The Machine Anatomy

physical AI system is defined by the physical apparatus through which it acts. The first law of The Four Bedrock Laws holds that this apparatus cannot take back the work it delivers, and Part I turns that law into numbers. It asks how far the machine travels before it stops, how much torque its drives can deliver and how much winding heat and rail droop they tolerate before damage, how quickly its evidence ages, and which of these limits binds first. The answers come from the plant, the learned proposer, and the permission path, in that order.

Principle 1: The irreversibility law

Invariant: Once a permitted command crosses the causal boundary, the energy it delivers becomes motion, strain, or heat that no software action can recall. During a pre-brake delay \(\tau_{\text{delay}}\) the machine travels \(v\,\tau_{\text{delay}}\) before any response begins, so a stop requires \(d_{\text{stop}} \le D_{\text{clear}}\), with every term of \(d_{\text{stop}}\) taken from a measured limit of this machine under stated conditions (Kinetic Momentum).

Implication: Each part of the machine carries budgets in time, distance, torque, heat, and voltage. Every check that protects the plant must finish before actuation and inside those budgets, and a design is admissible only when it can say which budget binds first, how that budget was established, and what the machine does when it is exhausted.

The Physical Body (The Physical Body): Decides which physical budget binds first and how its value was established, and produces the limit record from which every later record descends.
The Cognitive Brain (The Cognitive Brain): Decides what a learned proposer can deliver on time and what memory and latency that costs; it produces no record of its own, and its proposer limits enter the handoff record in the limit record’s format.
The Nervous System (The Nervous System): Decides how often the permission path must check and how long a proposal may drive the actuators, and produces the handoff record together with the header that every proposal carries.

Part I hands forward three things. From The Physical Body comes the limit record, the form in which every budget that can end in damage (stopping distance, delivered torque, winding heat, rail voltage, and measurement age) states its conditions and its category. The chapter fills that form on the machine for two limits, the credible deceleration behind the stopping distance and the dropout of the shared control rail. From The Cognitive Brain comes the proposer’s supply: how many future setpoints one chunk covers, how long a new chunk takes, and how quickly the evidence behind it ages. From The Nervous System comes the handoff record: the lease the permission path derives from the stopping budget, the tick at which it checks, the handoffs between proposer and permission path, and one worked budget that couples all three chapters on the running machine.