What are Uncle Blocks?
What is an uncle block?
Imagine Ethereum as a worldwide group chat where everyone is trying to add the next message (block) at the same time. Only one message can become the official next one. Sometimes two miners create a valid block at almost the same moment.
Both blocks are valid. Only one gets added to the official chain. The other block becomes an uncle block.
Why do uncle blocks happen?
Ethereum nodes are spread all over the world. When one miner finds a block, it takes a short time for that block to reach the rest of the network. During this short delay, another miner might also find a valid block.
Now the network has two valid candidates for the next block. Eventually the network settles on one. The block that is not chosen becomes an uncle.
## Why are uncle blocks rewarded?
The miner who created the uncle block still performed real work and produced a valid block. It simply arrived a little too late. Ethereum gives a partial reward to encourage decentralization and to avoid punishing miners who are physically far from large mining pools.
Do uncle blocks matter?
Yes. Even though they do not become part of the main chain, uncle blocks help the network in several ways:
- They reduce wasted mining work
- They make mining more fair for smaller or slower miners
- They increase network security
- They give miners an incentive to include uncle references in future blocks
Summary
An uncle block is a valid block that lost a timing race. It was correct. It was just a little too slow to reach the network.##
