June 23 (UPI) — Lab experiments have confirmed the 50-year-old theory that an alien civilization could exploit a black hole for energy.
More than a half-century ago, British physicist Roger Penrose surmised that energy could be harvested from a black hole by dropping an object into it’s ergosphere, the outer layer of the black hole’s event horizon.
The object would need to be quickly split in two, allowing half to fall into the black hole and the other half recovered. According to Penrose’s theory, the recoil action would provide the recovered half of the object a loss of negative energy. It would, in effect, gain energy.
Not just any aliens could carry out such a complex engineering feat, Penrose acknowledged. If aliens were to harvest energy from a black hole, they’d need to be highly advanced.
In 1971, two years after Penrose published his theory, another physicist, Yakov Zel’dovich, claimed the idea could be put to the test on Earth using twisted light waves bounced off the surface of a cylinder spun at just the right speed. Zel’dovich claimed a phenomenon known as the rotational doppler effect would cause the reflected light waves to bounce back with surplus energy.
Zel’dovich’s proposal has gone untested, in part due to the need for the cylinder to rotate at speeds in excess of a billion revolutions per second — a technological impossibility.
To finally put Penrose’s original theory to the test, researchers at the University of Glasgow, in Scotland, developed an alternative experiment using sound waves instead of light waves. By using waves with lower frequencies, the test wouldn’t require the cylinder to spin so fast.
Researchers at the University of Glasgow’s School of Physics and Astronomy set up a unique combination of speakers to create a twist in the sound waves. Scientists directed the twisting sound waves toward a foam disc. Behind the disk, the team positioned a microphone.
Instead of bouncing off the foam disk, the sound waves traveled through and were picked up by the microphone on the other side. Recordings of the altered sound waves revealed changes in frequency and amplitude consistent with the doppler effect predicted by Zel’dovich.
Researchers detailed the results of their experiment this week in the journal Nature Physics.
“The linear version of the doppler effect is familiar to most people as the phenomenon that occurs as the pitch of an ambulance siren appears to rise as it approaches the listener but drops as it heads away,” lead study author Marion Cromb, a doctoral student at Glasgow, said in a news release. “It appears to rise because the sound waves are reaching the listener more frequently as the ambulance nears, then less frequently as it passes.”
“The rotational doppler effect is similar, but the effect is confined to a circular space,” Cromb said. “The twisted sound waves change their pitch when measured from the point of view of the rotating surface. If the surface rotates fast enough then the sound frequency can do something very strange — it can go from a positive frequency to a negative one, and in doing so steal some energy from the rotation of the surface.”
When researchers accelerated the spin of the foam disk, the sound from the speakers quieted, becoming too low to hear. As the disk spun faster, the pitch got higher and higher until it returned to its original pitch — only louder, with an amplitude 30 percent greater than before.
“What we heard during our experiment was extraordinary. 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,” Cromb said. “Those negative-frequency waves are capable of taking some of the energy from the spinning foam disc, becoming louder in the process — just as Zel’dovich proposed in 1971.”
Researchers suggest their surprise discovery has paved the way for a variety of new physics experiments. Scientists hope their test can be replicated using electromagnetic waves or some other kind of waves.