Probabilistic Finality

Probabilistic finality is a consensus property where transactions become progressively more final and irreversible as additional blocks are appended to the blockchain, rather than being final immediately upon block creation. In proof-of-work systems like Bitcoin, the probability that a transaction will be reversed decreases exponentially with each new block mined on top of it. An attacker would need to control more than 50% of the network's hash power to reorganize the chain and reverse a transaction, making older transactions effectively immutable. This differs from absolute finality, where a transaction is instantly guaranteed irreversible. Example: Bitcoin transactions are considered probabilistically final. After six confirmations (approximately one hour), the probability of a transaction being reversed is less than one in a billion, though technically it remains theoretically possible if an attacker suddenly gains majority hash power. Why it matters for blockchain technology: Probabilistic finality explains why proof-of-work chains require confirmation times and why exchanges wait multiple blocks before crediting deposits. Understanding this model helps users assess transaction security and risk tolerance when determining adequate confirmation thresholds for high-value transfers.

Category: blockchain technology, mining staking

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