Warp drives have been non-existent for a long time, despite their ubiquitous presence in science fiction. Author John Campbell first introduced the idea in a science fiction novel called “Islands of Space.” Today, the term is very common, thanks largely to Star Trek. It is almost a general term for superliminal travel through hyperspace. Whether or not warp drives will ever exist is a physics problem that researchers are still trying to solve, but for now it is theoretical in nature.
Recently, two researchers studied what would happen if a warp-drive ship entered a black hole. The result is an interesting thought experiment. It may not lead to spaceship-sized warp drives, but it could one day allow scientists to develop smaller versions.
NASA's Eagleworks attempted to test Alcubierre's warp drive concept. Image credit: 2012
Remo Garattini and Kirill Zatrimaylov have theorized that such a drive could survive in what is known as a Schwarzschild black hole, provided the ship crosses the event horizon at a speed less than that of light. In theory, the black hole's gravitational field would reduce the amount of negative energy required to keep the drive going. If that were the case, the ship could fly through and somehow use it to get somewhere else without being crushed. Moreover, the mathematics behind this idea points the way to the possible development of mini-warp drives in the laboratory.
What is a warp drive?
Could scientists build a micro or mini warp drive in the lab? Good questions. To understand the team's work, let's look at the main players in this research: warp drives and black holes.
The idea is inspired by the fact that nothing can travel faster than the speed of light. Given the distances in space, a trip to the nearest star would take years (if we could travel at the speed of light). Traveling across a galaxy or to more distant galaxies would take years and many lifetimes. So if you want to be a space-faring species, you need to travel faster than light (FTL).
How would you do that? That's where warp drives come in. In theory, they allow you to put your spaceship in a bubble that can glide through space at faster-than-light speeds. This is how the spaceships in Star Trek (and other science fiction stories) travel great distances so quickly. The Star Trek ships use a power source in a “warp core” to power warp field generators. They create the warp bubble in subspace. The ship uses this to get to where the crew needs to be.
Do physicists like warp drive?
Such a warp drive is a tempting idea with many caveats. For example, generating a warp field requires an incredible amount of energy. Some physicists believe that it would require more energy than we can generate. To generate this energy, huge amounts of exotic matter would be needed – something like “unobtanium”. So that is a problem.
Others say that developing such a drive contradicts our current understanding of spacetime physics. But that doesn't stop anyone from speculating about ways it could become possible. Mexican physicist Miguel Alcubierre, for example, had an idea for such a drive in 1994. He suggested that it could create a bubble that shifts space around an object. He has continued his research into a ship that could travel to a destination faster than light. However, he and others continue to point out several problems with developing and maintaining a warp drive. These include the idea that such a drive effectively isolates itself from the rest of the universe. Among other things, this means that the ship cannot control the engine that powers it, so there are still some bugs to work out.
This artist's illustration shows a spacecraft using an Alcubierre warp drive to warp space and “travel” faster than light. Image credit: NASA
About Black Holes
We know black holes best in terms of stellar mass and supermassive black holes. These also have accretion disks that push material into the black hole. The central supermassive black hole in our own Milky Way, called Sagittarius A*, for example, regularly devours material. Then it lets out a burst of radiation. Other, more active galaxies emit jets of material that are released as the central supermassive black hole continually gives way.
Simulation of a black hole. (Source: NASA/ESA/Gaia/DPAC)
A black hole is a concentration of mass with such strong gravity that nothing, not even light, can escape. In their study of black holes and warp drives, the authors used Schwarzschild black holes. These so-called simple “static” black holes curve space-time, have no electrical charge, and do not rotate. Essentially, they are good approximations for mathematically studying the properties of slowly rotating objects in space.
When a ship with warp drive enters a black hole
The Schwarzschild black hole is the “perfect” black hole for this theoretical study of a warp drive crossing the event horizon. To understand the scenario, Garattini and Zatrimalov decided to mathematically combine the equations describing the black hole and those describing the warp drive. Among other things, they found that it is possible to “embed” the warp drive in the outer region of the black hole. The warp bubble itself is much smaller than the black hole and must move toward it. The gravity of the black hole affects the energy conditions required to create and maintain the warp drive. This means that, in theory, one can reduce the amount of negative energy required to maintain the warp bubble. In addition, the researchers suspect that if the warp bubble moves slower than the speed of light, it will effectively obliterate the black hole's horizon.
The research team also described the idea that such an event could cause the conversion of virtual particles into real ones in an electric field. If this were the case, it could lead to the development of mini-warp drives in the laboratory.
Change the black hole a little
Interestingly, the team also suggests that the entropy of the black hole could increase if the warp bubble is moving slowly and is much smaller than the black hole's horizon. However, as they note in their closing arguments, “there are potentially problematic issues in other physical situations: namely, if the warp drive is completely absorbed by the black hole, this can reduce its mass and thus its entropy.”
If a larger warp bubble were to pass through a black hole, it would create a “shielding effect” and effectively eliminate the horizon, making it impossible to define the black hole's entropy in Hawking's sense. If warp drives are possible in nature, these problems show that we still do not understand them from a thermodynamic point of view.”
Warp drive technology remains to be seen
While this research could theoretically prove valuable and lead to the creation of mini black holes in the lab, many questions remain. In the future, if we understand the quantum mechanics behind these two objects, warp technology may be a no-brainer. If that's the case, we could be in for some strange times with ships traveling through black holes. For example, signals from inside a black hole could be transmitted by a warp bubble emerging from the singularity. This would allow us to send pictures or recordings of what it looks like inside the event horizon – something no one knows today. There's also the possibility that these fearsome black holes could make warp drive easier, since they don't require as much exotic “negative energy” feedstock.
More information
Black holes, warp drives and energy conditions
The warp drive: hyperfast travel within the framework of general relativity
Schwarzschild Black Hole Simulations
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