A blockchain is a distributed, decentralised digital ledger that records transactions across a network of computers in a way that is transparent, immutable, and tamper-resistant. Each “block” contains a batch of validated transactions plus a cryptographic hash of the previous block — chaining them together in chronological order. Altering any historical block would require recalculating every subsequent block’s hash and outpacing the computational power of the entire network simultaneously, making fraud astronomically expensive. This architecture is what makes Bitcoin and other cryptocurrencies trustworthy without needing a central authority.
Key blockchain concepts: Nodes — computers that store a full or partial copy of the blockchain and validate new transactions; Consensus mechanism — the rules by which nodes agree on which transactions are valid (Proof of Work uses computational energy; Proof of Stake uses staked collateral); Immutability — once confirmed, transactions cannot be reversed or altered; Transparency — all transactions are publicly visible on block explorers like Etherscan or blockchain.com; Smart contracts — self-executing code stored on the blockchain that automates agreements without intermediaries. Blockchains can be public (permissionless — anyone can join), private (permissioned — restricted access), or a hybrid.
Beyond cryptocurrency, blockchain technology is being applied to supply chain verification, digital identity, voting systems, healthcare records, and tokenisation of real-world assets. However, public blockchains face a fundamental tension: the “blockchain trilemma” of balancing decentralisation, security, and scalability simultaneously.
Example: When you send Bitcoin, your transaction is broadcast to the network, validated by nodes, bundled into a block by a miner, and permanently added to the chain within ~10 minutes. You can verify this in real-time on blockchain.com by searching your wallet address — every transaction in history is visible to anyone.
Learn more: Investopedia — Blockchain Explained
