Sep 7, 2021 10:05 PM
(This post was last modified: Sep 8, 2021 08:20 PM by C C.)
New Theory for Detecting Light in the Darkness of a Vacuum: Dartmouth research proposes an experiment to produce ‘something from nothing.’
https://home.dartmouth.edu/news/2021/09/...ess-vacuum
RELEASE: Black holes are regions of space-time with huge amounts of gravity. Scientists originally thought that nothing could escape the boundaries of these massive objects, including light.
The precise nature of black holes has been challenged ever since Albert Einstein’s general theory of relativity gave rise to the possibility of their existence. Among the most famous findings was English physicist Stephen Hawking’s prediction that some particles are actually emitted at the edge of a black hole.
Physicists have also explored the workings of vacuums. In the early 1970s, as Hawking was describing how light can escape a black hole’s gravitational pull, Canadian physicist William Unruh proposed that a photodetector accelerated fast enough could “see” light in a vacuum.
New research from Dartmouth advances these theories by detailing a way to produce and detect light that was previously thought to be unobservable.
“In an everyday sense, the findings seem to surprisingly suggest the ability to produce light from the empty vacuum,” said Miles Blencowe, the Eleanor and A. Kelvin Smith Distinguished Professor in Physics at Dartmouth and the study’s senior researcher. “We have, in essence produced something from nothing; the thought of that is just very cool.”
In classical physics, the vacuum is thought of as the absence of matter, light, and energy. In quantum physics, the vacuum is not so empty, but filled with photons that fluctuate in and out of existence. However, such light is virtually impossible to measure.
One part of Einstein’s general theory of relativity, the “equivalence principle,” establishes a connection between Hawking’s prediction for radiating black holes and Unruh’s prediction for accelerating photodetectors seeing light. Equivalence says that gravity and acceleration are fundamentally indistinguishable: A person in a windowless, accelerating elevator would not be able to determine if they are being acted on by gravity, an inertial force, or both.
Therefore, if black hole gravity can create photons in a vacuum, so can acceleration.
With science already demonstrating that observation of light in a vacuum is possible, the Dartmouth team set out to find a practicable way to detect the photons. The Dartmouth research theory, published in Nature Research’s Communications Physics, predicts that nitrogen-based imperfections in a rapidly accelerating diamond membrane can make the detection.
In the proposed experiment, a postage stamp-sized synthetic diamond containing the nitrogen-based light detectors is suspended in a super-cooled metal box that creates a vacuum. The membrane, which acts like a tethered trampoline, is accelerated at massive rates.
The research paper explains that the resulting photon production from the cavity vacuum is collectively enhanced and measurable, with the vacuum photon production undergoing a phase transition from a normal phase to “an enhanced superradiant-like, inverted lasing phase” when the detector number exceeds a critical value.
“The motion of the diamond produces photons,” said Hui Wang, a postdoctoral researcher who wrote the theoretical paper while a graduate student at Dartmouth. “In essence, all you need to do is shake something violently enough to produce entangled photons.”
The Dartmouth paper investigates using multiple photon detectors—the diamond defects—to amplify the acceleration of the membrane and increase detection sensitivity. Oscillating the diamond also allows the experiment to take place in a controllable space at intense rates of acceleration. “Our work is the first to explore what happens when there are many accelerating photodetectors instead of one,” said Blencowe. “We discovered a quantum-enhanced amplification effect for light creation from vacuum, where the collective effect of the many accelerating detectors is greater than considering them individually.”
To confirm that the detected photons come from the vacuum rather than from the surrounding environment, the team demonstrates that the theory observes “entangled light,” a distinct feature of quantum mechanics that cannot originate from outside radiation. “The photons detected by the diamond are produced in pairs,” said Hui. “This production of paired, entangled photons is evidence that the photons are produced in vacuum and not from another source.”
The proposal to observe light in a vacuum does not have immediate applicability, but the research team hopes that it adds to the understanding of physical forces that contributes to society in the way other theoretical research has. In particular, the work may help shed experimental light on Hawking’s prediction for radiating black holes through the lens of Einstein’s equivalence principle.
“Part of the responsibility and joy of being theorists such as ourselves is to put ideas out there,” said Blencowe. “We are trying to show that it is feasible to do this experiment, to test something that has been until now extraordinarily difficult.”
A technical animation produced by the team depicts the creation of photons by the experiment. The detected light exists in microwave frequency, so is not visible to the human eye.
One lab’s quest to build space-time out of quantum particles
https://www.quantamagazine.org/one-labs-...-20210907/
EXCERPTS: The prospects for directly testing a theory of quantum gravity are poor, to put it mildly. To probe the ultra-tiny Planck scale, where quantum gravitational effects appear, you would need a particle accelerator as big as the Milky Way galaxy. Likewise, black holes hold singularities that are governed by quantum gravity, but no black holes are particularly close by — and even if they were, we could never hope to see what’s inside. Quantum gravity was also at work in the first moments of the Big Bang, but direct signals from that era are long gone, leaving us to decipher subtle clues that first appeared hundreds of thousands of years later.
But in a small lab just outside Palo Alto, the Stanford University professor Monika Schleier-Smith and her team are trying a different way to test quantum gravity, without black holes or galaxy-size particle accelerators. Physicists have been suggesting for over a decade that gravity — and even space-time itself — may emerge from a strange quantum connection called entanglement. Schleier-Smith and her collaborators are reverse-engineering the process. By engineering highly entangled quantum systems in a tabletop experiment, Schleier-Smith hopes to produce something that looks and acts like the warped space-time predicted by Albert Einstein’s theory of general relativity.
In a paper posted in June, her team announced their first experimental step along this route: a system of atoms trapped by light, with connections made to order, finely controlled with magnetic fields. When tuned in the right way, the long-distance correlations in this system describe a treelike geometry, similar to ones seen in simple models of emergent space-time. Schleier-Smith and her colleagues hope to build on this work to create analogues to more complex geometries, including those of black holes. In the absence of new data from particle physics or cosmology — a state of affairs that could continue indefinitely — this could be the most promising route for putting the latest ideas about quantum gravity to the test.
[...] Hayden sees this as the way of the future. “Instead of trying to understand the emergence of space-time in our universe, let’s actually just make toy universes in the lab and study the emergence of space-time there,” he said. “And that sounds like a crazy thing to do, right? Like kind of mad-scientist kind of crazy, right? But I think it really is likely to be easier to do that than to directly test quantum gravity.”
Schleier-Smith is also optimistic about the future. “We’re still at the stage of getting more and more control, characterizing the quantum states that we have. But … I would love to get to that point where we don’t know what will happen,” she said. “And maybe we measure the correlations in the system, and we learn that there’s a geometric description, some holographic description that we didn’t know was there. That would be cool.” (MORE - missing details)
Our Universe may have a fifth dimension that would change everything we know about physics
https://www.sciencefocus.com/space/fifth-dimension/
EXCERPTS: . . . we live in a Universe with four dimensions of space-time. [...] In that case, a fifth dimension would be an extra dimension of space.
Such a dimension was proposed independently by physicists Oskar Klein and Theodor Kaluza in the 1920s. They were inspired by Einstein’s theory of gravity, which showed that mass warped four-dimensional space-time.
[...] Could the other force known at the time (the electromagnetic force) be explained by the curvature of an extra dimension of space?
Kaluza and Klein found it could. But since the electromagnetic force was 1,040 times stronger than gravity, the curvature of the extra dimension had to be so great that it was rolled up much smaller than an atom and would be impossible to notice. When a particle such as an electron travelled through space, invisible to us, it would be going round and round the fifth dimension, like a hamster in a wheel.
Kaluza and Klein’s five-dimensional theory was dealt a serious blow [...] But the idea that extra dimensions explain forces was revived half a century later by proponents of ‘string theory’ ... String theory gave rise to the idea that our Universe might be a three-dimensional island, or ‘brane’, floating in 10-dimensional space-time...
There is a way to have a bigger fifth dimension, which is curved in such a way that we don’t see it, and this was suggested by the physicists Lisa Randall and Raman Sundrum in 1999. An extra space dimension might even explain one of the great cosmic mysteries: the identity of ‘dark matter’, the invisible stuff that appears to outweigh the visible stars and galaxies by a factor of six.
In 2021, a group of physicists from Johannes Gutenberg University in Mainz, Germany, proposed that the gravity of hitherto unknown particles propagating in a hidden fifth dimension could manifest itself in our four-dimensional Universe as the extra gravity we currently attribute to dark matter... (MORE - missing details)
https://home.dartmouth.edu/news/2021/09/...ess-vacuum
RELEASE: Black holes are regions of space-time with huge amounts of gravity. Scientists originally thought that nothing could escape the boundaries of these massive objects, including light.
The precise nature of black holes has been challenged ever since Albert Einstein’s general theory of relativity gave rise to the possibility of their existence. Among the most famous findings was English physicist Stephen Hawking’s prediction that some particles are actually emitted at the edge of a black hole.
Physicists have also explored the workings of vacuums. In the early 1970s, as Hawking was describing how light can escape a black hole’s gravitational pull, Canadian physicist William Unruh proposed that a photodetector accelerated fast enough could “see” light in a vacuum.
New research from Dartmouth advances these theories by detailing a way to produce and detect light that was previously thought to be unobservable.
“In an everyday sense, the findings seem to surprisingly suggest the ability to produce light from the empty vacuum,” said Miles Blencowe, the Eleanor and A. Kelvin Smith Distinguished Professor in Physics at Dartmouth and the study’s senior researcher. “We have, in essence produced something from nothing; the thought of that is just very cool.”
In classical physics, the vacuum is thought of as the absence of matter, light, and energy. In quantum physics, the vacuum is not so empty, but filled with photons that fluctuate in and out of existence. However, such light is virtually impossible to measure.
One part of Einstein’s general theory of relativity, the “equivalence principle,” establishes a connection between Hawking’s prediction for radiating black holes and Unruh’s prediction for accelerating photodetectors seeing light. Equivalence says that gravity and acceleration are fundamentally indistinguishable: A person in a windowless, accelerating elevator would not be able to determine if they are being acted on by gravity, an inertial force, or both.
Therefore, if black hole gravity can create photons in a vacuum, so can acceleration.
With science already demonstrating that observation of light in a vacuum is possible, the Dartmouth team set out to find a practicable way to detect the photons. The Dartmouth research theory, published in Nature Research’s Communications Physics, predicts that nitrogen-based imperfections in a rapidly accelerating diamond membrane can make the detection.
In the proposed experiment, a postage stamp-sized synthetic diamond containing the nitrogen-based light detectors is suspended in a super-cooled metal box that creates a vacuum. The membrane, which acts like a tethered trampoline, is accelerated at massive rates.
The research paper explains that the resulting photon production from the cavity vacuum is collectively enhanced and measurable, with the vacuum photon production undergoing a phase transition from a normal phase to “an enhanced superradiant-like, inverted lasing phase” when the detector number exceeds a critical value.
“The motion of the diamond produces photons,” said Hui Wang, a postdoctoral researcher who wrote the theoretical paper while a graduate student at Dartmouth. “In essence, all you need to do is shake something violently enough to produce entangled photons.”
The Dartmouth paper investigates using multiple photon detectors—the diamond defects—to amplify the acceleration of the membrane and increase detection sensitivity. Oscillating the diamond also allows the experiment to take place in a controllable space at intense rates of acceleration. “Our work is the first to explore what happens when there are many accelerating photodetectors instead of one,” said Blencowe. “We discovered a quantum-enhanced amplification effect for light creation from vacuum, where the collective effect of the many accelerating detectors is greater than considering them individually.”
To confirm that the detected photons come from the vacuum rather than from the surrounding environment, the team demonstrates that the theory observes “entangled light,” a distinct feature of quantum mechanics that cannot originate from outside radiation. “The photons detected by the diamond are produced in pairs,” said Hui. “This production of paired, entangled photons is evidence that the photons are produced in vacuum and not from another source.”
The proposal to observe light in a vacuum does not have immediate applicability, but the research team hopes that it adds to the understanding of physical forces that contributes to society in the way other theoretical research has. In particular, the work may help shed experimental light on Hawking’s prediction for radiating black holes through the lens of Einstein’s equivalence principle.
“Part of the responsibility and joy of being theorists such as ourselves is to put ideas out there,” said Blencowe. “We are trying to show that it is feasible to do this experiment, to test something that has been until now extraordinarily difficult.”
A technical animation produced by the team depicts the creation of photons by the experiment. The detected light exists in microwave frequency, so is not visible to the human eye.
One lab’s quest to build space-time out of quantum particles
https://www.quantamagazine.org/one-labs-...-20210907/
EXCERPTS: The prospects for directly testing a theory of quantum gravity are poor, to put it mildly. To probe the ultra-tiny Planck scale, where quantum gravitational effects appear, you would need a particle accelerator as big as the Milky Way galaxy. Likewise, black holes hold singularities that are governed by quantum gravity, but no black holes are particularly close by — and even if they were, we could never hope to see what’s inside. Quantum gravity was also at work in the first moments of the Big Bang, but direct signals from that era are long gone, leaving us to decipher subtle clues that first appeared hundreds of thousands of years later.
But in a small lab just outside Palo Alto, the Stanford University professor Monika Schleier-Smith and her team are trying a different way to test quantum gravity, without black holes or galaxy-size particle accelerators. Physicists have been suggesting for over a decade that gravity — and even space-time itself — may emerge from a strange quantum connection called entanglement. Schleier-Smith and her collaborators are reverse-engineering the process. By engineering highly entangled quantum systems in a tabletop experiment, Schleier-Smith hopes to produce something that looks and acts like the warped space-time predicted by Albert Einstein’s theory of general relativity.
In a paper posted in June, her team announced their first experimental step along this route: a system of atoms trapped by light, with connections made to order, finely controlled with magnetic fields. When tuned in the right way, the long-distance correlations in this system describe a treelike geometry, similar to ones seen in simple models of emergent space-time. Schleier-Smith and her colleagues hope to build on this work to create analogues to more complex geometries, including those of black holes. In the absence of new data from particle physics or cosmology — a state of affairs that could continue indefinitely — this could be the most promising route for putting the latest ideas about quantum gravity to the test.
[...] Hayden sees this as the way of the future. “Instead of trying to understand the emergence of space-time in our universe, let’s actually just make toy universes in the lab and study the emergence of space-time there,” he said. “And that sounds like a crazy thing to do, right? Like kind of mad-scientist kind of crazy, right? But I think it really is likely to be easier to do that than to directly test quantum gravity.”
Schleier-Smith is also optimistic about the future. “We’re still at the stage of getting more and more control, characterizing the quantum states that we have. But … I would love to get to that point where we don’t know what will happen,” she said. “And maybe we measure the correlations in the system, and we learn that there’s a geometric description, some holographic description that we didn’t know was there. That would be cool.” (MORE - missing details)
Our Universe may have a fifth dimension that would change everything we know about physics
https://www.sciencefocus.com/space/fifth-dimension/
EXCERPTS: . . . we live in a Universe with four dimensions of space-time. [...] In that case, a fifth dimension would be an extra dimension of space.
Such a dimension was proposed independently by physicists Oskar Klein and Theodor Kaluza in the 1920s. They were inspired by Einstein’s theory of gravity, which showed that mass warped four-dimensional space-time.
[...] Could the other force known at the time (the electromagnetic force) be explained by the curvature of an extra dimension of space?
Kaluza and Klein found it could. But since the electromagnetic force was 1,040 times stronger than gravity, the curvature of the extra dimension had to be so great that it was rolled up much smaller than an atom and would be impossible to notice. When a particle such as an electron travelled through space, invisible to us, it would be going round and round the fifth dimension, like a hamster in a wheel.
Kaluza and Klein’s five-dimensional theory was dealt a serious blow [...] But the idea that extra dimensions explain forces was revived half a century later by proponents of ‘string theory’ ... String theory gave rise to the idea that our Universe might be a three-dimensional island, or ‘brane’, floating in 10-dimensional space-time...
There is a way to have a bigger fifth dimension, which is curved in such a way that we don’t see it, and this was suggested by the physicists Lisa Randall and Raman Sundrum in 1999. An extra space dimension might even explain one of the great cosmic mysteries: the identity of ‘dark matter’, the invisible stuff that appears to outweigh the visible stars and galaxies by a factor of six.
In 2021, a group of physicists from Johannes Gutenberg University in Mainz, Germany, proposed that the gravity of hitherto unknown particles propagating in a hidden fifth dimension could manifest itself in our four-dimensional Universe as the extra gravity we currently attribute to dark matter... (MORE - missing details)