On July 20, Vitalik Buterin replied to a question from netizens "What is a global blockchain" on social media, saying that the blockchain is a "truth machine". In a specific sense, it provides a consensus approximation of the truth about when a message is sent, but it will not tell you whether the moon landing is true. This greatly reduces the attack surface of blockchain, but it does mean that we need other tools to actually perform (or assist) the latter kind of truth discovery.