For those that have not seen Sphere, I suggest you watch it before reading beyond this point, because I'm going to ruin the ending. Starting now...
The big idea in Sphere is a twist on the traditional "first contact" story. A ragtag bunch of scientists (and a psychologist played by Hoffman) are brought in secret to an underwater facility by the U.S. military. There they learn that the military has discovered a 300-year-old spacecraft, which they suspect to be alien. It turns out, however, that the craft is neither 300-years-old nor alien; rather, it is of American origin and from the future, having crashlanded in Earth's past after a brush with a black hole. To add to the mystery, the characters discover a strange sphere inside the ship (nobody knows if it's alien or not, and no answers are ever actually given). Eventually we discover that all those who go inside the sphere gain the ability to bring their thoughts to life.
In the concluding scenes (inside a decompression chamber), the surviving members of the team consider the implications of what they've learned. Hoffman's character rightly concludes that humanity is too primitive for the kind of power granted by the sphere, as their nightmarish foray in the underwater facility shows (they all more or less bring their nightmares to life). And so all three characters decide they will use the power to forget what happened, thereby denying humanity access to the information.
What I find compelling about this ending is how it fulfills its own prophecy. Because the ship is from the future, we're drawn to the realization that the choice of the characters to forget means that the mistakes which led them to this realization must always happen. It also means that humanity never actually learns the lesson that these individuals do, making it impossible for any kind of species-centered growth -- there will be no forewarning of the dangers, no future-reversion, in which technology from the future influences the technology of the past, leading us to that future point (yay, a paradox!). But the paradox lies in that problem: if the spacecraft has no record of what the scientists discovered in the past, then something must have happened to prevent that information from reaching the authorities. We're led to believe that this means nobody is meant to survive, but the truth is that the information is destroyed, making certain that nobody knows and that everything proceeds in blindness. Anyone thinking about this problem knows that something must happen or the whole world collapses (which is a problem for Sphere, a serious film, but not really one for Back to the Future, a humorous film).
That idea -- of meeting our future head-on and grappling with its implications, both technologically, socially, and psychologically -- is what SF does best. It doesn't really matter if Sphere is a great movie on its own; what matters is if its ending compels one to think -- and ask the big questions. How do we grapple with technology that makes the "dreams come true" idea a reality? What do we do when we know our own future, and it's immediate ramifications? And is it really possible to forget such power and history? And if you don't forget, does that mean your future changes? Do we fall into one of those weird Back to the Future paradoxes? Would you know if things changed?
And, of course, there's this one: What is the sphere? Where did it come from? Will we ever know?
I'll leave it there for now, because I want to see what others thought about the conclusion of Sphere. How did you interpret the paradoxes and ideas presented in those final moments?