Landauer's Principle - wikipedia.org  ## Metadata - Author: **wikipedia.org** - Full Title: Landauer's Principle - Category: #articles - URL: https://en.wikipedia.org/wiki/Landauer%27s_principle ## Highlights - **Landauer's principle** is a [physical principle](https://en.wikipedia.org/wiki/Principle#Principle_as_scientific_law) pertaining to the lower [theoretical](https://en.wikipedia.org/wiki/Theoretical_physics) limit of [energy consumption](https://en.wikipedia.org/wiki/Energy_conservation) of [computation](https://en.wikipedia.org/wiki/Computation). It holds that "any logically irreversible manipulation of [information](https://en.wikipedia.org/wiki/Information#As_a_property_in_physics), such as the erasure of a [bit](https://en.wikipedia.org/wiki/Bit) or the merging of two [computation](https://en.wikipedia.org/wiki/Computation) paths, must be accompanied by a corresponding [entropy](https://en.wikipedia.org/wiki/Entropy) increase in non-information-bearing [degrees of freedom](https://en.wikipedia.org/wiki/Degrees_of_freedom_(physics_and_chemistry)) of the information-processing apparatus or its environment". ([View Highlight](https://read.readwise.io/read/01jwafte1f9xetdfr6y3k3dcdr)) - Landauer's principle can be understood to be a simple [logical consequence](https://en.wikipedia.org/wiki/Logical_consequence) of the second law of thermodynamics, which states that the entropy of an [isolated system](https://en.wikipedia.org/wiki/Isolated_system) cannot decrease—together with the definition of [thermodynamic temperature](https://en.wikipedia.org/wiki/Thermodynamic_temperature). For, if the number of possible logical states of a computation were to decrease as the computation proceeded forward (logical irreversibility), this would constitute a forbidden decrease of entropy, unless the number of possible physical states corresponding to each logical state were to simultaneously increase by at least a compensating amount, so that the total number of possible physical states was no smaller than it was originally (i.e. total entropy has not decreased). Yet, an increase in the number of physical states corresponding to each logical state means that, for an observer who is keeping track of the physical states of the system but not the logical states, the number of possible physical states has increased; in other words, entropy has increased from the point of view of this observer. The maximum entropy of a bounded physical system is finite. (If the [holographic principle](https://en.wikipedia.org/wiki/Holographic_principle) is correct, then physical systems with finite [surface area](https://en.wikipedia.org/wiki/Surface_area) have a finite maximum entropy; but regardless of the truth of the holographic principle, [quantum field theory](https://en.wikipedia.org/wiki/Quantum_field_theory) dictates that the entropy of systems with finite radius and energy is finite due to the [Bekenstein bound](https://en.wikipedia.org/wiki/Bekenstein_bound).) To avoid reaching this maximum over the course of an extended computation, entropy must eventually be expelled to an outside environment. ([View Highlight](https://read.readwise.io/read/01jwag87try656fqfyep7wm2kj))