What happens if two miners solve the math problem at the same time
Introduction
When two miners solve the proof-of-work problem simultaneously, a temporary fork in the blockchain occurs. This situation, while rare, is an inherent part of Bitcoin’s design and is resolved through the following process:
Temporary Fork Creation
When two miners find valid blocks at nearly the same time, both blocks are broadcast to the network. Some nodes will receive one block first, while others will receive the other block first. This creates a temporary fork where two different versions of the blockchain exist simultaneously.
Network Propagation
Each miner will immediately broadcast their “winning” block to their neighboring nodes, which then propagate the block across the network. Due to network latency and geographical distribution of nodes, different parts of the network may temporarily recognize different blocks as the latest valid addition to the blockchain.
Block Acceptance
Nodes on the network will typically accept the first valid block they receive and temporarily reject any conflicting blocks. This means that for a short period, there will be two competing versions of the blockchain, each considered valid by different portions of the network.
Resolution Process
The resolution of this fork occurs through the following mechanisms:
Continued Mining: Miners will continue to work on the chain they view as the longest (or more precisely, the chain with the most accumulated proof-of-work).
Next Block Discovery: The fork is typically resolved when the next block is discovered. Whichever fork has a new block added to it first will become the longest chain.
Longest Chain Rule: As per the Bitcoin protocol, nodes will always switch to the longest valid chain. When one fork becomes longer, all nodes will switch to that chain, abandoning the shorter fork.
Orphaned Blocks
The block that ends up on the shorter chain becomes an “orphan” or “stale” block. The miner of this orphaned block loses the block reward and any transaction fees associated with it.
Transaction Handling
Transactions that were included in the orphaned block but not in the winning block are returned to the mempool to be included in future blocks. This ensures that valid transactions are not lost due to the temporary fork.
Conclusion
It’s worth noting that this process happens quickly, usually within minutes, and is a normal part of Bitcoin’s consensus mechanism. The system is designed to handle these occasional forks and quickly converge on a single, agreed-upon blockchain state.
