Wormholes are theoretical tunnels through spacetime that connect two distant regions of the universe, and they emerge directly from the mathematics of Einstein’s general theory of relativity. They are, in that sense, just as valid a prediction of the theory as black holes. But while black holes have been observed, photographed, and detected through gravitational waves, no wormhole has ever been found. The gap between mathematical permission and physical reality is enormous, and bridging it has driven some of the most creative work in theoretical physics over the past century.
Where Wormholes Come From in Physics
The idea dates to 1935, when Albert Einstein and Nathan Rosen noticed that the equations describing a black hole could be extended to describe a bridge connecting two separate regions of spacetime. This “Einstein-Rosen bridge” was the first wormhole, though the term itself came later. The original version was not something you could travel through. It existed as a geometric feature of the Schwarzschild solution for a non-rotating, uncharged black hole, and it pinched off too quickly for anything, even light, to cross.
Generalized versions of the Einstein-Rosen bridge have been explored for rotating and electrically charged black holes. In these cases, the internal geometry is richer. A 2023 analysis showed that for both rotating (Kerr) and electrically charged (Reissner-Nordström) black holes, one-way Einstein-Rosen bridges can exist inside the black hole, connecting to what the mathematics describes as an infinite succession of other universes.1arXiv. Generalized Einstein–Rosen bridge inside black holes “One-way” is the key qualifier: these bridges, if they exist at all, only allow passage in one direction through time and space. You could fall through, but you could never come back.
Even the classic Schwarzschild wormhole turns out to be deeply fragile. Work on the gravitational effects of matter and radiation accumulating near its horizons showed that the wormhole geometry is unstable. Infalling energy gets blue-shifted to extreme intensities, and the gravitational focusing produced by this “blue sheet” of energy eventually collapses the structure into an ordinary black hole.2Oxford Academic. Blue-Sheet Instability of Schwarzschild Wormholes So the simplest wormholes that general relativity predicts destroy themselves almost immediately.
The Exotic Matter Problem
If you want a wormhole that stays open long enough for something to pass through, you need to prop it open. In the late 1980s, physicists Kip Thorne and Michael Morris worked out what a traversable wormhole would require, and the answer was unsettling: you need matter with negative energy density. This is sometimes called “exotic matter,” and it is not the antimatter of science fiction. Exotic matter would have to exert a kind of gravitational repulsion, pushing the walls of the wormhole’s throat apart instead of letting gravity squeeze them shut.3The European Physical Journal C. Properties of the wormhole model in de Rham–Gabadadze–Tolley like massive gravity with specific matter density
Nothing we have ever observed in nature behaves this way on large scales. Ordinary matter, dark matter, and even dark energy (which accelerates the universe’s expansion) do not produce the specific kind of negative energy density needed to hold a wormhole throat open at a size large enough for, say, a spacecraft. The requirement for exotic matter is arguably the single biggest obstacle to wormholes being real physical objects rather than mathematical curiosities.
A macroscopic traversable wormhole would also need to be gentle enough inside that the tidal forces do not tear apart anything passing through. A 2024 study examined this constraint and proposed that the limiting case of zero tidal forces could be enough to overcome restrictions imposed by quantum field theory.4arXiv. Macroscopic traversable wormholes: minimum requirements The paper framed this as a minimum requirement: even the most optimistic scenario for a wormhole you could travel through demands an interior that is essentially tidal-force-free.
Quantum Loopholes for Negative Energy
Quantum mechanics does allow negative energy densities to exist, at least in small amounts and under restricted conditions. The best-known example involves the Casimir effect, where two closely spaced conducting plates in a vacuum experience an attractive force because the quantum vacuum between them has lower energy density than the vacuum outside. Detailed calculations confirm that the energy density between the plates breaks into two parts: a negative, position-independent Casimir term and a positive, position-dependent term. In certain physically realizable configurations, the negative term dominates, making the overall energy density genuinely negative in a given region.5Physical Review D. The Energy Density in the Casimir Effect
The catch is scale. The Casimir effect produces measurable but tiny amounts of negative energy across microscopic distances. Scaling that up to hold open a wormhole throat wide enough for a person or a probe remains far beyond anything current physics can accomplish or even sketch a plausible path toward. The quantum effects are real, but they operate at distances measured in nanometers, not meters.
Can Modified Gravity Reduce the Need for Exotic Matter?
One of the more active areas of wormhole research involves changing the rules of gravity itself. General relativity is not the only theory that can describe gravity; it is the best-tested one, but physicists have explored families of “modified gravity” theories that add extra terms to Einstein’s equations. In some of these frameworks, wormhole solutions can exist with less exotic matter or, in certain formulations, none at all.
A 2025 study of rotating Casimir wormholes in one such framework highlighted the potential of modified gravity to support stable, traversable wormhole solutions with reduced reliance on exotic matter.6The European Physical Journal C. Rotating Casimir wormholes in f(R) gravity: a modified gravity extension of exotic spacetime models A separate study in a different modified gravity theory went further, demonstrating that wormholes with certain shape functions can satisfy all the standard energy conditions, meaning they would not require exotic matter at all.7Annals of Physics. Non-exotic wormholes in f(R,Lm) gravity
These results are mathematically rigorous within their chosen frameworks, but they come with a significant caveat. We do not yet know whether any of these modified gravity theories correctly describe the universe. General relativity has passed every experimental test thrown at it so far. Until a modified theory makes a testable prediction that differs from general relativity and is confirmed by observation, these exotic-matter-free wormholes remain possibilities within unconfirmed theories rather than predictions of established physics.
Entanglement, Wormholes, and the ER=EPR Conjecture
One of the most provocative ideas connecting quantum mechanics to wormholes emerged in 2013, when Juan Maldacena and Leonard Susskind proposed that quantum entanglement and wormholes might be the same thing viewed from different angles. Their conjecture, known as ER=EPR, suggests that two entangled particles (an Einstein-Podolsky-Rosen pair) are connected by a non-traversable wormhole (an Einstein-Rosen bridge).8PubMed. Probing the Connection between Entangled Particles and Wormholes in General Relativity The idea was developed from solutions in general relativity where two distant black holes are connected through their interiors via a wormhole, and these solutions can be interpreted as maximally entangled states of the two black holes.9arXiv. Cool horizons for entangled black holes
If ER=EPR is correct, it would mean that the fabric of spacetime itself is stitched together by quantum entanglement. Every entangled pair of particles in the universe would be linked by a tiny, non-traversable wormhole. This does not mean you could send messages through entanglement (quantum mechanics forbids that), but it does suggest that the geometry of space and the phenomenon of entanglement are two descriptions of a single underlying reality. The conjecture remains unproven, but it has become one of the most influential ideas in theoretical physics over the past decade, reshaping how physicists think about the relationship between gravity and quantum information.
Wormholes on Quantum Processors
In 2022, a team of researchers made headlines by claiming to have observed “traversable wormhole dynamics” on a quantum computer. The reality was more subtle than the headlines suggested, but the work is genuinely interesting. The researchers used Google’s Sycamore quantum processor to simulate a simplified version of a many-body quantum system called the Sachdev-Ye-Kitaev (SYK) model. This model has a special property: in certain limits, its behavior is mathematically equivalent, through holographic duality, to gravitational physics in a lower-dimensional spacetime that includes traversable wormholes.
Using learning techniques to build a sparsified version of the SYK model, the team ran a nine-qubit circuit with 164 two-qubit gates and observed dynamics consistent with traversable wormhole physics, including features like a Shapiro time delay, causal time-ordering of signals, and scrambling dynamics.10Nature. Traversable wormhole dynamics on a quantum processor Subsequent work has extended this approach. A teleportation protocol based on the SYK model achieved almost perfect fidelity, exhibiting many features of semiclassical traversable wormholes.11Journal of High Energy Physics. A traversable wormhole teleportation protocol in the SYK model More recent experiments have used chaotic binary sparse SYK models optimized for current noisy quantum hardware, dramatically reducing circuit depth while preserving the spectral chaos needed for the gravitational interpretation to hold.12arXiv. Quantum simulation of traversable-wormhole-inspired quantum teleportation in a chaotic binary sparse SYK model
It is worth being clear about what these experiments do and do not show. No actual wormhole was created in a laboratory. What the researchers demonstrated is that a quantum computer can simulate a quantum system whose mathematical description, through holographic duality, maps onto a gravitational system containing a traversable wormhole. The information that was “teleported” moved through quantum entanglement in a pattern that, if the holographic correspondence is correct, is described by wormhole geometry in a dual gravitational theory. This is a test of holographic duality and the ER=EPR framework, not a creation of a physical tunnel through space. Researchers have also extended the protocol to allow teleportation between two entangled copies of the SYK model communicating only through a classical channel, further probing the connection between entanglement and wormhole geometry.13arXiv. Long-range wormhole teleportation
Could We Ever Detect a Natural Wormhole?
If wormholes do exist in nature, they would likely look a lot like black holes from the outside. Both are compact objects with strong gravitational fields, and both would bend light around them. This makes telling them apart observationally very difficult, but not necessarily impossible.
One promising avenue involves the “shadow” that a compact object casts when backlit by hot gas or a distant light source. For a black hole, the interior of this shadow is completely dark because nothing can escape from inside the event horizon. A traversable wormhole, by contrast, has no true event horizon. Light from the other side could, in principle, pass through the throat and emerge on this side. A 2025 study showed that an accretion disk viewed through a wormhole would produce images fundamentally different from those around black holes: details would be visible inside the wormhole’s silhouette, something that is impossible for a black hole shadow.14arXiv. Observing an accretion disk inside a wormhole shadow The paper suggested that interferometric observations, of the kind performed by the Event Horizon Telescope collaboration, could in principle distinguish between the two.
Current instruments are not yet sensitive enough to make this distinction definitively. The Event Horizon Telescope images of the black holes in M87 and our own galaxy’s center are stunning, but their resolution is still relatively coarse. Future upgrades, including space-based interferometry and next-generation ground arrays, may push the resolution to the point where these subtle differences become detectable. Whether there is anything to find remains an open question.
Wormholes and the Birth of the Universe
Wormholes have also entered cosmology, particularly in discussions about the initial conditions of the universe. In quantum cosmology, physicists try to describe the universe’s origin using a wave function, and one of the oldest proposals for this is the Hartle-Hawking “no-boundary” proposal, which envisions the universe emerging smoothly from a compact Euclidean geometry with no singular beginning. This proposal has known technical problems, and recent work has explored whether Euclidean wormholes can do the job better.
A 2024 study found that Euclidean wormholes set natural initial conditions for inflation and that the resulting wave function can favor a long-lasting inflationary epoch, resolving a well-known issue with the no-boundary proposal.15PubMed. Inflationary Cosmology from Anti-de Sitter Wormholes A related essay on the topic noted that wormholes retain the appeal of the no-boundary approach while broadening the class of geometries that are physically relevant for inflating universes.16International Journal of Modern Physics D. Before the Bang: Wormholes at the dawn of the universe In the braneworld scenario, an alternative framework, the evolution of inflating wormholes has been studied directly: while some wormholes decay naturally, others satisfying certain initial conditions could collapse into black holes and persist indefinitely.17Classical and Quantum Gravity. Inflating wormholes in the braneworld models
These cosmological wormholes are not tunnels you could fly a spaceship through. They are mathematical contributions to the quantum wave function of the universe, and their role is to help explain why the universe began inflating in the first place and why it has the large-scale properties we observe. The word “wormhole” covers a surprisingly diverse family of objects across physics, from interstellar shortcuts to quantum computing protocols to primordial cosmological structures, and the cosmological variety is the most abstract of the lot.
Time Travel and the Chronology Protection Conjecture
If a traversable wormhole could be built and one of its mouths accelerated to near light speed or placed in a stronger gravitational field, time dilation would cause the two mouths to age at different rates. After a while, entering one mouth could, in principle, deposit you at the other mouth at an earlier time. This makes traversable wormholes the closest thing general relativity offers to a genuine time machine.
Stephen Hawking was deeply skeptical of this possibility. He proposed the “chronology protection conjecture,” which informally states that the laws of physics conspire to prevent time travel. The mechanism he suggested involves quantum vacuum effects: as a wormhole approaches the conditions needed to form a time machine (technically, as “closed timelike curves” begin to appear in the spacetime geometry), quantum fields near the wormhole’s throat would produce runaway amounts of energy. This energy buildup would destroy the wormhole before any time travel could occur. Analysis of these quantum vacuum polarization effects in spacetimes containing closed timelike curves has been a subject of ongoing study.18PubMed Central. From wormhole to time machine: Remarks on Hawking’s chronology protection conjecture
The conjecture has never been proven in full generality. It depends on our understanding of quantum field theory in curved spacetime, which is itself an approximation that breaks down where quantum gravity effects become strong. Some physicists take it as likely true on the grounds that the alternative, a universe where time travel is possible, creates paradoxes that seem incompatible with a self-consistent physical theory. Others view the question as genuinely open, arguing that a full theory of quantum gravity might allow structures that semiclassical analysis would forbid. For now, the question of whether physics forbids time machines or simply makes them extraordinarily difficult remains unanswered.
Wormhole Thermodynamics
Black holes famously have thermodynamic properties: they have entropy proportional to their event horizon area, they radiate at a temperature determined by their surface gravity, and they obey laws analogous to the laws of thermodynamics. Physicists have begun asking whether wormholes have similar properties, and the answer appears to be a qualified yes.
A study of evolving wormholes in modified gravity proposed that wormhole entropy is related to the area of its apparent horizon, analogous to the area law in black hole thermodynamics.19Physics Letters B. Thermodynamic insights into evolving Lorentzian wormholes in f(R,T) gravity If this analogy holds up, it means wormholes are not just geometric structures but thermodynamic objects with well-defined entropy, temperature, and energy relationships. This connects them to the broader program of understanding how gravity and thermodynamics are related, a program that has been one of the most productive in theoretical physics since the 1970s.
The thermodynamic perspective also strengthens the case for taking the ER=EPR conjecture seriously. If wormholes carry entropy and entanglement is a form of entropy, the identification of wormholes with entanglement becomes not just a geometric analogy but a thermodynamic one. The entanglement entropy between two systems and the geometric entropy of a wormhole connecting them would be measuring the same thing from two different perspectives. This is speculative, but it is the kind of speculation that has historically led to major advances in physics when it eventually finds either confirmation or a clear counterexample.