Study Finds Backward Time Travel Is Impossible in Most Universes

A theoretical study by physicist Hongsheng Zhang at the University of Jinan in China indicates that backward time travel is mathematically impossible across most conventional universal models. The research, currently awaiting peer review, demonstrates that the fundamental relationship between light and time prevents objects from returning to previous moments in their past under standard physical conditions.

According to the findings, the restriction relies on geometric principles within Albert Einstein's general theory of relativity. In spacetime, light establishes directional surfaces that slower or faster moving objects cross in only one direction. Zhang stated to ScienceAlert that the calculation relies on tracking directions within spacetime and does not require assumptions about exotic matter or quantum mechanics.

The study outlines two specific scenarios where theoretical loops in time, known as closed timelike curves, remain mathematically permissible. The first exception occurs near spinning black holes, where intense gravitational forces twist light rays into spirals rather than flat surfaces. Physicist Brandon Carter established in 1968 that extreme spacetime dragging around a rotating mass can curve a forward trajectory through time back into its starting point. NASA confirmed the existence of spacetime dragging around Earth in 2011 using its Gravity Probe B satellite.

The second exception involves global universal geometry, where the overall shape of spacetime allows a path moving continuously forward to loop back onto itself. Models involving wormholes rely on this geometric configuration to connect distant points in spacetime. Zhang acknowledged that while mathematical equations permit these two loopholes, the study does not prove whether physical nature actually allows such structures to exist.

In contrast to backward travel, forward time travel is an established reality governed by relativistic time dilation. Objects moving at high speeds or positioned in strong gravitational fields experience a slower passage of time relative to stationary observers. Data from the European Space Agency confirms that astronauts serving aboard the International Space Station return to Earth several thousandths of a second younger than people who remained on the surface.

Written by Martina Kirchner martina.kirchner@alpineweekly.com