Evrim Yazgin
Cosmos science journalist
Physicists have simulated a black hole in a lab. Then it started glowing.
This allowed the team to realise that their black hole analogue may help explain so-called “Hawking radiation”, theorised to be emitted by black holes in nature.
Their analysis of the black hole in a bottle is presented in a paper published in the Physical Review Research journal.
Hawking radiation is a consequence of the extremeness of black holes. Because of the immense gravitational pull of these cosmic giants – which not even light can escape – black holes cause disturbances in the fabric of spacetime itself, leading to the emission of particles due to interruptions in fluctuations of quantum fields.
This type of radiation was first theorised by Stephen Hawking in 1974, but has never been observed because it is too faint for even our best telescopes.
But being able to produce and study Hawking radiation may help resolve the seemingly irreconcilable theories of nature: the general theory of relativity, which describes gravity, and quantum mechanics, which describes the behaviour of particles.
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Because of the extreme gravity and prevalence of bizarre quantum effects, black holes are thought to be prime candidates for finding out how to make these two theories get along.
Creating a black hole analogue is not new, but this new research allowed the physicists to “tune” their black hole and observe radiative effects in this type of experiment for the first time.
Black hole analogues were first put forward by Canadian physicist William Unruh, who conceptualised the “sonic black hole” in a 1981 paper. Unruh’s sonic black hole was based on the notion that sound vibrations, phonons, are unable to escape a region of fluid in which the fluid is flowing faster than the speed of sound in the local region (similar to light being unable to escape a black hole in space).
In essence, it’s too hard to make a black hole and study it because they are so wildly unstable. So, the physicists set out to just simulate conditions at a black hole’s event horizon (the point in space at which the black hole’s gravity is too strong for light to escape).
Led by Lotte Mertens, a PhD researcher at the University of Amsterdam in the Netherlands, the team produced their simulated event horizon using a single-file chain of atoms. Electrons ‘hop’ along the chain in ways that could be easily influenced by the physicists.
By tuning the hopping, the physicists could cause certain properties to vanish. They created a kind of event horizon that interfered with the wave-like nature of the electrons.
Meddling with the electrons’ field, the scientists found their event horizon rising in temperature. The radiative effect matched theoretical expectations that would be seen in an equivalent black hole system, but only when part of the chain extended beyond their event horizon analogue.
The results suggest that particles that are entangled across the event horizon are instrumental in generating Hawking radiation.
They found that their simulated event horizon only displayed thermal radiation under certain conditions. This suggests that Hawking radiation, too, may only be thermal in specific situations, including when there is a change in how spacetime warps because of gravity.
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We don’t have a unified theory yet, but the model offers a way for physicists to probe Hawking radiation without the extreme conditions of black holes.
Plus, the experiment is startlingly simple, offering up many avenues of further study.
“This can open a venue for exploring fundamental quantum-mechanical aspects alongside gravity and curved spacetimes in various condensed matter settings,” the researchers write in their paper.