First of all, I am fairly new to relativity, but not clueless. I am not saying that FTL is possible. I am not denying relativity principles. I am stating that FTL may be plausible. Relativity gives flexibility to how you can synchronize clocks and that does not affect outcomes of most equations and measurements. However, I believe that there are two ways to understand Maximum/Unlimited "faster than light speed" with causality and simultaneity in mind, which depends on which "synchronization method" will be used. For the sake of clarity, I will not involve moving objects, so all speeds and distances will involve distances and times between objects that don't move wrt themselves. If we were to look at a distant (or any) object, we will be receiving a delayed image of it. Arbitrary clock synchronization methods would allow us to perceive that the delayed image is in fact a target of our maximum velocity (that is FTL) so that sending something at maximum velocity to "now" at that location would be traveling to impose that something over that received image at t+1 observer's time. In that case, indeed FTL would mean that we would go back in time at which we could send signals to the past of what we consider the "present". Basically if we consider Einstein's definition of spacetime (where no observers agree on simultaneity of events and where definition of simultaneity is somewhere arbitrary, to become a definition of the universe) we determine maximum speed to be distance traveled (constant) over time the trip took time (~0) and allow the time at target to be anywhere in the range of 2t length of a time period - where t is defined to be the half of the time it takes for light to go from source to target and come back. If we were to define "present" to be a time that is synchronized per Einstein's synchronization, then FTL shouldn't necessarily imply paradoxes. If we define that present to be t0 at A = t0 at B where t0 is the clock reading on Einstein's synchronized clocks then the "maximum speed" would be defined as v=dt where d is the distance between the objects, t is the time it takes for the event to travel (~0) but the target's time at the arrival of the superluminal event is actually defined! Even in this case FTL does lead to some bizarre things, but I believe none lead to "traveling to the past". For example, if some observers were to observe a near-instantaneous superluminal travel from earth to Centauri: - On earth: An observer would observe the maximum-velocity superluminal traveller just leave earth and continue to approach Centauri over a course of 4 years. - On Centauri: An observer would see the traveller appear instantly before them, but there would appear to be three copies of the traveller: 1) One that is the image of him at "now" living his normal life on Centauri. 2) Another with him traveling BACK to Earth, that the observer would observe over a period of 4 years. 3) Another with him drinking his coffee on earth or whatever during a course of 4 years with the final event of that image joining #2 at his apparent time of takeoff from earth. - On a space station forming a 4-ly equilateral triangle with Centauri and earth: An observer would not actually see anything interesting until about midway through the 4th year. Most of the time he would see the traveler living his normal life on Earth. Starting mid-4th year, he would see additional two images of the traveler splitting from the mid-point between Centauri and Earth. One image would be approaching earth and another Centauri. The "show" would end at the end of the 4th year with near-simultaneous launch of the travel from Eaarh and arrival on Centauri, at which point both split-images would join up with the events. I don't see any logical issues with the thought experiment here besides bizzareness of the events. If we "replace" the traveler with "superluminal message" or even "a conversation", I still don't see any logical flaws that produce causality problems. Can someone help iron this out?