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A new model for faster-than-light travel that uses conventional physics

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Re: A new model for faster-than-light travel that uses conventional physics

#151

Post by yellowapple »

bitdizzy wrote: post #148
yellowapple wrote: post #144

Earlier quoted context omitted.

> The wikipedia page has a worked out example. If you can go back and forth between 2 places FTL you can arrive before you left and interfere with your departure. That example has multiple assumptions that seem to make said example only relevant to a very specific case, rather than to superluminal communication in general (least of all to approaches specifically designed to avoid those assumptions): 1. Alice and Bob…

The name tachyonic antitelephone is a bit unfortunate because it need not involve tachyons. All it takes is the ability to send a message outside of your light cone. Along the path actually taken need not be the case, we are reasoning about the endpoints of the communication independent of the means. In particular it does not matter whether you use a warp drive or not. The violation occurs relative to reference frame…

So first, I'd like to say thanks for bearing with me here. I know it's probably frustrating when someone you're talking to just... ain't... getting... it...

...which is why I hate to say that I still ain't getting it, lol

> Along the path actually taken need not be the case, we are reasoning about the endpoints of the communication independent of the means.

So the means doesn't matter at all? It doesn't matter that as far as the endpoints are concerned they're at a fixed distance from one another? That seems hard to believe - not to mention contrary with the math presented in that antitelephone article, which seems to make a big and explicit deal about the relative movement between the two endpoints.

Even when factoring outside observers...

> The violation occurs relative to reference frames outside of the warp bubble where special relativity fully applies.

...how would this apply if the information in question is constrained to that warp bubble between its transmission and receipt? What would there be to observe? If we're talking about side effects of that communication (say, our Alcubierre messenger pigeon drops a feather back into "normal" space somehow), would the propagation of those side effects not just revert back to being subluminal? That is: from every local perspective, the pigeon is traveling subluminally, so this should still apply in the event the pigeon or any signal from it escapes its bubble and reenters "normal" spacetime, no?

> Here, explicitly looks like a worked out example: http://exvacuo.free.fr/div/Sciences/Dossiers/Time/A%20E%20Ev...

Thanks, this is useful.

...unfortunately, I don't know if it's really agreeing with you. Or me, for that matter.

Namely, it seems to admit that the metric as Alcubierre describes[1] would not produce a closed timelike curve; the paper instead describes ways to produce custom metrics separate from Alcubierre's which introduce the possibility of CTCs, in which case it seems like the answer would simply be to... just not do that, right? Indeed, the paper speculates that there might be other mechanisms that would prevent such a metric from being constructed (specifically naming Hawking's chronology protection conjecture).

That is:

> But the ability to perform such FTL tricks implies the possibility of constructing a closed timelike curve so long as you're talking about a localized phenomenon like a warp drive or tachyon where special relativity holds outside of a negligible area.

Only, from what I can gather, if these equations are indeed the only ones at play, which even that paper admits might not be the case.

----

[1]: https://arxiv.org/pdf/gr-qc/0009013v1.pdf

Re: A new model for faster-than-light travel that uses conventional physics

#152

Post by Doxin »

vanderZwan wrote: post #124

> To put this into context, we’ll catch you up to (warp) speed. The colloquial term “warp drive” comes from science fiction, most famously Star Trek. The Federation’s FTL warp drive works by colliding matter and antimatter and converting the explosive energy to propulsion. Star Trek suggests this extraordinary power alone pushes the ship at FTL speeds. I'm surprised that so far nobody here has complained that they go…

As far as I've gleamed from watching star trek the "warp core" is really just a power plant. It's the nacelles doing the propelling.

Re: A new model for faster-than-light travel that uses conventional physics

#153

Post by vanderZwan »

Doxin wrote: post #152
vanderZwan wrote: post #124

> To put this into context, we’ll catch you up to (warp) speed. The colloquial term “warp drive” comes from science fiction, most famously Star Trek. The Federation’s FTL warp drive works by colliding matter and antimatter and converting the explosive energy to propulsion. Star Trek suggests this extraordinary power alone pushes the ship at FTL speeds. I'm surprised that so far nobody here has complained that they go…

As far as I've gleamed from watching star trek the "warp core" is really just a power plant. It's the nacelles doing the propelling.

Yeah but doesn't the warp core also require "dilithium crystals" to run?

But still, fair point: that does suggest "warp core" is a bit of a misnomer. Then again, we all know the difficulty of naming things properly ;)

Re: A new model for faster-than-light travel that uses conventional physics

#154

Post by bitdizzy »

yellowapple wrote: post #151
bitdizzy wrote: post #148

Earlier quoted context omitted.

The name tachyonic antitelephone is a bit unfortunate because it need not involve tachyons. All it takes is the ability to send a message outside of your light cone. Along the path actually taken need not be the case, we are reasoning about the endpoints of the communication independent of the means. In particular it does not matter whether you use a warp drive or not. The violation occurs relative to reference frame…

So first, I'd like to say thanks for bearing with me here. I know it's probably frustrating when someone you're talking to just... ain't... getting... it... ...which is why I hate to say that I still ain't getting it, lol > Along the path actually taken need not be the case, we are reasoning about the endpoints of the communication independent of the means. So the means doesn't matter at all? It doesn't matter that a…

So the thing that paper does is it assumes you can make warp bubbles in any reference frame. The original paper makes one warp bubble and this doesn't lead to anything paradoxical.

But if I can make two warp bubbles in two different frames, I can make a round trip that arrives before it starts.

So you need to violate special relativity in a global way to avoid these issues. You have to have a spacetime where only certain warp geometries are possible.

I apologize for being a bit impatient before, these issues are subtle. The only real way to get it is to bear with the math onesself.

Re: A new model for faster-than-light travel that uses conventional physics

#155

Post by r-zip »

alex_young wrote: post #116

I really don’t understand why people are so hung up on the clocks back home. I mean, sure it would be nice to take a trip to Alpha Centauri, come back home, and boast about it to all of your friends, but really wouldn’t getting to see a few tens of thousands of years go by be even cooler? To the constantly accelerating interstellar traveler distances get really small after a year or so. You’d be able to make it to th…

Because by leaving on that journey you would be effectively dead to everyone you knew?

Re: A new model for faster-than-light travel that uses conventional physics

#156

Post by AnimalMuppet »

yellowapple wrote: post #147
AnimalMuppet wrote: post #146

Earlier quoted context omitted.

> > 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? Yes, and so is my distance from my current position to X, which I use to calculate my value of t1, which I use to calculate my value of T1. All the numbers are different for all the observers. Special relativity tells us how to convert the numbers betwee…

> 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 c…

Yes, 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.

Re: A new model for faster-than-light travel that uses conventional physics

#157

Post by ConceptJunkie »

GuB-42 wrote: post #68
papaf wrote: post #16

Earlier quoted context omitted.

My feeling is that interstellar travel will be slow and require many generations of travelers -- or not done by human beings at all.

Interstellar travel doesn't have to be slow for the travellers. You could get to Alpha Centauri and back to Earth in a day (at least as far as relativity is concerned), but for those who stayed on Earth, a decade would have passed. That's the twin paradox btw.

At 1g constant acceleration, you could reach the center of the galaxy in your lifetime (~50 years). Everyone else... not so much.

Re: A new model for faster-than-light travel that uses conventional physics

#158

Post by yellowapple »

SideburnsOfDoom wrote: post #150
yellowapple wrote: post #143

Earlier quoted context omitted.

> 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…

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 hair…

Welp, looks like this turned sour again. Whoops! But hey, I tried, I guess.

> Can recommend again that you turn to books on this subject

Got any recommendations? In fact, I asked you this already, the last time you dickishly suggested I go read books (as if I haven't done that already).

> This sentence is pure gibberish

Then go read Alcubierre's paper[1]. Expanding spacetime on one side of an object and contracting it on another is exactly what's being described. Maybe "without acceleration in the local frame of reference" rather than "without movement" makes more sense to you?

> The math checks out? What math?

[0]: https://arxiv.org/abs/gr-qc/0009013

Oh, or this one from NASA, which even includes pretty slides that your galaxy brain can understand: https://ntrs.nasa.gov/api/citations/20110015936/downloads/20...

Now, I tried to be civil, and even went so far as to recognize when I stopped being civil, apologized for it, and tried again. Yet you still insist on being an asshole about it. Well guess what:

> There's no math here, just waffle.

Yep, "just waffle" is all you've contributed to this discussion, and by the looks of it all you intended to contribute. Gotta flex your intellectual superiority, right? Too bad you're - like me - just another guy on the Internet, so any such superiority you think you might have is illusory, at best.

> and I don't mind being a Jerk now

You clearly didn't mind being a jerk from the get-go. Probably because that's all you can contribute, but here I was hoping that maybe you'd contribute something else.

Oh well. Have a good one, I guess. Maybe next time we run into each other it'll be on more civil terms.

Re: A new model for faster-than-light travel that uses conventional physics

#159

Post by yellowapple »

AnimalMuppet wrote: post #156
yellowapple wrote: post #147

Earlier quoted context omitted.

> 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 c…

Yes, 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'r…

I 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.

Re: A new model for faster-than-light travel that uses conventional physics

#160

Post by yellowapple »

bitdizzy wrote: post #154
yellowapple wrote: post #151

Earlier quoted context omitted.

So first, I'd like to say thanks for bearing with me here. I know it's probably frustrating when someone you're talking to just... ain't... getting... it... ...which is why I hate to say that I still ain't getting it, lol > Along the path actually taken need not be the case, we are reasoning about the endpoints of the communication independent of the means. So the means doesn't matter at all? It doesn't matter that a…

So the thing that paper does is it assumes you can make warp bubbles in any reference frame. The original paper makes one warp bubble and this doesn't lead to anything paradoxical. But if I can make two warp bubbles in two different frames, I can make a round trip that arrives before it starts. So you need to violate special relativity in a global way to avoid these issues. You have to have a spacetime where only cer…

> I apologize for being a bit impatient before, these issues are subtle.

No worries, and thanks again :)

> But if I can make two warp bubbles in two different frames, I can make a round trip that arrives before it starts.

Even for the metric as Alcubierre describes? Or for one that's modified per Everett? Now that I'm rereading the Everett paper, I'm not really sure where he's getting his "Lorentz boost"; if there's technically no actual "motion" (because everything's locally at rest and the warp bubble is outright expanding/contracting space around it), then I'm having a hard time figuring out what there would be to "boost", since the relevant Lorentz transformations should be no-ops if everything's locally at rest. Is Everett moving the ship itself at relativistic speeds within the bubble? Is an observer moving at relativistic speeds outside the bubble?

> So you need to violate special relativity in a global way to avoid these issues.

Which the universe kinda already does, no? The mechanism here (from what I understand) is the same as the one driving universal expansion (the difference being that there's no corresponding contraction in the universal case - right?). If that expansion were to be reversed somehow, would that, too, result in causality violations?

And further, doesn't special relativity already only hold in cases with low gravitational potential - so i.e. not in a gravitational field?

Sorry if these are kinda dumb questions.

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