Travelling faster than the speed of light without using negative energy may be feasible within the framework of Einstein’s laws of physics. The warp drive, which brings a spacecraft travelling through space to its destination by warping the fabric of space-time much faster than conventional methods, first appeared in the Star Trek series and was used to power Federation fleet vehicles, among other things. The concept, as later described by Mexican physicist Miguel Alcubierre, is that warp warp drive, powered by an antimatter-matter reactor, compresses the fabric of space-time in front of the ship and expands it behind the ship, allowing it to escape from three-dimensional space and enter hyperspace, where it can travel faster than the speed of light.
Normally, the speed of any object cannot exceed the speed of light, a principle laid down by Einstein and which has proved to be a valid principle ever since.
The imaginary warp drive, on the other hand, circumvents this rule by rearranging the distribution of energy, since in this case it is not the spaceship itself but the surrounding space-time, the universe itself, that would accelerate, while the vehicle in the bubble would continue to obey the known physical principles. The idea of the science fiction series has been well received on the screen, so much so that researchers have begun to seriously explore the possibility of developing technology that would allow interstellar travel and reduce the travel time for “trips” around our galaxy to a fraction of the time it takes to travel in real life.
As far as we know today, our Universe is probably teeming with gravitational waves, since every colliding pair of black holes or neutron stars, every collapsing supernova and, in particular, the Big Bang itself, must have created strong ripples in space-time. In 2013, NASA’s Jet Propulsion Laboratory physicist Harold G. White began a $50,000 project to explore the mathematics of warp drive, which White says was the first step towards realising a concept that was not at all in the realm of fantasy, but rooted in reality. “Space has been expanding since the big bang, which was 13.7 billion years ago,” the physicist told the New York Times, “If you look at cosmological models, you see that there were early periods when the universe was expanding explosively, when two points were moving away from each other at very high speeds.” In other words, it also exceeded the speed of light.
“Nature can do it. The question is, can we do it?”
NASA has also unveiled an animation illustrating the spacecraft concept, created by Dutchman Mark Rademaker. The research, like many others since, was based on the work of the aforementioned Miguel Alcubierre, who published his paper on warp drive in 1994, outlining the warp bubble hypothesis. His hypothesis was that, although there would be extraordinary forces at the edge of flat space-time due to warp, these forces would not be felt inside the spacecraft, the passengers would not be subjected to acceleration g-forces, but would be in a continuous free-fall. There is, however, a big problem with Alcubierre’s theory, namely that it is not feasible. This is what the physicist himself thought, that the hypothesis was only a thought experiment, not a description of a future technology.
The problem is that creating a curvature of space-time would use so much energy that it would exceed the mass of the universe many times over. It would take the equivalent of minus ten to the sixty-sevenths, or ten undecillion grams, of energy to transport a small spacecraft from one end of the Milky Way to the other, as Dr David Lewis Anderson explains in detail (the researcher is exploring radical ideas such as time travel alongside warp drive). The point of negative energy is that, due to the relationship described by the equation e=mc², if energy is negative, so is mass, and, while positive masses attract, negative ones repel, in which case gravity would have a repulsive effect. This is not impossible according to quantum theory, but as far as we know, exotic matter or negative energy is a requirement for warp drive that makes it impossible to build.
In the next few decades, we are likely to colonise the Moon, leave our footprint on Mars and travel further in our solar system than we ever dreamed possible. According to a new paper published in Classical and Quantum Gravity, in which researchers from the Applied Physics Advanced Propulsion Laboratory (APL) describe the results of their research, space propulsion can work without negative energy, meaning it doesn’t have to break the laws of physics. Astrophysicist Alexei Bobrick, the author of the paper, explains that instead of negative energy, the well-known force of gravity itself could be used to warp space to such a large extent, but all it would take is is to somehow squeeze a huge mass, roughly the mass of a planet, into a much smaller shape, say ten metres in diameter.
Although it is beyond the limits of the available technical possibilities, it does not violate the laws of Einsteinian physics, so at some point in the very distant future, the engine could be transferred from the world of science fiction to reality. “The main conclusion of our study is that warp drives are simpler and much less mystical objects than the broader literary descriptions suggest when they cite Alcubierre’s work[… ] in this paper, we present the first general model of a subluminal, positive-energy, spherically symmetric warp drive, and derive superluminal drive solutions that satisfy quantum inequalities,” they write in the introduction to the paper, meaning that they explore the possibilities of several methods at once. The researchers say the shape of the resulting curvature bubble also matters – the flatter the bubble in the direction it travels, the less energy it requires to propel it.
The new concept, which Alcubierre himself has given his blessing to, could bring humanity one step closer to a mathematical description and understanding of how warp drive works, but unfortunately there is still a lot of work to be done before we can actually use it to travel interstellar distances.