Physicists at the University of New Hampshire in the United States have developed a mathematical model of gravity that could rule out travel to the past and prevent temporal paradoxes. The study by Mustafa Ismail and David Mattingly, published in the journal Physical Review D, offers a new solution to the chronology protection conjecture that Stephen Hawking put forward in 1992, infohub.kz reports.
Einstein's general theory of relativity mathematically permits the existence of closed timelike curves — paths along which a hypothetical traveler could return to their own past. To rule out such scenarios, the scientists turned to metric-affine gravity, in which the geometry of distances and the rules governing changes of direction operate more independently. On that basis, the physicists built the MAGIC (Metric-Affine Gravity Imposing Chronology) model, which sets a built-in direction of time under which motion is possible only forward.
However, the proposed concept has a serious flaw: it introduces an instability capable of causing exponential growth of small perturbations in the fabric of space-time. The main problem with the new theory lies in the emergence of an additional scalar mode of gravitational oscillation. Against the cosmological background, it suffers from gradient instability: instead of propagating as ordinary waves, the perturbations begin to grow rapidly, and the shorter the wave, the faster it grows.
In addition, the model so far guarantees chronology protection only locally and does not rule out failures of the metric under certain conditions, so the authors regard it as a first step toward a full-fledged theory.