A researcher claims to have produced a simulation of Hawking radiation, which if true will give physicists the chance to test one of Stephen Hawking's most significant predictions.
In 1974, Hawking upended ideas about black holes with his theory that just outside the event horizon, particle-antiparticle pairs should appear as a result of the black hole's gravitational field. One of these would be drawn into the hole, but the other escape. Since the appearance of the pair draws energy from the hole and only half of this is recaptured, the effect is to reduce the hole's mass, causing it to eventually evaporate.
Hawking's equations have won widespread support from physicists, and are a major contributor to his reputation. However, attempts to find evidence of escaping particles around black holes have so far been unsuccessful. In 2010, Franco Belgiorno of the University of Milan claimed to have produced Hawking radiation in the lab, but it is now thought their observations are something different.
Now Professor Jeff Steinhauer of the Technion-Israel Institute of Technology claims to be getting close. Steinhauer cooled rubidium atoms to less than a billionth of a degree above absolute zero. At this point, the rubidium becomes a Bose-Einstein condensate, a collection of bosons that collapse into their lowest quantum state. He then used lasers to vibrate the condensate, trapping sound waves from quantum fluctuations in a way he says mimic the way gravity traps energy around a black hole.
The fluctuations occur in pairs, modelling the particle-antiparticle pairs appearing around a black hole. Steinhauer adjusted the lasers so that the condensate had two “event horizons” the sound waves could not cross.
In Nature, Steinhauer reported, “the observation of Hawking radiation emitted by this black-hole analogue.” Moreover, he found that the standing wave produced between his “event horizons” experienced exponential growth, becoming self-amplifying, a predicted feature of Hawking radiation.
In a commentary in the same edition of Nature, Ron Cowen writes, “Such objects could one day help resolve the so-called black hole ‘information paradox’ - the question of whether information that falls into a black hole disappears forever.”
Cowen notes that it is still unclear how well Steinhauer's creation models a real black hole. “The amplification in Steinhauer’s model allows him to detect only one frequency of the radiation, so he cannot be sure it has Hawking’s predicted intensity at different frequencies that true Hawking radiation would have.“
However, Steinhauer has ideas on how to improve what he has made to resemble black holes further. If he succeeds, he may be able to answer one of the great questions of modern physics: how can quantum mechanics and general relativity be reconciled?
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