A new warp-speed experiment could finally offer an indirect test of famed physicist Stephen Hawking’s most famous black hole prediction.
The glow effect, called the Unruh (or Fulling-Davies-Unruh) effect, causes the space around rapidly accelerating objects to seemingly be filled with a swarm of virtual particles, bathing those objects in a warm glow. As the effect is closely related to the Hawking effect – in which virtual particles known as Hawking radiation appear spontaneously at the edges of black holes – scientists have long been keen to spot one as a clue to the existence of the other.
But spotting either effect is incredibly difficult. Hawking radiation only occurs around the terrifying precipice of a black hole, and achieving the acceleration necessary for the Unruh effect would likely require warp drive. Now a groundbreaking new proposal, published in an April 26 study in the journal Physical examination letters, could change that. Its authors say they have discovered a mechanism to dramatically increase the strength of the Unruh effect through a technique that can effectively transform question invisible.
“Now, at least, we know there’s a chance in our lifetime where we might actually see this effect,” co-author Vivishek Sudhir, assistant professor of mechanical engineering at MIT and designer of the new experiment, said in a press release. “It’s a tough experiment, and there’s no guarantee we’d be able to do it, but this idea is our closest hope.”
First proposed by scientists in the 1970s, the Unruh effect is one of many predictions from quantum field theory. According to this theory, there is no such thing as a vacuum. In fact, any pocket of space is teeming with infinite quantum-scale vibrations that, if given enough energy, can spontaneously burst into particle-antiparticle pairs that annihilate almost immediately. And any particle – whether matter or light – is simply a localized excitation of this quantum field.
In 1974, Stephen Hawking predicted that the extreme gravitational force felt at the edges of black holes – their event horizons – would also create virtual particles.
Gravity, according to Einstein’s general theory relativitydeformed space-timeso that quantum fields become more distorted the closer they get to the immense gravitational tug of a black hole singularity. Due to the uncertainty and weirdness of quantum mechanics, this distorts the quantum field, creating uneven pockets of differently moving time and subsequent energy spikes across the field. It is these energetic shifts that cause virtual particles to emerge from what appears to be nothing on the periphery of black holes.
“Black holes are thought to be not entirely black,” said lead author Barbara Šoda, a PhD student in physics at the University of Waterloo in Canada. said in a press release. “Instead, as Stephen Hawking discovered, black holes should emit radiation.”
Much like the Hawking Effect, the Unruh Effect also creates virtual particles through the bizarre fusion of quantum mechanics and relativistic effects predicted by Einstein. But this time, instead of the distortions being caused by black holes and the theory of general relativity, they come from speeds close to light and special relativity, which dictate that time slows down as an object moves. approaches the speed of light.
According to quantum theory, a stationary atom can only increase its energy by waiting for a real photon to excite one of its electrons. For an accelerating atom, however, the quantum field fluctuations can add up to look like real photons. From the perspective of an accelerating atom, it will move through a host of hot light particles, which will heat it up. This heat would be a telltale sign of the Unruh effect.
But the accelerations needed to produce the effect are far beyond the power of any existing particle accelerator. An atom would need to accelerate to the speed of light in less than a millionth of a second – experiencing an ag force of one quadrillion meters per second squared – to produce a glow hot enough for detectors to present spot it.
“To see this effect in a short time would require incredible acceleration,” Sudhir said. “If you had a reasonable acceleration instead, you would have to wait a huge amount of time – longer than the age of the universe – to see a measurable effect.”
To make the effect achievable, the researchers came up with an ingenious alternative. Quantum fluctuations are made denser by photons, which means that an atom made to move in a vacuum while being struck by light from a high-intensity laser could, in theory, produce the Unruh effect, even at relatively low accelerations. The problem, however, is that the atom could also interact with the laser light, absorbing it to raise the atom’s energy level, producing heat that would quench the heat generated by the Unruh effect.
But the researchers found another workaround: a technique they call acceleration-induced transparency. If the atom is forced to follow a very specific path through a field of photons, the atom will not be able to “see” photons of a certain frequency, essentially rendering them invisible to the atom. So, by daisy chaining all of these workarounds, the team would then be able to test the Unruh effect at that specific light frequency.
Making this plan a reality will be a difficult task. Scientists plan to build a lab-sized particle accelerator that will accelerate an electron to the speed of light while hitting it with a beam of microwaves. If they are able to detect the effect, they plan to conduct experiments with it, especially those that will allow them to explore possible connections between Einstein’s theory of relativity and quantum mechanics.
“The theory of general relativity and the theory of quantum mechanics are currently still somewhat at odds, but there must be a unifying theory that describes how things work in the universe,” co-author Achim Kempf, professor applied mathematics at university. University of Waterloo, said in a press release. “We’ve been looking for a way to unite these two great theories, and this work helps bring us closer by opening up opportunities to test new theories against experiments.”
Originally posted on Live Science.
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