The Basics of Bitcoins and Blockchains: An Introduction to Cryptocurrencies and the Technology that Powers Them

by Antony Lewis

Because Ethereum’s rate of block generation is much higher than Bitcoin’s (250 blocks per hour on Ethereum vs six blocks per hour on Bitcoin), the rate of ‘block clashes’ increases. Multiple valid blocks can get created at almost the same time, but only one of them can make it into the main chain. The other one ‘loses,’ and the data in them is not considered part of the main ledger, even if the transactions are technically valid. In Bitcoin, these non-mainchain blocks are called orphans, or orphaned blocks, and they do not form part of the main chain in any way and are never referenced again by any subsequent blocks. In Ethereum they are called uncles. Uncles can be referenced by a few of the subsequent blocks and although the data in them is not used, the slightly smaller reward for mining them is still valid.