Consensus

So far, what we know about blockchains is that:

• A blockchain network has one logical common ledger.

• A blockchain network is made up of several independent nodes.

• Each node has a copy of the ledger.

When new transactions are submitted to the network, a new block must be appended to the chain so that the global state of the ledger changes. But, if all nodes are independent of each other, who decides what transactions to include in a block? How is the uniqueness of the ledger preserved?

Metaphorically, we can picture this as a group of people deciding which restaurant to go to for dinner. If they agree on a common choice, the problem does not exist. They have reached a consensus. But we know well that this ...