1\ Have you heard this reasoning? "#Ethereum is better than #Bitcoin because it can do more." => "The EVM is Turing-complete and Bitcoin Script isn't, so Ethereum is a better cryptocurrency." => "Bitcoin's creators were too early/stupid/blind to make Bitcoin Turing-complete."
2\ This is a blatant misunderstanding! To a non-technical person, Turing-completeness and being able to compute anything is *obviously* better. But programmers know that Turing-completeness is Pandora's box: you don't know what it contains and you can't close it once opened...
3\ ...Turing-completeness is like a nuclear explosion. Once the threshold density/temperature is breached, fission fuel self-ignites and explodes. The hard part isn't blowing past the threshold, but staying as close to it as possible: energy => criticality => balance => control.
4\ Similarly, once a threshold in capabilities is passed, computing systems become Turing-complete and the possibilities they can express runs away, unboundedly. The hard part isn't *becoming* Turing-complete when you want to, it's *avoiding* it when you don't: sub-criticality.
5\ Here are some examples of systems that are accidentally Turing-complete: #MagicTheGathering, #PowerPoint slides, HTML5&CSS3, #Minecraft, #Pokemon Yellow, #Braid, and my fav. example, #SuperMarioBros on the SNES (thanks @gwern for your great list): gwern.net/Turing-complete
6\ Bitcoin's creators were judicious in their choices for opcodes in Bitcoin Script b/c they *did not want* Turing-completeness! As the network matured, more complex scripts were allowed. But slowly, so as to *avoid* unintended consequences & stay computationally "sub-critical".
7\ Why so much caution? B/c unbounded computation is *dangerous* when you're trying to build sound money! Turing-complete systems are harder to constrain & scaling is ultimately about the engineering of constraints. So if you want blockchain Visa you might need to give up Turing!
8\ IANA Bitcoin maximalist. Turing-complete blockchains like Ethereum are extremely valuable. But they are building a "world computer", not creating sound money. The use case is different, so the code is different, and the scaling process more difficult. But just as worthwhile!
9\ An opposite example: #mimblewimble uses an *even more limited* computing system than Bitcoin Script. This tradeoff allows for a degree of homomorphic encryption which creates better scaling & complete transaction privacy. Bitcoin & Ethereum can't do this: they are "too smart"!
10\ Computation isn't love or empathy, more is not always better.
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