We all learned at school that the speed of light in a vacuum is a universal constant, a sort of impassable cosmic limit. Recently, researchers have therefore tried to slow it down, or even stop it completely. How did they do it? By diving into the strange world of quantum physics and using a very particular state of matter: the Bose-Einstein condensate.
The Bose-Einstein condensate: an extraordinary state of matter
Imagine a gas cooled to a temperature close to absolute zero. The atoms that compose it then behave in a very strange way: they begin to act like one and the same object, a bit like a wave. This is called a Bose-Einstein condensate. This state of matter, predicted by Albert Einstein and Satyendra Nath Bose, was first observed in the laboratory in the 1990s.
These condensates exhibit fascinating properties. For example, they have zero viscosity, which means they can flow without any friction. They can also trap light. More precisely, think of them as a kind of “quantum molasses.” When light passes through this molasses, it interacts with the atoms that compose it. It's as if the photons found themselves trapped in a very fine net, formed by these atoms.
Slowing down light: a scientific feat
To slow down light, scientists used a cloud of sodium atoms cooled to form a Bose-Einstein condensate. They then sent laser pulses onto this cloud. By interacting with the atoms in the condensate, the light was slowed considerably, reaching a speed of only 17 meters per second, or approximately 61 kilometers per hour.
The researchers didn't stop there. Indeed, they even managed to completely stop the light for a brief moment, before releasing it.
Why slow down the light?
You may wonder why scientists are interested in slowing down light. The fact is that the potential applications of this research are numerous. By using slowed light to store and process information, it could in particular be possible to develop computers capable of performing calculations well beyond the capabilities of current computers. Slowed light could also be used to create ultra-fast optical memories or secure communications systems. Finally, by studying the behavior of light in Bose-Einstein condensates, researchers hope to better understand the laws of quantum physics and the interactions between matter and light.
This work therefore opens up exciting perspectives for fundamental research and technological applications. They remind us that our understanding of the Universe is constantly evolving and that the frontiers of science are constantly being pushed back.
Philosophical implications: redefining our perception of reality
This mastery of light also opens up fascinating philosophical reflections. By slowing down or stopping light, scientists are pushing the boundaries of our understanding of fundamental concepts like time and space. Being able to manipulate the speed of light could one day change our perception of reality itself, notably by calling into question notions that we thought were immutable. This area of exploration reminds us that, despite spectacular advances, we are only in the early stages of discovering the secrets of the Universe.
Details of this work are published in Nature.
