Law of motion

The First Law of Motion of Isaac Newton seems to concern moving objects: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. In fact, it applies perfectly well to an object whose velocity happens to be zero; that's to say, a stationary object. In other words, as long as no external force is applied to a stationary object, it will remain eternally motionless. Now, I often encounter intelligent individuals who seem to be convinced that, if an ancient structure has never yet fallen, in spite of its superficially unstable appearance, then this "proves" that it isn't likely to fall in the foreseeable future. They refuse to imagine that even the legendary butterfly, flapping its wings, could provide an external force capable of making things move.

A decade ago, my English friend Adrian Lyons was leading me on an inspection of a local dilapidated medieval castle, and he tried to reassure me when he saw that I wasn't too keen on crawling over rotted rafters: "This place was built centuries before we were born, and it'll still be standing long after us." Shortly after that outing, daredevil Adrian lost his life in the UK when he crashed his veteran jet aircraft while pulling out of a tight turn too close to the ground.

Here in the Vercors, many folk seem to consider that a precarious rock structure that hasn't yet crumbled and rolled down the slopes will no doubt remain in place forever. So, they don't sense its presence as a constant menace.

I see these cliffs, on the other side of the Bourne, from my bedroom window. In the center of the photo, the detached vertical pillar is most impressive when you look up at it from the Rouillard Bridge, a few hundred meters down from Gamone. It's composed of two sections, separated by a fissure, and the righthand section appears to be leaning down towards the road to Pont-en-Royans. If ever these rocks were to fall, they might not hurt anybody [because the zone is devoid of houses], but they would create a huge mess at the level of the road and the river.

I've often wondered whether specialists inspect such situations, to evaluate possible risks. I don't think so, because I have no idea how such an inspection could be carried out. After all, limestone cliffs of this kind are so crumbly that you wouldn't even find experienced rock climbers in such a place. So, we're left with the subjective appreciations of local folk who, for one reason or another, have their personal ideas about whether such-and-such a site is risky.

My neighbor Gérard Magnat, at Sirouza, lives quite close to this double pillar. From his balcony veranda, you look straight across at Mont Baret, and his house is located at roughly the same altitude as the pillar. When I called in at his place a few days ago, Gérard said to me, spontaneously: "For the last few months, I've had a strange feeling that the fissure between the two vertical sections of the pillar has widened a little. But I can't be certain, and people think I'm crazy..."