The Lightning Network
The Bitcoin blockchain cannot by itself handle the transaction volume of the whole world. This is because every peer on the Bitcoin network has to be notified of any transaction made and all transactions must be placed in blocks. The Bitcoin network regulates it's difficulty so that a new block is only found every 10 minutes, and each block has a size limit of a few megabytes (originally 1 MB but 2-4 MB with SegWit). This puts an upper bound on the capacity of the Bitcoin network.
The Lightning Network is a protocol that utilizes smart contracts to make payment channels. This means that a lot of transactions can take place outside the blockchain, while maintaining the same trust.
Not finished