Orphan Block

An orphan block, more precisely called a stale block in many Bitcoin contexts, is a valid block that is not included in the chain with the most accumulated work. These blocks can occur naturally when miners find competing blocks at nearly the same time.

Orphan blocks occur when two miners produce blocks at similar times or when an attacker attempts to reverse a transaction. The network will only adopt one branch, and the block that is not selected becomes an orphan block. Networks with faster block times, like Bitcoin Cash with its 10-minute target, experience orphan blocks as a regular part of operation. The probability increases during network congestion or when there are propagation delays between mining nodes.

Miners of an orphan block lose the block reward and the transaction fees they would have earned. It's as if their work never happened, even though the block they solved is just as valid as any other block. In some blockchain implementations like Bitcoin Cash, orphaned blocks might still receive partial compensation through protocols like GHOST (Greedy Heaviest Observed Subtree), which acknowledges the security contribution of orphaned blocks to the network.

The probability of creating an orphan block is reduced by having a good connection to the Bitcoin network, as this ensures that you hear about blocks first. Mining pools help reduce orphan rates for individual miners by combining resources. Bitcoin Cash's improved block propagation techniques and more consistent block times help reduce the orphan rate compared to some other networks, making mining operations more predictable and efficient.