In each epoch, validators are evenly distributed into slots and then subdivided into appropriately sized committees. A validator can only participate in one slot and one committee.
Original Source: The Beacon Chain Ethereum 2.0 Explainer You Need to Read First (ethos.dev)
Author: JosephC
Compiler: Xiang, W3.Hitchhiker
The engine was changed mid-flight! September 15, 2022, marked Ethereum’s transition to Proof-of-Stake (PoS).
That new engine is the Beacon Chain.
Now, let’s explore how it works.
The Ethereum Beacon Chain will be explained with clear examples, saving you time while providing a thorough understanding.
Slot and Epoch
The Beacon Chain serves as the heartbeat of Ethereum’s consensus.
- Each Slot lasts 12 seconds, during which a block is added.
- An Epoch consists of 32 slots (6.4 minutes).
Under optimal conditions, a new block is added every 12 seconds. Validators must synchronize their clocks.
A Slot may produce an empty block—Genesis Block was at Slot 0.
Validators and Attestations
In Proof-of-Work (PoW), miners dominate, but in Ethereum’s PoS, validators act as "virtual miners." They run Ethereum’s consensus mechanism.
- Proposer: A validator pseudo-randomly selected to build a block.
- Attesters: Validators voting on blocks via attestations (weighted by their stake).
Validators also monitor each other, earning rewards for reporting malicious behavior (e.g., double voting or proposing multiple blocks).
The Beacon Chain tracks:
- Validator addresses
- Validator statuses
- Attestations
- Activation/deactivation of validators
Staking Validators: Semantics
Validators are virtual and managed by stakers.
- Each validator requires 32 ETH to activate.
- A staker can stake any amount of ETH—each 32 ETH activates one validator.
Validators are executed via validator clients, which interact with Beacon Nodes (tracking the chain). One client can manage multiple validators.
Committees
A committee is a group of validators assigned to a slot.
- Minimum committee size: 128 validators (for security).
- Larger validator pools = multiple committees per slot.
Shuffling Algorithm:
- Validators are evenly distributed across slots per epoch.
- Committees are formed with balanced sizes.
This ensures:
- Resistance to attacks (probability of controlling ⅔ of a committee is negligible).
- Fair validator participation (each validator serves in one committee per epoch).
Beacon Chain Checkpoints
A checkpoint is the first block in an epoch. If no block is produced, the previous block becomes the checkpoint.
- Justification: A checkpoint gains ⅔ validator votes.
- Finalization: A checkpoint is finalized if the next epoch’s checkpoint is also justified.
Finality Timeline:
- Average: 14 minutes (2.5 epochs).
- Ideal case: Attestations are included by Slot 22 of the next epoch.
Attestations Deep Dive
An attestation includes:
- LMD GHOST Vote: For the current chain head.
- FFG Vote: For the epoch’s checkpoint.
Rewards & Penalties:
- Attester Rewards: Max rewards for timely, accurate votes.
- Penalties: For missed/inaccurate votes.
- Slashing: For malicious acts (e.g., double voting).
- Whistleblower Rewards: Reporting malicious validators.
Inactivity Leak:
- If finality stalls for >4 epochs, validators face escalating penalties until finality resumes.
Validator Lifecycle
- Activation: Stake 32 ETH in the deposit contract.
- Exit: Voluntary or forced (if balance < 16 ETH).
- Withdrawal: After 4 epochs (or 36 days if slashed).
Key Limits:
- Rate-limiting validator activations/exits prevents sudden systemic changes.
Conclusion
- FFG Voting: All validators vote to justify checkpoints.
- LMD GHOST Voting: Slot-assigned validators vote for the chain head.
Best Practices:
- Active, honest validators maximize rewards.
- Avoid slashing by never signing conflicting votes.
Since its launch (December 1, 2020), the Beacon Chain has grown to 400,000+ validators, securing Ethereum’s future.
FAQ
Q1: How often is a new block added to the Beacon Chain?
A1: Every 12 seconds (per Slot).
Q2: What’s the minimum ETH needed to become a validator?
A2: 32 ETH.
Q3: What happens if a validator goes offline?
A3: Penalties apply, scaling with downtime severity.
Q4: How are malicious validators punished?
A4: Via slashing (loss of stake) and forced exit.
Q5: Can a checkpoint be finalized instantly?
A5: No—it requires justification of the next checkpoint (2 epochs minimum).
Q6: What’s the "inactivity leak"?
A6: A penalty mechanism for prolonged finality stalls.
Reference: Ethereum PoS Consensus Specs.
Disclaimer: This content is for informational purposes only and does not constitute financial advice. Always comply with local regulations.