Rheya isn't even in the book. That's right: Rheya, the woman Kelvin married, died before the book opens, and we hardly get any sense at all of what their relationship was like. The Rheya(s) we see in the novel are projections pulled out of Kelvin's mind. She's not a real person or a real character, then, but a "stylized" representation as Kelvin says, "reduced to certain characteristic expressions, gestures and movements" (5.73). So Rheya isn't Rheya, and we don't know Rheya.
End of analysis, right? Well… not so fast.
The thing about the false Rheya is that it seems like the things the false Rheya does that shows she's false are actually kind of things that make her seem like the real Rheya—or a real Rheya—anyway.
For example, Rheya won't let Kelvin out of her sight. She's super-clingy, and when he locks her in the room by herself, she actually tears through the door to get to him. Is this because Rheya is a weird ocean-generated space critter who Hulks out when Kelvin steps away? Or is it because Rheya—the real Rheya—was unsure of her relationship and didn't want Kelvin to leave her? Either way, as an action, it creates a sort of sense of character around Rheya, even though she's fake and even though we're not entirely sure why she does what she does.
Throughout the book, Rheya keeps hurting herself, or trying to, anyway. This concept of hurt, and of expressing herself physically, come across as very real, as human characteristics. Except that these efforts to hurt herself consistently bring us up against the limits of Rheya's realness.
For instance, she tears through a door and cuts her fingers to the bone… but then regenerates. After she realizes she's not the real Rheya, she drinks liquid oxygen… and horrifyingly regenerates again, waking to stammer in a panic, "It… it didn't work" (9.123). Rheya both has very real desires by human standards, and very unreal limits to these aims. Finally, however, she gets Snow and Sartorius to zap her away.
But even this brings Rheya's realness and artifice careening into each other. Does Rheya kill herself because she's not the real Rheya? Or does she kill herself because that's what the real Rheya did, and as such, does again? Rheya, the real Rheya, killed herself, so when the false Rheya kills herself, too, it arguably makes her more like the real Rheya instead of less.
Finally, the book is filled with conversations between Rheya and Kelvin such as this one:
"Don't talk to me!"
"Rheya, what's the matter?"
I caught a glimpse of her tear-stained face, contorted with emotion. The big childish tears streamed down her face, glistened in the dimple above her chin and fell onto the sheet.
"You don't want me."
"What are you talking about?"
"I heard…" (8.3-9)
Supposedly, Rheya's upset because she's figuring out that she's not the real Rheya. But the conversation seems like it could be a fight between any two lovers; it's almost deliberately generic. Kelvin and Rheya could be having this fight on Earth, really. Maybe they did. Maybe they are. Who's to say? Not us, that's for sure.
The fact that the fight is so generic could mean it's a real fight, between real people, but it could also mean that it's staged—stylized, as Kelvin says—just the motions. The Rheya on the space station clings to Kelvin, she hurts herself, she fights with him. But does this make her the real Rheya? Or does this simply make her Kelvin's memory of Rheya?
The whole novel, really, could be Kelvin running through his grief over and over. He and Rheya fight; Rheya kills herself; Rheya comes back and they fight; Rheya kills herself. It's a nightmare of repetition, and eventually, Kelvin doesn't know which was the real Rheya and which is the memory. Is he in love with Rheya or her image? And do we ever meet Rheya, really, or is it just the image in Kelvin's mind, or in ours? Yeah, over to you, Shmoopers.