Understanding Ethereum Consensus: Is It Really Just Until the Next Block?
The world of blockchain and cryptocurrencies can be confusing, especially when it comes to consensus. In this article, we’ll delve into the concept of consensus in the context of Ethereum and explore whether there is a true agreement between nodes on the network or whether it’s just temporary until the next block.
What is consensus?
In a blockchain network, consensus refers to the process by which nodes agree on the state of the blockchain. This means that once a node has verified certain conditions, such as transaction validation and data consistency, it sends its findings back to the network. Receiving nodes then collaborate to update their copies of the blockchain, ensuring that everyone has an identical copy of the current state.
Ethereum Consensus Mechanism
Ethereum uses Proof of Work (PoW), a consensus algorithm developed by Vitalik Buterin. In PoW, nodes compete to solve complex mathematical puzzles that require significant computing power. The first node to solve the puzzle wins the right to verify transactions and create new blocks.
Scenario: Two Competing Blockchain Tips
Imagine two competing blockchain tips, each starting with block A as the parent block. The two tips are:
- Tip 1: “Block B is the correct state of affairs.”
- Tip 2: “Block C is the correct state.”
Both blocks start at block A and branch off into different branches, with both nodes agreeing on their respective versions of reality.
The First Few Blocks
In the first few blocks, we don’t know which tip is correct. Nodes are still working on verifying transactions and data consistency, but neither node has yet reached consensus. In fact, it is possible for a node to be in a state where it thinks block B or block C is valid, while another node thinks otherwise.
Next Block: Point of Agreement
When we reach block D (say), both nodes have reached a point where they agree on the state of the blockchain. They have verified all transactions and data consistency, and can now update their copies of the blockchain to reflect this agreement.
At this point, however, it is still possible that another block will arrive and challenge the current consensus. If such a block were to be broadcast, nodes would have to verify its validity before accepting it as part of the blockchain.
Next Few Blocks: Next Division
After block E (say again), both nodes again reach a point where they agree on the state of the blockchain. But now there is another branch that deviates from their agreement. In this case, the following block is:
- Hint 1: “Block F is the correct state.”
- Hint 2: “Block G is the correct state.”
Again, both nodes have reached a point where they agree on the state of the blockchain. However, it is now possible that another block will come along and challenge this new consensus.
Next few blocks: Another division
After block H (again), we see another divergence:
- Hint 1: “Block I is the correct state.”
- Hint 2: “Block J is the correct state of affairs.”
This process continues, with each node reaching an agreement on the state of the blockchain in subsequent blocks. However, it is possible that another block will come along and challenge this new consensus.
Conclusion
Finally, even though we have reached a point where both nodes agree on the state of the blockchain (block J), there is still no true consensus until the next block is broadcast. This is because each node independently reached an agreement at different points in time, and it may take several blocks for them to converge.
This phenomenon is known as a “blockchain fork,” where two or more competing versions of reality diverge from a single point.