Why a shared ledger exists

When you send a photo, you send a copy. The original is still on your phone. That is fine for pictures. It is a disaster for money.

If digital dollars were just files, anyone could duplicate them. So we invented trusted middlemen: banks, card networks, app stores, payment companies. They keep the official list of who owns what. That works — until the company freezes an account, raises fees, goes down on a Saturday, or simply decides you are no longer a customer.

Ethereum is a different answer. Instead of one company keeping the list, thousands of independent computers keep the same list, in public, and they only update it when the rules say so. Nobody gets to quietly edit your balance. Nobody has to stay open until 5 p.m.

That list is called a blockchain: a ledger of transactions grouped into blocks, each sealed onto the last. Ethereum adds something Bitcoin does not: the ledger can also run programs. Those programs are smart contracts. Together they make a computer anyone can use and no one can switch off.