The Alexandrian

Eclipse Phase - Postmodern StudiosThe Eclipse Phase universe, like a lot of science fiction universes, features faster-than-light travel (in the form of the Pandora Gates) and FTL communication (in the form of quantum-entangled transmissions). If relativity is true (and, in the real world, we have copious evidence that says that it is), then this is impossible.

This tends to get hackles raised from those who are unhappy with a universal speed limit, but this Wikipedia article gives a pretty good explanation of why FTL causes time travel. There’s really no way around it: If FTL communication is possible, then Alice really will receive an FTL reply from Bob before she sent the original FTL message. And once you can do that, it’s trivial to create causality violations. (Particularly if we replace “FTL message” with “FTL travel” so that Alice can go some place, come back before she left, and shoot herself in the head.)

The realities of relativistic speeds are deeply unintuitive to us, but they are no less real because of that. Without getting elbow-deep in the math so that we can really grasp what’s happening, we’re not going to spontaneously discover something that the last five generations of very clever scientists have overlooked. There is no easy escape hatch.

But recently I was drawn into a discussion of how the FTL “realities” of the Eclipse Phase universe could be handled. Here a few approaches you could take:


I guess relativity was wrong after all. Oops.

There’s really no way to pull this off without ignoring a century of scientific data, but we’re just going to ignore that: FTL works and there’s no causality violation because, ta-da, we said so.

To be fair, general relativity and quantum mechanics are fundamentally incompatible with each other and something’s going to have to give if we’re ever going to reconcile those theories. It could be the light speed limit that’ll need to be jettisoned (although it’s entirely unclear why or what form the resulting scientific theory would take).

This is, basically, the approach Eclipse Phase takes: QE-based communication alone completely ruptures relativity at a local and immediate level. Ergo, relativity must not be true. Fly, Skylark, fly.


But let’s wave our hands a little faster.

It turns out that hyper-luminal drives actually increase the local speed of light not just for the ship, but for all spacetime within the light cone of that ship. There are no causality violations because the ship never actually goes faster than light (just faster than light was going last week), but suddenly the radio waves from Earth are reaching Mars much faster than they were before. In fact, it turns out that most of the dark energy in the universe is just a by-product of extragalactic FTL civilizations and tachyons are basically a form of interstellar pollution.

For the purposes of Eclipse Phase, let’s just ignore QE-communication for the moment and focus our attention entirely on the Pandora Gates. It turns out that this “speeding up the speed of light” effect of hyper-luminal travel is heavily gradated due to the vast distances being traversed by the Gates. But people begin to suspect what’s happening when scientists begin detecting small “speed-ups” in interplanetary communication systems. (And it’s possible the scientists weren’t the first ones: There have some anomalous trades on the Planetary Stock Exchange that could only be possible if someone knew they could take advantage of discontinuities in communication speeds.)


Or maybe causality violations resolve themselves through some variant of the many-worlds hypothesis: Alice leaves at FTL speeds, returns before she left, and then shoots herself in the head. But causality isn’t violated because Alice the Murderer can still trace her personal timeline into a different world where the shooting never took place.

The universe where this happens, however, is a complete disaster: Causality may not technically be violated as it leaps from one spacetime to another, but from a local perspective it’s shredded into pieces. The solar system becomes filled with nonsensical events that we can’t really comprehend: Revolutions are thwarted before they started, but then instantly won by time-traveling revolutionaries who blah blah blah, my brain hurts.

Interesting thought experiment, though: What does the universe where Alice the Murderer zoomed off at FTL speeds look like? Well, in that universe she simply disappears the minute she turns around and violates causality (having skipped into a different universe where her return isn’t an immediate paradox). In this scenario you might actually end up with a very large number of universes which this causality-violating Alice simply “skips through” creating ghostly, quantum-froth blips as she sequentially violates causality in one after another. (Once again, we could hand-wave violently and pretend these causality-busting events are happening around us all the time and are the source of dark energy or quantum manifestations or any number of things.)

But here’s the important bit: In the universe where we sent Alice away at FTL speeds, she simply vanishes and we will never see her again. If she turns around and tries to come back, she (and anyone else trying that stunt) will vanish into an alternate dimension never to be seen again.

In the Eclipse Phase universe, though, we’ve been doing this for awhile now: We send Alice out at FTL speeds through the Pandora Gates and we bring Alice back at FTL speeds through the Pandora Gates. Everything seems fine. But then we crack the science and discover that Alice can’t come back: When she comes back, she flips out of this dimension and is never seen again.

But if Alice can’t come back… who the hell is the “Alice” who came back through the Gate? What the hell is the Alice who came back through the Gate?

Eclipse Phase: Gatecrashing

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13 Responses to “Eclipse Phase: Faster Than Light Musings”

  1. GreyKnight says:

    The implications in that final “what” are awesome. I want to write a game about this now. In fact I think I shall! 😉

  2. 1d30 says:

    I don’t think the quantum entanglement thing requires FTL travel. Or, it’s a meaningless artifact of spinning two quantum things together and separating them. Here’s the meaningless explanation:

    We spin up particles A and B, separate them, and Alice gets one and Bob gets one. Alice checks hers, which was always an “A” spin (none of this dumb “it is both until she measures), and finds out it’s an A spin. We now know Bob’s is a B spin. If Alice changes her particle to a B spin, Bob’s particle stays B because Alice’s particle doesn’t interact with Bob’s since they’re separate.

    Here’s the worthwhile explanation:

    As above, except if Alice, after reading her spin, changes her particle’s spin to A then Bob’s changes to B automatically to compensate.

    I haven’t heard of an experiment where #2 was performed successfully. I think people are all too excited to make a leap in saying instant communication is possible. All we know in #1 is that when you spin two particles together, they will have opposite spins. HO HUM.

    Here’s the thing: let’s say #2 is possible somehow. It allows instantaneous transfer of information from one place to another. You might call that travel, but I don’t, because the two particles are not traveling. They’re just interacting in some way we don’t understand yet. They’re not traveling, they’re actually still touching in some way!

    Again, science fiction here. Throw in some sub-space or extra dimensions mumbo-jumbo.

    Anyway, the idea that two particles are still connected though they appear to be physically separated is okay, though we would need some new physics to understand why it works that way. If you can transfer information instantly, that’s fine too. If it’s Universal Time 12:00 on Earth and I send a message instantly to something 5 LY away, they get the message right then, but if I also send it over microwave or something they get it 5 years later.

    Clearly this is not possible within our current physics model, but what I’m saying is if we find some way to entangle particles in a meaningful way it doesn’t mean it’s FTL communication. It’s non-moving communication, not fast. We can’t just look at the result (communication between two places 5 LY apart without a delay) and say it’s just sending a beam of light REALLY FAST.

    This is partly a result of physicists making claims using plain language that carries special meaning for them, based on assumptions that aren’t part of the claim. Also, assumptions that make sense based on our current model but are not neccessarily required for the model to work.

    Again, the SF book says they discovered new physics in the future so new stuff is possible. No big deal. Sure we don’t understand it and it breaks our current physics. That’s why it’s SF.

  3. 1d30 says:

    Also, about Alice coming back and killing herself.

    Let’s say Alice leaves Planet X and arrives at Planet Z immediately. The planets are 5 LY apart.

    As soon as Alice leaves, light that had struck her and bounced off (creating her image) flies in all directions including toward Planet Z. Alice waits around for 5 years and with a powerful enough telescope she can see herself pushing the button at Planet X and disappearing. Remember, this is just the light, it’s not actually Alice she sees.

    Let’s say Alice doesn’t wait. She vanishes from X and arrives at Z, then immediately turns around and travels back to X. Let’s assume she spent a tiny bit of time at Z because she had to push the button there. She arrives back at X just after she left. She can’t kill some other copy of herself, because she isn’t in two places at once. She left X and went to Z, then left Z and went to X.

    I don’t see a problem with this if we say the SF future has some new physics to allow instantaneous travel rather than just accelerating somebody using today’s physical model. Don’t bother with acceleration and light-speed.

  4. Justin Alexander says:

    @1d30: Remember when I said that without getting elbow-deep in the math so that you can really grasp what’s happening, you’re not going to spontaneously discover something that the last five generations of very clever scientists have overlooked?

    Yeah. That’s what’s happening right now. You’re arguing in English that the Earth can’t be spinning because birds would be flung out into space, but Newton’s actual equations are telling you that this isn’t the way it works and the Earth really is spinning round and round.

    You don’t have to take my word for it. Follow the Wikipedia link: If Alice can travel at FTL speeds, she really will get back before she left. Not images of Alice: Alice herself. The Earth really is spinning and FTL travel really is time travel.

    And, sure, we can simply pretend that isn’t true. It’s an old and proud tradition dating all the way back to The Skylark of Space. I’m perfectly willing to do that in the name of enjoying a good story. But at this point it really is the equivalent of saying:

    “Wait… how are you flying?”
    “Well, it turns out that Newton’s gravity was just a theory! It wasn’t true after all!”

    While it’s true that exceptions to Newton have been found, gravity still exists. Similarly, at this point we’re not going to find something that causes relativity to be completely negated: It’s going to be something fundamentally compatible with relativity as we know it.

  5. Justin Alexander says:

    Speaking of QE-based FTL communication in Eclipse Phase, I ended up giving it short shrift because I didn’t have any really strong ideas about it. But I had some weird dreams last night, so here we go:

    QE-based communication isn’t actually as reliable as the Eclipse Phase rulebook would have you believe: Sometimes messages don’t make it through. Sometimes they’re delayed. (Often this delay is so marginal that people don’t really notice it, and it’s never longer than the delay you’d experience using traditional, light-based communication systems.)

    The reason for this is that every QE communicator masks a lump of computronium inside its entangled q-bits. And that lump of computronium hosts an AI. And the job of that AI is to review messages in real-time and delete or delay any messages which would cause local causality violations.

    In Option #2, they’ve found that the “luminal speed-up” effect collapses rapidly if the causality violations are kept local. These AI-guided communications essentially isolate the causality violations to the AI, which results in the slow-crawl speed-up described above. (The maths here are similar to the collapse of a probability wave in quantum mechanics, but I’m not going to show it here because it’s fictional.)

    In Option #3, the inside of a QE-communicator is a seething froth of many-world ghosts and insane causalities. But the AI’s job is to contain those problems so that they don’t “leak out” and turn the known reality of the solar system into swiss cheese. I mean, reality actually is an incomprehensible swiss cheese that makes R’lyeh look like a pocket of calm sanity, but maybe we can keep fooling ourselves a little while longer.

    The problem with either of these approaches, though, is that the AI involved is completely insane. It is, after all, locked in a box with causality violations so surreal that it would make your brain melt just looking at them. And these AIs actually need to dive in, try to understand them, and extra something that keeps local causality consistent.

    More worrisome, perhaps, is when you realize that these AIs aren’t actually insane at all: They are, after all, perceiving reality as it actually is and coping with it. We’re the ones that are insane, locked away inside a padded room that lets us pretend that our insanity is normalcy.

  6. Allan Grohe says:

    But if Alice can’t come back… who the hell is the “Alice” who came back through the Gate? What the hell is the Alice who came back through the Gate?

    Alice = Nyarlathotep 😀


  7. Leland J. Tankersley says:

    I’ve been fooling around with ideas for a SF game, and my desire (/curse) to figure a way to make FTL-ish travel workable without trivially leading to things I know are impossible has led me to adopt the many-worlds interpretation as the only viable answer.

    > But if Alice can’t come back… who the hell is the “Alice” who came back through the Gate? What the hell is the Alice who came back through the Gate?

    Well, if the Alice that appears (in whatever universe/coherent blob of probability amplitude that you the observer happen to occupy/be entangled with) is composed of particles arranged in a pattern that is close to “identical” (acknowledging that that’s a highly-loaded term in this context) with the Alice that left, then in a real sense it *is* the same Alice, at least as much as the Bob inside a house is the same Bob that was standing outside before walking through the door. Particles don’t have serial numbers or any memory of who they “belong” to; the concept of “Alice” is just a tag assigned to a cluster of phenomena, and if a cluster is sufficiently similar you might as well just call it “Alice.”

    This may cause existential angst, but I think that in effect what you can do is just continue living your life — “it all adds up to normality.” Think of it from Alice’s perspective — when you jump/pass through a gate/whatever, you are deleted from universe A. But if in universe B a cloud of particles highly similar to Alice suddenly comes into being, then for all intents and purposes an Alice has just materialized there. We don’t actually carry a history of our identity around with us — it feels like it because we remember with our brains, and the arrangement of particles that make up our brains have been affected by our history. But any cloud of particles in the same arrangement would generate the same sensation of memory/history, even if those particles hadn’t actually even existed in that universe up to that point. So that new Alice will “remember” leaving universe A, because that’s the pattern that the particles of her brain are in. And it might be that universe B’s Alice had been deleted, disappearing from some location in spacetime that may (or may not) be in the “past” w.r.t. the appearance of the new Alice in universe B. The appearance in universe B is that of FTL travel – Alice disappeared from *there* and appeared *here*. Of course, maybe an Alice disappears from universe C and no replacement ever appears there. The people that live in universe C say that “Well, jump accidents happen — sometimes people just disappear into the void and are never seen again.” But that doesn’t prevent lots of Alices from appearing in other universes “remembering” having left universe C. Hell, Alices could remember leaving universe C even if there had never been an Alice in universe C. There’s a sense in which that Alice is a “bad copy,” but what difference does it make? The universes can never really interact, so who will ever know?

    But what does it mean if the “new” Alice isn’t a perfect copy? Actually, it couldn’t possibly be — the new particles of the new Alice won’t be properly entangled/coherent with the rest of the universe initially, even if their internal arrangement were “identical” with that of the original. Among other things, this might be a nice justification for “jump shock” for creatures and computers, which IMO is a nice feature for an interesting SF universe. So now you have justification for things being … off … when you use FTL travel. Carte blanche for messing with your scenario in ways both subtle and drastic, depending on your preferences. For a more traditional space-opera setting, you would posit that the differences between universes (other than the biggie of people and objects disappearing and appearing out of nowhere to fulfill the appearance of FTL) are slight. Or you could go full-tilt gonzo universe-hopping, where the only (near-) constant is the identity of the characters as they bounce from universe to universe. And even character identity might drift — who’s to say whether it’s the character’s memory that has changed, or the universe’s history? Does that question even have a meaning? Plenty of fodder there for messing with people’s heads, if that’s what you’re looking for.

  8. Tom says:

    And yet:

  9. Justin Alexander says:

    @Leland: First, a bit of context-by-analogy in case you’re not familiar with EP. The Pandora Gates were built by Cthulhu. The point is the creepiness that happens when you realize that what you thought the Gates were doing is not, in fact, what the Gates are doing.

    With that being said, your analysis is off. If Alice goes out and comes back at FTL speeds she will travel backwards through time. The many worlds hypothesis lets Alice get away with this by sending her back through time and into a different world. But that doesn’t mean that a doppelganger Alice will just pop into our universe as if relativity didn’t exist.

    Think of it like this:

    Alice 1 leaves at Time X, goes for 0.5 time and comes back for 0.5 time. If relativity didn’t exist, we would expect to arrive at Time X+1. But relativity does exist so she instead travels back in time, leaves our universe, and arrives in some other universe at Time X-Y.

    Alice 2 does the same FTL thing, travels back in time, and enters our universe. But the only way she arrives at Time X+1 is she if left for her trip at Time X+1+Y. Which is not at all the time that Alice 1 left. Which means she has a different set of experiences from Alice 1.

    So while it’s possible that an Alice 2 will appear (possibly due to some multiversal principle of conservation), it isn’t going to be an exact duplicate of Alice 1.

    (I’m using abstract figures here because I don’t really want to get caught up in the specific math. Hopefully it’s clear enough.)

  10. Koewn says:

    I just finished Old Man’s War – they do it like this, heavily paraphrased, more or less what Leland suggested:

    The ‘skip’ drive essentially uses the theory that there’s a multiverse, which includes an essentially infinite number of universes, branching off from quantum probabilities. So there’s one where I just typed this, and there’s another where I typed this and some electron in my monitor went a different speed. That small of a difference.

    The skip drive places the ship at it’s intended destination.

    However, everyone in it is now at a different universe. Why?

    There’s an overriding theory of ‘conservation of probability’ – since that ship popping from point A to point B was *so improbable*, they were shunted off to a twin universe that was as close as possible to the one they came from except for maybe one other electron in the whole universe did something different.

    Alice 1 and Alice 2 are on Earth. If Alice 1 jumps to Alpha Centauri, and Alice 2 jumps to Sirius, they can both meet up at Vega at the same time with no dilation.

    But the Alices that are meeting on Vega arent’ the same ones that were on Earth. That was 2 universes ago for both Alices.

  11. Leland J. Tankersley says:


    No, I’m not familiar with EP. I’m really talking more in general, though. But I think that the many-worlds interpretation has creepiness and to spare even without invoking Cthulhu.

    Re: sending Alice back in time into a different universe: that’s one way to interpret the event, but it’s not the only way. The very notion of Alice as a separate entity is questionable, actually — but that’s getting into the philosophy of identity along with QM. There’s a difference between an object moving faster than light (and thus back in time), and something spontaneously appearing out of nothing.

    You’re absolutely right that there’s no guarantee that a close-to-duplicate Alice will pop into a particular universe at the right location in space-time to be consistent with the “original” Alice disappearing from that universe at some other space-time location (which might include arriving before the original leaves in some frame of reference). But that’s where the hand-waving of the “jump drive” comes in — the magic here isn’t really that ANYTHING is moving faster than light, since that’s impossible. Instead, we’re postulating that somehow (hey, look over there, a comet!) we can cause ships, people, and whatnot to just spontaneously appear in a universe in a fashion where they are unentangled with their surroundings. Then we can wave our hands and invoke conservation of energy to require that, to create people and stuff from nothing *here*, we’ll have to destroy an equivalent amount of stuff from that universe to make the books balance. That might be a way to “arrive” in a universe that’s similar to the one you left.

    From one point of view, making a jump is equivalent to suicide. You have to have a certain agility of thinking (or a strong sense of denial) to destroy yourself like that. But if you can be mentally flexible enough to be willing to say “okay, now my personality inhabits *this* body at *this* location” (and who better to do this than RPG players?) then I think that narratively you can make it work in a game. It may be true that characters (and universes) effectively cease to exist every time you make a jump, but if you’re willing to shift perspectives (or ignore the fact that it’s happening, and just “inhabit the now”) I think it works for a game. It can also spur philosophical discussions, which are a good time-waster…

  12. Catprog says:

    My understanding of the formula in the wiki article is you need to have a v>c. But if you are traveling back to A then wouldn’t v would be negative?

  13. Joe says:

    I had a long comment which I guess got deleted by your spam detector.

    It’s all put up here on my blog:

    In brief, you can get around the paradoxes :-)

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