Throughout Sea of Tranquility, multiple characters grapple with the interplay between reality and simulations.

Gaspery, notably, joins Zoey’s investigation with the Time Institute to look for substantiating proof of the “simulation hypothesis.” Within the context of the narrative, the simulation hypothesis is the theory that the entirety of reality itself may be a simulation. This, Zoey suggests, might explain the strange glitch the siblings are investigating. When she refers to “file corruption” as the cause of the glitch, she is suggesting that the files constituting the simulation itself are misbehaving and causing moments in time to accidentally connect with each other.

As he investigates the anomaly, Gaspery finds himself contemplating what it would mean to be in a simulation and constantly questioning what is and isn’t real. When he mentions it to Talia, she dismisses the hypothesis entirely. The colonies are in disrepair, she points out—if they were in a simulation, why would someone choose for the streetlights outside to be broken?

Olive, too, struggles with this notion along a different axis. Her distaste for Jessica Marley’s memoir is based on Jessica’s assertions that growing up on the moon, in an ersatz version of Earth, involves a degree of poetic artifice. Olive, also raised in the colonies, finds this completely unrelatable. The more time she spends on Earth, the greater the distance from her family and the emptier each hotel room feels. The moon’s environment may be a simulation of atmospheric conditions on Earth, but her most authentic life is still always under the dome back on Colony Two.

After spending much of the narrative wrestling with this question, Gaspery finds that his contented life on the farm with Talia finally brings him to a conclusion: his life is as real as his experience of it. “If definitive proof emerges that we’re living in a simulation,” he muses, “the correct response to that news will be so what. A life lived in a simulation is still a life.”

Themes of causality, culpability, and consequences are explored through various characters in Sea of Tranquility.

When Edwin is first introduced, he is navigating the consequences established by his father for his rebellious anticolonialism and considers himself in “exile” in Canada. Later, this same character will visibly wrestle with the consequences of combat as he struggles, and ultimately fails, to overcome the trauma of what he experienced on the battlefield.

Gaspery spends much of his narrative worried about causality while time-traveling, eventually leveraging that causality in the hopes of facilitating a very specific set of consequences—namely, the survival of both Olive Llewellyn and Edwin St. Andrew. In Olive’s case, he succeeds, and the author lives. In Edwin’s case, he fails, and the veteran dies two days earlier than planned.

For both of these infractions, Gaspery accepts blame and welcomes the inevitable consequences. He is sent back in time to serve a jail sentence in Ohio, applied as punishment for a crime he, ironically, is not actually culpable for. Zoey, too, faces material consequences as a result of Gaspery’s actions, though her true culpability for the events of the narrative is up for debate.

In one of Olive’s lectures on her book tour for Marienbad , she cites the unique case of the Antonine plague: the Romans, having no other explanation for the sudden illness now decimating their population, eventually came to believe the pestilence arose as a cosmic punishment for their misdeeds at war. They had destroyed a temple of Apollo in the city of Seleucia and believed the sickness to have emerged from a specific...