Physicists Find a Shortcut to Seeing an Elusive Quantum Glow

There are many strange and wonderful concepts in theoretical physics, such as quantum foam and multiverses. The problem is that it is almost impossible to create and test such things in a laboratory. An experimental setup might be on the horizon for one such theory.

Researchers at the Massachusetts Institute of Technology and the University of Waterloo in Ontario say they have found a way to test the Unruh effect, a bizarre phenomenon predicted to arise from objects moving through empty space. If scientists can observe the effect, they could confirm some assumptions about the physics of black holes. Their proposal was published in Physical Review Letters.

If you could see the Unruh effect in person, it would look like jumping to hyperspace in the Millennium Falcon, a sudden rush of light bathing your view of an otherwise black void. An object is swaddled in a warm cloak of glowing particles when it is in a vacuum. The glow is warmer when the speed of the acceleration is faster.

It comes from the fact that empty space is not empty at all but rather suffused by energetic quantum fields. Fluctuations in these fields can give rise to particles and can be sparked by a body. An object speeding through a field-soaked vacuum picks up a small amount of energy, which is then reemitted as Unruh radiation.

The effect is named after Bill Unruh, a theoretical physicist who described his phenomenon in 1976. The formula was worked out by two other researchers, Stephen Fulling and Paul Davies.

Davies, who is now a regents professor at Arizona State University, remembers it vividly.

Davies and Unruh met at a conference where Unruh was giving a lecture. Davies was surprised to hear that Unruh had described a similar phenomenon. The two struck up a partnership that lasted several years.

Davies, Fulling and Unruh never expected anyone to design a real-world experiment around their work. As technology advances, ideas that were once considered to be theoretical can be seen. The Unruh effect could help cement another far-out physics concept.

The reason people are working on the Unruh effect is not because they think that accelerated observers are important, according to a professor at Michigan State University.

The Unruh effect is a flip side of a famous physics phenomenon called Hawking radiation, which theorizes that a halo of light should leak from black holes as they slowly evaporate.

The warm fuzzy effect is caused by particles being pulled into a black hole by gravity. The Unruh effect is a matter of acceleration, as per Einstein's equivalence principle.

You are in an elevator. For a moment, you feel yourself pulled toward the floor when the car rushes up to the next floor. From your point of view, that is essentially the same as Earth's gravity suddenly being turned up.

He says that the same holds true from a math perspective.

Scientists have yet to observe the Unruh effect. They haven't been able to see Hawking radiation. The Unruh effect has long been considered difficult to test. In order to produce a measurable emission, researchers would need an object to accelerate up to 25 quintillion times the force of Earth's gravity. If more accessible accelerations were used, the experiment would need to run continuously for billions of years. The authors believe they have found a loophole.

By grabbing hold of a single electron in a vacuum with a magnetic field, the researchers were able to boost it up to a higher energy state. Researchers could pick out Unruh radiation surrounding the particle without having to apply so many g-forces if they used the electron as a sensor.

We don't want that to happen because an energy-boosting photon bath adds background noise and quantum-field effects in the vacuum. The experimenters should be able to prevent interference by controlling the electron's trajectory.

The Unruh effect simulation could be set up in most university labs, unlike the kit required for most other cutting-edge particle physics experiments. The students are currently designing a version that they hope to have running in the next few years.

The new research is an elegant synthesis of several different disciplines, including classical physics, atomic physics and quantum field theory. It is clear that this calculation has been done before.

The potential to test the effect could open up exciting new doors for both theoretical and applied physics.