Spacetime May Be Just One Layer of the Universe—Embedded in a Deeper Reality We Don’t Understand, Physicist Suggests

7 min readHere’s what you’ll learn when you read this story:Physicists have long struggled to make the general theory of relativity and quantum mechanics agree, and some scientists believe that there’s a sign that there might be something deeper at play.One scientist, Mayank Mehta, believes that his mathematics point to something beyond our familiar four dimensions. Instead, Mehta suggests that space-time could be just one layer of reality—embedded in a higher-dimensional space. In the brilliant Einsteinian universe we have inhabited for more than a century, space-time is the stage and matter the actors. His general theory of relativity tells us that planets, stars, galaxies, and even you move through a four-dimensional arena, where matter and energy bend and warp the stage beneath us. This is why some of the spectacular James Webb Space Telescope images we devour online show distant galaxies curved into strange, banana-like shapes: massive foreground galaxies and galaxy clusters buckle space-time, bending the path of the light traveling through it. But what if the Einsteinian stage is not as rock-solid as we thought? What if space-time has something to do with a deeper layer of reality we have yet to fully understand?Physicists have good reason to ask. General relativity works spectacularly well on the cosmic scale. The trouble begins when they try to reconcile it with quantum mechanics, the theory describing the microscopic world with equally astonishing accuracy. Try making Einstein’s smooth space-time obey the strange, probabilistic rules of quantum mechanics, and the two theories become stubbornly incompatible. A century later, physicists are still trying to figure out how gravity and quantum mechanics can both be right—and how the two fit together. But perhaps this incompatibility is trying to tell us something much more radical: space-time may not be the most basic layer of reality at all.Some researchers imagine space-time emerging from deeper quantum structures; theoretical physicist Mark Van Raamsdonk has explored the possibility that space-time itself may be stitched together by quantum entanglement, the strange connections linking quantum systems. Reduce that entanglement in his mathematical description, and regions of space-time begin to pull apart from one another. Cognitive scientist Donald Hoffman skews digital, proposing that space-time is more like the desktop on a computer—a useful interface hiding an underlying reality that, in his theory, is built from networks of conscious agents. And theoretical physicist Nima Arkani-Hamed has supplied perhaps the most ominous verdict: “space-time is doomed.”Mayank Mehta, PhD, a physicist and neuroscientist at UCLA, thinks his own mathematics points beyond the familiar three dimensions of space and one of time. His calculations, he says, suggest that the physics of our universe may be embedded in a higher-dimensional space, making the space-time we experience only part of a larger unseen structure. But to understand how he arrived at that possibility, we first have to go back to the century-old clash between relativity and quantum mechanics, and to the physicists who first tried to bridge it.Our first stop is 1920s Britain. There, a young physicist named Paul Dirac is trying to bring quantum mechanics into Einstein’s relativistic universe when the mathematics begins misbehaving, spitting out seemingly impossible negative-energy solutions—states suggesting that electrons could occupy energies below what physicists thought should be the lowest possible level. As Dirac wrestles with what those strange solutions could mean, his theory leads to an astonishing prediction: the electron should have a mirror counterpart, identical in mass but opposite in charge. Within a few years, scientists find it. Antimatter is real.But the mathematical headaches don’t go away. In the decades that follow, physicists including future Nobel laureates Richard Feynman and Julian Schwinger develop increasingly powerful ways of describing the quantum world. One particularly useful trick is to translate calculations from the space-time of relativity into a mathematically friendlier version known as Euclidean space. But with matter particles such as electrons, that translation introduces its own complications. In some formulations, the mathematical objects used to describe these particles have to be doubled. In Mehta’s telling, physicists could make the calculations work—but they treated the extra pieces as mathematical devices, not as real particles.By the 1970s comes supersymmetry, an audacious idea proposing that every known particle has a hidden counterpart, or “superpartner.” None has ever been found, but put these hypothetical partners into the equations and some troublesome quantum effects neatly cancel one another out. Fast-forward to around 1990, supersymmetry became the subject of Mehta’s PhD research at the Indian Institute of Science in Bangalore.Digging through earlier attempts to describe fermions (the tiny building blocks of matter that include the familiar electron in Euclidean space) and the later mathematics of supersymmetry, Mehta spotted what he thought was a problem. “These two worlds had never talked to each other,” he says, referring to Euclidean fermions and supersymmetry. Specifically, the extra fermions introduced in the earlier mathematical treatment created a problem when brought into supersymmetry, Mehta explains.To remedy this, Mehta developed a framework that replaced what he regards as the mathematical “duct tape” of the earlier treatment with a mathematically rigorous description of Euclidean fermions. More radically, Mehta argues that the extra pieces appearing in the mathematics aren’t just calculation tools: they represent another set of particles and antiparticles that should actually exist.Take those extra particles seriously, and suddenly the universe contains much more than just the familiar matter and antimatter we know. His mathematics points to what he calls a “quadruple universe”: matter and antimatter would be joined by a second, still-undetected set of matter and antimatter. “The matter that we see is only 1/4,” Mehta says. “Three-fourths of the matter is missing, hidden in these extra fermions, according to my theory.” This raises an obvious question: if Mehta’s mathematics predicts all this additional matter, where is it?Here the story brushes against another cosmic mystery. Astronomers already know that the ordinary matter we can see accounts for only a small fraction of the cosmos (5 percent, versus roughly 27 percent dark matter and 68 percent dark energy). Mehta is now investigating whether the additional fermions predicted by his mathematics could have something to do with dark matter. He hasn’t completed those calculations, however, and the connection remains a hypothesis.It’s an audacious idea. So much so that, when Mehta first developed his theory of Euclidean fermions as a graduate student, he says his thesis adviser was so appalled that he fired him and told the university dean that Mehta had “lost his mind” and “should be put in a mental hospital.” But the mathematics did eventually make it into print. In 1990, Mehta published a paper in Physical Review Letters proposing a way to carry the Dirac fermion from ordinary space-time into Euclidean space without doubling its degrees of freedom. He followed it with papers exploring how this treatment of Euclidean fermions interacted with supersymmetry and higher dimensions. It was in this subsequent work, Mehta says, that the additional fermions underlying his “quadruple universe” emerged.Mehta says the reaction from some eminent physicists was startling. One Nobel laureate wrote to him calling the work “the biggest discovery since the theory of relativity,” he recalls. Later, he says, Nobel laureate Abdus Salam examined his proof and encouraged him to pursue it—but warned that such an extraordinary claim would struggle for acceptance without support from established figures.Yet even if the UCLA professor’s missing particles exist, an obvious question remains: what does any of this have to do with space-time itself? His theory may have added new actors to the universe, but has it really changed Einstein’s stage? Mehta thinks the answer may be yes. Look back at Dirac: an attempt to make quantum mechanics work with Einstein’s relativity ended up predicting an entirely new form of matter—antimatter. For Mehta, that is a clue that the stage and the actors, or matter and space-time, may not be fundamentally separate things at all. The mathematics governing one, he says, keeps having unexpected consequences for the other.Not everyone is convinced there is something behind Einstein’s stage, though. Nicola Kistler, PhD, a mathematician at Goethe University Frankfurt, argues that the century-long failure to reconcile relativity and quantum mechanics doesn’t by itself demonstrate that space-time is emergent—or doomed.“I would be extremely, extremely cautious,” Kistler says. Before abandoning space-time as fundamental, he wants something considerably harder than an unresolved theoretical conflict: “a counterexample, a smoking gun”—something grounded in mathematics or experiment.After all, a century can feel like an eternity in physics, but not necessarily in mathematics. The failure to solve a problem, Kistler argues, doesn’t tell us that its premises are wrong. Perhaps relativity and quantum mechanics really are “built [...] on sand,” as he puts it. Or perhaps the mathematics required to reconcile them is simply extraordinarily hard.So where does that leave space-time?Mehta thinks there may be another possibility. His calculations, he says, point beyond the familiar four-dimensional picture. Instead, the standard model—which is physics’ remarkably successful recipe for explaining almost everything that happens at the smallest scales (with gravity as the conspicuous exception)—appears to be “embedded in a higher-dimensional space,” he told an audience of scientists at an invitation-only meeting in San Diego this summer, where Popular Mechanics was the only media outlet in attendance. If so, our familiar three dimensions of space and one of time may be only one layer of a structure extending beyond the dimensions we ordinarily experience.Yet Mehta himself is skeptical of claims that cannot ultimately be tested. Beautiful mathematics is not enough to rewrite reality. At the meeting, while discussing another speculative idea, Mehta made the point himself: eventually, a theory has to make a prediction that scientists can actually go out and test. Until then, he said, it remains “in the world of possibilities.”The question remains whether space-time is the whole stage or merely one level of a larger reality that extends beyond the four dimensions we live in. But one thing’s for certain: Einstein’s space-time isn’t doomed—yet.Special Digital IssuesAugust/September 2026Download HereThis issue is optimized for mobile/tablet viewing.It's also available on Apple News+.Featuring:➡ A Luxury Resort Hid a Secret Government Doomsday Bunker Below It for 35 Years. The Clues Were Everywhere.➡ 7 People Have Confessed to Being D.B. Cooper. Is One of Them Telling the Truth?➡ A B-52 Accidentally Lost Two Hydrogen Bombs Over North Carolina. One Nearly Detonated. 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This Weapon Can Save It.October/November 2022Download HereThis issue is optimized for mobile/tablet viewing.It's also available on Apple News+.Featuring:➡ Can America's M1 Abrams Still Compete With China's and Russia's Latest Battle Tanks?➡ Inside the Final Minutes of the Concorde Disaster—and How It Doomed Supersonic Travel for Decades➡ How the Massive Cargo Ship Felicity Ace Sank, Taking $400 Million Worth of Exotic Supercars With It➡ I Turned My Old Gas-Guzzler Into a Zippy EV for $15,000August/September 2022Download HereThis issue is optimized for mobile/tablet viewing.It's also available on Apple News+.Featuring: ➡ Cosmic Secrets of the 17 Most Powerful Mega-Telescopes on Earth—and Beyond➡ Can the Air Force's Secret, Hypersonic Jet Reclaim the Skies From Russia and China?➡ For 50 Years, the Zodiac Killer's 340 Cipher Stumped the FBI—Then Three Amateurs Cracked the Code➡ America's Most Fearsome Howitzer Has Entered the War in UkraineJune/July 2022DOWNLOAD HEREThis issue is optimized for mobile/tablet viewing.It's also available on Apple News+.Featuring:➡ Every Single Drone Fighting in the Skies Over Ukraine➡ How to Buy a New Car in 2022 Without Getting Fleeced➡ This Megastructure Could Keep Us Alive Forever➡ The Race to Revolutionize EV BatteriesStav Dimitropoulos is a Gold and Community Anthem Award–winning journalist, and writes about consciousness, science, and culture for Popular Mechanics, Nature, and the BBC. Her work often explores mind-stretching angles where science meets philosophy. Her debut nonfiction book, Slow, Lazy, Gluttons (Greystone Books, 2026) asks: What if the traits society shames — laziness, darkness, nostalgia, and more — are actually survival superpowers?