(I've never read the book so I'm basing my interpretaton of the story only on the film adaptation)
(spoilers ahead)

I'm just so overwhelmed by the harmful opinions about this movie. It has been trashed by public, by critics, by almost everyone. Yet when I looked at forums, reviews and comments about "Solaris" it has occured to me that nobody actually made the effort to understand the movie. And it's both a shame and a waste.

Steven Soderbergh made a true, cinematic masterpiece. He captured the very idea of love, the emotion, the feeling itself in carefully composed film frames, in two heartbreaking performances from George Clooney and Natasha NcElhone and with help of Cliff Martinez in heartbreaking, stunnigly beautiful music.

Chris Kelvin lost his wife. He's in grief. It was his fault and now it's too late. Few years later he's being called to arrive on spaceship inspecting mysterious planet - Solaris. Shortly after that event, his dead wife...reappears.

It is so simple to understand that movie, the only thing you have to do is to open your heart and carefully observe. We see all the events from Chris's point of view, except for one short scene concerning Rheya.

Chris sees Rheya in train. She has door knob in her hands. She looks at him, she gets off the train, she smiles.
Shortly after that Chris arrives at his friends party. He circles the room and Rheya is there. She notices him (the look in McElhone eyes when she recognizes him is one of the film's most memorable aspects). They talk. "Don't blow it" she says.
They leave the party together. They're in elevator. Finally they grab each other hands.

Those scenes present so simply, so delicately the love between them. Those are one of the rare moments in the movie when those two are actually happy. They've been lost, they've been alone for so long. And now They have found each other.
Chris asks Rheya to marry him, she agrees. And then, or maybe even before that things got worse.

First clue to how understand the movie and probably the most important one is the conversation Rheya and Chris have at his friend's dinner. Chris is not religious man, he thinks the concept of God is ridicilous. Rheya on the other hand strongly believes that there is some sort of higher intelligence somewhere out there. She's trying to prove that by saying that 'people are the only creatures in the world which are aware of their mortality'. Chris ignores her, she leaves.

The second clue, but this time to understand Rheya's character, is another conversation they have. Rheya is talking about her complicated relationship with her insane mother. Insanity. Disequilibrium. Confusion.

Those are exactly the feelings Rheya has when she finds out she's pregnant. She terminates the pregnancy and she tells Chris about it. He doesn't understand, he's not trying to. He leaves her. She shouts she cannot live without him. He leaves anyways.

She kills herself. She's wearing red dress, which will be important later on.Chris comes back minutes later. He finds her dead body. He knows it's all his fault. She has a page with their favourite poem in her clenched fist:

"And death shall have no dominion.
Dead men naked
they shall be one with the man in the wind
and the west moon.
When their bones are picked clean
and the clean bones gone
they shall have stars at elbow and foot.
Though they go mad they shall be sane.
Though they sink through the sea they shall rise again.
Though lovers be lost love shall not.
And death shall have no dominion."

That one moment when he left lead her to end her life and for him, to live, but in sadness, in emptiness. It wasn't fair. It wasn't fair to lose someone close to him in such a way.

And then he gets on the spaceship. I'm gonna avoid mentioning secondary characters and all of that, it's not relevant to the main story in any way.

Rheya appears. He knows she's not real, she's fake. He locks her up in the capsule and he sends her in infinate space. The moment he does that he regrets his actions. He hopes HE HOPES she will come back. And she does.

Rheya on the ship is the perfect and faithful projection of Chris' memories about her. He remembers her silence, she's silent. He remembers her crying - she cries. He remembers making love to her - they make love. finally he remembers she's suicidal. She kills herself. And he has to witness that again.

But the projection of Rheya can't die. She is resurrected by Solaris.

Chris is willing to stay there with her. Rheya is growing more concious of what she is. She wants him to go home. He says he want to stay with her, that they can have life there, that is all he needs. "You are all I see..." (Brilliantly showed by Soderbergh when Chris is close to death himself and all he can see is Rheya in various points of her life, when he saw her in train, when he asked her to marry him, when she was at his home)

Rheya cannot live like that. She remembers things Chris remembers + the moments leading to her suicide. She decides to die once and for all.

After her death Chris is moments away from leaving Solaris. He can't do it. He wanders in ship shouting for Rheya, wanting her to come back again. The ships is about to get destroyed. One of Solaris other projections, little boy is reaching his hand toward Chris. He grabs it. He dies and he belongs to Solaris now.

He's not aware of it at first.
He thinks he's on earth, in his apartment. Suddenly he accidently cuts his finger with knife (similiar scene was in the beginning of the film). He notices that the cut is healing itself (just as Rheya was able to resurrect herself).

He closes his eyes, he hears her voice. Rheya is wearing blue dress now, not the red one, that she had on when she died. Chris asks her wheter he's alive or dead, she say's all it's forgiven and they don't have to think like that anymore. They embrace and now they can live forever, after death, in Solaris. Happy at last.

So in my theory Solaris is the higher intelligence Rheya was talking about. It has ability to project our dreams, even after we die. If we handle grief, sandess, negativity we can have perfect life there.

Why do I think it's really Solaris? Earlier in the movie Rheya says Chris's apartment was devoided of photos. In the ending scene, there is a picture of Rheya on the fridge. It is her reality now since she died before Chris did. And also the very last shot in the film is the one of Solaris in distance.

The cinematography and music in this film are just drop-dead-gorgeous. The solaris ocean is photographed with such intensity and mystery it is just breathtaking. Natasha McElhone is terrific, watchful Rheya and Clooney gives first truly fantastic performance in his career (second one being Michael Clayton with performance so strong and mindblowing I still can't find words accurate enought to describe it).

This is one of the most beautiful love stories and most hopeful movies I've seen.