Professor Hewitt, I am a big fan of your work, but I am struggling a bit with understanding this claim from another article you wrote in CACM[0]:<p>> Actor message passing machines can perform computations that a no lambda expression, nondeterministic Turing Machine, Simula-67 program, or pure Logic Program can implement.<p>You go on to quote [Plotkin 1976], but I just can't connect the dots. I don't doubt that the Actor Model is a more powerful abstraction than a Turing Machine, but I do wonder if it isn't possible for a Turing Machine to simulate the Actor Model, and thereby achieve the same power of expression.<p>I also know I'm in way over my head with the math, but if it's possible for you to come up with a proof that an undergraduate/high-school student could follow, that would surely help out a lot!<p>[0]<a href="https://cacm.acm.org/blogs/blog-cacm/231495-what-turing-and-church-left-out/fulltext" rel="nofollow">https://cacm.acm.org/blogs/blog-cacm/231495-what-turing-and-...</a>