Scientists have created a lab-grown analogue of a black hole to test one of Stephen Hawking’s most famous theories – and it’s behaving exactly as he predicted.
The experiment, created by using a single-file chain of atoms to simulate the event horizon of a black hole, added further evidence to Hawking’s theory that black holes should emit a faint glow of radiation from virtual particles that appear randomly near their borders. . In addition, the researchers found that most of the light particles, or photons, should be produced around the edges of the cosmic monsters. The team published their findings Nov. 8 in the journal Physical Review Research.
According to quantum field theory, there is no such thing as an empty vacuum. Instead, space is full of tiny vibrations that, if imbued with enough energy, randomly burst into virtual particles—particle-antiparticle pairs that almost immediately annihilate each other, producing light. In 1974, Stephen Hawking predicted that the extreme gravitational force felt at the mouths of black holes—their event horizons—would summon photons into existence in this way. Gravity, according to Einstein’s theory of general relativity, distorts spacetime, so that quantum fields become more distorted the closer they get to the immense gravitational pull of a black hole singularity.
Because of the uncertainty and weirdness of quantum mechanics, this warping creates uneven time zones that move differently and subsequent energy spikes in the field. It’s these energy mismatches that cause virtual particles to shoot out of what appears to be nothing at the edges of black holes, before annihilating to produce a faint glow called Hawking radiation.
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Physicists are interested in Hawking’s prediction because it is made at the extreme limit of two grand but currently irreconcilable theories of physics: Einstein’s theory of general relativity, which describes the world of large objects, and quantum mechanics, which details the strange behavior of smaller ones . particles.
But direct detection of the supposed light is something astrophysicists are unlikely to ever achieve. First, there are the considerable challenges of both traveling to a black hole—the closest known one being 1,566 light-years from Earth—and, once there, not being engulfed and spaghettified by its immense gravitational pull. Second, the number of Hawking photons appearing around black holes is thought to be small; and in most cases it would be drowned out by other light-producing effects, such as high-energy X-rays spat out from matter swirling around the black hole’s abyss.
In the absence of a true black hole, physicists have begun searching for Hawking radiation in experiments that simulate their extreme conditions. In 2021, scientists used a one-dimensional array of 8,000 supercooled, laser-confined atoms of the element rubidium, a soft metal, to create virtual particles in the form of wave-like excitations along the chain.
Now, another atomic chain experiment has accomplished a similar feat, this time by tuning how easily electrons can jump from one atom to another in the line, creating a synthetic version of a black hole’s space-time warp horizon. After adjusting this chain so that part of it fell above the simulated event horizon, the researchers recorded an increase in temperature in the chain – a result that mimicked the infrared radiation produced around black holes. The discovery suggests that Hawking radiation could arise as an effect of quantum entanglement between particles positioned on either side of an event horizon.
Interestingly, the effect only appeared when the amplitude of the hops went from a few set configurations of flat spacetime to a warped one—suggesting that Hawking radiation requires a change in specific energy configurations of spacetime to be produced. Because the strong distortions of gravity produced by the black hole are absent from the model, what this means for a theory of quantum gravity and for potential real Hawking radiation produced naturally is unclear, but it nevertheless provides a tantalizing glimpse into previously unexplored physics.