Black hole drive in the film Event Horizon

[Cody Richeson]

Black hole drive in the film "Event Horizon"

Cheesy movie, right? A lot of fun though. For those who don't know, there is a starship in the film called the Event Horizon, which utilizes an artificial black hole drive/engine in order to allow it to fold space, although it's probably more accurate to say that it's an artificial worm hole. Two questions:

1) Would this actually work? Or would the artificial worm hole have to be large enough for the entire ship to fit through? In the movie it's only about the size of a car.

2) Would it be more efficient if the source of power were an artificial sun, instead? I seem to remember reading somewhere about a fictional starship that used such an engine.

 

[soothsayer]

1) From what I understand, you can theoretically construct a wormhole in General Relativity, but it could not be achieved by creating a black hole. Everything we know about black holes tells us they are one way, dead end streets. As for size constrictions, I believe that the wormhole being depicted in the movie would realistically tear the ship to pieces. It's hard to get a grasp of the relativistic effects at play in a wormhole.

2) Would it be more efficient than...what? Would a star drive (huge fusion reactor) be more efficient than a wormhole drive? Or would a star drive be a more efficient source of energy for creating a wormhole?

In general, it requires astounding amounts of power to "fold" space. Probably more than is contained in the whole universe, but some counts I have read about Alcubierre drives. Even a star's worth of energy would not succeed in creating a wormhole.

 

[JesseM]

In general, it requires astounding amounts of power to "fold" space. Probably more than is contained in the whole universe, but some counts I have read about Alcubierre drives. Even a star's worth of energy would not succeed in creating a wormhole.

I don't think anyone really knows of a process that would create a wormhole from scratch--such a thing would involve changing the topology of space, which AFAIK isn't possible in general relativity though there are reasons to think it would be possible in a theory of quantum gravity (we don't have a full-fledged theory of quantum gravity but there are some works-in progress, especially string theory and loop quantum gravity). So, I don't think one can say with much confidence how much energy would be needed. On the other hand, the energy needed to keep an already-existing wormhole open and stable could theoretically be reasonably small, see this paper:

http://arxiv.org/abs/gr-qc/0301003

 

[PAllen]

I don't think anyone really knows of a process that would create a wormhole from scratch--such a thing would involve changing the topology of space, which AFAIK isn't possible in general relativity though there are reasons to think it would be possible in a theory of quantum gravity (we don't have a full-fledged theory of quantum gravity but there are some works-in progress, especially string theory and loop quantum gravity). So, I don't think one can say with much confidence how much energy would be needed. On the other hand, the energy needed to keep an already-existing wormhole open and stable could theoretically be reasonably small, see this paper:

http://arxiv.org/abs/gr-qc/0301003

Of course, that is not a small amount of ordinary energy, but a small amount of 'exotic matter'. Does anyone have a recipe for it?

 

[PAllen]

I don't think anyone really knows of a process that would create a wormhole from scratch--such a thing would involve changing the topology of space, which AFAIK isn't possible in general relativity

Maybe this statement should be weakened?:

http://arxiv.org/abs/0811.2962

 

[JesseM]

Of course, that is not a small amount of ordinary energy, but a small amount of 'exotic matter'. Does anyone have a recipe for it?

It's thought that the energy density between parallel plates in the Casimir effect is negative, so it's been proposed that this effect might satisfy the conditions needed to hold open a wormhole. See Wormholes, Time Machines, and the Weak Energy Condition, especially the paragraph on p. 2 that begins 'The following model explores the use of the "Casimir vacuum" (a quantum state of the electromagnetic field that violates the unaveraged weak energy condition) to support a wormhole'. The Raycahudhuri's theorem and exotic matter section of the wiki "wormhole" article has a little more discussion of the subtleties of which energy conditions would need to be violated (with links to papers), but the upshot seems to be that at present it's still at least plausible (though not certain) that the Casimir vacuum could qualify as the kind of "exotic matter" needed.

 

[JesseM]

Maybe this statement should be weakened?:

http://arxiv.org/abs/0811.2962

Ah, interesting. Well, if anyone here can actually follow this paper, I'd be curious to know whether the spacetime they give is the unique maximally extended spacetime that satisfies the initial conditions before the wormhole appears, or if there might be other solutions with the same initial conditions where no wormhole forms.

 

[PAllen]

It's thought that the energy density between parallel plates in the Casimir effect is negative, so it's been proposed that this effect might satisfy the conditions needed to hold open a wormhole. See Wormholes, Time Machines, and the Weak Energy Condition, especially the paragraph on p. 2 that begins 'The following model explores the use of the "Casimir vacuum" (a quantum state of the electromagnetic field that violates the unaveraged weak energy condition) to support a wormhole'. The Raycahudhuri's theorem and exotic matter section of the wiki "wormhole" article has a little more discussion of the subtleties of which energy conditions would need to be violated (with links to papers), but the upshot seems to be that at present it's still at least plausible (though not certain) that the Casimir vacuum could qualify as the kind of "exotic matter" needed.

That's what I was wondering. Thanks for the additional information.

 

[PAllen]

Ah, interesting. Well, if anyone here can actually follow this paper, I'd be curious to know whether the spacetime they give is the unique maximally extended spacetime that satisfies the initial conditions before the wormhole appears, or if there might be other solutions with the same initial conditions where no wormhole forms.

I didn't have the impression they used any stated initial conditions (e.g. in the ADM formalism sense). Their claim, instead, seems to be: here is a manifold with a non-eternal worm hole that is valid GR solution. [edit: wait, as I read more, they do worry about initial data in some sense, but I am not clear what sense.]

 

[JesseM]

I didn't have the impression they used any stated initial conditions (e.g. in the ADM formalism sense). Their claim, instead, seems to be: here is a manifold with a non-eternal worm hole that is valid GR solution. [edit: wait, as I read more, they do worry about initial data in some sense, but I am not clear what sense.]

Even if they didn't formulate it that way, I wonder if it would be possible to foliate the spacetime into a stack of spacelike hypersurfaces (possible for any "globally hyperbolic" spacetime I believe), such that in earlier ones there is no wormhole and in later ones there is. If it is, then it might be possible to imagine a "sufficiently advanced civilization" manipulating the matter fields to closely match the initial conditions in this solution, then let it evolve naturally to create a wormhole--though for this to plausibly work if would also have to be the unique extension of the initial conditions rather than just a weird possibility created by "gluing" (like the simple case of a Minkowski spacetime where two spacelike hypersurfaces are glued together so the time dimension "loops around"), which is why I asked the earlier question about this.

 

[pervect]

Maybe this statement should be weakened?:

http://arxiv.org/abs/0811.2962

My recollection is that it requires a time machine to form a wormhole in classical GR. The reference I read this in is Kip Thorne's book https://www.amazon.com/dp/0393312763/?tag=pfamazon01-20 pg 597.

Thorne refers to a 1967 paper by Geroch to justify this claim, http://jmp.aip.org/resource/1/jmapaq/v8/i4/p782_s1?isAuthorized=no

 

[PAllen]

Even if they didn't formulate it that way, I wonder if it would be possible to foliate the spacetime into a stack of spacelike hypersurfaces (possible for any "globally hyperbolic" spacetime I believe), such that in earlier ones there is no wormhole and in later ones there is. If it is, then it might be possible to imagine a "sufficiently advanced civilization" manipulating the matter fields to closely match the initial conditions in this solution, then let it evolve naturally to create a wormhole--though for this to plausibly work if would also have to be the unique extension of the initial conditions rather than just a weird possibility created by "gluing" (like the simple case of a Minkowski spacetime where two spacelike hypersurfaces are glued together so the time dimension "loops around"), which is why I asked the earlier question about this.

My reference (which was published in Phys.Rev D):

1) Claims exactly what you describe; some complete hypersurfaces have the wormhole, some don't. They describe this as a key difference from many earlier attempts.

2) [Re: Pervect's post] They mention Geroch's proof, but claim their weak singularity gets around it. In fact, they use Geroch's proof to argue that some earlier claims singularity free formation must be false because of this. They then state, these earlier claims failed in one of two way:

- the wormhole really was eternal
- or there really was a singularity, but the prior authors missed it.

 

[solar71]

I really liked event horizon. It scared the crap out of me.
Cool premiss.

 

[DHF]

It was a horror movie with a sci-fi window dressing so I try give it a wide berth however, I will say the concept of the movie seemed rather skewed. If humanity had some breakthrough that allowed them to build or harness black holes, wouldn't the logical step be to use this power source in more conventional means rather then using it to create a wormhole? if they had access to such an unbelievable amount of power I would think they would have started off using this thing to power entire cities. Even when it came to star travel wouldn't it make more sense to use such incredible power to move a ship in a more conventional sense? ie. if they used the black hole to produce kinetic energy they could move their ship at a large fraction of the speed of light and cross the entire solar system in a matter of hours rather then months or years.

Then again this is all orbiting the impossibility that a mid 21st century society could create a black hole. one would think you would have invested far more energy into creating the thing then you could ever hope to get out of it.

Right, horror movie...ok taking a deep breath now.

 

[Kepler20f]

I really liked event horizon. It scared the crap out of me.
Cool premiss.

Me too. I was in my late 20s at the time, watched it alone at home, had to sleep with the lights on!

 

[Finthefox]

I've only recently watch Event Horizon (thanks to netflix and being bored) - I have to say the concept of the engine was pretty neat, even if the movie scared my pants off. Or maybe that is just my excuse for being lazy in my underwear and watching netflix all weekend. Either way, still a neat concept!