The most striking idea in modern quantum gravity is that a gravitational theory in a region of space can be equivalent to a non-gravitational theory living on that region’s boundary — the holographic principle 19, 21, made precise by the AdS/CFT correspondence 14 and sharpened into the statement that the bulk is literally a quantum error-correcting code written on the boundary 1, 16, 17. This note is written for a graduate reader who knows quantum mechanics and a little general relativity but is still climbing into holography. We first explain, plainly, what AdS/CFT and holographic error correction actually say. We then introduce a very different- looking research programme — a finite quantum-error-correction (QEC) “substrate” in which space is the ordered phase of a discrete, self-correcting register network — and ask, honestly, how the two relate. The answer is a clean three-part verdict. They share a deep principle (bulk-in-boundary error correction) and a deep law (entanglement entropy = a geometric area). They differ in two concrete, checkable ways: the substrate’s elementary code is not a perfect tensor of the Pastawski–Yoshida–Harlow–Preskill (HaPPY) type, and its spacetime is not anti- de Sitter — it is flat with a de Sitter cosmology, and its “boundary” is a causal/cosmological horizon, not a conformal boundary at infinity. The consequence is that the natural bridge is to de Sitter / cosmological-horizon holography — the open, under-served side of the subject — where the substrate offers something the field largely lacks: a concrete microscopic holographic code with explicit boundary dynamics. We make precise which AdS/CFT tools transfer and why, verify the Ryu–Takayanagi area law directly on the lattice, and close by relating the picture to the programmes of Susskind (the holographic principle, complexity, ER=EPR) and Baez (the discrete-versus-continuum question, and physics as computation), whose work this both draws on and, we hope, complements. 2026-06-20 canon refresh: Brief canon-refresh errata added: HBC scope caveat, RT/min-cut plus service-current stress tensor now supports linearized Einstein source form, observed Planck hierarchy still nonlocal/span-gated; build/render checked locally; not Zenodo-synced. 2026-06-21 canon refresh: This version incorporates the 2026-06-21 ANCHOR/DRIFT/PTMS canon refresh and rebuilt local PDF.
David Elliman (Sun,) studied this question.