Spacetime Bounds on Consciousness

Is an ant colony conscious? What about a group of people talking, a cloud-hosted language model, or even a galaxy? Can a conscious mind only get so big? Does consciousness depend only on what is computed, or when and where? I see two possibilities affecting the answers to these questions. I name them Chord and Arpeggio, and formalize the distinction mathematically. If the ingredients of a subjective experience must be simultaneously true at one objective instant and causally exchange influence within a time window θ, then the system diameter D satisfies D ≤ κvθ, where v is the signal speed ceiling and κ depends on exchange architecture. I call this requirement Chord, because it is like a musical chord whose notes sound together. The alternative is Arpeggio. It asks only that each ingredient occur somewhere in the window. I prove that Arpeggio is strictly weaker than Chord, and that architectures with limited concurrency can satisfy Arpeggio while structurally forbidding Chord. I argue for Chord on formal, neuroscientific, and architectural grounds. A mechanistic model confirms a fragmentation transition at the theoretical threshold. I examine primate corpus callosum data to estimate empirical lower bounds on θ. I provide case studies showing that under Chord, ant colonies and human populations are ruled out as single conscious entities, cloud-hosted AI is constrained by co-instantiation rather than diameter, and brain-computer interface hybrids face latency-dependent limits. A mind can only get so big. Arpeggio is far more permissive, implying consciousness seemingly everywhere.