No, physicists didn’t make a real wormhole. What they did was still pretty cool

Wormholes are a science fiction classic in popular media, if only because they provide such a handy futuristic plot device to avoid the problem of violating relativity with faster-than-light travel. In reality, they are purely theoretical. Unlike black holes, which were also thought to be purely theoretical, no evidence of an actual wormhole has ever been found, although they are fascinating from an abstract theoretical physics perspective. You could be forgiven for thinking that the undiscovered status had changed if you just read the headlines this week announcing that physicists had used a quantum computer to make a wormhole, reporting on a new paper published in Nature.

Let’s set the record straight: this is not a bona fide traversable wormhole, meaning a bridge between two regions of spacetime that connects the mouth of one black hole to another, via of which a physical object can pass, in any real physics. sense. “There’s a difference between something being possible in principle and being possible in reality,” co-author Joseph Lykken of Fermilab said during a media briefing this week. “So don’t hold your breath to send your dog down a wormhole.” But it’s still pretty smart, cool experiment in its own right that provides a tantalizing proof-of-principle for the kinds of quantum-scale physics experiments that might become possible as quantum computers continue to improve.

“It’s not the real thing; it’s not even close to the real thing; it’s barely a simulation of something that’s not close to the real thing,” said physicist Matt Strassler. he wrote on his blog. “Could this method lead to a simulation of a real wormhole someday? Maybe in the distant future. Could it lead to making a real wormhole? Never. Don’t get me wrong. What they did is pretty cool! But the hype in the press? Wild, spectacularly exaggerated.”

So what is this that was “created” in a quantum computer if not a real wormhole? An analog? A toy model? Co-author Maria Spiropulu of Caltech referred to it as a novel “wormhole teleportation protocol” during the briefing. You could call it a simulation, but as Strassler wrote, that’s not quite right either. Physicists have simulated wormholes in classical computers, but no physical system is created in these simulations. For this the authors prefer the term “quantum.” experience” because they they could use Google’s Sycamore quantum computer to create a highly entangled quantum system and make direct measurements of specific key properties. These properties are consistent with theoretical descriptions of the dynamics of a traversing wormhole, but only in a special simplified theoretical model of spacetime.

Happiness he described it in The New York Times as “the tiniest, nastiest wormhole you can imagine making.” Even then, perhaps a “collection of atoms with certain wormhole-like properties” might be more accurate. What makes this breakthrough so intriguing and potentially significant is how the experiment builds on some of the most influential and exciting recent work in theoretical physics. But to understand precisely what was done and why it matters, we have to take a somewhat meandering journey through some pretty heady abstract ideas spanning nearly a century.

Revisiting the holographic principle

Let’s start with what is popularly known as the holographic principle. How I wrote previously, nearly 30 years ago, theoretical physicists introduced the mind-boggling theory that posited that our three-dimensional universe is actually a hologram. The holographic principle began as a proposed solution to the Black hole information paradox in the 1990s. Black holes, as described by general relativity, are simple objects. All you need to describe them mathematically is their mass and spin, plus their electric charge. So there would be no noticeable changes if you threw something into a black hole, nothing to provide a clue as to what that object might have been. This information is lost.

But problems arise when quantum gravity enters the picture because the rules of quantum mechanics hold that information can never be destroyed. And in quantum mechanics, black holes are incredibly complex objects and should therefore contain a great deal of information. Jacob Bekenstein realized in 1974 that black holes also have entropy. Stephen Hawking tried to prove him wrong, but ended up proving him right, concluding that black holes must therefore produce some form of thermal radiation.

Therefore, black holes must also have entropy, and Hawking was the first to calculate this entropy. He also introduced the notion of “Hawking radiation”: the black hole will emit some energy, decreasing its mass by a corresponding amount. Over time, the black hole will evaporate. The smaller the black hole, the faster it disappears. But what about the information it contained? Is it really destroyed, thereby violating quantum mechanics, or is it somehow preserved in Hawking radiation?

According to the holographic principle, information about the interior of a black hole could be encoded in its two-dimensional surface (the “boundary”) rather than its three-dimensional volume (the “volume”). Leonard Susskind and Gerard ‘t Hooft extended this notion to the entire universe, comparing it to a hologram: our three-dimensional universe in all its glory emerges from a two-dimensional “source code.”

Juan Maldacena later discovered a crucial duality, technically known as the AdS/CFT correspondence—which amounts to a mathematical dictionary that allows physicists to go back and forth between the languages ​​of two theoretical worlds (general relativity and quantum mechanics). Dualities in physics refer to models that appear to be different but can be shown to describe equivalent physics. It’s a bit like ice, water, and steam are three different phases of the same chemical, except that a duality looks at the same phenomenon in two different ways that are inversely related. In the case of AdS/CFT, the duality is between a model of spacetime known as anti-de Sitter space (AdS)—which has constant negative curvature, unlike our own Sitter universe—and a quantum system called conformal field theory (CFT). ), which has no gravity but does quantum entanglement.

It is this notion of duality that explains the wormhole confusion. As noted above, the authors of the Nature paper did not make a physical wormhole: they manipulated some quantum particles entangled in normal flat spacetime. But this system is conjectured to have a dual description as a wormhole.