# University of Jinan physicist's proof bars travel to the past in a broad class of model universes

- Published: 2026-11-09 14:10 UTC
- Section: Science › Physics
- Tags: time travel to the past, closed timelike curves, Hongsheng Zhang, University of Jinan, general relativity, spacetime topology, wormholes, spinning black hole, Brandon Carter
- URL: https://realtech.media/news/rt-b55397dbab687d49011ab2e3_university_of_jinan/

**A theoretical paper, submitted for peer review, finds that closed timelike curves require either twisted light rays or a special spacetime topology.**

![University of Jinan physicist's proof bars travel to the past in a broad class of model universes](https://realtech.media/media/2026/11/31811e35dbe9f288.avif)
*euronews.com*

Hongsheng Zhang, a physicist at the University of Jinan in China, has shown that in a broad class of theoretical universes travel into one's own past is impossible, euronews.com reports. [1] The work has been submitted for peer review. It is a mathematical result about spacetime geometry, not an experiment.

The argument rests on one fact: "light can never point sideways to a traveller's direction in time," Zhang says. [1] Spacetime can be sliced into layers along which light itself travels. Anything slower than light must cross these surfaces in the same direction, like climbing a staircase that never lets you step down. [1]

## Closed timelike curves and two loopholes

Physicists call journeys to the past closed timelike curves: routes through spacetime that loop back to the place and moment where they began without exceeding the speed of light. [1] Einstein's equations allow such paths in a few scenarios, for example near the core of a spinning black hole. [1] According to Zhang's paper, there are only two ways around the barrier. [1]

The first is twist. Light rays spiral around one another like the strands of a rope, so the layers of light cannot form. [1] Near the centre of a spinning black hole, the dragging of space and time is so strong that "forward in time" bends into a circle. Brandon Carter showed in 1968 that such loops exist inside spinning black holes. [1] Zhang stresses that twist alone does not create a closed curve: "It only blocks my argument," and as far as we know it is harmless. [1]

The second is topology, the shape of the universe itself. The staircase may be perfectly built yet lead around a building so that the top step returns to the bottom, as in an Escher drawing. [1] Most time machines designed on paper, including those built from wormholes, rely on this. Zhang considers topology the loophole to watch, and the one that looks least likely to arise without deliberate engineering. [1]

## Travel to the future is established

Trips forward in time are already well established. Einstein showed that moving very fast, or sitting in strong gravity, slows a clock relative to everyone else's. [1] According to the European Space Agency, astronauts returning from six months aboard the International Space Station are about five thousandths of a second younger than they would otherwise have been. [1]

Zhang notes the limits of the work: "This is not a claim that time travel is impossible." [1]

## Sources

1. [euronews.com](https://www.euronews.com/2026/11/09/where-would-you-go-in-a-time-machine-physicist-says-time-travel-only-goes-forward)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-b55397dbab687d49011ab2e3_university_of_jinan/