Proof of History (PoH) is a cryptographic clock that creates a verifiable sequence of events without requiring nodes to agree on timestamps. Each event is hashed together with the hash of the previous event, forming an ordered chain that anyone can verify. PoH does not replace consensus mechanisms like Proof of Stake. It provides an immutable ordering that consensus protocols reference when determining transaction sequence. Solana is the most prominent blockchain using PoH. Because the ordering is pre-established by the PoH clock, validators can verify transaction order without the communication overhead of traditional consensus. This lets the network process thousands of transactions per second. The tradeoff is that PoH requires a single leader node to produce the hash chain, which introduces a centralization point. But anyone can verify the chain independently, and leadership rotates among validators.
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