Saturday 30 April 2022 The Guardian •World^47
Andrew Staff ordO
n a Friday in
April 1979, John
Mainstone , a
physics professor
at the University of
Queensland (UQ)
in Australia, rang his wife. He
wouldn’t be back that evening, he
told her. For 18 years, he had looked
after the pitch drop experiment,
a long-form demonstration of the
extreme viscosity of pitch. For the
fi rst time since 1970, the pitch was
about to drip from its funnel, and
he didn’t want to miss it.
Pitch is a resin – a viscoelastic
substance derived from petroleum
or coal tar, used in bitumen, and for
waterproofi ng. Which is ironic, for
as solid as it appears, pitch is fl uid:
at least, it is when you put it in a
funnel, the sloping sides of which
create a pressure gradient.
Mainstone stayed up all night.
He continued to keep watch on
the Saturday, telling his wife he
wouldn’t be home that night,
either. Still, the globule of (literally)
pitch-black liquid hung by a thread
from the bottom of its funnel. On
Sunday evening, exhausted by hisvigil, he went home. By the time he
returned to work on Monday , the
pitch had dropped into its beaker.
The pitch drop experiment was
set up by Mainstone’s predecessor
Thomas Parnell. In 1927 Parnell
heated and liquefi ed some pitch,
poured it into a sealed funnel, and
set it over the beaker inside a large
bell jar. In 1930, he cut the stem of
the funnel – and waited.
Nearly a century later, the
longest-running lab experiment
in the world is in the foyer of the
physics building in the Great Court,
at the heart of the UC campus. The
jar is set inside a protective plastic
cube, with an analogue Casio desk
clock observing each moment as
students and staff wander past.
The funnel is held aloft by a brass
tripod; at the bottom, a shiny black
balloon of pitch hovers above the
empty beaker.
Mainstone took on the pitch drop
experiment in 1961 and brought
it to popular attention. He also
mentored its third and current
custodian, Prof Andrew White,
who has watched over it since
Mainstone’s death in 2013. Like
Parnell, Mainstone died without
seeing a drop fall. “I am in no way
fi lling John’s shoes,” White insists.
“He was the heart and soul of this.”
Mainstone’s dedication was
legendary. In 2005, he and(posthumously) Parnell were
awarded the Ig Nobel prize – a
satirical award noting arcane and
trivial achievements in scientifi c
research. The Ig Nobel prize aims
to honour work that makes people
laugh, but also makes them think.
The author Nick Earls fi rst
encountered the experiment as
a medical student at UQ in the
1980s, later writing about it in
his novel Perfect Skin. “It was
a demonstration that all is not
necessarily as it seems,” he says.
“There is pitch – something that
goes into the making of roads,
something we think of as totally
solid – and it turns out it’s not.
It’s just 230m times more viscous
than water, and it fl ows, albeit
very slowly.” How slowly? “Far
slower than grass growing, far
slower than paint drying,” White
says, mock-off ended by such
banal comparisons. “We’re talking
more than 10 times slower than
continental drift!”
He directs my attention to the
joining of four tiles on the fl oor.
“Those tiles are moving north at
68 mm a year, because Australia is
moving north at 68 mm a year. It’s
one of the fastest continents, as far
as continental drift goes. The pitch
drop is moving at least 10 times
slower than that! So it’s literally
slower than watching Australiadrift north, and people log in live
on the internet to watch it. Which I
fi nd really fascinating.”
It’s true. More than 35,000
people in 160 countries are
sweating on the 10th drop of pitch.
They’ll be waiting a while yet.
Since Parnell cut the stem of the
funnel in 1930, just nine drops have
fallen: in December 1938, February
1947, April 1954, May 1962, August
1970, April 1979, July 1988 (when
it became a popular exhibit at
Brisbane’s Expo 1988), November
2000 and April 2014.
White prefers to call the pitch
drop a demonstration, rather than
an experiment, as it has never
been controlled, and thus has
been subject to environmental
fl uctuations. For its fi rst 30 years,
it sat in a cool dark cupboard.
Mainstone put it on display, and the
pitch maintained its average of one
drop every eight years until, in the
80s, the physics building was air-
conditioned , which blew it out to
every 13 years or so.
“At one stage, someone swapped
the fl uorescent lights above the
display, which were very cool, to
halogens, which are very hot,”
White says, shaking his head. “ It
was fl owing like a tap.”
And yet, to this day, no one has
seen a drop fall. Not at Expo (White:
“There were four or fi ve people
watching it, it was a hot day, I think
they went out for fi ve minutes to
get some cordial”), not even when a
live stream was fi rst set up in 2000.
Mainstone was watching from
London. On that occasion a classic
Brisbane thunderstorm disrupted
the power supply, cutting the lights
and camera feed.
Mainstone died of a stroke in- In a cruel twist, the last drop
fell in April 2014, a few months
after his death. Except, it didn’t
technically drop. It just oozed into
the eight drops that had already
fallen and solidifi ed in the small
beaker under the funnel in a
bell jar, without breaking away.
Reluctantly, White swapped
the beaker over, sourcing an old
imperial-measurement model to
match the original.
Since then, the beaker has sat
in place – empty. The lights are
now LEDs. “We had a very fresh
start,” White says. “And so, when
anyone asks me when it will drop,
I can genuinely say that I have no
idea. Because the conditions have
changed, as they have throughout
most of the last 95 years. ”
Just a few met res below the pitch
drop experiment is a basement
dedicated to quantum technology.
There, White says, a lab makes
pulses of light that are one hundred
million billionth of a second long.
And here in front of us, he says
proudly, “we have something that
has an event every 10 to 20 years.
It really captures the diff erent
timescales of the physical world .”
He looks at the funnel. There
is still quite a bit of pitch in there.
The experiment, he says, will
long outlive all of us. “Quantum
mechanics is as far as you can get
from bits of coal that have been
heated up and are slowly pouring
through a glass tube ,” he says. “I
am glad that we got a new beaker in
there that will be good for another
100 years or so. ”
Waiting for the
pitch to drop
Experiment
that has been
going with the
fl ow since 1927
The apparatus
in the physics
building in 2013.
Above, the sixth
drop fell in 1979
PHOTOGRAPHS:
UNIVERSITY
OF QUEENSLAND▲ Wait for it ... just nine drops of the
pitch have fallen since 1930, but no
one has witnessed any of them▲ Prof Andrew White is the current
custodian of the experiment, which
was set up by Thomas Parnell in 1927‘For pitch fl ow, we’re
talking more than
10 times slower than
continental drift’Prof Andrew White
Queensland University