Is the Universe a Quantum Computer?

 The idea that the Universe (whatever we may mean by this) is a some sort of a computer is a recurring theme. Recently, Nature published an article by David L. Chandler that is entitled Could the Universe be a giant quantum computer? This article is actually a tribute to Edward Fredkin, who passed away last June. The main contribution of Fredkin to the philosophy of science is his "digital philosophy" that advocates the idea that the universe is a computer and everything in our universe is discrete. I would not like to argue against the validity of these ideas (I have done so in Hypercomputation: Computing Beyond the Church-Turing Barrier and in Demystifying Computation: A Hands-On Introduction). However, I would like to point out that if the Universe is not a computing device, in general, then it cannot be a quantum computer, in particular. Also, what I did not like with Chandler's article is that it takes it for granted that the Universe is a computer. He did not even got in to the trouble to check whether there are people who object to this idea! So I guess it was a mistake that Nature published this article. 

PS Recently, Gregory Chaitin gave an interview to Godelian Letters. In this interview he was asked the following question:

You propose the hypothesis: “All is algorithm. God is a Programmer.” This hypothesis is sometimes used in favor of the argument that we live in a computer simulation. Some recent papers suggest that the chances that our universe is a pure simulation are 50–50. What do you think?

And he replied as follows:

I do not think that we live in a computer simulation, unless it is a simulation in the mind of God. A computer capable of simulating the universe would have to be bigger than the universe.

This means that a computer realizing the Universe has to be bigger than the Universe...