What is a consensus mechanism?
Answer
A consensus mechanism is the method by which distributed blockchain nodes agree on the valid state of the ledger without a central authority. Without consensus, different nodes could have conflicting views of the blockchain. Key mechanisms: (1) Proof of Work (PoW) — miners compete to solve a computationally difficult puzzle; the winner adds the next block and receives a reward. Secure but energy-intensive (Bitcoin, Litecoin); (2) Proof of Stake (PoS) — validators are chosen to propose/attest blocks based on staked cryptocurrency. Much more energy-efficient; slashing punishes malicious behavior (Ethereum post-Merge, Cardano, Solana); (3) Delegated PoS (DPoS) — token holders vote for delegates who validate blocks (EOS, TRON); (4) Proof of Authority (PoA) — trusted validators (identified entities) validate blocks; used in private/consortium blockchains; (5) Proof of History (PoH) — Solana's mechanism using a cryptographic clock to order events. Consensus mechanisms determine a blockchain's security, decentralization, and scalability trade-offs.