Part 5/10:
This challenge led to the invention of the blockchain by the mysterious Satoshi Nakamoto. Think of blockchain as a giant, transparent ledger shared across a network in the sky, recording every transaction and preventing double-spending. When Bob sends Bitcoin to Julian, and Julian to Moku, every move is logged publicly. If someone tries to spend a Bitcoin twice, the system detects and blocks the attempt. This innovation effectively removes the need for trusted third parties.