Blockchain Technology

A blockchain is a distributed ledger — a chain of records (blocks) cryptographically linked and stored across thousands of computers simultaneously, making alteration of any record computationally prohibitive. Bitcoin (2008, Satoshi Nakamoto) used blockchain to create the first trustless digital currency. Ethereum (2015, Vitalik Buterin) extended the concept to 'smart contracts' — self-executing code that runs when predefined conditions are met. Blockchain enables trustless transactions — parties can transact without trusting each other or a central authority, because the network enforces rules. Applications include cryptocurrencies, decentralized finance (DeFi), NFTs, supply chain tracking, voting systems, and identity verification. The energy consumption of Bitcoin's proof-of-work consensus (consuming more electricity than many countries) is its most-criticized aspect; Ethereum switched to proof-of-stake in 2022, reducing its energy use by 99.95%.