Is a warp drive possible?​​

Make it so.

Credit: Willrow Hood / 362693204 via Adobe Stock

The distances between the stars are so vast that they can make your brain melt. Take for example the Voyager 1 probe, which has been traveling at 35,000 miles per hour for more than 40 years and was the first human object to cross into interstellar space. That sounds wonderful except, at its current speed, it will still take another 40,000 years to cross the typical distance between stars.

Worse still, if you are thinking about interstellar travel, nature provides a hard limit on acceleration and speed. As Einstein showed, it's impossible to accelerate any massive object beyond the speed of light. Since the galaxy is more than 100,000 light-years across, if you are traveling at less than light speed, then most interstellar distances would take more than a human lifetime to cross. If the known laws of physics hold, then it seems a galaxy-spanning human civilization is impossible.

Unless of course you can build a warp drive.

Warp speed!

Ah, the warp drive, that darling of science fiction plot devices. So, what about a warp drive? Is that even a really a thing?

Let's start with the "warping" part of a warp drive. Without doubt, Albert Einstein's theory of general relativity ("GR") represents space and time as a 4-dimensional "fabric" that can be stretched and bent and folded. Gravity waves, representing ripples in the fabric of spacetime, have now been directly observed. So, yes spacetime can be warped. The warping part of a warp drive usually means distorting the shape of spacetime so that two distant locations can be brought close together — and you somehow "jump" between them.

This was a basic idea in science fiction long before Star Trek popularized the name "warp drive." But until 1994, it had remained science fiction, meaning there was no science behind it. That year, Miguel Alcubierre wrote down a solution to the basic equations of GR that represented a region that compressed spacetime ahead of it and expanded spacetime behind to create a kind of traveling warp bubble. This was really good news for warp drive fans.

The problems with a warp drive

There were some problems though. Most important was that this "Alcubierre drive" required lots of "exotic matter" or "negative energy" to work. Unfortunately, there's no such thing. These are things theorists dreamed up to stick into the GR equations in order to do cool things like make stable open wormholes or functioning warp drives.

It's also noteworthy that researchers have raised other concerns about an Alcubierre drive — like how it would violate quantum mechanics or how when you arrived at your destination it would destroy everything in front of the ship in an apocalyptic flash of radiation.

Warp drives: A new hope

Credit: Primada / 420366373 via Adobe Stock

Recently, however, there seemed to be good news on the warp drive front with the publication this April of a new paper by Alexey Bobrick and Gianni Martre entitled "Introducing Physical Warp Drives." The good thing about the Bobrick and Martre paper was it was extremely clear about the meaning of a warp drive.

Understanding the equations of GR means understanding what's on either side of the equals sign. On one side, there is the shape of spacetime, and on the other, there is the configuration of matter-energy. The traditional route with these equations is to start with a configuration of matter-energy and see what shape of spacetime it produces. But you can also go the other way around and assume the shape of spacetime you want (like a warp bubble) and determine what kind of configuration of matter-energy you will need (even if that matter-energy is the dream stuff of negative energy).

Warp drives are simpler and much less mysterious objects than the broader literature has suggested.

What Bobrick and Martre did was step back and look at the problem more generally. They showed how all warp drives were composed of three regions: an interior spacetime called the passenger space; a shell of material, with either positive or negative energy, called the warping region; and an outside that, far enough away, looks like normal unwarped spacetime. In this way they could see exactly what was and was not possible for any kind of warp drive. (Watch this lovely explainer by Sabine Hossenfelder for more details). They even showed that you could use good old normal matter to create a warp drive that, while it moved slower than light speed, produced a passenger area where time flowed at a different rate than in the outside spacetime. So even though it was a sub-light speed device, it was still an actual warp drive that could use normal matter.

That was the good news.

The bad news was this clear vision also showed them a real problem with the "drive" part of the Alcubierre drive. First of all, it still needed negative energy to work, so that bummer remains. But worse, Bobrick and Martre reaffirmed a basic understanding of relativity and saw that there was no way to accelerate an Alcubierre drive past light speed. Sure, you could just assume that you started with something moving faster than light, and the Alcubierre drive with its negative energy shell would make sense. But crossing the speed of light barrier was still prohibited.

So, in the end, the Star Trek version of the warp drive is still not a thing. I know this may bum you out if you were hoping to build that version of the Enterprise sometime soon (as I was). But don't be too despondent. The Bobrick and Martre paper really did make headway. As the authors put it in the end:

"One of the main conclusions of our study is that warp drives are simpler and much less mysterious objects than the broader literature has suggested"

That really is progress.

More From Adam Frank
Related Articles

An Olympics without fanfare: What would the ancient Greeks think of the empty stadiums?

In ancient Greece, the Olympics were never solely about the athletes themselves.

Photo by Despina Galani on Unsplash

Because of a dramatic rise in COVID-19 cases, the opening and closing ceremonies of the 2021 Olympics will unfold in a stadium absent the eyes, ears and voices of a once-anticipated 68,000 ticket holders from around the world.

Keep reading Show less

Bad at math? Blame your neurotransmitters

A new brain imaging study explored how different levels of the brain's excitatory and inhibitory neurotransmitters are linked to math abilities.

Mind & Brain
  • Glutamate and GABA are neurotransmitters that help regulate brain activity.
  • Scientists have long known that both are important to learning and neuroplasticity, but their relationship to acquiring complex cognitive skills like math has remained unclear.
  • The new study shows that having certain levels of these neurotransmitters predict math performance, but that these levels switch with age.
Keep reading Show less

Epiphenomenalism: one of the most disturbing ideas in philosophy

Do our thoughts have any meaning whatsoever?

Credit: NeONBRAND via Unsplash
Mind & Brain
  • Epiphenomenalism is the idea that our conscious minds serve no role in affecting the physical world.
  • On the contrary, our thoughts are a causally irrelevant byproduct of physical processes that are occurring inside of our brains.
  • According to epiphenomenalism, we are like children pretending to drive a car — it can be great fun, but we are really not in charge.
Keep reading Show less