Foundations of Blockchain Technology

Ethereum's transition to Proof of Stake with "The Merge" represents a fundamental shift from energy-intensive mining to capital-based security. The system operates on a slot-based timeline where each 12-second slot should produce one block, and 32 slots compose an epoch. Validators are randomly selected to propose blocks based on their effective stake weight, using RANDAO (a verifiable random number generator) to ensure fair selection. During each slot, validators not selected as proposers participate as attesters, submitting votes that indicate their view of the canonical chain head. These attestations are weighted by the validator's stake, creating an economic signal that guides fork choice. The LMD-GHOST (Latest Message Driven Greedy Heaviest Observed Sub-Tree) fork choice rule selects the chain head with the greatest accumulated validator support. Casper FFG provides finality by requiring validators to vote on epoch boundaries as checkpoints. When 2/3 of validators agree on a checkpoint, it becomes finalized and cannot be reverted without slashing a large portion of the validator set. This dual mechanism provides both liveness (through slot-based proposals) and safety (through checkpoint finality), making the network resilient to both network partitions and malicious validators.