All right, I'll grant you that some of the science in "Doppelganger" (or "Journey To The Far Side Of The Sun") is kind of dopey.The idea of an entire planet existing undetected (because we can't see it on the other side of our sun) doesn't hold up at all - any Astronomy 101 student knows that another planet the size of Earth would cause gravitational perturbances in the motions of other planets. That's how astronomers deduced the existence of Pluto, after all, and that's how they find comets and asteroids and moons on a regular basis.<br /><br />And the idea that a mirror image Earth somehow evolved in almost perfect parallel to our Earth, down to English speaking scientists and human counterparts for each human born on our Earth...that takes things out of 'hard science' fiction and into "Twilight Zone" territory. That's not necessarily a bad thing, but it requires a major suspension of critical thinking to accept and enjoy. <br /><br />But man, this movie knocked my socks off as an adolescent. I was still used to fairly cheerful, upbeat science fiction films when the hero won through in the end - even "2001" could be interpreted as having an 'upbeat' ending. <br /><br />But in this case: Thinnes attempted to dock with his orbiting mothership so he could return to his own Earth, only to be bounced back out of his docking berth (Something about 'the polarities not being reversed because his 'doppelganger' wasn't doing the same thing. Apparently Thinnes' 'doppelganger' had decided he was happy in his new home.) Thinnes' ship started the descent back to the CounterEarth launch site, and I was certain that he would somehow get the damaged craft to land safely and try again, armed with the new info that would let him and his backers succeed. He was The Hero after all, and the Hero always wins through in the end. <br /><br />Instead, Thinnes couldn't maintain control of the crippled craft, and the ship's subsequent crash into the launch site was so horrible and devastating that it killed everyone (except for the chief project leader) and destroyed all records of the project and Thinnes' existence. Thinnes never got to go home, and he perished uselessly, his secrets never revealed. <br /><br />Except for the Planet Of the Apes series, I had never seen such a sad and downbeat ending, and it always stuck in my mind - especially the ferocious devastation of the crash scene near the beginning of the move (you knew that spaceship was NEVER going to fly again!) and the one at the very end. <br /><br />I'd love to see this movie again, and see how well it held up over the years.