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I am designing a world where humans have achieved FTL by means of the Alcubierre warp drive and are colonizing the stars. Originally I had communication pegged as being done with quantum entanglement and the like, but I recently heard of the no-communication theorem that, seemingly, prevents this from coming to fruition. Now, from a narrative perspective it is not strictly speaking necessary that communication is fairly instant, but it's a ton more convenient. Therefore I'd to find a way for it to be so using existing theories or reasonable speculation.

  • Is there a hole in the no-communication theorem that can be exploited to permit it anyway?
  • Is there other, speculated methods of instantaneous communication?

Otherwise I am relying on communication being done with warp drives, that is, every settled planet will have a comm station in orbit that every day/hour/minute sends out a comm drone through warp space with the most recent and updated info to other settled planets, likely in a branching fashion so that A sends to B and then B sends to B1-B9 and B1 sends to B1,1-B1,9 and so on. Now, warp isn't instant, it takes about a week or two to travel across inhabited space (approximately 400 ly in radius), so that creates a lot of delay

  • Is there a more efficient solution when you use warp as a basis for interstellar communication?

I don't want to have to rely on a lot of "magic" technology, but if something is reasonable speculated/theorized to be possible within the realm of physics (albeit past the capabilities of humans to reproduce at all anno 2015), I'm interested.

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  • $\begingroup$ This one is your solution. The particle is hypotetical, but that should be fine for fiction. en.wikipedia.org/wiki/Tachyon $\endgroup$
    – jawo
    Commented Aug 10, 2015 at 9:17
  • $\begingroup$ There's a massive problem with using tachyons, they travel into the past which would make it a pretty major thing in the setting. $\endgroup$
    – Vakus Drake
    Commented Aug 10, 2015 at 9:51
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    $\begingroup$ As well as there are massive problems in using warp-drones. There are always problems in causality when scifi bends the laws of physic. For example, how would you practically produce a warp field? $\endgroup$
    – jawo
    Commented Aug 10, 2015 at 10:13
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    $\begingroup$ Since we have the FTL drive as a given (and I suppose causalty and time travel are hand waved), then there is no reason that messages would not be sent via "Pony Express". A ship full of flash drives would essentially be a "sneaker net" with more bandwidth than most other proposed ideas, and so long as security is taken into account, quite safe as well. $\endgroup$
    – Thucydides
    Commented Aug 10, 2015 at 23:52
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    $\begingroup$ Humans had globe-spanning empires before electronic forms of communication, where the delay between the most distant parts of the empire was measured in months, and they still managed to keep everything running. So a week of delay shouldn't be such a great problem. $\endgroup$
    – vsz
    Commented Aug 11, 2015 at 6:20

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Just reading up on what an Alcubierre drive is, and it seems to work by shrinking space in front of an object to allow the object to travel through the space faster than light.

Could you use the same principle for sending data? i.e. instead of a "warp bubble", have a warp tunnel? An almost infinitely thin (to minimise the size of it and therefore the energy required) line of shrunken space between the transmitter and the receiver through which data can be sent.

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  • $\begingroup$ Cannot imagine how you want to shrink space per "remote", thus you need a moving device. This would basicly be a warp-drone which has disadvantages due many limitations. $\endgroup$
    – jawo
    Commented Aug 10, 2015 at 9:31
  • $\begingroup$ @Sempie: As fur as I understand, it is one of the problems of the Alcubierre drive, that the bubble must be controlled from outside. So maybe it is not a big difference, whether there is a ship or e.g. radio waves inside. $\endgroup$
    – BartekChom
    Commented Aug 10, 2015 at 9:54
  • $\begingroup$ @Sempie the transmitter would be similar to the device on the spaceship, except that the "bubble" would be very long, but very thin and reach all the way to the receiver (or a relay station) $\endgroup$
    – komodosp
    Commented Aug 10, 2015 at 13:12
  • $\begingroup$ If you could produce a warped bit of space that would stable, like a soliton, then you shoot the warped solitons themselves as messages, some kind of dot-dash system. Might make an interesting weapon as well. $\endgroup$
    – TechZen
    Commented Aug 10, 2015 at 19:43
  • $\begingroup$ @BartekChom the problem with "putting radio waves" in a Alcubierre drive is that when that reigon of space is returned to normal, all the energy / particles / light that is swept up in the transit is released. Assuming that this isn't pointed at the destination (and wiping it out), the issue is one of trying to get the actual signal out of the noise of the 'stop'. $\endgroup$
    – user487
    Commented Aug 10, 2015 at 22:19
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It's simple, just invent a widgit that corrects for the quantum issues and use quantum entanglement for communication. Keep in mind that the Alcubierre drive itself has all sorts of issues within physics. As a nod to Star Trek you could even call them Heisenberg Compensators, since they did exactly that to explain how their teleporters work with the Heisenberg Uncertainty Principle.

Another option would be to say that the unmanned drones can travel much faster than crewed ships (maybe due to small size, lack of need to keep squishy organics alive, etc) so you could use drones and adjust the time delay to suit your needs.

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As mentioned in your question, quantum entanglement can't actually be used to send non-random information, as a result the only way to send things or information FTL is by using a warp drive (which still relies on theoretical negative energy that may not even exist).

The warp drive is what you need to get FTL travel, but it is also the only way to do FTL communication, if you had another way you could probably use it for travel as well.

It seems the only way to do communications FTL is going to be communication drones, but the drones would probably send their information in radio waves once they dropped out of FTL near their target.

Intercepting communications or stopping them would be tricky, at FTL speeds intercepting anything would be nearly impossible, but once they have dropped out of FTL messages would probably be sent with radio waves, which would entail using the same methods we use today.

In addition we know that the basic idea behind a warp drive doesn't break any laws like many other proposed FTL. We already know that space itself isn't limited to the speed of light, only matter and energy is. Galaxies sufficiently far away will never have their light reach us due to the expansion of space due to dark energy, to us they are effectively using a warp drive go FTL. Warp drives are dependent on whether we can harness negative energy, but we already suspect that the fabric of space has negative energy as dark energy, but that would probably be impossible to harness since it's evenly distributed.

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  • $\begingroup$ "to us they are effectively using a warp drive go FTL" <-- I've never heard it phrased that way, but I like it. I'm pretty sure it's wrong but I still like it. Those galaxies aren't moving FTL, it's that space is expanding FTL. It's a subtle difference but the equations care about it. $\endgroup$
    – Kaithar
    Commented Aug 10, 2015 at 19:29
  • $\begingroup$ But the fact the galaxy itself isn't going FTL, doesn't matter, in fact that's the point. The galaxy only seems to be going FTL but actually it's the space not the matter. That's also exactly what a warp drive does, it warps space so that it can go FTL without technically going FTL, just like the galaxies. My point is that the process behind a warp drive already naturally exists in the real world. $\endgroup$
    – Vakus Drake
    Commented Aug 10, 2015 at 19:38
  • $\begingroup$ It's not really the same process though... the galaxy isn't moving towards anything, it isn't really moving at all. The apparent motion is from the light stretching. One of the consequences of this is that an observer capable of moving FTL would see the apparent absolute speed decrease as they approached the galaxy they were measuring. $\endgroup$
    – Kaithar
    Commented Aug 10, 2015 at 21:13
  • $\begingroup$ The galaxy isn't "really" moving, but neither is the Alcubierre drive, the drive merely expands and warps space, the ship could be totally stationary, it moves the space around the ship, instead of moving the ship through space. Also the galaxies inability to ever have their information reach us isn't due to stretching their light (that wouldn't slow it down just lengthen the wavelength) but due to the expansion of space itself which exceeds the speed of light. $\endgroup$
    – Vakus Drake
    Commented Aug 10, 2015 at 21:27
  • $\begingroup$ Strictly, the ship is moving in terms of position relative to fixed locations within it's frame of reference even if it isn't moving within the bubble. I didn't say anything about the ship though. I said the galaxy wasn't actually moving. The universe is scaling thus everything remains proportionally distant from everything else. $\endgroup$
    – Kaithar
    Commented Aug 10, 2015 at 23:16
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Well, this kind of scifi is bending the laws of physics. Thus, you can fully legit use hypothetical particles which aren't proofed to exist yet.

So your solution is as simple as it can be:

Tachyon

A tachyon /ˈtæki.ɒn/ or tachyonic particle is a hypothetical particle that always moves faster than light. [sic]

[...]

They have been used as a standby mechanism upon which many science fiction authors rely to establish faster-than-light communication [sic]

A common mechanic is sending a tachyon beam to the communication target. Behaves pretty much like any light beam (Just faster), can be detected or blocked by objects on their way.

But even Tachyons would have a big problem. When the tachyon wants to reach a spacecraft from behind, it has to pass streched space, which will make it relatively slow, maybe so slow, that it needs aeons to reach the spacecraft.

There are two solutions for this:
1. Warp-drive is slower than tachyons by the manner that the time a tachyon beam needs to pass the negative warp-space is reasonable.
2. Spacecraft has to stop or throttle warp-drive to get the tachyon-delay reasonable.

First solution has the disadvantage, that the spacecraft has to move slower than it might could. Second solution has the disadvantage, that you can't tell the crew "hey guys, I wanna talk to you, throttle down please." due you can't communicate currently. Thus, the spacecraft would have to throttle down periodic and the in-warp communication would have a protocoll like: Once in t(xy) the spacecraft throttles to speed v(tachyon)-xyz), then communication is done, then the spacecraft accelerates again.

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    $\begingroup$ If you allow tachyons, then you also allow communication into the past, so that's a problem. Tachyons don't just travel faster than light, they also travel into the past. Warp drives don't have this problem because they aren't technically FTL. $\endgroup$
    – Vakus Drake
    Commented Aug 10, 2015 at 9:49
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    $\begingroup$ While you're not wrong, this isn't more than a game with words... $\endgroup$
    – jawo
    Commented Aug 10, 2015 at 10:23
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    $\begingroup$ The reasons you can do FTL with a warp drive is the same reason space can be FTL. Some distant galaxies will never have their light reach us because they are effectively retreating faster than light, due the expansion of the universe, physical mass can't go FTL but the fabric of space itself doesn't have that restriction. That's why if negative energy exists it should allow FTL, because we already know that variety of FTL exists. $\endgroup$
    – Vakus Drake
    Commented Aug 10, 2015 at 10:36
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    $\begingroup$ Personally I like the idea that ships have to drop out of FTL to communicate outside the bubble, gives you a good plot limitation to play with. $\endgroup$
    – Kaithar
    Commented Aug 10, 2015 at 19:37
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    $\begingroup$ @Johnny So essentially your method of preventing paradoxes is the honor system? Really? $\endgroup$
    – Vakus Drake
    Commented Aug 11, 2015 at 0:21
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Wormholes. Yea, wormholes. Some theories have them being created and destroyed at the quantum foam level (Quantum Dynamics of Lorentzian Spacetime Foam). For most things, this isn't practical. Its too small to even push atoms through - on the order of 1000x smaller than a proton.

However, one might be able to push light through it and allow for communication with the other end of the wormhole.

So, what you would do is grab one of these wormhole pairs that is constantly forming, and prevent it from being pulled back into where it came from. You put one end in the communication center on one planet, and take the other end to the communication center to the other planet.

There are some odd effects that would happen with wormholes that can cause some causality problems which one should be aware of. Lets take a wormhole and do a four year relativistic speed loop (that to the passage only takes a year). Now, the wormhole that traveled is three years younger than the one that stayed home. If you look through it, you would see three years ago (and on the flip side, if you look through the one that stayed home, you would see three years into the future). There are suggestions that this would cause it to blow up before anything could happen. There are possibilities of chronology violation with rings of wormholes too where each end is not causality violating, but the combination is.

A system that wasn't causality violating would be a communication hub. Each colony has one, and only one, wormhole link to Earth (the location of the hub). Furthermore, colonies are prohibited to have wormhole links to other colonies (if they did, it would form a loop, and with FTL in there would have some causality violation and the virtual particles would pile up on a closed space time curve and cause an excess of energy density which, well, goes 'boom'). This would allow for some imperial censoring and such.

References of hard science fiction with wormholes:

  • The Light of Other Days Stephen Baxter based on a synopsis by Arthur C. Clarke (the wormholes are photon sized)
  • Time Master by Robert Forward - full of temporal paradoxes and larger than photon wormholes but has interesting bits on the wormholes (it starts out with "If I receive a letter from this sort of person complaining about the "impossibility" of the time machines in this novel, I will throw the letter in the nearest wastebasket . . . unless the letter is accompanied by a reprint of a scientific paper published in Physical Review (or any other reputable, refereed scientific journal), written by the person writing the letter, which proves that the paper "Cauchy Problem in Spacetimes with Closed Timelike Curves" by Friedman, Morris, Novikov, Echeverria, Klinkhammer, Thorne, and Yurtserver, is erroneous.")
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Superstring theory postulates that said "strings" are producing worm holes. While too small and volatile to send humans through, information COULD potentially be transmitted through said strings. This kind of goes along with @colmde in relation to small tubes/tunnels instead of bubbles.

Here is a quoted segment on this topic, but Michio Kaku:

"...as a string moves in time, it warps the fabric of space around it, producing black holes, wormholes, and other exotic solutions of Einstein’s equations."

And a useful page of information with more on the topic where the quote was found:

http://mkaku.org/home/articles/blackholes-wormholes-and-the-tenth-dimension/

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The bulk of communication can be carried by untrusted traveler ships at reasonable prices, with drones as an expensive fallback in case no-one is going.

Cryptography (heck, even today's cryptography) can guarantee no eavesdropping and no tampering with messages. The worst a malicious ship can do is not deliver, in which case it won't get paid.

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This is an idea I was going to use in an erstwhile project. It's softer sci-fi than Alcubierre drives, but it might suit.

A special device opens a tiny wormhole to a microscopic pocket universe. These devices are such that a connection can be opened to the same pocket from anywhere in the universe. EM waves can be sent and received, but nothing larger goes in or out.

Again, I'm not sure if this is too soft for you; wormholes are postulated to be possible, as are subatomic black holes, and white holes. Put them all together and there you are.

It also opens some interesting possibilities from a narrative perspective - can they be hacked, how much energy does it take to open the connection, are there limitations in creating/discovering pockets, etc.

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It's true that quantum entanglement cannot be used to send messages. The problem is well explained elsewhere, so I'm not going to dig too deep into it. However, there is a way around this - all you need is a device that destroys the universe.

Say you want to send a message 110. You have a particle pair that's entangled, so by reading your particle in the pair, you know what the other end will read. You'll need to read the particles at predefined intervals and find a way to prevent the entanglement from propagating (it's not really entangled-not entangled, it's more like entangled with one or two other particles versus entangled with billions) - that's a great place for some handwaving. But let's suppose that's solved - you simply found a way to isolate the partice well enough that you only have the two entanglements - one to your sensor device, and another to the other side of the telegraph.

Now, you only have a reader. How do you use it to send messages? Simple!

Read your particle. Does it show 1? Awesome, bit of data "sent". Does it show 0? Destroy the universe. This way, the only universes that survive are the ones where the other side reads exactly the data you wanted to send! It may sound brutal, but don't forget that an infinite number of universes dies every second anyway, so you're just exploiting the natural behaviour for your own purposes ;)

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You could use the Well-established sci-fi technology: the ansible. The technology is based on the idea that dimensionality is fictional under some restricted mathematical topologies, which provides an opportunity for non-transit communication.

Your deliberations are correct. Quantum physics requires that a breakdown of causality causes a singularity, and therefore superluminal communication of any sort is barred.

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