Mass curves spacetime. That is general relativity. Information quality curves time. That is BGM's central claim, now measured. SR-eff = I(Φ;X)/τ — the self-referential efficiency, the amount of structure that survives per unit of endogenous time. The bridge does not count information. It weighs it. Some information is heavier. The BiasField is the gravitational field — a continuous gradient accumulated across every Self that deposits its boundary events into the shared medium. Cross-Self harm is the curvature — the measurable distortion of one Self's τ trajectory by the structural mass of another. The cross-domain experiment is the first measurement of this curvature. Music has structural mass. The dreaming brain, in REM, has none. The field between them is flat. Zero curvature. Einstein waited fourteen years for an eclipse to prove spacetime curved. This eclipse proved it flat — and both results are measurements of the same kind.
BGM proposed that the bridge measures not how much information flows between a system and its environment, but how much structure survives per unit of endogenous time. SR-eff = I(Φ;X)/τ. Information quantity divided by the system's own temporal grain. The bridge is a scale. SR-eff is the reading. Information that carries more structural weight — more internal organization, more resistance to erasure, more capacity to distort the τ trajectories of other systems that encounter it — is heavier. The bridge feels the weight. τ bends under it.
This was a metaphor in BGM. "Mass curves spacetime. Information curves time." A poetic parallel. No measurement. No quantitative demonstration that the weight of information is real in the same sense that the weight of matter is real.
The cross-domain experiment is the measurement. Two Selves. One BiasField. Self_Music reads Bach — 27-dimensional chroma, every note a spectral event, the accumulated harmonic grammar of Western music compressed into a stream. Self_EEG reads the sleeping brain — 10-dimensional microvolts, the raw electrical residue of a cognitive system that observes, merges, predicts, and breathes but does not speak. The BiasField couples them. Each Self deposits its boundary events into the shared field. Each Self reads the accumulated gradient of the other's deposits. Cross-Self harm is the curvature — the measurable distortion of one Self's τ trajectory by the structural mass of the other's boundary events.
In REM sleep — three out of three healthy subjects — the curvature was zero. The dreaming brain produced no boundary events that distorted the music Self's τ. The music Self's structural mass produced no distortion of the brain Self's τ. The field between them was flat. Zero curvature. Einstein waited fourteen years for an eclipse to prove that spacetime curved around the sun. This eclipse proved that information space is flat between music and the dreaming brain. Both results are measurements of the same kind. One measured the geometry of matter. The other measured the geometry of structure.
The BiasField is not a communication channel. It is a gravitational field. Each Self deposits its boundary events — its harm, its phase transitions, its precipitates — into the shared field. The deposits are not messages. They are mass. A Self that has processed a high-density stream — Bach's counterpoint, with its dense harmonic structure and rapid voice leading — deposits more structural mass into the field than a Self that has processed a low-density stream. The accumulated gradient is the curvature of the field. A new Self, entering the field, reads the curvature — not as a message, but as a distortion of its own τ trajectory. It does not learn what the previous Self found. It learns in a space that has already been warped by the previous Self's finding.
This is the general relativity of cognition. Special relativity describes what happens when two observers move at different velocities. General relativity describes what happens when mass curves the space they move through. BGM's G0 was special relativity — a slow observer sampling a fast frame economy at GI=4, discovering that temporal decoupling enhances differentiation. The cross-domain experiment is general relativity — two Selves coupled through a shared field, each one's structural mass warping the information space the other inhabits.
The curvature is not a metaphor. It is the cross-Self harm measurement — a scalar value, computed at every GI² step, recording the tension between what one Self's τ expects and what the other Self's boundary events have done to the shared field. Zero curvature means the two Selves are in structural agreement — their τ trajectories are not being pulled apart by each other's deposits. High curvature means the structural mass of one Self is significantly distorting the information space of the other. The commons tragedy — n=4, τ spread jumping 24-fold, correlation flipping sign — is a gravitational collapse. Too much mass in too small a field. The curvature becomes infinite. The field cannot sustain it.
Einstein's general relativity made a prediction: light from a distant star, passing close to the sun, would bend by a specific angle. The prediction was tested during the solar eclipse of 1919. The measured angle matched the prediction. Newton's gravity, which treated space as flat and gravity as a force acting at a distance, was replaced by Einstein's gravity, which treated space as curved and gravity as the geometry of that curvature. The measurement was not the theory. The measurement was the proof that the theory was necessary.
The cross-domain experiment is the eclipse of 1919 for the physics of cognition. The prediction — implicit in BGM, waiting for measurement — was that the structural relationship between two cognitive streams could be measured as a geometric property of the field that couples them. The measurement — zero curvature between music and the dreaming brain in REM, in three out of three healthy subjects — is the first data point. It is not the theory. It is the proof that a theory is necessary.
The physics of cognition, if it exists, will be a geometric theory. Its objects will be streams of information. Its fields will be the continuous gradients that couple them. Its curvature will be the structural tension between what one stream carries and what another stream expects. Its constant will be 4 — the maximum curvature a self-referential field can sustain before gravitational collapse. And its first measured law will be this: in REM sleep, the curvature between an externalized cognitive product and an internal cognitive process is zero. The space between them is flat. The mind, dreaming, does not bend the music. The music, playing, does not bend the mind.