As we know, the blocks are spreading through the network via gossiping. Due to the network latency or some other reason, is it possible that a node mining a block before it sync the latest block? namely it's not mining on the top of longest chain. and will this block be considered invalid?

1 Answer 1


Yes this is totally possible, and a real part of the logic integrated in node software. These blocks are called "uncle blocks" on Ethereum.

  • I read through some wiki and blogs. I may be wrong, my understanding is that "uncle blocks" is basically the same with "orphan blocks" but rewarded. namely "uncle blocks" is minded on top of the longest chain, but is mined out with less PoW at the similar time with the "accepted block". so "uncle block" is more about timing and simultaneousness. thoughts?
    – Bernie G
    Sep 18, 2018 at 21:06
  • Indeed the difference between uncle blocks and orphan blocks is just that you are rewarded for them. In terms of what they represent, they are the same, which is technically valid blocks on "lesser forks" of the main chain. The people who mined those blocks probably thought they were doing the right thing and making the "new longest chain", but as you mentioned in your question, these people were mistaken for latency reasons or something else, and the network will ultimately reject the chain and block coming from that node. Sep 18, 2018 at 21:11
  • Might be cool for you to check out this video: youtu.be/rpeceXY1QBM?t=263 Sep 18, 2018 at 21:16

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