Why don't we have a 'Star Wars' hyperdrive yet?

With the opening of "Star Wars: The Last Jedi" on Dec. 15, more than likely you're going to see at least one ship using hyperspace drive to travel faster than the speed of light. It's a staple of the "Star Wars" universe, dating back to the first movie in 1977, when Han Solo and his trusty band of renegades zipped between stars using the Millennium Falcon.

But is this hyperspace drive really a thing? Can you go faster than the speed of light? Like anything else in physics, the answer is complicated. The bottom line is maybe – but only if we can figure out how to get around some technological obstacles. ["Star Wars" Spaceships: Vehicles from a Galaxy Far, Far Away]

The speed limit

The first problem with a hyperspace drive is anything with mass – a starship, people, Wookiees – cannot go faster than the speed of light without fancy physics (which we'll get into in a moment.) That's a rule from Einstein's Special Theory of Relativity. Simply put, the problem is your Millennium Falcon would acquire an infinite mass when it approaches lightspeed. That would mean you'd need an infinite amount of energy to move it – even more than the amount of energy used to blow up Alderaan. So that's a no-go.

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But there's nothing in Einstein's equations that ban you from bending space to go faster than the speed of light. As you probably know, in our ordinary world we live in three dimensions of space and one dimension of time. (Some physicists call this space-time.) The sphere of space itself can – and has – traveled faster than the speed of light. For example, shortly after the Big Bang that formed our universe, space-time itself expanded (or inflated) faster than the speed of light.

The Alcubierre drive is a concept that takes advantage of bending space to make a ship go superfast – even faster than light. There still are a lot of problems with the concept, so it only exists as a mathematical idea. In theory, the drive would cause space-time to contract in front of the starship, and space-time would expand behind it.

In separate interviews with Space.com, physicists Eric Davis (at EarthTech International) and Gerald Cleaver (with Baylor University) independently compared the phenomenon to a surfer on a wave. Imagine that the surfboard is a starship; the surfer is the crew. The surfer is standing (relatively) still on their surfboard while the wave moves toward the shore. In the same way, a starship would stay still in space-time while space-time warps around it. [Warp Speed? The Hype of Hyperspace]

Alcubierre drive limitations

But there are a lot of problems that physicists need to figure out before we can use the Millennium Falcon to escape Kylo Ren. Cleaver has looked into some of these problems in collaboration with Richard Obousy (who was then his graduate student and now works with Icarus Interstellar) and Jeff Lee (who is also at Baylor.)

The problem begins with putting the Falcon into ignition. "The amount of energy to start the process would have to be on part with the total mass-energy of the planet Jupiter," Cleaver said in an interview. "There have been proposals for alternatives, however, and if you can get that process going that is a technological issue." (Davis said the mass requirements range from the mass of the galaxy to the mass of the sun, but the principle still holds – it's a lot of energy.)

But say you can overcome that and start your space-warping. The next problem is keeping the energy going. As the Alcubierre drive approaches the speed of light, photons from the cosmic microwave background – that's the leftover radiation from the start of our universe – will be absorbed into the starship. That's bad news for both the spaceship and the occupants on board.

"Those [photons] will get radically blueshifted in the direction of motion towards the destination star," Davis said in an interview, meaning that the ship will travel so fast that the photons will be compressed and their frequency will increase. "Then they will become super-intense radiation and kill everyone aboard the starship."

Meanwhile, the ship itself will start to stall due to a problem with space-time.

"There will be a continual energy loss … due to the energy converted into the blueshift of photons," Cleaver said. "There has to be an energy source on board the ship … to balance things, so that whatever energy is used for blueshifting has to be provided towards the front." So under that model, you'd need an extraordinary amount of energy to continue – an amount that Cleaver doesn't think is technically feasible to produce.


A new hope?

Davis and Cleaver are collaborators, and Davis recently gave a presentation that dealt with variations of the Alcubierre drive while visiting Baylor. He mentioned some recent reading of his – looking at a 2002 paper from C.B. Hart et al on the prepublishing site Arxiv, which often publishes papers during or before peer review. It's called "On the Problems of Hazardous Matter and Radiation at Faster than Light Speeds in the Warp Drive Space-Time." (Cleaver was not aware of the paper until recently and could not comment on it for this story.) [40 Surprising "Star Wars" Facts You Should Know]

Hart uses work from his own team, and summarizes several other physicists, to point out other problems with Alcubierre drives. One is the deadly potential for a ship – even the Millennium Falcon – if it smashes into an asteroid or some other object at near light-speed. Without some sort of shield, careening around space escaping the dark side of the Force would be a bad idea.

Also, the radiation surrounding the Alcubierre drive wouldn't allow the spaceship to communicate to anyone outside the bubble – so forget telling your family that you'll be back on-planet for dinner. Worse, the physics of the situation doesn't even allow you to steer space-time to control where you're going.

But there are ways to modify the equations to get around some of these issues, according to Hart and some of the other authors cited in Hart's paper.

Hart cites physicist Chris Van Den Broeck (with the National Institute for Subatomic Physics in the Netherlands), who did a modification of Alcubierre's warp drive. In an interview, Davis said the math is too complicated to explain to a non-mathematician. But essentially, Van Den Broeck multiples a mathematical function by a part of the space-time metric that creates the warp drive. Result? It lowers the amount of energy required to make Alcubierre work. (In the case Van Den Broeck used, it lowered the energy from the mass of the galaxy to the mass of the sun. Still a big barrier, but certainly an improvement!)

Hart's group then did some more mathematical work and essentially made an Alcubierre warp drive with a bubble surrounding the bubble, according to Davis. Or in other words, a sort of a shield for the occupants inside.

"The effect of the interior warp bubble is to cure the problems of the exterior warp bubble. You don't have the dangerous radiation, or the problem with the starship not being able to communicate with the outside universe," he said. "It also drastically reduces the amount of negative energy to produce the warp drive."

Davis cited several variations of how the bubble's shielding would work, but the end result is usually the same – as long as you can get the Alcubierre drive working, the shield might be able to protect it. Although, of course, more research is needed.


Tesseracting and EmDrive

If Alcubierre doesn't work, there are at least a couple of other ways you might be able to get the Millennium Falcon moving through space quickly and effectively.

The first is a wormhole , which is a theoretical connection between two points in space. (Some researchers say this could happen through a black hole, but nobody has observed this yet.) A classic example of how a wormhole works is explained in the Madeleine L'Engle book "A Wrinkle in Time" (1962), which will be retold in film in 2018.

In the book, the girl Meg learns about a concept called a "tesseract," which the book also refers to as a "wrinkle in time." Meg is asked to picture an ant marching along a sheet of paper. The sheet of paper represents time. You can shorten the ant's path simply by folding the paper – folding space-time itself.

"If we have humans doing this, it's difficult to wrap our minds around how this works. We have intuition for a 3-D world and can't imagine a 4-D," acknowledged Patrick Johnson, a physics researcher at Georgetown University and author of the 2017 book "The Physics of Star Wars."

The problem is, he added, that a wormhole bends space-time, which generates a lot of energy. In the movie "Interstellar" (2014), the ship entered a wormhole near Saturn. "If a wormhole was that close to Saturn, that would tear Saturn to shreds," Johnson said, adding that the amount of energy required is "monstrously huge."

Another option is the EmDrive , a concept tested by NASA researchers and others that could make traveling through space much faster. We won't go too deep into the physics on this drive, but it essentially bounces microwaves around in a chamber and appears (somehow) to create thrust . Many researchers say this violates the laws of physics, although EmDrive has been tested by several groups and is the subject of at least one peer-reviewed paper. NASA EmDrive researcher Harold "Sonny" White's schedule did not allow for an interview before the deadline for this story had passed.

But whether or not hyperspace is possible in real life, it certainly is a lot of fun to play with in science fiction. "Star Wars," of course, is not alone in imagining traveling faster than the speed of light . Variants of warp speed are a staple of franchises such as "Star Wars," "Battlestar Galactica," "Farscape" and, of course, "Doctor Who," with its famous TARDIS (Time and Relative Dimension in Space).

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