Warp Drive Question

[Junghalli]

In my own universe I use a form of warp drive that is somewhat similar (but not identacle) to an Alcubierre drive. Basically it bends spacetime around the ship to make the trip artificially "shorter".
So, for those of you who are knowledgeable about physics, what effect would this have on sensors and communications of the ship? Would you still be able to see outside? Would radar stop working? How would passive sensors be effected?

[Admiral Valdemar]

Sensors would not work because you are going FTL for starters, then there's the whole warping of space thing which tends to ruin measurements. The big problem with the Alcubierre drive (apart from it being impossibly power hungry) is that you cannot see where you are going for rather obvious reasons. This means flying from here to the nearest star could be a real trip for disaster if you don't make some magical new sensor suite that uses tachyons or something similarly unknown to us at present that doesn't rely on subluminal or lightspeed velocities.

[Junghalli]

Sensors would not work because you are going FTL for starters, then there's the whole warping of space thing which tends to ruin measurements. The big problem with the Alcubierre drive (apart from it being impossibly power hungry) is that you cannot see where you are going for rather obvious reasons. This means flying from here to the nearest star could be a real trip for disaster if you don't make some magical new sensor suite that uses tachyons or something similarly unknown to us at present that doesn't rely on subluminal or lightspeed velocities.

So I was right, that's what I thought originally. I started thinking about how red/blue-shifting would work with such a thing and eventually came to the conclusion that it wouldn't get through the warp bubble, but I wanted to double-check.
As for navigation it's done by dead reckoning. You calculate the amount of time it should take you to get to the destination, point the ship at the correct star, and program the engine to shut off when the timer winds down. Not very reliable but it works.
Communications is still possible, using a tachyon radio.

[Admiral Valdemar]

I take it then that you also have some form of navigational deflector, as it were. The risk of hitting a hydrogen atom at that speed is bad enough. Hitting a rogue comet now on your charts would ruin your day without some form of shielding.

Unless this is real hard SF, just gloss over a lot of the details. The art of good SF is usually in merging a good plot and characters with some fantastic future setting with technology that need only be mentioned, not dissected by a mid-story thesis on how we overcame relativity's restrictions.

[Junghalli]

I take it then that you also have some form of navigational deflector, as it were. The risk of hitting a hydrogen atom at that speed is bad enough. Hitting a rogue comet now on your charts would ruin your day without some form of shielding.

True, if you hit anything you're dead, but interstellar space is empty enough that that's not much of a risk. Even the biggest ship is a mighty small target to meteors. It's probably safer than driving. And the warp field brushes aside little things like dust and gas particles.

Unless this is real hard SF, just gloss over a lot of the details. The art of good SF is usually in merging a good plot and characters with some fantastic future setting with technology that need only be mentioned, not dissected by a mid-story thesis on how we overcame relativity's restrictions.

Generally I don't go into Treknobabble-style discussions on the tech, but whether or not sensors would work makes a huge difference to navigation. You also want to get some basic ground rules for how your tech works, or it becomes a plot device.

[Wyrm]

I take it then that you also have some form of navigational deflector, as it were. The risk of hitting a hydrogen atom at that speed is bad enough. Hitting a rogue comet now on your charts would ruin your day without some form of shielding.

If you can't detect anything before you, then nothing before you can hit you. An object can't outrace its own light cones, remember? (The drive allows you to go globally FTL by dragging your light cones with you.) Therefore, if the light cones of the object cannot reach you, neither can the object.

[General Trelane (Retired)]

Or another way of saying it is that, since the drive warps space-time around the vessels, and objects outside exist in 'normal' space-time, then those objects are, by definition, bent around the vessel, so they can't hit it. Navigational deflectors wouldn't even be necessary. In fact, I'd suggest that such a warp drive acts as a natural cloak. . .in both directions.

As for hitting hydrogen atoms (assuming they don't get bent around the vessel), two things:

1. Interstellar space is not a perfect vacuum, so the chances of this happening are a given (streamlining a high-sublight spacecraft is a benefit even if it won't ever operate in atmospheres).

2. If 'movement' is accomplished by warping space-time, is the vessel really moving? In other words, would such hydrogen atoms necessarily have high kinetic energy relative to the vessel? I would argue 'no' emphatically. Drop the warp bubble, and the vessel immediately slips into 'normal' space. I argue the same regarding Trekkie claims for adding high KE to warhead yield for warp-speed torpedoes--there's no basis from which to make such a claim. Besides, (1/2)mv^2 just doesn't cut it when m is infinite.

In the end, though, it's your unvierse, so you can make things work however you want. But I'd agree that some sort of new 'technology' would be required in order to sense things outside the warp bubble. In fact, it might me interesting to have some forces with such technology and others without; you needn't have a consistent technological baseline for everybody.

I do agree with your intentions--it makes for a better (more consistent) story (or game?) if you have thought out the basics of your fictional technology before you start.

[Prozac the Robert]

I wonder how smoothly is space warped. If it were done right, maybe you could even travel through a planet. On the other hand, maybe you'd rip it to shreds, or just overload your warp field some how, and explode.

Large objects might stop it anyway, expanding the space between bit's of a planet would probably require more energy than between empty space due to gravity and whatnot.

More wondering how far you can extend the idea of everything being warped around a ship. Does it extend to weapons? Activating your drive would imediately end any engagement, which could make it hard to come up with interesting battles.

Hmm, unless you used space warping weapons. They could cause damage by breaking things apart, and also rip through a warp bubble preventing escape.

If warp bubbles took time to form, or at least time to get moving, then trying to run away while under fire would be somewhat suicidal.

[CoyoteNature]

Since you are in effect creating small localized bubbles of space time, couldn't you use something like quantum entanglement as a communication method, that or natural micowormholes at the Planck scale. Both of these might allow you to communicate or use sensors outside of the bubble.

And yes I know in the real world you probably couldn't use entanglment to communicate, and natural wormholes would have to be expanded quite a bit if you wanted to get a message through(if they exist at all), but then tachyons have many of the same problems.

Um if I were Trekkie, why not just accelerate in normal space say a asteroid or comet, use the warp drive thingy to refuel the engine pushing the object, once you have real space velocity of high C, warp it to any place you need a kinetic planetkiller.

[drachefly]

Using quantum entanglement for communication is about as far removed from reality as using a rigid rod stretched from here to Pluto for superluminal communication.

[CoyoteNature]

As opposed to using tachyons(which only exist theoretically) or warp drive using exotic matter, wormholes, etc. thats realistic I suppose.

[GrandMasterTerwynn]

Sensors would not work because you are going FTL for starters, then there's the whole warping of space thing which tends to ruin measurements. The big problem with the Alcubierre drive (apart from it being impossibly power hungry) is that you cannot see where you are going for rather obvious reasons. This means flying from here to the nearest star could be a real trip for disaster if you don't make some magical new sensor suite that uses tachyons or something similarly unknown to us at present that doesn't rely on subluminal or lightspeed velocities.

So I was right, that's what I thought originally. I started thinking about how red/blue-shifting would work with such a thing and eventually came to the conclusion that it wouldn't get through the warp bubble, but I wanted to double-check.
As for navigation it's done by dead reckoning. You calculate the amount of time it should take you to get to the destination, point the ship at the correct star, and program the engine to shut off when the timer winds down. Not very reliable but it works.
Communications is still possible, using a tachyon radio.

You wouldn't want to dead-reckon your way around space when you're effectively blind while you're travelling. You could encounter a cloud of dust or gas you failed to notice, or a dark-matter halo that would do interesting things to you if you ran into it at full speed.

You'd either have to stop every so often and deploy your telescopes for a good, long look at the space ahead of you . . . or, if you like throwing around energy, you could simply spawn thousands of microscopic wormholes ahead of you. Each of them would capture a few photons and transport them inside your warp-field. Of course, you're probably not going to be able to predict exactly how long each wormhole is, or where its end outside your warp-field winds up, so the resulting sensor picture is going to be really low-resolution, and really high-noise, but it might just save you a few telescope re-orientation stops.

[CoyoteNature]

On further thought I think that as long as you are in the universe using your drive, you might try and use measurements of the disruption of your own field by natural warps in the universe(i.e. stars planets, etc.).

Since you are using negative energy, it probably having a negative warp in space time relative to positive warp(normal matter), maybe you could use the disruption of the negative warp by the positive warp of normal matter.

Or you could use many throwaway unmanned probes who would go ahead of the ship jump into normal space, then send a message back using some sort of warp message buoy.


That or you might simply have to jump out into normal space periodically and take information on the local neighborhood, what obstacles are there, etc.

[Admiral Valdemar]

If you can't detect anything before you, then nothing before you can hit you. An object can't outrace its own light cones, remember? (The drive allows you to go globally FTL by dragging your light cones with you.) Therefore, if the light cones of the object cannot reach you, neither can the object.

That's like saying because you can't see the parked car at night when driving, you won't hit it. We can slow light down artificially, but it doesn't mean the object that light is reflecting off won't appear faster if you rush towards it.If the object exists in real space, you will hit it. Unless, of course, this drive warps everything around you as you exist in a bubble of hyperspace. If it is simply the equivalent of an escalator - moving the space you occupy by compression and expansion - then you will come across something that gets in that field and simply hits you anyway given it too will be compressed and expanded along with your ship. In other words, you can't avoid an object unless you physically aren't on that plane. Warping the space still means the objects exist.

[Junghalli]

You wouldn't want to dead-reckon your way around space when you're effectively blind while you're travelling. You could encounter a cloud of dust or gas you failed to notice, or a dark-matter halo that would do interesting things to you if you ran into it at full speed.

The warp field itself brushes aside gas and dust as it moves, so that isn't a worry. Big things like asteroids will still kill you if you run into them, but space being pretty damn empty the risk is acceptable (your chances would be much less than the odds of having an auto accident on the open road probably).
For FTL comm I use a tachyon radio system than can communicate through the warp field but not terribly well, and it can't be used as a sensor.
Weapons definitely can't get through the warp field, even if targeting was possible. The sensor blindness warp causes makes using it tactically pretty much impossible. It's basically a carrier system; just a way for the ship to get between solar systems, and not good for much else.

You'd either have to stop every so often and deploy your telescopes for a good, long look at the space ahead of you

The ships stopping to take an occasional "sounding" would probably be a good idea, yeah. Especially for long voyages were errors in calculation and measurement can mean you miss your target by light years. Thanks.

Since you are using negative energy, it probably having a negative warp in space time relative to positive warp(normal matter), maybe you could use the disruption of the negative warp by the positive warp of normal matter.

Ugh, no negative energy. The warp drive (actually it's properly called a quantum distortion drive) uses... some other mechanism. A bit of handwavium there, but frankly I prefer that to negative energy; a concept which by all appearances AFAIK is unlikely to ever exist on anything but paper.

[Wyrm]

That's like saying because you can't see the parked car at night when driving, you won't hit it. We can slow light down artificially, but it doesn't mean the object that light is reflecting off won't appear faster if you rush towards it.

The situation you describe is far different. We can slow down light, but only by scattering it off of a medium. This causes the light to, on average, not travel on a null-ray from its source. This is the only way that you can get objects traveling faster than the local speed of light.

But here, the space may be distorted so the null-rays are all distorted, but light still travels on null-rays because it's in a vacuum! There's (almost) no matter to scatter the light and mess things up. In order to outrace its own light beams, the object has to cross that cone of null rays. Therefore, the object has to achieve spacelike motion at some point on its worldline, which it cannot do! Therefore, if the light from the object can't reach your spaceship, neither can the object. QED.

If the object exists in real space, you will hit it. Unless, of course, this drive warps everything around you as you exist in a bubble of hyperspace. If it is simply the equivalent of an escalator - moving the space you occupy by compression and expansion - then you will come across something that gets in that field and simply hits you anyway given it too will be compressed and expanded along with your ship. In other words, you can't avoid an object unless you physically aren't on that plane. Warping the space still means the objects exist.

And before that you will get a burst of lethal gamma rays as the light emitted by the object (and it will emit some EM radiation) is really blueshifted by the compressed spacetime up front, frying you and your little spaceship too. But, you see, that's a different problem! The light IS getting through that distortion!

[Admiral Valdemar]

Someone needs to clarify what this warp drive really is, because otherwise we're just talking about a whole load of possible outcomes from going FTL rather than what may actually happen. I always found it easier to just have wormhole travel and be done with it. Warping space or disconnecting from real-space is a whole new can of worms.

[Wyrm]

Now that I think about it, this sweep-aside effect implies that there is a region of spacetime where particles are being repelled from the centerline before the ship, and are pushed back to their rightful place after the ship. Or, to put it another way, you have a repelling (negative energy) region before you and an attracting (positive energy) region behind you -- an Alcubierre drive with the gearshift in reverse! In a hard SF work, the damn thing will go backwards! Even if you embed an Alcubierre drive going the right way inside, globally, it will still look like an Alcubierre drive going the other way!

The scheme used in the Alcubierre drive works is because the attraction/repulsion effect of a region works on other regions: the positive-energy region attracts the negative-energy region after it, and the negative-energy region repels the positive-energy region before it.

If you embed an Alcubierre drive going the right way inside this region, it is quickly destroyed. A negative-energy region between two positive-energy regions will stretch out and would likely be destroyed. More worrisome, a positive-energy region between two negative-energy regions would be compressed, maybe forming a black hole. EEK!

[Admiral Valdemar]

I had thought they'd rectified such an anomaly by bringing in the exotic matter and arranging it in such a way as to get the desired compression effect. The major pitfall was you can't see where you're going (assuming you got the negative energy and exotic matter first).

[Wyrm]

The exotic matter creates the expansion field, not the compression field. Exotic matter has a negative energy density, leading to expanding spacetime, and the pushing effect of the drive. Ordinary matter in sufficient quantity suffices for the positive energy density region, which is where spacetime contracts. (This is why real masses are attracted to each other, right?)

The real problem with the Alcubierre drive remains the same problem with the wormhole: you need exotic matter to create it, and no one knows where to get it or how to make it. If you can't make the drive, then whether you can see where you're going is rather moot anyway.

Anyway, the point of my post was that Junghalli was making a metric that would, rather than make the spaceship go forward, would actually make it go backward because it's precisely an Alcubierre metric in reverse. So, instead of going to the stars, the ship would mash into the space station behind it, and would then require a call to All-Space Insurance.

[Junghalli]

Someone needs to clarify what this warp drive really is, because otherwise we're just talking about a whole load of possible outcomes from going FTL rather than what may actually happen. I always found it easier to just have wormhole travel and be done with it. Warping space or disconnecting from real-space is a whole new can of worms.

The quantum distortion drive uses quantum turbines (yes, they are pure technobabble, I have no idea how they'd work) to distort space. The drive compresses spacetime in front of it to effectively "shorten" the trip, then pushes it along the sides of the ship to generate momentum (sort of a rowboat, with spacetime being the water). I imagine that anything caught in the field would probably first be drawn toward the ship like a vacuum cleaner by the compaction effect, then pushed to the side by the "rowboat" effect, so that's why gas and dust doesn't hit the ship.

[Wyrm]

The quantum distortion drive uses quantum turbines (yes, they are pure technobabble, I have no idea how they'd work) to distort space. The drive compresses spacetime in front of it to effectively "shorten" the trip, then pushes it along the sides of the ship to generate momentum (sort of a rowboat, with spacetime being the water). I imagine that anything caught in the field would probably first be drawn toward the ship like a vacuum cleaner by the compaction effect, then pushed to the side by the "rowboat" effect, so that's why gas and dust doesn't hit the ship.

So there's an avenue of escape in the middle of the forward compression field, and there's nothing in back restoring the distance. This really isn't like an Alcubierre drive, and your universe can't be strictly hard sci-fi and expect this contraption to work as an FTL drive. Something has to push the compression field forward (otherwise, you'll just crash into it, and that'll end your trip pretty quick), and in the Alcubierre drive this is the expansion field to the rear. Secondly, spacetime is not conserved and carries no momentum. Only stress-energy (embodied in particles) carry momentum, but that's subject to the laws of Special Relativity: no amount of momentum added will allow you to travel FTL.

Since the hard SF will not allow this drive to work, you're allowed to make other allowances to add sensors and communications by appealing to softer SF rules. This includes FTL sensor and communication suites.

[Junghalli]

So there's an avenue of escape in the middle of the forward compression field, and there's nothing in back restoring the distance. This really isn't like an Alcubierre drive, and your universe can't be strictly hard sci-fi and expect this contraption to work as an FTL drive. Something has to push the compression field forward (otherwise, you'll just crash into it, and that'll end your trip pretty quick), and in the Alcubierre drive this is the expansion field to the rear.

I was wondering about whether or not an expansion field would be necessary. Thanks.
So you've got a compaction field at the front and an expansion field at the back... would going through interstellar gas and dust pose problems? The real reason I thought up the "rowboat effect" was basically because I didn't want to have to deal with my ships getting blown up by stray dust particles.

Secondly, spacetime is not conserved and carries no momentum. Only stress-energy (embodied in particles) carry momentum, but that's subject to the laws of Special Relativity: no amount of momentum added will allow you to travel FTL.

I thought a bias drive or reactionless drive used spacetime as the working fluid?
OK, we can ditch the "rowboat" concept I guess.

Since the hard SF will not allow this drive to work, you're allowed to make other allowances to add sensors and communications by appealing to softer SF rules. This includes FTL sensor and communication suites.

Technically the system isn't really hard SF anyway because quantum turbines are pretty much pure technobabble. But thematically I actually rather like the idea of the ship being blind in FTL and forced to navigate by dead reckoning and occasional "soundings". I do have an FTL comm system, using tachyons.
Thanks for the help!

[Wyrm]

I was wondering about whether or not an expansion field would be necessary. Thanks.
So you've got a compaction field at the front and an expansion field at the back... would going through interstellar gas and dust pose problems? The real reason I thought up the "rowboat effect" was basically because I didn't want to have to deal with my ships getting blown up by stray dust particles.

That's easy. Make the little pocket the spaceship sits in pretty big. Inside the pocket, normal Special Relativity applies. Any offensive matter (ie, proton and electron stuff) can be ionized and tossed out back with magnetic fields. You'll need pretty hefty radiation shielding to have your crew survive the intense gamma radiation that comes from blueshifting of the radiation ahead of you, though.

By the way, the tidal forces at the front will basically tear up any extended object trying to get in. Really fine dust is probably all you have to contend with.

I thought a bias drive or reactionless drive used spacetime as the working fluid?

There's no working fluid in such a drive. The reason these drives work as FTL drives is because we're setting up a faster timelike connection between A and B, not trying to actually get around the light barrier through ridiculous acceleration. You don't get transfer of momentum because there is no acceleration. All the accelerometers remain stubbornly at 0 m/s^2. No acceleration, no momentum change in any reference frame that is initially comoving with you.

And that's your Relativity lesson for the day!

Technically the system isn't really hard SF anyway because quantum turbines are pretty much pure technobabble.

That's not really what makes SF hard or soft. Charles Scheffield's One Man's Universe, the principle source of energy for the McAndrew Balanced Drive is a doohicky that extracted the ambient vacuum energy, and the balancing disk itself was made out of some densified osmium alloy, both of which were justified with technobabble, but the story is considered hard SF. The difference between hard and soft SF can be summarized as the following: The Hard SF writer is permitted to foresee the automobile so provided he also foresees the traffic jam...

But thematically I actually rather like the idea of the ship being blind in FTL and forced to navigate by dead reckoning and occasional "soundings". I do have an FTL comm system, using tachyons.

...and you do! Congrats! A hard SF universe is born!

/me hands out cee-gars!

Light up, shriners!

[Junghalli]

That's easy. Make the little pocket the spaceship sits in pretty big. Inside the pocket, normal Special Relativity applies. Any offensive matter (ie, proton and electron stuff) can be ionized and tossed out back with magnetic fields.

So we're talking something sort of like a ramscoop but in reverse? Designed to push gas and dust toward the sides of the ship.
That shouldn't be too hard. Especially since it wouldn't have to extend over the outrageously huge area a ramscoop would; just keeping a hundred meters or so of clearance around the ship should be fine.

You'll need pretty hefty radiation shielding to have your crew survive the intense gamma radiation that comes from blueshifting of the radiation ahead of you, though.

I always wondered what would happen to radiation when it went through the warp field. Hmm, I guess the hull is going to have to be somewhat thick, and heavily impregnated with radiation-reflective materials (lead or something).
As a side point I take it that these spacecraft are probably going to have to be completely windowless, like submarines?

By the way, the tidal forces at the front will basically tear up any extended object trying to get in. Really fine dust is probably all you have to contend with.

Would that still be dangerous though?

And that's your Relativity lesson for the day!

Thanks.