Quote from: meberbs on 07/21/2017 04:20 pmThe only thing logically impossible is FTL.Never say something is impossible because sooner or later, someone or something comes along and proves you wrong.
The only thing logically impossible is FTL.
The only thing logically impossible is FTL. You seem to claim that the difference between the time ship 1 enters FTL and the time ship1 exits FTL is the same in both frames even though time is flowing differently in both frames (earth frame and ship 2 initial frame). That is illogical. To get from my unprimed frame to yours, just subtract 5 weeks from t and 10 light years from x. To get from my primed frame to yours, add 483 weeks to t' and subtract 13.902 lightyears from x'. As they should, the effect of the results does not depend on the choice of origin.Since you insist, lets use your 2 coordinate systems. The coordinates of the event "ship 1 enters FTL" in the unprimed frame at x = -500 light-weeks (10 light-years), t = -5 weeks(c = 1 light-week per week)t' = 1.4*(-5 - 0.7c*-500/c^2) = 1.4*(-5+0.7*500) = 483x' = 1.4*(-500-0.7*-5) = -695.1 light-weeks = -13.902 light-yearsUnsurprisingly, this result is exactly equivalent to what I calculated before.The switching of past and future is expected, because FTL entrances and exits occur in a space-like interval, not a time-like one. This causes no logical problems as long as you don't have FTL travel.
QuoteAccording to Ship 2 when ship 1 exits FTL, it is still years before ship 1 had entered FTL, no matter where you choose the origin of this frame.is logically and physically impossible. If this is what the Lorentz transformation is telling you, you're doing something wrong.
According to Ship 2 when ship 1 exits FTL, it is still years before ship 1 had entered FTL, no matter where you choose the origin of this frame.
Quote from: meberbs on 07/21/2017 04:20 pmThe only thing logically impossible is FTL. You seem to claim that the difference between the time ship 1 enters FTL and the time ship1 exits FTL is the same in both frames even though time is flowing differently in both frames (earth frame and ship 2 initial frame). That is illogical. To get from my unprimed frame to yours, just subtract 5 weeks from t and 10 light years from x. To get from my primed frame to yours, add 483 weeks to t' and subtract 13.902 lightyears from x'. As they should, the effect of the results does not depend on the choice of origin.Since you insist, lets use your 2 coordinate systems. The coordinates of the event "ship 1 enters FTL" in the unprimed frame at x = -500 light-weeks (10 light-years), t = -5 weeks(c = 1 light-week per week)t' = 1.4*(-5 - 0.7c*-500/c^2) = 1.4*(-5+0.7*500) = 483x' = 1.4*(-500-0.7*-5) = -695.1 light-weeks = -13.902 light-yearsUnsurprisingly, this result is exactly equivalent to what I calculated before.The switching of past and future is expected, because FTL entrances and exits occur in a space-like interval, not a time-like one. This causes no logical problems as long as you don't have FTL travel.Idk, but it seems to me that your math is flawed. The proper length of the trip is the length of the path in the "rest frame" of Earth. If the distance from where ship 1 exited FTL and Earth is 500 light weeks (10 light years) in the rest frame. Then, in the frame of ship 2 passing ship 1 where it exits FTL is t=t'=0, the distance to Earth is then shorter, not longer;L = 10 ly/1.4 = 7.1 ly
If you want to resolve the paradox, you need to make the S and S' systems coincident at the same Event in space-time. The location where ship 1 and ship 2 are at the same place, at the same time is when ship 2 receives the signal from ship 1. This is defined as the origin where the x, t coordinates of ship 1 and ship 2 are the same, where x=x'=t=t'=0. Since t=t'=0, then v*t=v*t'=0.
Now, from this point, the distance to Earth is 7.1 ly in the primed frame. Which is shorter than it is in the unprimed frame. When ship 2 engages FTL toward Earth, it will arrive at Earth in 3.57 weeks, still moving at 0.7c relative to Earth after it exits FTL. The signal will be received by Earth 8.57 weeks AFTER ship 1 left.
There is no reference frame where ship 1 and ship 2 are at the same place, but ship 2 is years in the past of ship 1. Ship 1 moving at FTL did not bring it out of FTL in the past, the FTL warp drive I propose has the clock on the ship 1 ticking at the same rate as the clock back on Earth.
Quote from: WarpTech on 07/21/2017 03:51 pmQuoteAccording to Ship 2 when ship 1 exits FTL, it is still years before ship 1 had entered FTL, no matter where you choose the origin of this frame.is logically and physically impossible. If this is what the Lorentz transformation is telling you, you're doing something wrong.It really really seems illogical doesn't it? But that really is how it works. And as long as you allow no speed faster than light then there are no paradoxes and so while it is weird it isn't illogical.Now you can claim that relativity must be wrong in some way. But first you need to show that you understand what relativity is claiming. From the look of it you don't.
Quote from: ppnl on 07/21/2017 06:22 pmQuote from: WarpTech on 07/21/2017 03:51 pmQuoteAccording to Ship 2 when ship 1 exits FTL, it is still years before ship 1 had entered FTL, no matter where you choose the origin of this frame.is logically and physically impossible. If this is what the Lorentz transformation is telling you, you're doing something wrong.It really really seems illogical doesn't it? But that really is how it works. And as long as you allow no speed faster than light then there are no paradoxes and so while it is weird it isn't illogical.Now you can claim that relativity must be wrong in some way. But first you need to show that you understand what relativity is claiming. From the look of it you don't.Now I understand why @meberbs was confused about ship 2 moving away vs moving toward the earth. In the frame of ship 2, moving away from Earth, at 0.7c, the event of ship 1 leaving Earth and entering FTL is in the future. When it turns around to deliver the message, the primed space-time axis flip to -0.7c, moving toward the Earth. In this frame, the event of ship 1 leaving Earth is in the past.One can think of an FTL signal as being identical to an FTL ship. If ship 2 emits an FTL signal or FTL ship 3 back toward Earth, the space-time axes still flips from v to -v. In the frame of the signal and the event of ship 1 leaving Earth is still in the past. Ship 2, nor the signal it sends to Earth can travel backwards in time.
Quote from: JasonAW3 on 07/21/2017 04:43 pmQuote from: meberbs on 07/21/2017 04:20 pmThe only thing logically impossible is FTL.Never say something is impossible because sooner or later, someone or something comes along and proves you wrong.Rather than say "impossible", a better word is perhaps "undefined" or "apparently paradoxical".In a way, "undefined" is even more damning than "impossible", because people who claim FTL is possible without defining what happens when apparent paradoxes are implimented are making a statement without meaning.On the other hand, unlike "impossible", We can validly say FTL is undefined, and this statement will not be refuted even if in the future it becomes defined. Our statement will remain true in the context it was given, when FTL did not have this definition.
Or maybe it has been defined by some one, but is buried under mountains of knowledge and we just don't realize it yet.
It really does not need to be this confusing. What I am looking for is descriptions of what happens when someone tries to implement one of the paradoxes. How are the apparent paradoxes resolved. What. Actually. Happens.
In General Relativity, the paradoxes due to assuming FTL travel indicates FTL travel won't work. You can't implement the paradox. If FTL is possible, it's new physics requiring new theories to improve on GR. Without new theories, you can't get past the paradoxes.
Quote from: RonM on 07/22/2017 05:22 amIn General Relativity, the paradoxes due to assuming FTL travel indicates FTL travel won't work. You can't implement the paradox. If FTL is possible, it's new physics requiring new theories to improve on GR. Without new theories, you can't get past the paradoxes.Very possibly, but there might be loopholes. I think (just a layman's guess) one possible loophole could be to move your 'stargate' ends so far apart that the expansion of the universe puts them into otherwise causally disconnected parts of the universe. I think the paradoxes would not be implementable in that case.There might be less extreme examples.
Such a method would allow you to achieve the same "apparent" relative velocity w.r.t. the universe as you would via being limited to the speed of light except now you can make the trip there and back, still being alive and having exceeded the light speed limit, and return the same linear age as your relatives when you return.
I think they key to understanding what WarpTech is saying is that locally he his modifying the passage of time and speed of light. Well in a way it is non-locally modifying it. The occupants should be unaware of this change in the speed of light locally.
Quote from: dustinthewind on 07/22/2017 03:22 amI think they key to understanding what WarpTech is saying is that locally he his modifying the passage of time and speed of light. Well in a way it is non-locally modifying it. The occupants should be unaware of this change in the speed of light locally. But that just can't matter. The time dilation, time offset and space contractions aren't some physical effect that is mechanically caused by your motion. It is geometry. You cannot speak of being in your neighbor's house across the road without being across the road. It is nonsense to think that some kind of warp drive will let you visit your neighbor without you being across the road. Warp drive, teleporting or magic poofing just can't matter. It makes no difference.Similarly relativity pretty much defines traveling faster than light as time travel. If you can do it then you can return home before you left. This isn't a mechanical effect of speed or acceleration that you might find some way to prevent. It is an unavoidable property of the geometry of spacetime. Warp drive, teleporting or magic poofing just can't matter.To do it you will have to break and disprove relativity and dump that geometry. Well I'm all for that if it can be done but you first have to understand the problem.
The whole problem of assuming your moving backwards in time is probably because your not eliminating relativistic effects and still assuming your exceeding c. In such a case you can go back in time but takes more than infinite energy and is impossible. Basically inverting time and space so you go back in time. You cant relativistically exceed c.
Regardless of what some think, the vacuum does appear to have associated frames,
Quote from: dustinthewind on 07/22/2017 11:30 pmThe whole problem of assuming your moving backwards in time is probably because your not eliminating relativistic effects and still assuming your exceeding c. In such a case you can go back in time but takes more than infinite energy and is impossible. Basically inverting time and space so you go back in time. You cant relativistically exceed c. It is not turning off relativistic effects for the ship that is required to fix the problem. It is turning off relativistic effects for the entire universe. Since we have observed relativistic effects, this is contradictory.Your post reads as if you haven't read a single post in this thread from any of the people who understand relativity, including the one you quoted.Quote from: dustinthewind on 07/22/2017 11:30 pmRegardless of what some think, the vacuum does appear to have associated frames,regardless of what you think, this statement is false. This has been proven by experiment. And "frame dragging" is not some kind of exception. It does not mean one frame is special, it means that all frames (which are all equally valid) are bent by a rotating massive object.You might want to learn what you are talking about before making statements that both prove your ignorance and make it sound like you think all physicists are idiots. (Because that is what I hear when you claim that the very basis of both special and general relativity is wrong.)
Quote from: KelvinZero on 07/22/2017 07:45 amQuote from: RonM on 07/22/2017 05:22 amIn General Relativity, the paradoxes due to assuming FTL travel indicates FTL travel won't work. You can't implement the paradox. If FTL is possible, it's new physics requiring new theories to improve on GR. Without new theories, you can't get past the paradoxes.Very possibly, but there might be loopholes. I think (just a layman's guess) one possible loophole could be to move your 'stargate' ends so far apart that the expansion of the universe puts them into otherwise causally disconnected parts of the universe. I think the paradoxes would not be implementable in that case.There might be less extreme examples.I have seen serious suggestions that if you created a closed timelike loop using wormholes, some sort of feedback mechanism would cause the wormholes to collapse. Specifically, the wikipedia pageon chonology protection references a book on GR called "Black Holes and Time Warps" which apparently proposes a specific mechanism involving vacuum fluctuations, but this sounds like it would require quantum gravity to truly analyze, which is a theory that doesn't exist yet.