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Physicists find a shortcut to see the elusive quantum glow

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Physicists find a shortcut to see the elusive quantum glow

Theoretical physics is full of amazing and wonderful concepts: wormholes, quantum foam and multiverses, and these are just some of them. The problem is that although such things easily arise from the equations of theorists, they are virtually impossible to create and test in the laboratory. But for one such “untested” theory, an experimental setup can only be on the horizon.

Researchers from the Massachusetts Institute of Technology and the University of Waterloo in Ontario say they have found a way check the Unruh effect, a bizarre phenomenon that is projected to arise from objects moving through empty space. If scientists can observe the effect, this feat may confirm some long-held assumptions about the physics of black holes. Their proposal was published in Physical review letters April 21.

If you could observe the Unruh effect in person, it might look like a jump into hyperspace in Millennial Falcon– a sudden surge of light covers your gaze on the black void. When an object accelerates in a vacuum, it wraps itself in a warm cloak of luminous particles. The faster the acceleration, the warmer the glow. “It’s extremely strange,” because the vacuum must be empty by definition, explains quantum physicist Vivishek Sudhir of the Massachusetts Institute of Technology, one of the study’s co-authors. “Do you know where it came from?”

Where this comes from is due to the fact that the so-called empty space is not empty at all, but filled with overlapping energy quantum fields. Fluctuations in these fields can be caused by photons, electrons and other particles and can be caused by an accelerating body. In essence, an object moving through a vacuum impregnated with a field takes up a fraction of the energy of the fields, which is then re-emitted as Unru radiation.

The effect is named after the physicist-theorist Bill Unru, who described his eponymous phenomenon in 1976. But two other researchers – mathematician Stephen Fuling and physicist Paul Davis – developed the formula independently three years after Unru (in 1973 and 1975, respectively). ).

“I remember it vividly,” says Davis, who is now a professor-regent at Arizona State University. “I did the calculations while sitting at my wife’s dressing table because I had neither a desk nor an office.”

A year later Davis met Unru at a conference where Unru was lecturing on his recent breakthrough. Davis was surprised to hear Unru describe a phenomenon very similar to what followed from his own dressing table calculations. “And then we got together at the bar,” Davis recalls. The two quickly established a collaboration that lasted several years.

Davis, Fuling, and Henro approached their work from a purely theoretical standpoint; they never expected anyone to do around this a real experiment. However, as technology advances, ideas that were once attributed to the world of theory, such as gravitational waves and the Higgs boson, may become within the reach of real observation. And observing the Unru effect, it turns out, could help solidify another distant concept of physics.

“The reason people are working on the Unru effect is not that they think accelerated observers are so important,” said Christoph Adami, a professor of physics, astronomy and molecular biology at the University of Michigan who was not involved in the study. “They’re working on it because of the direct connection to black hole physics.”

In essence, the Unru effect is the reverse of a much better-known phenomenon in physics: Hawking radiation, named after physicist Stephen Hawking, who theorized that an almost imperceptible halo of light should emanate from black holes if they slowly evaporate.

In the case of Hawking radiation, this warm fuzzy effect is essentially the result of the involvement of particles in a black hole under the action of gravity. But for the Unru effect it is a question of acceleration, which, according to Einstein’s equivalence principle, is mathematically equal to gravity.

Imagine you are standing in an elevator. With a push the car goes up to the next floor, and for a moment you feel that you are being pulled to the floor. From your point of view, “it is, in fact, indistinguishable from the earth’s gravity, which suddenly arose,” – says Sudhir.

The same is true, he says, in terms of mathematics. “It’s so simple: there’s an equivalence between gravity and acceleration,” Sudhir adds.

Despite theoretical fame, scientists have not yet observed the effect of Unru. (And for that matter, they also failed to see Hawking’s radiation.) This is because the Unru effect has long been considered extremely difficult to test experimentally. In most cases, researchers will need to subject the object to a ridiculous acceleration – more than 25 quintillion many times the force of gravity of the Earth – to produce a measurable emission. Alternatively, more accessible accelerations can be used, but in this case the probability of obtaining a visual effect will be so low that such an experiment must be conducted continuously for billions of years. However, Sudhir and his co-authors believe they have found a loophole.

By capturing one electron in a vacuum using a magnetic field and then dispersing it through a carefully tuned photon bath, the researchers realized they could “stimulate” a particle by artificially raising it to a state of higher energy. This extra energy increases the effect of acceleration, which means that by using the electron itself as a sensor, the researchers were able to isolate the Unru radiation that surrounds the particle without applying as much g-force (or wait for eons).

Unfortunately, the photon bath, which boosts energy, also adds background “noise,” amplifying other effects of the quantum field in a vacuum. “This is exactly what we do not want to happen,” Sudhir said. But by carefully monitoring the trajectory of the electron, experimenters must be able to nullify this potential interference – a process that Sudhir compares to throwing an invisible cloak on a particle.

And unlike the kit needed for most other advanced particle physics experiments, such as giant superconducting magnets and the Large Hadron Collider beam lines at CERN, the researchers say their UNRU simulation can be created at most university labs. “It doesn’t have to be some big experiment,” says co-author Barbara Shoda, a physicist at the University of Waterloo. In fact, Sudhir and his doctor of philosophy. students are currently developing a version they intend to build, and hope it will work in the next few years.

Adam sees the new study as an elegant synthesis of several different disciplines, including classical physics, atomic physics and quantum field theory. “I think this paper is correct,” he said. But, like the Unru effect itself, “to some extent it is clear that this calculation was made earlier.”

For Davis, the ability to test the effect could open new interesting doors for both theoretical and applied physics, further confirming the almost unobservable phenomena predicted by theorists while expanding the range of tools that experimenters can use to study nature. “What makes it such a successful discipline in physics is that experiment and theory go very hand in hand,” he says. “Two in a step.” Unruh effect testing promises to be a top achievement for both.

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