Why is energy conserved?

Energy is conserved because every change is a double entry, with what leaves one place arriving at its neighbor in the same event. The one move available is repair, where two neighbors whose shared readings disagree both move to the midpoint. That leaves their total alone, as it must, since a move that changed a total would need to know it, and no register anywhere holds one. Luca Pacioli printed the Venetian merchants' method in 1494, every transaction written twice, as debit and credit, so a single-sided entry cannot be written. Energy, the rate at which repair works through a region, is that bookkeeping read as a rate. The rule is identical at every boundary and every event, with nothing marking a when, which is the old result that energy is conserved because the laws do not care when.

Also in Chapter 5: Why Do You and I See the Same Table?.