Wormholes are a classic trope of science fiction in popular media, if only because they supply such a handy futuristic plot device to avoid the problem of violating relativity with faster-than-light travel. In point of fact, they’re purely theoretical. Unlike black holes—also once considered purely theoretical—no evidence for an actual wormhole has ever been found, although they’re fascinating from an abstract theoretical physics perceptive. You is likely to be forgiven for pondering that undiscovered status had modified when you only read the headlines this week announcing that physicists had used a quantum computer to make a wormhole, reporting on a recent paper published in Nature.
Let’s set the record straight straight away: This is not a bona fide traversable wormhole—i.e., a bridge between two regions of spacetime connecting the mouth of 1 black hole to a different, through which a physical object can pass—in any real, physical sense. “There is a difference between something being possible in principle and possible in point of fact,” co-author Joseph Lykken of Fermilab said during a media briefing this week. “So don’t hold your breath about sending your dog through a wormhole.” Nevertheless it’s still a reasonably clever, nifty experiment in its own right that gives a tantalizing proof of principle to the sorts of quantum-scale physics experiments that is likely to be possible as quantum computers proceed to enhance.
“It’s not the actual thing; it’s not even near the actual thing; it’s barely even a simulation of something-not-close-to-the-real-thing,” physicist Matt Strassler wrote on his blog. “Could this method result in a simulation of an actual wormhole someday? Perhaps within the distant future. Could it lead to creating an actual wormhole? Never. Don’t get me unsuitable. What they did is pretty cool! However the hype within the press? Wildly, spectacularly overblown.”
So what is that this thing that was “created” in a quantum computer if it isn’t an actual wormhole? An analog? A toy model? Co-author Maria Spiropulu of Caltech referred to it as a novel “wormhole teleportation protocol” throughout the briefing. You could possibly call it a simulation, but as Strassler wrote, that is not quite right either. Physicists have simulated wormholes on classical computers, but no physical system is created in those simulations. That is why the authors prefer the term “quantum experiment” because they were capable of use Google’s Sycamore quantum computer to create a highly entangled quantum system and make direct measurements of specific key properties. Those properties are consistent with theoretical descriptions of a traversable wormhole’s dynamics—but only in a special simplified theoretical model of spacetime.
Lykken described it to The Recent York Times as “the smallest, crummiest wormhole you possibly can imagine making.” Even then, perhaps a “collection of atoms with certain wormhole-like properties” is likely to be more accurate. What makes this breakthrough so intriguing and potentially significant is how the experiment draws on a number of the most influential and exciting recent work in theoretical physics. But to understand precisely what was done and why it matters, we want to go on a somewhat meandering journey through some pretty heady abstract ideas spanning nearly a century.
APS/Alan Stonebraker
Revisiting the holographic principle
Let’s start with what’s popularly referred to as the holographic principle. As I’ve written previously, nearly 30 years ago, theoretical physicists introduced the mind-bending theory positing that our three-dimensional universe is actually a hologram. The holographic principle began as a proposed solution to the black hole information paradox within the Nineties. Black holes, as described by general relativity, are easy objects. All you want to describe them mathematically is their mass and their spin, plus their electric charge. So there could be no noticeable change when you threw something right into a black hole—nothing that will provide a clue as to what that object may need been. That information is lost.
But problems arise when quantum gravity enters the image because the foundations of quantum mechanics hold that information can never be destroyed. And in quantum mechanics, black holes are incredibly complex objects and thus should contain a terrific deal of knowledge. Jacob Bekenstein realized in 1974 that black holes even have entropy. Stephen Hawking tried to prove him unsuitable but wound up proving him right as a substitute, concluding that black holes, subsequently, had to supply some form of thermal radiation.
So black holes must even have entropy, and Hawking was the primary to calculate that entropy. He also introduced the notion of “Hawking radiation”: The black hole will emit a tiny little bit of energy, decreasing its mass by a corresponding amount. Over time, the black hole will evaporate. The smaller the black hole, the more quickly it disappears. But what then happens to the knowledge it contained? Is it truly destroyed, thereby violating quantum mechanics, or is it one way or the other preserved within the Hawking radiation?
Per the holographic principle, details about a black hole’s interior might be encoded on its two-dimensional surface area (the “boundary”) fairly than inside its three-dimensional volume (the “bulk”). Leonard Susskind and Gerard ‘t Hooft prolonged this notion to the whole universe, likening it to a hologram: our three-dimensional universe in all its glory emerges from a two-dimensional “source code.”
Juan Maldacena next discovered a vital duality, technically referred to as the AdS/CFT correspondence—which amounts to a mathematical dictionary that enables physicists to go backwards and forwards between the languages of two theoretical worlds (general relativity and quantum mechanics). Dualities in physics seek advice from models that seem like different but will be shown to explain equivalent physics. It is a bit like how ice, water, and vapor are three different phases of the identical chemical substance, except a duality looks at the identical phenomenon in two other ways which are inversely related. Within the case of AdS/CFT, the duality is between a model of spacetime referred to as anti-de Sitter space (AdS)—which has constant negative curvature, unlike our own de Sitter universe—and a quantum system called conformal field theory (CFT), which lacks gravity but has quantum entanglement.
It’s this notion of duality that accounts for the wormhole confusion. As noted above, the authors of the Nature paper didn’t make a physical wormhole—they manipulated some entangled quantum particles in atypical flat spacetime. But that system is conjectured to have a dual description as a wormhole.
Wormholes are a classic trope of science fiction in popular media, if only because they supply such a handy futuristic plot device to avoid the problem of violating relativity with faster-than-light travel. In point of fact, they’re purely theoretical. Unlike black holes—also once considered purely theoretical—no evidence for an actual wormhole has ever been found, although they’re fascinating from an abstract theoretical physics perceptive. You is likely to be forgiven for pondering that undiscovered status had modified when you only read the headlines this week announcing that physicists had used a quantum computer to make a wormhole, reporting on a recent paper published in Nature.
Let’s set the record straight straight away: This is not a bona fide traversable wormhole—i.e., a bridge between two regions of spacetime connecting the mouth of 1 black hole to a different, through which a physical object can pass—in any real, physical sense. “There is a difference between something being possible in principle and possible in point of fact,” co-author Joseph Lykken of Fermilab said during a media briefing this week. “So don’t hold your breath about sending your dog through a wormhole.” Nevertheless it’s still a reasonably clever, nifty experiment in its own right that gives a tantalizing proof of principle to the sorts of quantum-scale physics experiments that is likely to be possible as quantum computers proceed to enhance.
“It’s not the actual thing; it’s not even near the actual thing; it’s barely even a simulation of something-not-close-to-the-real-thing,” physicist Matt Strassler wrote on his blog. “Could this method result in a simulation of an actual wormhole someday? Perhaps within the distant future. Could it lead to creating an actual wormhole? Never. Don’t get me unsuitable. What they did is pretty cool! However the hype within the press? Wildly, spectacularly overblown.”
So what is that this thing that was “created” in a quantum computer if it isn’t an actual wormhole? An analog? A toy model? Co-author Maria Spiropulu of Caltech referred to it as a novel “wormhole teleportation protocol” throughout the briefing. You could possibly call it a simulation, but as Strassler wrote, that is not quite right either. Physicists have simulated wormholes on classical computers, but no physical system is created in those simulations. That is why the authors prefer the term “quantum experiment” because they were capable of use Google’s Sycamore quantum computer to create a highly entangled quantum system and make direct measurements of specific key properties. Those properties are consistent with theoretical descriptions of a traversable wormhole’s dynamics—but only in a special simplified theoretical model of spacetime.
Lykken described it to The Recent York Times as “the smallest, crummiest wormhole you possibly can imagine making.” Even then, perhaps a “collection of atoms with certain wormhole-like properties” is likely to be more accurate. What makes this breakthrough so intriguing and potentially significant is how the experiment draws on a number of the most influential and exciting recent work in theoretical physics. But to understand precisely what was done and why it matters, we want to go on a somewhat meandering journey through some pretty heady abstract ideas spanning nearly a century.
APS/Alan Stonebraker
Revisiting the holographic principle
Let’s start with what’s popularly referred to as the holographic principle. As I’ve written previously, nearly 30 years ago, theoretical physicists introduced the mind-bending theory positing that our three-dimensional universe is actually a hologram. The holographic principle began as a proposed solution to the black hole information paradox within the Nineties. Black holes, as described by general relativity, are easy objects. All you want to describe them mathematically is their mass and their spin, plus their electric charge. So there could be no noticeable change when you threw something right into a black hole—nothing that will provide a clue as to what that object may need been. That information is lost.
But problems arise when quantum gravity enters the image because the foundations of quantum mechanics hold that information can never be destroyed. And in quantum mechanics, black holes are incredibly complex objects and thus should contain a terrific deal of knowledge. Jacob Bekenstein realized in 1974 that black holes even have entropy. Stephen Hawking tried to prove him unsuitable but wound up proving him right as a substitute, concluding that black holes, subsequently, had to supply some form of thermal radiation.
So black holes must even have entropy, and Hawking was the primary to calculate that entropy. He also introduced the notion of “Hawking radiation”: The black hole will emit a tiny little bit of energy, decreasing its mass by a corresponding amount. Over time, the black hole will evaporate. The smaller the black hole, the more quickly it disappears. But what then happens to the knowledge it contained? Is it truly destroyed, thereby violating quantum mechanics, or is it one way or the other preserved within the Hawking radiation?
Per the holographic principle, details about a black hole’s interior might be encoded on its two-dimensional surface area (the “boundary”) fairly than inside its three-dimensional volume (the “bulk”). Leonard Susskind and Gerard ‘t Hooft prolonged this notion to the whole universe, likening it to a hologram: our three-dimensional universe in all its glory emerges from a two-dimensional “source code.”
Juan Maldacena next discovered a vital duality, technically referred to as the AdS/CFT correspondence—which amounts to a mathematical dictionary that enables physicists to go backwards and forwards between the languages of two theoretical worlds (general relativity and quantum mechanics). Dualities in physics seek advice from models that seem like different but will be shown to explain equivalent physics. It is a bit like how ice, water, and vapor are three different phases of the identical chemical substance, except a duality looks at the identical phenomenon in two other ways which are inversely related. Within the case of AdS/CFT, the duality is between a model of spacetime referred to as anti-de Sitter space (AdS)—which has constant negative curvature, unlike our own de Sitter universe—and a quantum system called conformal field theory (CFT), which lacks gravity but has quantum entanglement.
It’s this notion of duality that accounts for the wormhole confusion. As noted above, the authors of the Nature paper didn’t make a physical wormhole—they manipulated some entangled quantum particles in atypical flat spacetime. But that system is conjectured to have a dual description as a wormhole.
