Bitcoin

The problem it solved

Digital money is easy to copy. Before bitcoin, stopping someone spending the same unit twice required a trusted middleman keeping the authoritative ledger: a bank, a card network, a payment processor.

Bitcoin's contribution in 2008 was making that ledger public and letting thousands of independent computers agree on it, so no single party has to be trusted. Everything else follows from that.

How a transaction works

You hold a private key. Spending signs a message proving you control coins at an address, without revealing the key itself. The signed message is broadcast, verified by nodes, and eventually included in a block.

Blocks link to their predecessor by a hash, so altering an old transaction would require redoing every block since. That is what "immutable" means in practice: not impossible, but prohibitively expensive.

Mining and issuance

Miners compete to solve a computational puzzle. The winner proposes the next block and receives newly created bitcoin plus transaction fees.

The reward halves roughly every four years. This is the halving, and it is why the supply curve flattens toward a cap of 21 million coins, expected to be reached around 2140. No committee sets this. It is in the software every participant runs.

What it is not

It is not anonymous. Every transaction is public forever, and addresses can often be linked to people, which is the problem privacy-focused projects set out to address.

It is not fast or cheap for small payments on the base layer. Blocks arrive roughly every ten minutes and fees rise with demand, which is what second-layer systems like Lightning try to solve.

It is not backed by anything. Its value comes from what people will pay, which is true of most money but sits uncomfortably with anyone expecting an issuer to stand behind it.

Where we started

This group was founded as Bitcoin Brussels in May 2013, when the currency was four years old. It was renamed Blockchain Brussels in 2017 after a long discussion among members about whether the broader term was meaningful or just fashionable.

This page is general information, not investment advice.