[LEAPSECS] drift of TAI

[Zefram]

David Malone wrote:

>The cueues for this frequency shift look just like a 4 hour phase

>shift every day.


Except that it's a continuous `shift', rather than an instantaneous
four-hour jump.


>                 Of course, there could be a long-term adaption

>I guess.


That's what I'm expecting.  With jetlag you're expected to retain the
same frequency and shift phase, so there's no adaptation to a different
frequency.


>Unless you were living divorced from daylight, it's unlikely this

>is your natural period.


I had *some* exposure to the outdoors, but this was only a couple of
percent of the time, when taking buses between home and campus.  Half the
time this did not involve sunlight.  At both ends of that journey I
lived a completely indoor existence, without unobstructed sight of an
external window.  So desynchronisation seems quite feasible.

Probably relevant: before the free-running period I was accustomed to
irregular sleep periods that had little synchrony with the planet.
Even when I had lectures to go to, I kept completely ad hoc hours.
In those years I could shift phase to an arbitrary extent within
two days, by simply staying up until the bedtime of the target phase.
Nowadays I've become conditioned to working (approximately) office hours,
and I seem to be much more tied to the regular cycle: I have difficulty
staying up as much as 24 hours.  When I need to, though, I still break
phase entirely rather than shift gradually.


>	http://www.hno.harvard.edu/gazette/1999/07.15/bioclock24.html


Interesting work.  This still, like the discredited earlier work, shows
a biological cycle longer than the natural solar day.  Evolutionarily
you'd expect us to be built for a shorter cycle, since the Earth rotated
faster in our evolutionary past.  But the day was only a few minutes
shorter when our ancestors switched from nocturnal to diurnal behaviour,
so there shouldn't be much in it.


>a 28 hr day is long enough to prevent people's hormones getting in

>sync with the day.


They're drawing a strong distinction between the hormone-controlled
circadian rhythm and actual sleep/wake rhythm.  I hadn't thought about
this before.  On those occasions when I've stayed awake for lengthy
periods of time, occasionally 60 and once over 70 hours, I've certainly
had periods of lowered body temperature and lower physical activity,
matching what they describe for the hormonally-sleepy phase.  I recognised
it as such at the time.  But the regular 40-hour cycle was different.
As I recall, I just didn't feel sleepy at all until I'd been up more
than 20 hours.  The cycle of 24 hours awake and 16 asleep felt like a
normal circadian rhythm, not overriding the natural state at any point.

-zefram