4 ms·

> If I can travel FTL, I can find a frame of reference where T2 < T1 How? Sure, it's possible that the light from an event happening at T2 arrives before the

> If I can travel FTL, I can find a frame of reference where T2 < T1 How? Sure, it's possible that the light from an event happening at T2 arrives before the light from an event happening at T1, but that says nothing about when those events actually happened - just like how if we hear one lightning strike before another, that doesn't mean the one we heard first actually happened first. That is: this notion that all superluminal travel somehow magically necessitates the possibility of backwards time travel doesn't seem to be logically sound, and seems to be one of these things that people keep repeating without bothering to actually explain why that is. Specifically, this "FTL necessitates backwards time travel" argument seems to depend on some notion that light is infinitely fast (because the only way to go back in time is to have a speed greater than infinity - i.e. one where the t component in d/t is negative), which is empirically false (we can measure light's speed, and it's clearly finite).

SideburnsOfDoom 6y ago
> How? > this notion that all superluminal travel somehow magically necessitates the possibility of backwards time travel doesn't seem to be logically sound. There is literally decades worth of physics that answers your how, and explains the soundness of it, I would urge you to study the subject in well, any depth at all before naively dismissing it as "unsound". I mean, who's more likely wrong: Physics since Einstein's 1905 papers, or guy on the internet who's been thinking about it for 10 minutes, and has questions with basic misconceptions in them. Asking for answers in the comments is a very poor way to approach a subject like this. All you'll get are quick responses and displays of ignorance.
- yellowapple 6y ago
  > There is literally decades worth of physics that answers your how And as I've already stated, none of it has been even remotely adequate. If it was, then I wouldn't be asking stupid questions with "basic misconceptions" in them. Maybe I'm too stupid to understand it. > or guy on the internet who's been thinking about it for 10 minutes, and has questions with basic misconceptions in them. Care to actually articulate those misconceptions? Like, I'm under no illusion that I'm correct here. I'm literally a community college dropout. I'm only attempting to find answers to questions I've been asking for years and for which I've yet to find an answer. Instead of an answer, it seems like today I'll be getting downvotes and ad hominem dismissals. Oh well. > Asking for answers in the comments is a very poor way to approach a subject like this. It's called having a discussion, which is quite literally the point of this website. If you don't want to engage in that discussion, then nobody is forcing you to.
  - SideburnsOfDoom 6y ago
    Misconception: > because the only way to go back in time is to have a speed greater than infinity > Instead of an answer, it seems like today I'll be getting downvotes and ad hominem dismissals. Oh well. Probably because your approach is very confrontational for someone who claims to be "just asking questions" e.g. "unsound", "not remotely adequate". And then you're dismissive - get directed to a wikipedia page where it's answered, and the mechanics of it are done in mathematics, and: "That doesn't answer the question. ... by what mechanisms?" OK, maybe that approach isn't for you you. Pop science books are a thing, try those instead? I'll add one thing: I'm a software engineer, but if you gave me 1000 lines of Rust to read, all I could say is "I have a very superficial reading of this code based of function and struct names, because I don't really know Rust at all." There's nothing wrong with that: specialised topic is specialised. It's ok to admit you don't know the details. What I would not say is "this program is not an answer, because I don't understand it." That would just be an egocentric misconception. > nobody is forcing you to You're right, if someone is being obnoxious and pointlessly confrontational, they won't get the best from the people who interact with them. No-one is forcing them to do it! But combining that with "oh why am I getting downvoted and dismissed" wailing seems disingenuous though.
    - yellowapple 6y ago
      > because the only way to go back in time is to have a speed greater than infinity And how is that a misconception? That seems to be exactly the thing the "answers" describe: the time it takes to travel from point A to point B being negative, somehow. Even when discussing problems where we've defined that duration to be positive. > Probably because your approach is very confrontational Just because you perceive it to be so doesn't mean it is. Just like, relevantly, how two signals arriving at a reference frame doesn't necessarily indicate the causality of whatever generated those signals. > get directed to a wikipedia page where it's answered It's not answered in said page. If it was then I'd be discussing that answer, rather than continuing to ask for that answer. (Not to mention that just linking some Wikipedia page without any attempt at providing context is itself pretty dismissive, but whatever) Specifically, the "answer" in that page only seems to describe the situation where the signal in its own reference frame is actually travelling faster than c, whereas the very premise of things like warp drives is to, you know, warp spacetime such that the distance covered in that signal's own reference frame is substantially shorter than normal. That is: a tachyonic antitelephone assumes that, you know, the signal exists as tachyons. Citing the concept of a tachyonic antitelephone in the context of a discussion around warping spacetime to shorten the distance entirely (i.e. remove the reliance on tachyons entirely) suggests - to me, at least, with my dumb dropout monkey brain - some implication that any situation where a signal from Point A arrives at Point B (where A and B are, say, 1 lightsecond away) any sooner than 1 second after being sent from Point A necessitates that signal to be treated as tachyonic, no matter what the signal "perceives" in its own reference frame. Thus, my question: why? And if you can't answer that question, then that's perfectly fine! I can't answer that question, either, so it ain't like I'd hold it against you. But if you're going to take the time to dismiss that question as being stupid or misguided or what have you, the least you could do is attempt to explain why it's a stupid question - or, better yet, just answer the question. > Pop science books are a thing, try those instead? Would you care to recommend one? > But combining that with "oh why am I getting downvoted and dismissed" wailing seems disingenuous though. If you actually believed me to be the disingenuous one in this conversation, then why bother continuing to comment? If you don't have anything to contribute, and don't believe I have anything to contribute, then, you could always, you know, leave me to my ignorant wailing :)
- Rule35 6y ago
  Hey. Uh, this flame war you're having is all you. The rules clearly say not to engage with trolls, not to attempt to fight them to a standstill. That said, I don't think yellowapple is trolling, I this he's saying "that article isn't accessible at my level".
AnimalMuppet 6y ago
It's not a question of which light arrived first. I see light arrive from X at some time T1+t1, I look at how far away I am from X, I do a little math to calculate how long it took the light to get there (t1), I subtract, and now I know what T1 is. Same for T2. The issue isn't when the light arrived. The issue is that I can find a frame of reference where T2 < T1, that is, the actual events occurred in the other order. It's not when the light reached me. The problem is the time of the events themselves.
- yellowapple 6y ago
  > I see light arrive from X at some time T1+t1 Except that your notion of T1+t1 is already going to be different from any other (non-stationary) observer's, yes? > I do a little math to calculate how long it took the light to get there (t1) Doesn't this assume that light has a fixed speed? We know already that this ain't necessarily the case, even in a vacuum; there are plenty of things - like sufficiently strong gravity wells - that can slow down light considerably. And in the context of situations involving warp drives and wormholes and other things bending spacetime willy-nilly, that further throws a wrench in attempting to figure out how long it took light to reach you. > and now I know what T1 is More like you have a vague idea of what T1 should be, assuming a flat spacetime. My point is that spacetime curvature can already throw this out the window, and that it therefore doesn't seem like we should be taking that estimated departure time as fact. That is: if how an observer is perceiving something is indeed what actually dictates reality, then I don't see how causality can actually exist in the first place, because different observers can perceive the same events in different sequences based on their relative movement. If causality is to exist at all, even under normal conditions, then it seems like it needs to be possible for observers to be wrong, no? So maybe I need to ask this even more specifically: > The issue is that I can find a frame of reference where T2 < T1 Okay, which frame of reference would that be? Under what conditions? By what mechanisms that would apply to literally all cases of superluminal communication (even ones explicitly formulated to avoid things like relativistic relative speeds upon which thought experiments like the tachyonic antitelephone depend)?
  - AnimalMuppet 6y ago

SideburnsOfDoom 6y ago

> How? > this notion that all superluminal travel somehow magically necessitates the possibility of backwards time travel doesn't seem to be logically sound. There is literally decades worth of physics that answers your how, and explains the soundness of it, I would urge you to study the subject in well, any depth at all before naively dismissing it as "unsound". I mean, who's more likely wrong: Physics since Einstein's 1905 papers, or guy on the internet who's been thinking about it for 10 minutes, and has questions with basic misconceptions in them. Asking for answers in the comments is a very poor way to approach a subject like this. All you'll get are quick responses and displays of ignorance.

yellowapple 6y ago
> There is literally decades worth of physics that answers your how And as I've already stated, none of it has been even remotely adequate. If it was, then I wouldn't be asking stupid questions with "basic misconceptions" in them. Maybe I'm too stupid to understand it. > or guy on the internet who's been thinking about it for 10 minutes, and has questions with basic misconceptions in them. Care to actually articulate those misconceptions? Like, I'm under no illusion that I'm correct here. I'm literally a community college dropout. I'm only attempting to find answers to questions I've been asking for years and for which I've yet to find an answer. Instead of an answer, it seems like today I'll be getting downvotes and ad hominem dismissals. Oh well. > Asking for answers in the comments is a very poor way to approach a subject like this. It's called having a discussion, which is quite literally the point of this website. If you don't want to engage in that discussion, then nobody is forcing you to.
- SideburnsOfDoom 6y ago
  Misconception: > because the only way to go back in time is to have a speed greater than infinity > Instead of an answer, it seems like today I'll be getting downvotes and ad hominem dismissals. Oh well. Probably because your approach is very confrontational for someone who claims to be "just asking questions" e.g. "unsound", "not remotely adequate". And then you're dismissive - get directed to a wikipedia page where it's answered, and the mechanics of it are done in mathematics, and: "That doesn't answer the question. ... by what mechanisms?" OK, maybe that approach isn't for you you. Pop science books are a thing, try those instead? I'll add one thing: I'm a software engineer, but if you gave me 1000 lines of Rust to read, all I could say is "I have a very superficial reading of this code based of function and struct names, because I don't really know Rust at all." There's nothing wrong with that: specialised topic is specialised. It's ok to admit you don't know the details. What I would not say is "this program is not an answer, because I don't understand it." That would just be an egocentric misconception. > nobody is forcing you to You're right, if someone is being obnoxious and pointlessly confrontational, they won't get the best from the people who interact with them. No-one is forcing them to do it! But combining that with "oh why am I getting downvoted and dismissed" wailing seems disingenuous though.
  - yellowapple 6y ago
    > because the only way to go back in time is to have a speed greater than infinity And how is that a misconception? That seems to be exactly the thing the "answers" describe: the time it takes to travel from point A to point B being negative, somehow. Even when discussing problems where we've defined that duration to be positive. > Probably because your approach is very confrontational Just because you perceive it to be so doesn't mean it is. Just like, relevantly, how two signals arriving at a reference frame doesn't necessarily indicate the causality of whatever generated those signals. > get directed to a wikipedia page where it's answered It's not answered in said page. If it was then I'd be discussing that answer, rather than continuing to ask for that answer. (Not to mention that just linking some Wikipedia page without any attempt at providing context is itself pretty dismissive, but whatever) Specifically, the "answer" in that page only seems to describe the situation where the signal in its own reference frame is actually travelling faster than c, whereas the very premise of things like warp drives is to, you know, warp spacetime such that the distance covered in that signal's own reference frame is substantially shorter than normal. That is: a tachyonic antitelephone assumes that, you know, the signal exists as tachyons. Citing the concept of a tachyonic antitelephone in the context of a discussion around warping spacetime to shorten the distance entirely (i.e. remove the reliance on tachyons entirely) suggests - to me, at least, with my dumb dropout monkey brain - some implication that any situation where a signal from Point A arrives at Point B (where A and B are, say, 1 lightsecond away) any sooner than 1 second after being sent from Point A necessitates that signal to be treated as tachyonic, no matter what the signal "perceives" in its own reference frame. Thus, my question: why? And if you can't answer that question, then that's perfectly fine! I can't answer that question, either, so it ain't like I'd hold it against you. But if you're going to take the time to dismiss that question as being stupid or misguided or what have you, the least you could do is attempt to explain why it's a stupid question - or, better yet, just answer the question. > Pop science books are a thing, try those instead? Would you care to recommend one? > But combining that with "oh why am I getting downvoted and dismissed" wailing seems disingenuous though. If you actually believed me to be the disingenuous one in this conversation, then why bother continuing to comment? If you don't have anything to contribute, and don't believe I have anything to contribute, then, you could always, you know, leave me to my ignorant wailing :)
Rule35 6y ago
Hey. Uh, this flame war you're having is all you. The rules clearly say not to engage with trolls, not to attempt to fight them to a standstill. That said, I don't think yellowapple is trolling, I this he's saying "that article isn't accessible at my level".

AnimalMuppet 6y ago

It's not a question of which light arrived first. I see light arrive from X at some time T1+t1, I look at how far away I am from X, I do a little math to calculate how long it took the light to get there (t1), I subtract, and now I know what T1 is. Same for T2. The issue isn't when the light arrived. The issue is that I can find a frame of reference where T2 < T1, that is, the actual events occurred in the other order. It's not when the light reached me. The problem is the time of the events themselves.

yellowapple 6y ago
> I see light arrive from X at some time T1+t1 Except that your notion of T1+t1 is already going to be different from any other (non-stationary) observer's, yes? > I do a little math to calculate how long it took the light to get there (t1) Doesn't this assume that light has a fixed speed? We know already that this ain't necessarily the case, even in a vacuum; there are plenty of things - like sufficiently strong gravity wells - that can slow down light considerably. And in the context of situations involving warp drives and wormholes and other things bending spacetime willy-nilly, that further throws a wrench in attempting to figure out how long it took light to reach you. > and now I know what T1 is More like you have a vague idea of what T1 should be, assuming a flat spacetime. My point is that spacetime curvature can already throw this out the window, and that it therefore doesn't seem like we should be taking that estimated departure time as fact. That is: if how an observer is perceiving something is indeed what actually dictates reality, then I don't see how causality can actually exist in the first place, because different observers can perceive the same events in different sequences based on their relative movement. If causality is to exist at all, even under normal conditions, then it seems like it needs to be possible for observers to be wrong, no? So maybe I need to ask this even more specifically: > The issue is that I can find a frame of reference where T2 < T1 Okay, which frame of reference would that be? Under what conditions? By what mechanisms that would apply to literally all cases of superluminal communication (even ones explicitly formulated to avoid things like relativistic relative speeds upon which thought experiments like the tachyonic antitelephone depend)?
- AnimalMuppet 6y ago