Difficulty Bomb
Introduction
In general terms, the Difficulty Bomb is a piece of blockchain code that adds to a Proof-of-Work (PoW) chain's difficulty level in predefined increments. It operates separately from a blockchain's difficulty retargeting mechanism, which increases or decreases the difficulty to mine a new block in response to the rate of new block creation to keep production times within a specified range. Instead, the Difficulty Bomb periodically increases the difficulty, thereby slowly reducing block production times, until it eventually "freezes" transactions (i.e., brings the chain to a halt). The result is the chain becomes unusable.
The Difficulty Bomb's origins lie within the creation of Ethereum. Co-Founder Vitalik Buterin and other early Ethereum contributors envisioned Ethereum transitioning from its current PoW stage to a new Proof-of-Stake (PoS) network with improved functionality (dubbed Ethereum 2.0) down the road. Ethereum developers embedded the Difficulty Bomb into the Ethereum codebase to act as a not-so-gentle reminder for users to switch to Ethereum 2.0 when the new network launched. The bomb also prevents users from continuing to use the original chain without executing a fork, which can be a time and resource-intensive process.
Ethereum core developers have since issued several delays to the Difficulty Bomb, also referred to as Ethereum's "Ice Age." The delays help Ethereum's research teams buy more time to build and deploy Ethereum 2.0, which remains in development. On the flip side, the need to address the Difficulty Bomb on a semi-regular basis led some Ethereum community members to question whether the bomb is more trouble than it's intended value. Opponents also believe the Difficulty Bomb’s purpose could be obsolete now that Ethereum 2.0 will launch a separate chain, not a direct upgrade to the original network. The Ice Age’s fate remains an open debate.
Suggested Reading
Behind the (Difficulty) Bomb: Breaking down Muir Glacier and the future of Ethereum's Ice Age
Ethereum Muir Glacier Upgrade by Pooja Ranjan (Ethereum Cat Herders)
Bump, Bump, Boom! by James Hancock
It's Not That Difficult by Thomas Jay Rush
EIP-2384: Difficulty Bomb Delay on Fellowship of Ethereum Magicians
Hard Fork to Address the Ice Age (EIP-2387) on Fellowship of EThereum Magicians
Difficulty Bomb musings on the All Core Devs Gitter channel
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