The danger of Alcubierre warp drive, and not to the ship itself

[Z-Man]

If anyone is interested, this is the paper the research team of University of Sydney wrote about the Alcubierre Warp Drive that the article quoted. More detailed and science-y than the article in OP.

Quote from the article: "The following analysis is restricted to the t-x plane". And by "following", they mean "whole". They only consider particles moving on the symmetry axis. Drawing conclusions from there to the general case is like claiming a sphere cannot possibly move through an incompressible medium because all the liquid on the symmetry axis will block it.

[K^2]

Quote from the article: "The following analysis is restricted to the t-x plane". And by "following", they mean "whole". They only consider particles moving on the symmetry axis. Drawing conclusions from there to the general case is like claiming a sphere cannot possibly move through an incompressible medium because all the liquid on the symmetry axis will block it.

Warp ship is moving at, above, or near the speed of light in that analysis. Deviations from symmetry plane are negligible. You might hit a stray oh-my-god particle that's going to come at an odd angle, but almost everything you will encounter during the voyage can be analyzed in T-X plane.

[Z-Man]

No. The relevant variables of the particle before the encounter are just its regular 3-momentum(*) in the reference frame the warp drive started at and the spot it hits the bubble. Both will deviate significantly from the case studied for a generic particle.

*: that's even in their analysis. Particles with a negative initial x-velocity all just pass through the bubble, only those with a positive initial x-velocity get caught:

"We found that when a bubble catches up to a particle with a nonzero global velocity in the same direction as the ship, u_t diverges, which implies <stuff I can't paste here>."

[AngelLestat]

nobody did a virtual representation how things will look from inside the bubble and from outside?

[K^2]

No. The relevant variables of the particle before the encounter are just its regular 3-momentum(*) in the reference frame the warp drive started at and the spot it hits the bubble. Both will deviate significantly from the case studied for a generic particle.

I might be too used to this from particle physics, so I'm not clear why this is troubling you. Longitudinal momentum is always far more important than transverse. We have non-relativistic particles encountering a hyper-relativistic object. Significance of longitudinal momentum in chosen frame is inflated. Significance of transverse component becomes minuscule. Even when both particles are relativistic, transverse component doesn't play as major of a role. Warp drive encountering space dust is effectively a 1D + time problem.

Sure, I would also like to see corrections from a proper 3+1 treatment, but they aren't going to invalidate these results. Merely refine them.

nobody did a virtual representation how things will look from inside the bubble and from outside?

Oddly enough, no. I've seen a paper that does all of the necessary calculations, then says, "Well, from these, it's clear what the outside world will look like from the bridge of the ship," and just leaves it there. One of these days, if I get some free time, I might dig up that paper and write a visualization sim.

Qualitatively, what you'll see is the sort of distortion that makes things to the side of the ship appear to be somewhat lagging behind. If you go FTL, things behind you are going to start disappearing from view, but you'll still appear to have a 360° view, so things that are behind and a bit to the side will appear to be directly behind. In addition, things in front of you will be getting severely blue-shifted. Dim brown dwarves will shine like small suns. And vice versa. Things behind you will be getting very red shifted, to the point where things appearing directly behind you fade out completely.

But it's one thing to picture all of this, and another to see. And it shouldn't be all that difficult to simulate. Just a bit time consuming.

Edited December 24, 2014 by K^2

[AngelLestat]

Let us know if you achieve this.. of course is time consuming.

Just some ray cast of few particles will be enoght to have an idea. But it sounds hard anyway.

[Z-Man]

I might be too used to this from particle physics, so I'm not clear why this is troubling you. Longitudinal momentum is always far more important than transverse. We have non-relativistic particles encountering a hyper-relativistic object. Significance of longitudinal momentum in chosen frame is inflated. Significance of transverse component becomes minuscule. Even when both particles are relativistic, transverse component doesn't play as major of a role. Warp drive encountering space dust is effectively a 1D + time problem.

They are not troubling me. Two problems in your line of argumentation:

The momentum you speak of does not exist here, or is insignificant. Look at the particles that move against the warp ship with low global velocity. They also pass the center of the bubble at low velocity relative to the ship. The warp bubble simply carries them along. Sure, movement does exist and is relevant, but not momentum.

More importantly, since you bring up particle physics, this very much is a scattering problem. Do you know a nontrivial particle-particle scattering problem where a pure x-t treatment gives even approximately correct results? I don't. Take classic Rutherford scattering: your prediction would be that the alpha particle is always reflected, the scattering angle is 180 degrees 100% of the time. The full 3+1d treatment is not just a refinement of that, the 1+1d treatment only covers a very small subset of the full problem and is dead wrong on the whole. Only when the scattering target is much wider than the particle beam and the wavelength of the incoming particle is larger than the microscopic length scale of the target (tunnelling problems, mirror reflection) and it is impossible for the particle to miss the target, it can be adequate. That's not the case here.

See, in the reduced x-t problem, there are only three possible outcomes: the particle passes through, it gets reflected or it gets caught. Here, for the case where the ship moves > c, the reflection outcome is forbidden (Sort of. The particle could leave the bubble in the back with reversed global velocity, but that doesn't seem to happen either), leaving only two possible outcomes. There is not even room for deflection in the model, the outcome that is the most likely in all other scattering experiments (well, second most if you count 'no interaction happens'). The 1+1d reduced model simply can't claim to be universally even approximately right.

Now, what we CAN read from the paper is that given the right initial state, there is the possibility that particles interacting with the bubble can spend an arbitrarily long time caught in it and gather an arbitrarily high momentum before they are released.

[K^2]

Do Rutherford scattering in the case where alpha particle is stationary, and it is hit with gold foil traveling at near c with M >> m. You will find that there are just two possible outcomes. Alpha either passes straight through, or is sent directly backwards. All other outcomes, where alpha is scattered to the side, are forbidden by conservation laws. Id est, no other scattering conserves both momentum and energy. Relativity.

Now, for a subluminal warp, we might be interested in what happens in the frame where bubble is stationary. But for superluminal warp, it is not even a proper question. And in either case, for the chosen frame, 1+1 assumption is valid.

[Kerbart]

On the plus side, NASA is now going to get funds from the military to research the Alcubierre drive.

[G'th]

What I find interesting is that even in Star Trek (which inspired the Alcubierre concept), its technically a huge no-no to engage the warp drive within a solar system IIRC. You're supposed to only enter and exit warp in interstellar space and then use impulse for anything within a solar system.

[Scotius]

With Alcubierre Drive it makes perfect sense - not much chance of hitting anything important with a deadly burst of radiation on the outskirts of star system. In Trek-verse ships travelling at speeds above Warp 5 supposedly damage sub-space with their warp-bubbles - with unpleasant consequences for inhabitated worlds.

http://en.memory-alpha.org/wiki/Force_of_Nature_%28episode%29#Continuity

[Iskierka]

The thing is that the apparent relative velocity between craft and particle isn't relevant, because the particle will retain its local velocity until it gets caught in the region where space is actually being "destroyed" in front of the craft. The particle will retain its velocity in the very compressed space up to this point, albeit with (from external reference) greatly reduced ship-relative x velocity. The reason the x-only study is limited is because it isn't considering how long the particle spends in compressed space before it hits the destruction zone, and whether or not lateral velocity would allow the majority of particles to escape to the side - it may be that most or all particles simply get "bounced" around the front with no contact with the problem zone whatsoever.

Additionally, by neglecting lateral velocities, they don't consider fully whether these particles would be trapped - is there any reason why they would lose lateral velocity once captured? If not, and especially if they might gain it due to bubble geometry, even if all particles did get captured, the worst that would happen is that an operational Alcubierre drive would generate a gentle gamma ray shower in a cone in front of it as it travelled along, as even if you could go fast enough to travel between stars in hours, millimetres per second laterally would be sufficient to leave.

Also, regardless of whether the Alcubierre drive generates gamma rays, whether continuously or in a burst, it's very simple to solve. Observe destination system to determine its ecliptic, and aim 50-100 AU above or below, or further if it's required to keep the target out of the gamma ray cone. Then, aim straight down at the sun where no inhabited bodies or structures should exist, and jump in to a suitable observation distance, depending on the stellar intensity. From there, you can find all the planets you want, then do similar jumps to ones you wish to visit, identify the extent of their system and then travel slightly off-angle towards them to avoid radiation showers. In theory you could likely steer the Alcubierre drive to pull in closer as you approached, if you could identify all moons and habited satellites to avoid, potentially even getting into a medium orbit by keeping them just out of the radiation cone. I would say low orbit, but getting into that much particle density probably -isn't- a good idea, and you probably haven't been able to identify all risk debris yet.

And yes, that procedure does make some accounting for if there were an advanced species that might get annoyed by your gamma shower, but that is likely the most difficult case, so given it can work with that, all other cases should be fine.

[trekkie_]

I would assume that the drive is flawed to begin with, because the collisions along the way will probably pass through the bubble and hit you. You may be bending space, but it's still like ramming a brick wall into a car, along with other side effects like trapping the radiation inside the bubble with you. It may be possible to create some kind of space bending pattern to disperse the particles around you rather than into you.

But people also think too big. There's no reason why we can't for example, stop and go rapidly to discharge build ups if that was indeed the case.

You also would be able to use such a drive for slower cruising speeds and other maneuvers too. People seem to forget this fact.

[Technical Ben]

On the plus side, NASA is now going to get funds from the military to research the Alcubierre drive.

That's an interesting flow of results. Any funds going in that direction cannot be bad, when the end result cannot be a weapon (as I don't think it's possible ). Risk is they discover something ELSE in the process and weaponize that.

[trekkie_]

That's an interesting flow of results. Any funds going in that direction cannot be bad, when the end result cannot be a weapon (as I don't think it's possible ). Risk is they discover something ELSE in the process and weaponize that.

it's actually even easier to make it into a weapon, if you get it functional. all one would need is probably a handheld sized ship, fly it out into space a bit, then back toward earth like a rocket, releasing a blast of its radiation in the general direction of say, a city block or a country.

[Iskierka]

The current design is looking at half a ton of mass-energy conversion to exceed c. Even with hydrogen fusion at 100% efficiency (maximum ever likely is less than 10%), that's 75 tons of fuel and a massively complex machine into orbit for a simple gamma ray burst device. If you wanted to do massive damage to a target, nuke or dirty bomb is a million times more efficient whether you want total destruction or to leave most infrastructure intact. Pretty much every other weapon type developed is more effective.

[Technical Ben]

Read the other reply. With such a device, other options become available (possibly).

Besides, I thought the energy currently needed was that of Jupiter? where did the half ton of matter/antimatter come from?

[SargeRho]

No, currently the energy need is the mass of Voyager 1. Jupiter was before some more work was done on it.

[Iskierka]

The evolution has been initial design of either a spherical or point field generator, I believe, which was calculated as being a galaxy's worth of energy to initiate it. Then a ring reduced the requirement to Jupiter, which was a "heh, maybe for the most advanced interstellar civilizations wishing to become intergalactic." Now toroidal field generators have been shown to have an estimated energy requirement of just Voyager 1, which takes it from "lol, maybe in millions of years" to "oh ... we could do that. It's crazy, but that -is- less energy than the human race has generated in the past century." Hence the sudden burst of interest in verifying the theories and device feasibility - if this device can work, it would 100% be worth that much energy to get at least one of them going.

[Mazon Del]

The guy (Harold White) that figured out the drop from Jupiter to Voyager 1 mass, found a way to decrease it further. He didn't discuss it much at the grand unveiling of the first part (he hadn't finished the calculations), but it apparently had a rather large-ish effect on the remaining needs. From what I remember, it was basically instead of throwing 'full power' at the engine, the intent was to set up some sort of oscillation. Flicking it on/off or high/low rather than just pure on/max-power.

[KSK]

That's starting to get crazy close to a Trek style drive if I'm remembering my technobabble correctly. Maybe he should look into a twin dipole arrangement for generating the warp field.

[Bill Phil]

If we manage to use antimatter to power it, and then we find a material like unobtainium or dilithium, it would be like Star Trek.

[Dr-Drunk]

Considdering that technology is still completely theoretical and has never been tested we wouldn't even know what happens when we create said warp buble in space. I mean for all we know it could generate black holes or something and drag anything allong with it. It could also be that the energy required to even produce the buble could create huge explosions and the like.

I'd love to source the article to you but it's been lost to the history of the interwebz but basically some people have the same fears they used to have when they thought the hadron collider would destroy earth.

Either way, I'd have loved to see humanity go off into space and explore the far beyond. But given the Wait-Calculation it sadly won't be anywhere near our lifetimes.

[Dominatus]

Not absolutely true... I think. I have a thread I just started that brings up the issue, and potential solutions to the exotic matter problem.

[Silver_Swift]

The way I understood it (that is to say, very badly), is that there are a lot more fundamental problems with the Alcubierre than collateral damaged and potentially non-existing unobtanium. Not least amongst them the fact that FTL travel, regardless of how you do it, allows you to break causality.