The meaning of information loss
Ralf Landauer demonstrated that if an operation is information reversible, that is, in a logic gate the output can be inferred from the input and the input can be inferred from the output (see earlier Quantum Physcis #2) , then because information is not destroyed no heat is emitted from the device. If a system doesn’t lose information then it doesn’t interact with the environment. Systems, when they are quantum do not exchange energy with environment, that is, they do not release information. This is the same as saying that they are not “measured” by the environment. In the early days of modern quantum physics (if you get my meaning), it was inferred that measurement required the presence of a human or a human made device. This of course isn’t true. Whether humans are present or not doesn’t matter. To briefly explore this issue more I want to give a few paragraphs on the meaning of information.
Seth Lloyd of MIT notes: “all physical systems are computers: rocks process information: every electron, photon, elementary particle stores bits of data. Every time two particles interact the bits are transformed, physical existence and information contents are inextricably linked”.
The way to convert a container full of steam into one of ice is allow the container to lose heat. By doing so it loses information. A container of ice is a much simpler system than one of steam. David Deutsch of Oxford University says that an information rich system is one that would require a much bigger computer program to simulate, than an information poor system. If I was asked to program a computer to precisely simulate the contents of the container, the water present as ice would a much simpler system and hence would require a much shorter program to simulate it than the same container and the same water in the form of steam. The information difference has been lost as heat, just as Ralf Landauer’s principle identified.
Profoundly, Sean Carrol of Caltech, defines information in the following way: “processing information allows us to extract useful work from a system in ways that would have otherwise been impossible”. As a thermodynamicist, this hits the bullseye for me.
If you agree with the above argument then hold tight (can you wait?- OK maybe you can) for the next installment. If you agree or disagree with the line of thought so far, it would be great to hear from you. Establishing these ground rules, I can progress onto more controversial issues.