How a blockchain keeps copies in sync
A blockchain is a shared record book maintained by computers called nodes. Instead of relying on one central database, participating nodes keep copies of the ledger and exchange proposed new entries. A computer can check whether an entry follows the network’s rules—for example, whether it is properly formatted and authorized—before accepting it.
Entries are grouped into blocks, and each block is linked to the one before it using a cryptographic fingerprint: a compact value calculated from the block’s contents. Change an old entry, and its fingerprint changes, breaking the link to the next block. That makes tampering detectable; the network’s agreement process then determines which valid sequence of blocks becomes the shared record.
Agreement is about the record, not the world
This process can make it difficult to quietly alter an accepted entry, but it cannot independently verify what that entry describes. If someone records that a shipment contains a particular product, for instance, the ledger can preserve the claim and show whether it was changed. It cannot inspect the shipment. People or devices must supply that information, and they can be mistaken or dishonest.
That distinction separates integrity—confidence that a record has not been secretly changed—from truth—whether the record was accurate in the first place. A blockchain can provide a durable trail of who submitted information and when, depending on how the system is set up. It does not turn an unverified claim into a verified fact.
So the ledger’s strongest guarantee is narrow but useful: participants can coordinate around the same history without trusting one central keeper to control it. Whether that history matches events outside the network still depends on the evidence and people that put information in.
