The quest to use quantum mechanics to extract energy from nothing

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Hotta discovered, to his surprise, that a simple sequence of events could, in fact, induce the quantum vacuum to go negative, giving up energy it apparently did not have. “At first I thought I was wrong,” he said, “so I calculated again and checked my logic. But I couldn’t find any fault.”

The problem arises from the strange nature of the quantum vacuum, which is a quirky kind of nothing that comes dangerously close to resembling something. The uncertainty principle prohibits any quantum system from settling into a perfectly silent state of exactly zero energy. As a result, even a vacuum must always crackle with fluctuations in the quantum fields that fill it. These endless fluctuations imbue each field with a minimal amount of energy, known as zero-point energy. Physicists say that a system with this minimum energy is in the ground state. A system in its ground state is a bit like a car parked on the streets of Denver. Although it is well above sea level, it cannot go any lower.

And yet Hotta seemed to have found an underground garage. He realized that to open the door he only had to exploit an intrinsic entanglement in the crackle of the quantum field.

The ceaseless fluctuations of the vacuum cannot be used to power a perpetual motion machine, for example, because the fluctuations at any given location are completely random. If you imagine connecting a fancy quantum battery to a vacuum, half of the fluctuations would charge the device while the other half would drain it.

But quantum fields are intertwined: fluctuations in one place tend to coincide with fluctuations in another place. In 2008, Hotta published an article describing how two physicists, Alice and Bob, could exploit these correlations to extract energy from the ground state surrounding Bob. The schema is something like this:

Bob is in need of power, he wants to charge that fantasy quantum battery, but all he has access to is empty space. Fortunately, his friend Alice has a fully equipped physics lab in a far away place. Alice measures the field in her laboratory, injecting energy there and learning about the fluctuations from it. This experiment takes the general field out of the ground state, but as far as Bob can tell, his vacuum remains in the lowest energy state, fluctuating randomly.

But then Alice texts Bob her findings about the vacuum around his location, essentially telling Bob when to plug in his battery. After Bob reads the message from him, he can use the new knowledge to set up an experiment that draws energy from the vacuum, up to the amount injected by Alice.

“That information allows Bob, if he wishes, to time the fluctuations,” he said. Eduardo Martin Martinez, a theoretical physicist at the University of Waterloo and the Perimeter Institute who worked on one of the new experiments. (He added that the notion of time is more metaphorical than literal, due to the abstract nature of quantum fields.)

Bob cannot extract more energy than Alice put in, so energy is conserved. And he lacks the knowledge to extract the energy until Alice’s text arrives, so no effect travels faster than light. The protocol does not violate any sacred physical principles.