The longest chain is the chain with the largest number of blocks that represent the complete transaction history of the blockchain network. It is a key element of distributed ledgers, where a consistent sequence of data is maintained by the network participants.

This principle ensures the integrity of the blockchain and prevents duplicate data. The network relies on consensus to ensure that only one true chain is considered relevant.

How is the Longest Chain Formed?

The longest chain is created through consensus, a process that allows the network nodes to agree on a single version of the registry. In the case of the Bitcoin network, a Proof-of-Work mechanism is used, where miners solve complex math problems to add new blocks to the chain.

Sometimes branching, or forks, can occur if two miners simultaneously find a block to add to the chain. In this case, the network temporarily accepts both branches until a new block is added to continue one of the branches. The world's largest chain becomes dominant, and the second branch is considered obsolete.

Records for Long Chains

The "longest" chain is the one with the most work. A chain's work is equal to the expected number of hashes it would take for someone to replicate a chain of the same number of blocks and the exact same difficulty steps.

Currently, each block adds about 266 work to the chain because it takes on average ~266 hashes to solve a block with the current difficulty. Blocks with less difficulty add less work. However, two blocks in the same difficulty period always add the same amount of work to the chain. A block with a lower hash is not considered better than one with a higher hash.(bitcoin.stackexchange.com)

Examples of Long Chains

Bitcoin and Ethereum are examples of blockchains with long chains. Each time a miner successfully adds a block, the chain grows. In Bitcoin, miners are rewarded for their efforts, creating an incentive to continue working on the longest chain.

How Often Do Chain Conflicts Occur?

Chain rearrangements are rare, but their likelihood depends on the speed of mining and delays in the propagation of blocks through the network. For example, on the Bitcoin network, such conflicts are resolved within minutes.

What are Forks?

A fork occurs when a blockchain splits into two separate paths. This can happen if two miners find a block at almost the same time. Each of these blocks creates a temporary split in the chain.

Forks can be either soft or hard. A soft fork is backward-compatible, meaning old nodes still accept new blocks. A hard fork, however, creates a completely new version of the blockchain. It is not compatible with older nodes.

Why Do Forks Occur?

Forks primarily occur due to two reasons: network latency and software updates. Network latency can cause blocks to be received at different times, leading to a split.

What Happens to Transactions from Obsolete Blocks?

When a block becomes obsolete due to circuit reorganization, its data is no longer validated by the network. However, transactions from that block are not lost: they are returned to the mempool and wait to be reinserted into a new block.

What Are the Risks Associated with Chain Realignments?

Chain rebuilds are usually limited to a few blocks, but there are risks involved:

• Loss of confidence in transaction confirmations.
• The possibility of attacks, such as the 51% attack, where an attacker controls a large portion of the computing power.
• Prolonged reconfiguration can disrupt the system, especially in networks with less decentralization.

Effectiveness and relevance of the concept

Comparison between the chain selection rules of the longest chain and GHOST

The longest chain principle plays a critical role in the security and resilience of the blockchain. Through it, it achieves:

• Consistency of data in a decentralized network.
• Resistance to manipulation.
• Effective prevention of double-spending.

This principle not only builds trust in blockchains but also provides a foundation for their further development.