H.G. Wells’ The Time Machine ignited the world’s imagination, but Einstein was the first of the super-physicists to show how explorers might actually rocket across the ages. He focused on racing into the future, but now astronomers seek time portals that work in both directions

The Twins Paradox, born of Einstein’s Special Theory of Relativity, was an astonishing thought experiment tied to his fantastical cosmos: the pilot of a spacecraft sees the flow of time almost halt as he approaches the speed of light, even as centuries pass for his twin on Earth.

Hyper-velocity spaceflights - a distant dream when Einstein began reimagining the universe - are on the horizon, holding out the prospect of trekking forward in time: A fleet of starships now being created to explore Alpha Centauri will reach one-fifth the speed of light.

The laser-powered nanocraft bound for the triple-star system will serve as precursors to human capsules that likewise incorporate photonic propulsion, say founders of the Breakthrough Starshot project. The ultimate goal is ships that narrow the gap with the speed of light.

The flow of time freezes at light speed, and reverses beyond it, Einstein posited. Yet matter, like spaceships and astronauts, can never quite reach that speed. So physicists are exploring other channels to move backwards through time - wormholes that might crisscross the cosmos.

Stephen Hawking, who spent a lifetime modeling alternate universes out of Einstein’s relativity equations, predicted ancient wormholes could be discovered, or new ones created, to catapult aeronauts across time’s borders. Einstein’s cosmic maps and insights will guide this quest.

Einstein was the first to hypothesize a labyrinth of wormholes, spread out across the geometry of spacetime, connecting distant sectors of the universe. Hawking and other titans in physics realized that these ethereal tunnels might also link distant epochs in time.

“Wormholes, like any other possible form of travel faster than light, would allow one to travel into the past,” Hawking says in “A Brief History of Time”. Although extremely unstable, wormholes might be reengineered by “an advanced civilization” into safe time machines.

As a spacefaring civilisation explored and mapped a kaleidoscope of star systems, wormholes could be charted in a cosmic atlas of time. Physicist Kip Thorne, Hawking’s longtime friend, warns some wormholes feature intense gravity fields that would crush any would-be traveler.

Yet Einstein’s equations provide guidelines to craft wormholes that are perfectly traversable, says Nobel prizewinner Thorne, a world leader in building virtual wormholes. These “could be used as a galactic or intergalactic transportation system … [or] for backward time travel.”