  I show that, by the same criteria that led to Galilean and Special Relativity
and gauge symmetries, there is no way to identify a unique set of observables
that give the structure of space or spacetime. In some sense, space is lost in
the state space itself. Moreover, the relationship between the observables and
the physical properties they represent becomes relative. But we can verify that
they are not relative, and the spacetime structure is unique. I show that this
implies that not all structures isomorphic with observers can be observers,
contradicting Structural Realism and Physicalism. This indicates a strong
connection between spacetime and the sentience of the observers, as anticipated
by some early contributors to Special and General Relativity.
