Hypothetical effects of the hypothetical Alcubierre drive

[rtxoff]

A couple of things I'd like to point out. IRL Earth's 'sphere of influence is infinite and can never really be escaped. Relativity says nothing can go faster than the speed of light, and the AD won't violate that.

Think of a submarine, which doesn't carry a substance to 'exhaust' out the back. It is embedded in its propellant and uses the fluid around it (water) to move through space. In my visualization of this, the AD uses space and time as a sort of propulsive fluid. The AD latches on to space/time, 'piling' (expanding) it up behind the ship ( while stretching [contracting] space out in front, in a sense, shortening the distance traveled through space and time ). The ship then 'surfs' along on this wave.

I don't think it matters which way you 'point' the ship, what's important is the velocity vector of the craft when the AD is engaged ( tee hee. I can't believe we're far enough into the future to seriously discuss this.... Make it so! :^)

Basically we're talking about an inertia-less (space) time machine.

Yeah i am fine with everything you said here beside following sentence: The ship then 'surfs' along on this wave.

Why should it?

So: Does the AD bend space time? Yes

Does it shorten your path in the given direction? Yes

Will that reduce travell time? Yes

Will it apply motion to your ship? No, because it would be something like the reactionless drive then, generating thrust without any need of outside force or net momentum exchange to produce linear motion. It will simply break laws of classical physics.

[Aethon]

You may then have haltet all movement relative to the center of the Universe. But there would be no way to tell if Universe itself is moving

Yeaaaaahhh. That's what stopped me in my tracks there. Can that be right?? Will the ship shoot off into.... wherever 'cause of the residual motions of any one of many different quantities? The expansion of space-time and the initial motion of the big bang blast foremost amongst them.

Edited June 15, 2014 by Aethon

[Aethon]

K. My brain's starting to hurt.

Yeah i am fine with everything you said here beside following sentence: The ship then 'surfs' along on this wave.

Why should it?

I can see it two ways. There is an elastic property to space time, and this causes the 'pile' behind the ship to spring back to it's previous shape, in a sense pushing the ship forward, while a 'vacuum' ahead pulls the ship along, like surfing a wave. This however would seem to imply a Luminiferous Ether...

The other way I see it is that the 'stretching' of space time shortens the distance ahead creating sort of a downhill run... which also seems to imply a Luminiferous Ether.

I'll stop speculating... beginning to feel dirty... going for a shower...

[Aethon]

The next questions that comes up, is the ship able to accelerate while the AD is active. I guess this is something particle theoreticians have to find out because i for myself can't imagine what is going to happen if i fire my rocket and the exhaust gases are hitting the expanded spacetime in the warp field behind me.

I imagine that you would accelerate by varying the strength of the warp field. Your 'speed' limited only by the amount of energy you could supply to the dern thing.

Another thing that makes me hazy ( is it them or me that's crazy - Einstein ) what happens when you turn the headlights on in the warp bubble?

Edited June 15, 2014 by Aethon

[rtxoff]

What happens when you turn the headlights on in the warp bubble?

[JOKEMODE] They get coverted into lazors and do pew pew [/JOKEMODE]

[Aethon]

"No tidal forces" to me indicates that my previous statement about gravity may be true...

Inside the bubble yes, but along the edge of the bubble there would be huge tidal forces that would tear apart most matter entering and leaving the bubble.

Look, aren't we flushing Einstein down the toilet here ( maybe a good thing )??? Tachyons and Naked singularities- I mean, with this I can go back in time and kill my own grandfather ( but then I would never do that 'cause he was a truly wonderful human being... so maybe causality is preserved).

I'm gonna be sick....

Edit- Just found this. Remember, just 'cause your English isn't great doesn't mean you're not brilliant.

http://ccrg.rit.edu/files/FasterThanLight.pdf

There once was a young lady named Bright,

who could travel much faster than light.

She departed one day,

in a relative way,

and returned on the previous night!

Edited June 16, 2014 by Aethon

[K^2]

Well, static towards what? What do you take as you reference point to be static towards?

Whatever you want. That's the point.

I never said you had to be moving to activate the AD. The only thing i am saying is that activating the AD will probably not have the effect you desire if you are not already moving towards an target while facing it.

Well, that's not true either. Warp bubble moves along an arbitrary world-line, which is part of the definition of the relevant warp metric. Alcubierre wrote his paper in coordinate system in which ship is initially at rest, and it still carries it to the destination which is also at rest with respect to the ship. He chose a straight line for ship's trajectory, but it's something you can get creative with as well.

Does it shorten your path in the given direction? Yes

That's a common misconception. It's not actually what Alcubierre Drive does. What it does is locally tilts your light cone. What Aethon says about riding a surf wave is far from physics of it, but it's a very good metaphor for what happens. Normally, inertia means that you have to apply force to start going. But when space-time metric changes, inertia can mean that you have to apply force to prevent yourself from being swept along. If the ship doesn't fight warp, it will carry it along. This is similar to concept of frame dragging.

So it's not about ship already traveling towards destination, and AD making the path shorter, but about AD actually carrying it along towards the destination.

Edited June 16, 2014 by K^2

[rtxoff]

So the AD takes that space inside the warp field where your ship is and moves it along to your destination, violently spaghettifying everything that comes in it's way.

This could have it's advantages. You would not have to worry about hard radiation/debris hitting your ship because nothing is going to hit you when everything of this is flying around you in the bend space time.

Edited June 16, 2014 by gpisic

[K^2]

You would not have to worry about hard radiation/debris hitting your ship because nothing is going to hit you when everything of this is flying around you in the bend space time.

There are trajectories for particles impacted by your bubble that will pass through the center, right where your ship is. So you do have to worry about radiation. But these particles will slow down with respect to ship, so you won't be slammed as hard. (Naturally, if you're in FTL warp, you can't have a particle actually hit you at FTL speeds. At close range, all relative speeds must be within c even in GR. So particles that pass into the bubble do pick up speed, but not enough to actually accumulate in the bubble.) I'll have to look up that article on geodesics of Alcubierre Metric. These computations tell you exactly how energetic the particles are going to be, and that would let one estimate the levels of radiation. Off the top of my head, I honestly couldn't tell you how bad it's going to be. IIRC, for FTL warp it's bad. But I'm not sure if I've ever even seen figures for sub-light warp.

[rtxoff]

That means that some sort of shielding will be obligatory if you want to have a safe passage through warp.

I assume some ship beeing in such a warp bubble will be barely visible maybe not at all. All that light going to hit it will be bend in some way and also the light that will be emitted from the ship.

There would be no clear picture if you going to make a high speed photo of such a ship flying by. All you are going to see on that picture would be some sort of glowing stripe?

[rtxoff]

Following scenario: 2 identical stars (A and at an fixed distance of 1 ly to each other. Our AD ship is orbiting star A and is about to warp to star B. At the moment when the ship is closest to star B it activates it's AD with it's facing right onto it.

The question: Will the flight path be a straight line to star B? When the AD is shut down at the same distance to star B as the distance it was orbiting star A, will the ship find itself in orbit around star B?

Or will the flight path not be an straight line at all? Will the ship have to target to some other point to achieve the same effect?

[Cmdr. Arn1e]

Using the 'Surfing' analogue, it is similar in a way - when you observe the various bits of rubbish floating on water, they get picked up and carried by the currents and eddies in the water. when they get close enough to shore for waves to occur, they are pushed along by the wave, with no input/energy expended by the piece of rubbish (I'm imagining a piece of polystyrene or similar that would float...)

Or imagine a surfer waiting for a wave to surf on... they wait motionless at the point where the waves have started forming so they can gauge the possible height, and if it is the height they want they will expend a small amount of energy to start going the same direction (much like the way you seem to be imagining the AD deive to work at the moment).

The difference between a surfer and AD is the fact that there aren't many 'waves' in the time/space medium, but we can calculate movement through the medium as though it were a fluid (which is why fluid dynamics is used to work out everyting from ocean liners to stratocruiser planes...). The biggest difference is, the AD drive basically creates it's own 'wave' in the spacetime medium, which it then 'surfs' along (because it is in 'contact' with the surface of the medium it is travelling through).

Of course, it is easy to see how this works from a traditional space ship point of view; fire engines, create thrust against the molecules behind the ship, get pushed forward. It's much harder to imagine something that would somehow 'latch on' to time itself to provide a downward/gravitational force which would have the effect of moving a ship across the 'surface' of the spacetime curves... You'd think if we could work that out, we would be able to create a clock that was powered by time itself somehow... and would always be 100% accurate... but going off on another tangent there I think!

And yes, this type of discussion certainly causes brain overheating >.<

[rtxoff]

Hmmm to provide a downward/gravitational force would imply that the ship is gaining momentum which was already stated to be false, also such an effect could never accelerate the ship into FTL speeds.

I don't think now that an warp drive will create a wave to ride on. I would describe it more as ripping the space around the ship and what's in it out of the rest of space and fiery drilling through it until you deactive the devil's machine(AD) to have arrived in a big blast of light at your destination.

Edited June 16, 2014 by gpisic

[Cmdr. Arn1e]

that' why my last post was an 'analogue' - it doesn't actually work like that, but is the closest aproximation we can make without one of the scientists working on it explain it, possibly using words invented for the purpose, which we (and by 'we', I mean most humans) would require an analogue to understand properly...

and yes, we would supposedly get some sort of exit-effect, but what this would be exactly (light, radiation of some form) we just don't know yet - even the scientists who proposed it can't say either way how much of an effect, or even if there will be an effect, until it is tried. We might find out with the preliminary mini-tests they are trying to carry out, which may or may not prove or disprove the naked singularity theory... A naked singluarity might only appear when the science/machinary is scaled up, otherwise we could end up with all those fears about CERN coming true!

[Aethon]

... which may or may not prove or disprove the naked singularity theory... A naked singluarity

I.. I, I just can't wrap my head around it. IMHO we'll never be able to see a naked singularity. Relativity forbids them to exist. Look, a black hole as described by relativity is a very simple object. If black holes have no hair, then all that can ever be said to describe one within relativity is it's mass, it's charge, and it's angular momentum (spin). If you could directly observe a point of infinite density, then Einstein is wrong in a big way and we need something beyond relativity, just as relativity went beyond Newton.

IMHO, with frame dragging and time dilation, the universe isn't old enough for a black hole to have formed in it's lifetime. As a star collapses past the stability provided by the Pauli exclusion principle and towards a black hole, it's proper time seen from our perspective would slow effectively to a stop and no further evolution (towards blackholedom) could occur.

What this means for warp drive, who knows. We might be bumping into some of the logical inconsistencies here which may make the warp drive impossible.

Edited June 16, 2014 by Aethon

[rtxoff]

What this means for warp drive, who knows. We might be bumping into some of the logical inconsistencies here which may make the warp drive impossible.

I would not write it off immediately, it may just work a little bit different then we have it in our minds at this point.

[Cmdr. Arn1e]

I would not write it off immediately, it may just work a little bit different then we have it in our minds at this point.

Exactly; what we really have is a lot of speculation, including from the experts on the subject... until experimentation is complete, they aren't even sure their device will work!

For some reason black holes always end up being discussed when powerful, possibly fabric-of-the-universe-rending technology is put forward... but did the LHC create black holes? No. So even with the most powerful machine currently on the planet, capable of smashing atoms together at huge force, is incapable of creating the most powerful and destructive force currently known to man... thankfully!

Has it avanced science and understanding? A resounding Yes - the Higgs boson may not have changed much yet, but who knows what another 10 years of study will show?

So, back on-topic, do we know what will happen when they experiment with the AD? not yet... will their findings be reported? you bet your life they will, even if it's "We were wrong, we're giving up for now and going back to the theory to continue working out kinks..."

Is it still worthy of discussion? of course - even though we may not be scientists, we can still come up with pertinent questions and possible outcomes that the scientists themselves don't think of, that's the way science works!

After all, we have some very youn people coming up with totally new answrs to very old questions just because they have a fresh perspective, and a good grasp of how things work, which can be lost if you end up studying the same thing for a long time and get used to how you know how to do it...

I'm hoping their experiments do help humanity in some way, even if it isn't what was originally intended... after all, some of the greatest inventions of the 20th century started off as something else entirely

[Stargate525]

What this means for warp drive, who knows. We might be bumping into some of the logical inconsistencies here which may make the warp drive impossible.

Just because it doesn't make sense doesn't mean it's impossible. Pretty much anything that happens at scales smaller than an atom are logical inconsistencies.

[Aethon]

I don't know what will happen to the ship if warp takes it out of the system that it didn't have velocity to escape, though. That's an interesting question. I think I'll have to run a simulation on that and see if there is an inherent problem. Might not be. Strictly speaking, energy need not be conserved, since you might be supplying energy via the warp bubble. On the other hand, momentum should be conserved. Otherwise, it's a gravitational wave drive, which is probably the least energy-efficient method of propulsion in existence. You definitely would want to avoid that.

Wow. Took a rereadthrough but that is interesting. Whether you go pro-grade or retrograde Galactically speaking, the warp bubble would steal momentum from the solar systems' motion through the Milky way...??

Plus when the Drive comes on gravity will mostly be warped around the mass of the ship?? (Everything is a question.)

Edit- Agreed Cmdr. Arn1e, This has been a fun one.

Edited June 18, 2014 by Aethon

[Z-Man]

Wow. Took a rereadthrough but that is interesting. Whether you go pro-grade or retrograde Galactically speaking, the warp bubble would steal momentum from the solar systems' motion through the Milky way...??

No, that would be a non-local interaction. Instead, it's probably best to think of the momentum being "borrowed". Remember how the warp drive requires negative energy densities, so negative mass? Well, negative mass going in the same direction as the spaceship will have momentum pointing to the other direction. That would cancel out the spaceship's momentum, so at all times, the total momentum of spaceship plus warp bubble is zero. (The full picture is more complicated than that.)

Plus when the Drive comes on gravity will mostly be warped around the mass of the ship??

I don't quite understand the question. If you mean the gravity generated by the bubble itself, the AD geometry is as flat (gravity free, especially tidal forces free) as you like inside the bubble. It's a "wishful thinking" kind of spacetime specifically constructed with that property. If you mean gravity from external sources, that still influences the bubble and the spaceship.

[K^2]

Whether you go pro-grade or retrograde Galactically speaking, the warp bubble would steal momentum from the solar systems' motion through the Milky way...??

No, that's precisely something it can't do. Momentum has to be conserved. It's a local conservation law, but because it's a bulk quantity, that implies global conservation. The only way a ship could gain momentum using gravity, without a reaction mass, is with gravity waves carrying away the momentum. And that requires a lot of energy. (300MJ / Ns) And odds are, it will be less efficient than photon drive, which does the same thing.

So whatever else happens, warp along a given trajectory will have to conserve momentum.

Energy is also conserved, but energy changes are not as significant. If we end up with a trajectory where we have to pump extra energy into warp field to compensate, it's something we can live with.

Following scenario: 2 identical stars (A and at an fixed distance of 1 ly to each other. Our AD ship is orbiting star A and is about to warp to star B. At the moment when the ship is closest to star B it activates it's AD with it's facing right onto it.

The question: Will the flight path be a straight line to star B? When the AD is shut down at the same distance to star B as the distance it was orbiting star A, will the ship find itself in orbit around star B?

Or will the flight path not be an straight line at all? Will the ship have to target to some other point to achieve the same effect?

Alcubierre Drive can take an arbitrary trajectory. But in this case, yes, I think a straight line is optimal. One will not encounter any curvature along that path. And if stars A and B are of the same mass, then by symmetry, when you come out of warp, you will be moving at the same orbital velocity as you left A with. So you'll be able to go from orbiting A to orbiting B.

Assuming, there are no problems in the middle. I'd need to do the computations, but it's foreseeable that proper-velocity of the ship would turn complex in map coordinates. That's not a problem by itself, because it's purely an issue with a coordinate system, but it should imply a coordinate singularity in between. Also, if you dropped out of warp in the middle, what should happen? And if you can't drop out of warp, what's actually preventing you. My best guess is that you end up with an event horizon on the bubble, and that's clearly bad mojo.

This is the main reason why I'm much happier with the idea of using warp only after you got yourself going at an escape velocity.

I'll play around with humbers, though. I've been meaning to do so, but it would take up a better chunk of the day, and I haven't had that sort of time lately.

[Aghanim]

What? So a warp drive could be potentially used as a black hole creator?

[K^2]

What? So a warp drive could be potentially used as a black hole creator?

It's more like, if you can make a warp drive, you can make black holes as well. The thinner you can make the warp bubble, the less energy you need, and you only get reasonable energy amounts when you get really close to Plank scales.

[rtxoff]

Another question: Is it possible to leave the galaxy with an AD ? SciFi literature mentions something like a galactic barrier, how much fiction is in this statement?

[Z-Man]

A hundred percent. You will have to work your way out of the gravity well, but that's only about ten times harder than getting out of the Sun's gravity well, so trivial compared to the other problems. And, of course, even at substantial FTL speed, it would still take ages to get anywhere.