[jeffreyH]

That would require infinite speed.

[dutch]

Surely, the fastest anything could get anywhere would be instantly.

The problem with this statement is that different frames of reference disagree on what "now" is.

The Lorentz Transform is:

t' = γ ( t - v x )     (with c = 1 units)

The above equation allows us to transfer from any one inertial reference frame to another (in flat spacetime).

If I let t = 0 then   t' = -γ v x   their "now" t' depends on distance x (as viewed by me) and according to me my "now" does not.

However, in order to keep the speed of light constant in a moving reference frame (relative to you) the slope of the "plane of simultaneity" is - γ v. This means clocks are out of sync in reference frames moving with respect to you. These un-synchronized clocks allows the other frame to measure c for the speed of light in all directions. They don't measure a faster light-speed in one direction and slower in the other because their clocks are out of sync when viewed by me. Likewise, they see my clocks out of sync keeping relativity symmetric.

Reference frames do not agree on what "instantaneous" means. IF all inertial reference frames are truly identical (and they appear to be) then ALL these planes of simultaneity are equally valid.

Depending on what v is, instantaneous messages as viewed by another reference frame can appear to move into the future or the past. ANY faster than light message will appear instantaneous to some reference frame and to other reference frames instantaneous may send messages backwards into the past or forward into the future. The "now" plane is sloped with changing v.

There are three options (regardless of MWI):

1) FTL (even if a solution from GR) is impossible and thus it doesn't matter what occurs FTL.

2) FTL only occurs off of one reference frame thus violating Relativity faster than light. Planes of simultaneity appear real for each reference frame for speeds c or less but to FTL messages only one reference frame (or foliation in GR) is real. This could be right because we've never tested anything moving faster than c. This would require a modification to Relativity FTL.

3) There is no agreed upon cause and effect for FTL. This requires time travel to the past (or future) for FTL

You're thinking the second one is correct because you're looking at the problem in a classical way. However, the second one requires some form of preferred frame and no such thing as ever been found. This would mean one frame's simultaneity would be more "right." The Theory of Relativity does not work this way.

No FTL has been seen. Virtual particles go FTL sometimes in Quantum Field Theory but these don't carry causal efficacy and are born out of the uncertainty principle (they aren't "real" particles and often described as a by-product of how we describe quantum fields). Wormholes and warp drives require exotic matter (we don't know if this exist). Time travel to the past also breaks other laws like the conservation of energy. Having a spaceship appear somewhere in the past from the future changes the energy content of the past frame. Even if a parallel universe breaks off this near twin universe would still have more energy appearing in it's past reference frame. However, General Relativity still has solutions possibly allowing time travel to the past. GR also doesn't globally conserve energy (think expansion of the universe).

[PmbPhy]

1) FTL (even if a solution from GR) is impossible and thus it doesn't matter what occurs FTL.

Nothing in science prevents motion FTL,  nothing. Hence the possible existence of tachyons. Don't confuse the fact that no tardyon can be accelerated from v < c to v = or v > c with a particle being created already moving at v > c.

2) FTL only occurs off of one reference frame thus violating Relativity faster than light.

FTL does not violate FTL and never has.

Then there's the notion that we might discover something in the future which defies known science. In fact any reasonable scientist knows that what we understand of science today will change as it always has in he past. Our laws of physics will be updated when we learn new things. Take NASA's EmDrive as an example. It defies the laws of physics.

https://www.forbes.com/sites/briankoberlein/2016/11/19/nasas-physics-defying-em-drive-passes-peer-review/#435aff4a659d

NASA's Physics-Defying EM Drive Passes Peer Review

The reactionless thruster known as the EM Drive has stirred heated debate over the past few years. If successful it could provide a new and powerful method to take our spacecraft to the stars, but it has faced harsh criticism because the drive seems to violate the most fundamental laws of physics. One of the biggest criticisms has been that the work wasn't submitted for peer review, and until that happens it shouldn't be taken seriously. Well, this week that milestone was reached with a peer-reviewed paper. The EM Drive has officially passed peer review.

It's important to note that passing peer review means that experts have found the methodology of the experiments reasonable. It doesn't guarantee that the results are valid, as we've seen with other peer-reviewed research such as BICEP2. But this milestone shouldn't be downplayed either. With this new paper we now have a clear overview of the experimental setup and its results. This is a big step toward determining whether the effect is real or an odd set of secondary effects. That said, what does the research actually say?
...

Its also fallacious to assert that the physics community discounts FTL altogether. In fact there was an article in Scientific American some years ago entitled Faster than Light?

Experiments in quantum optics show that two distant events can influence each other faster than any signal could have traveled between them

Even recently there's been notions which appear to indicate that some neutrinos are in fact tachyons. This appeared in the highly respectable science journal Nature

http://www.nature.com/news/neutrino-experiment-replicates-faster-than-light-finding-1.9393

Latest data show the subatomic particles continue to break the speed limit.

Physicists have replicated the finding that the subatomic particles called neutrinos seem to travel faster than light. It is a remarkable confirmation of a stunning result, yet most in the field remain skeptical that the ultimate cosmic speed limit has truly been broken.
...

See also:


Superluminal signal velocity by G. Nimtz, Ann. Phys 7 (1998), 7-8, 618-624

Superluminal Tunneling Devices - G¨unter Nimtz, November 2001 -  https://cds.cern.ch/record/547324/files/0204043.pdf

Can EPR-correlations be used for the transmission of superluminal signals? by P. Mittelstaedt, Ann. Phys. 7 (1998). 7-8, 710-715

Faster-than-c signals, special relativity, and causality,Annals Phys. 298 (2002) 167-185
https://arxiv.org/abs/gr-qc/0107091

Abstract - Motivated by the recent attention on superluminal phenomena, we investigate the compatibility between faster-than-c propagation and the fundamental principles of relativity and causality. We first argue that special relativity can easily accommodate -- indeed, does not exclude -- faster-than-c signalling at the kinematical level. As far as causality is concerned, it is impossible to make statements of general validity, without specifying at least some features of the tachyonic propagation. We thus focus on the Scharnhorst effect (faster-than-c photon propagation in the Casimir vacuum), which is perhaps the most plausible candidate for a physically sound realization of these phenomena. We demonstrate that in this case the faster-than-c aspects are ``benign'' and constrained in such a manner as to not automatically lead to causality violations.

Note: Ann. Phys. is the journal Annals of Physics

For those of you out there with a serious and open minded desire to learn about the current research being done at NASA by scientists on FTL travel then you should watch the video of one of their lead scientists discuss it at

https://www.nasa.gov/ames/ocs/2014-summer-series/harold-white

He's the scientist who showed that a modified Alcubierre warp drive could work using much less energy

https://en.wikipedia.org/wiki/Alcubierre_drive

In 2012, physicist Harold White and collaborators announced that modifying the geometry of exotic matter could reduce the mass–energy requirements for a macroscopic space ship from the equivalent of the planet Jupiter to that of the Voyager 1 spacecraft (~700 kg) or less, and stated their intent to perform small-scale experiments in constructing warp fields.[7] White proposed changing the shape of the warp bubble from a sphere to a torus. Furthermore, if the intensity of the space warp can be oscillated over time, the energy required is reduced even more.

End story - Contrary to the assertion made by dutch, there are plenty of serious physicists currently working on both FTL communication and FTL travel and thus dutch's claims that its impossible are his and his alone.

[dutch]

Nothing in science prevents motion FTL,  nothing. Hence the possible existence of tachyons. Don't confuse the fact that no tardyon can be accelerated from v < c to v = or v > c with a particle being created already moving at v > c.

There are three options (regardless of MWI):

FTL does not violate FTL and never has.

What does your sentence mean? Your sentence makes no sense. My sentence was saying Relativity could be violated faster than light. This should obviously be interpreted as the Principles of Relativity could be violated FTL. Could there still be a violation to Relativity outside of what we've tested? YES. My sentence makes sense. I'm sorry, I don't understand your sentence or your point.

Then there's the notion that we might discover something in the future which defies known science. In fact any reasonable scientist knows that what we understand of science today will change as it always has in he past. Our laws of physics will be updated when we learn new things. Take NASA's EmDrive as an example. It defies the laws of physics.

I had stated relativity could be violated faster than light as one of the options... I don't get your point. I did have three very different options. I'm not seeing how the EM Drive relates to anything I wrote.

Even recently there's been notions which appear to indicate that some neutrinos are in fact tachyons. This appeared in the highly respectable science journal Nature

I will reply to your Nov 2011 article with my own Mar 2012 article from the same source:

https://www.nature.com/news/neutrinos-not-faster-than-light-1.10249

It's important to remember to replicate experiments multiple times before daring to say current well-tested laws of physics were violated. In the case of your article it was experimental error and the article is outdated. It's not a recent article. I remember the entire physics community watching the results of the first experiment very closely and I remember when they announced the cause of their error...

See also:

Superluminal signal velocity by G. Nimtz, Ann. Phys 7 (1998), 7-8, 618-624

Superluminal Tunneling Devices - G¨unter Nimtz, November 2001 -  https://cds.cern.ch/record/547324/files/0204043.pdf

Can EPR-correlations be used for the transmission of superluminal signals? by P. Mittelstaedt, Ann. Phys. 7 (1998). 7-8, 710-715

These are old and from the 1990s and very early 2000s. No one has ever sent information faster than light. In the 90s and early 2000s we didn't know as much about entanglement and quantum tunneling as we do now. For quantum tunneling group, and phase velocities of a wavefunction can go faster than the speed of light but the front velocity never has. This means information isn't moving faster than light. This has been described like train cars leaving a long train moving at speed v. If the train cars uncouple fast enough the center of the train could move forward at such a rate that it moves faster than v. However, the front car was still moving at v and never moved faster than v. We always had a probability of detecting the particle at that more forward position at time t. Entanglement also does not send information FTL but is only a correlation. If information was sent faster than light please provide proof of it. Otherwise it's just speculation.

There is no signal (information) moving faster than light in any quantum mechanical experiment and most physicist don't think its possible (No Communication Theorem). The newest source you provided of the above three is about 16 years old...

https://en.wikipedia.org/wiki/Faster-than-light_communication
https://en.wikipedia.org/wiki/No-communication_theorem
https://en.wikipedia.org/wiki/Wightman_axioms#W3_.28local_commutativity_or_microscopic_causality.29

Faster-than-c signals, special relativity, and causality,Annals Phys. 298 (2002) 167-185
https://arxiv.org/abs/gr-qc/0107091
Quote
Abstract - Motivated by the recent attention on superluminal phenomena, we investigate the compatibility between faster-than-c propagation and the fundamental principles of relativity and causality. We first argue that special relativity can easily accommodate -- indeed, does not exclude -- faster-than-c signalling at the kinematical level. As far as causality is concerned, it is impossible to make statements of general validity, without specifying at least some features of the tachyonic propagation. We thus focus on the Scharnhorst effect (faster-than-c photon propagation in the Casimir vacuum), which is perhaps the most plausible candidate for a physically sound realization of these phenomena. We demonstrate that in this case the faster-than-c aspects are ``benign'' and constrained in such a manner as to not automatically lead to causality violations.

This is hypothetical and way beyond anything we could test (also from 2002). The speed of light would increase by 1 part in 10^36 if we put two plates a micrometer apart. A millionth of a meter is tiny distance and even nano meters or femto meters wouldn't be much better. This is tens of orders of magnitude below anything we could measure. Even if this effect is correct how would Jack move to Alpha Centuri FTL? Even if FTL does occur I gave options...

https://en.wikipedia.org/wiki/Scharnhorst_effect

For those of you out there with a serious and open minded desire to learn about the current research being done at NASA by scientists on FTL travel then you should watch the video of one of their lead scientists discuss it at

https://www.nasa.gov/ames/ocs/2014-summer-series/harold-white

He's the scientist who showed that a modified Alcubierre warp drive could work using much less energy

https://en.wikipedia.org/wiki/Alcubierre_drive
Quote
In 2012, physicist Harold White and collaborators announced that modifying the geometry of exotic matter could reduce the mass–energy requirements for a macroscopic space ship from the equivalent of the planet Jupiter to that of the Voyager 1 spacecraft (~700 kg) or less, and stated their intent to perform small-scale experiments in constructing warp fields.[7] White proposed changing the shape of the warp bubble from a sphere to a torus. Furthermore, if the intensity of the space warp can be oscillated over time, the energy required is reduced even more.

Then we'll wait and see if his speculative theories actually do something in the lab. If they actually have positive results then we'll wait for others to replicate the effects... In any case, we'll see which one of my three options occurs.

My options in simple language:

1) We won't see FTL. I don't care about effects that seem FTL. This is information going FTL.

2) We'll see it and Relativity will be violated. This could happen because we haven't tested relativity FTL. We'd have to add/remove postulates to relativity.

3) We'll see it and Relativity won't be violated leading to at the very least a loss of cause → effect for some. MWI may keep links between events and may prevent certain paradoxes but it still doesn't change this.

thus dutch's claims that its impossible are his and his alone

Again... I gave three options and I've given these three options from the start. Please tell me what other option exists?

Also BTW nothing here you wrote was ever new to me in the least. I only took so long to reply because I said I was going to hold my tongue. However, with your inaccuracies I can't. There isn't much use to a forum that let's moderators mislead this much.

[lcrane]

You don't need to travel faster than light to see the past. Everything you see now is past information, just past by differing amounts of time. If magically one could exceed the speed of light and get beyond the 'now' wave front at the instant of your departure and, say, instantly travel to the surface of neptune with a good telescope, and look back at earth, then the info coming in would be past, and you might be able to observe yourself pondering leaving before you left. AFIK such magic is not known, or if 'known', unproven to be of any practical use.

[puppypower]

Many people work under the assumption that space-time has to always remain integrated.

I don't even know what that means if it were true.

Spacetime is merely a mathematical object called a manifold. The elements of this manifold are called events where an event is a place and a time, i.e. (r, t). There has never been any requirement or assumption that space-time has to always remain integrated. Spacetime is often used in relativity merely as a way to describe what happens in nature. The mathematical object we call spacetime has curvature described by Einstein's field equations. There is a correspondence between the mathematical object and what we observe in nature. That's all.

It must be kept in mind that space and time are physically very different things.

All I did was extrapolate the standard manifold of space-time to allow separated space and separate time, both which can act independently of the other. If we act in time but without the restriction of space, we can be anywhere in zero time. This allows for faster than light affects. Since this is only time, it is not a velocity base affect so it does not violate the speed of light. This extrapolation also allows for other types of affects such as integrated large scale systems where light speed becomes limiting in terms of integration over long distances.

A spiral galaxy that is 100,000 light years across acts like an integrated object. Even though the forces may take thousands of years between objects within the galaxy, the galaxy is not subject to endless randomization in shape.  The superstructures of the universe is another application. It is integrated in time, regardless of the huge distances, that should limit its integration using forces limited to light speed. This is governed by time potential and not space-time.

Moving faster than light, using time potential, allows you too see into the future. The objects in the galaxy know where to be, to maintain integration, even before the light speed limited force reaches it. It is where it needs to be ahead of time,  allowing it to greet the late signal. Time potential is not a speed, or t is not d/t.