Miners race to find a number that, hashed with the block's contents, produces a result below a target. Finding it is pure trial and error and takes enormous computation; verifying it takes one hash. That asymmetry is the whole design — the work is costly to produce and trivial to check, so the network can confirm a block was expensive to create without repeating the expense.
Security follows from the cost. Rewriting history means redoing that work faster than the rest of the network produces new blocks, which for a large chain requires more hardware and electricity than the attack could plausibly return. The difficulty target adjusts as hash rate joins or leaves, keeping the interval between blocks steady, and the energy consumption this implies is the mechanism's central criticism.
Why does proof of work use so much electricity?
The energy is the security. Because the cost of attacking the chain equals the cost of out-computing it, lowering the electricity spent would lower the cost of rewriting history in the same proportion.
Last updated October 17, 2026