What is virtual voting?

Hedera uses a gossip protocol, in which the participants don’t just gossip about transactions - they also gossip about gossip. By adding information about their previous gossip to every current gossip message, participants are able to jointly build a hashgraph reflecting the history of all of the gossip events. Participants then analyze that shared history in order to determine a consensus timestamp for all transactions. The Byzantine agreement mechanism participants use is called virtual voting. Alice's computer does not send Bob's computer a vote over the internet, about what order the transactions were received. Instead, Bob calculates what vote Alice would have sent, based on his knowledge of what Alice knows, and when she learned it, according to the history in the hashgraph. This yields fair Byzantine agreement on a total order for all transactions, with very little communication overhead beyond the transactions themselves.