[aeternus]

The problem then becomes how do you determine the 'real' Ethereum. For Bitcoin, it is generally understood as the blockchain with the most proof of work.

With proof of stake, what's the disincentive to participate in all forks, or even a large number of alternate histories. If there are multiple Ethereum blockchains using PoS, how can I as a new user determine which one is 'the' Ethereum?

[feedjoelpie]

The one with the most utility (connected services, ability to spend, and other infrastructure).