Unit 1 · Level 1 · What is a blockchain
Money before crypto
In autumn 2008, banks were collapsing and governments spent hundreds of billions bailing them out. On 31 October 2008, someone calling themselves Satoshi Nakamoto published a 9-page paper describing digital cash that needs no bank at all. Bitcoin's very first block, mined in January 2009, contains a newspaper headline: 'Chancellor on brink of second bailout for banks'. Satoshi chose that headline deliberately. It reads like a mission statement.
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What you get asked
What problem was Bitcoin designed to solve?
Before Bitcoin, every digital payment needed a trusted middleman (a bank or card network) to keep the books. Bitcoin's whole point was removing that requirement.
You email a photo to a friend, and now you BOTH have a copy. Why is copy-paste a disaster for digital money?
If digital coins were ordinary files, you could 'pay' two people with the same coin. This is the famous double-spend problem, the puzzle Bitcoin cracked.
Spending the same digital coin twice is called the ___ problem.
Banks solve double-spending with one central ledger they control. Bitcoin solved it with one public ledger that thousands of computers check together.
Match each kind of money to what keeps it honest
Every form of money needs something that stops cheating. Bitcoin's bet: replace the trusted institution with verifiable math.
In 2008, banks needed massive government bailouts. What was Bitcoin's radical answer to that?
You don't have to trust a promise if you can verify the math yourself. Hold that idea. The next lessons show exactly how the verifying works. 🐜
The rest of this unit
Blocks, consensus, and why any of this works without a boss.