APRIL 17
Consensus
How Bitcoin Agrees Without a Boss
The Signal
Bitcoin does not vote on what is true. Independent nodes follow the same rules and reach the same answer.
The Reading
Imagine ten people each holding the same calculator. Everyone types 7 × 8. Nobody votes. Nobody asks a leader. Every calculator gives the same answer: 56. That is the simplest way to understand Bitcoin consensus. Thousands of nodes around the world check Bitcoin for themselves. They use the rules in the software they choose to run. If a block follows those rules, they can accept it. If it breaks even one rule, they reject it. Ten thousand other nodes cannot vote your node into accepting something it says is invalid.
Sometimes two miners find valid blocks almost at the same time. Some nodes may see one first and other nodes may see the other. For a short time, the network can have two valid tips. Bitcoin already has a rule for this. Nodes follow the valid chain with the most accumulated proof of work. As more work is added, the network normally returns to one shared history.
Now imagine changing your own calculator so 7 × 8 shows 57. You have changed your calculator. You have not changed anyone else’s. Bitcoin works the same way. Anyone can change the software on their own computer. But that cannot force other nodes to change their rules. There is no fixed percentage of nodes that can vote a new rule into Bitcoin. To remain part of one Bitcoin network, people must keep using rules that are compatible with each other. That is consensus: no boss, no central vote, just independent computers checking the same rules and arriving at the same result.
First Principles
Nodes check; they do not vote.
The most-work valid chain becomes the shared history.
Changing your rules does not change everyone else’s.
Today’s Challenge
Ask someone at home to open a calculator. Both type 7 × 8. Both should see 56.
Now imagine you secretly change your calculator so it shows 57. Did their calculator change? Did every calculator in the world change?
No. You changed your machine, not theirs. Bitcoin consensus works the same way: staying together depends on using compatible rules.
Tomorrow’s Signal
Private Keys