Vitalik argues: There will be a multi-chain future, but not a cross-chain future.

L1 public blockchains are flourishing, and Ethereum's battle with fees and speed has nurtured other emerging ecosystems. This has also strengthened people's confidence in the current and future coexistence of multiple chains.

Ethereum co-founder Vitalik Buterin commented on the 8th, stating that he believes in a multi-chain future, but not a cross-chain one. Source

Optimistic about Multi-Chain, Pessimistic about Cross-Chain

Vitalik believes there are fundamental security limitations with cross-chain bridges that are the key reason for his skepticism. He thinks to understand these limitations, one must assess whether a combination of multiple blockchains and cross-chain bridges can withstand a 51% attack. He stated, "Many people think, 'If a blockchain is attacked by 51%, everything will collapse, so we must do everything to prevent a 51% attack from happening even once.'" Vitalik said, "I really disagree with this way of thinking; in fact, even after a 51% attack, the blockchain still retains many guarantees, which is very important."

For example, Vitalik explained that if you have 100 ETH on Ethereum and Ethereum is subject to a 51% attack, some transactions may be scrutinized or rolled back. However, you still have your 100 ETH. Even if a 51% attacker wants to take away your ETH, they cannot produce a block that takes your ETH because such a block would violate protocol rules and be rejected by the network. Even if 99% of the computational power or stake wants to take your ETH, every person operating a node will follow the chain operated by the remaining 1% because only its blocks comply with the rules.

In a more practical example, if you have an application on Ethereum and a 51% attack occurs, there may be scrutiny or rollback for a period, but the end result will be consistent. So, if you have 100 ETH and sell it for 320,000 DAI on Uniswap, regardless of a severe attack on the blockchain, you will still end up with two known outcomes: either you have 100 ETH or 320,000 DAI. If any result is due to a violation of protocol rules, you won't get it, or you may get both results. Note: Due to the occurrence of a hard fork.

Using Solana as an Example to Discuss Cross-Chain Limitations

Vitalik shifted the discourse to cross-chain scenarios. He mentioned that if you move 100 ETH to a cross-chain bridge on Solana and receive 100 Solana versions of WETH (wrapped-ETH), what would happen if Ethereum experiences a 51% attack?

Vitalik believes that an attacker could deposit a pile of their ETH into the Solana version of WETH, then confirm it on Solana, and immediately roll back the transaction on Ethereum. Consequently, the Solana version of WETH contract would no longer be fully reserved, and your 100 Solana-WETH might only be worth 60 ETH.

Vitalik stated that even with a perfect ZK-SNARK-based cross-chain bridge that can fully verify consensus, it is still vulnerable to such theft from a 51% attack.

For this reason, Vitalik believes holding native assets on individual chains is the safest approach.

In this scenario, Ethereum refers not only to the base chain but also to the Layer 2 solutions built on top of it. If Ethereum experiences a 51% attack and transaction rollbacks, Arbitrum and Optimism will also experience rollbacks, ensuring consistency with the Ethereum base chain. Moreover, if Ethereum is not attacked by 51%, attacking Arbitrum and Optimism separately is not possible, making the wrapped assets on top secure.

Issues Arising from Multi-Chain Cross-Chain

Vitalik believes that the aforementioned problems worsen when there are more than two chains. If there are 100 chains, many interdependent applications will emerge between these chains. Once an attack occurs, it will lead to systemic propagation, threatening the entire ecosystem. Vitalik thinks the reason for the likelihood of interdependent regions being closely linked to sovereign regions is that applications in the Ethereum universe interact closely with each other, as do applications in the Avax universe, but the Ethereum universe and Avax universe should not be closely intertwined.

Therefore, he emphasized that rollups should not easily access another data layer but should only use the Ethereum data layer to avoid confusion at the bridging end. Vitalik mentioned that if the data of a roll-up is stored in Celestia or BCH, while the assets are still on Ethereum, when a 51% attack occurs, even if the DAS on Celestia can resist a 51% attack, it still needs vulnerable cross-chain bridges for reading.

He concluded by stating that these issues will not arise immediately. Although a 51% attack, even on a single chain, is difficult and expensive, the more cross-chain bridges and applications are used, the more severe the issues become. No one would execute a 51% attack on Ethereum just to steal 100 Solana-WETH, or attack Solana just to steal 100 Ethereum-WSOL. However, if there are 10 million ETH or SOL in cross-chain bridges, the incentive to attack increases, and large mining pools may collaborate effectively in such attacks. Hence, cross-chain activities exhibit anti-network effects: while infrequent occurrences are relatively safe, as the frequency increases, so does the risk.