What are the Orphaned Blocks?
Sep 12, 2014

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There are plenty of people out there who are upset at the amount of computing power and electricity that is currently going into Bitcoin mining, and these people would likely be even more upset after learning about the intricacies of orphaned blocks. Although the first person to find a particular block’s hash is the individual who gets to take home the block reward and have their proof of work placed in the blockchain forever, the reality is that these blocks are sometimes found at nearly the same time by multiple parties. There can be only one winner in the lottery known as Bitcoin mining, so one of these winners will find out that they will not actually receive a block reward if their new entry into the blockchain was not used by the next block’s miner.

The Blocks are Not the Orphans

One of the main reasons that orphaned blocks are a confusing topic of conversation for even some of the experienced Bitcoin miners is that the terminology is a bit off. After all, orphaned blocks are not actually orphans because they do have parents in the form of the previous blocks in the chain. The part of the blocks that are actually orphaned are the payouts. It is likely that this incorrect terminology began due to the fact that these “stale blocks” are referred to as orphaned blocks in the Bitcoin reference client. It’s actually possible for an orphan block to also have children of their own.

How Often Do Orphaned Blocks Appear?

Although orphan block can be quite a headache for miners, they actually occur more often than most Bitcoin enthusiasts would like to admit. Blockchain.info keeps track of all the orphaned blocks that appear on the network, and there is usually 1-3 of these mishaps every single day of the week. There is a new block mined roughly every ten minutes, which means there are 144 block rewards available to miners every day. This also means a little over 1% of the blocks that are mined every day are orphaned.

Orphaned Blocks and 51% Attacks

In addition to situations where two or more miners have found a block at roughly the same point in time, orphaned blocks can also pop up in attack situations. The infamous 51% attack is one of the few flaws of the Bitcoin blockchain where an attacker can use their majority share of the network hashrate to create their own version of the blockchain. The longest chain is the most important factor when it comes to which block is going to be viewed as valid by the Bitcoin network, but a miner who owns 51% of the network is able to work on their own blockchain at a faster rate than everyone else. In other words, an attacker could create their own chain of orphaned blocks in order to take control of the Bitcoin ledger. If someone is able to centralize power over Bitcoin’s history of events, then they also have the power to double-spend their bitcoins and block others from using the network.