Pendulum (Symbol)
In the video game Three Body, both the first and last civilizations Wang Miao visits (Civilization 137 and Civilization 192) feature pendulums. A pendulum's symbolic associations are fairly obvious: It's a piece of technology that measures time (among other things, historically, including the acceleration of gravity). In The Three Body-Problem in particular, pendulums can be seen as symbols of a civilization's progress or effort. 137 uses numerous pendulums in an attempt to hypnotize God, with multiple workers pulling ropes to keep them moving; 192 has a "completely modernized" single massive pendulum. The leaders of Civilization 192 themselves admit that they built their pendulum as a symbol—"It's a monument for Trisolaris, as well as a tombstone"—because they've given up trying to solve the three-body problem.
The pendulum appears at other points as well, usually as a rhetorical device rather than a literal one. For example, on page 39, as Ye Wenjie hallucinates while she freezes, she imagines the red flag waving "like a perpetual pendulum, counting down the remainder of her short life." There is an actual pendulum on real-world Trisolaris (or at least the Trisolaris that humans imagine), which the princeps orders to be stopped—they no longer need the pendulum to hypnotize god.
Fire (Motif)
Fire appears as a motif in the novel. Many of Lui's rhetorical devices center around fire, heat, and flames, particularly in the Ye Wenjie chapters. There are frequent images of sunrises, sunsets, and light. Fire as a motif has strong resonances with the natural world—fire is strong, uncontrollable, deadly, and also life-preserving and integral to humanity's technological development—and it additionally echoes the three burning suns of the Trisolaran system.
Lipstick and High Heels (Symbol)
Ye Wenjie's best friend and advisor, Professor Ruan Wen, kills herself the same day Ye's father is beaten to death in a struggle session. Ruan was also subjected to struggle sessions at the university, during which the Red Guard "hung a pair of high heels around her neck and streaked her face with lipstick to show how she had lived the corrupt lifestyle of a capitalist" (page 21). The heels and lipstick are obviously symbols of capitalism, not only to the reader but to the Red Guard as well.
Ye Wenjie observes that before Ruan took the sleeping pills, she put on lipstick and high heels. By properly wearing the symbols the Red Guard used to mock and attack her, perhaps Ruan is deliberately altering the symbols' meaning, turning them from capitalist excess to an anti-Cultural Revolution statement, or a confirmation of her own spirit in spite of her suicide.
Suicide (Motif)
Because the plot centers around trauma and hope (or lack thereof), suicide or killing of the self recurs throughout The Three-Body Problem. Ye Wenjie's best friend and her daughter kill themselves; her father doesn't commit suicide, but he willingly dies during a struggle session rather than submit; her mother basically stops existing, refusing to acknowledge the past, annihilating her "self" in a different way. Many nameless scientists commit suicide in the novel as well—the Battle Command Center has a long list—but the suicide motif largely centers around Ye Wenjie. This could simply be because she's a tragic character, so she needs a tragic backstory. On the other hand, the high rate of suicide around her could be an intentional device, to highlight her survival in a period that others couldn't or wouldn't live through—at least until the final page, as her vision goes black and she accepts "her sunset."
Yang Dong's Suicide (Allegory)
Ye Wenjie's daughter, Yang Dong, has no dialogue in the text of The Three-Body Problem, but her presence influences Wang Miao's psyche throughout. Her suicide, which predates Wang's involvement in the plot, is his entree into the mystery of the ETO. Yang Dong's entire life centered on theoretical physics, and when physics seemed to be disproven, she killed herself, leaving only a simple note (page 61, Chapter 4). Ye Wenjie reflects that this was because she "had nothing to lean on to keep on living" once her theories fell apart.
Yang Dong's life and death provide an allegorical warning for Wang Miao. He has the potential to follow in her footsteps when his faith in the universe's constitution is shaken, but he doesn't. When theories fall apart, he's devastated—but, partially with Yang Dong as a warning, and partially with Da Shi to lead the way, he finds real-world things to lean on to survive.
