Theoretical analysis has reignited debate among physicists over whether time travel into the past could one day move beyond science fiction. Researchers have shown that a particular type of wormhole — a ring-shaped tunnel through spacetime — could, under the right gravitational conditions, create closed loops in time that would allow a traveller to return to an earlier moment.
The study, by Valeri P Frolov and Andrei Zelnikov of the University of Alberta working with Pavel Krtouš of Charles University in Prague, was accepted for publication in Physical Review D in 2023. It demonstrates that gravity acting near the two mouths of a traversable ring wormhole can throw them out of temporal sync. After sufficient time has passed, a path through the wormhole and back through ordinary space can form a closed timelike curve — the precise mathematical structure required for travel into the past.
Theoretically this could be used as a time machine – although the authors stress that no one is on the verge of building one. The finding lives firmly inside the equations of general relativity and shows that at least one realistic-looking wormhole geometry can admit time loops.
The result builds on earlier breakthroughs that first brought the idea out of pure speculation. In 1988, Kip Thorne and colleagues produced solutions describing traversable wormholes that could exist in more ordinary models of the universe, rather than the highly artificial rotating cosmos imagined by Kurt Gödel in 1949. Those wormholes opened the theoretical door to time travel.
Frolov and Andrei Zelnikov’s analysis strengthens the case that such pathways need not remain purely mathematical curiosities.
Classic paradoxes still loom large. The grandfather paradox — in which a traveller prevents their own birth — has long been used to argue that backwards time travel must be impossible. Physicists including Igor Novikov have countered with the self-consistency principle: any actions taken in the past must already form part of the history that produced the traveller.
Calculations by Mr Thorne’s group in the early 1990s, using billiard-ball models, suggested that self-consistent outcomes always appear possible.
Sceptics remain. The late Stephen Hawking argued that deeper laws of physics would prevent macroscopic closed timelike curves from ever forming — a “chronology protection” that keeps history safe. His famous 2009 party for time travellers, to which invitations were sent only after the event, drew no guests.
Yet the recent ring-wormhole paper adds weight to the view that the equations of general relativity do not forbid time travel. Maintaining such a structure would still demand exotic matter with negative energy density, something never observed in usable quantities. Practical realisation remains remote.
Nevertheless, the accumulation of theoretical work — from Mr Thorne’s traversable wormholes to this summer’s ring-wormhole analysis — has shifted the conversation. What was once dismissed as pure fantasy now sits within mainstream theoretical physics. Scientists emphasise that no experiment has produced a wormhole or sent anything into the past. The significance lies in the changing status of the idea itself: time travel is no longer ruled out by the mathematics of spacetime.
