Public blockchains are secure and decentralized, but they are not fast. Bitcoin handles only a handful of transactions per second and Ethereum only a few dozen, so fees rise as soon as demand grows. This tension is known as the blockchain trilemma: it is hard to improve decentralization, security and scalability all at once.
You'll start with the trilemma itself, then look at Layer 2 solutions that move work off the main chain while still relying on its security. These include payment channels such as the Lightning Network, and optimistic and ZK rollups such as Arbitrum, Optimism and zkSync. The module finishes with cross-chain bridges, which let assets and data move between separate blockchains, and the security risks that come with them.
This is the final lesson module of the course. Once you've finished it, move on to Projects to apply everything you've learned.
Why decentralization, security and scalability pull against each other, and why most blockchains have to give up something to gain something else.
How payment channels move Bitcoin transactions off-chain, how multi-hop payments are routed, and what limits the Lightning Network.
How rollups execute transactions off-chain and post the data to Ethereum, and how fraud proofs (Optimism, Arbitrum) differ from validity proofs (zkSync, StarkNet).
How bridges connect separate blockchains by locking, minting and burning tokens, and why they are a common target for attacks.