Weak Subjectivity

Weak subjectivity is a concept in blockchain networks, particularly those using Proof of Stake (PoS) consensus. It refers to the need for nodes to rely on some external information or trust to determine the valid blockchain state after being offline for a long time. Unlike Proof of Work systems, where the longest chain is always the valid one, PoS systems can have multiple chains with valid signatures. Nodes must occasionally synchronize with trusted sources to ensure they follow the correct chain. This requirement introduces a slight level of trust, hence the term "weak subjectivity."