On the subway I worked out one question: if money becomes less efficient, what scarcity appears first? And what will people use to pay, exchange, and coordinate?

One sketch: chain every person's phone hardware into a single network, and grow an accounting system unlike existing money — counting contribution and energy instead of currency units.

There are two layers to this.

The sociological layer: how contribution is seen, acknowledged, and settled. That is really an identity and credit problem — who has done what, and can a stranger verify it.

The physical layer: energy is the only accounting unit that is hard to fake. Every activity pays real work, and output can be measured. If payment is denominated in energy, inflation stops being only a matter of printing and becomes a matter of thermodynamics.

If such a system holds, scarcity is no longer just "not enough money" but "energy and attention allocated to the wrong places." What gets paid for shifts from what you own to what you have done.

Whether this is designable or only imaginable, I have not finished the arithmetic.