What superluminal velocities might be required

New possibility for space flights with faster than light speed?

The fascination of looking at the starry sky at night is often mixed with a good dose of sadness: practically everything out there beyond the planets will most likely remain inaccessible to mankind, at least for the next few centuries. The idea is tempting to leave the limitations of special relativity behind you through some as yet unknown loophole. So far, however, a travel speed beyond the speed of light seems to be possible only theoretically and under very bizarre physical conditions.

With Alcubierre to the stars

This includes, for example, the famous warp drive, on which, among other things, the spaceship Enterprise from the Star Trek universe relies. Such a drive could actually work on paper, wrote the Mexican physicist Miguel Alcubierre in 1994. His theoretical solution for locomotion at faster than light speed does not contradict at least the general and special theory of relativity. The thought experiment, also known as the Alcubierre drive, is based on a local deformation of space-time, like a wave on which a hypothetical spaceship could even reach ten times the speed of light.

The principle behind it is based on the fact that although no matter can move at the speed of light or beyond, changes in space-time are exempt from this iron rule - this results from Einstein's field equations in general relativity. A hypothetical spaceship would therefore need an apparatus on board that shortens the distance to the next star by compressing space-time in the direction of flight and expanding it again behind it. The Alcubierre drive shifts space-time around the spaceship, so to speak, so that it appears as if it would arrive at the target star faster than the light in the unchanged space-time.

Particle physics abracadabra

There are, of course, a few hurdles in the way of building an actual warp drive, first and foremost the fact that Alcubierre's equations operate with matter and states that only exist in theory. The proposed mechanism implies a negative energy density, which in turn requires exotic matter with negative mass or the manipulation of dark energy. The warp drive initially sounds largely like particle-physical abracadabra, with no chance of being realized anytime soon. However, this does not prevent theoretical physicists and space agencies such as NASA from grappling with these ideas.

You can also do it without exotic material

It is possible that a researcher from the University of Göttingen has now found a mathematical way out of the impasse with the exotic negative masses: The physicist Erik Lentz designed a new class of hyper-fast "solitons", a kind of stable waves in space that theoretically Should enable travel at any speed.

When analyzing previous work on the Alcubierre drive, Lentz noticed a number of gaps in the theoretical structure, including configurations of the space-time curvature that have not been investigated in more detail and that are organized in the "solitons" mentioned. A soliton - to put it very simply, a "warp bubble" - is a compact wave that retains its shape and shortens or expands space at a constant speed. Contrary to previous calculations, it is very possible to generate the space-time geometries in a way that also works with conventional energy sources.

Avoid the twin paradox

Given enough conventional energy, the solitons could be configured to contain a region with minimal tidal forces so that the passage of time inside the soliton corresponds to that outside: an ideal environment for a spaceship. This means that the complications of the so-called "twin paradox" would not arise, in which a twin traveling near the speed of light would age much more slowly than the other twin who stayed on earth: in fact, both twins would follow be the same age as the new equations when they are reunited.

For Lentz, the idea of ​​traveling at faster than light speed with its mathematical solutions has moved a step towards conventional basic physics - and it is thus closer to a potential realization. "This is the first example of hyper-fast solitons from known and trusted sources. This could reopen the discussion about faster-than-light mechanisms that are rooted in conventional physics," writes Lentz in the journal "Classical and Quantum Gravity".

Hundreds of Jupiter's masses of fuel

But before one can turn to the first warp drive experiments, the next big hurdle must be cleared out of the way: Even if the technology should work with conventional energy - the amount required would still be literally astronomical: "The energy, which is necessary for this propulsion at the speed of light for a spaceship with a radius of 100 meters is in the order of magnitude of a hundred times the mass of the planet Jupiter, "says Lentz. "The energy savings would have to be drastic, in the range of around 30 orders of magnitude, to be within the range of modern nuclear fission reactors." (tberg, red, March 19, 2021)