3 ms·

> Signals slower than the speed of light (or even at the speed of light, e.g. radio signals in space) are ordinary and have no paradox, so there's nothing to de

> Signals slower than the speed of light (or even at the speed of light, e.g. radio signals in space) are ordinary and have no paradox, so there's nothing to debate. Okay, but that's the thing: from one perspective (the signal's) the signal is indeed subluminal, but from another (an observer's, e.g. the sender or recipient) it's not. So which math applies? > The answer is that light takes 104 years to travel from our solar system to the Illus system, so yes it very much is superluminal, there's no way around that. Except there is a way around that, no? Specifically that from the signal's point of view it was not actually superluminal, and therefore not subject to the infinite energy requirements of locally-superluminal travel? If A sends a message at tA=1, and it takes one second for the message to reach B (so, tB=2), then how does that result in tA > tB? No matter which frame of reference we're using (A's, B's, the signal's), I'm failing to see where causality would invert. That is, going back to the start of this conversation: > If you end up outside of your own light cone, no matter how, there's a causality paradox. From which frame of reference is that light cone authoritative? If I'm B, and A sends me two copies of a message - one by some wormhole or warp pigeon or whatever, and one by radio - and the W message takes 1 second while the R message takes 10, then where does that leave room for the W message to reach me before it was sent? The math behind a tachyonic antitelephone - as far as I can tell - only answers this for cases where the signal is itself traveling faster than c within its own frame of reference, but that wouldn't be the case in this situation.

SideburnsOfDoom 6y ago
> Okay, but that's the thing: from one perspective (the signal's) the signal is indeed subluminal, but from another (an observer's, e.g. the sender or recipient) it's not. So which math applies? All observers are valid. The maths answers differ due to different inputs but they apply the same formula. All should get self-consistent results, though not necessarily the same results: the idea that two events are "simultaneous" is observer-dependant. Details here https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://en.wikipedia.org/wiki/Relativity_of_simultaneity If _any_ observer, including one not on the fast spaceship, can communicate FTL, that will lead to paradoxes. > Except there is a way around that, no? No. > Specifically that from the signal's point of view it was not actually superluminal, Irrelevant. Another observer - for whom the signal is superluminal - can leverage that. > and therefore not subject to the infinite energy requirements of locally-superluminal travel? I didn't mention infinite energy, and it's a problem for FTL, but not the problem that we were talking about. > If A sends a message at tA=1, and it takes one second for the message to reach B (so, tB=2), then how does that result in tA > tB? No matter which frame of reference we're using (A's, B's, the signal's), I'm failing to see where causality would invert. If a signal can travel at lightspeed or lower from A to B, causality of A -> B cannot invert. if it _cannot travel_ , then all bets are off, which is pretty much the point. Basically by stretching "Relativity of simultaneity" to breaking point. > From which frame of reference is that light cone authoritative? All frames of reference are equally valid. > where does that leave room for the W message to reach me before it was sent? An observer moving with respect to A and B can "hack" this to produce effects before cause in their frame of reference. It's no co-incidence that Alice and Bob in the Tachyonic antitelephone are moving with respect to each other, therefor with different frames of reference. > the signal is itself traveling faster than c within its own frame of reference, That's not a thing. The tachyonic antitelephone is a dialog between two observers with different frames of reference. The "Tachyons" could be miniature starship enterprises in "stationary" warp bubbles, flying back and forth; and it would work the same. So in line with "this has been said before" it's what is here: https://news.ycombinator.com/item?id=26617487 https://news.ycombinator.com/item?id=26617487 Note "I can find a frame of reference" - all frames of reference are valid, and should be free of paradox.
- yellowapple 6y ago
  > An observer moving with respect to A and B can "hack" this to produce effects before cause in their frame of reference. Again, though: how? Specifically: how would a third observer have any impact at all? He's an observer. Judging by that new Wikipedia article, the answer seems to be "well the observer will perceive events at different times from when they actually happened, and therefore two simultaneous lightning strikes weren't actually simultaneous because the observer didn't see them simultaneously", but I'm failing to see why we should be treating the observer's interpretation as fact: just because the observer perceived something at various times doesn't mean that's how they actually played out. Further: > It's no co-incidence that Alice and Bob in the Tachyonic antitelephone are moving with respect to each other, therefor with different frames of reference. Are they, though? This seems to assume that their movement around and perception of each other is only happening through "normal" space, but the very premise of this discussion states otherwise: that they are communicating via a region of spacetime where their distance is fixed (or at least changing much more slowly than the relativistic speeds given in those Wikipedia examples). If Alice and Bob are talking to each other through a wormhole, for example, then through that wormhole they are (approximately) stationary, and therefore there'd be no significant time dilation as far as that communication is concerned. Same deal if they're communicating via "miniature starship enterprises", as you put it. The very premise of a warp drive is to get an object from A to B without any actual movement from A to B - specifically by warping spacetime such that the distance from A grows and the distance from B shrinks. This therefore creates a pathway between A and B where they are effectively stationary relative to one another, specifically because the message is stationary relative to each of them. Therefore, messages conveyed on this pathway don't seem to leave any possibility of time dilation, and therefore no possibility of inverted causality. Now, obviously I'm missing something here, but from what I can tell, the math checks out fine. And a lot of physicists who are not community college dropouts like I am seem to agree (or else they wouldn't be putting forward hypotheses involving warp drives and wormholes and such as a means to achieve superluminal communication without time-dilation-related effects).
  - SideburnsOfDoom 6y ago
    Can recommend again that you turn to books on this subject; Posting long rants on the internets won't get you anything. You're clearly not learning, and neither are you intellectually impressing anyone. > get an object from A to B without any actual movement from A to B This sentence is pure gibberish: You got from A to B in time T ... but you also didn't get from A to B in time T? Ok, whatever. You're splitting hairs about "actual movement" and again in the long and utterly incoherent text about "Alice and Bob in the Tachyonic antitelephone" moving but also not, which I can't be bothered to untangle because I'm not paid to teach people who think they already know a lot more than they really do. Buy a book on the subject, those authors do get paid for this. This kind of posting doesn't help you learn anything. > but from what I can tell, the math checks out fine. I'm going to draw a line here, and I don't mind being a Jerk now, so: What the actual fuck are you talking about? In Physics, "the math" isn't a metaphor, it's math. The math checks out? What math? There's no math here, just waffle. The math is the real thing, as observed here https://www.youtube.com/watch?v=NbzWYjVrvpI&t=55s https://www.youtube.com/watch?v=NbzWYjVrvpI&t=55s

SideburnsOfDoom 6y ago

> Okay, but that's the thing: from one perspective (the signal's) the signal is indeed subluminal, but from another (an observer's, e.g. the sender or recipient) it's not. So which math applies? All observers are valid. The maths answers differ due to different inputs but they apply the same formula. All should get self-consistent results, though not necessarily the same results: the idea that two events are "simultaneous" is observer-dependant. Details here https://en.wikipedia.org/wiki/Relativity_of_simultaneity https://en.wikipedia.org/wiki/Relativity_of_simultaneity If _any_ observer, including one not on the fast spaceship, can communicate FTL, that will lead to paradoxes. > Except there is a way around that, no? No. > Specifically that from the signal's point of view it was not actually superluminal, Irrelevant. Another observer - for whom the signal is superluminal - can leverage that. > and therefore not subject to the infinite energy requirements of locally-superluminal travel? I didn't mention infinite energy, and it's a problem for FTL, but not the problem that we were talking about. > If A sends a message at tA=1, and it takes one second for the message to reach B (so, tB=2), then how does that result in tA > tB? No matter which frame of reference we're using (A's, B's, the signal's), I'm failing to see where causality would invert. If a signal can travel at lightspeed or lower from A to B, causality of A -> B cannot invert. if it _cannot travel_ , then all bets are off, which is pretty much the point. Basically by stretching "Relativity of simultaneity" to breaking point. > From which frame of reference is that light cone authoritative? All frames of reference are equally valid. > where does that leave room for the W message to reach me before it was sent? An observer moving with respect to A and B can "hack" this to produce effects before cause in their frame of reference. It's no co-incidence that Alice and Bob in the Tachyonic antitelephone are moving with respect to each other, therefor with different frames of reference. > the signal is itself traveling faster than c within its own frame of reference, That's not a thing. The tachyonic antitelephone is a dialog between two observers with different frames of reference. The "Tachyons" could be miniature starship enterprises in "stationary" warp bubbles, flying back and forth; and it would work the same. So in line with "this has been said before" it's what is here: https://news.ycombinator.com/item?id=26617487 https://news.ycombinator.com/item?id=26617487 Note "I can find a frame of reference" - all frames of reference are valid, and should be free of paradox.

yellowapple 6y ago
> An observer moving with respect to A and B can "hack" this to produce effects before cause in their frame of reference. Again, though: how? Specifically: how would a third observer have any impact at all? He's an observer. Judging by that new Wikipedia article, the answer seems to be "well the observer will perceive events at different times from when they actually happened, and therefore two simultaneous lightning strikes weren't actually simultaneous because the observer didn't see them simultaneously", but I'm failing to see why we should be treating the observer's interpretation as fact: just because the observer perceived something at various times doesn't mean that's how they actually played out. Further: > It's no co-incidence that Alice and Bob in the Tachyonic antitelephone are moving with respect to each other, therefor with different frames of reference. Are they, though? This seems to assume that their movement around and perception of each other is only happening through "normal" space, but the very premise of this discussion states otherwise: that they are communicating via a region of spacetime where their distance is fixed (or at least changing much more slowly than the relativistic speeds given in those Wikipedia examples). If Alice and Bob are talking to each other through a wormhole, for example, then through that wormhole they are (approximately) stationary, and therefore there'd be no significant time dilation as far as that communication is concerned. Same deal if they're communicating via "miniature starship enterprises", as you put it. The very premise of a warp drive is to get an object from A to B without any actual movement from A to B - specifically by warping spacetime such that the distance from A grows and the distance from B shrinks. This therefore creates a pathway between A and B where they are effectively stationary relative to one another, specifically because the message is stationary relative to each of them. Therefore, messages conveyed on this pathway don't seem to leave any possibility of time dilation, and therefore no possibility of inverted causality. Now, obviously I'm missing something here, but from what I can tell, the math checks out fine. And a lot of physicists who are not community college dropouts like I am seem to agree (or else they wouldn't be putting forward hypotheses involving warp drives and wormholes and such as a means to achieve superluminal communication without time-dilation-related effects).
- SideburnsOfDoom 6y ago
  Can recommend again that you turn to books on this subject; Posting long rants on the internets won't get you anything. You're clearly not learning, and neither are you intellectually impressing anyone. > get an object from A to B without any actual movement from A to B This sentence is pure gibberish: You got from A to B in time T ... but you also didn't get from A to B in time T? Ok, whatever. You're splitting hairs about "actual movement" and again in the long and utterly incoherent text about "Alice and Bob in the Tachyonic antitelephone" moving but also not, which I can't be bothered to untangle because I'm not paid to teach people who think they already know a lot more than they really do. Buy a book on the subject, those authors do get paid for this. This kind of posting doesn't help you learn anything. > but from what I can tell, the math checks out fine. I'm going to draw a line here, and I don't mind being a Jerk now, so: What the actual fuck are you talking about? In Physics, "the math" isn't a metaphor, it's math. The math checks out? What math? There's no math here, just waffle. The math is the real thing, as observed here https://www.youtube.com/watch?v=NbzWYjVrvpI&t=55s https://www.youtube.com/watch?v=NbzWYjVrvpI&t=55s