Alcubierre Drives

Kjbartolotta · Nov 5, 2016

I need something to take my mind off the election. Anyone want to talk Alcubierre drives? My understanding is they're plausible (ish) as long as they keep under the speed of light. Assume far future tech and no FTL nonsense, what would the engineering concerns be? What would your reactionless drive look like? Added points if you want to write up some starships. I promise I won't use them, I've got enough of my own! There's some good stuff on the Orion's Arm website, but as usual, they require godlike technology to develop and operate, something I'm fine with, but looking to downplay.

Dennis E. Taylor · Nov 5, 2016

Alcubierre drives depend on warping the fabric of space. The only way we know to do that, at the moment, is with a large mass. So you need an unobtainium module to make it work. Once you do that, there's no reason in particular to stick to the Alcubierre concept.

Steven Baxter did something vaguely similar in Ark, where the ship flies in a "pocket" in space, so that the actual contact with our universe is essentially a pinhole. Still not FTL, but it avoids a lot of the mass and relativity issues.

Still unobtanium, though.

jjdebenedictis · Nov 5, 2016

My understanding is you could go much faster than light (sort of) without acceleration using an Albucierre drive, because it's spacetime that is being forced to move (sort of), not your ship. Also, that no, it's not plausible from an engineering standpoint for the reason Dennis said: we don't have a way to warp spacetime to our liking.

I seem to recall other issues like creating a lot of particles that could kill you because you're warping spacetime so violently and also not being able to turn the drive off, because it takes so long for the "turn off" signal to travel forward to the warped region of space where the effect is taking place.

By the way, I am excavating all this from hazy memories while in a state of sleep-deprivation, so anyone, feel free to correct me.

Megann · Nov 6, 2016

I wonder how the use of such a drive would tie in to relativity. One of my favorite kids shows once had an episode where they showed what would likely happen to time on earth if you traveled at the speed of light for 24 hours. I think about 70 years would pass. But would that also apply if you warp spacetime around your ship. As I understand it that is how such a drive would work. I always found it strange that in Star Trek they could warp from one place and back and the people they left behind would still be the same age.

Anyway this shows how much I understand of physics, which is not much at all.

RX-79G · Nov 6, 2016

It is more a thought experiment than anything else. If you plug "negative mass" into the standard equations you get these cool effects, but that really is trading in one impossibility for another. I read a book in the '80s that had something like this - the ships were endlessly "falling" toward a fake mass out in front of the ship. Eventually that point would accumulate enough dust and junk to form a ball of matter that also helped shield the ship. But an Alcubierre Drive story is probably a story about "negative mass" or "negative energy" and how it came to be, rather than the drive itself.

For a fast sub light drive, Alastair Reynolds uses ship drives that get their energy from quantum vacuum states - referred to in other places as "zero point energy". This is slightly more plausible, and allows an immense ship to produce several gravities of acceleration without expending fuel. It, like Reynolds, has a grounding in real theoretical physics - rather than just a thought experiment.

Another method would be a way to uncouple inertia, allowing incredibly small amounts of propellant to cause incredible acceleration. But that might make it impossible to live in the ship.

What would your reactionless drive look like?

I would assume that it wouldn't look like any sort of pusher drive at all. A sealed box inside the ship, or maybe something on an armature out in front.

RX-79G · Nov 6, 2016

Megann said:
I wonder how the use of such a drive would tie in to relativity. One of my favorite kids shows once had an episode where they showed what would likely happen to time on earth if you traveled at the speed of light for 24 hours. I think about 70 years would pass. But would that also apply if you warp spacetime around your ship. As I understand it that is how such a drive would work. I always found it strange that in Star Trek they could warp from one place and back and the people they left behind would still be the same age.

Anyway this shows how much I understand of physics, which is not much at all.

One way that time dilation can be looked at is as the result of applying acceleration to an object. If you compare two objects moving away from each other, the object that is accelerating away dilates, not the one that isn't accelerating - even though they are both "moving" relative to each other. Even just sitting in the "acceleration" of a gravity well, as we do here on earth, means that we are running slightly slower than an object out of Earth's gravity.

If you could "warp", you would be changing location without acceleration, which maybe/sorta means your aren't causing dilation to occur. But you're causing all sorts of other problems with causality.

Laer Carroll · Nov 6, 2016

From a practical writer's standpoint you should avoid explaining the theory behind any far-future drive with current "modern" science, as it's almost certainly going to be outdated. Instead I'd focus on the sensory experiences of those traveling in such a spaceship.

Seasoned travelers will take for granted the mundane oddities of space travel the same way we face the mild inconveniences of air travel, not turn over in their mind the theory behind aerodynamic lift.

"Joan's concentration was broken by the usual slight nausea which came and almost instantly went when the ship began traveling faster than light. She glanced at the viewscreen on the wall of her cabin. Random swirls of rainbow light had replaced the black of space dotted with hard pinpoints of the light from the stars. She watched the light show for long moments before returning to the puzzle of the latest mercantile upset."

Those responsible for piloting spaceships will likewise usually ignore theory for the details of their job. They would be more concerned about the effects of the theory on their task, for instance the difference between the time flow within the spaceship versus the time passing outside it.

"Max closed his eyes and let his neural net paint a 3D image of local space around Earth. It surrounded them out to 12.5 light years and contained 33 stars. A mental command and the view spun to show Struve 2398 directly ahead and above the equatorial plane by about 30 degrees. It was a pair of small red dwarfs 11.6 light years away. The interstellar medium between Earth and it was relatively sparse, but he told the navigator software to plot a course with a medium-high shield strength and a week's travel time. That should be ultra-safe and let him catch up on his studies."

Layla Nahar · Nov 6, 2016

Laer Carroll said:
From a practical writer's standpoint ...

(I have a feeling that^ is not the OPs concern...)

Kjbartolotta said:
I need something to take my mind off the election. Anyone want to talk Alcubierre drives?

Something I'm thinking that I always thing about this stuff is - if you warp space, and you want to travel via that warped space, how do you not get warped, too?

Kjbartolotta · Nov 6, 2016

@Dennis- It all comes down to those unobtanium modules, doesn't it? As far as my understanding goes, ultra-dense, Tardis-like modules are fairly essential to the operation. Should read more Baxter, I know he's OG in this department.

@JJBenedict- Hiya! No interest in going faster than light personally. I'm not as concerned with you first point (the fact that it's not plausible), the idea of a metric drive is definitely 'Big Lie' territory, I'm happy as long as I can vaguely map out the technology with some important handwavium elements I seem to neglect ever explaining. Your second point is a major concern to me, how to turn that warp bubble on and off without wrecking all the finely-wrought equipment and organisms inside. Grr, I'm starting to understand why Douglas Adams had the best starship drives.

@Megann- Yeah, I never even made it to physics class in high school. If my high school had offered a magic class, I'm sure I'd've done fine, but there you are. Yeah, Trek is indisputably the Greatest Thing Ever, but I never try to get too bogged down in the inconsistencies. Still, that, and the artificial gravity, always bugged me.

@RX-79G- You talkin' about House of Suns? Cause this topic could have just as easily been titled 'How Do I Rip Off House of Suns and Get Away With It'. Not sure which 80's scifi book you read, but that sounds about what I have envisioned. It seems to make sense, and serves as a pretty metaphor for how the ship is traveling through space. Also, it maintain the ship's proper up-down orientation and offers an elegant solution to shielding.

One way or another, I'm bound to go down the ZPE rabbit hole. I embrace this. So much about Zero Point Energy is hard to understand, because it's gotten mixed up in the whole world of entertaining-but-hokum pseudoscience. Any thoughts you have on how such a drive would operate would be greatly appreciated. Also, tell me more about this inertial uncoupling, not all ship need to be habitable. Some can be processors with drives attached, crews can be AI or uploads. Glad to know I don't need a pusher plate, the two options you suggest are my preferred ones.

@Laer- You've quite excellently surmised my goal here, those little details and quirks of the process are always far more valuable than pages of GUT theory splashed across the page. It's also helpful than my MC is rather dense and incurious when it comes to the nature of drive technology.

@Layla- Yes, exactly. A bubble inside the bubble that unwarps the warping? That's more of a koan than an answer. Again, the easiest solution involves AI and uploads, a super-advanced solid state computer is going to be less concerned with being distorted than a squishy puny human. I want space arks though!

Thanks everyone! On a side note, anyone ever read the Neverness series by David Zindell? It's a weird and kinda pervy Dune clone, but highly underrated with it's own crazy charm, and it includes my favorite stardrive concept ever. Though the technology is never quite explained, it involved pilots (who are initiates in a mathematical cult organization) traveling through a hyperspace dimension by solving formulae. Different theorems act as highways, with the safer and more reliable mapped out concepts serving well-traveled areas, and chaotic mathspace compromising the great unknown. It's surprisingly fun and exciting.

Laer Carroll · Nov 6, 2016

If you DO want to get into the theory of the space drive in your books, it's best to make up your own theory rather than use modern physics. Unless you have a degree in modern physics or read lots of books on the subject, you're likely to make laughable mistakes.

A good example is in David Weber's Honorverse space war books. In it (if I remember rightly) he hypothesizes that "ordinary" space is just one of several "bands" of superspace. In the next band up from ground-level space the speed of light is several dozen times as fast and the energy needed to move vehicles is correspondingly less. Ditto each "higher" band. Each band is also more perilous to traverse, requiring ships to be sturdier and nimbler. Commercial spaceships thus tend to travel in the slower bands, military craft in the higher ones.

RX-79G · Nov 6, 2016

@RX-79G- You talkin' about House of Suns? Cause this topic could have just as easily been titled 'How Do I Rip Off House of Suns and Get Away With It'.

Reynolds is philosophically against FTL, so most of his books use sublight. But the details I mentioned are more from the Revelation Space series and the "Conjoiner drives".

Kjbartolotta · Nov 6, 2016

Ah, yes.

RX-79G · Nov 6, 2016

Thinking more about this, Alcubierre Drives fall into the class of fictional drives that we call "warp drives" - Star Trek and whatever. The universe distorts and the ship hurtles through it as if there was no light speed barrier.

Star Wars, Iain Banks' Culture are "hyperdrive" stories, where the ship travels into a different kind of space to transit, then pops back out. The functional difference between this and a wormhole is that the wormhole is permanent, while the ship makes its hyperspace passage itself.

And you can subdivide the hyperspace drives by those that allow interaction in hyperspace - like when ships are fighting in hyperspace in Culture stories, or the Star Wars version where hyperspace is a discreet place of safety for the ship.

Speaking of Laer's made up physics, I have always appreciated the way Iain Banks constructed his hyperspace physics. There was mention of the full shape of the hyper universe, how ships interacted with hyperspace and how even static objects could have components in hyperspace. It was all pure fiction, but so nicely consistent and fleshed out to have that air of authenticity that makes for great sci-fi.

Kjbartolotta · Nov 6, 2016

I definitely want to avoid hyperspace wherever possible, though I agree with you that Banks always put a refreshing and appealing varnish on his gobbledygook. It started getting too baroque for me in the later novels, and I got the impression he rejiggering some of the hyperspace concepts in preparation for novels he never got around to writing. Sigh, the world need Culture now more than ever, and he is sadly missed.

Bringing up Reynolds again again, I like his Poseidon's Children series for this same reason. For all his grounding, he never bothers to explain the drives more than he has to, leaving all the heavy lifting to handwavium processes and even admitting in the afternote that their bunk.

Simpson17866 · Nov 6, 2016

You would have to be careful where you stopped: as soon as you "landed" the bubble of fast-moving space and settled back into normal space, unimaginable amounts of radiation would shoot out from the front of where the bubble had been.

This would be extremely useful as a weapon of mass destruction, but less so for transportation.

King Neptune · Nov 6, 2016

The Alcubierre warp drive is a very interesting arena for thought experiments to try to better understand general relativity and quantum field theory, but it should give you zero hope for actually building a spaceship some day. Some of the many problems are discussed on Wikipedia:

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.
http://jalopnik.com/the-painful-truth-about-nasas-warp-drive-spaceship-from-1590330763

I remember reading this or something similar a few years ago. I think it is not impossible, but the energy requirements put it outside possibility for a very long time to come or longer.

Kjbartolotta · Nov 6, 2016

@Simpson- Hmm, been thinking about that, actually trying to figure out ways to weaponize it

@Lord Poseidon, Earth-Shaker of the Golden Trident, Who's Steeds the Foam Divides- I remember that article too. I thought I heard that the Alcubierre drive are semi-plausible as long as you're not trying to break the light speed barrier with it, but as I type it, I realize how ill-informed that statement sounds. Well, I guess it's still more plausible than the Dean Drive.

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.

This seems to be the problem facing most hypothetical drives. I'm beginning to see that my starships are going to have to run entirely on vague wording and careful obfuscation, a Quantum Shrug Drive the likes of which the worlds has never seen.

King Neptune · Nov 6, 2016

Kjbartolotta said:
@Lord Poseidon, Earth-Shaker of the Golden Trident, Who's Steeds the Foam Divides- I remember that article too. I thought I heard that the Alcubierre drive are semi-plausible as long as you're not trying to break the light speed barrier with it, but as I type it, I realize how ill-informed that statement sounds. Well, I guess it's still more plausible than the Dean Drive.

This seems to be the problem facing most hypothetical drives. I'm beginning to see that my starships are going to have to run entirely on vague wording and careful obfuscation, a Quantum Shrug Drive the likes of which the worlds has never seen.

There's something part way plausible about it, but the devils are in the details. I think someone thought they could make something that approximated it that might work. Probably too good to be possible.

Laer Carroll · Nov 7, 2016

When you make up your own space drive it helps make it seem realistic to give it various limits and idiosyncrasies. This also gives you complications for your plot.

Think about current vehicles and use their qualities for inspiration: the need to refuel periodically, cases where the engine might overheat or otherwise warn that the engine needs to rest, problems arising from the vehicle being too large or too small, etc.

One limit your craft will have if they travel great distances: the speed of light. For instance when a craft pauses or slows beyond the edge of a star system light and radio waves from the inner system will be late by several hours. So if it is a warship joining other craft in a space war the crew of the late-comer begins by viewing out-of-date data.

Another limit is a possibility: a starship may gather electromagnetic energy and space dust around itself as it travels. You would likely have to slow at the edge of a star system to let that unwanted load to bleed off harmlessly and unnoticed before traveling inward.

jjdebenedictis · Nov 7, 2016

The Alcubierre drive is supposed to move you faster than light without the time dilation effects of relativity. It seems like people aren't understanding what it does.

The early universe expanded faster than what we'd call light speed because spacetime can do that and matter-energy cannot. The Alcubierre drive is supposed to allow a ship to surf a similar effect, where a skin of spacetime does all the weird stuff for you while the ship coasts along in a bubble of normal spacetime.

Alcubierre Drives

Kjbartolotta

Potentially has/is dog

Dennis E. Taylor

Get it off! It burns!

jjdebenedictis

is watching you via her avatar

Megann

RX-79G

RX-79G

Laer Carroll

Aerospace engineer turned writer

Layla Nahar

Seashell Seller

Kjbartolotta

Potentially has/is dog

Laer Carroll

Aerospace engineer turned writer

RX-79G

Kjbartolotta

Potentially has/is dog

RX-79G

Kjbartolotta

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Simpson17866

King Neptune

Kjbartolotta

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King Neptune

Laer Carroll

Aerospace engineer turned writer

jjdebenedictis

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