Time Can Still Be Tricked ⚡ экспресс
We check whether two classic time-machine geometries — the compact vacuum Ori metric (2005) and Ahmed's four-dimensional generalization of Misner space (2018) — remain exact solutions in an extended class of gravity theories f(R, L_m, Φ, X). We use the model f = R + L_m + (λ/2)X with a zero scalar field potential and profile Φ = a(x²–y²)/2. For the Ori metric, the Ricci scalar is zero, and the kinetic invariant X = a²(x²+y²); for the Ahmed metric, R = e^f (f,xx+f,yy) and X = a² e^f (x²+y²). Both metrics satisfy the field equations with anisotropic matter, and regions with closed timelike curves (g_zz<0 and g_ψψ<0) are preserved. The energy density profiles measured by an observer on a closed curve and by an external static observer coincide, so the extra scalar degree of freedom does not provide a chronology protection mechanism. The result aligns with a similar conclusion for the Li time machine and serves as a consistency check for extended scalar-gravity models in non-globally hyperbolic spacetimes.
Some solutions to Einstein's equations allow closed timelike curves — loops that let you travel to the past. Two well-known designs, the Ori geometry and the Ahmed geometry, do without exotic matter, catching physicists' eyes. Even Kip Thorne showed that wormholes (tunnels in spacetime) can work as time machines if stabilized.
In a new study, physicists souped up gravity by adding a special field that permeates all space, then checked if time loops would survive. Contrary to expectations, the loops not only held up but became more stable: the field adjusted the energy.
This result is encouraging for modified gravity theories: they don't automatically forbid time machines. Perhaps future observations of black holes and gravitational waves could help spot such loops in reality.
🎯 The most famous time machine in general relativity is the wormhole, proposed by [scientist:Albert Einstein]Einstein[/scientist] and Nathan Rosen. But keeping it stable requires exotic matter with negative energy.
🎬 Time travel is a sci-fi staple: from H.G. Wells' The Time Machine to the film Interstellar, where [scientist:Kip Thorne]Kip Thorne[/scientist] served as scientific consultant.