Alien Civilization Could Use a Black Hole to Generate Energy – 50-Year-Old Theory Experimentally Verified

[flash13]

Alien Civilization Could Use a Black Hole to Generate Energy – 50-Year-Old Theory Experimentally Verified

Artist’s impression of an inner accretion flow and a jet from a supermassive black hole when it is actively feeding, for example, from a star that it recent tore apart. Image: ESO/L.

 

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A 50-year-old theory that began as speculation about how an alien civilization could use a black hole to generate energy has been experimentally verified for the first time in a

 

Glasgow research lab.

 

In 1969, British physicist Roger Penrose suggested that energy could be generated by lowering an object into the black hole’s ergosphere – the outer layer of the black hole’s

 

event horizon, where an object would have to move faster than the speed of light in order to remain still.

 

Penrose predicted that the object would acquire a negative energy in this unusual area of space. 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 scale of the engineering challenge the process would require is so great, however, that Penrose suggested only a very advanced, perhaps alien, civilization would be

 

equal to the task.

 

 

 

Two years later, another physicist named Yakov Zel’dovich suggested the theory could be tested with a more practical, earthbound experiment. He proposed that ’twisted’ light

 

waves, hitting the surface of a rotating metal cylinder turning at just the right speed, would end up being reflected with additional energy extracted from the cylinder’s rotation

 

thanks to a quirk of the rotational Doppler effect.

 

But Zel’dovich’s idea has remained solely in the realm of theory since 1971 because, for the experiment to work, his proposed metal cylinder would need to rotate at least a

 

billion times a second – another insurmountable challenge for the current limits of human engineering. 

 

Now, researchers from the University of Glasgow’s School of Physics and Astronomy have finally found a way to experimentally demonstrate the effect that Penrose and

 

Zel’dovich proposed by twisting sound instead of light – a much lower frequency source, and thus much more practical to demonstrate in the lab.

 

In a new paper published on June 22, 2020, in Nature Physics, the team describes how they built a system that uses a small ring of speakers to create a twist in the sound waves

 

analogous to the twist in the light waves proposed by Zel’dovich.

 

Credit: University of Glasgow

 

Those twisted sound waves were directed towards a rotating sound absorber made from a foam disc. A set of microphones behind the disc picked up the sound from the

 

speakers as it passed through the disc, which steadily increased the speed of its spin.

 

What the team were looking to hear in order to know that Penrose and Zel’dovich’s theories were correct was a distinctive change in the frequency and amplitude of the sound

 

waves as they traveled through the disc, caused by that quirk of the doppler effect.

 

Marion Cromb, a PhD student in the University’s School of Physics and Astronomy, is the paper’s lead author. Marion said: “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. 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. 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.”

 

As the speed of the spinning disc increases during the researchers’ experiment, the pitch of the sound from the speakers drops until it becomes too low to hear. Then, the pitch

 

rises back up again until it reaches its previous pitch – but louder, with amplitude of up to 30% greater than the original sound coming from the speakers.

 

Marion added: “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. 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.”

 

Professor Daniele Faccio, also of the University of Glasgow’s School of Physics and Astronomy, is a co-author on the paper. Prof Faccio added: “We’re thrilled to have been able to

 

experimentally verify some extremely odd physics a half-century after the theory was first proposed. It’s strange to think that we’ve been able to confirm a half-century-old theory

 

with cosmic origins here in our lab in the west of Scotland, but we think it will open up a lot of new avenues of scientific exploration. We’re keen to see how we can investigate the

 

effect on different sources such as electromagnetic waves in the near future.”

 

Reference: “Amplification of waves from a rotating body” by Marion Cromb, Graham M. Gibson, Ermes Toninelli, Miles J. Padgett, Ewan M. Wright and Daniele Faccio, 22 June

 

2020, Nature Physics.

DOI: 10.1038/s41567-020-0944-3

 

The research team’s paper, titled ‘Amplification of waves from a rotating body’, is published in Nature Physics. The research was supported by funding from the Engineering and

 

Physical Sciences Research Council (EPSRC) and the European Union’s Horizon 2020 program.

 

Source

[flash13]

Can energy be sucked out of a black hole?

 

 

A rotating black hole is such an extreme force of nature that it drags surrounding time and space around with it. So it is only natural to ask whether black holes could be used as

 

some sort of energy source. In 1969, mathematical physicist Roger Penrose proposed a method to do just this, now known as the "Penrose Process."

 

The method could be used by sophisticated civilizations (aliens or future humans) to harvest energy by making "black hole bombs." Some of the physics required to do so,

 

however, had never been experimentally verified — until now. Our study confirming the underlying physics has just been published in Nature Physics.

 

Around its event horizon (the boundary around a black hole beyond which nothing, not even light, can escape), a rotating black hole creates a region called the "ergosphere." If

 

an object falls into the ergosphere in such a way that it splits — with one part falling into the black hole and the other escaping — the part that flees effectively gains energy at

 

the expense of the black hole. So by sending objects or light toward a rotating black hole, we could get energy back.

 

But does this theory hold up? In 1971, the Russian physicist Yakov Zel'dovich translated it to other rotating systems that could be tested back on Earth. The black hole became a

 

rotating cylinder made from a material that can absorb energy.

 

Zel'dovich imagined that light waves could extract energy from the cylinder and become amplified. For the amplification effect to work, however, these waves need to have

 

something called "angular momentum," which twists them into spirals.

 

When twisted light waves hit such a cylinder, their frequency should change because of something called the "Doppler shift." You have most likely experienced this when listening

 

to an ambulance siren. When it moves toward you it has a higher pitch than when it moves away from you — the direction of travel changes the pitch of the sound. In a similar

 

way, changes in rotational speed alter the perceived frequency of a light wave.

 

If the cylinder rotates fast enough, the altered wave frequency should drop so low that it will become negative (which simply means that the wave spins in the opposite direction).

 

Positive frequency waves should be partly absorbed by the cylinder, losing energy. But the negative frequency waves would transform this loss into gain and instead become

 

amplified by the cylinder. They would extract energy from the rotation, just like the object escaping from Penrose's black hole.

 

Testing Zeldovich's theory may appear simple. But the rotating object needs to spin at the same or higher frequency as the waves. To amplify visible light waves, which oscillate at

 

a frequency of hundreds of trillions of times a second, you would need to rotate an absorbing object billions of times faster than anything that's mechanically possible today.

 

Breakthrough at last

Light travels at about 300 million meters per second. So to make the theory easier to test, we opted to use sound waves, which travel roughly a million times slower, meaning we

 

didn't need the absorber to rotate so quickly.

 

To create a twisted sound wave, we used a ring of speakers all emitting the same frequency but starting at slightly different times, so the sound follows a spiral. For our rotating

 

absorber we used a piece of sound-absorbing foam attached to a motor. Microphones placed inside the foam allowed us to record the sound after it had interacted with the

 

rotating absorber.

 

We found that when the foam span slowly (at a low frequency), the sound we recorded was quieter because it had been absorbed by the foam. But when we spun the foam fast

 

enough for it to Doppler shift the frequency of the sound waves enough to make them negative, the sound became louder.

 

This can only mean that the sound wave had taken energy from our rotating absorber, finally proving the 50-year-old theory.

 

Black hole bomb

 

All this of course does not explicitly verify that Penrose's idea for energy extraction will actually work for a black hole. Rather, our experiments verify the counter-intuitive

 

underlying physics by showing that shifting wave frequencies from positive to negative results in the waves gaining rather than losing energy.

 

While we are not anywhere close to extracting energy from a rotating black hole, this doesn't mean it couldn't be done by a very advanced alien civilization — or indeed our own

 

civilization in the distant future. Such a civilization could build a structure around the black hole that rotates with it and then drop asteroids or even electromagnetic waves into it

 

what would be reflected with more energy.

 

Even better, they could build a so-called black hole bomb by completely surrounding the black hole with a reflecting mirror shell. Light shone into the black hole would return

 

amplified, and then reflected back by the mirror to the black hole to be amplified again, and so on.

 

The energy would increase exponentially in a back-and-forth runaway explosion. But by letting some of this amplified light out of the shell through a hole, you could control the

 

process and produce essentially limitless energy.

 

Although this is still science fiction, in a very distant future when the universe has all but died and the only remnants of galaxies and stars are black holes, this method would be

 

the only hope for any civilization to survive. This would be a universe with immense, isolated sources of energy, shining bright in an otherwise completely black sky.

 

Source

[Karlston]

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