In the early seventies it was realized that the notion of particles depends on the specific details of the quantum measurement process used to detect them, and that the state of motion of the measuring device can determine whether or not particles are observed. This discovery has created a new viewpoint which was prompted by Fulling, Unruh and Hawking’s work demonstrating that the number of particles found in a region depends on the acceleration of the measuring device. For example, the vacuum, i.e. a region that contains no particles at all, would be seen by an accelerated observer as a region with particles. The number of particles and their energy would increase with increased acceleration. This effect is known as the Unruh effect.
Our group in collaboration with Benni Reznik and Ignacio Cirac have studied the feasibility of the experimental realization of these effects in BEC. We have proposed a way to measure the Unruh effect in Bose Einstein Condensates which serves as a simulator for the real vacuum. In this proposal the Unruh temperature would reveal itself by the number of particles of a specific kind.