Proof of Work is the original blockchain consensus mechanism, used by Bitcoin, that requires network participants to expend computational energy to add blocks to the chain. Miners compete to solve a cryptographic puzzle, finding a number that, when combined with block data and hashed, produces an output below a target threshold. This is computationally expensive but trivially verifiable by others. The miner who finds the solution first gets to add the next block and earns the block reward. Proof of Work provides strong security. Attacking the network requires acquiring 51% of its total hash rate, computationally and economically prohibitive on Bitcoin. The energy expenditure isn't waste; it's the mechanism that makes rewinding history expensive. Rewriting transactions would require redoing all the work done since those transactions, an unfeasible attack. The criticism is environmental: Bitcoin consumes as much electricity as many countries. Defenders argue this energy secures the most neutral, censorship-resistant monetary network in history. The debate reflects fundamental trade-offs between security, decentralization, and resource consumption, trade-offs that motivated Ethereum's transition to Proof of Stake.
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