[dollylambda]

In a sense, a POW blockchain such as bitcoin can convey global time/global clock if all participants understand the average block propagation is 10 "minutes"? Sometimes longer, sometimes shorter but converges to 10 minutes in aggregate.

Over great distances this breaks down given limits on the speeds of transmition (speed of light), however, if transmission was instantaneous (quantum entanglement?), that would solve the dilemma of what does "now" mean light-years away given our relativistic idea of time between here and there.

[OneDeuxTriSeiGo]

Oh yeah. Sorry I misspoke a bit. I should have said that global time/clocks are an unsolved problem in non-proof-of-work systems.

Proof of work does a decent job approximating a monotonic clock but that only works when you are expending obscene amounts of energy on a global scale. And like you said it breaks down over longer distances (however luckily we don't have to deal with that too much now).

But in any non-PoW system, a "trustless" global clock is extremely non-trivial.

[dollylambda]

Thats because POW solves the Byzantine Generals problem as I understand it. Before POW, that problem was intractable (extremeley non-trivial). Its always lammented that so much energy is needed to solve the problem, although that seems to be the nature of the problem. Maybe time and energy are inexorably linked.