Timepieces! Ancient calendars, ancient clocks,
beautiful clocks, atomic clocks and the clocks built into your brain that determine how you perceive time and form memories. All the good stuff is inside:
How we count and perceive time is fascinating.
Very early civilisations developed sophisticated calendars: the
Sumerians 5,000 years ago in what's now Iraq; Stonehenge 4,000 years ago (and more recently,
ManhattanHenge); the
Chinese calendar system between 3,500 - 4,000 years ago; Calendars from North American societies
dating from 500BC; the Julian Calendar from 45BC; and finally our current Gregorian calendar in 1582. Much younger but arguably just as important as the other calendars is
Epoch or Unix time, the common time counted by UNIX and LINUX-based computers worldwide, providing a foundation for communication across networks. (
previously)
More recently, clocks have become crucial. Harrison's very beautiful series of clocks (
H1,
H2,
H3,
H4) were
accurate enough to calculate longitude and opened the seas for reliable trade, exploration and systematic mapping. The spread of fast travel by rail lead to the standardisation of time zones, with towns in Britain and the USA moving from local solar time to "
railway time". Knowing the right time rapidly became a commodity: three generations of
the Belville family made their living by providing London's clock-owning homes and businesses with the correct time. Our best atomic clocks can now be accurate to within
1 second every 300 million years and are essential for systems like
GPS and global communications. At the other end of the scale, the Long Now foundation wants to build a clock to measure
10,000 years. If you'd prefer something a little more practical, you could always get this wall-mounted
100 year alarm clock instead.
We have a multitude of different clocks ticking away inside our brains and bodies. An healthy heart, for example, will keep a steady rhythm indefinitely without any signals from the brain. Our second best-known timekeeper is the
suprachiasmatic nucleus. It keeps us on an amazingly accurate cycle that
averages 24h11m +- 16 minutes, keeping our bodies to this cycle even if forced to live a 28-hour day or
living in a light-free cave with no watch. This 24-hour cycle controls an amazing array of bodily functions,
including hormone levels, body temperature, your immune system's activity and much more. It gets re-adjusted daily by sunlight so we can trick it into adopting longer days,
which will be useful for when humans get to Mars. Jet-lag sufferers (
whose "deep sleep" clock becomes detached from their REM sleep clock) know that this isn't nearly enough, so will be interested that eating breakfast after at least 16 hours without food beats jet lag by immediately kicking your cycle into "morning" mode,
at least in mice and
one Formula 1 driver (about 50 minutes in, probably UK only). Shorter times (fractions of seconds to hours) are counted by several different systems including the
basal ganglia and the parietal lobe.
The rate at which these clocks tick determines how fast we perceive the world and form memories; so by altering these ticks we can seem to speed time up or slow it down. It's well known that various drugs can affect our perceptions of time:
Caffeine makes time go slower, anaesthetics make it speed up. THC can give a sense of timelessness, possibly by blocking a
a clock circuit that measures time in the seconds to minutes range. Memory load, time of day and mood also have effects, but surprisingly,
one of the biggest factors seems to be body temperature.
Just like in The Matrix,
fear really does make time seem to go slower, letting us pick out details that otherwise we couldn't perceive. Some people claim that they've learned to exploit this in sports and actually
stretch their perception of time to see the ball moving slower to get an advantage.
Finally, this is what started me down this train of thought: a thought-provoking radio programme from the BBC, in which
an astrophysicist, a classicist and an author talk about what time means to them.
posted by BrotherCaine at 2:51 PM on May 18, 2009