What is the Alcubierre “Warp” Drive?

It’s always a welcome thing to learn that ideas that are commonplace in science fiction have a basis in science fact. Cryogenic freezers, laser guns, robots, silicate implants… and let’s not forget the warp drive! Believe it or not, this concept – alternately known as FTL (Faster-Than-Light) travel, Hyperspace, Lightspeed, etc. – actually has one foot in the world of real science.

In physics, it is what is known as the Alcubierre Warp Drive. On paper, it is a highly speculative, but possibly valid, solution of the Einstein field equations, specifically how space, time and energy interact. In this particular mathematical model of spacetime, there are features that are apparently reminiscent of the fictional “warp drive” or “hyperspace” from notable science fiction franchises, hence the association.

Background:

Since Einstein first proposed the Special Theory of Relativity in 1905, scientists have been operating under the restrictions imposed by a relativistic universe. One of these restrictions is the belief that the speed of light is unbreakable and hence, that there will never be such a thing as FTL space travel or exploration.

Visualization of a warp field, according to the Alcubierre Drive. Credit: AllenMcC

Even though subsequent generations of scientists and engineers managed to break the sound barrier and defeat the pull of the Earth’s gravity, the speed of light appeared to be one barrier that was destined to hold. But then, in 1994, a Mexican physicist by the name of Miguel Alcubierre came along with proposed method for stretching the fabric of space-time in way which would, in theory, allow FTL travel to take pace.

Concept:

To put it simply, this method of space travel involves stretching the fabric of space-time in a wave which would (in theory) cause the space ahead of an object to contract while the space behind it would expand. An object inside this wave (i.e. a spaceship) would then be able to ride this region, known as a “warp bubble” of flat space.

This is what is known as the “Alcubierre Metric”. Interpreted in the context of General Relativity, the metric allows a warp bubble to appear in a previously flat region of spacetime and move away, effectively at speeds that exceed the speed of light. The interior of the bubble is the inertial reference frame for any object inhabiting it.

Since the ship is not moving within this bubble, but is being carried along as the region itself moves, conventional relativistic effects such as time dilation would not apply. Hence, the rules of space-time and the laws of relativity would not be violated in the conventional sense.

Artist’s concept of a spacecraft using an Alcubierre Warp Drive. Credit: NASA

One of the reasons for this is because this method would not rely on moving faster than light in the local sense, since a light beam within this bubble would still always move faster than the ship. It is only “faster than light” in the sense that the ship could reach its destination faster than a beam of light that was traveling outside the warp bubble.

Difficulties:

However, there is are few problems with this theory. For one, there are no known methods to create such a warp bubble in a region of space that would not already contain one. Second, assuming there was a way to create such a bubble, there is not yet any known way of leaving once inside it. As a result, the Alcubierre drive (or metric) remains in the category of theory at this time.

Mathematically, it can be represented by the following equation: ds2= – (a2 – BiBi) dt2 + 2Bi dxi dt + gijdxi dxj, where a is the lapse function that gives the interval of proper time between nearby hypersurfaces, Bi is the shift vector that relates the spatial coordinate systems on different hypersurfaces and gij is a positive definite metric on each of the hypersurfaces.

Attempts at Development:

In 1996, NASA founded a research project known as the Breakthrough Propulsion Physics Project (BPP) to study various spacecraft proposals and technologies. In 2002, the project’s funding was discontinued, which prompted the founder – Marc G. Millis – and several members to create the Tau Zero Foundation. Named after the famous novel of the same name by Poul Anderson, this organization is dedicated to researching interstellar travel.

In 2012, NASA’s Advanced Propulsion Physics Laboratory (aka. Eagleworks) announced that they had began conducting experiments to see if a “warp drive” was in fact possible. This included developing an interferometer to detect the spatial distortions produced by the expanding and contracting space-time of the Alcubierre metric.

The team lead – Dr. Harold Sonny White – described their work in a NASA paper titled Warp Field Mechanics 101. He also explained their work in NASA’s 2012 Roundup publication:

“We’ve initiated an interferometer test bed in this lab, where we’re going to go through and try and generate a microscopic instance of a little warp bubble. And although this is just a microscopic instance of the phenomena, we’re perturbing space time, one part in 10 million, a very tiny amount… The math would allow you to go to Alpha Centauri in two weeks as measured by clocks here on Earth. So somebody’s clock onboard the spacecraft has the same rate of time as somebody in mission control here in Houston might have. There are no tidal forces, no undue issues, and the proper acceleration is zero. When you turn the field on, everybody doesn’t go slamming against the bulkhead, (which) would be a very short and sad trip.”

In 2013, Dr. White and members of Eagleworks published the results of their 19.6-second warp field test under vacuum conditions. These results, which were deemed to be inconclusive, were presented at the 2013 Icarus Interstellar Starship Congress held in Dallas, Texas.

When it comes to the future of space exploration, some very tough questions seem unavoidable. And questions like “how long will it take us to get the nearest star?” seem rather troubling when we don’t make allowances for some kind of hypervelocity or faster-than-light transit method. How can we expect to become an interstellar species when all available methods with either take centuries (or longer), or will involve sending a nanocraft instead?

At present, such a thing just doesn’t seem to be entirely within the realm of possibility. And attempts to prove otherwise remain unsuccessful or inconclusive. But as history has taught us, what is considered to be impossible changes over time. Someday, who knows what we might be able to accomplish? But until then, we’ll just have to be patient and wait on future research.

We have written many articles about the Alcubierre “Warp” Drive for Universe Today. Here’s Warp Drives Probably Impossible After All, Warp Drives and Cloaking Devices not just Science Fiction Anymore, Warp Drive May Come with a Killer Downside, Astronomy Without a Telescope – Warp Drive on Paper, and Zoom, Zoom, Zoom: Gorgeous Warp Ship Design Delights The Internet.

If you’d like more info on the Alcubierre “Warp” Drive, check out an article from Wikipedia. Also, check out another article about the warp drive spaceship engine.

We’ve also recorded an entire episode of Astronomy Cast all about Light Echoes. Listen here, Episode 215: Light Echoes.

Sources:

Will We Ever Reach Another Star?

We hear about discoveries of exoplanets every day. So how long will it take us to find another planet like Earth?

There are two separate parts of your brain I would like to speak with today. First, I want to talk to the part that makes decisions on who to vote for, how much insurance you should put on your car and deals with how not paying taxes sends you to jail. We’ll call this part of your brain “Kevin”.

The rest of your brain can kick back, especially the parts that knows what kind of gas station you prefer, whether Lena Dunham is awesome or “the most awesome”, whether a certain sports team is the winningest, or believes that you can leave a casino with more money than you went in with. We will call this part “Other Kevin”, in honor of Dave Willis.

Okay Kevin, you’re up. I’m going to cut to the gut punch, Kevin. Between you and me, it is my displeasure to inform you that science fiction has ruined “Other Kevin”. Just like comic books have compromised their ability to judge the likelihood of someone acquiring heat vision, science fiction has messed up their sense of scale about interstellar travel.

But you already knew that. Not like “Other Kevin”, you’re the smart one. In the immortal words of Douglas Adams, “space is big”. But when he said that, Douglas was really understating how mind-bogglingly big space really is.

The nearest star is 4 light years away. That means that light, traveling at 300,000 kilometers per second would still need 4 YEARS to reach the nearest star. The fastest spacecraft ever launched by humans would need tens of thousands of years to make that trip.

But science fiction encourages us to think it’s possible. Kirk and Spock zip from world to world with a warp drive violating the Prime Directive right in it’s smug little Roddenberrian face. Han and Chewy can make the Kessel run in only 12 parsecs, which is confusing and requires fan theories to resolve the cognitive space-distance dissonance, and Galactica, The SDF 3, and Guild Navigators all participate in the folding of space.

And science fiction knows everything that’s about to happen, right? Like cellphones. Additionally Kevin, I know what you’re thinking and I’m not going to tear into Lucas on this. It’s too easy, and my ilk do it a little too often. Plus, I’m saving it up for Abrams. Sorry Kevin. Got a little distracted there.

The point is, science fiction is doing colossal hand waving. They’re glossing over key obstacles, like the laws of physics.

Stay with me here.This isn’t like jaywalking bylaws that “probably don’t apply to you at that very moment”, these are the physical laws of the universe that will deliver a complete junk-kicking if you try and pretend they’re not interested in crushing your little atmosphere requiring, century lifespan, conventional propulsion drive dreams.

So let’s say that we wanted to actually send a spacecraft to another star, whilst obeying the laws of physics. We’ll set the bar super low. We’re not talking about massive cruise ships filled with tourists seeking the delights of the super funzone planetoid, Itchy and Scrachylandia Prime.

David Hardy's illustration of the Daedalus Project envisioned by the British Interplanetary Society: a spacecraft to travel to the nearest stars.  (Credit: D. Hardy)
David Hardy’s illustration of the Daedalus Project envisioned by the British Interplanetary Society: a spacecraft to travel to the nearest stars. (Credit: D. Hardy)

I’m not talking about sending a crack team of power armored space marines to defend colonists from xenomorphs, or perhaps take other more thorough measures.

No, I’m talking about getting an operational teeny robotic spacecraft from Earth to Alpha Centauri. The fastest spacecraft we’ve ever launched is New Horizons. It’s currently traveling at 14 kilometres per second. It would take this peppy little probevette 100,000 years to get to the nearest star.

This is mostly due to our lack of reality shattering propulsion. Our best propellant option is an ion engine, used by NASA’s Dawn spacecraft. According to much adored Ian “Handsome” O’Neill from Discovery Space, we’d be looking at 19,000 years to get to Alpha Centauri if we used an ion engine and added a gravitational assist from the Sun.

Just think of what we could do with those 81,000 years we’d be saving! I’m going to learn the dulcimer!
We can start shearing back the reality curtain and throw money and resources to chase nearby speculative propulsion tech. Things like antimatter engines, or even dropping nuclear bombs out the back of a spacecraft

The best idea in the hopper is to use solar sails, like the Planetary Society’s Lightsail.
Use the light from the Sun as well as powerful lasers to accelerate the craft.

Ion Propulsion
Ion Propulsion System Test for Deep Space 1. Image Credit: NASA/JPL

But if we’re going to start down that road, we could also send microscopic lightsail spacecraft which are much easier to accelerate. Once these miniprobes reached their target, they could link up and form a communications relay, or even robotic factories.

Sorry, I think that was my “Other Kevin” talking. So where are we at, fo’ reals?

Harold “Sonny” White, a researcher with NASA announced that they’ve been testing out a futuristic technology called an EM drive. They detected a very slight “thrust” in their equipment that might mean it could be possible to maybe push a spacecraft in space without having to expel propellent like a chemical rocket or an ion drive.

What’s that, Kevin? Yes, you should totally be skeptical. You’re right, that last bit was a salad of weasel words.

Even if this crazy drive actually works, it still needs to obey the laws of physics. You couldn’t go faster than the speed of light and you would need a remarkable source of energy to power the reactor. Also, yes, Kevin, you’re right NASA is working on a warp drive. There’s no need to yell.

NASA is also working on an actual warp drive concept known as an alcubierre drive. It would actually do what science fiction has claimed: to warp space to allow faster than light travel. But by working on it, I mean, they’ve done a lot of fancy math.

But once they get all the math done, they can just go build it right? This concept is so theoretical that physicists are still arguing whether powering an alcubierre drive would take more energy than contained within the entire Universe. Which, I think we can call an obstacle.

Oh, one more thing. “Other Kevin”, thanks for being so patient. Here’s your reward. Unicorns are real, and Kevin has been lying to you this whole time. Go get ‘em tiger. Place your bets. When do you think we’ll send our first probe towards another star? Predict the departure date in the comments below.