# What is time dilation? Is it possible

## Travel faster than light

It is impossible to imagine science fiction without it - the “warp drive”. Because without him, journeys from star to star at faster than light speeds would be unthinkable. The construction of such a drive could actually be possible, claims Erik Lentz from the University of Göttingen. In the journal "Classical and Quantum Gravity" the astrophysicist presents theoretical considerations on a new form of distortion of space-time, with which journeys faster than light could be realized.

The closest star, Proxima Centauri, is four light years away from us - so it takes light four years to get to earth. And nothing can move faster than light, as Albert Einstein's special theory of relativity says. Nevertheless, according to this theory, it is possible to reach Proxima Centauri considerably faster than in four years. Because if a spaceship moves at almost the speed of light, the distances in the direction of movement shrink due to the relativistic contraction of length. In this way, the flight time for astronauts could be reduced to months or even weeks - provided there is sufficient drive energy.

However, there is a catch: From the outside, the spaceship is by no means moving faster than light, so it still takes four years to fly. This relativistic time dilation leads, among other things, to the famous twin paradox. Because an astronaut who traveled from Earth to Proxima Centauri and back would only have aged a few months, but his twin who stayed on Earth would have been over eight years older. Because since the traveling twin would move much faster than his twin brother on earth, time would have passed much more slowly for him.

In 1994 the Mexican physicist Miguel Alcubierre presented a surprising solution for a drive with faster than light speed. His approach was based on a distortion of spacetime consistent with the theory of relativity, which shortens the space in front of a spaceship and expands it behind the spaceship. The spaceship would not move within this distortion - so there would be no time dilation. At the same time, however, the route would be shortened at will due to the distortion. But such a drive could only be realized with a hypothetical form of matter, which, however, does not yet exist.

Lentz is now presenting a new form of spacetime distortion - a special kind of standing waves, so-called solitons, that move constantly without changing their shape. Inside such a distortion, time would run just as quickly as outside, so there would be no time dilation. “This means that faster-than-light phenomena are in the realm of known physics,” the researcher says happily. “This work has brought the problem of traveling at faster than light speeds one step closer to technology.” However, the amounts of energy required for the drive are enormous. Because the journey of a 200-meter-long spaceship to Proxima Centauri would require about a hundred times the mass of the planet Jupiter. Lentz is nevertheless optimistic that these energy requirements can be reduced significantly through further research.