The geometry of a spinning black hole might allow messages to travel backward
In short: Traveling into the future is already happening—gravity and speed simply stretch our timeline. But traveling to the past requires bending spacetime so severely that cause and effect begin to warp. According to general relativity, certain rotating structures in space could theoretically create pathways where you meet your own past.
To understand backward time travel, one must look at Einstein's field equations for General Relativity. While flat spacetime is simple, Karl Schwarzschild first described non-flat spacetime that revealed the existence of black holes. In these regions, gravity is so intense it creates a 'valley' in space. As an object falls toward a black hole, its light cone—the path of all future events—begins to tilt. At the event horizon, the cone tilts 45 degrees, pointing entirely inward. Eventually, at the singularity, the light cone points completely toward the center, making the singularity a future moment in time rather than just a physical location.
Standard black holes trap everything because of this horizon. However, the Kerr-Newman metric describes rotating black holes, which behave differently. If a black hole spins fast enough, the math suggests the event horizon can disappear, leaving behind a 'naked singularity.' Without an event horizon to act as a one-way door, an object could theoretically approach the center and return to the outside universe. This removes the physical barrier of being trapped while still interacting with the extreme curvature of the interior.
The most specific mechanism for backward travel involves 'closed timelike curves' (CTCs). In a rotating black hole, the singularity is not a point but a one-dimensional ring. Spacetime can curve so intensely around this ring that it forms loops. Quantum information scientist Seth Lloyd suggests these pathways could allow an observer to move forward in time only to arrive back at their own past. While scientists cannot yet confirm if CTCs exist in our universe, the fact that black holes are plentiful and most of them spin makes the existence of these theoretical 'time machines' a plausible possibility under current physics.
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Sources
- Summary by Intellect · source: How Time Travel is Possible through a Black Hole...to the PAST!
- Also: How to send a message back in time—black hole required
- Also: www.space.com — Could humans use black holes to time travel?
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