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> Start by learning the Lorentz Transform Which specifically describes coordinate transformations between two reference frames in motion relative to one anothe
by yellowapple 6y ago
> Start by learning the Lorentz Transform
Which specifically describes coordinate transformations between two reference frames in motion relative to one another, right? My whole point is that in this context the reference frames are not (significantly) moving relative to one another - that relative movement is exactly what things like wormholes and warp drives are designed specifically to avoid.
So no, that doesn't clear up much at all, unfortunately.
To expand on that, because I still think we're talking past each other here:
> If causality is to exist at all, then 1) causal signals can't travel faster than the speed of light, and 2) neither can an observer.
Okay, which wormholes, warp drives, etc. seem to satisfy:
1. The causal signals - from the reference frames of the signal, sender, and recipient - are all moving such that v is less than c, because spacetime has been warped accordingly
2. In order to observe these signals, the observer would, too, have to be part of that system of warped spacetime (i.e. inside the wormhole, or in the path of our Alcubierre pigeon, or what have you). Otherwise, how would the observer actually see anything?
In any case, thanks for bearing with me here.
- AnimalMuppet 6y agoYes, the Lorentz Transform describes coordinate transforms between two reference frames in motion relative to each other. For the question of why FTL travel blows up causality, that's exactly where you should be looking. You asked how to find a frame of reference where causality was backwards, well, if you learn the Lorentz Transform your questions in that area will be answered. Now, the warp does affect things. We're now playing with general relativity, not just special. You're locally moving at less than light speed. Does that warping also fix causality? I'd want to see that proven, not just assume that it magically does so.
- yellowapple 6y agoI think we're on the same page, then. Or at least close to it. > Does that warping also fix causality? I'd want to see that proven, not just assume that it magically does so. Fair. My impression is that it does fix causality, since the warping eliminates the need to (locally) move at relativistic speeds (and therefore reduces any time dilation to negligibility, and thus the opportunities for retrocausality). So I guess I'm more coming at it from the opposite direction: that if any superluminal communication violates causality (which seems to be a common assertion, both in this thread and elsewhere), then I'd want to see that proven, rather than assume it does so. At most, what I can gather is that it's mathematically possible to construct a warp bubble capable of backwards time travel, just like how it's mathematically possible to construct a wormhole that can do so; when you're mangling spacetime, that obviously opens the door for all sorts of wacky shenanigans. Possibility != certainty, though, and various online discussions (including this one) feature folks who seem to assert that all FTL travel/communication must violate causality, which leaves me wondering why - especially when, to your point, plugging the relevant numbers into the Lorentz transformation doesn't transform anything (no local movement, so v = 0, so the Lorentz factor becomes 1, and vx/c^2 = 0, therefore no time dilation - is that math right?). There's also Hawking's chronology protection conjecture. Yeah, just a conjecture, so it can obviously be disproven at some point, but from what I understand string theory seems to support it (reading the relevant papers is on my TODO list). In any case, thanks again. I don't feel like I'm closer to a definitive answer, but at least I'm left with more to think about.