By now, you might have heard that physicists have created a wormhole, which heretofore has existed, as far as we know, only in the imaginations of physicists and science-fiction writers. The story begins with a paper titled, "Traversable wormhole dynamics on a quantum processor."
The paper's abstract invokes terms like entanglement, teleportation, holography, qubits, quantum gravity and spacetime geometry. A clever AI-bot, you might suspect, generated this buzzword salad after scanning papers by cranks. But no, the paper was written by physicists at Caltech, Harvard, MIT, Fermilab and Google, and it was published in the prestigious journal Nature on November 30.
On that same day two top-notch physics reporters, Dennis Overbye of The New York Times and Natalie Wolchover of Quanta, posted articles spelling out the paper's significance. Although Overbye's article is far more skeptical, he and Wolchover both suggest that the Nature authors "created" an actual wormhole. A leader of the research, Maria Spiropulu of Caltech, makes this same claim in a 17-minute video, "Wormhole in the Lab," released by Quanta. The wormhole produced by her group is "traversable," she announces. "It opens, you really can go through."
Here's the problem. According to qualified critics, Spiropulu's group created only a crude simulation of a wormhole based on highly speculative, untested theories. Peter Woit, a physicist at Columbia and long-time critic of untestable speculation in physics, calls the claim that physicists created an actual wormhole "complete bullshit" and a "publicity stunt."
Scott Aaronson, a quantum-computing expert who often debunks extravagant claims made for quantum computers, told Overbye, the Times reporter: "If this experiment has brought a wormhole into actual physical existence, then a strong case could be made that you, too, bring a wormhole into actual physical existence every time you sketch one with pen and paper." Aaronson says on his blog that the wormhole episode "risks damaging trust in the scientific process itself."
Below is my attempt to make sense of the controversy. The "traversable wormhole" work is the latest wrinkle in physicists' quest to unify Einstein's theory of gravity, general relativity; and quantum theory, which accounts for electromagnetism and the nuclear forces. The two theories are mathematically and conceptually incompatible.
Physicists hope a unified theory—also called a quantum-gravity theory, final theory or theory of everything—will provide a compact and yet complete description of the cosmos. Leaders of the quest have described it in hyperbolic terms. Nobel laureate Steven Weinberg said the final theory might reveal how our universe came to be, and why it takes a form that allows for our existence. Stephen Hawking claimed a final theory might help us know "the mind of God."
This grand quest, which drew me to science journalism in the 1980s, has spawned fantastical conjectures involving infinitesimal strings and extra dimensions and parallel universes. Although these ideas are mathematically compelling (or so proponents assure us), they cannot be tested; the strings and extra dimensions and universes are experimentally inaccessible. The unification quest hasn't lived up to its hype, not even close, but hope dies hard.
One recent stab at unification involves entanglement, a quantum effect whereby particles influence each other at faster-than-light speeds. Einstein, who had a hard time accepting entanglement, famously derided it as "spooky action at a distance." But entanglement has been empirically verified; this year's Nobel Prize in physics was awarded to three physicists for experiments on entanglement.
A decade ago, Juan Maldacena and Leonard Susskind, leading quantum-gravity theorists, proposed that entanglement might be mediated by wormholes. Their conjecture is based on a speculative notion called the holographic principle, which postulates deep mathematical linkages between relativity and quantum theory.
Like black holes, wormholes are a hypothetical consequence of general relativity. Science fiction writers love wormholes, just as they love multiverses; wormholes let you whisk a spaceship from one universe to another instantaneously. But whereas there is circumstantial evidence for black holes, there is none for wormholes.
Back to the claims of Spiropulu et al. What distinguishes their work from most quantum-gravity speculation is their use of a quantum computer. Called Sycamore and built by Google, the computer carries out computations with particles nudged into superposition, meaning that the particles, like Schrodinger's cat, occupy more than one state at the same time. Superposed particles serve as the basis of qubits, which encode more information—and hence can carry out more computations--than ordinary bits in ordinary computers.
The Nature group performed its experiment with a nine-qubit version of Sycamore. Nine qubits is a modest number; Sycamore can't compute anything beyond the range of a conventional computer. The researchers nonetheless used Sycamore to construct a cartoonishly simple mathematical model of a "wormhole" connecting "black holes" in a "spacetime" based on a simple version of the holographic principle. The researchers say they "teleported" information through the "wormhole" in a manner consistent with the Maldacena-Susskind conjecture. Teleportation is a term used to describe certain interactions between entangled particles.
I can see only one way in which Spiropulu et al. could claim they have created an actual as opposed to simulated wormhole. Quantum computing exploits entanglement as well as superposition. If you assume the Maldacena-Susskind conjecture is true, you could claim that the entangled particles in your quantum computer are linked by actual wormholes.
The problem with this argument is that it assumes what it purports to prove; it is a spectacular example of begging the question, or circular reasoning. Also, by this logic, any physicists who produce entangled particles, in a quantum computer or elsewhere, could claim they have "created a wormhole." And physicists can make this claim without constructing a simulation of a wormhole based on an untested quantum-gravity theory. The simulations are unnecessary—unless of course your intention is to obscure the line between what is simulated and what is real.
On his blog, Peter Woit notes that I warned in my 1996 book The End of Science that the quest for a unified theory was dragging physics into a "speculative post-empirical mode." Woit suggests that the wormhole incident bears out my prediction. Yes, I suppose it does, and I appreciate Woit's hat-tip. The irony is that I have recently become more optimistic about physics, and science as a whole, because of advances in quantum computing.
Two years ago, as part of my attempt to learn quantum mechanics, I read a little book called Q Is for Quantum, which gave me a better understanding of quantum computing. I subsequently had email and zoom exchanges with the author, Terry Rudolph, a quantum theorist and co-founder of the quantum-computing company PsiQuantum. Rudolph's optimism about quantum computing rubbed off on me.
In April 2021 I wrote a column, "Will Quantum Computing Ever Live Up to Its Hype?", that channeled the views of Rudolph and Scott Aaronson. After noting the over-the-top claims made for quantum computers, I ended my column on a hopeful note. If quantum computing "gives scientists more powerful tools for simulating complex phenomena," I wrote, "and especially the quantum weirdness at the heart of things, maybe it will give science the jump start it badly needs."
I still hope quantum computing leads to exciting advances, both practical and theoretical, that propel physics forward. But those advances might be hard to spot beneath all the bullshit and publicity stunts that quantum computing enables. And I no longer believe that physicists will ever find a true unified theory, which tells us how we came to be. That belief, I've decided, was always delusional.
Update: On his blog Not Even Wrong, Peter Woit notes that the "wormhole publicity stunt just keeps going." He points out that The New Yorker just published an article about Google's quantum-computing program, which played a key role in the wormhole stunt.
Update: Some commenters on this column say all the physicists including Einstein are wrong about quantum mechanics and other stuff. We in the business call these commenters "cranks." I decided not to enable cranky comments, but then I felt like a hypocrite, because I can be pretty cranky myself. So I'm enabling a few.
This is not a wormhole.