What is Consensus?
Consensus is the process through which distributed participants use shared rules to agree on which records are considered valid.
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What does consensus mean?
Consensus refers to the rules and processes that determine which transaction history network participants will accept as valid. Since blockchains lack a central registry administrator, computers must be able to reach the same conclusion among conflicting records. Establishing a common ordering is particularly important in cases where there is an attempt to spend the same asset with two different recipients.
This does not mean that all users vote individually for every transaction. Network software audits transactions for compliance with rules. Block production, the sequencing of blocks, and the selection between alternative histories are carried out according to the specific network’s mechanism. Bitcoin and Ethereum do not handle this process in the same way.
What happens if the same money is sent twice?
Consider a scenario where someone tries to send the same spendable Bitcoin to both Alice and Bob. Both transactions cannot be recorded in the valid history simultaneously. In addition to signatures, nodes verify previous expenditures. Once one of the transactions is included in the chain accepted by the network, the other becomes invalid as it attempts to re-spend the same funds.
Due to network latency, different nodes may briefly see different blocks. The consensus mechanism determines how these forks are resolved. Therefore, the visibility of a transaction and the point where the possibility of reversal becomes negligible—or when it reaches protocol finality—are distinct stages.
Where do PoW and PoS come in?
Proof of Work uses computational effort for block production, while Proof of Stake utilizes deposited economic collateral. However, it is incorrect to reduce consensus solely to these labels. Block selection, penalty rules, network communication, and finalization methods are also crucial. The information that a network “uses PoS” does not mean two networks are equally secure or operate at the same speed. It is necessary to examine who validates the network and under what conditions.