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Forget even the most outlandish solar schemes—what if your local power plant were a black hole ?
That over-50-year-old theory began with an idea about what happens when you lower a tester into the mouth of a black hole. Physicists at the time thought they’d need an impossible machine to prove their theory, but now, researchers at the University of Glasgow have found a black hole lifehack.
The idea is simple ... by quantum and black hole standards, at least. In the mouth of a black hole, the combination of infinite density and strangeness inside the black hole and the rapidly rotating outer ergosphere would make the dangling object travel faster than light in order.
Think of how a needle stays poised on the surface of a spinning vinyl record: the record is spinning rapidly while the needle stands still. In 1969, physicist Roger Penrose developed this theory and hypothesized that the object would have “negative energy.”
So where does power generation come in?
“By dropping the object and splitting it in two so that one half falls into the black hole while the other is recovered, the recoil action would measure a loss of negative energy—effectively, the recovered half would gain energy extracted from the black hole's rotation,” the University of Glasgow explains in a statement. By playing off the different layers of wildly different mass, force, and more, an observer to this phenomenon could harness the energy deficit.
That observer would have to be advanced beyond anything humans can imagine today, like the makers of a hypothetical Dyson sphere or any other cosmic power structure. For this reason, the theory’s consequences have always been assigned to some alien civilization within the long timescale of the universe.
Two years after Penrose’s theory emerged, the soviet physicist Yakov Zel'dovich suggested a way to test it on Earth, but even his test required something beyond what humans could engineer: a cylinder like the one in the theory, spinning nearly as fast.
Now, researchers have found a way to subvert the conditions of the original test using sound instead of light. The Glasgow team writes:
“This concept, which is a key step towards the understanding that black holes may amplify quantum fluctuations, has not been verified experimentally owing to the challenging experimental requirement that the cylinder rotation rate must be larger than the incoming wave frequency. Here, we demonstrate experimentally that these conditions can be satisfied with acoustic waves.”
Sound waves travel much more slowly than light and occupy a much lower range of frequencies. The scientists cite the Doppler effect, which accounts for how sound distorts as a passing car honks its horn, for example. They positioned a ring of speakers around a rapidly rotating, sound-absorbing foam disc.
“What's happening is that the frequency of the sound waves is being doppler-shifted to zero as the spin speed increases. When the sound starts back up again, it's because the waves have been shifted from a positive frequency to a negative frequency,” researcher Marion Cromb explains in the statement. Then the sound began again and registered as 30 percent louder—because the negative frequency waves had stored energy, the way Penrose and Zel'dovich predicted.
The results aren’t just the stuff of science fiction, either.
“These experiments address an outstanding problem in fundamental physics and have implications for future research into the extraction of energy from rotating systems,” the researchers write. “We're keen to see how we can investigate the effect on different sources such as electromagnetic waves in the near future,” researcher Daniele Faccio adds in the statement.