Time Can Still Be Tricked express
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 Einstein 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 Kip Thorne served as scientific consultant.