What the hell is blockchain, really? — Key concepts

BlocksEach block is a batch of transactions plus metadata: block number, timestamp, parent hash, transaction root (Merkle root), and who produced it (miner/validator).

Cryptography is about how to maintain control over information.

— Shafi Goldwasser

These pieces let anyone see when the block landed, how many transactions it includes, who proposed it, and how it links to the block before it.

HashesA hash is a short fingerprint of data: a fixed-size output that represents the whole input.

If any byte changes, the hash changes unpredictably—there’s no way to “tweak” the input to get the same hash without doing the full work.

Each block stores the previous block’s hash, creating a chain. That link makes edits obvious because a single change breaks every later hash.

Immutability in practiceTo change block N, you would need to re-compute block N’s hash and every block after it—while honest nodes keep building on the original. That’s why edits are loud and costly.

ConsensusNodes follow rules (e.g., proof of stake) to agree which block is next. The chain with the most accumulated work/stake that follows the rules wins.