🚀 go-pugleaf

Quite a while ago, I asked the net the question mentioned in
the subject line. A little while later I detailed my question 
because so many people answered "They don't!". That question
was something like "Why do people THINK that left and right
are reversed, but not up and down?". 

Now trivedi@yukawa.uchicago.edu (Anil Trivedi) writes:

>I think this thread can use one more contribution.

>First of all, while most of you certainly know this, I should say it
>anyway: mirrors *can* produce upside-down images; it is just that
>the common plane mirrors do not do so. :-)

OK

>Now to the serious stuff. The question is: why do Left/Right behave
>differently from Up/Down? This has nothing to do with mirrors, really.

>The basic thing to understand is that neither Left/Right nor Up/Down 
>have any fixed meanings in space (the Universe).

Agreed.

>However, the notion of Up/Down is reasonably stable on the surface
>of the Earth; you have to travel far for it to shift.  It is defined
>with respect to the center of the Earth and has nothing to do with
>*your* personal orientation.

Well, someone might disagree: she could define "up" as the direction
of her body (the direction her hair points to). But this is
not very relevant.

>The notion of Left/Right, on the other hand, is defined with respect
>to your body; to use the stock market jargon, that makes it much more 
>volatile. Its meaning in space changes as you walk around. Face another 
>person: it takes no mirror to arrive at situation when *his left* is
>on *your right*. Forget another person; just turn around yourself: what 
>used to be to *your* left is now to *your* right. And so on...

You're right.

>In the (plane) mirror, the image of *your* left hand is, amazingly,
>still on *your* left. But it is the right hand of the *other guy*.
>However, as I said, you don't need a mirror for this subjective switch 
>of direction: if a real person was standing there, the "left/right"
>disagreement would be much the same. 

Yeah, but the question remains: why is there a "left/right" disagreement,
and not an "up/down" disagreement? 

> Mirrors do not reverse Left/Right
>any more than a cocktail party does.  :-)

But why do cocktail parties always turn my house upside down? (^8


-- 
Maarten J. Landzaat (analyst/programmer, bass player, Atari/midi freak)
BSO/Aerospace & Systems			Mail: Spuistraat 97
Email: maarten.landzaat@fel.tno.nl	      1012 SV  Amsterdam
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