EDGE: Could it be that the universe is a computational device?
DAVIES: It's interesting to look back through history on this one. Each age has its pinnacle of technology, and each age uses that technology as a metaphor for nature, for the universe. In ancient Greece, the technological marvels were musical instruments and the ruler and compass. The Greek philosophers tried to build an entire cosmology from number, harmony, proportion, form, and so on from mathematics, basically. Remember the music of the spheres? The Pythagoreans believed that nature was a manifestation of rational mathematics. Later on the pinnacle of technology was the clockwork. Newton wanted a clockwork universe, the entire universe as a gigantic clockwork mechanism, with all the parts interlocking and ticking over with infinite precision. Then in the 19th century along came steam power, and the universe was then depicted as an enormous heat engine, or thermodynamic machine, running down toward its heat death. Today the computer is the pinnacle of technology, so it's now fashionable to talk about nature as a computational process. All of these ways of describing the world capture to a certain extent the way it is, but I would say that the universe is a universe, not merely a clockwork or a computer or whatever.
EDGE: Isn't your heart a pump? Isn't your brain a computer? Don't you clear your RAM by taking a long run, or getting some sleep?
DAVIES: The helpful way of thinking about the universe is in terms of information processing. Just think of the solar system, of the planets are going around the sun; if we write down the positions and motions of all the planets today then that can be considered as some input information for an algorithmic process. We can let the solar system run and then measure those quantities again next week; that's the output information. You could say that the solar system has mapped the input into the output, which is a computational process. You could look at the whole of nature like that. What impresses me is that if you look at the subatomic level, or the quantum level, what you find is that the information processing power of nature goes up exponentially. The information can attach to the amplitude of the wave function, rather than the probability. It is much greater because it involves interference effects and phase information. If you can maintain quantum coherence, the amount of information you can process is staggeringly bigger than with classical material objects.
The computers that we have on our desks are classical computers, they compute using ordinary on-off type switches. The quantum computer can be in superpositions of on and off states, so if you have a whole collection of switches then the number of possible combinations goes up exponentially. If you can keep quantum conference, you can compute with enormous power. Now why has nature got that? Why do we live in a universe that has the capability of processing such a huge amount of information at the subatomic level? Of course, that's not a scientific question, it's a philosophical question. But I've a sneaking feeling I know the answer, which is that it plays a crucial role in the origin of life, and possibly in the nature of consciousness too. I'm less sure about the consciousness.
Life is a clear example of where nature is a computational process, because the living cell is not some sort of magic matter, but an information replicating and processing system of enormous power. If you consider the structure and operation of the living cell, it is a very particular and peculiar state of matter, a very odd combination of molecules, which you wouldn't expect to create if you just shuffle them around at random. How did nature discover life? How did matter go from a disorganized jumble of molecules into something so special and so specific as a living organism? You can regard this question as a type of search problem, requiring a search algorithm. Imagine a network of possible chemical reactions in some primordial pre-biotic soup. It constitutes a vast decision tree; every time a chemical reaction occurs there's a new branch on that decision tree. Over time one is dealing with an almost infinitely complex tree, with some tiny little twiglets on the tree representing this very special and peculiar thing we call life. The rest is chemical junk.
How does nature find such a weird state amid the oceans of junk? The answer could be quantum computation. Quantum computation would enable one to search enormous databases with extraordinary efficiency. So if nature somehow harnessed the power of information processing at the subatomic level, it could be that this is how life began: a quantum search of the chemical decision tree, with life being 'the winner.' To be sure, that's a rather speculative hypothesis. But I come back to this question, why does nature need all that computational power? Why can't we live in a universe that just processes information in the classical way? Maybe the answer is because we couldn't live in such a universe, because life itself depends on precisely that enormous computational power. But that's a quasi-religious statement, that's not a scientific statement.
To finish where we started, I was amused to see that in Timeline Michael Crichton makes use of the ideas of quantum computation as a way to travel backward in time. Basically, quantum spacetime foam provides a labyrinth of tiny wormholes through which (at least in the story) the time traveller's atoms can be squeezed one by one. This could be a much better method of time travel than harnessing a single giant wormhole. So maybe there is link between life, quantum information processing and time travel? That would be something!