Money doesn’t move

When you pay a friend $20, nothing travels. No coin leaves your bank and lands in theirs. Your bank writes −20 in its notebook, their bank writes +20 in theirs, and the payment is the moment both notebooks agree to change together. Once I saw it this way, most of the payments world made more sense. Clearing houses, central-bank accounts, the two days a transfer “takes”: they all exist to make that agreement safe. Who keeps the notebooks? Who checks them? What happens if one changes and the other doesn’t? That last case has a name, settlement risk, and a surprising amount of plumbing is there just to shrink it. It also changes the question I ask about AI agents. The interesting part isn’t how an agent moves money, because nothing moves. It’s whose notebook the agent is allowed to write in, how much, and who signs off when it does.