Lower block times are clearly desirable. Why does not Bitcoin reduce block creation times to 15 seconds just like Ethereum in this case? Because it would lead to too many forks. The main problem with forks is not the lack of rewards for stale blocks. It is the convergence time and wasted computation.

Let us suppose Bitcoin will reduce block creation times to 15 seconds and call it Bitcoin-15 for the sake of the discussion:

Is there a reason Ethereum does not have as many forks as Bitcoin-15 would? Or perhaps it does but the forks are not as harmful? For example, if the transactions from the uncle blocks had been merged with the transactions in the main branch, the computation would not have been wasted. However, the transactions from the uncle blocks are not merged. The fact that the miners of uncle blocks are rewarded does not solve the problem of wasted computation or convergence time.

2 Answers 2


A block discovery takes some time to propagate across the network due to network latency. That means a portion of the total hash power is always mining on the wrong block because they haven't heard the news. That portion increases with short block time targets. For example, if blocks take five seconds to propagate and block time is also five seconds, then possibly a majority of miners will be working on the wrong chain at all times. That would not be good.

Instead of just ignoring orphan blocks as bitcoin does, Ethereum captures the orphans as uncle blocks. Ethereum rewards them and reincorporates them into the canonical chain. Doing so negates the efficiency penalty of aiming for faster blocks. The hash power that was invested in discovering an uncle is reflected in the canonical chain.

Lower block times are generally desirable in their own right for performance, throughput and user-experience reasons.

Hope it helps.

  • Thanks for the information. But my main question is still remained unsolved. So, I have edited the question to make it clearer.
    – MHT
    Commented Nov 26, 2019 at 16:01
  • Both chains would have the same divergence/waste at faster block time, e.g. 15 seconds. Ethereum innovates in a way that recaptures what would be wasted, while Bitcoin does not. That is the what and the why. How related to the treatment of uncles. Commented Nov 26, 2019 at 19:05

I don't think that I'd say uncle blocks directly improve throughput. In Ethereum, the block time and gas limit combine are what defines the number of transactions that can be submitted to the network.

The idea of uncle blocks in ethereum also exist in bitcoin - generally called orphan blocks. Uncles / orphans are part of the reason you do not accept your transaction as final as soon as it is included in one block. On bitcoin generally you wait 6 blocks (1 hour) before you consider your transaction final. On ethereum 12 blocks (3 minutes). Waiting a certain amount of blocks gives you statistical confidence that your transaction is not in a chain that will be orphaned or uncled.

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