PoW is Efficient
EXCERPT
The Bitcoin ledger can only be immutable if and only if it is costly to produce.The fact that Proof of Work (PoW) is “costly” is a feature, not a bug. Until very recently, securing something meant building a thick physical wall around whatever is deemed valuable. The new world of cryptocurrency is unintuitive and weird — there are no physical walls to protect our money, no doors to access our vaults. Bitcoin’s public ledger is secured by its collective hashing power: the sum of all energy expended to build the wall. And through its transparent costly design, it would take an equivalent amount of energy to tear it down (unforgeable costliness).
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