Why is scaling a problem?
Ethereum can process about 15-30 transactions per second (tps). Visa handles 24,000 tps. During periods of high activity, Ethereum gas fees can reach hundreds of dollars per transaction. Layer 2 solves this without compromising security.
How does Layer 2 work?
L2 protocols process transactions off Ethereum mainnet, then send a compressed "proof" or batch of transactions to L1. Users get fast and cheap transactions while inheriting Ethereum's security.
Optimistic Rollups
Arbitrum and Optimism are the largest Optimistic Rollup L2s. "Optimistic" means: transactions are assumed valid, but there's a 7-day challenge period. EVM compatible — the same Solidity code works as on Ethereum mainnet. Fees are 10-50x lower.
ZK-Rollups
zkSync Era and Starknet use Zero-Knowledge proofs — cryptographic proofs that verify transaction correctness without revealing the data itself. Finality is instant (no 7-day challenge period).
Bitcoin Lightning Network
Lightning is an L2 for Bitcoin. Users open "payment channels" between each other, conduct millions of small off-chain transactions, and publish the final balance to the Bitcoin blockchain. The result: instant, near-free BTC transactions.
Bridge risks
Moving funds between L1 and L2 is done through bridge protocols. Bridge hacks are among the largest in crypto history. Always use the platform's official bridge and double-check the URL.