NOTE: Proof-of-Entropy-Minima is based heavily off of Proof-of-Work Nakamoto Consensus. A strong understanding of Proof-of-Work consensus is highly recommended before reading the PoEM documentation. A detailed explanation of Nakamoto Consensus can be found here. The formal Proof-of-Entropy-Minima research paper can be found here.
Blockchain nodes work together to agree on a list of transactions and the order in which they should be recorded. How these nodes come to agreement, called a consensus mechanism, is crucial for ensuring that the blockchain is reliable and censorship-resistant.
In Quai Network, a consensus mechanism called Proof-of-Entropy-Minima (PoEM) is used. PoEM is inspired by Bitcoin's consensus mechanism called Proof-of-Work (PoW) Nakamoto Consensus. PoEM, like PoW, uses hashes generated by competing miners to verify the validity of a proposed block. However, PoEM differs from PoW in how these hashes are compared and measured.
Unlike PoW, which treats all blocks that meet a certain difficulty level as equally valid, PoEM measures the intrinsic block weight to calculate the entropy, or randomness, removed by each proposed block. This ensures that all nodes will always prefer one particular block over any other options.
Under PoEM, all nodes immediately agree on the next block as soon as they become aware of it, eliminating any disagreements caused by delays in the network. Two nodes running PoEM will always agree on which block is next in the chain.
By removing contention from consensus, PoEM allows all nodes to remain in continuous agreement. This is different from all other consensus algorithms, which take time to reach consensus or resolve conflicts.
PoEM's "perpetual consensus" provides a variety of benefits over existing consensus mechanisms like PoW and Proof-of-Stake, including instantaneous fork resolution and faster finality. These properties give PoEM the unique ability to remain in consensus while coordinating an infinite number of execution shards.
Instantaneous Fork Resolution: Given the same set of information, every node in the system will always make the same decision on the next block in the sequence.
Faster Finality: Proof-of-Entropy-Minima offers a faster mathematical guarantee of on-chain inclusion than all existing consensus mechanisms.
Coordinating Infinite Execution Shards: Perpetual consensus is a prerequisite to coordinating an infinite number of execution shards. Mechanisms that take any time to resolve contention in consensus are ineffective at coordinating more than one chain.