This question already has an answer here:
I wonder where "Smart Contracts" are actually running: Are they running on every node in the network? I rather doubt this, given the costs for running the contrat.
If my assumption is correct and the "Smart Contract" is only running on one single machine: How can the network ensure that the output of this Smart Contract is correct? Am I supposed to trust the machine that is running the Smart Contract?
Thanks for a quick reply.