Warp Drive May Be More Feasible Than Thought, Scientists Say • Hacker News Board

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#181

Post by Dylan16807 » Sun, Sep 23, 2012, 5:35 AM UTC

nessus42 wrote: post #180

Dylan16807 wrote: post #179

Earlier quoted context omitted.

There are other solutions, too. It might simply be infeasible to accelerate an FTL device to sufficiently relativistic speeds. Or what if there were fields coming off of FTL devices that interfered with the speed when they criss-crossed. That one would stop any sort of loop and it wouldn't require the universe to somehow specifically forbid paradoxes.

FTL devices don't have to "criss-cross" for you to be able to create causal loops. And even if you don't have any causal loops, other violations of causality violate thermodynamics. It's not as if if you've solved the problem of causal loops--which as far as I'm aware, no one has done without postulating a preferred frame of reference, which is basically rejecting Relativity outright--then you're off the hook. All vi…

By 'criss-cross' I mean that your FTL devices in different reference frames need to repeatedly get close enough for causal contact. Is there another way to make a loop using simple FTL devices?

And I might not have been clear enough on acceleration. I meant you might be able to construct a device capable of FTL transport, but it might be far harder to traditionally accelerate this entire device to high speed. The FTL isn't moot, but if your FTL is only 5c and you can't accelerate your turned-off FTL device faster than .1c you're not going to make any loops with it.

In other words, in this scenario, there isn't a preferred frame of reference per-se, but there's no way for such a large and complex construct as an FTL device to get far enough away from the galaxies' default reference frame.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#182

Post by [deleted] » Sun, Sep 23, 2012, 7:47 AM UTC

Dylan16807 wrote: post #181

nessus42 wrote: post #180

Earlier quoted context omitted.

FTL devices don't have to "criss-cross" for you to be able to create causal loops. And even if you don't have any causal loops, other violations of causality violate thermodynamics. It's not as if if you've solved the problem of causal loops--which as far as I'm aware, no one has done without postulating a preferred frame of reference, which is basically rejecting Relativity outright--then you're off the hook. All vi…

By 'criss-cross' I mean that your FTL devices in different reference frames need to repeatedly get close enough for causal contact. Is there another way to make a loop using simple FTL devices? And I might not have been clear enough on acceleration. I meant you might be able to construct a device capable of FTL transport, but it might be far harder to traditionally accelerate this entire device to high speed. The FTL…

[deleted]

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#183

Post by nessus42 » Sun, Sep 23, 2012, 8:45 AM UTC

Dylan16807 wrote: post #181

nessus42 wrote: post #180

Earlier quoted context omitted.

FTL devices don't have to "criss-cross" for you to be able to create causal loops. And even if you don't have any causal loops, other violations of causality violate thermodynamics. It's not as if if you've solved the problem of causal loops--which as far as I'm aware, no one has done without postulating a preferred frame of reference, which is basically rejecting Relativity outright--then you're off the hook. All vi…

By 'criss-cross' I mean that your FTL devices in different reference frames need to repeatedly get close enough for causal contact. Is there another way to make a loop using simple FTL devices? And I might not have been clear enough on acceleration. I meant you might be able to construct a device capable of FTL transport, but it might be far harder to traditionally accelerate this entire device to high speed. The FTL…

You might be able to cook up something, but I doubt that it will be any more plausible than positing a preferred reference frame.

Personally, I think that supporters of FTL should stick with subspace and run with it. And, hey, the author of the FTL faq even wrote a whole subspace faq too.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#184

Post by SolarNet » Mon, Sep 24, 2012, 11:24 PM UTC

lmm wrote: post #176

SolarNet wrote: post #162

Earlier quoted context omitted.

So This may not be an FTL drive, but the way I always sort of pictured it is that the FTL moves you forward in time to the relative observer (so if you move distance x you move (c/x)^-1 forward in time). So if you send an FTL courier (assuming travel time of 2) from point A with times tA=102 tB=51 it would arrive at point B at times tA=52 tB=104 (A time 53 units in the future from tA), if it got sent back it would ar…

So as far as B's concerned, when he sends the FTL courier to A that courier will goes slower than a light-speed message? He could send a message at tB=53,tA=26.5 and it would reach A well before tA=106. This only works if you assume the FTL drive is fixed to some sort of absolute reference frame (which happens to be the same as A's frame). At which point you've given up on relativity, and I'll bet it's possible to co…

I realize how this violates relativity, but I don't understand your counter example (if it was one?) because I wasn't talking about absolute time frames, I'm talking about going forward in time when going FTL. And at no point in my example could B reply before A sends a courier.

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#185

Post by jonmrodriguez » Mon, Sep 24, 2012, 11:28 PM UTC

nessus42 wrote: post #79

jonmrodriguez wrote: post #77

Earlier quoted context omitted.

Since QED and relativity aren't consistent, and QED says that can photons travel at speeds less than and greater than c, isn't it possible that relativity is just probabilistically true but not "enforced" to be true?

Since I don't know anything about QED, I'm not equipped to answer this question. What I can say, however, is that much of what we consider to be "causality" is just a matter of probability. There's nothing in the fundamental laws of physics that says that a flower pot that fell off the window sill and broke into a million pieces an hour ago, can't now suddenly put itself back together and then fly back onto the sill,…

Do you think the big bang has universes on both sides of it?

Re: Warp Drive May Be More Feasible Than Thought, Scientists Say

#186

Post by lmm » Wed, Sep 26, 2012, 11:16 AM UTC

SolarNet wrote: post #184

lmm wrote: post #176

Earlier quoted context omitted.

So as far as B's concerned, when he sends the FTL courier to A that courier will goes slower than a light-speed message? He could send a message at tB=53,tA=26.5 and it would reach A well before tA=106. This only works if you assume the FTL drive is fixed to some sort of absolute reference frame (which happens to be the same as A's frame). At which point you've given up on relativity, and I'll bet it's possible to co…

I realize how this violates relativity, but I don't understand your counter example (if it was one?) because I wasn't talking about absolute time frames, I'm talking about going forward in time when going FTL. And at no point in my example could B reply before A sends a courier.

It's not a counterexample as such, but it seems obviously absurd (and violating relativity) that B's FTL message to A arbitrarily goes a lot slower than A's FTL message to B, given that the situation is completely symmetrical (you can even have them both send their messages at tA=100,tB=100, which is simultaneous from the point of view of an observer C who stayed behind on the asteroid where the two spaceships initially met up).

The point I was trying to make was that your example description makes sense if the FTL drive is somehow fixed to A's reference frame, i.e. A's reference frame is some kind of absolute reference frame and therefore the situation is not symmetrical between A and B. But that introduces its own problems.