We all know that invisibility cloaks can protect Harry Potter from Filch and his cat Mrs. Norris, but now physicists in France and the UK say they may be used to hide buildings from the devastating effects of earthquakes as well. Sound like fiction? It’s not! Stefan Enoch and his team at the Fresnel Institute in Marseilles, France have been studying other applications for the physics behind invisibility cloaks. The result of their research is an “earthquake cloak” that could render objects “invisible” to shocks, storm waves or tsunamis. And they aren’t even Level 8 mages!
How does the cloak work? In order to understand the mechanics, it’s important to know that the seismic waves of an earthquake fall into two main categories: body waves that roll through the Earth, and surface waves that travel, naturally, across the surface. The team’s findings show that controlling body waves would be too complex, but they’ve also concluded that controlling surface waves is possible within the constructs of conventional engineering. This conclusion actually works out quite well since it is surface waves that are more destructive, says team member Sebastien Guenneau at the University of Liverpool.
The conceptual cloak will be made up of several large, concentric plastic rings affixed to the Earth’s surface. In order for the destructive surface waves to pass smoothly into the plastic, the stiffness and elasticity of the rings must be very closely controlled. The waves that travel through the cloak are compressed into minuscule fluctuations in pressure and density and are able to travel along the fastest path available. The path can be molded into an arc that directs surface waves away from objects inside the cloak by tweaking the characteristics of the plastic. As soon as the waves exit the cloak, they return to their original, larger size.
Although the magical rings could render buildings “invisible” to earthquakes, it is possible to make the cloak itself invisible as well. Guenneau suggests that the structures could be built right into the foundation of the building itself. In terms of size, in order to protect a building 10 meters across, each ring would need to be about 1 to 10 meters in diameter and 10 centimeters thick.
Of course, all of these theories still need to be tested in real life experiments, but if Enoch’s findings do pan out, countless lives could be saved and disasters averted. Physicist Ulf Leonhardt at the University of St. Andrews, who was not involved in the study, said of the progress that it is possible that invisibility physics may see its first real world applications in manipulating seismic waves rather than rays of light. If successful, invisibility rings could also be scaled down to protect smaller objects.