Natural phenomena as computing processes. The physical limits of computation

Maxwell proposed this problem in 1871 [3]. Since then many attempts have been made to refute the argument, and save the second law of thermodynamics. A detailed discussion is made by Bennett in Refs. [18,13,19], who also arrived to the final solution of the problem. It has to do with Landauer s result in order to configure a true thermodynamical cycle, every time the demon makes a measurement on the speed of a molecule, it has to forget the previous measurement. But, according to Landauer s result, erasing information expends energy and increases entropy. Therefore, the demon cannot cheat the second law of thermodynamics  

5 NATURAL PHENOMENA AS COMPUTING PROCESSES. THE PHYSICAL LIMITS OF COMPUTATION 

This view has been deepened by Seth Lloyd [21], who considers natural phenomena, not only as analog to computation, but as a result of computation itself According to this view, the entire universe can be seen as a computer running a very peculiar program the 

Suppose that at f = fo the spin is in the eigenstate t). Then, a magnetic field of amplitude S is applied along the x-direction. This field will interact with the magnetic moment according to the Hamiltonian 

The action of the field on the spin is to produce a torque that causes the spin to rotate about the field direction. Quantum mechanics tells us that the state evolution during an interval of time At is given by  

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Natural phenomena as computing processes. The physical limits of computation... 

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See also in sourсe #XX -- [ ]

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