Warp drive experiment to turn atoms invisible could finally test Stephen Hawking's most famous prediction

A new warp speed experiment might finally put scientist Stephen Hawking's most famous prediction about black holes to the test.
Scientists may capture a glimpse of the ethereal quantum glow that envelops things traveling at near to the speed of light by coaxing an atom to become invisible, according to the new idea.

The Unruh (or Fulling-Davies-Unruh) effect causes the area surrounding quickly speeding objects to appear to be filled with a swarm of virtual particles, bathing them in a warm glow. Because the phenomenon is so closely connected to the Hawking effect, in which virtual particles known as Hawking radiation spontaneously appear at the fringes of black holes, scientists have been looking for signs of the other's existence for a long time.

However, detecting either impact is extremely difficult. Hawking radiation only exists on the frightening edge of a black hole, and reaching the necessary acceleration for the Unruh effect would very certainly need the use of a warp engine. Now, a startling new suggestion published in the journal Physical Review Letters on April 26 has the potential to change that. The researchers claim to have discovered a way to greatly increase the power of the Unruh effect by using a technology that basically turns matter invisible.

"Now at least we know there is a chance in our lifetimes where we might actually see this effect," said co-author Vivishek Sudhir, an assistant professor of mechanical engineering at MIT and one of the experiment's designers. "It’s a hard experiment, and there’s no guarantee that we’d be able to do it, but this idea is our nearest hope." 

The Unruh effect, first hypothesized by scientists in the 1970s, is one of numerous quantum field theory predictions. There is no such thing as an empty vacuum, according to this notion. In reality, any pocket of space is densely packed with infinite quantum-scale vibrations that, given enough energy, can spontaneously explode into particle-antiparticle pairs that nearly instantly destroy each other. And each particle, whether matter or light, is nothing more than a localized excitation of this quantum field.

Stephen Hawking predicted in 1974 that the intense gravitational force felt at the margins of black holes, called their event horizons, would produce virtual particles.

According to Einstein's general theory of relativity, gravity bends space-time, causing quantum fields to become increasingly twisted as they grow closer to the massive gravitational drag of a black hole's singularity.

The quantum field is warped as a result of the uncertainty and strangeness of quantum physics, resulting in unequal pockets of unevenly flowing time and consequent energy spikes across the field. At the outskirts of black holes, these energy mismatches cause virtual particles to arise from what appears to be nothing.

"Black holes are believed to be not entirely black," said lead scientist Barbara Oda, a physics PhD student at the University of Waterloo in Canada. "Instead, as Stephen Hawking discovered, black holes should emit radiation." 

The Unruh effect, like the Hawking effect, produces virtual particles through a strange blending of quantum physics with Einstein's expected relativistic effects. But this time, rather than being produced by black holes and general relativity, the distortions are created by near light-speeds and special relativity, which states that time slows down when an object approaches the speed of light.

A stationary atom can only grow its energy by waiting for a genuine photon to excite one of its electrons, according to quantum theory. However, perturbations in the quantum field can build enough to seem like genuine photons to an accelerating atom. From the perspective of a speeding atom, it will be passing through a mob of warm light particles, all of which will heat it up. The Unruh effect's heat would be a clear symptom.

However, the accelerations necessary to achieve the effect are significantly greater than any particle accelerator now available. To create a glow hot enough for current detectors, an atom would have to accelerate to the speed of light in less than a millionth of a second – encountering a g force of a quadrillion meters per second squared.

"To see this effect in a short amount of time, you’d have to have some incredible acceleration," Sudhir added. "If you instead had some reasonable acceleration, you’d have to wait a ginormous amount of time — longer than the age of the universe — to see a measurable effect." 

The researchers devised an inventive solution to make the illusion possible. Photons make quantum fluctuations denser, therefore an atom moving in a vacuum while being blasted by light from a high-intensity laser might theoretically create the Unruh effect, even at low accelerations. The concern is that the atom may interact with the laser light, absorbing it and raising the atom's energy level, creating heat that would drown out the Unruh effect's heat.

However, the researchers discovered another another workaround: acceleration-induced transparency. If an atom is compelled to take a particularly specific path through a field of photons, it will be unable to "see" photons of a particular frequency, thereby rendering them invisible to the atom. The researchers would be able to test for the Unruh effect at this exact frequency of light by daisy-chaining all of these workarounds.

It will be difficult to make that strategy a reality. The researchers intend to construct a laboratory-scale particle accelerator that will accelerate an electron to light speed while striking it with a microwave beam. They want to perform tests using the effect if they can detect it, particularly those that would allow them to investigate the probable links between Einstein's theory of relativity and quantum mechanics.

"The theory of general relativity and the theory of quantum mechanics are currently still somewhat at odds, but there has to be a unifying theory that describes how things function in the universe," said co-author Achim Kempf, an applied mathematics professor at the University of Waterloo. "We've been looking for a way to unite these two big theories, and this work is helping to move us closer by opening up opportunities for testing new theories against experiments."