What Is An Orphan Block?
An orphan block, also known as a stale block, is a valid block that is mined at almost the exact same time as another valid block which causes a short term split in the blockchainWhat Is The Blockchain? The blockchain is the public record of bitcoin transactions, which are organized into blocks that are all chronologically linked to one another. Because every block is.... Only one of the 2 chains will be built upon and the other will be dropped or “orphaned” and its transaction will revert back to the MemPoolWhat Is The MemPool? The MemPool, short for memory pool, is a short-term database of unconfirmed transactions that is kept by each node. Although the term "MemPool" is frequently used,... to await confirmation.
When two different miners produce blocks at roughly the same time, it’s possible that those blocks could be propagated to different parts of the network before the network learns about the other block – in this case, the bitcoin network will only recognize one of the blocks, and the other block becomes an “orphan” and all of the transactions in that block will revert back to the MemPool to be added to a later block.
When a block becomes orphaned, the miners who found that block will not receive the block reward for their valid proof of work and all of the transactions in that block simply are reverted back to the MemPool where they wait to be added to a later block.
The bitcoin protocol incentivizes bitcoin miners to work on extending the longest bitcoin blockchain as that is how they receive their rewards – through the Nakamoto consensusWhat Is Nakamoto Consensus? Nakamoto consensus is the mechanism that allows the bitcoin network to maintain an agreement on the state of the blockchain. It is named after Satoshi Nakamoto,..., the network of bitcoin miners agree to only propagate blocks that extend the longest chainWhat Is Nakamoto Consensus? Nakamoto consensus is the mechanism that allows the bitcoin network to maintain an agreement on the state of the blockchain. It is named after Satoshi Nakamoto,... and thus orphaned blocks are rejected and not added to the bitcoin blockchain.
There is also a financial incentive for bitcoin miners as well – if a bitcoin miner were to mine on top of an orphaned block, they would essentially be wasting their time and resources as their proof of workWhat Is Proof Of Work? Proof Of Work, often abbreviated as PoW, is both the method for achieving consensus across the entire Bitcoin network as well as a piece of... would not be included in the bitcoin blockchain.
The Nakamoto Consensus is designed to avoid orphaned blocks by strictly following the longest chain rule. Under this rule, bitcoin miners must always build on top of the longest chain of blocks.
As a result, any blocks that do not form part of the longest chain are automatically dropped by the network and revert back to the mempool. This ensures that every bitcoin miner is working on the same set of blocks, and prevents a chain split.