POS under Casper require validators to stake a portion of their Ethers to start validating blocks. This means when they discover a block which they think can be added to the chain, they will validate it by placing a bet on it. If the block gets appended, then the validators will get a reward proportionate to their bets. However, if a validator acts maliciously and tries to do a “nothing at stake,” they will immediately be reprimanded, and their entire stake will be slashed.
Casper is designed to work in a trustless and excessively complicated system. Anyone who acts in a spiteful manner will get immediately punished by having their stake slashed off. This is where it differs from most other POS protocols. Spiteful elements have something to lose so it is impossible for there to be nothing at stake.
Casper and Proof Of Stake implementing are flawless and it might be critical if Ethereum plans to scale up.
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