The network goes through a number of steps to confirm this change. As the proposal propagates over the network the various nodes check, by inspecting the ledger, whether
Alice actually has the bitcoin she now wants to spend. If everything looks kosher, specialized nodes called miners will bundle Alice’s proposal with other similarly reputable transactions to create a new block for the blockchain.
The technology behind bitcoin lets people who do not know or trust each other build a dependable ledger.
This has implications far beyond the cryptocurrency
Jesper Carvalho Andersen 