Vitalik: The future will be multi-chain, but I'm pessimistic about cross-chain applications
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Vitalik: The future will be multi-chain, but I'm pessimistic about cross-chain applications
Cross-chain activities have a negative network effect: although they occur infrequently and are relatively safe, the more frequently they happen, the greater the risk becomes.
Navigating Web3 tides with focused insightsAuthor: Vitalik
Translation: BitpushNews
Ethereum co-founder Vitalik Buterin (Vitalik) posted on Reddit Friday, stating that the future will be *multi-chain*, but not *cross-chain*, due to fundamental security limitations of bridges spanning multiple "sovereign zones".
Vitalik noted that cross-rollup applications within a single sovereign zone are still feasible, and this is not a limitation on the vision of "modular blockchains": you cannot simply choose a separate data layer and security layer—your data layer must also be your security layer.
Below are Vitalik’s detailed explanations:
The fundamental security limits of “bridges” are actually a key reason why, although I am optimistic about multi-chain blockchain ecosystems (there truly are independent communities with different values, and it's better for them to each have their own space than for everyone to fight over influence on the same chain), I remain pessimistic about cross-chain applications.
To understand why bridges face these limitations, we need to examine how various combinations of blockchains and bridging mechanisms survive 51% attacks. Many people think, “If a blockchain suffers a 51% attack, everything collapses, so we must prevent any 51% attack at all costs.” I strongly disagree with this mindset; in fact, even after a 51% attack, blockchains maintain many guarantees, and preserving these is crucial.
For example, suppose you hold 100 ETH on Ethereum, and Ethereum suffers a 51% attack, resulting in certain transactions being censored or reverted. Regardless of what happens, you still have your 100 ETH. Even a 51% attacker cannot take away your ETH because such a block would violate protocol rules and be rejected by the network. Even if 99% of the hash power or stake wanted to seize your ETH, every node operator would simply follow the remaining 1% of the chain, as only that 1% produces blocks adhering to protocol rules. Put simply, if you have an application on Ethereum, a 51% attack might censor or revert it temporarily, but eventually, state consistency will be preserved. If you had 100 ETH and sold it on Uniswap for 320,000 DAI, even under arbitrary extreme attacks on the blockchain, you would ultimately end up with a valid outcome—one where you either keep your 100 ETH or receive your 320,000 DAI. An outcome where neither happens (or, in some cases, both happen) violates protocol rules and thus won’t be accepted.
Now imagine what happens if you bridge 100 ETH via a Solana-based bridge to obtain 100 Solana-WETH, and then Ethereum suffers a 51% attack. The attacker deposits a large amount of their own ETH into the Solana-WETH system, then immediately reverts that transaction on the Ethereum side after confirmation on the Solana side. The Solana-WETH contract is now under-collateralized, and perhaps your 100 Solana-WETH is now worth only 60 ETH. Even a perfectly implemented ZK-SNARK-based bridge that fully verifies consensus remains vulnerable to theft via such a 51% attack.
Therefore, holding native assets on their home chains—Ethereum assets on Ethereum or Solana assets on Solana—is always safer than holding Ethereum assets on Solana or Solana assets on Ethereum. In this context, “Ethereum” refers not just to the base layer but also to any proper L2 built on top of it. If Ethereum suffers a 51% attack and reverts, Arbitrum and Optimism will revert as well, meaning that “cross-rollup” applications maintaining state across Arbitrum and Optimism remain consistent even after such an attack. If Ethereum does not suffer a 51% attack, there is no way to independently execute a 51% attack on Arbitrum or Optimism. Therefore, holding wrapped tokens issued on Optimism but held on Arbitrum remains completely secure.
The problem worsens when operating across more than two chains. With 100 chains, there will inevitably be numerous interdependencies among dApps, and a 51% attack on even one chain could trigger systemic contagion, threatening the entire ecosystem economically. This is why I believe interdependent zones are likely to align closely with sovereign zones (thus, many Ethereum ecosystem applications are tightly connected with each other, many Avalanche ecosystem applications are tightly connected among themselves, etc., but not so much between Ethereum and Avalanche ecosystem applications).
Incidentally, this is also why rollups cannot simply “use another data layer”. If a rollup stores its data on Celestia, BCH, or anywhere else, but settles assets on Ethereum, you’re compromised if that external layer suffers a 51% attack. The 51% attack resistance provided by DAS on Celestia doesn’t actually help you, because the Ethereum network doesn’t read that DAS—it reads bridge data, which remains vulnerable to 51% attacks. To be a rollup securely supporting applications using Ethereum-native assets, you must use Ethereum’s data layer (and similarly for any other ecosystem).
I certainly don’t expect these issues to materialize immediately. A 51% attack on even a single chain is difficult and costly. However, the more cross-chain bridges and applications are used, the more severe the problem becomes. No one would launch a 51% attack on Ethereum just to steal 100 Solana-WETH (or a 51% attack on Solana just to steal 100 Ethereum-WSOL). But if bridges hold 10 million ETH or SOL, the incentive to attack grows significantly, and large mining pools might well coordinate such an attack. Thus, cross-chain activity has negative network effects: while infrequent usage is relatively safe, the more it occurs, the greater the risk becomes.
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