Wormholes are commonly depicted as cosmic shortcuts, a concept that originates from a misunderstanding of a 1935 work by physicists Albert Einstein and Nathan Rosen. Einstein and Rosen introduced a "bridge" as a mathematical link between two symmetrical copies of spacetime, designed to maintain consistency between gravity and quantum physics, not for travel. The association of these bridges with traversable wormholes developed later, despite their original intent and theoretical limitations within general relativity.
A New Interpretation of Einstein-Rosen Bridges
Recent research offers a different interpretation of the Einstein-Rosen bridge, suggesting it represents something more fundamental than a wormhole. Instead of a passage, the bridge is proposed to function as a mirror in spacetime, connecting two microscopic arrows of time. This perspective addresses how quantum fields behave in curved spacetime, a key challenge in reconciling quantum mechanics (governing microscopic scales) with Einstein’s theory of general relativity (applying to gravity and spacetime).
The Misunderstood Wormhole Metaphor
The "wormhole" interpretation gained traction decades after Einstein and Rosen's initial work, particularly in the late 1980s. However, analyses from that period clarified that such travel is forbidden within general relativity; the bridge collapses faster than light can traverse it, making it non-traversable. Einstein-Rosen bridges are considered unstable and unobservable mathematical structures. Despite this, the wormhole metaphor has significantly influenced popular culture and speculative theoretical physics, leading to numerous discussions about black holes connecting distant cosmos or acting as time machines. Currently, there is no observational evidence for macroscopic wormholes, nor strong theoretical support for them within Einstein's theory without invoking highly conjectural extensions of physics.
Two Arrows of Time and Quantum Symmetry
The new work re-examines the Einstein-Rosen bridge using a modern quantum interpretation of time, building on concepts by Sravan Kumar and JoĂŁo Marto. Many fundamental laws of physics exhibit symmetry, meaning they remain valid if time or space is reversed. Taking these symmetries seriously, the Einstein-Rosen bridge can be understood as two complementary components of a quantum state: one where time flows forward, and another where it flows backward from a mirror-reflected position.
This symmetry is crucial because, at the microscopic level, quantum evolution must remain complete and reversible, even with gravity, once infinities are excluded. The "bridge" indicates that both time components are necessary for a complete physical description. While physicists typically focus on a single arrow of time in ordinary situations, both directions must be included for a consistent quantum description in contexts like black holes or expanding/collapsing universes.
Resolving the Black Hole Information Paradox
This framework provides a potential resolution to the black hole information paradox. Stephen Hawking demonstrated in 1974 that black holes emit radiation and can eventually evaporate, seemingly erasing information about objects that fall into them. This contradicts the quantum principle that information must be preserved during evolution.
The paradox arises if horizons are described using a single, one-sided arrow of time. If the full quantum description incorporates both time directions, information is not lost; instead, it transitions from our time direction to the reversed one. This preserves completeness and causality without requiring exotic new physics.
While macroscopic beings experience only one direction of time due to the tendency of entropy to increase, quantum mechanics allows for more subtle behavior. Evidence for this hidden structure may exist in the cosmic microwave background, which exhibits a small but persistent asymmetry in spatial orientation, an anomaly that standard models find unlikely unless mirror quantum components are included.
Echoes of a Prior Universe
This perspective suggests a deeper possibility: the Big Bang might not have been an absolute beginning but a "bounce"—a quantum transition between two time-reversed phases of cosmic evolution. In such a scenario, black holes could bridge not just time directions but different cosmological epochs. Our universe could potentially be the interior of a black hole formed in an earlier, "parent" cosmos, which collapsed and then expanded to form the universe observed today.
If this hypothesis is correct, relics from the pre-bounce phase, such as smaller black holes, could survive and reappear in our expanding universe, potentially accounting for some of the unseen matter attributed to dark matter. This view posits that the Big Bang emerged from conditions in a preceding contraction, with the bridge being temporal rather than spatial, making the Big Bang a gateway instead of a beginning.
Conclusion
This reinterpretation of Einstein-Rosen bridges does not offer shortcuts across galaxies or time travel, but it provides a more profound understanding. It offers a consistent quantum picture of gravity where spacetime embodies a balance between opposite directions of time, and suggests our universe may have a history predating the Big Bang. This work aims to complete, rather than overthrow, Einstein’s relativity and quantum physics, potentially revealing that at microscopic levels and within a bouncing universe, time can flow in both directions.