Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic is a post-coital pillow talk scene in which a couple debates determinism and free will. The man argues that if every moment is just the product of an earlier state, then free will cannot exist. The woman counters with the idea that a computer predicting a man's actions could be thwarted if the man simply reads the prediction and chooses differently. The man rebuts that such a computer would be part of the system it's trying to simulate, meaning it would need to be larger than itself -- an impossibility.

The woman then raises the possibility that a quantum computer, where each qubit can represent multiple states, might be able to simulate a system bigger than itself. The man concedes this point -- unless the symbolic apparatus required to make predictions demands the computer be larger than the system in question. The joke culminates with the man having a philosophical breakdown, screaming that free will is a lie, while the woman moans his name -- revealing that his existential crisis doubles as impressive bedroom stamina. His final punchline attributes his stamina to "the boundary conditions of the universe," tying the determinism argument back to the bedroom context in an absurd loop.