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The blockchain trilemma — coined by Vitalik Buterin — states that a blockchain can optimise for at most two of three properties: decentralisation, security, and scalability. This lesson explores the techniques and architectures designed to push past this limitation.
Decentralisation
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Security -------- Scalability
| Property | Description |
|---|---|
| Decentralisation | Many independent nodes participate; no single point of control |
| Security | The network is resistant to attacks and data is immutable |
| Scalability | The network can handle a large number of transactions per second |
| Network | TPS (approximate) | Finality |
|---|---|---|
| Bitcoin | ~7 | ~60 minutes (6 confirmations) |
| Ethereum (L1) | ~15-30 | ~12 minutes (finality) |
| Visa | ~65,000 (peak capacity) | Seconds |
| Solana | ~4,000 (theoretical: 65,000) | ~0.4 seconds |
| Arbitrum (L2) | ~4,000 | Seconds (inherits Ethereum finality) |
Layer 2 (L2) solutions process transactions off the main chain (Layer 1) while inheriting its security:
Rollups execute transactions off-chain and post compressed data back to L1:
| Type | Description | Data on L1 | Fraud Handling |
|---|---|---|---|
| Optimistic Rollups | Assume transactions are valid; allow a challenge period | Transaction data | Fraud proofs (challengers can dispute within ~7 days) |
| ZK-Rollups | Generate a cryptographic proof that all transactions are valid | Validity proof + minimal data | Zero-knowledge proofs (mathematical guarantee) |
1. Users submit transactions to the L2 sequencer
2. Sequencer batches transactions and posts data to Ethereum L1
3. Transactions are assumed valid (optimistic)
4. 7-day challenge period: anyone can submit a fraud proof
5. If fraud is proven, the invalid batch is reverted
6. After the challenge period, transactions are final
| Optimistic Rollup | Description |
|---|---|
| Arbitrum | Largest optimistic rollup by TVL; Nitro architecture |
| Optimism | OP Stack framework; used by Coinbase (Base) |
| Base | Coinbase's L2 built on the OP Stack |
1. Users submit transactions to the L2 operator
2. Operator executes transactions and generates a ZK proof
3. The proof + compressed state diff is posted to Ethereum L1
4. L1 smart contract verifies the proof
5. Transactions are immediately final (no challenge period)
| ZK-Rollup | Description |
|---|---|
| zkSync Era | General-purpose ZK-rollup with EVM compatibility |
| StarkNet | Uses STARK proofs; custom language (Cairo) |
| Polygon zkEVM | EVM-equivalent ZK-rollup |
| Scroll | EVM-equivalent ZK-rollup |
| Linea | ConsenSys ZK-rollup |
| Feature | Optimistic Rollups | ZK-Rollups |
|---|---|---|
| Proof type | Fraud proofs (interactive) | Validity proofs (mathematical) |
| Withdrawal time | ~7 days (challenge period) | Minutes (proof verification) |
| Computation cost | Lower (no proof generation) | Higher (proof generation is expensive) |
| EVM compatibility | Full (EVM-equivalent) | Improving (some are EVM-equivalent now) |
| Maturity | More mature | Rapidly advancing |
State channels allow two or more parties to transact off-chain and only settle on-chain when necessary:
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