I laugh when scientists based on theories of things they can't test say something is "impossible". They have been proven wrong over and over again.
Britain's minister of science at the turn of the last century (thereabouts anyway) said "spaceflight was impossible". Reason why? The physicists of the day had calculated how much fuel would be needed to reach the moon and established that the engine and fuels tanks alone would have to be so large that you could never carry enough fuel to get the ship free of earth's gravitational pull.
Based on some of Goddard's pioneering, Werner Von Braun came along and said, "Then let's break the spaceship into pieces and drop off the empty fuel tanks as we go." Relayy simple idea--took almost a century for anyone to think opf it.
Ironically, Jule's Verne's story From Earth to the Moon was what polarized public interest into space flight and it was dissecting his device of firing an artillery shell spaceship to the moon that was the basis for the royal academy's proclamation.
Sceince fiction writers have consistently theorized things long before scientests could accept they would be possible--ever.
The primary scientific rejection of man ever finding a possible way to exceed light speed travel is that causality would violated in this universe and then you get into mutiple universe theory and it is just scientifically not 'politically correct" at the moment.
So time travel as stated by mainstream scientists is at present "impossible"...until someone comes along and thinks of how to break the spaceship into pieces.
To accomplish ftl travel, one will also be accomplishing time travel and that's why its such a hotly attacked subject in the scientific community.
I look at the history of science fiction and how often it has hit the nail on the head far before science and when I think of that and "impossible", I am always reminded of a statement written by pre-iron age Hebrews thousands of years ago:
Genisis 11:6b
Quote:And this is what they began to do, and now nothing which they purpose to do will be impossible for them.