It from Bit (Wheeler) - physical reality supervenes on information
Wheeler spent decades developing the implications. His delayed-choice experiments are physical tests of the idea. The holographic principle (Bekenstein, 't Hooft, Susskind) puts it in precise mathematical form: S ≤ A/(4ℓₚ²) — entropy (information) bounded by area, not volume. This is physics, not poetry.
Correct! This is exactly what [[008_A2.1_Substrate-Requirement|A2.1]] (Substrate Requirement) addresses. "It from Bit" doesn't deny substrates; it orders them. Bits are primary; physical instantiation is secondary. The substrate question leads to [[011_D2.2_Chi-Field-Properties|χ-field]].
Bell's theorem + experimental violations of Bell inequalities refute local hidden variables. Quantum mechanics is incompatible with "things have definite properties before measurement." The moon's macroscopic stability is explained by decoherence ([[046_A6.2_Collapse|A6.2]]-related), not by pre-existing classical properties.
We infer them from gravitational effects — informational signatures. If dark matter has no informational interaction at all, it is operationally non-existent. The "It" of dark matter comes from the "Bits" of galaxy rotation curves and CMB observations.
Original thought experiment (1978):
A photon passes through a double-slit. AFTER it passes, choose whether to:
Key insight: The choice made NOW determines what the photon "was doing" THEN. The "It" (particle trajectory) comes from the "Bit" (measurement choice).
Cosmic delayed-choice (Wheeler 1978, realized 2017):
Light from a quasar, gravitationally lensed by a galaxy, reaches Earth. We choose NOW whether to measure which-path or interference—for photons that began their journey BILLIONS of years ago.
Jacques et al. (2007): Laboratory delayed-choice with single photons. Results: The measurement choice retroactively determines the photon's history.
Supervenience relation:
Let B = space of all possible bit-strings (information states)
Let P = space of all physical configurations
Wheeler's claim: There exists a surjective map f: B → P such that:
\forall p \in P, \exists b \in B: f(b) = p
Every physical fact corresponds to some bit configuration. No "It" without a "Bit."