For a long long time, I was very sympathetic towards the point of view that the universe is one gigantic digital computer. This point of view has been championed by many people, including Ed Fredkin and Stephen Wolfram. Seth Lloyd has recently writen a book in which he updates this point of view, taking the point of view that that the universe is one gigantic quantum computer. One of the essential reasons for believing this sort of things is that computers (classical or quantum) can be used to simulate the physics of the universe. Of course there are all sorts of issues with this idea, for example, the simulations are invariably done up to a certain fixed accuracy. So while you can certainly do the simulaton on a quantum computer, as the physics becomes more and more accurate, you will need to believe that the computer doing the simulation is larger and larger. There is nothing intrinsicaly wrong with this notion, and indeed it may be that at its bare base there is a final discrete unit, but until such a unit shoes up in experiment, the hypothesis seems to me indistinguishable from not believe that the universe is a quantum computer. But this isn’t why I’ve become more skeptical of the universe as a computer point of view.
The reason I’ve become more skeptical is that I do not believe in computers. Er, well, at least I do not believe in digital perfectly working computers, nor do I believe in exact perfectly working quantum computers. When we dig down into the bowls of our computers we find that in their most basic form, these computers are made up of parts which are noisy or have uncertainties arising from quantum theory. Our digital computers (like the coming quantum computers) are emergent phenomena, and, further, it seems that in this emergence, nothing resembling absolutely perfect fault-tolerant computation is possible. Fault-tolerance can only be achieved over a certain time horizon (in both classical, where we currently have very very low error rates, and in quantum, where we are struggling to get the emergence to give us very low error rates.) Now of course, one can always work with the model of a perfect computer (neglecting a meta-level of thinking about what “working” means in terms of you, who are also a computer.) But if you do this, you must admit that you are talking about an entity that does not exists, as far as we known, in our universe. So somehow we are supposed to be comfortable in looking at the universe as a perfect computer, when such objects don’t exist in our universe? This makes me feel uncomfortable.
So I guess this makes me the anti-Wolfram, not subscribing to the view of our universe as a computer. Does this mean that I think that computation or information theory doesn’t have anything to say about physics? Actually, the answer is no. I’m just unconfortable with a naive translation of what it means for the universe to be a computer where everything is perfect and error free. Somehow I think the real answer must, somehow, be much deeper.