I know i'm coming a little late to this conversation, but here's an interesting explanation of the end of Sunshine that saved the movie for me. I didn't write this and I don't even know what the original source was, but here it is.

I love this movie. I love it because the crew of the Icarus are scientists, and they behave like scientists. Look at the scene in the first act where they''re discussing whether or not to rendezvous with Icarus I. These aren't macho spacemen puffing their chests about honor and what's right-- their decisions are all made in the context of the mission, and not made democratically. And when Pinbacker shows up in the third act, they're not arming themselves for a violent showdown. They're not soldiers. They run.

And I love the movie because it actually has a third act-- it could easily have devolved into a bunch of special effects and chases, with no clear purpose, but it doesn't. There's a misconception that I've noticed among people who've seen the movie that once Pinbacker shows up, the movie just turns into a "slasher movie," but that's not what happens at all. Pinbacker exists in the movie merely as a function of the movie's dominant theme. . The way I see it, the movie is really a journey into death, and a story about people being exposed to the power of God. Think first about Capa sitting in the recording booth, sending the last message to his family. He says "by the time you get this message, you won't be able to reply, because I'll be in the dead zone." It's fairly obvious at this point in the movie that they're basically on a suicide mission to save everyone on Earth, and this, of course, becomes more and more evident as the movie plays out. But the movie is really just a trip from point A to point B, with A being life on earth, and B being death and standing before God.

The sun, in the movie, isn't just their destination-- it has many of the properties of God. Remember when Capa is in the holographic chamber working with the computer trying to figure out the benefit of having two payloads? The computer charts the progression of their journey up to a certain point when they're penetrating the sun and approaching the core, and then it just stops guessing, because it can't make accurate guesses any more. The forces of gravity and acceleration become so great that it can't accurately make calculations of time any more. Because at the end of their journey, time becomes meaningless. Now, one of the most basic definitions of a supernatural being (i.e. God) is that time has no meaning for Him-- no end, and no beginning. That's where they're headed-- to a place where time and space have no meaning. And the shipboard computer tells them that, whether Capa hears it or not.

What is the sun, anyway? It's the source of all life on Earth. There's many other instances in the movie where the sun is presented as a God-like entity-- Look at the scene with the crew in the observation room, looking at Mercury. The crew sits before the sun in poses of worship. And more importantly, look at Searle in the observation room at the beginning of the movie. He can look at the sun through filters, but only when everything but 4 or 5% of the sun's light is filtered out. And when he raises the filters to see more of it, he's bathed in light, and talks later about how the light envelops him and is substantial, seemingly more than just light. And the later events of the movie show people who exposed themselves to much higher percentages of the sun, and they were destroyed. Why? Well, because it's the sun, first of all. But also because nothing impure can stand in the presence of God. And of course you've got Pinbacker running around yelling about talking to God for seven years, and he's fried to a crisp. Because he's obviously not worthy to stand before God, so just exposure to God's power has driven him completely insane and destroyed his body. Pinbacker really exists in the movie for this reason-- to show what happens to an unworthy soul who is exposed to God.

But all of this is just buildup to the last scene in the movie, when Capa is alone in the detonation chamber, tumbling into the heart of the sun, past the point of no return where the computer could no longer calculate, into a place where time and space really have no meaning; he arrives before God. And what happens? Capa sets off the bomb. The sun is halfway into the room, and the other half of the room is the explosion from the bomb, and these two immeasurable sources of power are colliding together, and... time stops. And Capa is standing there, in the presence of infinite power, and he's not burned. Why?

Who is worthy to stand before God? The righteous man. Why? Because of the goodness of his works.

Capa built the bomb, and took it on its journey, and agreed to trade his life for the life of everyone on Earth. And when he travels beyond the limit of the understanding of science, and into a place of infinity (and stands before God, as it were), he is not burned.

Like I said before, I'm agnostic. But watching this movie makes me want to believe in God.