Presentation on D. Lairez

The principles of neopositivism and the laws of thermodynamics

Mon, 01 Jun 2026 00:00:00 +0000

The second law of thermodynamics, which deals with irreversibility and makes the theory so special, is usually considered empirical. The definition of equilibrium as an attractor, on the other hand, requires a postulate. This article shows that both are actually already contained, even if hidden, in the fundamental principles of neopositivism, which are widely accepted in all fields of science. In particular, from the definition of information as a truth that can only come from an observation but cannot be redundant, we obtain Clausius’ inequality.

The principles of neopositivism and the laws of thermodynamics

Mon, 01 Jun 2026 00:00:00 +0000

Activity 2025 of the association for popular education 'Les Petits Débrouillards de Bourgogne-Franche-Comté'

Thu, 28 May 2026 00:00:00 +0000

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Disentangling Brillouin's negentropy law of information and Landauer's law on data erasure

Mon, 01 Dec 2025 00:00:00 +0000

The link between information and energy introduces the observer and his knowledge into the understanding of a fundamental quantity of physics. Two approaches compete to account for this link, Brillouin’s negentropy law of information and Landauer’s law on data erasure, which are often confused. The first, based on the Clausius’ inequality and Shannon’s mathematical results is very robust, while the second, based on the simple idea that information needs a material embodiment (data-bits) is today perceived as more physical and prevails.

Disentangling Brillouin's negentropy law of information and Landauer's law on data erasure

Mon, 01 Dec 2025 00:00:00 +0000

Energy and information: a chronicle of hesitations on the role of the observer in physics

Sun, 12 Oct 2025 00:00:00 +0000

Energy is a fundamental concept in physics which, since its origins in the 19th century with thermodynamics, has been intimately linked to the observer and the information he has. But this connection conflicts with the Plato’s and Descartes’ dualism of body and mind, which leads us to hope to access, by the mean of reason, to the intrinsic properties of things. This dualism is traditionally opposed by the materialist monism of Aristotle and Epicurus: everything is only matter and our knowledge of the world can only come from its observation. But how then can we justify the use of logic? Unexpectedly, this age-old debate continues uninterrupted to this day. Its chronicle shows us the clash and alternating influence of these two conceptions of the object of science, which have driven its progress.

Energy and information: a chronicle of hesitations on the role of the observer in physics

Sun, 25 May 2025 00:00:00 +0000

Energy has no definition, except that given by a conservation principle which essentially amounts to defining it as the elements of an open list of unknown cardinality. Entropy, identified by Shannon as information we lack, has too many definitions. This results in an unstable and hesitant interpretation of their link.

Thermodynamics, the science of changes in form of energy, is phenomenological, all its laws are induced from observation. From the origin, the concept of energy is linked to the observer’s knowledge, to the information he has: what and where to look and with what instruments. Thermodynamics only addresses the sensible world. It is Aristotelian. But this is disturbing if we consider that reason can give us access to Plato’s intelligible world, the one that is beyond the sensible world and independent of us. This is disturbing if we consider that science can access to the intrinsic properties of things, those which are independent of us. This is disturbing if we have a purely Platonic conception of science. Hence the statistical mechanics approach (“The rational foundation of thermodynamics”, J.W. Gibbs). This is the first pendulum movement of ideas, whose oscillations continue to this day, because unfortunately statistical mechanics introduces many inconsistencies, mainly due to the ergodic hypothesis. Luckily, these inconsistencies are all solved by Shannon’s information theory. Sadly, information theory is too Aristotelian and too conceptual. Fortunately, Landauer principle makes it more \textquote{physical}. This is currently the latest attempt to bringing the notions of energy and information back to what is considered the right side of science, that of Plato. Landauer principle is now commonly regarded as a fundamental law of physics. Unpleasantly, it can be shown that this principle is not one.

Ionic current through nano-channels

Tue, 04 Feb 2025 00:00:00 +0000

Membranes (natural or artificial) are ubiquitous. They ensure compartmentalization, in living organisms at all scales (nucleus, mitochondria, cell, organ, organism), but also in all artificial electrochemical devices (batteries, power cells). Basically, the role of this compartmentalization is to slow down the chemical reactions between constituents of each compartment. But these chemical reactions are nevertheless necessary for the device to operate. A membrane plays thus a double and contradictory role : it must separate, but not too much. For this, membranes are generally equipped with pores (holes with length and diameter of the same order of magnitude) or channels (length much greater than diameter) allowing the transport of ions or molecules from one compartment to the other. We are interested to these latter.

The fundamental difference between Boolean logic and thermodynamic irreversibilities, or, why Landauer's result cannot be a physical principle

Fri, 29 Nov 2024 00:00:00 +0000

Landauer’s “principle” claims that erasing one bit of information necessarily dissipates at least Tln2 of heat into the surroundings, making a possibly logically irreversible Boolean operation also thermodynamically irreversible. It is commonly accepted that this result is a fundamental principle of physics that definitively establishes the link between information and energy. Here, we show that this result cannot be general. In fact it comes (1) from a confusion between logical and thermodynamic irreversibilities and between logical and thermodynamic states, which is reminiscent of the classic Gibbs paradox about the joining of two volumes of the same gas, and (2) from two unnecessary constraints imposed on the erase procedure. Clarifying these points permits us to dissociate the two irreversibilities; to invalidate Landauer’s result as being a general physical principle; and to open the door to hardware implementations allowing erasure to follow a thermodynamically reversible, or at least quasistatic, path.

What is science?

Tue, 08 Oct 2024 00:00:00 +0000

Science is experiencing disenchantment. It disappoints, it worries, it annoys. Above all, it is misunderstood. But science is like wine, it can be tasted, horizontally and vertically. When tasted, it turns out to be the oldest collective project, which should attract and seduce everyone. But to be appreciated, tasting requires an initiation. We must understand the object of science. We must also understand how it is constructed using concepts that are often arbitrary, conventional and always likely to evolve or be abandoned. We must understand that in science, truths are always provisional and therefore that we can be wrong while having been right to do so. We must be able to distinguish a scientific statement from another that is not. We must know how to appreciate why one theory is better than another…

Thermostatistics, information, subjectivity, why is this association so disturbing?

Sat, 11 May 2024 00:00:00 +0000

Although information theory resolves inconsistencies (known under the form of famous enigmas) of the traditional approach of thermostatistics, its place in the corresponding literature is not what it deserves. This is interpreted as being mainly due to epistemological rather than scientific reasons: the subjectivity introduced into physics is perceived as a problem. This paper attempts to expose and clarify where exactly this subjectivity lies: in the representation of the reality and in probabilistic inference. Two aspects which have been integrated into the practice of science for a long time and which should no longer frighten anyone, but which become explicit with information theory.

On the supposed mass of entropy and that of information

Mon, 15 Apr 2024 00:00:00 +0000

In the theory of special relativity, energy can be found in two forms: kinetic energy and rest mass. Potential energy of a body is actually stored under the form of rest mass, interaction energy too, temperature is not. Information acquired about a dynamical system can be potentially used to extract useful work from it. Hence the “mass-energy-information equivalence principle” that has been recently proposed.

In this paper, it is first recalled that for a thermodynamic system made of non interacting entities at constant temperature, the internal energy is also constant. So that, the energy involved in a variation of entropy (T ΔS) differs from a change in potential energy stored or released and cannot be associated to a corresponding variation of mass of the system, even if it is expressed in term of quantity of information. This debate gives us the opportunity to deepen the notion of entropy seen as a quantity of information, to highlight the difference between logical irreversibility (a state dependent property) and thermodynamical irreversibility (a path dependent property) and to return to the nature of the link between energy and information that is dynamical.

Thermodynamical versus logical irreversibility : a concrete objection to Landauer's principle

Tue, 01 Aug 2023 00:00:00 +0000

Landauer’s principle states that the logical irreversibility of an operation, such as erasing one bit, whatever its physical implementation, necessarily implies its thermodynamical irreversibility.

In this paper, a very simple counterexample of physical implementation (that uses a two-to-one relation between logic and thermodynamic states) is given that allows to erase one bit in a thermodynamical quasistatic manner (i.e. that may tend to be reversible if slowed down enough).

Two-to-one implementation of a bit inspired by my practice of bicycles: the two bit-values correspond to one single thermodynamic state. Erasing the bit (setting it to 0) is necessarily thermodynamically reversible.

Measuring Zeta potential of nanochannels wall

Sat, 01 Jul 2023 00:00:00 +0000

In the study of the transport properties of electrolytes through nanochannels , surface effects become very important. One of them concerns the interactions due to electrostatic charges that may be present on the surface of the channels-wall. Being able to measure the electrical potential that these charges produce at a distance from the wall (namely the Zeta potential of the wall) is often crucial for the understanding and improvement of membranes properties.

Plea for the use of the exact Stirling formula in statistical mechanics

Fri, 17 Feb 2023 00:00:00 +0000

In statistical mechanics, the generally called Stirling approximation for N! is actually an approximation of Stirling’s formula. In this article, it is shown that the term that is dropped is in fact the one that takes fluctuations into account. The use of the Stirling’s exact formula forces us to reintroduce them into the already proposed solutions of well-know puzzles such as the extensivity paradox or the Gibbs’ paradox of joining two volumes of identical gas. This amendment clearly results in a gain in consistency and rigor of these solutions.

A short derivation of Boltzmann distribution and Gibbs entropy formula from the fundamental postulate

Fri, 03 Feb 2023 00:00:00 +0000

Introducing the Boltzmann distribution very early in a statistical thermodynamics course (in the spirit of Feynmann) has many didactic advantages, in particular that of easily deriving the Gibbs entropy formula. In this note, a short derivation is proposed from the fundamental postulate of statistical mechanics and basics calculations accessible to undergraduate students.

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What entropy really is : the contribution of information theory

Fri, 21 Oct 2022 00:00:00 +0000

Even today, the concept of entropy is perceived by many as quite obscure. The main difficulty is analyzed as being fundamentally due to the subjectivity and anthropocentrism of the concept that prevent us to have a sufficient distance to embrace it. However, it is pointed out that the lack of coherence of certain presentations or certain preconceived ideas do not help. They are of three kinds : 1. axiomatic thermodynamics; 2. inconsistent solutions of certain paradoxes; 3. reluctance of physicists to the simplification provided by information theory. The purpose of this paper is to examine these points in a didactic way by paying attention to the structure of the theory, what are the foundations, how ideas articulate, with a peculiar focus on their consistency and economy. It is shown how entropy can be introduced in a more consistent and economical manner with the help of information theory, which from the start takes into account its subjective nature, finally allowing a more intuitive understanding.

Modeling the equilibrium shape of adsorbed vesicles of lipid bilayers

Fri, 01 May 2020 00:00:00 +0000

Lipid bilayers are often taken as experimental models for biological membranes. In many cases, the investigation of their biochemical properties, such as their chemical affinity for one or the other conpound, is carried out either on adsorbed vesicles or on bilayers supported by solid subtrates. For these studies, neutron reflectivity is an exceptional tool (see for instance the impresive list of experiments in this field that have been done on MARIA neutron reflectometer ). However, with neutron reflectivity the data analysis (in jargon “data fitting”) is really a tricky problem. Reducing the number of free parameters is crucial. In the case of adsorbed vesicles this can be done by modeling the equilibrium shape that they adopt depending on some physical parameters (rigidity, adsorption constant, size etc.).

Neutron scattering

Wed, 01 Apr 2020 00:00:00 +0000

Neutron scattering techniques are privileged tools to probe soft matter. This is mainly due to their strong interaction with protons (H¹) which differs widely from that with deuteriums (H²), allowing the labelling of organic molecules.

These techniques are not the only ones I have used and developped for my own experimental researches . But in parallel to these from 1993 to 2019, it was a part of my job at Laboratoire Léon Brillouin (the french neutron research facility ) to host scientists from all over the world to perfom their experiments on the small angle scattering spectrometer PACE and latter on the time-of-flight reflectometer HERMES and to guarantee the quality of the measurements they made there.

Biological membranes and peptide pores

Thu, 31 Jan 2013 00:00:00 +0000

The interaction of cell membranes with the molecules adsorbed on their surface and the way in which the incorporation of these molecules takes place is still poorly understood. We are interested in antimicrobial peptides that form the keystone of the innate immune system of multicellular organisms. Basically, these peptides make membranes permeable by forming pores in them. Their universal presence in the animal and plant kingdoms, their non-specific and broad-spectrum action as well as their very elementary structure suggest a mode of action according to physical mechanisms that are also very general and universal. We have addressed this problem through patch-clamp experiments (consisting in measuring the transmembrane ionic current while a given voltage is applied) coupled with neutron reflectivity. In particular, we showed that pore openning exhibits a slow dynamics typically observed near the glass transition, which could be governed by concentration fluctuations of peptides on the surface as it is predicted by the RSA model (“Random Sequential Adsorption”). We are also interested in the thermodynamics of pore opening as a function of temperature and applied voltage. Our results allow us to propose a new physical mecanism where adsorption of peptide and the electric field both contribute to membrane bending. With this mecanism the main entropy cost to pore opening comes from an “exclude area” effect for lipid translation.

Enzyme degradation of a gel

Fri, 01 Jun 2007 00:00:00 +0000

The extracellular matrix is a gel. That is to say a solid network of macromolecuiles linked together, here mainly proteins like collagen. This matrix surrounds and delimits organs. So that, cell invasion and tumor vascularization necessarily imply its crossing by cells, which for this produce proteolytic enzymes (proteinases) which break the links of this network. Uderstanding how they work is therefore important to fight against the spread of cancer cells.

Associative polymers

Fri, 01 Jan 1999 00:00:00 +0000

Associative polymers assemble into supramolecular structures whose formation and arrangement result from the delicate balance between contradictory forces. Among these, the entropic forces related to the loss of degrees of freedom of molecules, for example freedom of translation or freedom of conformation etc. They perfectly illustrate the various problems encountered in the study of soft matter. Mainly studied from the 1980s in the absence of solvent, my contributions in the field relate to the structures obtained in solution.

On the universal nature of the behavior of polymers

Tue, 08 Dec 1998 00:00:00 +0000

A theory is an economy of thought (read E. Mach , P. Duhem , A. Einstein ). We make a representation of reality by establishing unlikely links between things or phenomena that are a priori very different. In the 1970s, P.G. de Gennes achieves a major advance of this type by noting that polymers were critical objects whose self-similarity makes it possible to establish universal laws of behavior (called scaling laws) for observable macroscopic quantities such as osmotic pressure, viscosity or elasticity when expressed as a function of carefully chosen variables (called reduced variables). This was followed in France (particularly at Saclay) for about twenty years by an abundant experimental activity which had a lasting impact on the physics of soft matter.