What Is Proof of Work? How Bitcoin Agrees on the Truth

Proof of work is the method Bitcoin uses to decide who gets to add the next page to its shared record. Computers around the world race to solve a pointless but very hard puzzle, and the first to find an answer publishes the next block of transactions and collects the reward. The answer is trivial for everyone else to check, which is the clever part: the work is expensive to do and free to verify.

What is the puzzle actually for?

It turns electricity into a queue. Without it, anyone could claim to have the correct version of history, and thousands of computers would have no way to choose between them. With it, the version of history that counts is simply the one with the most work piled behind it. Think of a raffle where tickets cannot be bought, only earned by burning fuel. Bitcoin's rules also adjust the difficulty roughly every two weeks, so however many machines join or leave, a new block still arrives about every ten minutes.

Why does this make Bitcoin hard to attack?

Because rewriting an old transaction means redoing its block and every block built on top of it, faster than the rest of the world is building new ones. Once a payment is a few blocks deep, that becomes wildly expensive — you would need to out-spend the entire mining industry, in real electricity, in real time. That cost is the security. It is also why people wait for a handful of confirmations before treating a large payment as final.

What does the miner get?

Newly issued coins plus the fees in the block. The new-coin part halves roughly every four years and currently stands at 3.125 BTC per block, on the way to zero once all 21 million exist. Our guide to how mining works covers the machines themselves.

The honest criticism of proof of work is its energy use, and it is the reason Ethereum abandoned mining in 2022 in favour of staking. Bitcoin kept it, on the argument that a real-world cost is exactly what makes the record hard to fake. If you want to see it happening, open any block explorer and watch new blocks land in real time.