One thing I noticed recently after seeing Star Trek IV was that for
the first time in many time travel movies, Kirk actually took someone
into the future with him. This would leave a major question mark in
the classic paradox of time travel, concerning the non-existence "Gillian"
(the whale expert) which Kirk took to the 23rd century. Her family would not
exist. And what about the Phaser and communicator that Chekov left on the
USS Enterprise (The aircraft carrier, not the spaceship)...Surely since he
left those gadgets behind, our society would have gained a technology leap.