Physicist Argues Time Travel to the Past Is Likely Impossible
New research suggests spacetime geometry restricts movement to a forward-only direction.
1Forward-Only Spacetime Geometry
Hongsheng Zhang from the University of Jinan proposes that traveling into the past is theoretically impossible in most universes. His research suggests that spacetime is structured like a staircase where movement is strictly unidirectional. This implies that while forward travel is possible, returning to a previous point in time remains fundamentally prohibited.
2The Light Direction Constraint
The core argument relies on the behavior of light within relativity. Light cannot sit at right angles to an object's path through time. Because objects must cross light-defined surfaces in a consistent direction, they are forced to move forward. This bookkeeping of directions prevents any possibility of returning to a starting point.
3Closed Timelike Curves Defined
Physicists define journeys to the past as closed timelike curves, which are paths looping back to their origin. While Einstein’s equations theoretically permit these loops in specific scenarios, such as near spinning black holes, Zhang’s work argues that these conditions are extremely rare and do not apply to the general structure of reality.
4Mechanism of Temporal Twisting
One potential method for backward travel involves light rays spiraling around each other, preventing the formation of standard spacetime layers. Near a spinning black hole, mass drags space and time, potentially bending forward movement into a circle. Physicist Brandon Carter identified these loops in 1968, showing how paths could theoretically return to origin.
5The Escher Universe Model
A second theoretical possibility involves the global shape of the universe itself. Similar to an Escher drawing, the universe could be structured so that climbing upward eventually leads back to the bottom. Most paper-based time machine designs, including those utilizing wormholes, rely on this geometric trick to bypass the standard forward-only progression.
6Limitations of the Theorem
Zhang acknowledges that his theorem does not definitively prove whether nature permits these exotic conditions. The research focuses on the mathematical possibility of these structures rather than their physical existence. Whether our specific universe allows for such extreme geometric configurations remains an open question that current physics has yet to fully resolve.
7Established Future Travel
Travel into the future is already scientifically established through time dilation. Moving at high speeds or experiencing intense gravity slows an individual's clock relative to others. Astronauts on the International Space Station return to Earth slightly younger than those on the ground, confirming that forward time travel is a verified physical reality.
8Scientific Outlook and Implications
While the allure of visiting the past remains a popular cultural trope, current theoretical frameworks prioritize forward movement. Zhang’s work emphasizes that without exotic matter or specific geometric anomalies, the universe functions as a one-way street. For now, humanity must focus on the future, as the past remains strictly beyond our reach.
Original article: Euronews – Latest — Physicist Argues Time Travel to the Past Is Likely Impossible