On Mon, Mar 12, 2018 at 08:30:36PM -0400, Jeff Zeitlin wrote:
> As far as engineering to adapt the world to the calendar... I don't
> think TL16 is enough to do it. TL20, maybe it's within the realm of
> possibility.

I was thinking more along the lines of constructed habitats, modified
asteroids, and possibly things like gas giant moons.  Though even
planets might have their rotation modified over longer timescales.
Significant orbital modification is probably a bit much at Traveller
TLs though.

> I believe that it's been found that in the absence of outside cues, the
> human circadian reverts to roughly 27 hours

I had read an average of just under 25 hours (one study measured an
average of 24.2 hours), but with some outliers in both directions in
absence of bright light cues.  In one experiment without any external
time cues, it appeared that a few people adapted to a 48-50 hour
"double cycle" alternating long sleep and shorter nap between waking
periods.

> but with appropriate cues, it can adapt to a bit of a wider rage - I
> don't recall exactly, but I think that 18-36 hours is not difficult

I read a study that found a 28-hour cycle was seriously deleterious
for most people, though some few were able to adapt with negligible
side effects.  Other studies appear to show that adapting to small
multiples of 12 hours was easier than periods significantly different
from those, but still with medically noticeable side effects when the
period was not near 24-25 hours.

> No, 100ks would actually be a good unit, because (a) 27 hours
> circadian fitting into a period of 27 7/9 hours on the clock, and
> (b) nicely 'metric' (divisible by powers of 10).

Per the previous studies, I doubt (a) very much.

> Swatch (the watch company) actually tried to 'invent' this in the
> real world

Yes, though they really only went partway.  There's not much point to
inventing a truly decimal calendar decoupled from any one planet's
rotation and orbit when the entire population lives on just one planet
and essentially everyone has biological cycles locked to its rotation.

- Tim