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I read a lot of sites and answers about uncle blocks in Ethereum, but I did not get it. I am coming from Bitcoin, it is completeley new for me.

Can anyone explain me uncle blocks using a concrete example please? As far as I understood, uncle blocks are mined or put in blockchain for security reasons ?

marked as duplicate by Richard Horrocks, Achala Dissanayake, Raghav Sood, Ismael, eth Aug 17 '18 at 7:22

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Uncle blocks are similar to what would be "orphaned" blocks in BTC. Assume we are at block height n, and two different valid blocks B and B' are published around the same time.

Then WLOG assume block C is mined on top of B. Then C could also include B' as an uncle.

The miner of the uncle gets a reward, and the uncle contributes to the total weight of the chain. The uncle block itself is not included, only the header, and the uncle has no effect on the state of the chain, only the weight for consensus purposes.

This way, orphans still contribute to the security of the chain, which allows for faster block times (faster block times cause more orphans)

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