# Non-causality-violating FTL travel. / Can omnipotence beat causality?

While building my sifi world I dug into ftl-travel and encountered these mean bullies, causality and relativity. They told me I can't have faster than light travel, because effect can't precede cause and it is easy to violate that using ftl. I really don't like that.

My idea to circumvent causality and time travel issues is to have the ftl machine send out an "editing wave" before the ftl event happens. The editing wave will be emitted from the entry and exit point of the ftl tranfer and all of the other fixed ftl points at the same time. It will be calculated what needs to be changed in the current state of information, energy and matter in the universe to ensure that no causality violation happens. There is no time travel, as the universe is only edited at light speed. The events that would have violated causality would still have happend, but their effects would be wiped out, preventing them from preceeding their causes. Essentially it is like committing a crime and then cleaning up so thoroughly that it seems the victim never existed in the first place.

This includes wiping out the entire existence and history of the vessel and it's crew. The editor considers this to be the path of least resistance. The ship arrives at the exit point as a strongly edited copy and the crew will have little memory and only vague intentions left. Any investigation will show that the vessel, the crew and the information were spontaneously created by a freak quantum event.

It is not possible to construct new ftl points, as they are artifacts of an elder civilisation and they prevented that anyone following them could mess with the universe the way they did.

I'm perfectly aware that this is $$handwavium^2$$. But I wonder if:

• This would actually work, given the editing ability mentioned above?

• Should it not work, how could I tweak it to work given the editing ability? Should this be the case use the new scenario as the baseline for the following questions.

• There would be any side effects I missed?

• Is there any reason not to make the transfer instantaneous?

• Is there any way to do this without making the editor omnipotent and omniscient?

• Is this actual ftl travel or just an elaborate way to commit suicide?

• Finally how severe would the editing have to be? I would like it to be as subtle as possible, human civilisation should still exist after the first time someone uses ftl.

NOTE: I wasn't sure whether to put this on worldbuilding or physics? Any opinions on that?

• Your "editing wave" would still be travelling at (at most) c, so you still don't have an FTL drive. You have a lightspeed drive. If your editing wave exceeds c, then it'd need its own editing wave to deal with its own causality violation. Turtles all the way down. – jdunlop Apr 4 at 17:45
• @jdunlop Maybe I should reword my question for clarity. The editing wave is the mechanism prohibiting causality violation. The actual travel happens via wormholes. – TheDyingOfLight Apr 4 at 17:55
• Also, did you mean "omniscient" rather than "omnivorous"? – jdunlop Apr 4 at 20:34
• Unfortunately, "simultaneous" doesn't really exist either: en.wikipedia.org/wiki/Relativity_of_simultaneity – Dayton Williams Apr 4 at 21:32
• You may want to see what Dr Luke Campbell did with wormhole networks to keep his VergeWorlds setting relativity- and causality-compliant. Those three sections are especially of interest there. – Eth Apr 5 at 11:04

Since you mention the FLT drive uses wormholes, your problem is already solved without your whole editing wave thing. A wormhole does not violate causality because it does not actually let you go faster than the speed of light. Instead it is a short-cut by which you travel at sub-light speeds over a much shorter distance to get between two points that are very far away. Think of it like this:

Imagine you have a lake that is 100km across and only 2km wide. You want to get to the otherside in under 1 hour, but the speed limit is 60km/hr. If you go around the lake at 100km/hr you would be breaking laws to get there pissing off the police. If you had a bridge across it, you could get there in 2 minutes without breaking any laws.

What makes this more complicated as Renan points out below is if the ends are framed to objects on either end and not each other, then this would create a freebee frame shift allowing you to effectively come out of the wormhole at a different speed than you went in for no extra energy investment creating a causality violation. This could probably be solved if your wormholes had some kind of drag factor where you had to expend extra energy while traversing the wormhole to make up for the stolen acceleration, which could in most cases be done with a less-than-relativistic energy expenditure.

But let's say your Wormholes don't do that and they just break special relativity because they can. Or maybe they don't really violate causality, but the intergalactic authorities perceive it as a violation; so, you need to hide your tracks, to keep them off your back. We 1st need to consider how the authorities would know you've done something wrong. They would presumably either need a technology for detecting violations of causality, or they would need to observe your ship in two places that it does not belong while presumably not violating their own rules.

In the first case, being 0.0003*C out of frame would be a pretty small violation that you might be able to explain away as a random cosmic event. Erasing a ship and crew from existence or creating a new one would be a huge violation of causality, and attract a lot more unwanted attention.

In the second case, let's assume they have long-range sensors that can see everything everywhere. If you jump 100 light years, it will take them 100 years for the proof of your crime to be detected, at that point, who cares? You've already grown old and died before they can do anything about it.

Lastly, if these aliens don't like causality being broken, then they would surely want to destroy any ship that just materializes out of nothing even if they can't prove where it came from. So, I don't foresee editing your past out of existence as being a deterrent to such an authority.

If you want to edit something, I would suggest edit your ship after you make a jump so that you blend in with your new location while leaving your past self alone. Scrub exotic particles from your ship that might have been introduced by the wormhole, apply radioactive decay to the alloys in your ship to make it look old enough to be a generation ship, fabricate a fake timeline of your ship flying to where you are from some time originating in the past before you left, things like that.

• Any two wormhole mouths at far enough distances to allow for effectuve FTL will be accelerating towards and from each other at relativistic speeds. Remember the twin paradox? After some iterations, each mouth will be in its own time, and you will be able to use them for time travel - hence, you will be able to break causality. – Renan Apr 4 at 21:43
• The wormhole can be stationary in its own inertial frame regardless of how timespace defforms. Because the wormhole never leaves it's inertial frame of reference, the twin paradox resolves just fine under the rules of special relativity. Going through a wormhole does not propel you at >C speeds. You fly in 10km/sec, you stay at 10km/sec just as if you flew through normal space to get there. Ignoring that other path that would have taken longer is like choosing to drive 5km east to reach a destination instead of flying west all the way around the world, it's just a shortcut. – Nosajimiki Apr 5 at 14:16
• the wormhole has mouths. If one is nesr Earth and the other is at Barnard's star, they are moving at 90km/s relative to each other, currently accelerating, but will decellerate at some point and start accelersti g again later. Each mouth will be at its own time frame. – Renan Apr 5 at 14:25
• Ah, I see what you getting at. If the ends are framed to objects on either end and not each other, then this would create a freebee frame shift. – Nosajimiki Apr 5 at 14:44
• Greg Egan in Diaspora argued, that although wormholes can be setup in causality-violating manner in theory, when two wormholes approach too much to this setup, there is path between them when a virtual particle can travel between the mouths in zero time. This effectively causes resonance, which destroys the wormholes approaching the causality violating setup. Demonstrating applet. Such model of FTL travel is non-causality violating. – Irigi Nov 28 at 19:14

Why not instead go for a theorized FTL drive that may be possible in our universe and doesnt have causality and relativity get in the way? I present to you the Alcubierre drive: https://en.m.wikipedia.org/wiki/Alcubierre_drive

This drive doesnt make the object move, but rather the space it is in. And that space can move faster than light without the object experiencing any of the relativity and causality problems because as far as the universe is concerned, the object inside the field is barely moving at all.

As for your solution, since the editing wave has to travel the speed of light it would mean that you first have to wait for that wave to actually get there.

Edit: for those who still think relativity and causality apply, watch this: https://www.youtube.com/watch?v=94ed4v_T6YM

Edit: in the discussion it came up that the particles that keep the bubble up have to travel FTL at some point. But it would be a smaller handwave to tunnel particles in place than to completely edit out all your actions before and after the travel (and what else can you edit? A planet?)

• It’s not often you get to say that general relativity simplifies a story, but there you are... – Joe Bloggs Apr 4 at 16:04
• But you can still get time travel paradoxes with the warp drive. For causality violation it doesn't matter how you traveled faster than light, it matters that you did. physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel – TheDyingOfLight Apr 4 at 16:26
• FTL of any kind implies time travel which implies causality violation. See en.wikipedia.org/wiki/Tachyonic_antitelephone . If you can send information superluminally, you're going to run into problems unless you break relativity via the good old privileged reference frame idea. – Starfish Prime Apr 4 at 18:10
• If you can send information faster than the speed of light, you can violate causality. Either the warp drive allows you to get somewhere faster than light (and therefore allows you to send information between two points faster than light and so potentially violate causality) or it only allows you to get somewhere slower than light. Are you talking about an STL warp drive? – Starfish Prime Apr 4 at 18:20
• I have seen your references. They do not say what you think they say. This is because they cannot say what you think they say. The possibilty of a warp drive and nature of space in the interior of the bubble is supremely irrelevant to the question of whether or not it can be used to convey information superluminally, and hence potentially violate causality. – Starfish Prime Apr 4 at 18:46

My advice would be to not bugger with ftl instead work on instantaneous travel through the manipulation of time and space. I am sure you have heard the concept of worm holes or strong gravity effects, start there. Ftl, is possible for certain things, for instance, space can travel faster than light. I would suggest you look at Star Trek for inspiration here, they have spent a lot of time with these concepts. Voyager introduced the concept of a "slip stream" drive in season 4 or 5 which might interest to you.

• Space does not travel, it expands. – Renan Apr 4 at 21:01
• @Renan Sure but it expands faster than the speed of light – Rob Apr 4 at 21:23
• @Renan Also, I am not sure why you would say that expansion can not be considered travel.. if I measure the edge of a balloon and mark the spot on the cement then i blow up the balloon has the edge of the balloon not traveled relative to my mark? – Rob Apr 4 at 21:34
• Your analogy makes no sense. If the ballon is the universe, and blowing it up is the expanding universe, what is the cement? Regardless it's not considered travel, because, to fix the ballon analogy, if you mark 2 points on the balloon and then blow the balloon up, the points have not moved on the balloon, rather the space between them has grown larger. – Snyder005 Apr 5 at 19:22
• @snyder005 In my analogy the balloon wasn't the universe it was just a balloon. There is nothing inherent in the definition of 'travel' that justifies your claim. In your analogy, the two points have not moved but that doesn't mean the distance between them hasn't increased. So why, in your mind, is that any different from traveling? That's simply a difference in perspective. To an outside observer sure it looks like the balloon expands but to someone on the balloon it certainly looks like the point is moving away from them. – Rob Apr 5 at 20:07