Thursday, March 3, 2011

FTL Part I: An Honest Cheat?


It might seem contrary to discuss FTL only after a post on interstellar empire, a concept that pretty much depends on star travel being cheap, convenient, and above all fast. (Yes, there are STL scenarios, but they are so stretchy that violating General Relativity suspends less disbelief.)

But in broader perspective it is our desire for interstellar empire, or other such cool settings, that calls out for the willing suspension of disbelief in the first place. All spaceships, as a commenter on this blog once observed, travel at the speed of plot, but that is especially true when it comes to FTL. Spaceships in the Plausible Midfuture have some of the constraints of real-world vehicles, and plots must work around them, but the only constraint on FTL is that it must sound convincing to readers who want to be convinced, at least while reading the story. (Although FTL systems in SF not infrequently fail even at that.)

Unlike last post, this time I remembered to link the relevant page at Atomic Rockets, which covers or links the relevant physics and pseudo-physics, and offers some useful FTL typologies. Also a link to my observation in the Tough Guide to the Known Galaxy that all FTL tech is equivalent to flipping tarot cards while chanting in Welsh - i.e., effectively it is magic.

And a post here from last year which noted that contemporary physics has just barely left the door open to FTL, subject to certain constraints. The relevant effect of these constraints - as I understand it (and General Relativity is not my field of expertise) - is that you can stay out of temporal trouble so long as your baseline FTL routes do not cross-connect.

To follow the rapid transit metaphor I used in that post, you can have multiple routes out from Earth (via wormholes or whatever), with as many branches and sub-branches as you want, and travel times can be as fast as you want them to be. But each station can only be on one line. If you can take two separate routings to reach a given destination, of differing length, then you have to pay the temporal piper.

For example, from Sol to Sirius is 8.6 light years, while from Sol to Wolf 359 is 9.0 light years. Given tramlines equipped with a suitable array of oscillating hands, you can reach either one in in a month by your onboard clock, or an hour, and return in similar time. In Earth's frame of reference, going outbound you are in fact travelling nearly a decade into the future, and returning you are going nearly a decade into the past. This produces no awkward time-travel-esque results, because you don't return to Earth before you left, and you can't get back to Sirius for a second visit prior to your first one.

From Wolf 359 to Sirius is 7.7 light years, so the roundabout route to Sirius via Wolf 359 is 16.7 light years. If you could simply open another tramline, you could travel to Sirius via the indirect route, arrive there 17 years from now, read some stock quotes, return by the same roundabout route to Earth, then go by the direct route, and invest in Sirian stocks years earlier. Big trouble, and not just for stock markets.

So, to avoid breaking causality, such routings must be ruled out, or at least force you to twiddle thumbs those extra eight years instead of raking in a bundle. I don't begin to understand the required coefficient of jive, but apparently it can be done without violating General Relativity, at the price of making such roundabout routings very inconvenient.

(Commenters who do understand this stuff are welcome - indeed, invited - to step in and expand on / correct these points.)

The hitch is that for story purposes we probably want those roundabout routings - not to travel into the past, but merely to run blockades and the like.

My impression is that there is still a workaround. Simply assume that all FTL travel to Sirius proceeds via Wolf 359, but that there are separate 'local' and 'express' tramlines along the route - the former stopping off at Wolf 359, while the latter passes right through without entering normal space.

If each entry or exit from a tramline involves a cost (e.g., reaching the jump point through normal space), then regular Sol-Sirius travel would follow the express tramline, passing by Wolf 359 nonstop. But the local routing, stopping off in normal space at Wolf 359, would remain available when needed for story purposes.

Yes, this is more than a little strained (and possibly downright wrong), but hey, we're talking about FTL. The alternative, so far as I can see, is simply blowing off a lot of well-establish physics entirely. Remember, it isn't as if Einstein kicked Newton onto the ash heap; old Sir Isaac still gives an approximation good enough for interplanetary travel planning.

Moreover, the above gimmickry can be almost entirely buried out of sight, at least so long as your intended flavor of FTL is jump-oriented, and you don't get deeply into the weeds about the sequence in which routes were established in the first place.


Having said that, this approach should probably be left to physicists, or people who do General Relativity as a hobby, and might as well be physicists.

My more general advice on FTL - which I seem to have arrived at via Wolf 359 - is to say as little about the mechanism as possible. Don't talk about wormholes, don't talk about Alcubierre, or any other present-day speculation. All you will do is date yourself, because I don't need to travel into the future to guess that these particular edge-of-the-envelope speculations will be superceded.

Bury all that theoretical stuff under a couple of toss-off jargon terms - Horst-Milne congruencies, Alderson Drive, whatever - and concentrate on what actually matters, which is how FTL actually operates in a setting: size and cost of the gizmo, apparent travel times, available routings, and so forth.

Some of which I will (probably) discuss next post.




Related links: Atomic Rockets, Chanting in Welsh, and Rapid Transit.

The image comes from a Battlestar Galactica website.

322 comments:

«Oldest   ‹Older   201 – 322 of 322
Tony said...

Raymond:

"I think a brief twitch of the hand in that direction wouldn't hurt, if only to placate those who do care. It doesn't take much - while you're mentioning the Whatever Drive and its limitations, just drop a reference to a special frame while talking (however briefly) about how the smartass engineers finally outfought Einstein's shadow."

I see it this way: from the purely commercial perspective, where FTL is concerned, there are more readers that care about not being bothered by genuflections to esoteric issues that don't have to effect the story than there are readers who have to have their professional egos storked. If we were talking about the accuracy of military SF, you would have a point, because a lot of SF readers are current or former military. But how many readers are relativists? See the difference?

Raymond said...

Tony:

And I see it this way: if you're going to have to mention capabilities of the FTL mechanism at all - which happens more often than not even in non-military SF - you might as well take the couple extra sentences to demonstrate you Did The Research. Which, to those who care about the verisimilitude you yourself have espoused elsewhere, indicates other areas of world-building will be more likely to receive similar respect.

Raymond said...

Rick:

Can you spring Luke's last couple forcibly-anonymous posts from the warp storms?

Citizen Joe said...

OK we're talking about differing experiments here.

Experiment 1:
Andy stays at origin and is our defacto rest mass observer.

Bob is traveling at relativistic speeds.

Charlie is a secondary traveler for comparative relativistic effects. (not used in all experiments).

Dave (or God) is a true rest mass observer, not actually possible since everything is moving, but he's the theoretical non-moving observer.

Since we're just looking for the theoretical perception of events, everyone has magical cameras that can see everyone else's clock.

Experiment 1:
Andy is sitting around at home base while Bob makes a 1 light year circuit at 0.8 c.

Results:
Andy sees Bob through the camera and Bob seems to be moving slowly. Bob looks at Andy through the camera and he seems to be moving very fast.

When Bob gets back to base, he has experienced 9 months of dilated time. Andy has experienced 15 months of 'normal' time.

To Bob, the has experienced FTL travel, i.e. traveling 1 light year in only 9 months, which would be 1.333 c. To Andy, Bob has only traveled at 0.8 c.

Now Dave, having watched all this from his hypothetical stationary cloud, doesn't notice Andy moving appreciably slower, although Bob seemed to be. However, due to the minute speed of Andy at the base station, we'll put Dave's elapsed time at 15 months and 1 minute.

Raymond said...

Citizen Joe:

A) Forgive me, but I'm not sure where you're going with this.

B) Bob actually sees a shorter distance than 1 light-year, due to distance compression in the direction of travel.

C) Dave would be the aforementioned privileged reference frame, which is forbidden under relativity. As long as we're not throwing relativity out the window, there can be no Dave.

Milo said...

Jollyreaper:

"About the only way to rationalize a lightsaber would be precognitive powers like the Jedi and it would STILL make more sense for them to fight with blasters. You can only hit someone within a few meters of you with the lightsaber but you can shoot someone a kilometer or two away due to your force-assisted aim."

I had the same thoughts. Actually, if I had Jedi powers, I would dual-wield a blaster in one hand and a main guache lightdagger in the other. The lightdagger (or might I as well go with a full-size lightsaber because they weigh nothing anyway?) is for parrying and reflecting enemy blaster shots, while my unfailingly accurate blaster would easily kill most stuff, and allow me to start threatening the only kind of enemy that can actually defend against it (namely other Jedi) before they're in range to hit back.


"The kind of awkward, painful kloodge you'd need to justify rapid-fire automatic weapons and hand weapons in a fight is saying that the armor is so freakin' awesome that it'll turn most laser and projectile fire but would be vulnerable to melee attack, either crushing through a hammer impact or a thin blade pushing through the joints. That's a huge pile of kloodge right there."

The obvious question is why don't you just throw blades or rocks at people? I'm pretty sure modern tech could create a pretty good rock-thrower, we just don't because there's no point.

Another answer is to have armor be sufficiently good that any weapon, melee or ranged, needs multiple hits to break thought it. If the armor takes long enough to break through, then enemies will have time to close into melee range before you can finish them off even with a machine gun, and so most combat will be finished hand-to-hand. This breaks down if the ranged combatant can continuously retreat, Mongol-style... Also, it's hard to find armor that can stand up to a nuke, or even a large conventional bomb.



Tim:

"The population(s) are mostly either bio-engineered or medicated for passivity and non-violence, with those even capable of violence relegated to the police, military or outlaw status."

I do not think that lobotimizing all of humanity is a good idea.



Luke:

"Claire sees that the space needle is 100 meters ahead of her. Dana is standing at a 45 degree angle with respect to Claire, but otherwise right next to Claire, and so she sees that the Space Needle is 70 meters in front of her and 70 meters to her right. From Claire's point of view, Dana's measurements are front contracted, everything is only 70% of the distance in front of Dana as it is in front of Claire."

Not true. The Space Needle 100 meters straight ahead of Claire is 70 meters ahead (and 70 meters to the right) of Dana. However, another object 70 meters ahead and 70 meters to the left of Claire would be 100 meters ahead of Dana, i.e., front-expanded rather than front-contracted.

Milo said...

Tony:

"But once you get on Arrakis, shields go out the window, because they aggravate the worms. But swords are still en vogue, because you don't build special armies and weapon systems for a single planet."

Humans have developed extensive weapon systems for use in ocean terrain, a region which is settled by exacty zero permanent inhabitants. Countries near the poles have developed ski-based vehicles, knowing that they would be useless against enemies in warmer climates. Etc.

If a particular area is of sufficient strategic importance - either to warfare in general, or to you personally because that's where you happen to be stuck living - then you'll develop weapons which work there.


"More likely the people who wanted to use force would adopt adaptations like frangible bullets that poke holes in people, but not in hulls."

Any hull weak enough to be punctured by a single small arms bullet is unsuited for permanent habitation. A spaceship might need thin hulls to save weight, but a domed city is going to be a lot tougher than that.



Rick:

"A useful question - which I am in no position either to answer myself or ask Luke to answer for us - is what constraints, in story terms, need to be put on FTL to avoid violations of causality and/or GR."

The easiest way is to postulate a favored frame of reference, for example comoving coordinates, or something tied to those gravity wells that FTL authors like so much.

Without that, you can still create a few wormholes, but run into the "once a romhole is created it prevents you from making other wormholes in the vicinity" issue that also prevents freeform FTL travel.

Milo said...

Raymond:

"In the absence of a privileged frame of reference (something forbidden under both special and general relativity)"

I'll say it again: relativity does not forbid a priviledged frame of reference. It merely doesn't define a priviledged frame of reference. In the sense that even if there existed a frame of reference which is privilidged in some manner, then it would be impossible to tell the difference measuring purely things understood by special/general relativity.

It is still perfectly consistent with relativity for there to be a frame of reference which has special treatment only with respect to people chanting in Welsh, since relativity doesn't model Welsh-chanting, and as long as no-one is chanting in Welsh, all predictions of relativity (including the inability to determine a preferred frame) hold.


"How a quantum-theory-based chronological protection effect would manifest is an open question, and depends on your interpretation of quantum mechanics."

I don't remember where, but I remember reading a hypothesis that took advantage of quantum mechanics' indeterminate nature.

The example in the article was a billiard ball table where the pockets had wormholes to the past. A skilled player can then try to push a ball at just the right angle that it falls into a pocket, gets sent back in time, and then hits its own past self and changes its course before it falls into the pocket, causing a paradox.

But! That's assuming the ball goes through the wormhole exactly as planned. But it won't - because its own future self will knock it aside! So what could actually happen is this. The player pushes the ball at an angle that he thinks will cause the above line to happen. But then before the ball falls into the pocket, it is hit by a ball that appears from the future, which knocks it slightly off-course. It still falls into the pocket and gets sent back in time, with enough accuracy to still hit its past self, but - because it was knocked slightly off-course - it does not succeed in deflecting its past self enough to prevent it from falling into the pocket (as the player intended and aimed for), and instead merely knocks it slightly off-course. Result: a self-consistent closed time loop!

Follow?

But now the thing is: there are multiple angles the ball could deflect itself at to create a self-consistent time loop. So which one actually happens?

This is where quantum mechanics comes into play.

The solution is to have not one determinate outcome, but rather a probabilistic distribution of all possible self-consistent time loops, which are then randomly chosen among - exactly how quantum mechanics already works!



Geoffrey S H:

"Thus a spacecraft must come to a complete stop"

Complete stop relative to what? Comoving coordinates? The intended other end of the wormhole (which, if a planetary surface, isn't even an inertial frame)?

Citizen Joe said...

Oh, I wasn't aware of the distance compression, just the time dilation.

And Dave is a hypothetical being, as I stated. If such a thing were possible, how would he view things. He exists only to point out that everything is moving.

Raymond said...

Citizen Joe:

The distance compression for Bob is necessary, or he'd outrace a light beam on the same path. Therefore he won't measure himself going at 1.33c, he'll measure the distance he travels as less than one light-year - 0.6ly, if in fact I have the math right.

Teleros said...

Rick: "A useful question - which I am in no position either to answer myself or ask Luke to answer for us - is what constraints, in story terms, need to be put on FTL to avoid violations of causality and/or GR."

If you have FTL you'll have to dump either causality or relativity, so in story terms I can't see there being any special constraints necessary.

"I emphasize 'in story terms' because as writers we can get away without explaining how our FTL works, but we want to avoid travel routings and such that 'should' permit time travel if they existed."

1. There was (further up) that stuff about wormhole networks between points that have only one route in / out of each point (ie Sol to Tau Ceti and Sol to Prox. Centauri, but no Tau Ceti to Prox. Cent. route).

2. A special frame of reference used for hyperspace and similar FTL methods. This is the easiest IMHO.

3. You can also simply ignore the issue of time travel - it just doesn't happen, period, for an unexplained reason, or...

4. Go the Skylark of Space route if you're really brave enough to toss Einstein out entirely. Screw modern physics, Newton was right all along damnit!

This doesn't include things like a "Natural Law Against Time Paradoxes", which may still leave open the door to non-paradox-causing time travel.



Raymond: "It also occurs to me that with Blogger's overeager spamfilter, we're seeing responses to posts which haven't appeared yet. We even have our special frame in the form of the email notifications - those of us following from hyperspace get a total ordering of events, not just a partial one.

Rick, was this object lesson your doing?"


I'll get worried when it starts looking redshifted...



Geoffrey SH: "They can only opened when stationary.

Thus a spacecraft must come to a complete stop- bear in mind that the planets, solar system, local star group, and the galaxy and galactic group, etc are all moving."


A complete stop... relative to what?

jollyreaper said...

Here's a thought.

Hey, you know how our FTL tech could create paradoxes?

Yes.

So how come we've never heard of one happening?

It would be dangerous.

Yeah but there are plenty of inquisitive idiots. Surely someone somewhere has tried.

What about that theory that says the universe will prevent a paradox? That the offender will be deleted from all existence at once, that it will be like he'd never been born?

Seems almost like divine intervention.

Yes, but you think someone somewhere would have tried this.

Yeah.

And we've never heard of anyone trying.

Yeah.

I don't know about you but that's one hypothesis I don't feel like testing.

(I'm sure this has already been done as a story?)

Milo said...

If anyone here understands comoving coordinates: is it always guaranteed that any object which obeys relativity (no FTL), but can otherwise move arbitrarily close to the speed of light in any direction, will always still be moving forwards in comoving time? (Even though comoving coordinates aren't an inertial frame as defined by general relativity.)



Meanwhile, back to the subject of immortality by preserving your memories, it occurs to me there's a darker side to that too. Any traumatic experiences and embarrassing stories will be remembered forever. Without death to wash everything away, if you manage to offend someone, he will remember this for the remainder of all time. Any mistake you make will be held against you for eternity.

That's a lot of pressure!

Rick said...

A belated welcome to a couple of new commenters!


Luke, the problem is probably not with your account, it is with the Force (sorry!) - or at any rate, Google's spam filter.

My take - and I think this is what Tony was getting at - is that in a world with FTL and preserved causality, time as measured for human purposes would be within the frame of reference of the wormhole network, and would always go the right way, even if at variant rates.

Physicists, and FTL techs, would be aware of other reference frames in which travel 'back in time' is common, and for some technical purposes that sort of time might be EXTREMELY important - but of no practical concern to anyone else.

At least that is my take. For story purposes, a toss-off line or two would be sufficient. But be careful, because a mistake on that point could be a glaring indicator* that you don't know what you're talking about.

* To the 0.001 percent of readers who have a working understanding of GR.


On social violence, I'm not inclined to dispute that, given the right (or wrong!) circumstances, people who have been profoundly nonviolent can turn out to be violent after all.

I think the real issue in discussion here, though, is ritualized versus 'instrumental' violence - or, put in English, how you get to a setting where people know about guns but use swords anyway.

Tokugawa Japan seemed to achieve, broadly speaking, for a pretty long time, though if we did not know it had existed we'd probably say the idea was wildly improbable.


More grist for future posts!

Luke said...

Milo:

Not true. The Space Needle 100 meters straight ahead of Claire is 70 meters ahead (and 70 meters to the right) of Dana. However, another object 70 meters ahead and 70 meters to the left of Claire would be 100 meters ahead of Dana, i.e., front-expanded rather than front-contracted.

But the analogy still holds. Time and spatial coordinates are rotated into each other. At a speed of 0.8 c, a time of 1 in the rest frame will transform into a time of 1.667, but a time of 1 and a position of -1*c will transform into a time of 0.333 and a position of 0.333*c. So because of the position coordinate the time coordinate gets contracted rather than dilated.

Milo said...

Rick:

"Tokugawa Japan seemed to achieve, broadly speaking, for a pretty long time, though if we did not know it had existed we'd probably say the idea was wildly improbable."

The Tokugawa shogunate is evidence of nothing more than that a sufficiently strong government is capable of instituting effective gun control, thus preventing guns from being used by anyone who isn't strong enough to overthrow the government. Crucially, the Tokugawa shogunate could do this because it was a period of peacetime, with no major internal or external threats - banning muskets would never have worked during the Sengoku period.

That they chose to continue allowing swords while banning guns is largely irrelevant.

Tony said...

Raymond:

"And I see it this way: if you're going to have to mention capabilities of the FTL mechanism at all - which happens more often than not even in non-military SF - you might as well take the couple extra sentences to demonstrate you Did The Research. Which, to those who care about the verisimilitude you yourself have espoused elsewhere, indicates other areas of world-building will be more likely to receive similar respect."

Once again, you're derailing the story for the purpose of impressing a miniscule portion of your audience.

Raymond said...

Tony:

"Once again, you're derailing the story for the purpose of impressing a miniscule portion of your audience."

A couple sentences is a derailment? You'd really dock a story for inserting a (very) brief mention during the (usually required) description of FTL tech? I'd say that's overly harsh.

Whatever story you're telling which is served by incorporating interstellar travel will be influenced by the details, however handwaved, if you're going for the sort of plausibility this blog is supposedly about. Politics, economics, demographics, and every other -ics will be shaped by the peculiarities of the Handwavium Drive. Especially if you're trying for hard SF of any kind, in which case you're probably incorporating all sorts of technological and engineering details, if only in the background. Two sentences to soften the blow to Einstein is too much? Really?

Raymond said...

Milo:

"I'll say it again: relativity does not forbid a priviledged frame of reference. It merely doesn't define a priviledged frame of reference. In the sense that even if there existed a frame of reference which is privilidged in some manner, then it would be impossible to tell the difference measuring purely things understood by special/general relativity.

It is still perfectly consistent with relativity for there to be a frame of reference which has special treatment only with respect to people chanting in Welsh, since relativity doesn't model Welsh-chanting, and as long as no-one is chanting in Welsh, all predictions of relativity (including the inability to determine a preferred frame) hold."


Perhaps this is a confusion of semantics. Let me back up and clarify, and consider my previous comments suitably amended.

A "preferred" or "privileged" inertial reference frame is one where the laws of physics are different, or more complete, than in any other inertial frame. Such a reference frame would violate general relativity's central assumption, and is therefore by definition forbidden if GR holds.

A "special reference frame" for the purposes of FTL travel doesn't necessarily have to be a "privileged" frame, but merely a common frame for all FTL travel. If you can define a frame which all objects moving FTL are at rest with respect to, then you don't run into any time-travel paradoxes, ever.

Nobody knows how that would be done, though.

"I don't remember where, but I remember reading a hypothesis that took advantage of quantum mechanics' indeterminate nature...."

I've heard similar, and that would probably describe chronological protection on a macroscopic scale. The microscopic version would probably be the one described earlier, where quantum "feedback" closes wormholes before they become CTCs. Either way.

"If anyone here understands comoving coordinates: is it always
guaranteed that any object which obeys relativity (no FTL), but can
otherwise move arbitrarily close to the speed of light in any
direction, will always still be moving forwards in comoving time?"


If I understand correctly, since comoving coordinates use cosmological time, by definition any such object will be moving forward in time. Remember that in the local inertial frame of curved space (especially near mass), the speed of light will be somewhat lower than c. Given what we've determined about the overall curvature of the universe, comoving distance will be less than proper distance, thus local lightspeed will be less than c, thus any object will always be moving slower than comoving c. Ergo, yes, all objects will be moving forward in time in comoving coordinates. (If I'm horribly out to lunch in all this, somebody let me know.)

jollyreaper:

"...I'm sure this has already been done as a story?"

I think Revelation Space has this as a plot point somewhere.

Thucydides said...

Not sure where the digression about hand weapons and armour came in (unless I am in the wrong frame of reference ;)).

If we need a handwave to eliminate causality issues, then we need to postulate that wormholes or whatever FTL mechanism you want to use follows the minimum potential energy path (Minimum collapsing world lines? Minimum aether density? Best phlogiston economy?)

As mentioned several times, FTL mostly exists in story terms in order to get the characters to whatever exciting event awaits next. In the 1930's, this was usually indicated by an animated line on the map moving from the United States to Shanghai, or wherever. Modern movie shorthand is an airliner approaching the runway on final approach. We can infer the heroes have just endured a 30 hour flight on a Pan Am clipper flying boat (or a 30 hour trip with 8 in the air and the remainder stuck in traffic, airport lounges, customs etc.) without actually having to experience it.

The clever writers who want/need to examine the consequences of relativity, causality or FTL will have incorporated that into the plot, which to my mind moves us from Hornblower in Space to true Science Fiction.

Anonymous said...

I think that a crew member and a passenger having a short discussion with the crew clearing up a couple of misundertandings about the stardrive on the passenger's part would not only give the reader a grasp on the stardrive, but would help define the two characters.

Ferrell

Milo said...

Raymond:

"A "preferred" or "privileged" inertial reference frame is one where the laws of physics are different, or more complete, than in any other inertial frame. Such a reference frame would violate general relativity's central assumption, and is therefore by definition forbidden if GR holds.

A "special reference frame" for the purposes of FTL travel doesn't necessarily have to be a "privileged" frame, but merely a common frame for all FTL travel. If you can define a frame which all objects moving FTL are at rest with respect to, then you don't run into any time-travel paradoxes, ever."


The only reasons why FTL travel could be limited to a single frame are if (A) universal law does not permit FTL travel in any other frame, meaning that frame is priviledged according to your definition, (B) humans voluntarily choose to only ever travel in one frame even though travelling in other frames would be possible, which is unlikely since despite its story-wrecking potential, time travel would be incredibly useful if we could make use of it, or (C) there is no initially preferred frame, but once having done some FTL travel in a particular frame we "lock" other FTL travel in the region into needing to use the same frame in order to not fall afoul of some chronology potection principle (like our wormhole network concept).

According to your definition, "the laws of physics are different, or more complete, than in any other frame" is what would happen in option (A), with in this case the difference in the laws of physics compared to other frames being "FTL is possible". The laws of physics are made more complete in this frame by the addition of FTL, but in all other respects (such as the behavior of STL motion and forces as described by general relativity), the laws of physics remain identical to the ones in every other frame. (Also, I left out your "inertial" since I see no reason to limit ourselves to inertial frames.)


"I've heard similar, and that would probably describe chronological protection on a macroscopic scale. The microscopic version would probably be the one described earlier, where quantum "feedback" closes wormholes before they become CTCs."

Which makes for a better story?

Milo said...

Ferrell:

"I think that a crew member and a passenger having a short discussion with the crew clearing up a couple of misundertandings about the stardrive on the passenger's part would not only give the reader a grasp on the stardrive, but would help define the two characters."

So would an annoying nerd trying to show off his knowledge by explaining FTL, and being cut off by the passenger who doesn't care :)

Anonymous said...

OK, someone with a better grasp on this than me; according to GR the only "privilaged" frame of reference/observation of FTL would be outside the universe? or, am I missing something?

Ferrell

Thucydides said...

Just rereading some earlier posts and a commenter wondered what sort of kludge would be needed to invoke both compact automatic weapons and edged weapons in the same setting. Consider that the vast majority of military issue rifles today fulfill both criterion when you fix bayonets.....

Of course the actual utility of bayonets can be questioned. As far back as the American Civil War, bayonet and sabre wounds accounted for only a small fraction (>5%, if I remember correctly) of battlefield injuries. OTOH, bayonets and various improvised edged and blunt weapons were very popular with trench raiding parties in WWI. By WWII, bayonets had fallen back to their Civil War status, but I have had conversations with British soldiers who participated in the "Troubles" in Northern Ireland where fixing bayonets was a powerful deterrent to civilian mobs intent on surrounding and killing them in the 1970's. Bayonets have also resurfaced in Iraq, where a British Corporal led a bayonet charge against 30+ insurgents in 2004.

No need for force fields to invoke edged weapons, just the right circumstances to "close with and destroy the enemy".

Raymond said...

Milo:

"The only reasons why FTL travel could be limited to a single frame are..."

Agreed. (That's why I said "not necessarily".)

"Also, I left out your "inertial" since I see no
reason to limit ourselves to inertial frames."


Perhaps. IIRC it's possible to define non-inertial frames where objects appear to move faster than light - limiting things to inertial frames makes some points more explicit. I could be wrong on that, though.

"Which makes for a better story?"

If you want to deal with time-travel hijinks, use the macroscopic version. If you don't, use the microscopic one. And remember that the "causality, relativity, FTL travel: chose any two" saying has a time travel corollary - causality, time travel, free will: choose any two.

Ferrell:

"OK, someone with a better grasp on this than me; according to GR the only "privilaged" frame of reference/observation of FTL would be outside the universe? or, am I missing something?"

Outside the universe relative to what? AFAIK, under GR there's no useful definition of "outside".

Milo said...

Raymond:

"causality, time travel, free will: choose any two"

I disagree that time travel violates free will. Knowing what choices I am going to make before I make them does not change the fact that, when I make them, they will be my choices. Time travel cannot force me to make choices inconsistent with my personality, it merely means that those choices will already start having an effect before I made them. Instead, the universe is forced to create only closed timelike loops that are consistent with my personality. If you look at a choice you are prophesized to make and feel "I would never do that", then inevitably by the time that happens, the choice will come to make sense to you. If you truly would never do that, then you will not be prophesized to do it.

Then again, why are you even listing causality there? I thought violating causality is the entire point of time travel? Unless you have "create a parallel universe without changing the one you came from" type time travel, maybe.

So yeah. I choose time travel and free will but no causality.

Raymond said...

Luke:

Thanks for the earlier answers, btw. Another batch, purely speculative (not advancing any conjectures), if you don't mind:

- Does non-paradoxical FTL require simply a canonical frame for all FTL travel, or that all FTL travelers are at rest WRT that frame?

- Does a quantum gravity theory necessarily quantize spacetime as well?

- Does a quantized spacetime necessarily imply a privileged frame?

- What sort of minimum mass are we talking about for a traversable wormhole?

Milo said...

Raymond:

"Does non-paradoxical FTL require simply a canonical frame for all FTL travel, or that all FTL travelers are at rest WRT that frame?"

This is a sticky question that requires you to define "at rest" for an object moving faster than light (which, intuitively, is not at rest at all).

At least in the case of Alcubierre drives there is a meaningful distinction since the ship explicitly isn't moving in an inertial sense, instead "surfing" on spacetime. In the case of fictional FTL systems with less scientific basis than the Alcubierre drive, though, it's pretty much arbitrary whether you consider your ship to be "at rest" at all. (Mind you, it would be pretty useful to be travelling faster than light without putting your crew through acceleration stresses.)

I think all that is required is that there is some frame in which you move in a strictly positive direction through time, irrespective of how fast or slow you are moving through space while you're at it. (If you're moving faster than light, then you'll appear to be moving backwards in time from some other frame, but this is not an issue.)

Milo said...

Put it this way. Look at two events which are separated by a spacelike interval - that is, they are further apart in space than in time. Thus, they are not causally connected without FTL travel.

Now, according to general relativity, there is no absolute way to say which event happened first, since you can define a frames of reference to set it either way.

For causality-preserving FTL, what you need is some rule that unambiguously defines, for any spacelike pair of events, which one happened first (and which remains consistent with the already-existing ordering of timelike separated events). It would then by possible to travel by FTL from one event to another event separated from it by a spacelike interval (something that is impossible to do STL, per definition of "spacelike"), but only if your rule sets the origin event as happening before the destination event.

(Remember, "event" is a special relativity terminology for a point in spacetime.)

Luke said...

Raymond:

Does non-paradoxical FTL require simply a canonical frame for all FTL travel, or that all FTL travelers are at rest WRT that frame?

While this would make for non-paradoxical FTL travel, FTL travel can still preserve causality without a common rest frame.

For example, suppose your wormhole route or the Causality Protection Regulation Board or whatever mean that when you go from Sol to Wolf 359 you go forward in time by 2 years according to the reference frame at Sol. Okay, so you choose your FTL reference frame so that trip takes you to the same time coordinate. In this FTL reference frame it is still possible to make jumps from Sol to Sirius that takes you back in time by 4 years (and going from Sirius to Sol takes you forward in time by 4 years) because if you jump from Wolf 359 to Sol to Sirius (and go back in time coordinate by 4 years) it still takes at least 7.7 years to get from Sirius back to Wolf 359 because Sirius and Wolf 359 are 7.7 light years apart. However, any FTL jump from Sirius to Wolf 359 would need to take you forward in time by 4 years.

In this example you have a bunch of local frames that together still do not allow you to violate causality. You might come up with other examples that do the same thing.

Does a quantum gravity theory necessarily quantize spacetime as well?

It is generally thought that it would, but no one is really sure and we won't be sure until we have a theory of quantum gravity supported by experiments.

Does a quantized spacetime necessarily imply a privileged frame?

Experimental tests have falsified this hypothesis (at least in the form of the simplest theories). Some indications were that quantized space-time would affect high energy photons more than low energy photons over very long travel distances. This was not supported by astronomical observations.

What sort of minimum mass are we talking about for a traversable wormhole?

As low as you think you need to make your setting interesting. The Visser wormhole is a valid geometry with zero mass. General relativity does not forbid negative mass wormholes (although it appears that quantum mechanics forbids these). Note that the magnitudes of the internal energies of these low mass wormholes can still be extraordinarily large. Visser's original wormhole geometry was cubic rather than a circle. The energy along each of the struts holding open the wormhole would be -1.52E43 J/m. That's about -28 Earth masses per meter. (For Planar Visser wormholes, such as the circular one I mentioned earlier, double the energy per unit length.)

Luke said...

There is one other restriction that will be applied to realistic FTL travel. The various conserved quantities (energy, momentum, angular momentum, electric charge) must be applicable locally. (For the cognisetti, I am assuming that you have asymptotic flatness, which will be the case for travel between planets, stars, black holes, pulsars, galaxies, and so on). This means if your spacecraft has a mass of 100 tons, it can't just appear in the middle of empty space - it must absorb or swap with 100 tons of stuff that is already there. The spacecraft will either be moving with the same speed as the stuff it absorbed or balance its momentum by giving a kick in the opposite direction to other stuff in the same vicinity. The spacecraft also can't just disappear, leaving only empty space. 100 tons of stuff or its energy equivalent must remain behind (if this 100 tons takes the form of radiation, it is an explosion of about 2,000,000 megatons).

Note that you can mostly sweep this under the rug if FTL travel only takes place at massive warp gates or jump points or some such. All the mass balance is handled by adding to or subtracting from the mass of the warp gates - but since they weigh so much anyway it is really a drop in the bucket.

Luke said...

Citizen Joe:

Raymond covered the most relevant points to your thought experiments. The main thing I have to add is that Bob may see Andy's clock going faster than his own, or slower than his own, depending on his acceleration at the time. For example, if Bob is coasting at 0.8 c, he will see Andy's clock ticking at 60% the rate of his own clock. If he is accelerating to move on a circle with circumference of 1 light year with a constant speed of 0.8 c (acceleration for the "centrifugal force") he will see Andy's clock ticking 33% faster than his own.

Raymond said...

Luke:

Thanks. If you're not tired of answering silly questions, I've got a couple on Alcubierre and variants:

- Supposedly objects inside the Alcubierre bubble follow a freefall geodesic - ie are at rest WRT local spacetime. Would this count as a common frame for all users of the drive?

- I know there's problems with bow shock for Alcubierre geometries, but only at FTL, correct? STL versions don't deal with naked singularities and Hawking radiation inside the bubble?

- STL versions also don't experience dilation, IIRC. What if you use an STL Alcubierre drive to move a wormhole? If I've got this figured, the Earth end of the wormhole would observe the full trip time instead of the dilated one, and the resulting wormhole connection wouldn't have the timelike separation that our original model did. Am I missing something?

Tony said...

Raymond:

"Especially if you're trying for hard SF of any kind, in which case you're probably incorporating all sorts of technological and engineering details, if only in the background. Two sentences to soften the blow to Einstein is too much? Really?"

Really. As discussed in a previous topic, Heinlein totally destroyed his credibility on relativity and computer science in the space of a few paragraphs in Starman Jones, an otherwise very worthy story.

We know it's science fiction, and that some physics is going to be stretched. Simply saying that you are making a hyperspace jump to get from here to there is all you need to do. As long as the rest of your physics is good, only ridiculously doctrinaire and pedantic physics professors are going to be offended. And, quite frankly, from my experience with PhDs in multiple fields, including physics, worrying about offending them is a major waste of time. The credentialed crank quotient is quite high in academia.

Luke said...

Raymond:

Alcubierre style warp drives end up having a few non-obvious peculiarities. Normally, we think of having a massive spacecraft (or other massive object) in a non-warping state (and in asymptotically flat space-time, just to put out all the caveats) which then turns on its warp drive and ends up someplace else in a non-warping state (in asymptotically flat space-time). Unfortunately, this is incompatible with the simultaneous conservation of energy, momentum, and angular momentum. This leads to the following possibilities:

[1] Warp travel is only possible along prepared routes. The prepared route is highly curved space-time, and thus travel along the route violates the assumption of separated asymptotically flat regions and energy, momentum, and angular momentum do not need to be locally conserved along the route (although they still must be globally conserved when considered from a viewpoint that observes the route as a whole.

[2] The spacecraft somehow dumps all of its mass as it activates the warp drive, and propagates as a massless object until it reaches its destination. At the destination, it must absorb enough energy equivalent to the mass it wishes to precipitate out of the warp bubble. Note that in this case it is probably impossible for the warp bubble and anything in it to interact with the external universe (since doing so would give it a non-zero energy).

Anyway, on to your specific questions ...

Supposedly objects inside the Alcubierre bubble follow a freefall geodesic - ie are at rest WRT local spacetime. Would this count as a common frame for all users of the drive?

It is not a common frame for observers in different warp bubbles. If Andy is warping in one bubble and Bob is warping in another bubble they can be in different frames of reference.

I know there's problems with bow shock for Alcubierre geometries, but only at FTL, correct? STL versions don't deal with naked singularities and Hawking radiation inside the bubble?

Perhaps more correctly, you can find warp geometries at STL that do not have bow shocks although there are (probably unphysical) geometries which warp at STL which also have singular surfaces. Note that you can get around the restriction on singular surfaces at FTL speeds if you set up a prepared track which warps on a pre-defined schedule.

STL versions also don't experience dilation, IIRC. What if you use an STL Alcubierre drive to move a wormhole? If I've got this figured, the Earth end of the wormhole would observe the full trip time instead of the dilated one, and the resulting wormhole connection wouldn't have the timelike separation that our original model did. Am I missing something?

That seems correct to me.

It is interesting to note that warp geometries that do not have mass magnitudes greater than that of the observable universe connect a "pocket universe" to the normal universe via a microscopic wormhole. The wormhole end in this universe is what is warped, and the pocket universe (and anything in it) goes along for the ride, as it were.

Sighman_Says said...

Probably only tangentially related to any of the subjects being discussed but I got a couple of questions.

First, about quantum entanglement. I'm aware that it cannot allow FTL communication. Still, as I understand it, two entangled particles can affect each other 'simultaneously' even across spacelike gaps... and yet GR disallows objective simultaneity. So, what is going on then? Or does this just happen to be one of those pesky questions that a theory of quantum gravity would need to solve?

Second, say you have two vessels (Alpha and Omega), both traveling at a seriously good pace (the same for both) for time/distance dilation to be pronounced. Both are heading for Wolf 359 and passing by Terra on the route. Omega is lagging behind Alpha a fair distance.

So when we start the observation Alpha is right next to Terra. From the reference of the vessel, the trip to Wolf 359 isn't 7.8 light years, but say, 1 for simplicity, because of length contraction.

Now I've got to be mistaken about something because it seems to me that that would imply that Alpha could send a normal light-speed signal to Wolf 359, 7.8 ly away from Terra's standpoint, and the message would take only 1 year to get there. Wolf 359 gets the message, replies immediately in Terra's direction.

We wait a bit and Omega is now next to Terra. From Omega's standpoint, the message took one year to get to them. From the Alpha/Omega frame of reference, a lightspeed message that would take 15.6 years from Terra's standpoint took only 2, and FTL communication can ensue. Or does it?

I seriously gotta be misinterpreting or forgetting something important here. Can someone correct me?

Rick said...

Tony - I would cut Starman Jones some slack regarding computer science, considering it was written in 1953. I assume you mean the enlisted guy thumbing a manual to convert base 10 to binary and back. But I also imagine that real world I/O of that time was pretty damn primitive.

Another Golden Age SF fave of mine, Clarke's The City and the Stars, of similar vintage, similarly assumes that humans of the remote future will use binary numbers.

(I do agree that Heinlein's mangling of relativity was awesome - though when I first read it, in 6th grade, I probably didn't know any better. In any case, what stuck with me was the control room drama, not the pseudo physics.)

Tony said...

Rick:

"Tony - I would cut Starman Jones some slack regarding computer science, considering it was written in 1953. I assume you mean the enlisted guy thumbing a manual to convert base 10 to binary and back. But I also imagine that real world I/O of that time was pretty damn primitive."

The UNIVAC I that was used to predict the outcome of the 1952 Presidential election was programmed by typing alphanumeric codes on a regular keyboard, which were then encoded onto magnetic tape, the tape then being mounted on a reel-to-reel reader to run the program. Presumably Heinlein could have been aware of this. It wasn't exactly a secret, even if it was a bit of techno-esoterica, then (and ever since).

Even if he didn't know about that, he would have presumably been familiar with Vannevar Bush's 1945 Atlantic Monthly article "As We May Think", which predicted things like the WWW and graphical user interfaces. When SJ came out, Doug Engelbart, who had been inspired by reading "As We May Think" while serving in the Army on Okinawa, was already working on foundation concepts that would lead to modern user interfaces.

I really don't think Uncle Bob has a good excuse here. And, anyway, even the best of us goof up every now and then.

"Another Golden Age SF fave of mine, Clarke's The City and the Stars, of similar vintage, similarly assumes that humans of the remote future will use binary numbers."

Never read it. It doesn't fall into my space opera and military SF weelhouse.

"(I do agree that Heinlein's mangling of relativity was awesome - though when I first read it, in 6th grade, I probably didn't know any better. In any case, what stuck with me was the control room drama, not the pseudo physics.)"

Y'know, I first read SJ about the same age. Unfortunately for me (I guess) my mother was heavily involved in the use of computers for business applications (being the manager of a major West Coast bank's Trust Accounting department). I just couldn't see flipping switches for input, and reading coded lights for output, when my world already included keypunch machines, tape drives, and 14x11" greenbar printouts.

Raymond said...

Luke:

"[2] The spacecraft somehow dumps all of its mass as it activates the warp drive, and propagates as a massless object until it reaches its destination. At the destination, it must absorb enough energy equivalent to the mass it wishes to precipitate out of the warp bubble. Note that in this case it is probably impossible for the warp bubble and anything in it to interact with the external universe (since doing so would give it a non-zero energy)."

Does this also apply to STL versions? To pocket universe versions?

"It is interesting to note that warp geometries that do not have mass magnitudes greater than that of the observable universe connect a "pocket universe" to the normal universe via a microscopic wormhole. The wormhole end in this universe is what is warped, and the pocket universe (and anything in it) goes along for the ride, as it were."

Is entry/exit to/from these pocket universes defined, or would that be an open question?

As for the STL-Alcubierre + wormhole setup, that would much more easily allow for criss-crossing and cyclic-graph wormhole networks due to the drastically lowered timelike separation, correct?

If so, I think that setup sounds like what Rick's looking for.

Milo said...

Here's a little something on time travel if you can comprehend it.



Raymond:

"STL versions also don't experience dilation, IIRC. What if you use an STL Alcubierre drive to move a wormhole?"

If you use STL without time dilation to deliver a wormhole, then it will take years before your interstellar tramline is open. In order to remedy out impatience with even the nearest interesting places probably being decades away, you need to either send your wormholes FTL so they take less time to arrive, or let them experience time dilation so they appear to take less time to arrive from the wormhole's frame of reference (and, as a corollary, from the person sending the wormhole's frame of reference).

Luke said...

Sighman_Says:

First, about quantum entanglement. I'm aware that it cannot allow FTL communication. Still, as I understand it, two entangled particles can affect each other 'simultaneously' even across spacelike gaps... and yet GR disallows objective simultaneity. So, what is going on then? Or does this just happen to be one of those pesky questions that a theory of quantum gravity would need to solve?

While there are many interpretations for what is happening (all of which give the same observables, and thus all of which are experimentally indistinguishable), the logic ultimately comes down to something like this:

I have a black marble and a white marble that are otherwise indistinguishable. I take both marbles and two boxes into a room without any light. I put one marble in each box. Then I go out of the room and give you one box. I keep the other box. I don't know if I have a white marble or a black marble in my box. I don't know if you have a white marble or a black marble in your box. However, as soon as I open my box and look in I also know what color of marble is in your box, no matter how far away your box happens to be.

There are fun things you can do with quantum superpositions that you can't do with marbles, but the logic of simultineity and spacelike gaps works out the same.

Second, say you have two vessels (Alpha and Omega), both traveling at a seriously good pace (the same for both) for time/distance dilation to be pronounced. Both are heading for Wolf 359 and passing by Terra on the route. Omega is lagging behind Alpha a fair distance.

So when we start the observation Alpha is right next to Terra. From the reference of the vessel, the trip to Wolf 359 isn't 7.8 light years, but say, 1 for simplicity, because of length contraction.


So just for concreteness, this puts us at a speed of 0.9917 c to four significant digits. To the same four significant digits the time dilation and length contraction factor is 7.778 - close enough to 7.8 for our purposes. For the remainder of this discussion I will use the value of 7.778 light years for the sol - Wolf 359 distance.

Now I've got to be mistaken about something because it seems to me that that would imply that Alpha could send a normal light-speed signal to Wolf 359, 7.8 ly away from Terra's standpoint, and the message would take only 1 year to get there. Wolf 359 gets the message, replies immediately in Terra's direction.

In Alpha's coordinate system it takes less than one year to get there, because Wolf 359 is moving toward the radio pulse. In Earth's coordinate system it takes 7.8 years to get there.

We wait a bit and Omega is now next to Terra. From Omega's standpoint, the message took one year to get to them. From the Alpha/Omega frame of reference, a lightspeed message that would take 15.6 years from Terra's standpoint took only 2, and FTL communication can ensue. Or does it?

No, because Earth's frame of reference, including the time coordinate, is different from that of the Alpha and Omega starcraft. Also note that from Alpha's standpoint, Earth is zipping away from the Wolf 359 radio pulse at high speed, so it will take lots more time to get there.

continued ...

Luke said...

Continued from previous post

Here's the math. First, define gamma=7.778 and beta=0.9917. The product beta*gamma we will denote delta=7.713. Furthermore, the following relation is exact:
1/gamma^2 = 1 - beta^2

We will let (t,x) represent the coordinate pair of time and distance in earth coordinates. (t',x') is the coordinate pair in Alpha/Omega coordinates. To go from one set of coordinates to another is
t' = gamma * t - delta * x
x' = gamma * x - delta * t
t = gamma * t' + delta * x'
x = gamma * x' + delta * t'
Time and distance are measured in consistent units, such as years and light years, or seconds and light seconds.

For convenience, we will set the event of Alpha passing earth at x=0,t=0 and x'=0,t'=0. Earth will always be x=0 and Alpha will always be x'=0. Label this event as 0
Event 0: Alpha passes earth, Alpha emits signal
x0 = 0
t0 = 0
x0' = 0
t0' = 0

From Alpha's point of view, it emits its radio signal at x'=0,t'=0. At t'=0, we know that Wolf 359 is at x'=1 ly due to length contraction. Assuming Wolf 359 is at rest with respect to earth, it will be traveling at a speed of -beta * c with respect to alpha, such that the coordinates of Wolf 359 at any time t' are
x' = 1 ly - beta * t'
You can easily verify that this gives x = gamma * 1 ly for any t, just as expected. Also, just as expected, Alpha will arrive at Wolf 359 at t' = 1/beta y (this is what gives x'=0, Alpha's position). Alpha's radio pulse has a distance coordinate of
x' = t'
because it is emitted at x'=0, t'=0 and travels at the speed of light. The radio pulse reaches Wolf 359 when the x' coordinate of the radio pulse equals the x' coordinate of Wolf 359.
x' = 1 ly / (1+beta) = 0.5021 ly
t' = 0.5021 y
which becomes in Earth's frame
x = gamma * x' + delta * t'= 7.778 ly
t = gamma * t' + delta * x'= 7.778 ly
This is exactly what we would expect from a pulse traveling the speed of light emitted from Earth's position traveling 7.778 light years distance. Label this event as 1
Event 1: Signal reaches Wolf 359, Wolf 359 emits return signal.
x1 = 7.778 ly
t1 = 7.778 y
x1' = 0.5021 ly
t1' = 0.5021 y

Now for Omega. From the way you stated the problem, I assume you mean to have Wolf 359 emit a radio signal back toward Earth as soon as it receives Alpha's signal. Also, I assume you mean to have Omega passing Earth just as the radio signal reaches Earth. For this, it helps to find Earth's position as a function of t' in the Alpha/Omega reference frame. Since we know it was at x' = 0 when t' = 0, and that it is moving at a speed of -beta*c with respect to Alpha, we have
x' = - beta * t'
We also know that the radio signal coming back from Wolf 359 has position coordinate
x' = x1' - (t' - t1')
When we solve for when these two positions are equal (corresponding to the radio pulse reaching Earth) we find
t' = (x1' + t1')/(1-beta) = 120.987 y
x' = -119.984 ly
where I am using more significant figures than is usually justified to avoid round-off error in the subsequent calculation, due to the cancellation of large numbers. In Earth's frame, this becomes
x = gamma * x' + delta * t' = -0.0084 ly
t = gamma * t' + delta * x'= 15.546 y
which is close enough to the exact values of x = 0, t = 15.556 y for our purposes (the difference is due to round-off error). Label this as event 2
Event 2: Return signal reaches Earth and Omega.
x2 = 0
t2 = 15.556 y
x2' = -119.984 ly
t2' = 120.987 y

Luke said...

Odd - in case my first post didn't get through, here it is again

Sighman_Says:

First, about quantum entanglement. I'm aware that it cannot allow FTL communication. Still, as I understand it, two entangled particles can affect each other 'simultaneously' even across spacelike gaps... and yet GR disallows objective simultaneity. So, what is going on then? Or does this just happen to be one of those pesky questions that a theory of quantum gravity would need to solve?

While there are many interpretations for what is happening (all of which give the same observables, and thus all of which are experimentally indistinguishable), the logic ultimately comes down to something like this:

I have a black marble and a white marble that are otherwise indistinguishable. I take both marbles and two boxes into a room without any light. I put one marble in each box. Then I go out of the room and give you one box. I keep the other box. I don't know if I have a white marble or a black marble in my box. I don't know if you have a white marble or a black marble in your box. However, as soon as I open my box and look in I also know what color of marble is in your box, no matter how far away your box happens to be.

There are fun things you can do with quantum superpositions that you can't do with marbles, but the logic of simultineity and spacelike gaps works out the same.

Second, say you have two vessels (Alpha and Omega), both traveling at a seriously good pace (the same for both) for time/distance dilation to be pronounced. Both are heading for Wolf 359 and passing by Terra on the route. Omega is lagging behind Alpha a fair distance.

So when we start the observation Alpha is right next to Terra. From the reference of the vessel, the trip to Wolf 359 isn't 7.8 light years, but say, 1 for simplicity, because of length contraction.


So just for concreteness, this puts us at a speed of 0.9917 c to four significant digits. To the same four significant digits the time dilation and length contraction factor is 7.778 - close enough to 7.8 for our purposes. For the remainder of this discussion I will use the value of 7.778 light years for the sol - Wolf 359 distance.

Now I've got to be mistaken about something because it seems to me that that would imply that Alpha could send a normal light-speed signal to Wolf 359, 7.8 ly away from Terra's standpoint, and the message would take only 1 year to get there. Wolf 359 gets the message, replies immediately in Terra's direction.

In Alpha's coordinate system it takes less than one year to get there, because Wolf 359 is moving toward the radio pulse. In Earth's coordinate system it takes 7.8 years to get there.

We wait a bit and Omega is now next to Terra. From Omega's standpoint, the message took one year to get to them. From the Alpha/Omega frame of reference, a lightspeed message that would take 15.6 years from Terra's standpoint took only 2, and FTL communication can ensue. Or does it?

No, because Earth's frame of reference, including the time coordinate, is different from that of the Alpha and Omega starcraft. Also note that from Alpha's standpoint, Earth is zipping away from the Wolf 359 radio pulse at high speed, so it will take lots more time to get there.

Luke said...

Raymond:

Does this also apply to STL versions? To pocket universe versions?

Yes. Momentum, angular momentum, and energy still must be conserved even when warping at STL.

Is entry/exit to/from these pocket universes defined, or would that be an open question?

So far no one has worked out how to go in or out, if that is what you are asking.

As for the STL-Alcubierre + wormhole setup, that would much more easily allow for criss-crossing and cyclic-graph wormhole networks due to the drastically lowered timelike separation, correct?

I don't know about more easily - the trick of taking one end of a wormhole generated at Wolf 359 through the wormhole to Sol and then through the wormhole to Sirius in order to get a direct wormhole connection from Wolf 359 to Sirius seems at least as easy. For example, when you take wormhole ends through wormholes you don't need to worry about how to find enough mass at Sirius to account for the mass of your wormhole end when you cannot interact with anything in the outside universe (and thus cannot see), as is likely the case for free-form warping.

But yes, you could get wormholes inter-connecting star systems that only require short STL jaunts between them.

Thucydides said...


[1] Warp travel is only possible along prepared routes. The prepared route is highly curved space-time, and thus travel along the route violates the assumption of separated asymptotically flat regions and energy, momentum, and angular momentum do not need to be locally conserved along the route (although they still must be globally conserved when considered from a viewpoint that observes the route as a whole.


If warp travel is only possible along strongly curved space time, then we are talking about something similar in concept to the Alderson drive (although the warping of spacetime envisioned by Pournelle is pretty shallow, actually)

In fact, the implication I'm getting from reading that is you don't go to the edge of the solar system to hook onto a tramline, but skydive close to the sun in order to reach the deepest, most curved part of spacetime locally available.

MRig said...

Here's a question that occurred to me while reading this comment thread: is there any reason to need a wormhole route that went from a spot on Earth to (say) a Lagrange point before heading to parts outward? In other words, is there reason for a train station in space?

Luke said...

Thucydides:

If warp travel is only possible along strongly curved space time, then we are talking about something similar in concept to the Alderson drive (although the warping of spacetime envisioned by Pournelle is pretty shallow, actually)

I'm not really sure of the rationalle behind the Alderson drive. I vaguely remember some sort of "disappear here, appear there" sort of behavior, without any long strings of tortured space-time between the jump points.

In fact, the implication I'm getting from reading that is you don't go to the edge of the solar system to hook onto a tramline, but skydive close to the sun in order to reach the deepest, most curved part of spacetime locally available.

A sun would not have enough curvature. As long as gravity is approximately Newtonian, energy, momentum and angular momentum are localized. What you need is gravity strong enough to give strong non-Newtonian effects. For example, in the space-time around a close near-contact black hole binary you might have warpage so extreme that energy & etc. cannot be localized and you could warp between and around the black holes without needing to worry about the usual conservation laws (although there may be other unfamiliar conservation laws which apply in such cases). Similarly, if you reach a cosmic string you might be able to warp along the length of the string to appear anywhere else along the string's path. But you couldn't, for example, warp from one black hole out across flat space-time to another black hole, or from one cosmic string to another. If there are no convenient cosmic strings or black holes strung out like beads of pearls along a desired travel path it may be possible to make an artificial trackway for your warp drive - a conduit of space-time stretched and distorted so severely that the old familiar conservation laws no longer apply along its path (although they still must be conserved according to distant observers viewing the trackway as a whole).

Thucydides said...

The Alderson drive is supposed to reflect the warping of space due to the massive gravitational influence of stars. The simple example is the universe as a rubber sheet and stars represented by bowling balls distorting the sheet.

Now in some cases, the distortions "run together" between two stars, making a path somewhat lower than the rest of the sheet between these two stars. This is the "tramline" which the Alderson drive follows between stars (The drive itself seems to fold space around the starship and drops out of this universe, along the tramline and back into this universe).

Now what you are talking about is gravitational fields orders of magnitude beyond this, and it would certainly need a super civilization to build black holes, harness cosmic strings etc. to make FTL work that way.

Actually, you said warp between and around the black holes. What does that mean, exactly?

Tony said...

Re: Alderson Drive

Alderson tramlines are supposed to be lines of "equipotential thermonuclear flux" between stars. Don't ask me what that's supposed to mean. apparently it meant something to Dan Alderson, but he's dead. As described by a character in "He Feel Into a Dark Hole", what the Alderson Drive does is tip the spaceship off the peak of a hill, and the ship races across the valley until it climes to peak of another hill and stops. According to other cannon evidence, this take precisely zero time, or at least an immeasurably short amount of time. My own conjecture (it's never directly addressed in cannon, that I can remember) about the need for specific points of departure and arrival along a tram line ("Alderson Points") is that the drive only works from point to point, each point being where the energy state of the tramline balances.

Rick said...

It only just dawned on me that I must have picked up the term 'tramline' from books featuring the Alderson drive, or discussions thereof.

In any case, like my own (much less developed) FTL ideas, it sounds like basically a retcon of the Starman Jones FTL to correct glaring errors.

(Side note that I was not aware of UNIVAC I and the 1952 prez election! And, just below the surface, there was something very steampunkish about Heinlein. I suspect he was not enough interested in computers to read even the semitechnical literature readily available to him at the time.)

Raymond said...

Luke:

"I don't know about more easily - the trick of taking one end of a wormhole generated at Wolf 359 through the wormhole to Sol and then through the wormhole to Sirius in order to get a direct wormhole connection from Wolf 359 to Sirius seems at least as easy. For example, when you take wormhole ends through wormholes you don't need to worry about how to find enough mass at Sirius to account for the mass of your wormhole end when you cannot interact with anything in the outside universe (and thus cannot see), as is likely the case for free-form warping."

Eh, I'm just trying to get a feel for options (and what wormhole network maintenance would look like).

Regarding moving a wormhole (in this example) from Wolf 359 to Sol to Sirius through the existing network: this doesn't mean the Wolf 359 -> Sirius wormhole is permanently dependent on the other two remaining open, does it? I can't think of a topological reason it would, but I don't have the math to prove it.

Also: you mentioned earlier the possibility of dilating one end of a wormhole by a stronger gravitational field. If you were to apply that to the origin of a wormhole, that would reduce the timelike separation between the two, wouldn't it?

Thucydides said...

Tony, thanks for reminding me!

I'm pretty sure the explanation of tipping the FTL ship off the top of a hill of potential energy is simply taking the previous example of the rubber sheet and flipping it over (in FTL space the gravitational wells become gravitational hills, and areas where the gravity wells run together are now represented by small ridgelines rather than small valleys in the inertial universe.)

"Equipotential thermonuclear flux" means whatever you want it to, evidently. I think it implies the energy generated by stellar fusion is also important in this scheme of things. The story being referenced (He fell into a dark hole) points out the ships can take the tramline from the normal star to the black hole terminus, but cannot escape the black hole until they devise a way to create a precisely timed burst of gravitational radiation to coincide with the starship's activation of the Alderson drive at the tramline terminus. (spoiler alert: someone pilots another trapped starship into the event horizon to do the deed...)

Alas, Luke seems to have discovered a way to spoil our fun in the next thread (a tramline would need to follow a cosmic string or similarly warped piece of spacetime).

Tony said...

Rick:

"In any case, like my own (much less developed) FTL ideas, it sounds like basically a retcon of the Starman Jones FTL to correct glaring errors."

According to Niven and Pournelle, they just went to Alderson and asked him to work out the specficis of a plausible FTL drive, and committed to living with the social and technical implications of the result. Where Alderson got his inspiration has never been mentioned in writing, that I know of, and people I know who have talked to Jerry about the CoDominium milieu never got into details about that.

"(Side note that I was not aware of UNIVAC I and the 1952 prez election! And, just below the surface, there was something very steampunkish about Heinlein. I suspect he was not enough interested in computers to read even the semitechnical literature readily available to him at the time.)"

Yeah...with a 1% sample they correctly predicted the outcome. Not having been there myself, and only having seen a few film clips of the CBS coverage, I think it was more in the nature of a stunt than anything else.

WRT Uncle Bob, I think we get all het up about his technical prowess from stories like "The Long Watch" and juveniles like Space Cadet and The Rolling Stones, where he threw out some high-speed, low-drag astrodynamics. But if you think about it, Heinlein never was all that technically detailed in his storytelling -- though his relativity did get better by the time he got around to Time for the Stars.

Tony said...

Thucydides:

"I'm pretty sure the explanation of tipping the FTL ship off the top of a hill of potential energy is simply taking the previous example of the rubber sheet and flipping it over."

Oh, I'm sure it is. But think of the implications of the illustration -- gravity sucks you in, while the Alderson force pushes you out. Also, with the Alderson force, the regions of low energy are where you move the fastest. It has a nice symmetry, which does nothing but help the plausibility.

Also, if you think about it, the only real improvement you can make on the idea is to eliminate the tramlines. In that case, you have to motor out to where the Alderson force can overcome the force of gravity, then you orient towards another star and flip the magic switch. When you get deep enough in the star's gravity well, it precipitates you out of Alderson space, back into relativistic space, and off you go, either deeper in the system you just arrived at, or over to piece of space on its outskirts convenient to continuing your journey.

Now, this has real cool implications, because the range limit on a jump is essentially the accuracy of you astrometric knowledge and the precision with which you can align yourself between the origin and destination stars. This eliminates the instant-anywhere drive, but leaves open the possibility of getting lost in space and could motivate risk-v-reward plotlines when time is of the essence. I like it...

Luke said...

Thucydides:

Actually, you said warp between and around the black holes. What does that mean, exactly?

Well, if you are orbiting around one of two close binary black holes, energy and momentum and angular momentum could well be non-local enough that you could warp someplace else around that black hole, or around the other hole, so long as you do not go far enough away that you are in the Newtonian limit. In principle, with an FTL drive you could even go inside the event horizon and then come back out again.

Luke said...

Raymond:

this doesn't mean the Wolf 359 -> Sirius wormhole is permanently dependent on the other two remaining open, does it? I can't think of a topological reason it would, but I don't have the math to prove it.

Nope. The Wolf 359 to Sirius line will remain open or not remain open independent or what happens to the Wolf 359 to Sol or Sol to Sirius lines.

Also: you mentioned earlier the possibility of dilating one end of a wormhole by a stronger gravitational field. If you were to apply that to the origin of a wormhole, that would reduce the timelike separation between the two, wouldn't it?

Yes. Any other method of supplying time dilation would also work. One of my favorites is shrinking the wormhole down, shedding most of its mass, giving it a large electric charge, and then letting it cool its heels going 'round and 'round in a cyclotron for several years at near light speed. This gives the usual time dilation for high speed travel, and can slow down wormhole ends that get too far behind everyone else.

Luke said...

Thucydides:

Alas, Luke seems to have discovered a way to spoil our fun in the next thread (a tramline would need to follow a cosmic string or similarly warped piece of spacetime).

Alternately, you can dump your mass before you leave and then pick it up again from something massive at your destination. Or the warped bit of spacetime that you follow might not actually go through our universe (that is, it is a wormhole). But it is one semi-realistic possibility.

Sighman_Says said...

Tony:
"Also, if you think about it, the only real improvement you can make on the idea is to eliminate the tramlines. In that case, you have to motor out to where the Alderson force can overcome the force of gravity, then you orient towards another star and flip the magic switch. When you get deep enough in the star's gravity well, it precipitates you out of Alderson space, back into relativistic space, and off you go, either deeper in the system you just arrived at, or over to piece of space on its outskirts convenient to continuing your journey.

Now, this has real cool implications, because the range limit on a jump is essentially the accuracy of you astrometric knowledge and the precision with which you can align yourself between the origin and destination stars. This eliminates the instant-anywhere drive, but leaves open the possibility of getting lost in space and could motivate risk-v-reward plotlines when time is of the essence. I like it... "


This is basically the kind of ftl drive developed in the webcomic 'Outsider'.
http://well-of-souls.com/outsider/forum_ftl_tech.html

Raymond said...

Luke:

Thanks again. Much fodder. WRT tramlines, unless we find convenient strings linking solar systems, I'm not sure what the advantage would be compared to wormholes - or is there even one?

Tony:

WRT the Alderson Drive, would a (very brief) mention of a special frame or cosmic strings detract any? A Mote In God's Eye hinges upon particular behavior of the drive, so an explanation has to go somewhere. Would a small nod to the ex-girlfriend in the bar be worse than pretending she doesn't exist?

Luke said...

Raymond:

WRT tramlines, unless we find convenient strings linking solar systems, I'm not sure what the advantage would be compared to wormholes - or is there even one?

The advantage would be that presumably one method or the other is possible or less expensive. If it is fundamentally impossible to alter the topology of spacetime, then wormholes will not work at all (at least, not to get elsewhere in this universe).

From a story standpoint, any advantage relies on what sort of flavor you are looking for.

Tony said...

Raymond:

"WRT the Alderson Drive, would a (very brief) mention of a special frame or cosmic strings detract any? A Mote In God's Eye hinges upon particular behavior of the drive, so an explanation has to go somewhere. Would a small nod to the ex-girlfriend in the bar be worse than pretending she doesn't exist?"

Well...since I act like she doesn't exist (invariant of whether I broke things off, she did, or it was mutual) I don't think you'll like my answer.

Basically, I think it's offensive (yes, I really do mean offensive) to bore the reader with any more technical detail that is absolutely required to justif a technical artifact's effect on the action. That's a big reason, aside from the Mary Suisms, that I could never get into the Honorverse. Half of the text was techno-wank.

Milo said...

Personally, I think both "any space opera story that doesn't mention relativity at least in passing is utter garbage and cannot be taken seriously" and "mentioning any hard science that doesn't outright form the basis of the plot is a pretentious distraction that ruins your pacing" are a little extreme. If you can work it in smoothly, then do. Otherwise don't.

Also consider leaving it out of the story proper and including it in a footnote, appendix, or one of those universe compendium thingamajigs that are only ever bought by the 1% most dedicated of your fanbase.

Rick said...

Pretty much all interstellar SF makes some nod to Einstein - that's pretty much what 'FTL' as a jargon term implies.

The issues here are not really about technojargon (or technobabble), I believe, but about what actually comes up on a story.

If I had Luke's comfort level with this stuff, I could probably work a couple of tossoff lines in a story that most readers would ignore, with no loss, but that would signal the cognoscenti that I knew my stuff and had done my homework.

Since I don't have mastery of this stuff, I would instead try and avoid saying anything that would tip off the informed that I was BS-ing.

Anonymous said...

Ok, so at some point, Luke said that jumping from one point to another required that mass at the destination point (equal to that of the spacecraft) needed to swap with the jumping spacecraft; so, would solar wind suffice? Or do you need mass that is closer to the density of the spacecraft?

Ferrell

Luke said...

Ferrel

Any way you can get enough energy to equal the mass energy of the stuff you are bringing out of FTL will work. Since the solar wind has a density of about 7E-21 kg/m^3, a 100 ton starcraft would need to interact with about 1.5E25 m^3, equivalent to a cube 250,000 km on a side. If you can do that, it should work. (Of course, there are large fluctuations in the density of the solar wind, so sometimes you could scoop out less volume, and sometimes you would need to scoop out more.) Typical speeds of the solar wind is about 400 km/s, so because of momentum conservation your starcraft would end up moving at about 400 km/s away from the star (again, with significant fluctuations).

jollyreaper said...

On a semi-related note, a map of all science fiction.

http://scimaps.org/submissions/7-digital_libraries/maps/thumbs/024_LG.jpg

scary huge but detailed and interesting.

jollyreaper said...

Basically, I think it's offensive (yes, I really do mean offensive) to bore the reader with any more technical detail that is absolutely required to justif a technical artifact's effect on the action. That's a big reason, aside from the Mary Suisms, that I could never get into the Honorverse. Half of the text was techno-wank.

I'd break this down into three categories:
1. Things you should never, ever do in fiction, regardless of genre, because it's a bad idea.
2. Things you might be able to get away with if you have a really good justification.
3. Writing for a known audience. Doesn't matter if nobody else is happy if they're the ones paying the bills.

Fanciful tech descriptions are actually exactly like explicit sex scenes -- some people will say too much ruins a story and other people are reading exactly for that and won't you please include some more?

I can't fault an author for knowing a given audience and catering to them, especially if it's the kind of story he wanted to write in the first place. Were there's some serious room for criticism is when an author really doesn't seem to understand what he's going for.

If you're talking Tom Clancy, of course it's war porn. The readers care more about the weapons than the characters. Lovingly detailed descriptions of tanks and bombers is exactly what the readers want to hear, all the technical goodies.

The least useful criticism comes from people who aren't really fans of what you're trying to do in the first place. If you want to tell a science fantasy story, the last person you should talk to is a dyed in the wool hard SF fan who hates FTL, aliens, and laser swords. Someone you should really listen to, especially for negative criticism, is an unabashed fan of that sub-genere. If a fan is pointing out problems, you know that you missed something big-time.

Thucydides said...

"Also, if you think about it, the only real improvement you can make on the idea is to eliminate the tramlines. In that case, you have to motor out to where the Alderson force can overcome the force of gravity, then you orient towards another star and flip the magic switch. When you get deep enough in the star's gravity well, it precipitates you out of Alderson space, back into relativistic space, and off you go, either deeper in the system you just arrived at, or over to piece of space on its outskirts convenient to continuing your journey.

While I like this in principle (a freeform FTL that has a semi plausible basis), the fact that it is freeform would imply you could create CTC's by accident or design. There is no obvious means to prevent such a thing from happening. Tramlines based on stellar activity can at least be handwaved into preventing CTC violations by invoking some sort of "physical" explanation, such as tramlines only form along minimum/maximum potential energy lines, and any lines which crossed to create a CTC would wink out of existence.

Luke,

I'm still not following your example with a binary black hole system. The implication I'm getting out of this is the system does not move you through physical space to otherwhere, but rather through a CTC into "otherwhen. Getting back will be a treat

Luke said...

Thucydides:

I'm still not following your example with a binary black hole system. The implication I'm getting out of this is the system does not move you through physical space to otherwhere, but rather through a CTC into "otherwhen. Getting back will be a treat

Perhaps you are trying to make things overly complicated :-) (My fault, of course, for not explaining clearly)

Here is the basic issue: in space-time which is flat enough that Newtonian gravity is a good approximation, energy and momentum and angular momentum are localized and thus must be conserved locally. This means if you are orbiting around Earth (where gravity is Newtonian to a very good approximation) you can't just warp out without leaving your energy and momentum and angular momentum behind. And if you warp to Jupiter you need to find some energy & etc. around in order to re-materialize in the normal universe.

In space-time where gravity is curved enough to be non-Newtonian, those flat spacetime conserved quantities are no longer local, but rather distributed around in the curved region of spacetime. Thus, it might well be possible to warp from one area of the curved spacetime to another area in that same patch of curved spacetime without needing to worry about accounting for your conserved quantities locally (they will still be conserved globally within the curved spacetime region). A close binary black hole is one example of a place where you would expect strong curvature. I am only considering warping within this universe, not something exotic like diving into a black hole and ending up somewhere or somewhen else - replace the close binary black holes with close binary neutron stars if you want, or a loop of cosmic string, or anything else where gravity is really strong.

However, in strongly curved spacetime there may be other quantities which are locally conserved even though the traditional flat spacetime conserved quantities are not. The details depend on the symmetries and geometry of the spacetime in question.

The black hole issue I was discussing is not relevant to the issue of time travel - it is bringing up another constraint on any form of FTL travel that abides by established physical laws.

Tony said...

Thucydides:

"While I like this in principle (a freeform FTL that has a semi plausible basis), the fact that it is freeform would imply you could create CTC's by accident or design. There is no obvious means to prevent such a thing from happening. Tramlines based on stellar activity can at least be handwaved into preventing CTC violations by invoking some sort of "physical" explanation, such as tramlines only form along minimum/maximum potential energy lines, and any lines which crossed to create a CTC would wink out of existence."

Not necessarily. A hyperjump need not be inertial. Or, if it's effectively inertial in hyperspace, most of the journey is made in the lowest possible energy state, meaning it is effectively non-inertial for chronology preservation purposes.

Rick said...

I am only considering warping within this universe, not something exotic ...

+10

Anonymous said...

Luke said:"Any way you can get enough energy to equal the mass energy of the stuff you are bringing out of FTL will work. Since the solar wind has a density of about 7E-21 kg/m^3, a 100 ton starcraft would need to interact with about 1.5E25 m^3, equivalent to a cube 250,000 km on a side. If you can do that, it should work. (Of course, there are large fluctuations in the density of the solar wind, so sometimes you could scoop out less volume, and sometimes you would need to scoop out more.) Typical speeds of the solar wind is about 400 km/s, so because of momentum conservation your starcraft would end up moving at about 400 km/s away from the star (again, with significant fluctuations)."


Ok, so if I have my starship Jump from one star to another, but have to jump from one stellar diameter 'above' a pole of one star to the opposite pole of another (and zip away from that star at 400 Kps), you'd still need an engine and propellent that can give your spacecraft a delta-V of at least 400 Kps. That's good to know; it gives a starting point for my starship design. Thanks! Hmmm...that also means that there is a limit on how close starships can be to each other when they jump...

Ferrell

Geoffrey S H said...

"If you're talking Tom Clancy, of course it's war porn. The readers care more about the weapons than the characters. Lovingly detailed descriptions of tanks and bombers is exactly what the readers want to hear, all the technical goodies."

The "Cardinal" of The Cardinal of the Kremlin I always thought was well-drawn. Red Storm Rising came across as almost anti-war in some places. Now yes, of course he likes to dabble in technical terms, but his early work I thought could be quite good prior to his post-Berlin Wall novels.

Having read alittle Dale Brown and Steven Coonts (Hong Kong comes to mind) I completley went off any techno-thriller writers... Clancy seems tame by comparison to them.

jollyreaper said...

@Geoffrey concering Clancy

I'm saying what I'm saying as a fan of the stuff when it came out. I grew up reading techno-thrillers and, pre-Wall Fall, it was good stuff. Ever since then the novels seemed like they were struggling for relevance. And yes, given that the bulk of Clancy's work was pre-Fall, his most important novels still seem acceptable given the context. His unsolicited disciples really beat the genre into the ground with a mallet.

The problem I had with post-Fall novels is that there was no world problem so complex and intractable that it could not be solved with the superior application of American firepower. Given that the Evil Empire was gone and there was no longer any credible threat to American hegemony, military techno-thrillers ended up seeming incredibly archaic and out of step with the times.

Rick said...

Hasn't this also been a problem for modern-era Bond films? Drug dealers? Gimme a break. Even Middle East terrorists simply do not have remotely the heft that the old USSR did.

Not that it matters, but if I were doing a Bond film, I would do it as an unabashed period piece, set in the early 60s - Mad Men with cool weapons. :-)

Scott said...

Lemme see if I can recap this without my head exploding...

There are effectively 2 means of FTL travel that don't abuse Einstein like a red-headed stepchild: Wormholes, and Alcubierre-style warping along cosmic strings.

Luke said...

Scott:

As far as we know, both wormholes or Alcubierre-style warp drives along a prepared passageway are not disallowed by physics. An additional form of FTL travel, the Krasnikov tube, also appears to be allowed.

There may be other methods not yet discovered. All such methods can be expected to share certain features, however - namely preservation of causality and local conservation of energy, momentum, angular momentum, and electric charge. These can be satisfied if all FTL happens along a certain path with massive endpoints (and whose endpoints balance out the mass of the FTL traveling thing), and if you assume that the paths are arranged so that no trip through any combination of paths can form a time machine. Similarly, non-time machine forming paths that have sufficiently extreme conditions along their length that they strongly warp space and time could satisfy these constraints. Wormholes are known to fall into the former. Warp drives could conceivably fall into either category. Krasnikov tubes would be in the latter category.

Rick said...

My bias would be to avoid specific present day speculations, because they is so early in the game, while adhering to the general conditions that Luke outlined - local conservations, and no time machines.

The last of these strikes me as by far the most problematic. Local conservations (it seems to me) can be handled by having jump points off in deep space somewhere - a familiar SF convention - and massive enough that the passage of individual ships does not majorly disrupt them. (If it makes FTL navigation tricky, that is also SF convention.)

But avoiding time machines has implications for the 'subway map' of available FTL routes, and that is where things get dicey.

I have approximately zero confidence in my ability to develop a causality-safe subway map, so I'd have little more than an incantatory mention of 'shared frame of reference' or some such, and otherwise just cross my fingers and hope that the relativity cops don't pull me over.

Thucydides said...

Period pieces really do depend a lot on setting. I recently came across a website promoting the movie release of "Atlas Shrugged"

While the idea of a philosophical "Lord of the Rings" is pretty cool, I was less impressed by the trailer, which seems to be set in the here and now. Given the plot revolves around heavy industry and railroads, this is pretty anachronistic (something Ayn Rand apparently never considered). I had always envisioned it as a sort of "Steampunk" setting, where WWII never happened and the Great Depression continued into the 1950's.

Perhaps the real problem is we are only considering how to do FTL in the here and now, when of course the problem will only be solved by nearly unimaginable technologies and techniques. To throw a wild one out there, a recent Technology Review blog post suggested that gravity comes from quantum information. http://www.technologyreview.com/blog/arxiv/24975/

Using extreme handwaves (and a bit of arm flapping) we can postulate that manipulation of quantum information could provide a rout to FTL (vastly powerful AI on the ship literally "thinks" you where you want to go)

Scott said...

Also, from the descriptions here, it sounds like there's no *instant* FTL, but all of it happening at some measurable multiple of c (based on ship's clocks versus spacetime distance). So, the traversable FTL (ie, hyperspace) trope isn't dead?

If you have enough transit time between FTL startpoints, might *that* be enough to keep the Causality Police from reducing you to your constituent atoms?

This might require a certain minimum distance between any two FTL startpoints, enforced by quantum mechanics... Don't jump too close together, now!

Luke said...

Rick:

I have approximately zero confidence in my ability to develop a causality-safe subway map, so I'd have little more than an incantatory mention of 'shared frame of reference' or some such, and otherwise just cross my fingers and hope that the relativity cops don't pull me over.

The easiest way is to make your subway map without mentioning the time part of it. There's a way to hook it up in time so that you can't get a time machine, but your protagonists won't care how it works (unless they are wormhole civic engineers, in which case the audience won't care and you can get away with some throw-away lines).

Or you can go with an acyclic graph, which is pretty much guaranteed not to have time travel (an acyclic graph, as you might guess, is one without cycles. A cycle, as you might guess, is where you can go around in a loop and come back to where you started without retracing your path backwards). If you want to add "cross routes" which would create cycles, you can make it less problematic by keeping the distance between main route and cross route termini quite significant (where "quite significant" depends on how much tolerance you figure your engineers need - maybe light days, maybe light microseconds).

In the end, you will probably have an army of planners and engineers and technicians who keep the network going, part of which will involve tweaking the time lags in the system so that you don't get time drifts that lead to time machines. You will need to mention this in your novel about as much as a modern day novel needs to mention the pumps in the subways that keeps the ground water out.

jollyreaper said...

I had always envisioned it as a sort of "Steampunk" setting, where WWII never happened and the Great Depression continued into the 1950's.

Not only that but the modern Republicans hate trains. They've been doing their best to spike high-speed rail projects around the nation. Hard to reconcile!

Actually, I think Atlas is a perfect example of the error of writing "take that!" polemics. It's a thought experiment that justifies a theory of the world by custom-crafting the scenario by which the theory is validated and the opponents of said theory -- proxies for the author's own enemies -- are all crushed by the weight of their own errors. It's really like making up handwavium for our stories -- works great on paper but don't try applying it in the real world!

Raymond said...

Scott:

"Also, from the descriptions here, it sounds like there's no *instant* FTL, but all of it happening at some measurable multiple of c (based on ship's clocks versus spacetime distance). So, the traversable FTL (ie, hyperspace) trope isn't dead?"

Well, if you're doing wormholes, they're instant-travel but sublight propagation (well, sorta - see below). If you're doing warping along cosmic strings, ask Luke. If you're doing freeform warping, you still have to set your path before you jump - no wandering or changing course.

If you're doing wormhole-to-another-universe-then-another-wormhole-back-into-ours, then navigate away. Just make magic-space interesting.

Rick, Luke:

I'm the kind of masochistic geek which regards the timelike separation of wormholes as an interesting spin on things, to be exploited for all its worth. I mean, if you've got wormholes (which can act as spacecraft on their own) which can be sent on their way as microscopic objects and decelerated easily (as the power generation can be done on the near side), then expanded at the destination, there are some cool consequences:

- Dilated wormholes mean travel into the future; that wormhole you've got headed to the other side of the galaxy is also headed for the far future by human standards.

- The time you wait for rescue, reinforcements or retaliation is different depending on the direction of travel. Outwards, it's much less than the lightyears you'd think. Inwards, it's way more. Cut off a far-flung colony, and you've got plenty of time to wait - generations, maybe. Piss off Earth, and their followup will be at your door in three years instead of thirty (tweak numbers to suit).

- If you find some hostile civilization out there, your options for retreat or retrenchment are similar to above.

- If you find another wormholing race, the first point of contact becomes all-important to prevent the quantum chronocops destroying one or both networks.

- The rate of expansion from Earth's reference frame can be FTL, even if the wormhole ends themselves never travel FTL.

- Your Explorator Corps is less tied to naval traditions and thinking, more tied to large, fixed installations. Different ways of thinking.

- You get incentives for trade (keep the mass balanced) and space stations (keep the wormholes in freefall away from planetary surfaces), which are always lovely tropes to have an excuse for.

Sounds more interesting than Ye Olde Magick Space, doesn't it?

Raymond said...

Apologies for the occasional repetition in the last post, btw. Blogger's tiny comment window + writing a couple sentences at a time = disaster.

Luke said...

Raymond:

I definitely think that the peculiarities of scientifically plausible wormhole travel would make an interesting setting (heck, it is my preferred setting). However, I wouldn't want to discourage people from trying to use scientifically plausible FTL just because they don't think they can deal with these complexities. They can sweep a lot of the problems under the rug, as long as they stay away from certain aspects of building the network. On the other hand, the peculiarities of scientifically plausible FTL would make really nifty plot points if you do feel comfortable with how things work.

I will point out again that wormholes naturally lead to encountering alien species of about our own level of technological advancement. This avoids A.C. Clarke's "angels or apes" problem, and allows meaningful trade, diplomacy, and warfare. We might develop wormholes next century, the Mants might develop wormholes 2,500,000 years from now in the Andromeda galaxy, and the Gummis might have developed wormholes 3,000,000 years ago in the triangulum galaxy. But because each species is expanding into space pretty close to their light cone, each encounters the other shortly after inventing wormholes, so we all meet at about the same level of technological development.

Raymond said...

Luke:

"However, I wouldn't want to discourage people from trying to use scientifically plausible FTL just because they don't think they can deal with these complexities."

Most certainly. If Rick wants wormholes without the temporal displacement, just drag them around by slowboat with low gamma and don't even mention it.

If one does want to play with the more complex version, though, one probably can't assume most people know how the timelike separation stuff works. How do you explain it briefly, and without pissing off the part of the audience like Tony who don't want physics lectures?

"I will point out again that wormholes naturally lead to encountering alien species of about our own level of technological advancement."

Wouldn't this apply only to relativistic, dilated wormholes, not the slower version?

jollyreaper said...


I will point out again that wormholes naturally lead to encountering alien species of about our own level of technological advancement. This avoids A.C. Clarke's "angels or apes" problem, and allows meaningful trade, diplomacy, and warfare. We might develop wormholes next century, the Mants might develop wormholes 2,500,000 years from now in the Andromeda galaxy, and the Gummis might have developed wormholes 3,000,000 years ago in the triangulum galaxy. But because each species is expanding into space pretty close to their light cone, each encounters the other shortly after inventing wormholes, so we all meet at about the same level of technological development.


Now that's one hell of an interesting thought. Angels or apes a giant argument against the usual scifi universe, or at least one where humans are encountering aliens for the first time. The only possible way to get something like that working is if there's an established galactic culture with shared tech, the newer races are invited into it. And even at that you'd have to assume some sort of tech plateau the younger races stay at while periodically some races or portions of races would do the transcend thing and move on.

Stross had one possible solution for the Fermi Paradox -- if singularities are possible, then perhaps alien races will convert their entire native systems to computronium and live in simulation as uploads. There's no need to go away from home for anything and even if they wanted to, they'd have to leave behind the cheap energy and easy simulation space. Singulatarians would become the ultimate homebodies.

That's another variation of the holodecadence idea I had previously. Races powerful enough to conquer the galaxy are simply disinterested in doing that sort of thing. Only the younger races think there's anything worthwhile in flying all over the place doing self-important things.

Rick said...

I will point out again that wormholes naturally lead to encountering alien species of about our own level of technological advancement.

I don't think that entirely holds up. After all, history (and presumably tech progress) don't end when a race develops wormhole tech.

Suppose for example that the Mants develop wormhole FTL 2,400,000 years from now in Andromeda. By the time a ship from AD 2111 Earth pokes through to Andromeda and encounters their network, they are 100,000 years ahead of us.

Similarly, the Gummis might only have developed wormhole FTL 2,900,000 years ago - so that when they first push through to the solar neighborhood, using 1st generation tech, it is about AD 100,000 on Earth.

The key issue here (I think!) is that civilizations cannot create or traverse all possible wormholes as soon as they have the technical capability, because resources are finite.

Wormhole explorations that are 'put off till later,' in any given homeworld's local frame of reference, will end up being traversed by ships of later generation and presumably higher techlevel.

As a side note, keeping historical chronologies straight will also be lots of fun!

Anonymous said...

Ok, here's a scenario: a civilization uses "jump" ships that move from star to star (with the whole mass/velocity swap thing going) but those are only scouts, military ships, and gate construction vessels; routine interstellar travel is by small shuttles via jump gates (again with the mass swap thing) that need two-way travel to keep the gates balanced. The gates could be built near where ever it is that is interesting in that system; a gate with a mass of 100 million tons and shuttles of 50 - 100 tons going back and forth should be ok. You would need an extensive space traffic control network (and communications through the gate network), but it seems like that should work. Does anyone see something I've missed?

Ferrell

Raymond said...

Ferrell:

"Does anyone see something I've missed?"

Just need a common frame of reference for your jump craft, as far as I can tell.

Milo said...

Rick:

"Suppose for example that the Mants develop wormhole FTL 2,400,000 years from now in Andromeda. By the time a ship from AD 2111 Earth pokes through to Andromeda and encounters their network, they are 100,000 years ahead of us."

But we wouldn't meet the center of their network. We would meet the edge, which is 100000 lightyears away from the center.

We would only reach their center if they let us borrow their wormholes. We can't build a backdoor without breaking causality.


"Wormhole explorations that are 'put off till later', in any given homeworld's local frame of reference, will end up being traversed by ships of later generation and presumably higher techlevel."

Yes, but there is a big difference between putting something off for two generations and putting it off for a hundred thousand years.

We might get a few centuries of difference in technical advancement, which is enough to lead to a Conquistadors and Natives scenario, but not nearly Apes or Angels. They will still be close enough to us to be comprehensible.

The problem comes if your million lightyear journey passes over thousands and thousands of habitable planets, and you wait a few generations colonizing each one before sending off the next wormhole...

Thucydides said...

Ayn Rand had nothing but scorn for the Republicans of her era, and I doubt today's versions would get off lightly. (Then again, I doubt most of us would survive either...).

From a plotting POV, Atlas Shrugged is a species of Science Fiction. It is set in an alternate timeline/Universe; it explores multiple "what if" questions and attempts to extrapolate them to their logical conclusions (including the introduction disruptive technologies like "Reardon Metal", "Project X" and the static electricity engine of John Galt). If you don't happen to agree with the premises, you are always free to write "Hercules Shrugged" in response...

The writing style is rather peculiar, although I did enjoy some passages like Francisco d'Anconia's paean to the virtues of money. Anyway, it certainly broadens the reader's horizons to try it on for size.

Back to our regularly scheduled debate, one wormhole answer which solves the Fermi paradox and avoids messy CTC issues would be to postulate advanced species use wormhole technologies not to travel but to inflate custom designed "basement universes" which they then expand into. If the wormhole does not pinch off after the race pulls their vanishing act, future explorers (in STL craft coming to colonize the galaxy) might find ruins and a massive gravitational anomaly orbiting the sun (the wormhole mouth). IF the vanishing act was long enough in the past (several eons ago), there might not be anything left except the wormhole mouth.

Tony said...

Thucydides:

"Ayn Rand had nothing but scorn for the Republicans of her era, and I doubt today's versions would get off lightly. (Then again, I doubt most of us would survive either...)."

Rand was a misanthrope. She celebrated the achievements of great scientists and industrialists, but condemned all the lesser (in her opinion) men and women whose work made the achievements of the great men possible.

Tony said...

Thucydides:

"Back to our regularly scheduled debate, one wormhole answer which solves the Fermi paradox and avoids messy CTC issues would be to postulate advanced species use wormhole technologies not to travel but to inflate custom designed "basement universes" which they then expand into. If the wormhole does not pinch off after the race pulls their vanishing act, future explorers (in STL craft coming to colonize the galaxy) might find ruins and a massive gravitational anomaly orbiting the sun (the wormhole mouth). IF the vanishing act was long enough in the past (several eons ago), there might not be anything left except the wormhole mouth."

Or what if we inhabit a basement universe that the makers simply haven't gotten around to colonizing yet?

Raymond said...

Tony:

"Rand was a misanthrope. She celebrated the achievements of great scientists and industrialists, but condemned all the lesser (in her opinion) men and women whose work made the achievements of the great men possible."

+10

I would add, though, that her prose was terminally unreadable.

Byron said...

On expansion speed:
If we throw the wormhole mouthes out at .999 c, then the apparent expansion rate for someone on Earth will be about 22 c (if I did the math right). At .99 c it will be around 7 c. If we can get the wormhole to the sort of speed particle have in the LHC (0.999999991 c), then it will be about 7450 c.
These ignore colony time and slowing the mouth down, but should give some idea of expansion speeds.

On contact:
I can see problems with this being fairly extensive. While I believe that being at the same tech level is fairly plausible, there are large chances for wormhole disasters. Take the following:
Humans and Andromedans meet in System A, with t=0. The humans are from System B, with t=-4. The Andromedans are from System C, with t=-3. The Humans are also in System D, t=-1. The Andromedans are sending a wormhole from C to D, and it will be at 0 as well. There is no malice, just different species.

I would immagine that if you desired, it would be easy to make a technobabble time machine detector. "Quantum fluctuations increasing, sir. We have indications of a CTC forming." or "This is my timey-wimey detector. It goes ding when there's stuff."
And I just destroyed my reputation as a hard sci-fi fan.

Static wormholes could lead to interesting military tactics. When the war starts, pile through to the opponet's side, and drag a bunch of asteroids through to drain your side low enough to make it impossible to launch a fleet through.

Tony said...

Byron:

"Static wormholes could lead to interesting military tactics. When the war starts, pile through to the opponet's side, and drag a bunch of asteroids through to drain your side low enough to make it impossible to launch a fleet through."

Ummm...how do you get home?

Raymond said...

Tony:

"Ummm...how do you get home?"

Fire a comm laser back through, telling the minder on your side to shove the asteroids back through.

"Come home with your shield, or on it."

Byron said...

You leave enough mass in to get home. Drain the wormhole to minimum+your fleet's mass, then come back. The point is that you can close a wormhole from the other side.

Byron said...

Actually, I should ammend the above statement. It's not closing the wormhole, it's making it impossible to transit. The really good part is that the it's easy for you to go out. If you want, the other end has pretty much the starting mass of both ends. That might not matter much if it's supermassive, and your entire fleet is 1%. However, if the wormhole is small, then it could be a big deal.

Scott said...

Let me clarify a statement here: If you have enough STL transit time between FTL startpoints, might *that* be enough to keep the Causality Police from reducing you to your constituent atoms?

This way, even though the FTL portions of your journey would apparently cause a CTC, the realspace travel times would prevent you from actually arriving before you left... If I've done the time-distance equations right.

Scott said...

And Ayn Rand was a serious fruitcake: her ideal man was a psychopathic sociopath!

Byron said...

If your FTL points are far enough apart that light can't arrive back at the origin before it left, then you don't have a CTC. If I have a wormhole at earth, and another one at the Earth-Sun L3 that I can loop to and arrive 10 minutes before I left, I don't have a CTC because any message will get to me a minimum of 6 minutes late.

mithril said...

if i understand the issue correctly, the main problem comes from the "dragging" one end into place, since the reletivistic effects of the trip combined with the nature of the wormhole end up with time effectively moving at different rates at each end, allowing time travel. and that if you have a "round trip" option that doesn't re-use the same wormhole, you result in potential paradoxes.

here is my question. is there anything in wormhole physics that would REQUIRE the two ends to be generated at the same point in space? in other words, do you have to make the two ends at earth then move one? is it possible to open on at earth and one at the destination at the same time?

if you can open the two ends in the desired locations at the same time (ideally through one set of actions), you side step the time travel issue since the rate time is moving at each end is effectively the same. then you could make a true network of wormholes and not have to worry about time travel issues.

Milo said...

Scott:

"Let me clarify a statement here: If you have enough STL transit time between FTL startpoints, might *that* be enough to keep the Causality Police from reducing you to your constituent atoms?"

Sort of, yes.

More accurately, any FTL, even one which does not actually cause a causality violation, would appear to do what you say (travel back in time, but to somewhere too far away to care about in STL) from some frame of reference.

It is more useful, however, to measure things from the frame of reference where this does not happen.

Luke said...

mithril:

here is my question. is there anything in wormhole physics that would REQUIRE the two ends to be generated at the same point in space? in other words, do you have to make the two ends at earth then move one? is it possible to open on at earth and one at the destination at the same time?

The same time in which reference frame? This gets to the problem again of choosing your reference frame to allow time travel.

mithril said...

basically, i'm wondering if you can open ends in two different places using actions occuring in only one ends referance frame.

so for example, you open one end on earth, and (reletively) the same time, the other end opens at alpha centauri as a reaction to the action on earth.

or could it be possible to "prime" an end at one or the other place, using a slowboat ship to bring a wormhole-generator-thingy to the destination, then power up but not create an actual wormhole. then send a message back for earth to do the same, then create the link between the two?

as long as you don't have one end undergoing more than normal reletivity effects (normal in this case being as a result of stellar and orbital motion), you should be able to side step the issue if time travel. even if you do have continuity issues, they'd presumably be far smaller than the years/centuries of the "conventioanl" approach..

Luke said...

mithril:

basically, i'm wondering if you can open ends in two different places using actions occuring in only one ends referance frame.

Almost certainly not, but this is fiction so lets ignore this and just focus on what the consequences would be if known physics still holds.

so for example, you open one end on earth, and (reletively) the same time, the other end opens at alpha centauri as a reaction to the action on earth.

In relativity there is no such thing as "the same time". What is the same time to one observer can involve one thing happening before the other to another observer - in either order, depending on positioning and relative velocity.

If the other end opens in the same frame of reference as the machine used to open the wormhole, then your causality problem becomes much worse. It becomes trivial to create a time machine by opening a wormhole from earth, going through, closing the wormhole, changing your velocity, and then opening a wormhole back to earth. Examples of this, with worked out numbers even, were posted by myself and Milo in the comment section to Rick's blog post immediately subsequent to this one - you can read those to see how easy it is to use FTL in arbitrary reference frames to go back in time to change the past.

Thucydides said...

I would dispute the idea Rand’s ideal man is a “psychopathic sociopath”, her intent is to celebrate creative individuals working at their capacity and able to freely interact with others.

There is a passage where Dagny is being introduced to the strikers in Galt’s Gulch. After meeting scientists, industrialists and artists she is brought to Ellis Wyatt’s shale oil rig and asks one worker:

“What were you outside? A professor of comparative philology I suppose?”

“No ma’am, I was a truck driver. But that’s not what I wanted to remain”

From a literary POV, Atlas Shrugged is a dense polemic, and like most polemics pushes ideas to extremes. Add a peculiar writing style and passages like the one above really do stand out. (I am re reading Atlas Shrugged in anticipation of the movie. A Philosophical “Lord of the Rings” is a pretty cool idea, and I am interested to see if they can pull it off)

Tony said...

Thucydides:

"I would dispute the idea Rand’s ideal man is a “psychopathic sociopath”, her intent is to celebrate creative individuals working at their capacity and able to freely interact with others.

There is a passage where Dagny is being introduced to the strikers in Galt’s Gulch. After meeting scientists, industrialists and artists she is brought to Ellis Wyatt’s shale oil rig and asks one worker:

'What were you outside? A professor of comparative philology I suppose?'

'No ma’am, I was a truck driver. But that’s not what I wanted to remain'"


The big fly in the soup is that one doesn't need Galt's Gulch to realize one's aspirations. Not even when Rand was writing Atlas Shrugged. My mother's father, for example, grew up in truck and cow farming rurla SOuthern Missouri. He went to work in the 1930s as a hard rock miner. By the late 1940s, after serving as a SeaBee in WWII, he was a tunnel digging supervisor on a major power project in British Columbia. After that he supervised on mine tunnels in Wyoming and Colorado, dams in Bangladesh and Afghanistan, the Pali tunnel on Oahu, and the Eisenhower Tunnel on I-70 in Colorado. Everywhere he went after about 1960 he was a trouble shooter that fixed jobs other men couldn't do.

On the basis of that description, one would think he was very much a self-made Randian man. But he was hardly John Galt. He never had more than an eigth grade education, he was a union Democrat (even after he became a job superintendant), and he would rather play cribbage or poker than talk philosophy with you.

He wasn't dumb by any means, but he was a practical man that didn't GAS about book learning. What his tunnelers knew from digging the rock, and what he knew from similar experience, meant more to him than any engineering analysis. He drove tunnels with determination and experience that other men had failed to drive by the book with Gantt charts. And those were the jobs he hated the most, because men died in the messes he was called in to clean up.

And Rand simply never got that. For all of the high ideals and intellectual heat that men like Ford and Eddison brought to the table, the actual people who got things done were very often rought men, up through the ranks, that would consider the big name men's best day in the shop or at the bench a light day's work.

All of which is not to sing the praises of the working class hero. It's just to recognize that great men start great things, but it's the men who know the work and how to get it done that finish them.

Thucydides said...

From the literary side, Rand seems to be telling people to look deeper into first principles and the origin of things. Truckers on strike are an inconvenience, but Rand's point is without the people who conceptualized and invented trucks (and all the associated infrastructure), there would be no truckers in the first place!

The passage about the trucker who works in Ellis Wyatt’s shale oil rig hints that she is well aware that not everyone is on the same level as John Galt (and there are other supporting characters who are also hard workers but not intellectual giants ), but since this is a story, the drama comes not from the thousands of people who go Galt towards the end of the book but the first few people who lead the way. ("I will stop the motor of the world!")

As for why Galt's Gulch exists, it is a literary device for the purposes of the story. (in the world outside, people are chained to their jobs by an "Equalization Board"). It would be more difficult to explain the concept of "internal emigration" in a dramatic fashion (the old Soviet era trope where people pretend to work and never get mentally or emotionally engaged in order to get by. To really understand this mentality you don't need Rand, rather you need Aleksandr Solzhenitsyn)

As a BTW, politically I am a small l libertarian, which my friends in both the Objectivist "Freedom Party" and the "Canadian Conservative Party" find annoying...

jollyreaper said...

My Rand objections mainly come from her ideas being developed in isolation from human compassion and reality. She writes novels in which she can construct "take thats!" against supposed real world analogues that are really just strawman fantasy constructs.

Her ideas work only so long as they're kept in isolation from the real world. When put into practice, they yield sociopathic results.

Rick said...

My main comment on Ayn Rand is that the book of hers I read must have been The Fountainhead, not Atlas Shrugged.

Because if I had read a book involving railroads and trains I'd probably remember it just for that, but whatever Rand book I did read made essentially no impression on me.

Scott said...

Rand's ideal man didn't show up in Atlas Shrugged, he only shows up in her diaries because she had not gotten around to writing about him.

paraphrasing, because I can't find the reference right now: 'A great man, that is, one unencumbered by the weight of society's expectations...'

The man she was writing about was in the newspapers of the day for being a kidnapper, murderer, and rapist. Ick.

But how'd we go from FTL to Ayn Rand?

=====
@Milo and Byron: Cool, this means that you can mathematically determine the minimum separation of two FTL portals based on their time-dilations. A useful thing to have for a writer!

Thucydides said...

But how'd we go from FTL to Ayn Rand?


Luke explained this mathematically upthread, but it is really due to entering the wrong frame of reference while avoiding a CTC.

;)

Anonymous said...

Thinking about the two extremes of FTL (expecially in fiction), you either have a big gray box with a 'here we are' display, a 'we want to go there' input, and a big red button; the 'Warp-o-matic', or you have a massive tangle of gizmos that require the engineers to explain how it works, constantly, for it to work properly.

If (or when) we come up with a real life method of FTL, it will most likely not involve time-travel, casuality violation, will involve a whole set of rules/laws/theories unique to the proccess, and a plethera of thechnical headaches...

Ferrell

Rick said...

Undoubtedly so. But given that even non-violating FTL is purely speculative, the practical question - as I mentioned in the Space Warfare XV thread - is how visible it is to the story.

Anonymous said...

I think that most here would agree that unless the details (or a detail) of the inner workings of your FTL drive is central to the story, just show the effects...kinda like a stew; spices in the background, meat and potatoes in the foreground.

Ferrell

zlionsfan said...

Re clones, existence and theft of: Farscape touched on these topics at different points in the series. At the end of one episode, Crichton is cloned ... but we don't see exactly how it happens, so there's no way for the viewer to tell which one is the original and which is the clone. Of course both believe themselves to be the original, and are treated as such going forward.

In the next episode, the cast and thus the Crichtons are split up: now that they have considerably different experiences, from their perspective, they become substantially different: however, from the reference of outside observers, even knowing there are two of them, the difference is not so obvious ... it's almost like they become identical twins with the same name in that they're different once you know what to look for, but it's easy to forget if you're not careful. (One Crichton is killed off; it takes a bit for some of the other characters to match their experiences with the correct Crichton - assuming he was present when such-and-such happened when really it was the now-dead one who was there.)

Eventually the thread is pretty much forgotten, probably for convenience as much as anything else, but it does make you wonder what the long-term effects of limited cloning would be. Would you remember that zlionsfan-beta was not the "original"? Would it matter, if he were the only survivor?

In two other episodes, Crichton finds himself in a situation very close to what jollyreaper describes, although it is he and not a (possible) clone who is involved. (This happens before the cloning ep.) In both cases, he has to figure out that he's in a simulation and also determine how to escape it ...

zlionsfan said...

(continued)

The catch in the first ep is that the simulation is based entirely on events from his own memory: to break the sim, he simply has to go someplace he'd never gone before. (That's a basic programming error - a lot of games these days that aren't nearly so immersive have ways around it - but in this case, the ones who set up the sim are not exactly hostile, so it's a little justifiable.)

In the second ep, the simulation is intentionally unrealistic, created by hostiles. Because it's unrealistic, there's no real way to "break out": something that would break known laws might be allowed to occur, or it might be modified, or it might just reset the sim. (Crichton escapes only through the help of a virtual character, one who's inside the sim but also aware of its true nature and how it's being run on the outside.)

I think those eps reveal some of the challenges with setting up a sandbox. In the first case, given restrictions that I think readers would follow (although I'm highly biased in this respect, being a programmer, so I might be overlaying my own expectations on my view of the "average" reader), it only makes sense to have an "easy" way out, or any way out at all, if the sandbox is run by non-hostiles. (If they're hostile and monitoring the sandbox, why wouldn't they just reset it any time you get close to escaping?) In that case, the purpose of the sandbox is likely more for inspection and evaluation than for discovery, although it can serve for both. (In this case, the non-hostiles were looking for a new planet on which they could coexist and were wondering how well Earth would work.)

In the second case, with hostiles running the sandbox, it's really hard to get your character out without a large can of handwavium. If there's a reasonable exit, then how competent are the bad guys if they can steal your clone and trap it but can't contain it? (Like how Lex Luthor is a criminal mastermind who keeps going to the same temp agency to hire assistants.) If there's no reasonable exit, someone on the outside has to help the clone, and if they can manage that, a) why did they let the clone get caught in the first place and b) why didn't they use that power earlier to discover what the clone knows themselves? (Particularly relevant in Farscape. Ironically, that situation is about Crichton's knowledge - or lack thereof - of wormhole travel.)

I'm sure there are ways you can work the latter case to make it plausible-in-your-universe, but I think it's difficult.

Rick said...

I should really make a more intelligent response than 'my head is exploding.' But ... my head is exploding.

Having said that, the broader question of immersive sims is of theological interest - think of Tolkien's remark on fiction writing as 'sub-creation.'

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