Yoann Bourgeois at the Pantheon in the Eye of a Physicist

From 3 to 14 October 2017, Yoann Bourgeois’ machines invaded the Pantheon to dialogue with Pendule de Foucault. Unlike the pendulum that swings alone, whether we are there or not, his machines must be “inhabited” by acrobats to become devices that explore movement. But, just like The Pendulum, these devices lead us again and again to the fundamental question: what is movement?

Yoann Bourgeois / La Mécanique de l’histoire au Panthéon. Photo Géraldine Aresteanu

Foucault Pendulum

I first discovered The Pendulum a long time ago when I was a physics student. I remember a twinge in my heart. Ever since Galileo, who opened up the science of motion to us, scientists have been in love with the Pendulum. It is a reasonable and measured love: circular trajectory, speed, acceleration, oscillation, energies, forces, gravity, period and measurement of time.

It gave us additional reasons to love it when it became “Foucault’s pendulum”: rotating frame of reference, force of inertia, Coriolis.

Observing Yoann Bourgeois’ four devices at the Pantheon, I felt this pinch in my heart again. With Foucault’s pendulum in the centre, the life that moves in Yoann Bourgeois’ model worlds puts the physics of movement at the heart of our existences. And to appreciate the beauty of this spectacle, you don’t need to be a surveyor.


In my world of physics, the one that falls and rises, we call it a system. This system is not isolated because it exchanges energy with the rest of the world around it. It falls. Its kinetic energy, determined by its speed, increases. Then it stops in the trampoline. Like speed, its kinetic energy is zero at that point of stopping, all the way down. In that very brief moment, when everything is motionless, all the energy of motion resides in the tension of the trampoline. The trampoline then returns the system. Suddenly the energy of movement becomes kinetic energy again. It rises. It loses speed. The kinetic energy decreases until it is zero. The energy, this time potential energy of gravity, is available for a new fall.

At the highest point of the trajectory, he gets back on his feet for a short while… Then he falls back down. I decide that this moment is the end of the sequence. A new one begins. Identical. Periodic motion is the image of permanence, of eternity. Physicists play with forces they call conservative. Weight is at the forefront of these forces. They describe reversible and total transformations of energy during movement. No loss. So time doesn’t pass. The future and the past are identical. Everything starts over again identically. Endlessly. No beginning. Ideal world.

But the world is not ideal. The pendulum always stops swinging because there’s friction somewhere. Energy is lost and becomes heat. It’s inevitable. When it’s supported at the top, the one who falls can fight against this dissipation of the energy of movement. By purposefully pushing his body upwards, he can increase his potential gravity energy. Thus, once again, he can compensate for the loss of energy and start a new sequence identical to the previous one. As long as his body is able to do so, he maintains the illusion of a seemingly free and endless repetition.


This fast-moving stage is a small, elementary world. Its simplicity makes it a laboratory for exploring our way of being in the world. To the usual constraints on our daily movements (weight, contact, friction, inertia), it adds the one induced by a world that rotates rapidly on itself. In this small world, we have to bend to stand, that is to say in balance and at rest. To be standing, one must inscribe one’s body in this new vertical defined by the combination of two forces.

Here the weight is combined with the inertial force due to the rotation of the plate. If all friction were suddenly removed, all anchors, men and objects would be ejected from the stage, they would continue in a straight line instead of rotating.


It’s a silent dialogue that is played out around this other stage: moving in pairs on the edge of balance and always pushing back the fall that comes. Feel this gap, feel how the other already corrects it with imperceptible movements. At the limit of perception, slowly, recovering at every moment, they explore this world as simple §one table, two chairs) as it is intractable.

These acrobatic feats echo, in mechanics, the impossible balance of the cone on its tip. In principle, a perfect cone ideally vertical, it stands upright. In practice, it falls immediately. Technically, we know how to make it stand upright. The very small deviation in the vertical is measured with sensors. This measurement then controls a device that corrects and prevents the fall. In the same way one stands in an unstable balance. Proprioception: Permanent and unconscious control of the body position.

The zero sum of the moments of the forces founds the physics of rotational equilibrium, it is the equilibrium of the balance. This same law defines the life of this couple on the table. It binds the two bodies closely together despite the distance. Invisible link, which passes through an unstable plate. Permanent and susceptible physical link, which very quickly amplifies any deviation. To live here as a couple is to try to move freely and together without any gap being created, by marrying movements that are barely felt.


To explore a new world by moving, Yoann Bourgeois first builds his stage. He thus chooses which links to reality will explore the dancer-acrobats of his company. These physical constraints will be tools of creation.

The most elementary of scenes comes from our everyday life. It is the stage of the theater. It underlines a body that is always heavy and a space above the ground that is inaccessible. It establishes permanent contact with the ground, and thus a radical separation between the vertical and the horizontal.

This balanced scale, an apparatus manufactured for the needs of the show, offers another stage. Settling down there immediately projects the body into another world. I’ve never been on this trip before. As a spectator, I am fascinated and perplexed. It’s a foreign world in which you have to learn to move by exploring it. No contact with the ground. The weight is always there, but the almost perfect balance provided by the counterweight allows the vertical to open effortlessly. All you have to do is move one leg, one arm. Barely. The balance allows immobility in the air. All the movements of the body revolve around the point of attachment of the balance, the centre of rotation, the heart of this world. Horizontal, vertical… it makes no sense for a body that now moves freely on the surface of a sphere. The device changes the symmetry of space, which becomes spherical. The mechanics of the balance is very well oiled. This allows to play with inertia. One can then move long and slowly, at very low speed, and without having to maintain the movement.

What an astonishing division then between the observer and the body moving in space! The first remains on the stage. The second one leaves it when it settles on the scales in front of the audience. At that moment he crosses the border between these two irreducible worlds. Sitting on the stage, the spectator watches a body explore this foreign world and play it for him.

“La Mécanique de l’histoire, une tentative d’approche d’un point de suspension – Exposition vivante au Panthéon, Yoann Bourgeois – CCN2-Centre chorégraphique national de Grenoble. Commissioned by the Centre des monuments nationaux as part of the Monuments in Movement operation in partnership with the Théâtre de la Ville, Paris.

Published by JoelChevrier

a physics professor at the university passionate about contemporary art . Scientific curator of the Soulages Arts&Sciences exhibition « Noir, c’est noir ? » Lausanne Switzerland (2016-2017) . Collaboration with Giuseppe Penone for artwork Essere vento : we pushed sculpture on sand grain down the micrometer size. Exhibition Corps de Pierre 2017. . Collaboration with choreographer Yoann Bourgeois for exhibition at Pantheon Paris 2017 . Member of Strategic Council at ENSCI Les Ateliers Paris (2017-…). . PI of Descitech project (2014-2018): « Sciences, design and society: the factory of contemporary worlds » . Member of the Board at Ecole Supérieure d’Arts et de Design Grenoble/Valence (2015-...) . Member of Scientific Comity of Exhibition “Science Frugale” at science museum Espace Pierre Gilles de Gennes . Member of Scientific Comity of Exhibition “Luminopolis” at science museum Cap Sciences (Bordeaux 2017-2018).

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: