The term "rollup" sparks a lot of thoughts:
Is it the future? Optimistic or ZK rollups? What exactly are ZK and Optimistic rollups?
With ongoing narratives, optimistic rollups like Base are gaining traction, while ZK airdrops face skepticism, However, Vitalik Buterin still believes that ZK rollups are the future.
It's time to really understand rollups!

I've read over 100 pages to explain ZK rollups to you in under 500 words. Let’s dive in👇👇

What Are Rollups?
Rollups are layer 2 scaling solutions that bundle transactions into batches off-chain, compute the transactions, store the state, compress the data, and post a summary to the main L1 blockchain. Off-chain computation and bundling enable faster transactions at a lower cost.
This is a lot to digest, so let's break it down:

Layer 1 blockchains are inherently slower and more expensive due to the blockchain trilemma (decentralization ↔️ security ↔️ scalability). To scale L1s, we use L2 solutions like rollups.

Instead of processing everything on the L1 blockchain, rollups handle transactions off-chain and bundle them together. They perform the computation (it’s just some calculations about if the transactions are correct) and store the state (the order of transactions) off-chain. They then send a summary of the bundled transactions to the L1. Think of it like sending a bundle of letters to an address instead of sending each letter individually.

But, here arises a question-
How do we ensure that the bundled transaction data computed off-chain is correct? This is where Optimistic and ZK approaches come in to prove data validity.

Optimistic Rollups operate on the assumption that all submitted transaction bundles to the L1 are valid until proven otherwise (called fraud proofs). If a fraud proof is valid, it nullifies the faulty transaction and re-executes it to update the rollup’s state. If unchallenged during the dispute period, the transaction data are successfully added to the main chain. Optimistic rollups can process transactions quickly due to this optimistic assumption, but the dispute period can delay finality, sometimes up to a week.

ZK-Rollups, on the other hand, assume all the transactions to be invalid until a zero-knowledge proof is provided about the validity of the transactions. A zero-knowledge proof is a cryptographic proof that the transactions and the state are valid without revealing the transactions themselves. ZK-rollups only need to provide these proofs to finalize transactions on Ethereum, instead of posting all transaction data on-chain like optimistic rollups. Also, there are no delays when moving funds with ZK-rollups because they do not require a dispute period. ZK-rollups offer enhanced privacy and security through zero-knowledge proofs but are much more complex.

Conclusion:
Rollups are revolutionizing how we scale blockchains by enabling faster and cheaper transactions. Understanding the nuances between these two approaches helps us appreciate the advancements in blockchain technology and why rollups are considered the future of scaling solutions.