Accelerative Relativity in True Zero Gravity
Einstein theory must allow the modelling of a limited theoretical probability of travel back into time (but never forward) as the logical conclusion of exceeding light speed. It is a necessary allowance within such an analytical framework as a concession to the question "what if" it were possible to travel faster than light. This necessary concession exposes the great weakness in Einstein theory which is that all the relative transformations are considered as applying only to the factor M in the equation F=MA. Any concession that relative transformations may also apply to the factor A, would instantly permit the theoretical possibility of faster-than-light travel. Modelling of possible relativistic transformations on A is extremely difficult since there is no easy way to yet generate a significant A (acceleration) on the human body once it is floating in space. Current thrust technology (chemical based) does not generate significant acceleration force on any orbital. A craft remaining within our solar system is also still subject to a not insignificant gravitational force of the sun (which is why our solar system remains an ordered system).
However if travel to another star were attempted, the vast majority of the distance travelled is within this minimalist gravitational zone (that is between two stars outside of their orbiting planet rings). Relativistic transformations on the A factor in F=MA will necessarily concern the contrasting nature of pull acceleration (any natural gravitational force) with any push acceleration (as an artificial gravity is generated). When there is minimal pull (in the minimalist gravitational zone between stars) the Einstein theory will cease to apply with any significant effect. That is to say the factor A in F=MA when consisting of the most minimal pull A and the maximum push A (say a 50G rocket powered acceleration) will negate factor M transformation to the point of near insignificance.
Accelerative Relativity in True Zero Gravity continued
Furthermore the relative values of transformation on push A should be subject to limit in itself to the universal value of the standard pull acceleration as we know it. This is to say absolutely confined to an upper limit of artificial gravity simulation of no more than 1 earth gravity. This derives from the fact that since we know of no life that exists outside of the range of 1G (our earth gravity) there is therefore no proof contrary to a good assumption that this is in fact a universal fixed value. That would mean a spacecraft occupied by humans once in the minimalist gravitational zone between the stars (the vast majority of the distance needing covered to make star travel possible) could travel at say 50G but be only experienced as a comfortable fixed value of 1G by occupants.
With M transformation being negated by the above relativity to the point of near insignificance, speeds in many multiple factors of light speed would be possible with a minimal loss of efficiency in energy force (F) conversion to the acceleration and de-acceleration of the spacecraft. This would allow spacecraft to travel between star systems in a matter of minutes provided enough force is generated to accelerate and de-accelerate.