Relativity of Reconstruction: Observer–Dependent Vacuum Energy in de Sitter Space

We propose that vacuum energy and spacetime curvature are not **observer–independent** geometric scalars but *observer–relative reconstructions*.  
Each observer \( q \) accesses only a causal subalgebra \( \mathcal{A}_q \) of the global quantum state \( \rho \), and we define the physical vacuum energy as
\[
\rho_{\mathrm{vac}}^{\mathrm{phys}}(q) := \langle (F_q T_{00}) \rangle_{\rho},
\]
with \( F_q \) a normalized, positive, horizon–adapted reconstruction map. This replaces the global quantity \( \rho_{\mathrm{QFT}} \sim M_{\mathrm{Pl}}^{4} \) with the operationally meaningful \( \rho_{\mathrm{eff}}(q) \) determined by causal access.

We propose an observer–relative semiclassical Einstein equation,
\[
G_{\mu\nu}[g_{(q)}] = 8\pi G\, T_{\mu\nu}^{(q)}, \qquad
T_{\mu\nu}^{(q)} := F_q(\langle T_{\mu\nu}\rangle_\rho).
\]
Curvature responds to reconstructed, rather than global, vacuum energy. For a static observer in de Sitter spacetime, \( F_q \) suppresses ultraviolet contributions and incorporates the Gibbons–Hawking modular term, giving
\[
\rho_{\mathrm{eff}}(q) \sim H^{2} M_{\mathrm{Pl}}^{2}.
\]
This reflects intrinsic reconstructed vacuum energy rather than renormalization or fine tuning. Full conservation of \( T_{\mu\nu}^{(q)} \) and its generally covariant formulation remain to be established.

Thus the \( 10^{120} \) discrepancy between ultraviolet \( \rho_{\mathrm{QFT}} \) and cosmological \( \rho_{\Lambda}^{\mathrm{obs}} \) is reinterpreted as a category error: the former is a global property of \( \rho \), while the latter is an observer–relative reconstruction. General relativity and QFT remain intact; what changes is the assumption that vacuum energy and curvature are universal rather than reconstruction–dependent.