Crypto glossary
Difficulty bomb
The difficulty bomb was code that made Ethereum mining exponentially harder over time, forcing regular upgrades and the move to proof of stake.
The difficulty bomb was a term added to Ethereum's mining difficulty formula from the network's early days. On top of the normal adjustment, it added an extra amount that doubled at regular block intervals, so block times would eventually stretch from seconds to minutes and the chain would slowly freeze, a scenario nicknamed the ice age.
Its purpose was political as much as technical: it gave core developers a deadline that forced regular hard forks and made it costly for miners to keep running an old proof-of-work chain once Ethereum moved to proof of stake. Several upgrades, including Byzantium, Constantinople, Muir Glacier, Arrow Glacier and Gray Glacier, did little more than push the bomb back.
Since the Merge in September 2022, Ethereum blocks are proposed by validators and there is no mining difficulty left to inflate, so the bomb no longer has any effect on mainnet. Forks that kept proof of work, such as Ethereum Classic or EthereumPoW, removed or defused it in their own code.
Example
Before the Gray Glacier upgrade in mid-2022, average block times on Ethereum were creeping upward because of the bomb, and developers delayed it once more to give the Merge time to ship.