Why does proof-of-work use so much energy?

Proof-of-work (PoW) uses energy as the mechanism that makes transaction ordering permissionless and censorship-resistant. Critics often focus on the cost without asking what the energy purchases: it buys a system where no government, corporation, or cartel can override transaction ordering without matching the network's total physical output. That physical requirement is what prevents any single powerful party from taking control of the ledger. Whether that tradeoff is worthwhile is a value judgment — but it is a tradeoff, not waste, and understanding the distinction matters when evaluating any PoW blockchain.