accompanied by kT ln2 of heat in Joules lost per bit. This is approximately 3 × 10-21 J at room temperature (300K). The opposite situation of storage of information then leads to the assertion that at least a free energy requirement in Joules of kT ln2 is needed to locally establish one bit of information on a substrate. Much discussion has appeared in the literature concerning these assertions. Some examples of the discussion of Landauer’s initial conjecture are in the works of Jarzynski (1997), Bennett (1973, 1982, 1989, 2003), Zuliani (2001), Scully et al. (2005), Esposito and van den Broeck (2011), and Sagawa (2014). Not all were entirely convinced that such a connection between information storage and the thermodynamics of the substrate really existed. But most accept that Bérut et al. (2012) finally verified experimentally that what is now known as Landauer’s principle is correct. This was done by using a 2μm diameter silica bead trapped at the focus of a laser beam in a double-well potential. The double-well is formed by focusing the laser alternately at two different positions with a high switching rate. By altering the level of the energy barrier between the two positions and using a piezoelectric motor, a tilting force is applied to the double-well, such that the bead can jump from one state to the other. The value 0 is assigned to one well and 1 to the other well. Calculating the amount of power used and measuring the time taken to achieve the successful erasure of state 0 to state 1, the amount of energy used can be measured (averaged over a number of experiments) and thus one can evaluate the mean dissipated heat used. This whole matter of information and its connection to the free energy levels of the substrate is linked to the “Maxwell’s demon” paradox raised by Maxwell (1857) concerning the thought experiment that he proposed. Supposing there was the possibility of an intelligence causing a separation of more excited molecules (that is hotter molecules) being separated from some less excited molecules (cooler), and thereby creating a heat difference between two sections of a container enclosing some gas. This then would mean that one could set up a heat engine enabling useful work to be done, and thus apparently breaking the second law of thermodynamics since disorganized thermal energy was being reversed into useful energy. Effectively the Landauer principle finally shows that such an ‘intelligence’ can only operate with at minimum a free energy cost in Joules of kT ln2 (and in reality, it will be a lot more than this in practice). What these recent findings have shown is that the principle of the second law of thermodynamics applies much more deeply than had at first been understood. The ubiquity and extent of the second law of thermodynamics has been extended to the situation of the presence of digital information. The paper by Boyd, Crutchfield, and Gu (2022, p. 2) has a very incisive introduction which we quote from here: The modern understanding of Maxwell’s demon no longer entertains violating the second law of thermodynamics. In point of fact, the second law’s primacy has been repeatedly affirmed in modern nonequilibrium theory and experiment. That said, what has emerged is that we now understand how intelligent (demon-like) physical processes can harvest thermal energy as useful work. They do this by exploiting Figure 2. Schematic of the experimental method used by Bérut et al. (2012) to prove Landauer’s principle. A silica bead is trapped at the focus of a laser beam in a double-well potential. The double-well is formed by focusing the laser alternately at two different positions with a high switching rate. By altering the level of the energy barrier between the two positions and tilting the potential double-well (both shown in the figure here), the bead can jump from one state to the other. MCINTOSH Language, codes, & interaction with thermodynamics 2023 ICC 319
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