Unruh effect creates particles out of thin air

Imagine yourself sitting alongside Han Solo and Chewbacca aboard the Millennium Falcon, one of the fastest ships in the galaxy. You hardly have time to buckle up before you’re ready to go: the spaceship accelerates and begins its journey through hyperspace. The dark surroundings are getting brighter and brighter, while lots of bright dots rush past you.

Star Wars fans probably remember the iconic film scenes that have captivated millions of people for decades. As exciting as the story is – it has little to do with real science. Actually, the points of light rushing past are supposed to represent the stars, but the Doppler effect would make them invisible at such accelerations. Nevertheless, the scene described at the beginning could not be that far removed from reality. In this case, the passing lights would not come from the stars, but from popping particles. In the coming years, physicists could even witness it.

We are talking about a relativistic phenomenon that, in contrast to the curvature of space and time or radiating black holes, is hardly known to the general public: the Unruh effect. This describes what an accelerated person moving through a vacuum experiences. She feels as if she is flying through an environment full of particles that create an elevated temperature. A stationary observer, on the other hand, sees none of this – except, of course, for the moving person. This gives Einstein’s theory of relativity a whole new dimension: now not only time spans and distances depend on the reference system – but also the existence of particles! …