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CERN
Gauguin’s questions
Pierre Maillard
Everything starts in childhood, whether it’s understanding the universe, becoming a watchmaker or a
physicist. You’re 12 years old and start dismantling
an old alarm clock found at the back of your granny’s
drawer because you want to know how those gear
wheels work, and suddeanly you’re a watchmaker.
Or gazing at the stars you dream of the infinite; you
want to know how the celestial mechanism works,
and you become an astrophysician. When you grow
up the question “how does it work?” takes on added
dimensions – “where do we come from, what are we
and where are we going?” Gauguin in his day asked
these existential questions in a painting – albeit
adorned by a few naked women, but who are we to
complain ? A young undergraduate at Cambridge,
John Ellis hung a reproduction of Gauguin’s
Polynesian triptych above his desk and started to
ponder the mysteries of time and space.
Several decades later, John Ellis, who had meanwhile become an expert in particle physics and a
world-renowned theoretical physicist, is still asking
the same “Gauguin’s questions.” But he has consolidated them to a single question, which in his
view contains all of them : “what is the nature
of matter ?” We know that all the matter in the
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universe is constructed from the same elements, the
same building blocks and the same atoms: electrons
orbiting a nucleus of protons and neutrons, which are
made up of elementary particles known as quarks.
The quaint names or “flavours” physicists give to
these particles are worth mentioning : Down, Up,
Strange, Charm, Top and Bottom. But what exactly
are these quarks, how do they interact and where
does their mass come from? And why are there these
different types of particles? What is the hypothetical
dark matter proposed by physical cosmologists? Can
the basic forces of gravity, electromagnetism, the
strong and the weak nuclear force ever be unified?
In short, what is the code of this cosmic DNA where
the answers might lie?
God in the gap. Some will unhesitatingly reply by
inserting God in the tiny gap left by science. As John
Ellis explains, “the laws of physics, from which God
is currently absent, started functioning one picosecond (1-12 seconds) after the Big Bang, but beyond
this threshold we are denied access, for our laws no
longer apply.” We can’t go further back in time.
But while we wait for a definitive answer to Gauguin’s
questions (which will probably never come) we
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have to go far as this decisive threshold. To get there,
John Ellis, and the thousands of other scientists taking part in the CERN* project in Geneva, will soon
have a formidable tool – the LHC or Large Hadron
Collider. This is the biggest and doubtless the most
complex man-made tool ever built. It’s a machine to
go back in time – a giant clock.
Energy takes you back in time. Today we live
among the detritus of the primordial explosion, the
Big Bang. We have known for several decades that
the universe has been expanding constantly since
this initial blast. Thus the young universe was more
condensed and hotter. Today the temperature of
the cosmic radiation is three degrees above
absolute zero. Some of the lightest elements such
as helium, lithium or deuterium could only have
been created in a universe around a thousand
times hotter and therefore much smaller and
denser than ours. Likewise the temperature of a
particle depends on its energy ; the hotter it is, the
higher the energy (you can observe this phenomenon simply by boiling water). If we were to go
back step by step in time to approach the initial
explosion, the temperature, and therefore the
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space
and time
energy, would increase rapidly : one second after
Big Bang we would still be at the current temperature of three degrees above absolute zero ; one
microsecond after Big Bang the temperature is at
a trillion degrees, a picosecond after big Bang it is
a thousand times hotter. Beyond that is the gap
where the laws of physics give up the ghost.
By imparting to sub-atomic particles a colossal
amount of energy, the LHC clock machine will
enable John Ellis and his colleagues to go back in
time to the fateful threshold of one picosecond
after Big Bang (its predecessor the LEP could only
get back 100 picoseconds). This will be achieved
by colliding beams of protons at the unimaginable
rate of one collision every 25 nanoseconds. To
observe what then takes place, every collision will
be photographed, and each photograph will have
25 superimposed images. “Then we have to filter
all these images electronically,” explains John
Ellis. “We’ll be left with one in ten millions, which
will be subjected to a complex process of analysis.
It’s as if at Christmas time you took 40 million pictures a second with your digital camera and kept
only about a dozen a second. To process all that
information, which in itself amounts to a few per62
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cent of all the electronic information in the world
(10 petabytes – 10 million gigabytes – a year ; the
Google servers, by comparison have two
petabytes of storage capacity), you will need the
equivalent of around 100,000 office computers.”
A mosquito with the energy of a 400-tonne train.
To break into the heart of matter, the LHC will accelerate each particle until it contains an inordinate
amount of energy. “It’s as if you gave a mosquito the
energy of an express train,” says Ellis. These collisions are bound to reveal some surprises – one of
them might even give a clue as to the nature of antimatter. As we know from experience, time doesn’t
retrace its steps. “We live in a universe that is constantly expanding and it’s not reversible. But in experimental conditions, an isolated particle is not
governed by the expansion of the universe and its
behaviour is reversible. For example a collision
between two particles, A and B, produces two other
particles, C and D. If we then collide C and D, we get
back to A and B. Time therefore becomes reversible.
But this reversibility is not total,” Ellis points out. “We
have discovered a small amount of irreversibility in
time. And that small portion allowed matter to be cre-
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ated in the universe.” Such a statement can only
leave the layman, including this writer, bewildered: so
matter is created from that small part of irreversible
time in the heart of a particle?
Ellis tries to make it clear : “for each particle that
moves forward in time, there’s a corresponding
anti-particle that goes back in time. But the antiparticle that goes back is not exactly equal to the
particle that advances. It’s this small difference that
could have created matter and ensured its dominance over antimatter.”
Can a tentative reply to Gauguin’s question be found
somewhere beneath CERN in a 27-kilometre-long
tunnel where 9,300 magnets, supercooled to minus
271.3°C accelerate beams of protons to 99.99% of
the speed of light, creating 600 millions of collisions
a second? The LHC provides not only the emptiest
vacuum in the solar system, but the coldest place on
earth – colder than intergalactic space – as well as
the hottest. When two beams of protons collide they
generate temperatures 100,000 hotter than the centre of the sun in a minute space. Who knows? They
might even create mini black holes.
If you ask John Ellis if his daily struggle to resolve
Gauguin’s questions scientifically has changed
anything in his relationship with time, he shrugs
and smiles in his beard. “No, I don’t think so. In fact
you should ask my wife. She’s the one who says
when I should get a haircut, change my shirt or pay
the insurance premiums… You know, these questions can be asked at any level : for oneself, for the
human race or in relation to the universe. As for
me, I have known since I was 12 years old that I
wanted to find the answers in particle physics.”
And when you ask him what watch he wears, he
looks at its digital dial and admits that he doesn’t
know what brand it is, but that he remembers paying eight dollars for it in San Francisco. No doubt it
has a countdown function.
•
John Ellis will deliver a public lecture at the CERN
main auditorium in Meyrin-Geneva on the open
day, April 6 at 09:30. Entrance is free. It will be the
last opportunity for the public to visit the LHC
before it goes into operation.
More information on the LHC at :
http://public.web.cern.ch/Public/en/LHC.
* CERN, the European Organisation for Nuclear Research,
operates the European Laboratory for Particle Physics.
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