Dirt Cheap Torchships?

[Johnny1A.2]

Originally Posted by acrosome

So, I've given up on the Alcubierre drive. I'm just going to use a more conventional (Lorentzian?) wormhole network for my FTL campaign. (And yes I'm going to make it branching without loops, to preserve causality.)

So now, to meet my campaign design goals, I need really cheap and really fast STL travel within systems once a ship pops out of the wormhole way out at the edge of the system. So I remembered this discussion from a few years ago and... let's discuss Visser wormholes.

So, a Visser wormhole is flat, not spherical, and can be made using (sort of) zero energy. They can also be made so that any matter that passes through them has its chirality flipped.

I'll let that sink in for a bit. Because you're probably not thinking big enough.

Yes, that means that your amino acids flip from left-handed to right-handed. Which is weird enough. But stuff all the way down to the subatomic level has it's chirality flipped. Things like spin.

Which means that you put matter in and get antimatter out. On demand. Sounds handy, doesn't it?

So imagine a drive based upon a short microscopic chirality-flipping Visser wormhole. You can use almost anything you want as reaction mass while feeding tiny amounts of it through the wormhole to interact with the remass in some sort of nozzle, and poof you have an Antimatter Plasma Torch from Spaceships 1 p. 23. (Or at least the Antimatter Plasma Rocket.) But importantly the antimatter is dirt cheap so you aren't paying those exorbitant fuel prices. Instead of $12,000,000/ton for antimatter-boosted hydrogen you just buy hydrogen at $2,000/ton, or heck water at $20/ton. It also works great with ammonia, methane, or about anything else you care to throw out the back of your rocket. (It wouldn't work with rock powder, since the particles would be too big. But you could still just feed hydrogen through the wormhole, I guess.)

Another benefit is that your torch engine makes the antimatter on demand so there are no tanks of highly explosive antimatter sitting around. I thus don't think it would count as an "explosive system" in GURPS terms.

So, is this at all plausible technobabble? I like it because I'm a believer that good science fiction only breaks one physical law and then keeps it consistent. So, my one break is easy wormhole production. Other implications are a society with ludicrously cheap and abundant energy, so I have to think that through, too.

Do your societies fight wars? Because ludicrously cheap, abundant antimatter and wars tends to produce total destruction. In some ways AM weapons are more tempting to use than conventional nukes, because they are in principle easily scalable and radiation effects are not necessarily as severe. At the other extreme, plentiful cheap antimatter makes world-wrecker bombs, E.E. Smith style, fairly easy to make.

[lwcamp]

Originally Posted by Flyndaran

Would they collapse from use or from merely existing?
I'm imagining ships only rarely getting "too close", but avoiding their use until later and separated.

The mere fact that a wormhole connection exists provides a pathway for information, even if the com is not being used. This allows closed light-like loops to form, which destroys the wormhole (and thus breaking the com).

Luke

[Flyndaran]

I felt so, but feelings mean little when dealing with physics. Thanks.

[Johnny1A.2]

Originally Posted by lwcamp

None that I have been able to identify. Physics is local (or at least the general relativity part of physics is) so the Visser wormhole would treat the space-time of the Lorentzian wormhole just like any other space-time and go along happily. The causality-isses with time lag and what not will be handled automatically with the small wormhole goes through the larger, so you shouldn't get any unexpected time loops that way.

Luke

Can the openings of the wormhole be of different sizes in the Visser case? If so, what if anything happens if you feed one end of the wormhole into the other?

[Anthony]

Originally Posted by Johnny1A.2

Can the openings of the wormhole be of different sizes in the Visser case? If so, what if anything happens if you feed one end of the wormhole into the other?

Feedback loop will generally destroy them if they get too close together.

[VonKatzen]

Much of Atomic Rockets is dedicated to why this stuff makes no sense. I suggest that it can be used as a technobabble explanation for cheap propulsion, but will almost invariably collapse upon serious examination.

As for Photons and "anti-Photons" the theory of why they're the same is because you can flip all their fundamental properties and end up with an exact neutralization - it doesn't matter which way you turn them, they're still just photons. It's like multiplying an negative by a negative while you multiply positives by negatives. The end result is indistinguishable from the initial conditions, you just invert two completely interchangeable integers. Also, photons just don't have many of the properties of matter so there's nothing to invert in these cases (unlike a neutron).

This Ars Technica post is relevant. Basically, according to relativity wormholes (if at all possible) would exist for less time than any chronologically enduring entity could possible observe. Basically, you might be able to throw a black hole through a wormhole but that's it. And that's only under certain theories about black holes. The only other alternative seems to be negative energy density, which would be an invulnerable super-material which we have no reason to think might even exist and can not so far formulate any possible situation that would produce it.

Personally I tend to think that interstellar travel (other than perhaps infectious machine ark ships) is basically magical nonsense and would be totally useless if possible because the tech and energy involved would make bothering to travel the stars utterly pointless as you'd be a galaxy-forging god by that point. Traveling through different parallel realities may even be more plausible than interstellar travel.

Trying to give reasonable engineering explanations for these things is like trying to explain magic wands. They're a narrative convenience, not a rational plot element. For that matter 90% of science fiction plots could take place in the Sol system with minimal alteration and be 10x less outlandish for it. While some settings/scenarios require interstellar travel most of them actually don't, it's more of a trope or a habit than a real function of the narrative. In fact a majority of science fiction could be rewritten to take place in the 1950s on Earth and actually make more sense for it. If you're trying to come up with a rational space fiction then why not just start with the enormous series of highly divergent bodies within the Sol system and all the possibilities of technology that don't violate causality? If you're more interested in setting aesthetics why bother trying to rationalize what is basically a 'scene fade' device?

The point isn't which option you take but rather why are you trying to make sense of wormhole technology either way? It seems like a lot of effort to go through for a game when it's just going to be a couple of numbers in practice, and as even the math-games of theoretical physics can't reach a consensus on whether it's even possible in purely abstract sense it's pretty much foredoomed to end in failure. I don't know how many questions of theoretical physics have been solved on the SJ Forums but I imagine not many. Wormholes are right up there with time travel as a TL^ entity, something that only 'works' if you leave half the equations out and still doesn't make sense because you'd have to detonate a galaxy or something to make one.

Basically, assign some particular problems and advantages to the technology, pick your numbers out, and call it good.

[Flyndaran]

Large scale interstellar travel within a single human lifetime is superscience.
But A.I. transit in a thousand years would just be extremely difficult.

[thrash]

Originally Posted by lwcamp

Note that the thin shell wormhole is defined by "Minkowski surgery" - cutting up Minkowski (flat) space-time.

Asymptotically flat, isn't it? "By construction, it is clear that the resulting spacetime is everywhere Riemann flat except possibly at the throat." (p. 165, emphasis mine) The 1995 book assumes that a traverseable wormhole requires equal amounts of positive and negative matter, hence the total "mass" is zero. Visser's 2003 paper, "Traversable wormholes with arbitrarily small energy condition violations," however, shows that the exotic matter can be confined to just the inflexion points in the metric. If I understand it correctly, the overall shape of the wormhole is still defined by the positive matter, hence a large, positive mass remains.

[lwcamp]

Originally Posted by Johnny1A.2

Can the openings of the wormhole be of different sizes in the Visser case? If so, what if anything happens if you feed one end of the wormhole into the other?

For the Visser wormhole, the very construction of the argument prevents them from being different sizes. You just take two prisms of space-time with the same cross section (in some given set of reference frames), remove the space-time inside, and identify their edges to the the same points in space-time. Relativistic length contraction can alter the shape somewhat to how you would measure it in your reference frame, but that's about it (and that won't let you get one through the other).

Luke

[lwcamp]

Originally Posted by thrash

Asymptotically flat, isn't it? "By construction, it is clear that the resulting spacetime is everywhere Riemann flat except possibly at the throat." (p. 165, emphasis mine) The 1995 book assumes that a traverseable wormhole requires equal amounts of positive and negative matter, hence the total "mass" is zero. Visser's 2003 paper, "Traversable wormholes with arbitrarily small energy condition violations," however, shows that the exotic matter can be confined to just the inflexion points in the metric. If I understand it correctly, the overall shape of the wormhole is still defined by the positive matter, hence a large, positive mass remains.

It is only asymptotically flat in the sense that you have regions of extremely high curvature right at the wormhole, but it is exactly flat everywhere else. To quote from Visser's book

Originally Posted by Matt Visser

15.1.1 Minkowski Surgery

The models of interest in this section can be very easily described. The basic idea is to take two ordinary flat universes and use surgical cut and paste techniques to join them together in a suitably simple way. These models are notable both because the analysis is not limited to spherical symmetry, and because it is possible to in some sense minimize the use of exotic matter. In particular, it is possible for a traveler to traverse such a wormhole without passing through a region of exotic matter [261].

Mathematically: Consider the following construction. Take two copies of flat Minkowski space, and remove from each identical regions of the form ...

(emphasis not mine). Where I stopped because it is hard to reproduce script and Greek letters and other mathematical markup using the available methods in this forum. So take any arbitrary closed surface around the wormhole end and use Gauss's law to measure the net energy (mass) inside. Because the space-time is flat, you will get zero net energy.

Luke