Ask A Scientist© Physics Archive

name         Don
status       other
age          50s

Question -   why does a mirror reflect my image right to left
but not top to bottom
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If you didn't have feet you wouldn't be asking this question.

The mirror doesn't reflect your image right to left.  Whatever is
actually on your left still appears to be on your left when you look in
the mirror.  The right-to-left business is all from the viewpoint of
some other person looking at you, and that person sees your left as
their right.

Why is this?  To put yourself in the position of someone looking at you
from behind the mirror, you could imagine a copy of yourself walking
through the mirror to the other side.  To see you, your copy would then
have to turn around, and this presents several options: people with
feet tend to rotate about the vertical, so that their feet remain on
the ground (and then they forget that a rotation has even taken place,
because it's such a common motion).  This rotation swaps right and left.
If you were a fish, you might equally well decide to rotate about a
horizontal line (i.e., do a half somersault), and this would swap top
and bottom.

Tim Mooney
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Don,

The mirror image is a reflection, not a reversal, of the incoming image
(light).  As the image hits the mirror, so is it seen in its reflection.  If
we stand in front of the mirror and hold our hand  and move it to our left,
we see the image also moving left.  The same applies to all other
directions, including 'up' and 'down'.  For a mirror to reverse things, i.e.
to project an 'up' movement as a reflection when a down is actually done, or
vice versa would be complex, and would have to be accomplished with
additional mirror(s) to invert the image in one way or another.  As it is,
it simply captures light and reflects it back at the viewer without
otherwise affecting the image.  You can imagine how altering the normal flat
mirror also could  produce effects you suggest.  An example of this would be
the funhouse mirrors with concave/convex and combination surfaces.  Those
mirrors also bend the image in various ways producing humorous results.

Thanks for using NEWTON!


Richard R. Rupnik
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