Hard Light Productions Forums
Off-Topic Discussion => General Discussion => Topic started by: Aardwolf on August 19, 2010, 01:54:06 am
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Ok, in a past shoutfest I had with Battuta, it was ultimately agreed that FTL travel and/or communication wouldn't work because it would break the universe.
The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Lets here some ideas!
Preferably focusing more on the high-level "rules" than the technobabble.
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How to square the circle with only compass and straightedge!
Let's hear some ideas!
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How to square the circle with only compass and straightedge!
Let's hear some ideas!
easy. draw two perpendicular diameters through the circle, and then draw tangent lines at each of the points where the diameters intersect the circle.
FTL, **** knows.
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"There is such a thing as a tesseract."
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The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Hey, that was my idea! You mean to say you had another FTL thread without me??? For shame...
EDIT: Oh wait, was it IRC?
Here it is: http://www.hard-light.net/forums/index.php?topic=69684.msg1377576#msg1377576
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easy. draw two perpendicular diameters through the circle, and then draw tangent lines at each of the points where the diameters intersect the circle.
Congratulations! You have just squared the circle!
I might want to say at this point that they were supposed to have the same area.
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Hey, quit it.
@Scourge of Ages: er, I think it was settled on IRC, but yeah that's the right thread.
Anywho, if you disallowed FTL comms, could a jump-based system (like FS and many other sci-fi universes have) avoid time-travel paradoxes? What would/could the rule be for getting away with it?
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Ok, in a past shoutfest I had with Battuta, it was ultimately agreed that FTL travel and/or communication wouldn't work because it would break the universe.
The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Lets here some ideas!
Preferably focusing more on the high-level "rules" than the technobabble.
Er wait, why is this true? If I sent a message to someone, and they sent the FTL message back instantaneously, I would still get it after I sent the message, as I would have to wait for my message to travel to them before they sent it back.
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Ok, in a past shoutfest I had with Battuta, it was ultimately agreed that FTL travel and/or communication wouldn't work because it would break the universe.
The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Lets here some ideas!
Preferably focusing more on the high-level "rules" than the technobabble.
Er wait, why is this true? If I sent a message to someone, and they sent the FTL message back instantaneously, I would still get it after I sent the message, as I would have to wait for my message to travel to them before they sent it back.
No, you wouldn't; at least not in all IRFs observing the exchange. In some IRFs the message will arrive before it is sent, and one of the fundamental laws of the universe is that no IRF is privileged, meaning if causality is violated in one it is violated in all and spacetime asplodes.
*sigh* Please don't make me do the math out. It's not hard but it's an algebra grind. :p
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Never say never guys (http://www.eetimes.com/electronics-news/4083120/Warp-Factor-10-Star-Trek-warp-drive-in-the-works)
EDIT: You know, this reminds me of a notorious quote by a then famous physicist:
I can state flatly that heavier than air flying machines are impossible
Cookie to anyone who gets who said it.
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Er, was it Wehrner von Braun(sp?) ?
Edit: Looked it up. Bleh, I would have never guesed... I'll let someone else have the virtual cookie, though.
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Never say never guys (http://www.eetimes.com/electronics-news/4083120/Warp-Factor-10-Star-Trek-warp-drive-in-the-works)
EDIT: You know, this reminds me of a notorious quote by a then famous physicist:
I can state flatly that heavier than air flying machines are impossible
Cookie to anyone who gets who said it.
That's an Alcubierre drive and we know aaaaaaall about it.
It could lead to practical FTL, but it's orthogonal to this particular discussion.
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Never say never guys (http://www.eetimes.com/electronics-news/4083120/Warp-Factor-10-Star-Trek-warp-drive-in-the-works)
EDIT: You know, this reminds me of a notorious quote by a then famous physicist:
I can state flatly that heavier than air flying machines are impossible
Cookie to anyone who gets who said it.
That's an Alcubierre drive and we know aaaaaaall about it.
It could lead to practical FTL, but it's orthogonal to this particular discussion.
I saw the words "FTL" and "travel" and got a little excited. :)
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Never say never guys (http://www.eetimes.com/electronics-news/4083120/Warp-Factor-10-Star-Trek-warp-drive-in-the-works)
EDIT: You know, this reminds me of a notorious quote by a then famous physicist:
I can state flatly that heavier than air flying machines are impossible
Cookie to anyone who gets who said it.
Regardless of who said it... through history there have always been dreamers and naysayers. Thank goodness for the dreamers.
Seriously... go back 100 years and tell someone that in 100 years time there will be a technology where you can communicate between people, in real time, to anyone on the planet using voice and video. You'd have to explain to them video first ... and then wait for their mind to be blown.
Give it a 100 years.
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FTL ftl?
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FTL ftl?
WTF? FTL FTW!
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A paradox is by definition something that cannot exist.
Therefore if a paradox occurs, it is no longer a paradox and the universe will probably just get over it. :P
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Ok, in a past shoutfest I had with Battuta, it was ultimately agreed that FTL travel and/or communication wouldn't work because it would break the universe.
The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Lets here some ideas!
Preferably focusing more on the high-level "rules" than the technobabble.
Er wait, why is this true? If I sent a message to someone, and they sent the FTL message back instantaneously, I would still get it after I sent the message, as I would have to wait for my message to travel to them before they sent it back.
No, you wouldn't; at least not in all IRFs observing the exchange. In some IRFs the message will arrive before it is sent, and one of the fundamental laws of the universe is that no IRF is privileged, meaning if causality is violated in one it is violated in all and spacetime asplodes.
*sigh* Please don't make me do the math out. It's not hard but it's an algebra grind. :p
Battuta, sure it would make the universe asplode. But then the developer running the simulation could just revert universe to the last saved restore point, update the code to handle it and off we go. Heck if we're lucky one of the other races already caused the issue to be debugged.
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Ok, in a past shoutfest I had with Battuta, it was ultimately agreed that FTL travel and/or communication wouldn't work because it would break the universe.
The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Lets here some ideas!
Preferably focusing more on the high-level "rules" than the technobabble.
Er wait, why is this true? If I sent a message to someone, and they sent the FTL message back instantaneously, I would still get it after I sent the message, as I would have to wait for my message to travel to them before they sent it back.
No, you wouldn't; at least not in all IRFs observing the exchange. In some IRFs the message will arrive before it is sent, and one of the fundamental laws of the universe is that no IRF is privileged, meaning if causality is violated in one it is violated in all and spacetime asplodes.
*sigh* Please don't make me do the math out. It's not hard but it's an algebra grind. :p
Er...what's an IRF?
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Starslayer: You sure the devs are competent? They may not be :P
Also, just because something can't accelerate to greater than c (such that γ > infinity), doesn't mean FTL can't exist. There is still a possibility of an Alcubierre drive, which has been mentioned and just fraks with the reference frames, or teleporters (wormholes, subspace, etc). So the naysayers can stop worrying.
Here's another perspective: If people can find a way to kill each other with it, they'll probably figure out how to make it happen. :P
UT: IRF = Inertial Reference Frame.
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Starslayer: You sure the devs are competent? They may not be :P
If they were competent it would already have a try catch block :D
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Ok, in a past shoutfest I had with Battuta, it was ultimately agreed that FTL travel and/or communication wouldn't work because it would break the universe.
The thing that caused the trouble was that if something at the destination could send an FTL signal back right away, it could/would arrive "before" the original signal was sent. So now I'm thinking... could a set of rules be devised which would avoid space-time paradoxen? Perhaps something with teleportation/jumps?
Lets here some ideas!
Preferably focusing more on the high-level "rules" than the technobabble.
Er wait, why is this true? If I sent a message to someone, and they sent the FTL message back instantaneously, I would still get it after I sent the message, as I would have to wait for my message to travel to them before they sent it back.
No, you wouldn't; at least not in all IRFs observing the exchange. In some IRFs the message will arrive before it is sent, and one of the fundamental laws of the universe is that no IRF is privileged, meaning if causality is violated in one it is violated in all and spacetime asplodes.
*sigh* Please don't make me do the math out. It's not hard but it's an algebra grind. :p
Er...what's an IRF?
Inertial reference frame (observation by a non-accelerating observer.)
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All that explains is that FTL Comms wouldn't work necessarily. No one said FTL Travel is impossible.
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Well, it is because FTL Communication and FTL Travel are pretty much the same thing, the transmission of information, information being anything such as the layman's definition of information to knowledge that a ship is traveling really, really fast.
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All that explains is that FTL Comms wouldn't work necessarily. No one said FTL Travel is impossible.
No, FTL comms are FTL travel. They're the same thing.
Imagine a message arriving before it's sent - that's FTL comms. Imagine a ship leaving a dockyard, traveling FTL, and then arriving back at the dockyard before it departs - and then blowing it up. That's FTL travel. Same problems.
FTL travel is not impossible in current models of physics; however it requires something like an Alcubierre drive or a wormhole and may still lead to causal connectivity between events with spacelike separation (possibly causing paradoxes).
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ok, so let me see if understand the problem.
we have 3 planets
A B C
arranged like that were B is more or less right between A and C, but with C further away from B than A is.
B transmits a RF message to A, then A transmits some sort of FTL response back to B. from C's perspective A transmits a FTL response, then B transmits it's initial message.
so from C's frame of reference the response came before the message that caused it.
This is the problem?
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This would suggest we have to remove the transit part to prevent paradox.
...subspace ftw?
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hold on, I want to make sure I've got that right before we jump to anything else.
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I think I need to remind you guys of one thing that leads to those things:
The speed of light is the highest velocity by which one can transmit any sort of information by the current understanding of the Physics. I'm not sure about how that works with those quantum thingies that seem to mirror each other, but never mind, I never liked quantum physics in any case.
That being said, would it instead be fruitful to discuss what would happen if there wasn't a velocity cap? Sometimes thinking of the opposite helps understanding why things are the way are now.
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ok, so let me see if understand the problem.
we have 3 planets
A B C
arranged like that were B is more or less right between A and C, but with C further away from B than A is.
B transmits a RF message to A, then A transmits some sort of FTL response back to B. from C's perspective A transmits a FTL response, then B transmits it's initial message.
so from C's frame of reference the response came before the message that caused it.
This is the problem?
Sort of. It depends on the relative velocity of the observer and the signalers.
It's a problem because you can construct the following scenario:
Carl is sitting on a chair. Under the chair is a bomb with a radio detonator.
Carl fires a signal from an FTL radio to detonate the bomb. The signal travels to the bomb and blows it up, detonating Carl.
However, in some IRFs, the bomb detonates before the signal is sent, causing a paradox.
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but that is only an apparent paradox, caused by you being in an odd position, it's like saying there is a sound activated flash bulb and you, standing far away from it, see the flash then hear the sound. it only seems like the flash went off first because the two signals are traveling at different speeds. causality only needs to hold within the frames that are relevant to the objects involved.
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but that is only an apparent paradox, caused by you being in an odd position, it's like saying there is a sound activated flash bulb and you, standing far away from it, see the flash then hear the sound. it only seems like the flash went off first because the two signals are traveling at different speeds. causality only needs to hold within the frames that are relevant to the objects involved.
Nope - this is a common misconception, but it's wrong. It's not analogous to the thunder/lightning situation at all. (For one - though it's not the key reason - the thunder will never, ever, ever precede the lightning.)
Causality must hold in all IRFs because no IRF is privileged. If causality breaks in one IRFs, and the laws of physics must be the same in all IRFs (which they must be, by one of the fundamental axioms of relativity), then it breaks in all IRFs.
So far this discussion is going exactly the way the one with Aardwolf did. I wish I'd taken notes. :nervous:
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I know it does not jive with relativity and we are walking down well traveled streets.
my question is what if causality only had to hold within reference frames relevant to the objects involved? or why is it that appearance of causality is so important? the isse is the bomb appears to go off before the signal because the speed of light is assumed (with volumes of evidence to support the assumption) to be the speed of propagation for everything in the universe.
keep in mind that an inertial reference frame is nothing more than a mathematical model, it might well be the case that FTL movement is completely possible but our models are only valid given that no FTL motion is present. So using the details of those models that break down with FTL to say FTL is not possible only points to the fact that that particular model does not work if FTL is present, it speaks nothing to the accuracy of the model (which, FTL aside, is otherwise almost perfect).
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as an asside
Never say never guys (http://www.eetimes.com/electronics-news/4083120/Warp-Factor-10-Star-Trek-warp-drive-in-the-works)
you know what I hate, when I see unqualified statements like "the amount of energy required would be enormous, equivalent to converting the entire mass of Jupiter to energy" that much energy would get us what? moving a speck of dust one inch at 2C? moving a galaxy five quadrillion lightyears in a billionth of a second? is it dependent on mass? volume? distance? speed?
just pisses me right off....
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I know it does not jive with relativity and we are walking down well traveled streets.
my question is what if causality only had to hold within reference frames relevant to the objects involved? or why is it that appearance of causality is so important? the isse is the bomb appears to go off before the signal because the speed of light is assumed (with volumes of evidence to support the assumption) to be the speed of propagation for everything in the universe.
keep in mind that an inertial reference frame is nothing more than a mathematical model, it might well be the case that FTL movement is completely possible but our models are only valid given that no FTL motion is present. So using the details of those models that break down with FTL to say FTL is not possible only points to the fact that that particular model does not work if FTL is present, it speaks nothing to the accuracy of the model (which, FTL aside, is otherwise almost perfect).
We've accelerated things to lightspeed and pumped enough energy into them that (if relativistic dynamics regarding IRFs did not hold true) they should have exceeded C easily.
They didn't. Instead they behaved exactly like relativity predicts. I know you're well aware of this (very well-informed and reasonable post by the way), but while it's interesting to postulate 'what if causality only had to hold within reference frames relevant to the objects involved?', it doesn't seem to work that way in real life - in part because of the laws of physics could be different in different reference frames then it would be easily testable.
This is the first postulate:
Under transitions between inertial reference frames, the equations of all fundamental laws of physics stay form-invariant, while all the numerical constants entering these equations preserve their values. Thus, if a fundamental physical law is expressed with a mathematical equation in one inertial frame, it must be expressed by an identical equation in any other inertial frame, provided both frames are parameterised with charts of the same type.
If different IRFs had different physical laws we could have detected it trivially by now.
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From experiment, we have determined that simply pumping kinetic energy into something will only accelerate it asymptoticly close to the speed of light, yes, but I don't think that directly addresses the issue of causality. Right now I believe the discussion is on the level of "depending on where you observe a series of interactions, if FTL is possible then the effect would precede the cause". Most of the causality violations I see in the examples seem to be an artifact of 'what is observed is what happened' that is to say that it assumes light to be the fastest thing so when the light from events reach an observer it is assumed that the order of events observed was the order in which they happened even if some of those events are FTL in nature.
I actually just reread your bomb example. if the triggering action was the reception of the bomb by the FTL radio, then in what reference frame would the bomb exploding precede the detection of the FTL signal?
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If your outside references do not have the capability of receiving/transmitting FTL signals, then they cannot observe the FTL transaction and then the discussion of IRFs is moot. This is also all assuming that you do not "shortcut" the LSC by some sort of dimensional hopping thru an environment where Lightspeed is not the highest speed possible. Most speculation leans in this direction. In SciFi NO ONE does FTL in Real Space.
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at least not since flash gordon.
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at least not since flash gordon.
Mass Effect called.
Granted they were exploiting loopholes, but...
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I think putting the ship into a mass neutralizing field counts as 'not real space'.
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GOOD NEWS EVERYONE!
(http://t2.gstatic.com/images?q=tbn:0LfyHNoNA6P6BM:http://img294.imageshack.us/img294/6681/farnsworthis0.jpg&t=1)
That warp drive... it was invented by Profesor Hubert Farnsworth, it's a drive that moves space around the ship, not the ship in space! (kind of :nervous: )
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I think putting the ship into a mass neutralizing field counts as 'not real space'.
It's actually exploiting a loophole that may or may not exist and giving the ship negative mass in real space, thus allowing it to exceed the speed of light.
...in theory.
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which I would file in the folder marked 'Not Real Space'
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Personally I don't think we (mankind) know enough to arbitrarily denounce FTL as impossible......tbh though I don't really understand why FTL has to involve time travel ?
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It's a consequence of Einstein's special relativity, which basically states that any form of faster-than-light travel is functionally equivalent to time travel.
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Let me quote good old Professor Farnsworth:
Take that causality!
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tbh though I don't really understand why FTL has to involve time travel ?
Because only a DeLorean is capable of exceeding speeds of 300,000 km per second, and it starts traveling through time at 88 mph. If and when it starts, that is.
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If your outside references do not have the capability of receiving/transmitting FTL signals, then they cannot observe the FTL transaction and then the discussion of IRFs is moot.
They can still see the FTL ship arriving out of nowhere and blowing itself up before it's even finished being constructed.
Paradox.
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Here's another idea: why do teleporters have to copy all your information, destroy it, and reproduce it on the other side? Wouldn't it make more sense to copy and send instead of copy, delete, and send? After all, if you could possibly send all this information lightyears away, would you want to spend the years traveling it or would a copy of you rather appear on the other side with no perception of time lost and no fatigue or degradation. I think our larger problem than reproduction is getting all the information instantly yet accurately. Besides, it'd be kind of cool to know that I flaked out of time for science.
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Assuming a time like particle such as a photon, what would it be like to be one? How does it see the world? What happens in the interaction between matter and photon? My limited understanding is that the photon itself doesn't age, but what else is there? This is a rather fun topic since I deal with photons every day in my work. But I have never really needed to think what really goes on there, as I can usually reduce them to rays. Come to think of it, how does the polarization even work in corpuscular model? What is it that my photons do to make the electrical field appear as polarized?
Electrical field = a cloud of small flishy-flashy wobbling balls that go extremely fast. That seen from their perspective, don't age at all. And pre-scan their direction of travel through whole spacetime, and then select the shortest route - and only after that, travel through it, lazy bastards. If somebody tries to outsmart them with interference stuff, they counter by interfering with themselves. Yeah, I wish I could make this up, but this just keeps getting better and better. Sneaky bastards those photons.
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Here's another idea: why do teleporters have to copy all your information, destroy it, and reproduce it on the other side? Wouldn't it make more sense to copy and send instead of copy, delete, and send? After all, if you could possibly send all this information lightyears away, would you want to spend the years traveling it or would a copy of you rather appear on the other side with no perception of time lost and no fatigue or degradation. I think our larger problem than reproduction is getting all the information instantly yet accurately. Besides, it'd be kind of cool to know that I flaked out of time for science.
The deletion is certainly not a necessary step (barring the need for destructive scanning to achieve sufficient resolution?), but it makes many people more comfortable because it preserves the illusion of a unitary conserved self.
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They can still see the FTL ship arriving out of nowhere and blowing itself up before it's even finished being constructed.
Paradox.
what it would look like and what was real are not necessarily the same things, if you look at a straw in a cup of water the different indices's of refraction of water and air will cause the straw to appear to be bent, when in reality it's actually quite straight. just because you can see a pair of space ships engage in a climactic final showdown that determines the fate of the galaxy before you can see traces of bronze age civilization on the planets from which they originated does not mean that, that is the actual state of those planets.
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They can still see the FTL ship arriving out of nowhere and blowing itself up before it's even finished being constructed.
Paradox.
what it would look like and what was real are not necessarily the same things, if you look at a straw in a cup of water the different indices's of refraction of water and air will cause the straw to appear to be bent, when in reality it's actually quite straight. just because you can see a pair of space ships engage in a climactic final showdown that determines the fate of the galaxy before you can see traces of bronze age civilization on the planets from which they originated does not mean that, that is the actual state of those planets.
Again, this is that common misconception that relativity is all an optical illusion. It's not that at all.
In this case we are not talking about what things look like. We are talking about what is real. And that is because the speed of light is an utter invariant which defines the causal separation of events.
For example, a person moving near lightspeed will see a meter-long stick (at rest in our IRF) as shorter than a meter. This is not an optical illusion. The stick has actually contracted...in that IRF. In our IRF it hasn't. Both IRFs are equally valid. Objects have different lengths (and masses) depending on the relative velocity of the observer.
Similarly in this case, the events actually swap order; the perception of the events is not all that's changed, the order of the events themselves has.
If you need more convincing I'll walk you through an introductory example I'm fond of.
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They can still see the FTL ship arriving out of nowhere and blowing itself up before it's even finished being constructed.
Paradox.
what it would look like and what was real are not necessarily the same things, if you look at a straw in a cup of water the different indices's of refraction of water and air will cause the straw to appear to be bent, when in reality it's actually quite straight. just because you can see a pair of space ships engage in a climactic final showdown that determines the fate of the galaxy before you can see traces of bronze age civilization on the planets from which they originated does not mean that, that is the actual state of those planets.
Again, this is that common misconception that relativity is all an optical illusion. It's not that at all.
In this case we are not talking about what things look like. We are talking about what is real. And that is because the speed of light is an utter invariant which defines the causal separation of events.
For example, a person moving near lightspeed will see a meter-long stick (at rest in our IRF) as shorter than a meter. This is not an optical illusion. The stick has actually contracted...in that IRF. In our IRF it hasn't. Both IRFs are equally valid. Objects have different lengths (and masses) depending on the relative velocity of the observer.
Similarly in this case, the events actually swap order; the perception of the events is not all that's changed, the order of the events themselves has.
If you need more convincing I'll walk you through an introductory example I'm fond of.
Walk IT!!
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Okay.
For this to work, you need to be aware of an experimentally demonstrable starting point: the speed of light (C) is the same no matter how fast you're going.
This is really weird. Normally, if you see a guy drive past at 30 mph, and he throws a ball forward from his car at a speed of 30 mph, the ball's gonna be going at 60 mph from your POV. But if that guy turns on a flashlight, the light won't move at C+30; it'll move at C.
This in turn suggests that to the guy driving at 30 mph (the wimp), the light is moving at C-30 from his POV...but no, even to him it's moving at C.
This is bizarre but true.
Right.
Imagine that Axem and I are going to have a gun duel. Because we're awesome, we're going to have this duel on a moving train car. Axem will stand at the front end of the car, and I at the rear.
When a light positioned exactly in the middle of the train car flashes on, that will be the signal to draw and fire. So as soon as the pulse of photons from the light, moving at C, strikes our eyes, we will fire.
We want to be extra sure that the duel is going to be fair, so we hire The_E to stand in the train car with us and verify that the light reaches each of us simultaneously. Since Axem, The_E and I are all inside the moving car with the light, we are all stationary relative to each other.
However, Axem's crazed fan Cobra sneaks onto a train platform that we pass at just the moment the light flashes. To Cobra, the train car - and the duelists within it, as well as the light - are moving rapidly across his reference frame from his left to his right.
Does The_E conclude that the duel is fair?
Does Cobra conclude that the duel is fair?
Recall that the speed of the light is independent of the motion of the source and that the criteria for fairness is that the light pulse reach both Axem and Battuta simultaneously.
Here's a picture:
| BATTUTA ........... LIGHT ............ AXEM| ------------------------------> direction of travel
COBRA
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Seems like an awful waste of good HLP members. If you kill Axem just remember you're filling his shoes for Diaspora.
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Seems like an awful waste of good HLP members. If you kill Axem just remember you're filling his shoes for Diaspora.
thees was my plan all along
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ok, so this does show that time slows for objects that move normally through space. the implication being that moving faster than light would cause time to flow backwards for that object, but perhaps there is some as yet unknown mechanism that could neutralize time dilation to some extent, this would break the rules of relativity that require the speed of light to be the speed of propagation in the universe. no matter what reference frame you work in time is always moving forward, so the only problem with FTL in this since is that time in an FTL frame would move backwards, so if this effect could somehow be countered then causality could be preserved. now this is just pie in the sky, but we all know that there is no known way to achieve FTL, and all we are talking about is the causality problem, so playing what if on the known rules I think should be acceptable.
so if we ignore the fact that moving faster than the speed of light would require more than infinite energy, would cause time for the moving object to travel backwards, would cause all objects to have negative dimensions and more than infinite mass, (I suppose this would be the same as modifying what C equaled within a local volume) I still don't see how cause and effect are effected by this. I am not aware of any observations that have established that C is the speed of event propagation, only that nothing has disproven it, and that it is the fastest propagation yet observed, though I'm not even sure how you would observe event propigation.
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Seriously, what about "subspace"-y schemes? Considering the object is effectively outside the universe as it's "in transit"...
Suppose you're doing a jump. If we define the IRF such that the position/velocity of the ship as it enters subspace is 0, and we require that the time of arrival be "later" than the time of departure (in that reference frame), and that the final velocity also be 0... (i.e. velocity in the original IRF is unchanged)...
:ick:
If another ship near the point of arrival has the same capabilities, and is moving rapidly "away" from the original position, then the same issue would arise; it could jump to where the first ship started out, and could conceivably arrive before the first ship departed.
So that's no good either... unless some other restrictions could be devised.
Actually, I reckon these restrictions might be determinable mathematically.
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ok, so this does show that time slows for objects that move normally through space. the implication being that moving faster than light would cause time to flow backwards for that object, but perhaps there is some as yet unknown mechanism that could neutralize time dilation to some extent, this would break the rules of relativity that require the speed of light to be the speed of propagation in the universe. no matter what reference frame you work in time is always moving forward, so the only problem with FTL in this since is that time in an FTL frame would move backwards, so if this effect could somehow be countered then causality could be preserved. now this is just pie in the sky, but we all know that there is no known way to achieve FTL, and all we are talking about is the causality problem, so playing what if on the known rules I think should be acceptable.
so if we ignore the fact that moving faster than the speed of light would require more than infinite energy, would cause time for the moving object to travel backwards, would cause all objects to have negative dimensions and more than infinite mass, (I suppose this would be the same as modifying what C equaled within a local volume) I still don't see how cause and effect are effected by this. I am not aware of any observations that have established that C is the speed of event propagation, only that nothing has disproven it, and that it is the fastest propagation yet observed, though I'm not even sure how you would observe event propigation.
When it comes to your latter question, see the thought experiment above. Consider the difference between The_E and Cobra's perceptions of the fairness of the duel, and the fact that it's the particular behavior of light that makes this weird asymmetry occur.
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Oh hey, and what about wormholes?
If both ends of a wormhole open simultaneously---that is, they have no velocity relative to one another, and thus in either endpoint's IRF they appear to have opened simultaneously---then could any time-travel issues arise out of the travel of a ship through that worm hole?
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well, their observations come via their eyes, which sense the world by the light which enters them, they are not seeing any objects only the light reflected or radiated off objects, so as I said, I don't know how you would go about disproving C as the speed of event propagation without first finding something that can sense via some FTL method, so we hit a tautologous catch 22, it can't be disproven until l it's disproved. :\
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Granted I've got the Maths of a 12 year old but where does it say that time ceases to flow forward and ONLY forward once you transcend lightspeed? Even if you somehow manage to accelerate to twice the speed of light, the nearest star is still 2 years away. Hell, it would take you 3 hours to fly to Jupiter. So I guess what I'm not understanding is how a ship could be constructed and then appear and destroy itself just by exceeding the speed of light.
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well, their observations come via their eyes, which sense the world by the light which enters them, they are not seeing any objects only the light reflected or radiated off objects, so as I said, I don't know how you would go about disproving C as the speed of event propagation without first finding something that can sense via some FTL method, so we hit a tautologous catch 22, it can't be disproven until l it's disproved. :\
I think I might need to ship you a relativity textbook.
Granted I've got the Maths of a 12 year old but where does it say that time ceases to flow forward and ONLY forward once you transcend lightspeed? Even if you somehow manage to accelerate to twice the speed of light, the nearest star is still 2 years away. Hell, it would take you 3 hours to fly to Jupiter. So I guess what I'm not understanding is how a ship could be constructed and then appear and destroy itself just by exceeding the speed of light.
Superluminal motion is equivalent to time travel in some IRFs. I can run through the math if you want. It needs high-school-level algebra and a willingness to accept the valid derivation of the Lorentz transformation.
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I suggest that this silly little diagram be used from now on whenever these debates crop up:
(http://upload.wikimedia.org/wikipedia/commons/e/e4/Lorentz_transform_of_world_line.gif)
Now can anybody address my wormholes question?
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Aardwolf, any form of FTL can be functionally equivalent to time travel. There are no exceptions.
At least, that's what people who know more about the subject keep telling me.
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But wasn't non-simply-connected space one of the things that general relativity didn't explicitly rule out?
Granted, I know even less about general relativity than I do about special relativity, but...
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Look, for the purposes of special relativity, it doesn't matter (much) how you go past c, the fact that you're arriving at your destination faster than the light could have bridged that distance is enough.
There's a reason why wormholes have a traditional place in time-travel-themed SF.
EDIT: Wrongness removed.
Read Wikipedia on the subject (http://en.wikipedia.org/wiki/Wormhole).
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But if there's a wormhole, then the light (or propagation of events) still reaches the destination faster than anything else possibly could (because the wormhole isn't just a shortcut for a spaceship, it's a shortcut for EVERYTHING)
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Yes, I realize that after reading up on it.
However, there's one major catch for wormholes: Noone has ever observed one. Yes, they are allowed in the relevant theories, but that doesn't mean they actually exist.
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Fine by me!
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Thing is that while static wormholes do not (normally) allow time travel, it's trivial to accelerate one end and thus create a problematic time machine.
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Thing is that while static wormholes do not (normally) allow time travel, it's trivial to accelerate one end and thus create a problematic time machine.
...assuming the endpoints can be accelerated at all. Would the 'acceleration' of an endpoint by gravitation (what with all the details of general relativity that I don't know about) cause any problem?
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Thing is that while static wormholes do not (normally) allow time travel, it's trivial to accelerate one end and thus create a problematic time machine.
...assuming the endpoints can be accelerated at all. Would the 'acceleration' of an endpoint by gravitation (what with all the details of general relativity that I don't know about) cause any problem?
Yes. Acceleration and gravity are equivalent in all ways including time dilation.
And the endpoints can be accelerated.
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Yes, I realize that after reading up on it.
However, there's one major catch for wormholes: Noone has ever observed one. Yes, they are allowed in the relevant theories, but that doesn't mean they actually exist.
The real question might be how to observe a wormhole in the first place. For all we could know, they could only form only during special cosmic events and be randomly (at least so far as we could observe) spit you out somewhere else, if it'd even be possible to move through space fast enough to transverse it. And what if you don't reach the other side? What if your particular hole closes before you can get through? Plotting space-time only works when you're using a single plane--it's easy to show how gravity has an effect on a 2D cross-section, but does that really tell us anything? And with 3D technology, can we even accurately observe 4+D events?
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Yes, I realize that after reading up on it.
However, there's one major catch for wormholes: Noone has ever observed one. Yes, they are allowed in the relevant theories, but that doesn't mean they actually exist.
The real question might be how to observe a wormhole in the first place. For all we could know, they could only form only during special cosmic events and be randomly (at least so far as we could observe) spit you out somewhere else, if it'd even be possible to move through space fast enough to transverse it. And what if you don't reach the other side? What if your particular hole closes before you can get through? Plotting space-time only works when you're using a single plane--it's easy to show how gravity has an effect on a 2D cross-section, but does that really tell us anything? And with 3D technology, can we even accurately observe 4+D events?
Yes. Your concerns about observation are not something to get too worked up over - if wormholes do exist, they have pretty trivially observable characteristics.
For instance there may be massive energy buildups on the Cauchy horizon which render the hole untraversable.
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For instance there may be massive energy buildups on the Cauchy horizon which render the hole untraversable.
Dangit, now I gotta go look that one up.
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Aardwolf, any form of FTL can be functionally equivalent to time travel. There are no exceptions.
Except, conversely, every form of FTL forms a time-space path from point A to point B which isn't dependant on the observation cones based on the assumption that speed of light is the fastest speed information can propagate through time and space.
Or, in other words, if you FTL from point A to point B, you're not actually moving through the space between the points at superluminal speed, you're making the distance shorter - depending on type of travel, the distance via FTL travel can be anything from astronomical units (Star Wars hyperspace) to order of thousands of kilometres (Babylon 5 hyperspace) or just kilometres (FreeSpace subspace) to zero (BSG type FTL jump drives).
FTL can't reverse causality, it just introduces a way for information (and therefore causality) to not be bound on the observation cones that are so commonly used to create "paradoxes".
General Relativity doesn't exclude the possibility of information travelling faster than speed of light in vacuum. It simply states that it is impossible for an object with rest mass to be accelerated by a force to speed of light when confined to the currently known time-space continuum.
Now, what comes to Alcubierre drive in which there technically is no force accelerating the ship, but space-time itself moving the ship on a wave... well, even then it's possible that waves in space-time continuum propagate at speed of light at most, in which case riding the wave wouldn't still quite bring you to superluminal speeds.
Except if you take into account time dilation. Which you can also interpret as making the way shorter rather than ship faster...
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Hey Aardwolf. You can travel to Alpha Centauri, which is 4.3LY away, in less than a year. Indeed, you could do it in less than a day.
Without breaking physics or using flashy wormholes. :)
Just travel at 0.99etc times the speed of light, and have fun missing out on four years of history. :P
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Yeah but I'd be killed by the acceleration/deceleration.
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Yeah but I'd be killed by the acceleration/deceleration.
Then choose a more distant target. Perhaps you'd like to visit Regulus at 77 ly away.
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You'd also need a ton of fuel. It's an ugly engineering problem.
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There's actually a finite limit on the maximum percentage of lightspeed you can reasonably accelerate to with most proplusion types, based on the point at which you start wasting fuel simply to carry more fuel for more acceleration as opposed to, you know, actually going anywhere.
Even an antimatter rocket only makes it to like .24 within those constraints IIRC.
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You'd also need a ton of propellant. It's an ugly engineering problem.
Fix'd.
Fuel != Propellant.
Propellant can be anything with mass accelerated into the direction opposite to desired acceleration. In chemical rockets, propellant is the exhaust gases from the nozzle; both oxidizer and fuel count as propellant; in solid rocket boosters, there's also usually catalyzing agents, binding and preserving agents and other stuff, which all is ejected from the business end of the rocket and used as propellant. Liquid fuel rockets usually use liquid oxygen as oxidizer and liquid hydrogen or kerosene as fuel; both act as propellant gases as they exit the nozzle.
In more effective thruster configurations, it is possible to derive the kinetic energy of the propellant from something else than a chemical reaction. This is the case with ion engines and the awesome planned NERVA thruster system which basically pumped hydrogen through the core of an active nuclear reactor to heat it to very, very high temperatures, expanding it and giving it ejection velocities higher than those achieved by chemical rockets.
Basically, what you want from your ship is specific impulse, or change of momentum. It is a simple factor of the entire mass of propellant you're carrying with, and the ejection velocity of said propellant. Opposite momentum is gained by the ship (although the acceleration given by the engine increases as amount of propellant carried by the ship reduces).
This means that the higher the ejection velocity, the less propellant you need to carry to achieve desired change of momentum.
So, anyway. Anything that can be shot away from a ship at high velocity is propellant. If you, say, had a ship on decaying solar orbit with disabled engines, but you still had the rotation control system online and enough energy for some serious railgun barrages... you could speed up your orbital velocity and slow down your fall towards the Sun. If you know what I mean. But if either RCS, reactor or gunnery control were off-line, you would be sort of screwed.
(Note for Battuta: This is mostly for the benefit of other people - you just gave me a good opening to go into lecture mode. :p)
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Yeah but I'd be killed by the acceleration/deceleration.
You'd also need a ton of fuel. It's an ugly engineering problem.
Valid points, but it still doesn't result in breaking the universe and ruining everyone's day. Maybe just yours, if you were stupid enough to subject yourself to 10+ g's of force. Or a lot more people if you accidentally smash into an inhabited planet at relativistic speed. :O
/me plays with the impact-effects calculator.
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Ah, I remember the other FTL discussion like it was three months ago...
Here's what I carried away from it:
1. An inertial reference frame is not necessarily an observer. As near as I can tell, it is any point or object that could make an observation. eg. the same way your left eye has a different reference than your right eye, and even the various sensor cells in your eye all have slightly different references, so one side of a ball would have a different IRF than the opposite side, and I extracted from that that every particle could have it's own IRF, possibly even every geometric point in the universe. So, one does not need to see something for an IRF to exist there.
2. The math we have, and the experiments we've run ("we" being humanity) have all pointed to FTL travel breaking reality by changing a certain value to a negative number, and that negative number causes the universe to fold in on itself or something. Perhaps the math is incomplete, but so far we've seen no evidence that it is.
3. Therefore, I speculated that the only way for every IRF in existence to be able to agree on causality is if the object travelling did so in a way without acceleration, ie. instantaneous teleportation. But even that would break the existing math in some other way, iirc.
4. Regarding fraction of light speed, what about a laser drive? If your propellant is light itself, couldn't you get going pretty fast? Though accelleration would be a beast. Laser drives as seen in the Man-Kzin Wars (http://en.wikipedia.org/wiki/Man-Kzin_Wars#First_Man-Kzin_War)
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One comment about velocities approaching c; as if the earlier difficulties weren't enough, small dust particles along the way might cause serious problems. Not only do the eat away any sort of shielding, but they might also cause a static discharge to build up.
I don't even want to guess how deep a small dust particle penetrates when a spaceship collides with it at relativistic velocity.
Also, if you haven't already seen these, here's (http://www.anu.edu.au/physics/Searle/) some interesting relativistic phenomena simulated in a ray-traced world.
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Borked link is borked.
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Ah, I remember the other FTL discussion like it was three months ago...
Here's what I carried away from it:
1. An inertial reference frame is not necessarily an observer. As near as I can tell, it is any point or object that could make an observation. eg. the same way your left eye has a different reference than your right eye, and even the various sensor cells in your eye all have slightly different references, so one side of a ball would have a different IRF than the opposite side, and I extracted from that that every particle could have it's own IRF, possibly even every geometric point in the universe. So, one does not need to see something for an IRF to exist there.
The "every geometric point" POV is the only true one.
2. The math we have, and the experiments we've run ("we" being humanity) have all pointed to FTL travel breaking reality by changing a certain value to a negative number, and that negative number causes the universe to fold in on itself or something. Perhaps the math is incomplete, but so far we've seen no evidence that it is.
Your understanding is incomplete. The thing to remember is that if you introduce time travel into a Universe, said universe becomes inconsistent.
3. Therefore, I speculated that the only way for every IRF in existence to be able to agree on causality is if the object travelling did so in a way without acceleration, ie. instantaneous teleportation. But even that would break the existing math in some other way, iirc.
Depends on the method. Wormholes could work. However, always remember that any method of circumventing c is also capable of allowing time travel. As said before, once you allow time travel, paradoxa are only an eyeblink away.
4. Regarding fraction of light speed, what about a laser drive? If your propellant is light itself, couldn't you get going pretty fast? Though accelleration would be a beast. Laser drives as seen in the Man-Kzin Wars (http://en.wikipedia.org/wiki/Man-Kzin_Wars#First_Man-Kzin_War)
That laser still has to be powered by something. It also has to be cooled, and it has to have a high enough precision to still hit its target at interstellar distances. Not to mention that without a corresponding laser on the other end or onboard fuel, you can't decelerate. Also note that photons are not known for the big amount of energy they carry.