Artificial “White Hole” Boosts Stephen Hawking’s Black-Hole Theory

Images Stephen Hawkings great discovery was that the mysterious regions in space we call black holes radiate heat through quantum effects. Hawking has said that "black holes are not really black after all: they glow like a hot body, and the smaller they are, the more they glow." Hawking's famous theory says that the temperature of a black hole varies inversely to its mass. The mathematician Louis Crane proposed a scifi-like scenario back in 1994 that billions of years in the future, after all the stars have burned out, that small black holes could be created to generate heat and guarantee survival of the species.

A team of UBC physicists and engineers have designed a experiment featuring a trough of flowing water to help bolster the 35-year-old theory proposed by Hawking. In 1974, Hawking predicted that black holes–often thought of having gravitational pulls so strong that nothing escapes from them–emit a very weak level of radiation. According to the theory, pairs of photons are torn apart by a black hole's gravitational field–one photon falls into the black hole, but the other escapes as a form of radiation.

In results outlined in the latest issue of Physical Review Letters, a team of UBC researchers led by international postdoctoral researcher Silke Weinfurtner put the test to Hawking's theory by creating a 'white hole' in a six-metre-long flume of flowing water.

Placing an airplane wing-shaped obstacle in the path of the flowing water created a region of high-velocity flow which blocked surface waves, generated downstream, from traveling upstream. The obstruction simulated a white hole, the temporal reverse of a black hole.

The shallow surface waves divided into pairs of deep-water waves, analogous to the photon pairs featured in Hawking's theory. Like in black holes, they showed that the analog would also emit a thermal spectrum of radiation.

"While this creative simulation obviously doesn't prove Hawking's theory, it does show that his ideas apply broadly," says UBC theoretical physicist William Unruh.

"This experiment also exemplifies all of the strengths of UBC's research enterprise–the involvement of students, our international outreach and connections, and a very open, collaborative way of looking at scientific questions," says Unruh.

Meanwhile, early last year in Hanover, New Hampshire a bold team of researchers at Dartmouth College proposed a new way of creating a reproduction black hole in the laboratory on a much-tinier scale than their celestial counterparts. The new method to create a tiny quantum sized black hole would allow researchers to better understand what physicist Stephen Hawking proposed more than 35 years ago: black holes are not totally void of activity; they emit photons, which is now known as Hawking radiation.

"Hawking famously showed that black holes radiate energy according to a thermal spectrum," said Paul Nation, an author on the paper and a graduate student at Dartmouth. "His calculations relied on assumptions about the physics of ultra-high energies and quantum gravity. Because we can't yet take measurements from real black holes, we need a way to recreate this phenomenon in the lab in order to study it, to validate it."

The researchers showed that a magnetic field-pulsed microwave transmission line containing an array of superconducting quantum interference devices, or SQUIDs, not only reproduces physics analogous to that of a radiating black hole, but does so in a system where the high energy and quantum mechanical properties are well understood and can be directly controlled in the laboratory.

"We can also manipulate the strength of the applied magnetic field so that the SQUID array can be used to probe black hole radiation beyond what was considered by Hawking," said Miles Blencowe, another author on the paper and a professor of physics and astronomy at Dartmouth.

"In addition to being able to study analogue quantum gravity effects, the new, SQUID-based proposal may be a more straightforward method to detect the Hawking radiation," says Blencowe.

In a paper published in the August 20 issue of Physical Review Letters, the flagship journal of the American Physical Society

Casey Kazan.


More information: Physical Review Letters paper: … 6/i2/e021302
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