Nov 3, 2026 10:59 PM
https://www.sciencealert.com/just-3-line...icist-says
INTRO: Time travel is a dream shared by pretty much all of us. But the dearth of visitors from the future – and the dismal turnout at the famed time traveler party – is alarming for hopefuls. Still, hypothetical time travel ideas abound, including traversable wormholes propped open by undiscovered exotic states of matter, and a rocket ship skirting billions of light-years around a spinning Universe to end up back in its past.
But a new study presents a surprisingly simple numerical basis for ruling out closed time loops in a wide class of possible universes, based on a single mathematical proof.
In yet-to-be peer-reviewed research, posted to the preprint repository arXiv, physicist Hongsheng Zhang from the University of Jinan in China repurposed a long-standing equation to offer a new numerical prohibition against time travel – further dashing our hopes of a history-bending romp as promised by Bill & Ted's Excellent Adventure.
The research used the "null eikonal equation," an old tool for exploring how light propagates, to surprising effect. "The first is how little the theorem needs. The proof runs to three lines and uses exactly one fact about directions: a light-like direction can never be perpendicular to a traveller's direction in time," Zhang told ScienceAlert.
"From that alone it follows that a certain function must grow along every possible journey, so no journey can return to its starting event." (MORE - details)
INTRO: Time travel is a dream shared by pretty much all of us. But the dearth of visitors from the future – and the dismal turnout at the famed time traveler party – is alarming for hopefuls. Still, hypothetical time travel ideas abound, including traversable wormholes propped open by undiscovered exotic states of matter, and a rocket ship skirting billions of light-years around a spinning Universe to end up back in its past.
But a new study presents a surprisingly simple numerical basis for ruling out closed time loops in a wide class of possible universes, based on a single mathematical proof.
In yet-to-be peer-reviewed research, posted to the preprint repository arXiv, physicist Hongsheng Zhang from the University of Jinan in China repurposed a long-standing equation to offer a new numerical prohibition against time travel – further dashing our hopes of a history-bending romp as promised by Bill & Ted's Excellent Adventure.
The research used the "null eikonal equation," an old tool for exploring how light propagates, to surprising effect. "The first is how little the theorem needs. The proof runs to three lines and uses exactly one fact about directions: a light-like direction can never be perpendicular to a traveller's direction in time," Zhang told ScienceAlert.
"From that alone it follows that a certain function must grow along every possible journey, so no journey can return to its starting event." (MORE - details)