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Galileo, not satisfied with dropping things from his balcony, climbed
up the tower of Pisa. Unable to climb any higher, he invented the telescope.
And although he was born a century too late to invent the microscope, he
was undoubtedly an enthusiastic user. Galileo was lucky. Even at these extremes
of scale, he had something that he could look at with the aid of a few glass
lenses.

Today’s physicists have a harder time of it. The quantum world that
many of them are investigating is much more difficult to see. But now it
is possible to go inside a particle accelerator and ride on the particles
that formed the early Universe. All you need is a few equations, ample computer
power, plenty of patience . . . and a vivid imagination.

Accelerating particles and smashing them into one another tells us about
events that take place on a scale ten million times smaller than those made
visible by a tunnelling microscope, which ‘sees’ distances of around a nanometre.
It also re-creates a tiny part of the Universe as it was less than a billionth
of a second after the big bang – something no telescope can see. The drawback
for any physicist wishing to extol the beauties of the quantum world is
that, after months of painstaking data collection, there is nothing to see
beyond a mountain of computer printouts and a large electricity bill.

Despite this, and with the help of enormous machines like those at Stanford
in California and CERN in Geneva, particle physicists have found out some
pretty stunning things about the structure of matter. For instance, elementary
particles include quarks – which make up the protons and neutrons that form
the atomic nuclei – along with the electron, the muon and the tau particles,
together with their associated neutrinos.

There are four fundamental interactions in nature: gravity, electromagnetism,
and the weak and strong interactions. Every interaction involves a particle
– gravity is mediated by the graviton (which has yet to be seen); electromagnetism
by the photon; the weak interactions by the W and Z particles; and the strong
interactions by the gluon. The lives of these elementary particles are far
from dull. They are constantly emitting and absorbing other particles or
changing their identity. More surprisingly, they appear and disappear, seemingly
from nowhere. The subatomic world is as astonishing as any science fiction,
and at ArSciMed in Paris we want to make experience of this world accessible
to all.

This is a tall order. Images of events at scales smaller than the wavelength
of visible light are, of necessity, indirect representations, not ‘pictures’
in the conventional sense. But like infrared images from satellites and
medical ultrasound images, they need be no less real for that. However,
entering the quantum world, even more complications arise. According to
Heisenberg’s uncertainty principle, one of the cornerstones of quantum physics,
you cannot simultaneously know the precise position of a particle and its
precise momentum: the more accurately you pin down one, the vaguer the
other becomes. In mathematical terms, the product of the uncertainties in
position and momentum cannot be smaller than the Planck constant.

So the film images that can be generated are not pictures of reality.
They are simplified, abstract representations – a form of visual art. To
create them on film we have to adjust everything to a human timescale and
make some fairly arbitrary choices. If we choose to fix precisely the position
of our particles they respond by staggering around like drunkards; if we
portray them at a specific energy, they float around like clouds. The trick
is to find a compromise that a computer can handle, but which still looks
something like real physics.

At ArSciMed we made a movie last year called Not so Elementary, the
Proton. It begins with a journey through the electron cloud that surrounds
an atom, then goes inside a proton to follow the quarks, their antiparticles
and the gluons, as they interact according to the rules of the strong interactions.
It is also an exercise in modesty – the real proton contains an unlimited
number of these ‘less than real’ particles, whereas we had to make do with
the tens of thousands of interactions of some thousands of particles. Even
so, generating one minute of animation, simulating a process that takes
10-22 seconds in real life, took several weeks of computing time.

This year we adapted our computer algorithm to re-create a brief moment
in the life of elementary particles in the early Universe – the only form
of matter that was around a millionth of a second after the big bang. There
were no galaxies, no stars, not even molecules, protons or neutrons: just
a quark-gluon plasma in the process of evolving into protons and neutrons.
The result is more than a film that you sit back and watch: if you have
access to a Silicon Graphics ‘Reality Engine’, you can ride on one of these
elementary particles and follow it to its fate.

To build this virtual sequence, which we call ‘Hot Early Universe Soup’
we began by choosing the types of particles and their interactions. Each
interaction is characterised by a set of probabilities that indicate how
the system may evolve from one frame to the next. Then we define the starting
point of the animation – the properties of some of the particles with which
the scene begins. From then on the computer takes over. It moves the clock
forward, deciding on the basis of the probabilities we defined which particles
will be produced and which annihilated, and how their properties will change.
The images above and below are ‘stills’ from our virtual world.

The sequence lasts 2 minutes and has 25 frames per second – 3000 frames
in all (although to compute this number of frames takes as much as a week).
In this synthetic universe, only frame 1 is predetermined. From then on
you can choose which particle to ride on, and follow it to its fate. If
you are alert you can change identity and switch to another particle, before
yours disappears. Otherwise your destiny is determined solely by the probabilities
programmed into the computer.

Simulation and visualisation are fun. And the techniques can be useful
too, for studying systems that have nothing to do with elementary particles.
Any system containing a large number of interacting objects can be tackled
this way. From sand to galaxies, from fluid to powder flow, the possibilities
for movie makers are endless.

Eyal Cohen is director of ArSciMed (art, science, media), a company
specialising in scientific art. To find out where you can ride the elementary
particles in Hot Early Universe Soup, contact ArSciMed at 100 rue du Faubourg
Saint Antoine, 75012 Paris, France; tel. +33 (1) 44 73 90 00; fax +33 (1)
44 73 90 50.