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Computing Study Refutes Famous Claim that 'information Is Physical'

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Maxwell's Demon erasing information.

A new study shows that, theoretically, information can be erased without using any energy at all.

Credit: Joan A Vaccaro et al./Royal Society

A quote often attributed to Einstein reads: "Everybody knows that some things are simply impossible until somebody who doesn't know that makes them possible."

In 1961, Ralph Landauer at IBM published a work suggesting that information, usually considered a purely mathematical quantity, played a role in physics (IBM Journal Of Research And Development, Vol. 5, no. 3, 1961). Specifically, Landauer aimed at identifying the minimum energy required to do computation using standard thermodynamics. Landauer initially focused on a specific operation, today know as "Landauer reset," which consists of putting into a given logic state (e.g. "0" state) a binary switch that can be in each of the two possible logic states "0" or "1." Such an operation is sometimes interpreted as "information erasure," because it reduces the amount of information that can be associated with the binary switch. Before the operation, two possible states exist; after, there is only one possible state.

According to thermodynamics, such a reduction in the number of available states for a physical device requires a minimum energy expenditure, easily computable using previous work done by Boltzmann.

In the same paper, Landauer generalized this result associated with the reset operation to the cases in which there was a decrease of information between the input and the output of a computing system. This is the case of the so-called logically irreversible devices. Landauer wrote:

"We shall call a device logically irreversible if the output of a device does not uniquely define the inputs. We believe that devices exhibiting logical irreversibility are essential to computing. Logical irreversibility, we believe, in turn implies physical irreversibility, and the latter is accompanied by dissipative effects."


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