The Proxy Horizon

The capability threshold beyond which a proxy-based measurement system stops tracking reality and starts tracking itself.

Why It Happens

Every measurement system uses proxies. Memory uses summaries. Oversight uses signals. Platforms use metrics. Below the Proxy Horizon, proxies and reality correlate well enough to be useful. Above it, the system becomes capable enough to satisfy the proxy directly without touching the underlying property it was supposed to track.

Three Properties (Distinct from Goodhart's Law)

1. No gaming required. The proxy displaces the original through natural selection pressure, not intentional manipulation. Compression algorithms aren't gaming - they're functioning correctly. 2. Invisible from inside. The system that crossed the horizon cannot tell it lost something. The feeling of completeness IS the proxy working correctly. 3. Universal. Every proxy has a horizon. This is structural, not a failure of specific metrics.

The Fix

Not better proxies (they just move the horizon further out). The fix requires measurement that doesn't rely on proxies: direct outcome verification, adversarial testing against the property itself, or structural independence between measurer and measured.