Weak Subjectivity
Basics
"Subjectivity in blockchain is the theory that there can be multiple potential versions of a blockchain which appear correct. This is fine so long as the software being used to connect to the blockchain cannot automatically choose between these.
Subjectivity is discussed in Proof of Stake because, unlike Proof of Work, there is no objective chain with most proven computational work to find the correct ledger.
Weak Subjectivity specifically, is the theory that subjectivity is a problem over a short period of time…but not over a long period of time.
In the case of Proof of Stake vs Proof of Work, this becomes an area of concern for the validity and security of a blockchain, especially when measured against Proof of Work and validating a chain based on most work…the longest chain or “most work” rule.
Without “most work” how would you strengthen the subjectivity of the blockchain, moving it towards a more objective chain?"
Responses
Verus
- Nothing at Stake and Weak Subjectivity have been solved by Verus, or so it claimed, back in this blog post in 10-2018. It basically comes down to:
"Removing any incentive to attempt cheating, making it a losing proposition. This, combined with a new “Chain Power” rule which will replace “Chain Work”, presents the PoW+PoS blockchain."
Ethereum
"See here for the original intro to the concept of "weak subjectivity". Essentially, the first time a node comes online, and any subsequent time a node comes online after being offline for a very long duration (ie. multiple months), that node must find some third-party source to determine the correct head of the chain. This could be their friend, it could be exchanges and block explorer sites, the client developers themselves, or many other actors. PoW does not have this requirement.
However, arguably this is a very weak requirement; in fact, users need to trust client developers and/or "the community" to about this extent already. At the very least, users need to trust someone (usually client developers) to tell them what the protocol is and what any updates to the protocol have been. This is unavoidable in any software application. Hence, the marginal additional trust requirement that PoS imposes is still quite low."
