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, “Traversable wormhole dynamics on a quantum processor,” by physicists at Harvard and Google, among other institutions. It was published in the prestigious journal Nature, along with commentary by two Stanford physicists.
Two top-notch physics writers, Dennis Overbye of The New York Times and Natalie Wolchover of Quanta, reported 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.”
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, calls the claim that physicists created an actual wormhole “complete bullshit” and a “publicity stunt.”
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. This quest for a unified theory 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. Some theorists have proposed that entanglement might be mediated by wormholes. This 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, which can’t compute anything beyond the range of a conventional computer. The researchers constructed 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 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.
I 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.
John Horgan directs the Center for Science Writings at Stevens. This column is adapted from one he wrote for his blog at johnhorgan.org.
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