New research "boldly goes" where physicists have never gone before, suggesting what would happen to the space around a failing warp drive.
Science fiction fans are more than familiar with the concept of a "warp drive," a device that allows spacecraft to travel at velocities faster than light, aka so-called "superluminal" speeds. These instruments are typically written as being able to manipulate the very fabric of space and time, or spacetime. Yet, even hard-core sci-fi aficionados may be surprised to learn there are a few theoretical musings about warp drives in true science as well. The most famous example is Mexican physicist Miguel Alcubierre's "Alcubierre drive."
In addition, a team from the Queen Mary University of London, Cardiff University, the University of Potsdam and the Max Planck Institute (MPI) for Gravitational Physics also discovered that if spaceships out there were already using superluminal warp drives, we could detect them via tiny ripples in spacetime called "gravitational waves" created if and when these drives break down.
"Even though warp drives are purely theoretical, they have a well-defined description in Einstein's theory of general relativity, and so numerical simulations allow us to explore the impact they might have on spacetime in the form of gravitational waves," team leader Katy Clough from Queen Mary University of London said in a statement.
Related: 'Warp drives' may actually be possible someday, new study suggests
Science fiction vs. science fact
Warp drives in both science fiction and true science are usually rooted in Albert Einstein's theory of gravity, known as general relativity. Postulated in 1915, general relativity suggests that objects with mass cause the four-dimensional fabric of spacetime to be warped. The effects of gravity that we experience arise from this warping.
The more mass an object has, the more extreme the curvature of space it generates and, thus, the stronger its gravitational effect. Light and other objects with mass are forced to journey around the complex warping of space.
General relativity also suggests that when objects accelerate, they cause spacetime to "ring" with gravitational waves. However, objects on a planetary scale, like an accelerating car, have too little mass to create significant gravitational waves. However, massive objects like black holes and neutron stars that swirl around each other in binaries and eventually collide do create gravitational waves that can be detected here on Earth.
Clough and colleagues suggest that warp drives could also emit gravitational waves, especially if they fail.
Furthermore, Einstein based general relativity on his 1905 theory of special relativity; the foundation of special relativity is that nothing with mass can move faster than the speed of light.
That means sci-fi writers have to introduce circumstances that allow this rule to be broken, or at least slightly twisted, in order to consider faster-than-light travel. In DC Comics, for instance, there exists a ubiquitous field outside spacetime called the "speed force" that gives Wally West, the Flash, the energy needed to outrace light (and Superman, if you ask me).
In Star Trek, exotic matter with negative mass allows the USS Enterprise to travel at faster-than-light or "warp speeds" by generating a warp bubble around the ship in which spacetime is warped, compressed ahead of the ship, and stretched out behind it. That means the USS Enterprise bends and warps spacetime itself, thus not breaking Einstein's special relativity rules, unlike the Flash and his speed force.
This team looked at what would happen if a warp bubble like the one used in Star Trek either collapsed or if the containment of this hypothetical concept failed. To do this, they started with creating numerical simulations of spacetime.
They found that such an event would generate a burst of gravitational waves that is more high frequency than the "chirp" of spacetime ripples created when binary black holes or neutron stars collide and merge.
Just as some light is too high frequency to be seen by our eyes, this high-frequency burst of gravitational waves would be beyond the detection capability of interferometers like the Laser Interferometer Gravitational-Wave Observatory (LIGO).
However, future gravitational wave detectors could be capable of detecting them.
"In our study, the initial shape of the spacetime is the warp bubble described by Alcubierre," team member Sebastian Khan of Cardiff University said. "While we were able to demonstrate that an observable signal could, in principle, be found by future detectors, given the speculative nature of the work, this isn't sufficient to drive future instrument development."
The team also found that a collapsing warp drive would emit alternating waves of "negative energy matter," then positive energy waves. Should these waves interact with ordinary non-exotic matter, that would give scientists another way of hunting for failed warp drives.
The team now intends to investigate how the gravitational wave signal would change when considering other models of warp drives and the consequences of a collapse occurring while traveling at superluminal speeds.
Of course, all this is speculation, albeit well-founded and mathematically robust, as there is no real evidence warp drives could exist. But that doesn't mean these findings are without applications.
"For me, the most important aspect of the study is the novelty of accurately modeling the dynamics of negative energy spacetimes and the possibility of extending the techniques to physical situations that can help us better understand the evolution and origin of our universe," team member Tim Dietrich from the Max Planck Institute (MPI) for Gravitational Physics said in the statement.
The team's research was published in the Open Journal of Astrophysics.
