A Simplified Guide to Bridges, Cross-chain, Omnichain & Multi-chain
First of all, These are all blockchain jargon.
Still getting confused, forget everything you thought you know & read this.
Before I deep dive into these terms, firstly, let's talk about blockchain interoperability.
Blockchain interoperability simply allows different standalone blockchains to actively communicate & interact with each other (can be to send messages, metadata & assets from one chain to the other).
The problem of blockchain interoperability led to the development of cross-chain technology, even before that Polkadot & Cosmos aimed at solving the blockchain interoperability which they're doing, but I won't focus on that.
So, we can simply achieve blockchain interoperability with cross-chain, which as the name implies simply means to move assets/metadata from one chain to the other without any intermediary.
On achieving Cross-chain interoperability in blockchains, it can be done through these 3 ways;
Sidechain: Sidechains are not layer 2 scaling solutions as they do not inherit the ETH security properties nor post state changes & transaction data back to the Ethereum mainnet unlike L2s.
They have their consensus algorithm but are connected to ETH mainnet by a two-way bridge.
However, they're EVM-Compatible. e.g Polygon, Skale e.t.c
Oracles: In regarding interoperability, they connect on-chain data - off-chain applications e.g Chainlink as they work across multiple blockchain platforms.
Bridges & Atomic Swap: Bridges are the most popular solutions to cross-chain which allows you to move assets from one chain to another, it simply works by lock & mint/burn model, locking assets on a source chain & minting the equivalent on the destination chain & to redeem, burning the asset on the destination chain & unlocking the asset on the source chain.
While atomic swap allows users to swap assets/exchange tokens from separate blockchains without any intermediary (like P2P trading of assets between two entities).
While Cross-chain interoperability is limited as it only solves half of the problem, In Ethereum Blockchain, It's limited to EVM Compatibility (including sidechains) but there have been some arguments on why the future will be multi-chain & not cross-chain.
Below attached is a post by Vitalik on his arguments for why it will be so, in which he hinted more in terms of security.
To solve these issues & break the barrier of cross-chain technology gives rise to a new form known as Omnichain.
Omnichain interoperability unlocks cross-chain composability by breaking the limitations of cross-chain making all blockchains interoperable and bringing together both EVM & Non-EVM compatible chains to build an interconnected Defi multi-chain ecosystem. Thanks to @Layerzero_labs who is already building the omnichain future.
Omnichain is the future of multi-chain (multiple blockchains) whereby all dapps, protocols & users on different standalone blockchains can seamlessly interact with each other in facilitating the growth of Crypto adoption & web3.