What does it mean that information can’t disappear?

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If information doesn’t disappear, what happens to it when it’s carrier stops existing? For example, the hard drive is disintegrated or a brain decomposed. Does it return to being energy? If so, doesn’t it mean that it disappeared?

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Anonymous 0 Comments

This is the distinction between macrostate and microstate.

Under many classical laws of physics, the information about microstate never lost: there is a one-to-one correspondence between each microstates at one point in time and microstates at some specific future time. The correspondence is not many-to-one, that is it is impossible for different microstate to result in the same microstate in the future. (relatedly, the correspondence is not one-to-many, this is known as determinism, we don’t gain information over time either)

The information about macrostate could be lost by transforming into information about microstate. This is what happen when the hard drive get disintegrated. Basically, this is the distinction between information that is practically accessible, and information that theoretically exist in the system.

The additional information that cannot be practically recovered, but still exists in the system, in measured in term of **entropy**. Entropy cannot decrease, and only increase.

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