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The title really speaks for itself. Given what we know about Alcubierre drives (and yes, I know they're extremely hypothetical, but for this question let's just assume they can exist as we currently understand them), and assuming some "magical" method of instant communication across many light years of distance, how might interstellar warfare play out between two states or coalitions, relatively equivalent in power and technology, spanning across scores or hundreds of stars?

Assume that each state or coalition feels sufficiently threatened by the other that the complete annihilation of the other seems to be the only way to reliably secure the permanence of their own existence, and that both sides have established some kind of Dyson swarm around at least some of the stars they own. What might this war look like? Would there be mutually assured destruction or would it just drag on forever? Would combat between Alcubierre drive powered ships be plausible, or even possible? How might they go about attacking a star system? Would there be any reasonable way to defend against such an attack? Ultimately, what would be the overall nature of such a war?

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closed as too broad by StephenG, Confounded by beige fish., Mathaddict, Renan, elemtilas Apr 16 at 16:50

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ As written this is really far too broad, IMO. WB SE questions should be more specific and allow members to generate focused answers. $\endgroup$ – StephenG Apr 16 at 13:45
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    $\begingroup$ The question is too broad and many SF novels/series/films/franchises/etc with interstellar space-faring civilizations (e.g. Star Trek) already effectively have this (minus the Dyson swarm). $\endgroup$ – Danijel Apr 16 at 13:57
  • $\begingroup$ What would be their level of weapon's technology? Or are you planning on weaponising the A drive, if so how? Could you please narrow your question down to one clear question, at the moment you have several. $\endgroup$ – Confounded by beige fish. Apr 16 at 14:09
  • $\begingroup$ Please note that Alcubierre drive alone does not allow "free travel". Someone must "blaze" the trail at sublight speed. If we want "Star Wars" (or "Star Trek") style travel at will, more exotic entities (like Tachyons) would be required. $\endgroup$ – Alexander Apr 16 at 16:41
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If you have Alcubierre drives, then I assume you can also have Alcubierre Torpedoes. If you have instantaneous communication, then this means you probably also have some form of instantaneous "radar" that can track things moving faster than light. A beam or other particle beams may actually be too slow to shoot each other with, but torpedoes armed with Alcubierre drives could move fast enough to intercept a ship in warp; so, that may be your main viable weapon. A second viable weapon is that instant communication means you have a way of instantly transmitting some kind of power; so, you may be able to use that same technology to teleport a larger, more destructive burst of energy into an enemy's ship.

As for destroying your enemy's dyson structure, there is no need. Since ships will still have ways to shoot each other, whoever wins the war for space will have the same tactical advantage as destroying an enemy's air force in modern warfare. If you take away their ships, you can force them into submission by threat of orbital assault.

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  • $\begingroup$ Why does instantaneous communication mean you can track things moving faster than light? Or is it just like you assume because I have a Lamborghini I have a swimming pool? $\endgroup$ – Willk Apr 16 at 15:18
  • $\begingroup$ @Willk I'm guessing that to be able to instantaneously communicate with something, you probably need to know where it is, and to know where it is, you'd have to have some way to track it. Of course, you could instead hand-wave a quantum entanglement mainframe and route communications instantaneously through that, and then you'd have no need to track allies' locations to communicate. So yeah, I don't think you necessarily have to be able to track FTL travel to be able to communicate, but then you need something else to explain instantaneous communication. $\endgroup$ – MrSpudtastic Apr 16 at 15:43
  • $\begingroup$ @Willk, instantaneous communication across light years implies you can manipulate some manner of energy that interacts with the physical world at superluminal speeds. Since he does not define how his communication works, I said "probably", but if it's based on some manner of particle or wave like every other form of communication we use, then it should be able to be used for active scanning as well. $\endgroup$ – Nosajimiki Apr 16 at 17:58
  • $\begingroup$ I asked because I thought maybe the one implied the other in some way I did not know about - like FTL implies time travel. Not obvious to the unschooled but once someone walks you thru you can see why. $\endgroup$ – Willk Apr 16 at 18:37
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    $\begingroup$ @Willk It's more like assuming that if you have Radio, you will (eventually) develop Radar $\endgroup$ – Chronocidal Apr 17 at 15:37
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The thing about relativity is that FTL travel and communication implies travel and communication backwards in time unless very restricted in some fashion. The Alcubierre drive doesn't seem to have such a restriction, as it (as I understand it) will allow FTL travel in any direction and at any distance, and assuming that FTL communication is based on the same technology and is similarly unrestricted, this leads to all sorts of things like sending a message to your past self or traveling to the past and prevent yourself from leaving.

This derives from the central part of relativity that has to do with the transformation of space-time vectors (or four-vectors) between different frames of reference. A four-vector where the space component is larger than the time component is called spacelike. Any FTL travel or communication by its very nature connects its beginning and end with such a vector. For any spacelike four-vector with a positive time component, you can find a frame of reference where the time component is zero or negative, with the latter implying arrival before departure. Since all frames of reference are considered equal, what is possible in one is also possible in all others. Hence, FTL travel and communication implies that a spaceship or message can arrive before it is sent.

Now, this does in itself imply any paradox, since at arrival, it would be impossible to route the spaceship or message ack to its point of origin before it departed with any non-FTL means. However, all directions in any frame of reference are equal, so if you can travel from A to B and arrive before you started, you can also then travel from B to A and arrive before you started, hence arriving at A before you originally departed.

The only thing that can prevent this sort of time travel is if FTL travel and communication are restricted in some manner; i.e., you cannot freely deside where (and when) to send your message or spaceship. This could e.g. be because FTL travel and communication is only possible through an established network of wormholes (which would shatter due to feedback loops of Cauchy energy if the system allowed a loop that leads back in time; a closed timelike curve). This is not the case for an Alcubierre drive or any other means of FTL allowing open travel options, whether through a hyperspace or folding space or whatever. This unfortunate fact is generally ignored by space opera writers.

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    $\begingroup$ Since he mentions Alcubierre drives, I think it is assumed he is using a model of timespace where this is not a problem. Remember, no one really knows what happens when you exceed the speed of light, and time travel is only one of many possible theories. $\endgroup$ – Nosajimiki Apr 16 at 14:55
  • $\begingroup$ To my knowledge, the Alcubierre drive doesn't make any assumptions of a spacetime structure that makes time travel impossible. And the Lorentz transformation of time and space coordinates is very basic to special relativity. I don't think you can get around that expect by a compleme overhall of relativity. $\endgroup$ – Klaus Æ. Mogensen Apr 17 at 7:51
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    $\begingroup$ I believe that @Nosajimiki wants to say that if the physics differs from the known physics to allow Alcubierre drives, it might also differ from the known physics by introducing Lorentz violation which manifests itself when using and Alcubierre drive. One has to pick Lorentz violation or possibility of CTCs (or both) when introducing any kind of FTL travel. $\endgroup$ – Danijel Apr 17 at 8:23
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The Alcubierre drive is itself a solar system destroyer.

https://www.extremetech.com/extreme/140635-the-downside-of-warp-drives-annihilating-whole-star-systems-when-you-arrive

. When activated, space behind an Alcubierre drive expands while contracting in front. The ship itself hums along in a stable pocket, or bubble in space. It turns out the bubble is the problem.

As your faster-than-light ship sails through the cosmos, it’s not alone. Although we often think of space as empty, there are loads of high-energy particles shooting through the void. The University of Sydney research indicates that these particles are liable to get swept up in the craft’s warp field and remain trapped in the stable bubble. ... The longer the journey lasts, the more of these dangerous particles build up....

The instant the Alcubierre drive is disengaged, the space-time gradient that allows it to effectively move faster than light goes away. All the energetic particles trapped during the journey have to go somewhere, and the researchers believe they would be blasted outward in a cone directly in front of the ship. Anyone or anything waiting for you at the other end of your trip would be destroyed.

Because of a funny little quirk of relativity, there is no upper limit to the amount of energy a Alcubierre drive could pick up. A long trip could vaporize entire planets upon your arrival. The researchers are beginning a new round of number crunching to see how bad the problem is. It’s possible the deadly particle beam could be projected in all directions, making Alcubierre drives unworkable. That spiffy warp ship might make a better weapon than method of transportation.

It has been proposed that peaceful travelers using these drives come out of warp at a safe distance from things that might get annihilated by the plume of particles. Or maybe stop periodically to dislodge accumulated particles in deep space.

If you want your drive to be a weapon, "no upper limit to the amount of energy" is pretty big. Turn their star into supernova with one torpedo. You can do it fast, because these drives are fast. There is no way I can think of to detect an incoming Alcubierre warp bubble.

I can think of only one way to block a blast of incoming particles from a Alcubierre torpedo coming out of warp. I would like to see what readers think of. Encrypt comments with your ideas using ROT13 please so everyone can have fun! https://en.wikipedia.org/wiki/ROT13

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    $\begingroup$ Space only has about 1000 molecules per cubic meter in most places and is mostly hydrogen. Even if you traveled 300 light years in deep space with a warp bubble surface area of 30,000m^2 you'd collect about ~1 gram of matter. Even if you flung that off at relativistic speeds, it would still not do much damage at any sort of range. $\endgroup$ – Nosajimiki Apr 16 at 17:24
  • $\begingroup$ Not to say you could not weaponize a warp drive by intentionally flying through a nebula or something, but it would not be dangerous under normal use. $\endgroup$ – Nosajimiki Apr 16 at 17:26
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    $\begingroup$ Probably the issue comes when you enter a heliosphere and encounter solar wind. That is why they might make you approach under impulse power. $\endgroup$ – Willk Apr 16 at 17:47

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