple and the right side is white.

Think about it.  When you walked to the other side of the mirror, how did you
do it?  You walked on the y = 0 plane.  Now, let's pretend that you are
Fred Astaire in Roman Holiday and that you can walk to the other side of the
mirror ON THE x = 0 PLANE.   But as you begin that walk, your perspectives of
your original cube are altered.  If you choose to still call the side facing
the mirror the front, then when you "stand" on the x = 0 plane (let's use
the position where your head is on the x > 0 side of the plane), the right
side (purple) is now the top, the left side (purple) is now the bottom,
the top (red) is now the left side, and the bottom (blue) is now the right.
When you reach the doppelganger cube after walking along the x = 0 plane,
again the left and right are reversed, while the top and bottom are not.
The red side is the left side of this cube and the blue side is the right!
But wait!!  That's the same doppelganger cube as before---nothing has
changed.  Before, when you walked along the y = 0 plane, the red and blue
sides were not "reversed" (in your perspective), but now they are!!

It just depends on how you choose to "walk around" (in your mind) to the
other side of the mirror.  As someone already said, mirrors don't reverse
left/right or up/down, they reverse back/front.  *BUT*, if the human mind
chooses to assume (note how many times I said "assume" in the proposition)
that front is "that side which is facing the mirror", then the reversal
will be perceived in one of the other two dimensions---height (up/down)
or width (left/right).  Because of our "horizontalist chauvinist
perspective", we choose to walk around the mirror on the floor when we
*re-visualize* the image in the mirror.  If we played Fred Astaire, we
could (if we chose to) visualize a different reversal---that which we
call up/down when we are standing 'normally' would indeed be reversed.

The philosophical question here really boils down to "Why do we have
this horizontal chauvinist perspective?"  What is going on physically
is a one dimension reversal, which the brain translates from a
back/front reversal to a left/right reversal.  Physical questions abound:
What would a mirror be like that reverses two dimensions?  (If a mirror
is perceived to reverse one dimension but not the other two, could it not
be perceived geometrically that the other two dimensions are the ones that
are reversed and not the first one?)  One that reverses three dimensions?
More?  Are there mirrors in Flatland? (I haven't read it yet.)
-- 
Pardon me for breathing...
	Rich Rosen    pyuxn!rlr