Thread by @CelestiaOrg

Sovereignty and communication between chains 🧵

Blockchains that are sovereign have freedom to choose their preferred execution environment. A sovereign blockchain on Celestia has no restrictions imposed on it, giving it the ability to upgrade or fork if necessary.

Ultimately a sovereign chain can make changes in accordance with its own social consensus, independent of Celestia or any other chain.

As such, these blockchains on Celestia are flexible in design possibilities. They can be composable shared environments for many applications…

or single instance applications that don’t require composability with other applications. What Celestia’s shared security provides is that clusters of blockchains can be created which facilitates trust-minimized communication between them.

Communication within the same cluster, and between different clusters have distinct properties.

Intra-cluster: Can communicate between chains in the same cluster in a trust-minimized way.

Inter-cluster: Can communicate between chains in different clusters by relying on a third party to facilitate communication.

Inter-cluster bridging typically involves a third party, like a committee, to operate the bridge, which is common among current bridge designs.

IBC is also an example of inter-cluster bridging that doesn't require a third party.

It instead uses light clients to track the consensus of an opposite blockchain.

Once a block header has been verified as valid, the state is then checked to see if it is stored on the chain by verifying a proof, such as a Merkle proof.

This allows the two chains to communicate with an honest majority assumption of their existing validator sets, as opposed to introducing a third party.

An example of intra-cluster communication is the bridges that rollups use with their parent chain.

What makes them trust-minimized is that they are validating bridges, where they use either fraud or validity proofs.

While the security profile of trust-minimized bridges is optimal, only rollups are capable of such bridges. Other chains require stronger trust assumptions for bridging, like an honest majority assumption.

Ultimately, many blockchains on Celestia will be sovereign with the ability to communicate via mechanisms that are suitable to their own security and trust preferences.