Re: boustrophedon (was: Atlantis II)

Roger Mills wrote:

> I've never quite understood the International Date Line.

Suppose it is midnight between the 28th and the 29th exactly where
you are.  If you turn your head west and look (with your more
than birdlike vision) into the next time zone, it is 11 PM on the
28th.  Looking further, it is 10 PM, and so on and so forth.

If OTOH you look east, then the next time zone is at 1 AM on the
29th, and the next at 2 AM on the 29th, and so on and so forth.
Somewhere around the curve of the planet, there must be a line
where the area in which it is the 28th and the area in which it
is the 29th meet.  By convention, that is the International Date
Line.

Without the Date Line, you could get into the following paradox:
Suppose *time is frozen* and you are going to circumnavigate the
earth, changing your otherwise unmoving watch for every time zone you
enter.  If you go westward, you will be setting the clock back
an hour in each zone (neglecting variant zones for the moment),
and when you get back home it will read exactly 24 hours earlier
than the present moment; so you and your stay-at-home twin will
disagree by a whole day, even though time is frozen.

But if you set your clock forward 24 hours on passing
the Date Line, you and your twin will agree exactly.  The self-same
argument works, of course, if you set your clock forward 24 times
and backward once when circumnavigating toward the east.

--
There is / one art             || John Cowan <jcowan@...>
no more / no less              || http://www.reutershealth.com
to do / all things             || http://www.ccil.org/~cowan
with art- / lessness           \\ -- Piet Hein

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