Rob Seaman said:
>> As I've said before, eventually the notion that the solar day contains
>> 24h of 60m of 60s will have to be abandoned.  It'll be awfully hard
>> to maintain when an "hour" involves two human sleep-wake cycles,
>> out in the limit when the Moon is fully tidally locked and 1 lunar
>> month = 1 solar day = 47 current solar days, more or less.

> Just returned from a conference three hours to the east.  The
> existence of
> jet lag suggests significant evolutionary pressure locking human sleep
> cycles to the length of the day.

Actually, the evidence from experiments is that the "natural" sleep-wake
cycle is about 27 hours long, but force-locked to the day-night cycle (it's
easier to synchronise a longer free-running timer to a shorter external
signal than vice-versa). So humans will cope until the solar day is about
27 (present) hours long, after which we'll probably start to move to a
system of two sleep-wake cycles per day.

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