Physicists have devised a way to see the elusive “Unruh Effect” in the lab

Physicists have devised a way to see the elusive "Unruh Effect" in the lab
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illustration: Karl Gustavson

A team of physicists say they did discovered two properties of matter’s acceleration that they believe could make a never-before-seen type of radiation visible. The newly described Properties mean that the observation of the radiation – the so-called Unruh effect – could take place in a benchtop laboratory experiment.

The unruh effect in nature would theoretically require ridiculous acceleration to become visibleand because it is only visible from the perspective of the accelerating object in vacuum, it is essentially impossible to see. But thanks to recent advances, it might be possible to observe the Unruh effect in a laboratory experiment.

In the new research, a team of scientists described two previously unknown aspects of the quantum field that could mean the Unruh effect could be observed directly. First, the effect can be stimulated, meaning that the normally weak effect could be tricked into becoming more visible under certain conditions. The second phenomenon is that a sufficiently excited accelerating atom can become transparent. The team’s research was released in Physical Review Letters this spring.

The Unruh effect (or Fulling-Davies-Unruh effect, so named after the physicists who first suggested its existence in the 1970s) is a phenomenon predicted by quantum field theory, which states that an entity (let it a particle or a spaceship ) accelerating in a vacuum glows – although this glow does notI will not hangwhat the hell any external observer who is not also accelerating in vacuum.

“Acceleration-induced transparency means that the Unruh effect detector becomes transparent to everyday transitions due to the nature of its movement,” said Barbara Šoda, a physicist at the University of Waterloo and lead author of the study, in a video call with Gizmodo. Just as Hawking radiation is emitted by black holes when their gravity attracts particles, the Unruh effect is emitted by objects as they accelerate in space.

There are a few reasons why the Unruh effect has never been observed directly. For one, the effect requires a ridiculous amount of linear acceleration to occur; to reach a temperature of 1 Kelvin at which the accelerating observer would see a glow, the observer would have to be acceleratedat 100 trillion meters per square second. The glow of the unruh effect is thermal; when an object accelerates faster, the temperature of the glow gets warmer.

Previous methods for observing the Unruh effect were suggested. But this The team believes their results give them a compelling chance of seeing the effect about the properties of the quantum field.

“We want to set up a specific experiment that can clearly demonstrate the Unruh effect and later provide a platform for studying various aspects related to it,” said Vivishek Sudhir, a physicist at MIT and co-author of the recent work. “Clearly, the key word here is that clusters of particles are really being accelerated in a particle accelerator, which means that it becomes very difficult to infer the extremely subtle Unruh effect amidst the various interactions between particles in a cluster.”

“In a sense,” Sudhir concluded, “we need to more accurately measure the properties of a well-identified single accelerated particle, which particle accelerators are not designed to do.”

Hawking radiation is predicted to be emitted from black holes, as these two are imaged by the Event Horizon Telescope.

Hawking radiation is predicted to be emitted from black holes, as these two are imaged by the Event Horizon Telescope.
picture: EHT collaboration

The essence of their proposed experiment is to stimulate the Unruh effect in a laboratory setting, using an atom as a detector of the Unruh effect. By irradiating a single atom with photons, the team would elevate the particle to a higher energy state, and its acceleration-induced transparency would silence the particle to any everyday sounds that would obscure the presence of the Unruh effect.

By nudging the particle with a laser, “you increase the likelihood of seeing the Unruh effect, and the likelihood is increased by the number of photons you have in the field,” Šoda said. “And that number can be huge, depending on how powerful your laser is.” In other words, because the researchers might strike a particle with a quadrillion pHotons increase the probability of the Unruh Effect occurring by 15 orders of magnitude.

Since the Unruh effect corresponds in many ways to Hawking radiation, the researchers believe that the two recently described quantum field properties could potentially be used to stimulate Hawking radiation and imply the existence of gravity-induced transparency. Since Hawking radiation has never been observed, unwrapping the Unruh effect could be a step in that direction better understanding of the theorized glow around black holes.

Of course, these results don’t mean much unless the Unruh effect can be observed directly in the laboratory – the researchers’ next step. Exactly when It remains to be seen whether the experiment will be carried out.

More: Black hole in lab shows Stephen Hawking was obviously right

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