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What would happen if a spaceship with an Alcubierre/Warp Drive went through a planet?

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willbell
#1
Nov7-12, 07:52 PM
P: 27
I am using this in a science fiction novel I am working on for National Novel Writing Month, most of my novel is "soft" but I want to know what we could actually know in this situation. If it helps any the spaceship is about the size of 20 Earths and its going through Saturn.
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Simon Bridge
#2
Nov7-12, 08:00 PM
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That would depend on the strength of the space-time distortion being generated by the drive I guess ... anything from a major explosion releasing the energy invested in the drive to going right through, but nobody inside the field noticing much.

Take another look at how much energy is involved.
willbell
#3
Nov7-12, 08:09 PM
P: 27
Quote Quote by Simon Bridge View Post
That would depend on the strength of the space-time distortion being generated by the drive I guess ... anything from a major explosion releasing the energy invested in the drive to going right through, but nobody inside the field noticing much.

Take another look at how much energy is involved.
Forgive me for being a little bit of a novice at this subject, but what exactly would you use to quantify the "strength of the space-time distortion being generated by the drive". What unit of measure would be used for that?
Assuming the ship manages to punch straight through Saturn, what amount of energy are we talking about, and what would humans see from Earth?

Simon Bridge
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Nov7-12, 10:08 PM
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What would happen if a spaceship with an Alcubierre/Warp Drive went through a planet?

Quote Quote by willbell View Post
Forgive me for being a little bit of a novice at this subject, but what exactly would you use to quantify the "strength of the space-time distortion being generated by the drive". What unit of measure would be used for that?
Any unit you like - the strength of the field would be whatever the ships engineers would use to say how well the warp bubble is maintained in the face of external events.
eg. when the warp bubble encounters matter, it has to do something about it. Whatever the designers have figured out is going to take energy and that energy has to come from someplace... presumably whatever is maintaining the warp. Higher densities of matter will require higher powers to compensate.

The drive works by imposing an odd shaped geometry on the regular "ambient" space curvature of, say, a planet or a star.

I could be that the ambient curvature and the interaction with matter could change the warp so that it will no longer support FTL - the spacecraft drops into normal space and...

Assuming the ship manages to punch straight through Saturn, what amount of energy are we talking about, and what would humans see from Earth?
Last I saw, the negative energy requirement can be as low as a few milligrams of exotic matter per atom of space-craft. E=mc^2. However this energy is generated - the bubble collapsing would mean dealing with it somehow. For an earth-mass ship you'd be looking at an explosion equivalent to hundreds of millions of supernovas[*].

Give your ship an extra supernovas worth of energy to play with and you probably won't notice any pesky gas giants in your way. From Earth - you'd notice a very bright light as Saturn disintegrates... if you want to do the calculation: assume the warp has been configured in such a way that it just pushes intervening matter to one side - thus the mass of Saturn in the direct path of the warp-envelope has to get pushed the radius of the envelope in the time it take the ship to travel into it [**]. Conservation of energy.

Basically what I'm saying is that your question is far too wide open to call.
Everything boils down to the details of the design of the drive.

--------------------------------
[*] Very roughly: 6x10^23 (1 mole) carbon atoms is about 12g
That would need 5x10^19kgc^2 of negative energy per kg of carbon.
The mass of the Earth is about 6x10^24kg and your ship is 3 of them?
So that's 9x10^44kgc^2 = 27x10^52J of energy just to make the drive work.
A supernova releases of order 10^44J of energy - so this is the same energy as about a billion supernovas. Not something you want to release all in one go.

OTOH: if the total mass-energy of the starship is 3-earths, then the ship itself must mass about 360000kg. So the energy equivalent is 5x10^33J ... which is "better".

[**] diameter of Saturn = 120000km
diameter of envelope 23000km (snug fit to 3-earth-size starship)
density of Saturn: 687kg/m^3
speed of light: 300000km/s

at lightspeed, ship will shunt aside 4.7x10^21kg/s of material
the average speed this matter has to have to get out of the way fast enough will depend on the geometry of the front of the envelope ... if it is conical, the apex angle needs to be less than 90 degrees (the matter is not inside the warp so it cannot exceed c).
willbell
#5
Nov8-12, 06:18 AM
P: 27
The thing is that my story isn't from the perspective of the ship, its from the perspective of Earth, humans never actually meet the creatures travelling faster than light through our system. So I was wondering what the previous commenter meant by the strength of the space-distortion.
mfb
#6
Nov8-12, 08:42 AM
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Quote Quote by willbell View Post
If it helps any the spaceship is about the size of 20 Earths and its going through Saturn.
The spaceship is like a planet itself? That is... gigantic.

Similar to Simon Bridge, I would expect a release of all the involved energy - even if the alcubierre drive does not have a significant amount of energy, the ship is so big that any impact (even at ~0 initial relative speed) will cause serious trouble in our solar system.


Just out of curiosity: Why do you expect that to happen? Space is big. To hit anything, you need very precise planning. If you just keep heading in some random direction, you won't hit anything in the galaxy with >99% probability (rough estimate, did not check the numbers).
Simon Bridge
#7
Nov8-12, 04:11 PM
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Oh it's 20 Earths! Good grief.
That makes the envelope diameter half that of Saturn!
The thing is that my story isn't from the perspective of the ship, its from the perspective of Earth, humans never actually meet the creatures travelling faster than light through our system.
No more Saturn then. People on Earth would see a really big explosion - briefly.

If the total mass-energy of the ship+drive is 20-Earths, then that would be 12x10^25kg total. The ship itself would mass 2400000kg ... catastrophic drive failure would release 4x10^34J - with that kind of energy to play with, it is probably reasonable to expect the ship to just shoulder Saturn aside. This is still an explosion big enough to destroy the planet.

Like I said - the scope is wide open for you.
The ships engineers will have had to do something about the effect of the ships mass on surrounding bodies anyway - assuming it was ever intended to rejoin Einstein space. How they got around the various design problems would affect the interaction with the Solar System and, therefore, what people on Earth would see.

You may want to try for a smaller ship, and, maybe a close pass to a gas giant.
How about something like a probe passing through Saturn's rings - blowing rock and ice all over the place. This would also allow your Earth-side scientists to postulate that there must be a great many of these things and go looking for signs of them.

I was wondering what the previous commenter meant by the strength of the space-distortion.
It is just what I said - a measure of how the warp envelope responds to external space-time curvature (and other interactions).

Do you know how one of these drives is proposed to work at all?
willbell
#8
Nov8-12, 04:53 PM
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Quote Quote by Simon Bridge View Post
Do you know how one of these drives is proposed to work at all?
I understand that they are designed so that they can shorten distances in space in front of them, and expand space behind them. It is kind of like a wave that you ride through space. Basically like this:
Simon Bridge
#9
Nov8-12, 05:44 PM
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The picture does not actually mean anything by itself - notice how the distance (measured along the surface) in front of the ship in the picture would actually be longer than if the big hump weren't there - for example?

In simplified-for-SF terms - the drive generates a special distribution of imaginary mass-energy which radically changes the curvature of space-time nearby. The result encloses the ship in a bubble whose time evolution, from outside, zips away FTL. Observers outside and inside the ship would probably still disagree about how much time the journey took - the special feature is that both will agree it was FTL.

Generally, energy will curve space-time according to the Einstein relations.
However, the relations can be worked backwards: so you can input the curvature you want and get the energy distribution out. This does not always produce a meaningful result ... imaginary mass is usually taken to mean that the space-time topography is not possible.

So a drive working on these principles uses "exotic matter" and "negative energy" in very large quantities ... presumably it generates it's own through <insert technobabble here> or maybe the ship-builders have discovered 20 planetary masses of the stuff someplace as a "lucky find". In which case they are overdue some bad luck aye?

It would tend to be a "point and shoot" kind of drive - since the inside is kind-of cut off from the outside.

One of these in free space would be very noticeable since the interstellar hydrogen (dust, other stuff) would form a plasma stream that is very bright and very very long. Think in terms of a contrail over interstellar distances.

The drive will be influenced by the ambient curvature as well - for an extreme situation - imagine it flew close by a black hole. The extreme curvature there will adjust the mass-energy distribution of the drive and so affect the topography of the warp bubble. It is a finely balanced thing so small changes to the bubble could have a big effect on performance (wikipedia will tell you that the earlier proposed topologies required more energy than exists in the Universe to work, but small tweaks to the formulas got it down to the figures I'm throwing around here. So imagine the ship encountering a bit of curved space-time which shifts the topology into a high-maintenance configuration: what would happen?) It needn't be a black hold - any large body could have a significant effect on the warp-bubble. How much the mass-energy distribution is sensitive to the ambient curvature of space-time would be important then. This would give you one measure of the strength of the bubble.

But the softer you go the easier it gets - the engineers could have solved a lot of these issues (may be interesting to associate historic astronomical events to early experiments with the drive in small ships) since they must have been flying these things for quite a while by the time this accident happens.

The more you do this, the more you get to pick any particular result you like.
I'm guessing your main problem is that you don't want things to be so much changed that Earth Scientists seeing the explosion would not suppose it to be evidence of an FTL visitor?

Really, though, any craft arriving with too much energy to have come from anywhere in the solar system is an extraterrestrial - you don't need FTL for that. But it's your story - you want FTL, you've got it, and I'm not going to second guess the role that plays.
mfb
#10
Nov9-12, 07:58 AM
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There was some recent work to reduce the required energy - to something which is "just" an engineering problem, you don't need to fuse the whole solar system to make it work. In a science-fiction setting, it is no problem to assume that this became real.
onomatomanic
#11
Nov9-12, 11:43 AM
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Quote Quote by Simon Bridge View Post
[...] may be interesting to associate historic astronomical events to early experiments with the drive in small ships [...]
I agree, that would make for a lovely premise. A bit like the "pyramids must have been built by ancient visitors from outer space" nonsense, but translated to outer space itself, which makes it a good bit less nonsensical.
Simon Bridge
#12
Nov9-12, 07:22 PM
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Hmmm... a ring of exotic matter flipping a spacecraft between the stars reminds me of the "Torus Drive" from Elite and Oolite.
Quote Quote by mfb View Post
There was some recent work to reduce the required energy - to something which is "just" an engineering problem, you don't need to fuse the whole solar system to make it work. In a science-fiction setting, it is no problem to assume that this became real.
So you need smaller amounts of unobtainium?

"...the warp drive could be powered by a mass about the size of a spacecraft like the Voyager 1 probe NASA launched in 1977."
... that would be a mere 2x10^11 Joules - 50megatonnes TNT - in mass-energy yet, that's better: fair enough. Though they don't tell you the mass-ratios. How big is that craft? How long would this be for?
Note - the Icarus Project (context is everything) is about unmanned probes, soooo ... kilograms of sensors? Have not found anything on their site involving this sort of drive ... but I did find Dr. Eric W. Davis on New Light-Speed Breaking Science that could help.
LPV man
#13
Nov10-12, 01:34 AM
P: 3
I think astronomers and such would less interested in how much energy has been released by the event and be more concerned with the amount of material that will begin to in fall into the inner system
Simon Bridge
#14
Nov10-12, 02:53 AM
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Welcome to PF, LPV man;
Astronomers are generally interested in the energetics of an event they see ... and it is important if you are worried about how much material is infalling. Mind you, with the bigger number calculations (above) they'd be too busy vaporizing to worry about anything much :)


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