⛓️How a Blockchain Works: Complete Technical Explanation
Summary
A blockchain is a distributed, immutable and decentralized database. These three attributes together create something unprecedented in human history: a transaction record that no one can falsify, alter or censor.
The problem it solves: trust
The fundamental problem of digital money before Bitcoin was "double spending": if money is a digital file, nothing prevents copying and spending it twice. Centralized systems solve this by being arbiters. Bitcoin solved this without a central arbiter: thousands of independent computers maintain the same ledger copy and agree through consensus.
Anatomy of a block
Each block contains: (1) Block header: previous block hash (creating the "chain"), timestamp, nonce and merkle root. (2) Merkle root: a hash summarizing all block transactions. (3) Transactions: the list of all transfers. (4) Block hash: unique digital fingerprint calculated with SHA-256.
Why it is impossible to alter the history
If you wanted to alter a transaction from block 100,000, you would need to recalculate the hash of all subsequent blocks faster than all honest miners. This would require more than 51% of the network total computing power, costing billions of dollars in hardware and electricity.
Key takeaways
- Distributed: thousands of copies on independent computers
- Immutable: changing one block invalidates all subsequent ones
- Decentralized: no entity has control
- The hash chains blocks making silent alteration impossible
- Security increases with network size (more miners = more secure)