What Is a Cryptocurrency
Mining doesn't make coins. It makes history expensive to rewrite.
The new bitcoin are the incentive that pays for the work. The work itself decides who writes the next block — and puts every transaction into an order that cannot be quietly changed afterwards.
The problem
Find a fingerprint you cannot aim at.
A candidate block gets a digital fingerprint — a hash. Only a fingerprint that meets the target counts as a solution. There is no way to work backwards to one. You change a number, look, and change it again.
The hash lottery
ILLUSTRATIVE MODELThe strings below are stand-ins, not real hashes, and the target here is set absurdly easy so the search finishes while you watch. Real mining runs the same rule at a scale this page cannot show, so no figure on this card is a real-world figure.
Press Start hashing. Nothing here is clever — it is a machine guessing.
There was no shortcut, because none exists. The only method is to change one number in the block — the nonce — recompute the fingerprint, and look again. That is why the attempts pile up, and it is why the finished block counts as evidence: a valid fingerprint could not have been produced any other way than by making the attempts. Hence the name — proof-of-work.
Finding it was expensive. Checking it cost a single step, and that asymmetry is what makes the system open: anyone may try, and nobody can fake having tried. It also sets up the half people skip — a miner only proposes a block. The nodes re-check the transactions and the proof-of-work condition and accept or reject it, and a block that breaks the rules is discarded no matter how much power went into it. The same arithmetic protects old history: every later block's work sits on top of the one below, so altering an old transaction means redoing all the proof-of-work that came after it and out-pacing the honest network while you do.
The definition
Three things people get wrong about mining.
Tap each card for what is actually going on.
Hands on
Add machines. Watch the rhythm refuse to move.
Difficulty is the dial the rules turn on their own. Drag the power and see what it absorbs.
Difficulty, doing its job
ILLUSTRATIVE MODELUnitless index numbers relative to a starting level — not real hash rates, not real difficulty values, not real energy figures. The shape of the response is the point.
The energy those machines draw is not a stray by-product to be tidied away later. It is the thing an attacker would have to out-spend, which is why it is described as part of the security model rather than an accident of it. That is a deliberate trade-off — and it is exactly the trade-off the next lesson's model declines to make.
The bridge
How a block actually comes into being.
Four phases, running worldwide at the same time — and a fifth line explaining why the finished chain is hard to touch.
Collect → race → check → reward. New bitcoin plus the transaction fees are the incentive to put computing power in; ordering and securing is what that power buys. A completely different answer to the same problem — capital at risk instead of energy spent — is what the next lesson takes apart: validators.
Check yourself
Five questions.
Answers come straight from this lesson. Submitting completes it.