You have N players == N computers to simulate. Assign randomly 5 computers to each player to emulate. Choose the result that majority of clients return and optionally punish cheaters.
EDIT: apparently simulation will go on even when players log out, so each connected client may need to simulate 100 in-game computers to account for that. Still less resource intensive than running everything on the server. But Notch thought about that much longer and surely have great reasons for his architecture.
Letting the clients handle the simulation would have a lot of problems for a MMO. Extra problems if you were doing the work for other players as well.
I think part of the point of it being a special emulated CPU set at a certain speed is to make it fair for each player, rather than the player having more processing power just because they have a better computer.
The easiest way to secure all that is to run it on the server. Anything going to the client or trusted coming from the client eventually gets hacked if there's much interest in doing so.
You could make the client run other player's CPUs, perhaps ones from accounts on a different server. If it's not someone you know or are playing with, then there's less incentive to cheat. You could even pass the same work to multiple clients and flag those that are tampering with the results.
You have N players == N computers to simulate. Assign randomly 5 computers to each player to emulate. Choose the result that majority of clients return and optionally punish cheaters.
EDIT: apparently simulation will go on even when players log out, so each connected client may need to simulate 100 in-game computers to account for that. Still less resource intensive than running everything on the server. But Notch thought about that much longer and surely have great reasons for his architecture.