When anyone can join a network, letting everyone propose the next transaction block creates confusion. Proof of work turns that proposal right into a computational race: participants search for a valid hash, and the first successful miner proposes the next block. section 12.1.3 section 12.2.2
Bitcoin’s proof-of-work process follows a few practical steps:
- Assemble transactions and the hash of the preceding block into a candidate block. section 12.2.2
- Change the block’s nonce, repeatedly or randomly, until its digest satisfies the difficulty condition, such as beginning with a required number of zeros. section 12.2.2
- Publish the valid block; the successful miner earns the right to decide the next transaction set and receives a reward and transaction fees. section 12.5
- If competing valid blocks create a fork, continue the chain containing the greatest amount of accumulated work. section 12.2.3
A toy blockchain
Imagine each block in a small interactive blockchain carrying its parent’s digest and a nonce. The nonce is adjusted until the digest starts with four zeros. Editing an earlier block changes its digest, breaks the next block’s reference, and exposes the modification.
Proof of work makes creating influence costly: adding more accounts does not provide the same advantage as adding hardware that computes more hashes. Difficulty adjusts when blocks arrive too quickly or slowly; Bitcoin targets roughly one block every ten minutes. The tradeoff is substantial electricity consumption compared with consensus approaches that do not rely on proof of work. section 12.2.3 section 12.3.5
