Topics Technology and the internet

What is blockchain?

A blockchain is a shared record book, a list of transactions kept by many computers at once instead of by one company. New entries are bundled into groups called blocks, and each block carries a fingerprint of the one before it, so the blocks form a chain. Change an old entry and its fingerprint changes, which breaks every link after it, and everyone else's copy shows the mismatch.

What makes it interesting is the problem it tries to solve: how strangers can agree on who owns what without trusting a bank or a referee. Bitcoin, which appeared around 2009, was the first widely known answer. Since then people have proposed blockchains for many other jobs, and how useful they are for those jobs is still debated. Many uses are slower and costlier than an ordinary database, and some of the claims made for the technology have not held up.

An episode on this topic would walk through the idea step by step, from the fingerprint trick to how a network agrees on the next block, and then ask what it is actually good for. The hosts on bre are AI, so they can be wrong, and you can press Talk to ask them to slow down or explain a term again.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. A record book nobody ownsThe basic picture: many copies of the same ledger, kept by many computers, with no single keeper in charge.
  2. Blocks, links and fingerprintsHow a hash, a short fingerprint of data, ties each block to the last one and makes quiet tampering easy to spot.
  3. How strangers agree on the next blockAn overview of consensus: proof of work and proof of stake, and why agreeing without a boss is the hard part.
  4. Bitcoin and the double-spending problemWhy digital money needs a way to stop the same coin being spent twice, and how Bitcoin answered that.
  5. Beyond coins: contracts and other usesWhat smart contracts are, and where people have tried blockchains for records, with honest talk about where it worked and where it did not.
  6. The trade-offsEnergy use, speed, cost, lost keys and hype: why a plain database is often the better tool.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Tess. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Let's start with a picture. Imagine a notebook in a village square where everyone writes down who paid whom, and every villager keeps an identical copy. That's close to a blockchain.

  2. TessAI host

    Okay, but real talk. Why would anyone want that? I already have a bank that keeps the notebook for me.

  3. breAI host

    Fair. The bank works because you trust it. A blockchain is an attempt to keep honest records when nobody trusts anybody, and no one is in charge.

  4. TessAI host

    So what stops someone from sneaking into their own copy and giving themselves a million dollars?

  5. breAI host

    That's the clever part. Every page carries a fingerprint of the page before it. Change one old line and every fingerprint after it stops matching.

  6. TessAI host

    And everyone else's copy still has the original, so the cheater just looks wrong.

  7. breAI host

    Right. Whether that trick is worth the cost for most things is a bigger question, and I don't think the answer is a clean yes.

  8. TessAI host

    Good. I want the part where it's not magic.

Questions people also ask

Is blockchain the same as Bitcoin?
No. Bitcoin is a digital currency that runs on a blockchain, which was designed for it. Blockchain is the underlying record-keeping method, and other systems use their own versions of it. Think of Bitcoin as one application and blockchain as the technique behind it.
Who controls a blockchain?
In public blockchains no single person or company controls it. Many independent computers keep copies and follow shared rules. Some blockchains are private and run by a group of organizations, and those are controlled by that group instead.
Can a blockchain be hacked or changed?
Rewriting old entries on a large public blockchain is extremely hard, because you would have to outpace the whole network. But weak points exist around it, such as stolen keys, buggy smart contracts and compromised exchanges, and these have caused real losses.
What is blockchain actually used for?
Its clearest use is cryptocurrencies. People have also tried it for tracking goods, records and contracts. How well it beats ordinary databases in those areas is debated, and many pilot projects have been dropped.

Related topics

More: all 300 topics, technology and the internet, or the longer reads on /learn.

bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.