Q: Why should the universe have been quantum-mechanical?He acts as if quantum mechanics is strange and complicated, and reality would be simpler if it were governed by classical mechanics.If you want, you can divide Q into two subquestions:

Q1: Why didn’t God just make the universe classical and be done with it? What would’ve been wrong with that choice?

Q2: Assuming classical physics wasn’t good enough for whatever reason, why this specific alternative? Why the complex-valued amplitudes? Why the unitary transformations? Why the Born rule? Why the tensor product?

I doubt it. Quantum mechanics allows for matter being composed of atoms, and being stable. I don't know how you get that in a classical theory. It also allows for human consciousness and free will. Again, I don't see how else you get that.

Scott explains:

Most importantly, people keep wanting to justify QM by reminding me about specific difficulties with the classical physics of the 19th century: for example, the ultraviolet catastrophe. To clarify, I never had any quarrel with the claim that,Here is an explanation of Wolfram's project:starting with 19th-century physics(especially electromagnetism), QM provided the only sensible completion.But, to say it one more time, what would’ve been wrong with a totally different starting point—let’s say, a classical cellular automaton? Sure, it wouldn’t lead to

ourphysics, but it would lead tosomephysics that was computationally universal and presumably able to support complex life (at least, until I see a good argument otherwise).Which brings me to Stephen Wolfram, who several commenters already brought up. As I’ve been saying since 2002 (!!), Wolfram’s entire program for physics is doomed, precisely because it starts out by ignoring quantum mechanics, to the point where it can’t even reproduce violations of the Bell inequality. Then, after he notices the problem, Wolfram grafts little bits and pieces of QM onto his classical CA-like picture in a wholly inadequate and unconvincing way, never actually going so far as to define a Hilbert space or the operators on it.

Even so, you could call me a “Wolframian” in the following limited sense, and in that sense only:

I view it as a central task for physics to explainwhyWolfram turns out to be wrong!

Wolfram’s framework is discrete, finite, and digital (based on a generalization of the cellular automata described in “A New Kind of Science”). Matter, energy, space, time, and quantum behavior emerge from underlying digital graphs. ...So in Wolfram's world, you have no free will, but you might be able to make decisions that others cannot predict because of computational complexity?Wolfram’s digital physics is fully deterministic, which seems to exclude free will.

But there is computational irreducibility: The strong unpredictability found in finite digital computations with simple evolution rules.

If you want to know what happens in the future of an irreducible digital computation, you must run the computation through all intermediate steps. There is no shortcut that permits predicting, with total certainty, what will happen in the future, without actually running the computation.

At this moment the question that I’m interested in is: Is computational irreducibility an “acceptable” replacement for free will?

Computer complexity is Scott's favorite subject, so I guess this has some appeal to him.