There is probably no other theoretical technology more famous both for its appearances in science fiction and for attracting the attention of serious scientists than the concept of the warp drive — an advanced propulsion technology that, in theory, could allow a spacecraft to traverse unfathomable distances at speeds faster than light.
The idea has roots in early science fiction dating back almost a century, although no appearances of warp drives in popular culture made them more famous than Star Trek, which began in the 1960s.
Although this hypothetical technology was long considered to be exclusively a fictional idea, a growing number of physicists have begun to wonder if warp drives might really be possible, and if not in a practical sense, at least on paper.
What do we know?
The quest for real-life warp drives
Einstein taught us that objects with mass can't accelerate through space beyond the speed of light, according to his theory of special relativity. However, a potential workaround for this was famously devised in 1994 by physicist Miguel Alcubierre, who argued that rather than using a propulsion system to accelerate the spacecraft itself, spacetime could be distorted around it.
As bizarre as it sounds, this hypothetical "Alcubierre drive" could work, at least in principle. At the heart of the idea is the production of a region commonly referred to as a "warp bubble," in which a spacecraft could be safely positioned and carried across great interstellar distances as spacetime is contracted ahead of it and expanded behind the bubble.
The result, according to Alcubierre's theory, could mean that at some point in the future, spacecraft could effectively traverse great stretches of the cosmos in record time, all without locally exceeding Einstein's cosmic speed limit.
What remains unknown?
Warping space around a spacecraft
So how would this work? According to Alcubierre, we know that while matter cannot travel through spacetime faster than light, spacetime itself isn't necessarily beholden to such restrictions. Because of this, early in the universe, space may have expanded so quickly that some regions were separated faster than light could have traveled between them.
By exploiting this feature of general relativity, warp drives could indeed work, at least in theory. The major issue is that while the idea looks good on paper, that doesn't necessarily mean it could be applied toward a practical warp drive technology any time soon. Still, given its feasibility, some scientists have even proposed detection methods we might be able to use for spotting warp drives developed by any advanced civilizations that could be awaiting discovery out there.
In Alcubierre's original concept, exotic matter would be a likely source of the negative energy density needed to facilitate the advanced spacetime geometries required for warp bubble creation. Here again, negative energy densities are conceptually valid, but the question of whether humans could ever produce and manipulate them in the ways required to bring Alcubierre's warp drive into reality is another matter entirely.
In recent years, a few physicists have explored different approaches to the question of warp drive feasibility, including what are known as subluminal warp bubbles—a variety of space-time distortions that would not allow faster-than-light travel per se, but which could still provide researchers with a deeper understanding of how compatible the warp drive concept is with known physics.
One of these researchers is Alexey Bobrick, an astrophysicist and theoretical physicist with Applied Physics, a think tank that focuses on the development and commercialization of advanced physics concepts, which includes research into warp drives. In 2021, Bobrick, along with Applied Physics CEO Gianni Martire, published a paper that expanded on Alcubierre's original work, fundamentally concluding that "subluminal, spherically symmetric warp drive spacetimes, at least in principle, can be constructed based on the physical principles known to humanity today."
In terms of who might build one of these warp drives, and when it might occur, Bobrick recently told Space in an email that "Practically, we are talking about either humanity in a relatively distant future, or other advanced civilizations, assuming they exist."
"Making a warp drive like the one we proposed would require dramatically manipulating objects of planetary mass," Bobrick added. As an example, the physicist explained that achieving this with an object the size of Jupiter would require roughly four quadrillion times as much energy as humanity produces in an entire year — equivalent to several hundred years of the sun's total energy output.
However, Bobrick says that if such effects were constructed at much smaller scales, the amount of energy required could be reduced as well, thereby making the process more feasible.
Even warp drives require propulsion
Among the most intriguing conclusions in Bobrick and Martire's 2021 paper was their observation that a warp drive is essentially a shell of material moving inertially, meaning that even a warp drive still requires propulsion.
"All the physical warp drives we know today require propulsion, which is a technological challenge," Bobrick explained. "The physics of propulsion is well understood, and known warp drives will have to satisfy a form of the rocket equation."
Given this reality, the next logical question would be what kind of propulsion source would be required to accelerate such a structure? Fortunately, Bobrick argues that if we presume that a warp drive could be built, adding an engine to it shouldn't be too much more difficult.
"For example, if manipulating matter is possible, one can just as well place a compact object (e.g. a small black hole) in it and use the power of accretion, which is about as good as one can get to converting matter into propellant," Bobrick said.
Physical obstacles to a physics breakthrough
Another aspect of Bobrick and his colleagues' work involves the identification of some of the greatest remaining physical obstacles to superluminal warp travel.
These include causality issues — which, as Bobrick explains, include the fact that "there will always be an observer for whom a superluminal warp appears to travel back in time, or infinitely quickly." Bobrick also points to the issue of stability, which, he says, "is more technological in nature."
Finally, problems associated "with accelerating/decelerating without releasing too much energy" should also be considered.
"Indeed, even the Alcubierre metric, if turned into a very thin sheet (the 'passengers' would need to be very flat too), can require much less negative energy," Bobrick told Space. "However, since we don't know whether negative energy exists or can be manipulated, such metrics are purely hypothetical and cannot be built in principle," Bobrick added.
The mystery remains
The physics of tomorrow, and the aliens who might already have it
So where does that leave us as far as the feasibility of warp drives?
For now, warp drives remain exclusive to the realm of theoretical physics. Still, researchers like Bobrick, Martire, and others continue exploring the concept and working to better understand both the formidable challenges involved and what the laws of physics may ultimately allow.
"So, it is still very challenging to produce, but at least it is possible," Bobrick concluded, adding that scientists should continue searching for new insights into this innovative area of research, while also remaining open to the possibility that someone out there in the cosmos may have already cracked this cosmic conundrum.
"If there are indeed other technologically advanced civilizations out there, some forms of warp bubbles may well be out there already," Bobrick said, "and should therefore be studied seriously."
