The probability of a miners to mine a block dynamically changes so that blocks are mined at regular intervals.How does block chains accomplish this without a central regulating body,
It is managed by the protocol using a formula (more info here : How is the Mining Difficulty calculated on Ethereum?). Difficulty is correlated to the total computing power (hashrate) provided by the miners. In Ethereum it is adjusted for every new block according to the time interval between the two previous blocks, the objective being 12 seconds.
In comparaison, blocks are mined on average every 10 minutes in Bitcoin, and the difficulty is adjusted every 2016 blocks, which represents approximately two weeks.