Too Long; Didn't Read
Block Propagation Problem in Blockchains is a well-known bottleneck that prevents Bitcoin from scaling. Block propagation time is an average time that is needed for the new block to reach the majority of nodes in the network. Long block propagation delay reduces the node’s resistance against 51% attacks and 51% mining. In order to address the problem, developers often try to keep the block propagation time less than 1% of the time to be the average block propagation to be less than less than 50% of nodes. The longer the propagation time, the more often miners mine on top of old blocks.