There’s been a great deal of confusion in regard to Ethereum’s new approach to Casper. Part of the confusion stems from the updated timeline for Ethereum’s PoS (proof of stake). And the other part of the confusion stems from this new “Beacon Chain” thingy.  Yes, I said ‘thingy’.

So, in this post I’m going to try to break things down in an easy manner for you guys. What exactly is the Beacon chain? And what role does it play in Proof Of Stake and Sharding

As usual, I’ll keep it simple – and avoid the unnecessary details.

Before we go any further, allow me to break down the structure of Ethereum’s Casper V2.  There will be three chains that we are concerned with:

1. The Ethereum PoW Chain
2. The Beacon Chain
3. The Sharding Chain(s).

All three of which will be linked together in Casper V2.

This is the chain that Ethereum is currently using. It’s using the traditional Proof Of Work (PoW) consensus method. In Ethereum’s Proof Of Work chain, miners currently validate blocks by running the PoW Cryptographic Puzzle.

However, Ethereum will be using Proof Of Stake in Casper. Miners will have to transition to the Proof of Stake chain if they want to keep validating blocks for the Ethereum Network.  To do so, they will have to deposit 32 Ether into the Beacon Chain. Once they do that, they will become Validators on the Beacon Chain.

Important:  Miners are not the only ones who can become validators. Anyone can deposit 32 Ether from the Ethereum PoW Chain to the Beacon chain to become a validator

Alright, so the Beacon Chain is where all the confusion stems from. But it’s actually quite simple. The Beacon Chain serves two primary roles

1. The main Proof Of Stake chain

2. The base layer of the Sharding solution

   
   

To Simplify: The Beacon Chain will link to the Shard Chains and “signal” which blocks from the Shards should be added onto the main chain. The main chain will be validated & finalized using Proof Of Stake. The main chain also resides on the Beacon Chain. The Beacon Chain will also play a crucial role with the Shard Chains. It links up to the Shard Chains to listen for blocks that will be included onto the beacon chain (the PoS chain).

Yes, there are going to be multiple Shard Chains. Remember, Sharding is an attempt to avoid having “every single node validate every single transaction”. This will allow for more scalability.  In order to do so, instead of having one single chain, we will have multiple shard chains. I explain Sharding in more detail in this article: Ethereum Sharding Explained Using An Analogy.

Essentially, you can think of the Shard Chain as a group/block of multiple chains. All the transactions will take place on these Shard Chains – and will be split between each shard.  The account data will also be stored on these shard chains.

Above, I mentioned the Beacon Chain links up to a Shard. Well, there’s also a link from the Shards to the Beacon chain. This link needs to be attested/signed-off by a sub-group of Validators that will be pseudo-randomly picked.
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Casper will be using Proof Of Stake which does not require “mining” to validate blocks. If a miner wants to continue validating blocks on Casper, he will have to deposit 32 Ether into the Beacon Chain like everybody else.

Once 32 Ether is deposited, the person will go into the “Queued Validator” pool and eventually get added to the “Active Validator” pool. Active Validators will be responsible for producing blocks, sign off on blocks and sign off on links (to shards).

You may be wondering why the Ethereum team chose the term “Beacon Chain?”.  The Beacon Chain was originally only part of the Sharding spec. It’s role was (and still is)  to link up to Shard Chains and signal which blocks should be added to the main chain. 

The Validators utilize the crosslinks between the two chains to “listen” for new blocks on the shard chains. They then sign off on the block and the crosslink if it is to be included on the main chain.

Beacon essentially means “Lighthouse/signal” – and that’s precisely what the role that the Beacon Chain serves.

Disclaimer: I’m sort of taking an educated-guess at this one. To be honest, a lot of the terminology in Sharding & Casper PoS is sorta...confusing (e.g: proposer, collator, validator, committee...come on Vitalik!)

As you can see, the Beacon Chain in the new Casper implementation isn't all that complicated. All you need to know is that it will serve as the foundation for the Proof Of Stake and facilitate the communication via the Shard Chains (via cross-links).  You can become a Validator on the Beacon Chain if you deposit 32 Ether from the current PoW Chain. Once you do that, you can take part in the Proof Of Stake consensus process as well. Validation & Finality  will take place on the Beacon Chain. Transactions & Account Data will be on the Shard Chain.

Simple, eh? Tbh, maybe all you need to read is the conclusion of this post. Damn. Oh well.

Follow up Reads:
1. Casper Roadmap Update Explained
2. ​Ethereum Sharding - A Simple Analogy
3. Finality: Understanding Settlement & Finality