Dirt Cheap Torchships?

[acrosome]

Originally Posted by lwcamp

Everything

As part of my single "making wormholes ain't that hard" breaking of physical law I was sort of assuming a means of producing a "virtual mass" to create and stabilize the wormholes. Because otherwise they're impossible at less than TL(absurd), whereas I'm aiming at TL10. But, again, in my vision this method requires flat space so there are no planetary-surface wormholes.

Also:

Originally Posted by lwcamp

Sure, maybe you can use your antimatter thrusters as the rocket that pushes the wormhole, but those thrusters don't have to be on the spacecraft. they can be left at home, shooting its exhaust through the wormhole. By local conservation of energy and momentum, the wormhole end out in space with the rocket exhaust shooting out of it acts like a rocket itself. So you have a wormhole opening out in space, and the engines and reactors and sensors and crew and whatnot are all safely back on their home planet.

How the heck does that work? That actually seems to violate conservation of momentum. Because presumably the rocket engine back home is under thrust from ejecting it's remass- even if it doesn't move because it's locked into some sort of cradle it's still feeling the force- but you say that the other end of the wormhole is also under thrust. So you basically just doubled the thrust you're getting for a given remass. And that's cheating. :)

[thrash]

Originally Posted by lwcamp

This gets kind of tricky. At the discontinuities of the edges that support the wormhole (and assuming negligible tension, and a planar shape), you require a linear energy density of -3.04E43 J/m, or -3.4e26 kg/m. That's a lot. But this wormhole is in flat space-time. This means it has no gravitational imprint on the surroundings. Someone floating next to it would feel no gravitational attraction. By the equivalence principle, this means that the wormhole mouth considered as a single object (rather than its constituent parts) has no net mass. Therefore, it would require no energy to create.

Cite? I think we're talking about different constructs.

I realize this is your area of expertise, but offhand I can't find anything in Visser's papers online or his book that describes what you're talking about. The traverseable wormholes in the literature I have access to are spherically symmetric and use an arbitrarily small amount of negative energy (and correspondingly large amount of regular mass-energy).

[lwcamp]

Originally Posted by acrosome

How the heck does that work? That actually seems to violate conservation of momentum. Because presumably the rocket engine back home is under thrust from ejecting it's remass- even if it doesn't move because it's locked into some sort of cradle it's still feeling the force- but you say that the other end of the wormhole is also under thrust. So you basically just doubled the thrust you're getting for a given remass. And that's cheating. :)

The rocket jet is shooting out of the wormhole end that is out in space. Say that the jet has a mass flow rate of m-dot, and is moving with a velocity v. Then the rate of change of momentum (the force) being added by the jet is m-dot * v. By conservation of momentum, the rate of change of momentum of the wormhole end in space most be - m-dot * v, and by conservation of energy the rate of change of its mass must be - m-dot. This just leads to the familiar Tsiolkovski rocket equation Delta-v = v ln(m_0/m_f) where m_0 is the initial mass of the wormhole before thrusting, and m_f is the final mass after thrusting. The wormhole itself is the rocket ship.

For this application, you can just ignore what is going on down on the ground. Sure, the engineers will need to take into account the forces produced by the rocket engine and on the groundside wormhole end and deal with it using proper bracing, but that's not the part that gets your other wormhole end out to where you want to go. There's no double thrust down on the ground, either - the rocket engine is getting pushed one way, the wormhole end is being pushed the other. Tie them together and neither is going anywhere since the forces exactly balance by Newton's third law of motion.

With a low enough mass projected wormhole, you can even move it around by shining a powerful laser through it, using the emerging beam of light as a photon rocket.

Luke

[lwcamp]

Originally Posted by thrash

Cite? I think we're talking about different constructs.

I realize this is your area of expertise, but offhand I can't find anything in Visser's papers online or his book that describes what you're talking about. The traverseable wormholes in the literature I have access to are spherically symmetric and use an arbitrarily small amount of negative energy (and correspondingly large amount of regular mass-energy).

Look in Lorentzian Wormholes: From Einstein to Hawking, by Matt Visser. Chapter 15 Thin Shells: Wormholes. Note that the thin shell wormhole is defined by "Minkowski surgery" - cutting up Minkowski (flat) space-time. The Visser wormhole described in Visser's original paper corresponds to the cubic wormhole and the dihedral wormhole mentioned in the next sections of the chapter as limits of the thin shell wormhole. Since, by definition, these wormholes are in flat Minkowski space-time, they cannot have any net mass, despite the extreme conditions holding them open.

Luke

[Anthony]

Originally Posted by lwcamp

Since, by definition, these wormholes are in flat Minkowski space-time, they cannot have any net mass, despite the extreme conditions holding them open.

So if you send spinning matter through them, the spin is reversed, there's nothing to absorb the difference, and we've broken conservation of angular momentum. Guess we don't actually need torch ships, it shouldn't be too hard to convert it into a reactionless thruster.

[Ulzgoroth]

Originally Posted by acrosome

As part of my single "making wormholes ain't that hard" breaking of physical law I was sort of assuming a means of producing a "virtual mass" to create and stabilize the wormholes. Because otherwise they're impossible at less than TL(absurd), whereas I'm aiming at TL10. But, again, in my vision this method requires flat space so there are no planetary-surface wormholes.

Even if you have to make them in space, would it be that hard to bring one down to planetside?

[Varyon]

Originally Posted by acrosome

Hmm. I really don't want FTL communications or an ansible. I'll have to think about that.

Is there any way to dictate that the small ship-board wormholes have some small maximum separation? You can't avoid FTL communications through the giant ship-transport wormholes, but there's a world of difference between radio through stationary wormholes and an ansible.

[lwcamp]

Originally Posted by Anthony

So if you send spinning matter through them, the spin is reversed, there's nothing to absorb the difference, and we've broken conservation of angular momentum. Guess we don't actually need torch ships, it shouldn't be too hard to convert it into a reactionless thruster.

Yeah, as I said, the Visser wormhole is an approximation. Although you can have massless stuff with angular momentum (circularly polarized light, for example).

Luke

[lwcamp]

Originally Posted by Varyon

Is there any way to dictate that the small ship-board wormholes have some small maximum separation? You can't avoid FTL communications through the giant ship-transport wormholes, but there's a world of difference between radio through stationary wormholes and an ansible.

The obvious limit is that you need to avoid creating closed light-like or time-like loops between multiple wormholes. If you only have one spacecraft exploring a new system this will not be a problem and you can put a communications wormhole on it to talk with the people back home, light years away. But if you have several spacecraft in a system, you are likely to get situations where you have incipient time machines as they all go back and forth, accumulating different levels of time lag between the wormhole ends. As soon as you are on the verge of creating a time machine, the weakest wormhole in the almost-time-machine loop will break. Eventually, you only end up with one spacecraft that has a communications wormhole (although with careful coordination of traffic, you might be able to get a few com-wormhole enabled spacecraft as long as they don't get too close to each other).

Luke

[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.