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**The Universe Is A Computer**

By Philip Ball

Nature.com

6-6-2

- What, then, is the Universe computing? "Its own dynamical evolution", says Physicist Seth Lloyd. As the computation proceeds, reality unfolds.
- We are all living inside a gigantic computer. No, not The Matrix: the Universe.
- Seth Lloyd, a physicist at the Massachusetts Institute of Technology in Cambridge, has estimated how much information the Universe can contain, and how many calculations it has performed since the Big Bang1.
- Lloyd views every process, every change that takes place in the Universe, as a kind of computation. One way of looking at the exercise is to imagine setting up a simulation of the Universe, particle for particle, on a hypothetical super-duper computer.
- To simulate the Universe in every detail since time began, the computer would have to have 1090 bits - binary digits, or devices capable of storing a 1 or a 0 - and it would have to perform 10120 manipulations of those bits. Unfortunately there are probably only around 1080 elementary particles in the Universe.
- Computer science
- Just as clocks were the favourite analogy for complex systems during the age of Newton, now scientists like to compare everything to computers. DNA is sometimes described as digital, and the human brain, consciousness and life itself are discussed as though they all involve computation. So is Lloyd taking it all too far, depicting the Universe as a computer?
- Perhaps; but Lloyd has a reputation as a challenging lateral thinker, especially in information theory. Two years ago he calculated the physical limits to computation: the constraints that physical laws place on the power of, say, a laptop-sized computer2. Now he's just doing the same for a Universe-sized computer.
- The Universe is computing its own dynamical evolution Seth Lloyd, Massachusetts Institute of Technology
- The concept of physics as a computational process was articulated by the US physicist John Archibald Wheeler in the phrase "It from Bit". And complexity guru Stephen Wolfram suggests in his recent book A New Kind of Science3 that all of reality might result from a kind of algorithm, like a computer program, being enacted again and again on the underlying building blocks of space and matter.
- We tend to associate computation with problem-solving, whereas it isn't clear that there is any 'problem' for the Universe to solve. But the connection between information science and physical processes appears once we think about events on the quantum scale.
- Quantum switch
- Every fundamental particle has a discrete number of different quantum states available to it. If a particle moves from one quantum state to another, this is rather like switching a bit in a computer from one state (say, 1) to another (say, 0).
- "If one regards the Universe as performing a computation", says Lloyd, "most of the elementary operations in that computation consist of protons, neutrons, electrons and photons moving from place to place and interacting with each other according to the basic laws of physics."
- What, then, is the Universe computing? "Its own dynamical evolution", says Lloyd. As the computation proceeds, reality unfolds.
- He estimated the maximum number of logical operations the Universe has performed by calculating its total energy with Einstein's E = mc2. The energy of any physical system determines how fast it can switch from one quantum state to another - how fast it can compute.
- References
- * Lloyd, S.Computational capacity of the Universe. Physical Review Letters, 88, 237901, (2002). * Lloyd, S.Ultimate physical limits to computation. Nature, 406, 1047 - 1054, (200o). * Wolfram, S. A New Kind of Science. (Wolfram Media, (2002).
- © Nature News Service / Macmillan Magazines Ltd
2002 http://www.nature.com/nsu/020527/020527-16.html

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