The World State in Ethereum

The world state in Ethereum represents the global state information of the Ethereum network, including account information and the data stored under those accounts (in the case of contract accounts). Each account has its own key-value storage space, and only the account itself can read from and modify the data within that space through the EVM. The processing of blocks by clients involves modifying the world state, so each client needs to maintain a local copy of the world state and compare it with other nodes' ledgers through cryptographic commitments.

Ethereum adopts a two-level Merkle Patricia Trie (MPT) structure to store the world state and declares the root of the latest world state MPT tree within each block. Based on the definition and cryptographic properties of the MPT, we can consider two MPT trees with the same root to have identical leaf nodes. Therefore, the root of the MPT can be seen as the cryptographic commitment of the world state. Once we have the commitment to an MPT tree, it is easy to generate a proof for a set of leaf nodes on that tree and verify it.

Suppose we only know the root of an MPT tree and have partial leaf nodes along with their existence proofs, without knowing the complete structure of the MPT tree. If we modify those partial nodes, we can still obtain the new root of the MPT tree based on their previous existence proofs.

After a block is successfully mined, the client responsible for mining includes the root of the world state MPT in the block header and propagates it to other nodes.