PHY.10:4.2 - Find a physical change that makes the accounts diverge

Trace the disputed difference forward to an observable consequence. Then ask which feasible change exposes it. For example:

• Change an amplitude, scale or operating regime when the accounts predict different dependence on it.
• Change the time course of a drive when the earlier input made different response laws coincide.
• Interrupt, reverse or refocus an interaction when the accounts retain different state or memory.
• Use a symmetry or balance when one account requires a response to vanish or remain within a bound.

Choose the change from the physical dependence at issue. PHY.4 supplies law constraints, PHY.5 examines a regime change and PHY.6-.8 derive the corresponding evolution or collective response.

Recompute both accounts under the proposed change. A prediction under the original preparation cannot be compared with a rival’s prediction under the new one. Retain any changed interaction that can imitate or obscure the intended difference.

If intervention on the subject is unavailable, look for an accessible physical contrast: for example, a naturally varying condition with an understood relation to the accounts. Identify other differences between the observed situations. Their effects remain part of the comparison; naming the contrast does not make it controlled.