Ethereum Metropolis Hardfork – Will It Delay the Difficulty Bomb?

The difficulty bomb is a part of the consensus algorithm; its goal is to make the difficulty of mining a block arbitrarily hard at some point in the future. When active, it will get increasingly hard for miners to create new blocks and therefore will get block rewards less frequently; which means less revenues. Exponentially. From the blog:

starting from block 200,000 (very roughly 17 days from now), the difficulty will undergo an exponential increase which will only become noticeable in about a year.

This is a very strong incentive to rapidly switch to the new network.

From https://github.com/ethereum/EIPs/blob/master/EIPS/eip-2.md:

Mining difficulty is calculated from the time difference between blocks. The exact formula will change in Homestead. The symbol // in the following denotes integer division.

• Frontier:

block_diff = parent_diff + parent_diff // 2048 * (1 if block_timestamp - parent_timestamp < 13 else -1) + int(2**((block.number // 100000) - 2))

• Homestead:

block_diff = parent_diff + parent_diff // 2048 * max(1 - (block_timestamp - parent_timestamp) // 10, -99) + int(2**((block.number // 100000) - 2))

EDIT:

The problem with the frontier formula and the reason for the change was that the frontier version doesn't take into account how far off from 13 seconds the block time was. A block mined 1 second after the previous one has the same effect on the difficulty as one mined after 12 seconds. This causes block difficulty to adjust to a median block time rather than a mean.

Again, check out the EIP for more details.