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An illustration of matter pouring into a black hole, crossing an Einstein-Rosen bridge and emerging into another region of the universe. | Credit: Robert Lea (Created with Canva)
This article was originally published at The conversation. The publication contributed the article to Space.com Expert Voices: Op-Eds and Perspectives.
Wormholes they are often imagined as tunnels through space or time—shortcuts through the universe. But this picture is based on a misunderstanding of the work of physicists Albert Einstein and Nathan Rosen.
In 1935, while studying the behavior of particles in regions of extreme gravity, Einstein and Rosen introduced what they called a “bridge”: a mathematical link between two perfectly symmetric copies of Spacetime. It was not intended as a pass for travel, but as a way to maintain consistency between gravity and quantum physics. Only later did Einstein-Rosen bridges become associated with wormholes, despite having little to do with the original idea.
But in new researchMy colleagues and I show that the original Einstein–Rosen bridge points to something much stranger—and more fundamental—than a wormhole.
The puzzle that Einstein and Rosen addressed was never about space travel, but about how quantum fields behave in curved spacetime. Interpreted this way, the Einstein-Rosen bridge acts as a mirror in space-time: a connection between two microscopic arrows of time.
Quantum mechanics governs nature at the smallest scales, such as particles, while Einstein’s the theory of general relativity it applies to gravity and spacetime. Reconciling the two remains one of physics’ most profound challenges. And interestingly, our reinterpretation may provide a way to do this.
A misunderstood legacy
The “wormhole” interpretation emerged decades after Einstein and Rosen’s work, when physicists speculated about passing from one side of spacetime to the other, especially in the research from the late 80s.
But the same analyzes also showed how speculative the idea was: within general relativity, such travel is forbidden. The bridge seizes faster than light can cross it, making it impassable. Therefore, Einstein-Rosen bridges are unstable and unobservable—mathematical structures, not portals.
However, the wormhole metaphor has flourished in popular culture and speculative theoretical physics. The idea that black holes could connect distant regions of the cosmos – or even act as time machines — has inspired countless works, books and films.
However, there is no observational evidence for macroscopic wormholes and no compelling theoretical reason to expect them in Einstein’s theory. While speculative extensions of physics—such as exotic forms of matter or changes in general relativity — have been proposed to support such structures, remain untested and highly conjectural.
An artist’s rendering of using a wormhole to travel through space. | Credit: NASA
Two arrows of time
Our recent work revisits the Einstein-Rosen bridge puzzle using a modern quantum interpretation of time, building on ideas developed by Sravan Kumar and João Marto.
Most fundamental laws of physics it does not distinguish between past and future, or between left and right. If time or space are reversed in their equations, the laws remain valid. Taking these symmetries seriously leads to a different interpretation of the Einstein-Rosen bridge.
Rather than a tunnel through space, it can be understood as two complementary components of a quantum state. In one, time flows forward; in the other, it flows back from its mirrored position.
This symmetry is not a philosophical preference. Once infinities are ruled out, quantum evolution must remain complete and reversible at the microscopic level—even in the presence of gravity.
The “bridge” expresses the fact that both time components are needed to describe a complete physical system. In ordinary situations, physicists ignore the time-reverse component, choosing only one arrow of time.
But near black holes or in expanding and collapsing universes, both directions must be included for a consistent quantum description. This is where Einstein-Rosen bridges naturally occur.
Resolving the information paradox
At the microscopic level, the bridge allows information to pass over what appears to us as a event horizon – a point of no return. Information does not disappear; it continues to evolve, but in the opposite temporal direction, the mirror.
This framework provides a natural resolution to the famous black hole information paradox. In 1974, Stephen Hawking showed that black holes radiate heat and can eventually evaporate, apparently erasing all information about what fell into them—contradicting the quantum principle that evolution must preserve information.
The paradox arises only if we insist on describing horizons using a single, one-sided arrow of time extrapolated to infinity—an assumption that quantum mechanics itself does not require.
If the full quantum description includes both directions of time, nothing is really lost. Information leaves our temporal direction and reappears along the reversed one. Completeness and causality are preserved without invoking exotic new physics.
These ideas are hard to grasp because we are macroscopic beings who experience only one direction of time. On a day-to-day scale, disorder – or entropy – tends to increase. A very ordered state naturally evolves into a disordered one, never the other way around. This gives us an arrow of time.
But quantum mechanics allows for more subtle behavior. Intriguingly, there may already be evidence for this hidden structure. The cosmic microwave background—the afterglow a Big bang — it shows a small but persistent asymmetry: a preference for a spatial orientation over the mirror image.
This anomaly has puzzled cosmologists for two decades. Standard models assign an extremely low probability to it – unless quantum mirror components are included.
Echoes of a previous universe?
This image naturally connects to a deeper possibility. What we call the “Big Bang” may not have been the absolute beginning, but a leap—a quantum transition between two time-reversed phases of cosmic evolution.
In such a scenario, black holes could act as bridges not only between time directions, but also between different cosmological epochs. our universe it could be the inside of a black hole formed in another parent cosmos. This could have formed as a closed region of spacetime collapsed, rebounded and began to expand as the universe we observe today.
If this picture is correct, it also provides a way for observations to decide. Relics from the pre-jump phase – such as smaller black holes – could survive the transition and reappear in our expanding universe. Some of the unseen matter we attribute to dark matter might actually be made of such relics.
From this perspective, the Big Bang evolved from the conditions of an earlier contraction. Wormholes are unnecessary: the bridge is temporal, not spatial – and the Big Bang becomes a gateway, not a beginning.
This reinterpretation of Einstein-Rosen Bridges offers no shortcuts across galaxies, no time travel, and no sci-fi wormholes or hyperspace. What it offers is much deeper. It provides a consistent quantum picture of gravity where spacetime embodies a balance between opposing directions of time—and where our universe may have had a history before the Big Bang.
It does not overturn Einstein’s relativity or quantum physics, but complements them. The next revolution in physics may not take us faster than light—but it could reveal that time, deep in the microscopic world and in a bouncing universe, flows both ways.