Devs' final episode answered many of fans' questions about the quantum computer at the heart of the Devs project, but mysteries about the computer and the characters' fates remain. The miniseries is an exclusive production between FX and Hulu, as part of the new FX on Hulu banner. Written and directed by Alex Garland, the show dives into some heady existential ideas, using the central mystery of Lily Chan (Sonoya Mizuno) investigating the mysterious death of her boyfriend as a vehicle to explore themes of quantum physics, determinism, and free will - all being manipulated behind the scenes of the nefarious tech company that she works for.
From the very first episode of the series, audiences were keyed into the fact that the tech corporation Amaya was working on a secretive project in their Devs division. The reveal came sooner than expected, as episode 2 confirmed the suspicions of the show's most ardent fans: the Devs team is working on an extremely powerful quantum computer, the purpose of which far exceeds the limitations of the real-world quantum computers being worked on at IBM and Google. Amaya's computer runs a specific set of data and code; more directly, the quantum computer is capable of distilling the universe down to matters of cause and effect, making it essentially able to predict the future.
The quantum computer's reliance on determinism, which focuses on a myopic cause-and-effect-dependent view of reality, has been the center of Devs' intra-character conflicts. Forest (Nick Offerman) fired Lyndon (Cailee Spaeny) because of their disagreement about the Many Worlds Theory and a Determinist understanding of reality, and leading into the finale, audiences were keenly aware of a statement made by Katie (Alison Pill) back in episode 6: the quantum computer can't see past a fixed point, one that involves Lily in the Devs laboratory. Episode 8's reveals answered fans' questions about the computer's functionality, but not all of the explanations hold up.
Throughout the series, Forest and Katie have ascertained that the quantum computer is determinist in theory and that no variations can occur because their reality is set in stone. This falls in line with Forest's personal philosophy and his reasons for clinging to determinism: if everything is predetermined, then he has no personal culpability in the death of Forest's wife and child. This extends to the murder of Sergei (Karl Glusman) and Katie's assistance in Lyndon's unexpected death. But after Lyndon improved the Devs projections by introducing the Many-Worlds Theory, it became clear that Forest and Katie were adhering to the quantum computer's projections not because they had to, but because they wanted to.
However, after Lily arrives at Devs, in episode 8, she sees the future predicted for her by Forest's deterministic projection: on the Devs screen, she shoots Forest in the face, and the bullet pierces the lift's glass, breaking the airtight seal that keeps the lift afloat. Lily plunges to her death. As the scene plays out, however, she tosses away the gun as the lift's doors close, ensuring that she won't follow the same sequence the computer predicted. Her choice breaks the deterministic framework that Forest and Katie have clung to throughout the series, and when Forest is reincarnated in the Devs simulation, he realizes that determinism was a faulty philosophy, a way of looking at the world that fails to fit with the data.
Lily's choice supports two concomitant theories in quantum physics. The Many-Worlds Theory, posited by Hugh Everett, has already been debated throughout the show's run, but since Lily's choice was motivated by her observation of the outcome, the Copenhagen Theory also has merit. As described by Katie's teacher in episode 5, the Copenhagen Theory "suggests that the act of measurement affects the system." Despite Katie scoffing at this theory, Devs' finale offers evidence for both the Copenhagen and Many-Worlds Theories.
There's a popular fan theory regarding the show that originated on Reddit, from user emf1200, that suggests the entire show takes place within a simulation. This comes from the fact that the projection software works by simulating events through the usage of the predictive algorithm: the Devs team isn't technically peering backwards through time; they're reconstructing time and viewing it like a movie. Episode 7 has a scene where Stewart (Stephen McKinley Henderson) shows off the computer's predictive capabilities to a group of employees, and casually mentions how "somewhere in each box, there's another box." This implies that within the simulation the Devs team is watching, there's another version of the Devs team watching another simulation, and so on and so forth. By this logic, there's enough evidence to suggest that the show fans are watching is not the prime universe, but simply a simulation somewhere within a stack of simulations.
Though the finale did not strictly follow this theory - there was indeed a prime reality - when Forest and Lily are reincarnated in the Devs computer, a life that Katie characterizes as "indistinguishable" from reality, they essentially enter the "box within a box." They each become Neo (Keanu Reeves), without superpowers, from The Matrix, knowing that they are in a simulation with the power to exercise free will within each reality.
Up until episode 4, the Devs team was convinced (at Forest's insistence) that the universe operated on the De Brogile-Bohm theory, a deterministic interpretation of quantum physics that suggests events are set in stone as the result of cause and effect. This produced some results, namely - the preliminary version of the projection that could only render hazy, static-filled visions of the past and future. However, in episode 7, Stewart and the rest of the team perfected the quantum computer by switching out Forest's determinist theory with Lyndon's Many-Worlds theory, which Stewart says "is the universe as is." But once the quantum computer operated under the Many-Worlds Theory, why did it fail to predict Lily's decision to throw away the gun? According to Stewart and Lyndon, the multiverse exists, but the predictions made by the project are only of one universe. All Lyndon's algorithm did was clear up the static, not change the nature of the prediction.
But this raises yet another question: why did the deterministic computer projection stop accurately predicting the future at the point of Lily's death, when the actual moment that violated the laws of determinism was her decision to toss the weapon, not when she died? This question brings up a frustrating issue with the show's conclusion. Each adherent to all of the theories about quantum superposition can find evidence to support his/her position, and Devs offers no definitive conclusion. Copenhagen enthusiasts note that Lily's observation affected the outcome, Many-Worlds theorists are pleased with the free will implications of Lily's decision, and Determinists note that despite Lily tossing away the gun, Forest and Lily still died in the same manner the computer predicted.
In the simulation Forest states that he "exercised a little free will" by giving each version of Lily and Forest in the Devs simulation knowledge of other worlds. This effectively deals with the show's recurrent themes about Forest using determinism as a scapegoat for personal accountability because each version of Forest must reckon with the knowledge that other Forests are living under better or worse outcomes. However, while the show's conclusion holds up thematically, the failure of the quantum computer to accurately predict the final episode's outcome remains a mystery, one that Devs as a whole didn't adequately address.
