One Mississippi, two
Mississippi, three... though
this way of counting seconds
works pretty well for playing
hide-and-seek, the atomic
clock is vastly superior when
it comes to accuracy. It
could run for 300 million
years and would not stray
from perfect time by one
second. Whereas counting
using words relies on how
fast you are speaking, the
atomic clock gets its
information from electrons
jumping around in atoms.
Such precision is needed for
GPS systems and global
telecommunication. Since
2014, The National Institute
of Standards and
Technology’s atomic clock
‘NIST-F2’ has set the
standard time in the US.
So how can atoms define a
second? Atoms contain
electrons, which change
energy levels when hit with
radiation at a certain frequency,
causing them to emit light. The
frequency at which electrons
of caesium atoms will change
state is 9,192,631,770Hz, and
is known as the ‘natural
resonance’ of the caesium
atom.
In 1967, the second was
defined as the duration of
9,192,631,770 periods of the
radiation corresponding to
the transition between two
electron energy levels of the
caesium-133 atom.
HOW IT WORKS
The ‘NIST-F2’ atomic fountain clock
Do insects sleep?
MICROWAVE CAVITY
- DETECTOR
Measures the light emitted by
atoms
LASERS
LASER
LASER
CAESIUM ATOMS
- PROBE LASER
Excites the caesium atoms,
causing them to absorb and
re-emit light- Lasers cool caesium
atoms and push them into a
ball, which is sent upwards.
When the ball of atoms
reaches the top of the clock,
it then falls back down like a
fountain
- Lasers cool caesium
The microwave
frequencies are
measured; the one that
causes the caesium
atoms to emit light is used
to define a second
Microwaves interact with
the caesium atoms
PHOTOS: MATT COLE/FLPA ILLUSTRATION: SAM FALCONER
Yes. They don’t have eyelids, so
they don’t close their eyes like
we do. Cockroaches, however,
will fold down their antennae
when they sleep, which has the
similar purpose of protecting
delicate sensory organs.
When asleep, insects aren’t
just resting – sleeping praying
mantises will droop downwards
and sleeping bees are harder to
startle than those that are
having a rest.
Laboratory experiments
have shown that fruit flies that
are forced to stay awake are
slower at learning their way
round simple mazes than fruit
flies that are allowed sufficient
sleep. LV