When, a long, long time later, he stares down at the silent blue marble of the earth and thinks of his sister, as he will at every important moment of his life. He doesn't know this yet, but he senses it deep down in his core. So much will happen, he thinks, that I would want to tell you.

This passage from Chapter Twelve very briefly flashes forward to Nathan’s future, when he has realized his dream of traveling in space. This scene inverts the moment before Lydia’s death, when she stares up at the stars. While she thought of nothing, Nathan thinks of her, as he does all his life. This is a key distinction between the siblings: the preferential treatment Lydia receives makes her selfish, a trait her early death prevents her from changing. As Nathan grieves her loss, however, he develops forgiveness, becoming an increasingly kind person.  Unlike his parents or Lydia, Nathan realizes the goals he sets for himself, perhaps because he can share his thoughts, feelings, and observations. In a novel in which characters often do not share, Nathan’s longing to have been able to “tell” Lydia things is an achievement.

Hannah, as if she understood her place in the cosmos, grew from quiet infant to watchful child: a child fond of nooks and corners, who curled up in closets, behind sofas, under dangling tablecloths, staying out of sight as well as out of mind, to ensure the terrain of the family did not change.

This passage, from the novel’s seventh chapter, demonstrates how the theme of space contributes to the development of the characters. The family is defined as a “cosmos,” but even as a young child Hannah understands that she has no real place in a space that should be vast. Folding onto herself, she tries to be as unobtrusive as possible. Despite the regularity with which she is ignored and overlooked, Hannah wants the family dynamics to remain as they are, a sign that even a child can grasp how fragile everything is. Finally, this passage demonstrates how the theme of space can represent both the family’s universe and each character’s literal place, the space they occupy, in the home.

Tipping her head back, she could not see the houses or the lake or the lamps on the street. All she could see was the sky, so huge and dark it could crush her. It was like being on another planet. No—like floating in space, alone. … This is what infinity looks like, she thought. Their clarity overwhelmed her, like pinpricks at her heart.

After Lydia rows to the middle of the lake in Chapter Eleven, she pauses and stares up at the night sky. Its immensity overwhelms Lydia, making her feel tiny and fragile. In this sublime moment, she enjoys the feeling of solitude. Floating, no longer being forced to fulfill the desires and disappointments of others, Lydia reaches a moment of painful clarify, in which other possibilities for her life become clear. Even though she tries to compare the stars to the posters that Nathan has in his room, they resist easy comprehension. The pleasure of floating that she gets from the sky is part of her decision to float in the water, a choice she makes in a moment of sublime excess. Rather than being at the center of a small cosmos, Lydia embraces the option, fatal as it turns out, to be lost in the world’s infinity.