Posted on Mar 16, 2019
“Space has been expanding since the Big Bang 13.7 billion years ago,” said Harold “Sunny” White, head of NASA’s Eagleworks Laboratories: Advanced Propulsion. “And we know that when you look at some of the cosmology models, there were early periods of the universe where there was explosive inflation, where two points would’ve went receding away from each other at very rapid speeds. Nature can do it. So the question is, can we do it?”
There have been hints the past few years that NASA may be on the path to discovering warp bubbles that could make the local universe accessible for human exploration. NASA scientists may be close announcing they may have broken the speed of light. According to state-of-the art theory, a warp drive could cut the travel time between stars from tens of thousands of years to weeks or months. They say they have found a way to configure the hypothetical negative energy matter so that the warping could be accomplished with a mass equivalent to the Voyager spacecraft.
“What this does is it moves the idea from the category of completely impossible to maybe plausible,” said White in a talk at NASA’s Ames Research Center in 2014. “It doesn’t say anything about feasible. And so, unfortunately, that point usually gets missed a lot.”
According to recent reports, NASA scientists are currently researching the feasibility of warp drive (and EMdrive and a number of other modes of faster than light travel); however, most scientists think that such forms of space travel simply aren’t viable, thanks to the fundamental physics of our universe.
“Routine travel among the stars is impossible without new discoveries regarding the fabric of space and time, or capability to manipulate it for our needs,” says Neil deGrasse Tyson, the “Cosmos famous” astrophysicist at the American Museum of Natural History, said “By my read, the idea of a functioning warp drive remains far-fetched, but the real take-away is that people are thinking about it — reminding us all that the urge to explore continues to run deep in our species.”
The catalyst for the warp-drive excitement is the Electromagnetic Drive or EM Drive, a thruster that was engineered to steer rockets which eliminates the use of a propellant originally intended for moon missions, Mars missions and low-Earth orbit (LEO) operations.The experiment that led to the possibility of faster than light interstellar travel took place in the vacuum of space.
According to posts on NASASpaceFlight.com, a website devoted to the engineering side of space news, when lasers were fired through the EmDrive’s resonance chamber, some of the beams appeared to travel faster than the speed of light. If that’s true, it would mean that the EmDrive is producing a warp field or bubble.
But “How?” If the laser beams are moving faster than the speed of light, then it would indicate that they are creating some sort of warp field, or bubble in the space-time foam, which in turn produces the thrust that could, in theory, power a spaceship bound for the center of the Milky Way or one of its dwarf galaxy satellites.
The bubble would contract space-time in front of the ship, flow over the ship, then expand back to normality behind it. It’s inaccurate to describe the spaceship as moving faster than the speed of light, but rather spacetime is moving around the ship faster than the speed of light.
Harold White and other NASA engineers are trying to determine whether faster-than-light travel — warp drive — might someday be possible. The team has attempted to slightly warp the trajectory of a photon, changing the distance it travels in a certain area, and then observing the change with a device called an interferometer.
In 1994, a Mexican physicist, Miguel Alcubierre, now director of the Nuclear Sciences Institute at the National Autonomous University of Mexico, theorized that faster-than-light speeds were possible in a way that did not contradict Einstein by harnessing the expansion and contraction of space itself by constructing a special solution to the general relativity equations that described a “warp bubble.” The bubble would shrink space in front and expand it in back, and a starship within the bubble would appear to move at a speed faster-than-light even though it remains stationary.
For example, writes Kenneth Chang in the New York Times, “Alpha Centauri, the nearest neighboring star system, is 4.4 light-years away. Put a starship in a warp bubble. Shrink the distance in front of the starship to a couple of inches, expand the space behind it to 4.4 light-years and then pop the starship out of the bubble. Voilà! The starship arrives at Alpha Centauri, in less than the 4.4 years it would take a beam of light to travel that distance.”
“It got me to thinking,” Dr. Alcubierre said, “if there was any way in which you could come up with a geometry of space-time that was similar to this idea of warp drive in science fiction that allowed you to travel faster than light.”
Alcubierre proposed a new kind of technology that would allow us to travel 10 times faster than the speed of light without actually breaking the speed of light. That seems a bit contradictory, after all, we’ve been told by Dr. Einstein and others that light is the galactic speed limit – nothing in the cosmos can travel faster than it (much less 10 times faster) and herein lies the key to the Alcubierre drive: When you use it, you aren’t actually moving through space.
This technology would not actually propel the ship to speeds exceeding light; instead, it uses the deformation of spacetime permitted by General Relativity to warp the universe around the vessel. Essentially, when the drive is activated, the spacetime behind expands, while in the front it contracts. In this respect, the path taken becomes a time-like free-fall –a propulsion system that manipulated space-time by generating a so-called “warp bubble” that would expand space on one side of a spacecraft and contract it on another. In this way, the spaceship will be pushed away from the Earth and pulled towards a distant star by space-time itself,” Alcubierre wrote.
Alcubierre, the New York Times, has likened it to stepping onto a moving walkway at an airport: An Alcubierre Warp Drive stretches spacetime in a wave causing the fabric of space ahead of a spacecraft to contract and the space behind it to expand. The ship can ride the wave to accelerate to high speeds and time travel. The Alcubierre drive, also known as the Alcubierre metric or Warp Drive, is a mathematical model of a spacetime exhibiting features reminiscent of the fictional “warp drive” from Star Trek, which can travel “faster than light.”
Alcubierre’s theory, however, depended on large amounts of a little understood or observed type of “exotic matter” that violates typical physical laws.
In general relativity, one often first specifies a plausible distribution of matter and energy, and then finds te geometry of the spacetime associated with it; but it is also possible to run the Einstein field equations in the other direction, first specifying a metric and then finding the energy-momentum tensor associated with it, and this is what Alcubierre did in building his metric. This practice means that the solution can violate various energy conditions and require exotic matter. The need for exotic matter leads to questions about whether it is actually possible to find a way to distribute the matter in an initial spacetime which lacks a “warp bubble” in such a way that the bubble will be created at a later time.
Yet another problem according to Serguei Krasnikov is that it would be impossible to generate the bubble without being able to force the exotic matter to move at locally FTL speeds, which would require the existence of tachyons. Some methods have been suggested which would avoid the problem of tachyonic motion, but would probably generate a naked singularity at the front of the bubble.
White believes that advances he and others have made render warp speed less implausible. Among other things, he has redesigned the theoretical warp-traveling spacecraft — and in particular a ring around it that is key to its propulsion system — in a way that he believes will greatly reduce the energy requirements. But ”We’re not bolting this to a spacecraft,” he said of the technology.
Richard Obousy, a physicist who is president of Icarus Interstellar, a nonprofit group composed of volunteers collaborating on starship design, said “it is not airy-fairy, pie in the sky. We tend to overestimate what we can do on short time scales, but I think we massively underestimate what we can do on longer time scales.”
White likens his experiments to the early stages of the WW 11 Manhattan Project, which were aimed at creating a very small nuclear reaction merely as proof that it could be done.
Still, one of the most dubious is Alcubierre himself. He listed a number of concerns, starting with the vast amounts of exotic matter that would be needed. “The warp drive on this ground alone is impossible,” he said. “At speeds larger than the speed of light, the front of the warp bubble cannot be reached by any signal from within the ship,” he said. “This does not just mean we can’t turn it off; it is much worse. It means we can’t even turn it on in the first place.”
Alcubierre’s ideas have lead to a number of interesting thought experiments in quantum field theory; however, as mentioned above, most scientists think that the technology will never actually work. When you think about it, that kind of makes sense. Obviously, warping space requires a lot of mass and energy, and ensuring that the space where you are located isn’t warped is tricky business.
Indeed, the proposition was mostly just a thought experiment when it was first proposed – not something Alcubierre thought was actually viable technology.
“In short, it requires negative energy densities, which can’t be strictly disproven but are probably unrealistic; the total amount of energy is likely to be equivalent to the mass-energy of an astrophysical body; and the gravitational fields produced would likely rip any ship to shreds,” says Caltech’s Sean Carroll. “My personal estimate of the likelihood we will ever be able to build a ‘warp drive’ is much less than 1%. And the chances it will happen in the next hundred years I would put at less than 0.01%.”
Image credit: DeviantArt Star Trek Warp Bubble