Fast, reliable synchronization is the biggest reason Solana is able to achieve such high throughput, and this is done with Proof of History or PoH. Leader nodes "timestamp" blocks with cryptographic proofs that some duration of time has passed since the last proof. All data hashed into the proof most certainly have occurred before the proof was generated. The node then shares the new block with validator nodes, which are able to verify those proofs. The blocks can arrive at validators in any order or even could be replayed years later. With such reliable synchronization guarantees, Solana is able to break blocks into smaller batches of transactions called entries. Entries are streamed to validators in realtime, before any notion of block consensus. This process is similar to verifiable delay functions (VDF).