Contemporary Theoretical Physics Research Articles

When may a system be referred to as complex?—an entropic perspective

Defining complexity is hard and far from unique—like defining beauty, intelligence, creativity, and many other such abstract concepts. In contrast, describing concrete complex systems is a sensibly simpler task. We focus here on such an issue from the perspective of entropic functionals, either additive or nonadditive. Indeed, for the systems currently referred to as simple, the statistical mechanics and associated (additive) entropy is that of Boltzmann–Gibbs, formulated 150 years ago. This formalism constitutes a pillar of contemporary theoretical physics and is typically grounded on strong chaos, mixing, ergodicity, and similar hypotheses, which typically emerge for systems with short-range space–time generic correlations. It fails, however, for the so-called complex systems, where generic long-range space–time correlations prevail, typically grounded on weak chaos. Many such nontrivial systems are satisfactorily handled within a generalization of the Boltzmann–Gibbs theory, namely, nonextensive statistical mechanics, introduced in 1988 and grounded on nonadditive entropies. Illustrations are presented in terms of D-dimensional simplexes such as nodes (D = 0), bonds (D = 1), plaquettes (D = 2), polyhedra (D = 3, …), and higher-order ones. A regularly updated bibliography is available at http://tsallis.cat.cbpf.br/biblio.htm.

Non-additive entropies and statistical mechanics at the edge of chaos: a bridge between natural and social sciences.

The Boltzmann-Gibbs (BG) statistical mechanics constitutes one of the pillars of contemporary theoretical physics. It is constructed upon the other pillars-classical, quantum, relativistic mechanics and Maxwell equations for electromagnetism-and its foundations are grounded on the optimization of the BG (additive) entropic functional [Formula: see text]. Its use in the realm of classical mechanics is legitimate for vast classes of nonlinear dynamical systems under the assumption that the maximal Lyapunov exponent is positive (currently referred to as strong chaos), and its validity has been experimentally verified in countless situations. It fails however when the maximal Lyapunov exponent vanishes (referred to as weak chaos), which is virtually always the case with complex natural, artificial and social systems. To overcome this type of weakness of the BG theory, a generalization was proposed in 1988 grounded on the non-additive entropic functional [Formula: see text]. The index [Formula: see text] and related ones are to be calculated, whenever mathematically tractable, from first principles and reflect the specific class of weak chaos. We review here the basics of this generalization and illustrate its validity with selected examples aiming to bridge natural and social sciences. This article is part of the theme issue 'Thermodynamics 2.0: Bridging the natural and social sciences (Part 2)'.

Whitehead and the Lisbon School of Quantum Physics

In the controversy on the philosophical foundations of quantum mechanics Whitehead's philosophy of organism has an essential place. But its realistic position invalidates any attempt to relate it to the School of Copenhagen's “orthodox interpretation”. Unlike, the Eurhythmic Physics developed by the Lisbon School has notable theoretical tunings with Whitehead's philosophy. In both, the notion of passive matter disappears; entities are understood as ecstatic process of becoming arising from a continuum of potentialities; and they achieve physical persistence grace to a set of synergistic interactions among their own regimes of rhythmical activity. The principle of Eurhythmy proposed by Prof. Croca then appears as the hypothesis, in contemporary theoretical physics, corresponding to the organicist vision of a universe in a developmental process of realization of the abstract potentiality of all possible worlds: a universe that, as a living organism, should be described as guided by an immanent teleological principle.

Wilsonian Renormalization in the 1970s

This paper examines the history of the renormalization group, a cornerstone of contemporary theoretical physics, focusing on the work of Kenneth Wilson (winner of the 1982 Nobel Prize in physics) and affiliated scholars in the 1970s. In particular, it reconstructs how studies of the renormalization group led to formative interactions between two distinct branches of physics, namely particle physics and condensed matter theory. Instead of explaining such intellectual coordination as the result of material and conceptual exchanges, as in Peter Galison’s widely influential discussion of the “trading zone,” my analysis emphasizes the pedagogical labor, social institutions, and political economic conditions that gave the renormalization group its mediating power. To that end, I show how early lectures and fast circulating pre-prints on the renormalization group created a population of physicists in the United States conversant in the rudiments of both condensed matter and particle theory. I then root the formation of a transatlantic network of renormalization group enthusiasts in the geopolitics of the Cold War, showing that the spread of Wilsonian ideas was made possible by a liberal internationalist program of academic exchanges and summer schools sponsored by the US state department and NATO. Finally, I argue that sharp cuts to basic science funding in the United States pushed young physicists seeking jobs in the 1970s to work across specializations, which visibly impacted how renormalization group ideas were interpreted and used—often against the objections of their original progenitors.

The Unity Principle – A New Paradigm in Theoretical Physics

Contemporary theoretical physics enters a deep crisis resulting from its positivistic and post-positivistic approach, which assumes that reality is mechanical and atomistic made of point-like particles or one-dimensional strings where the essence of matter, energy, space and time, gravity and other forces are undetectable mysteries. However, within this paper I will endeavour to show that the Universe (reality) is dialectical (relational) and is thus accessible by dialectical logic. The fundamental discovery of the Unity Principle derived on the base of dialectical logic is presented illustrating the exact mechanism how the physical Universe may work at its macro and micro levels. New fundamentals of theoretical physics are built

Scattering of mesons in quantum simulators

Simulating real-time evolution in theories of fundamental interactions represents one of the central challenges in contemporary theoretical physics. Cold-atom platforms stand as promising candidates to realize quantum simulations of non-perturbative phenomena in gauge theories, such as vacuum decay and hadron collisions, in prohibitive conditions for direct experiments. In this work, we demonstrate that present-day quantum simulators can imitate linear particle accelerators, giving access to S-matrix measurements of elastic and inelastic meson collisions in low-dimensional abelian gauge theories. Considering for definiteness a (1 + 1)-dimensional -lattice gauge theory realizable with Rydberg-atom arrays, we present protocols to observe and measure selected meson–meson scattering processes. We provide a benchmark theoretical study of scattering amplitudes in the regime of large fermion mass, including an exact solution valid for arbitrary coupling strength. This allows us to discuss the occurrence of inelastic scattering channels, featuring the production of new mesons with different internal structures. We present numerical simulations of realistic wavepacket collisions, which reproduce the predicted cross section peaks. This work highlights the potential of quantum simulations to give unprecedented access to real-time scattering dynamics.

Discerning Potential and Impact Information

This paper contains further analysis of the concept of information aimed at discovering new features of this mysterious but very important phenomenon. We base our analysis on the general theory of information and contemporary theoretical physics. This approach allows for the explication of two basic complementary types of information—potential and impact information. In such a way, we achieve a better understanding of information as a natural and social phenomenon, which serves as a base for developing novel tools for measuring information.

Only a unified ontology can remedy disunification

Contemporary theoretical physics is divided into diversified theories of different phenomena. These are characteristically frameworks for giving mathematical descriptions of perceptions, in the absence of understandable explanations or a unified worldview. This is not an optimal state of affairs, for people by nature desire to understand; this sets a major obstacle for an optimal progress rate of physics, for understandable explanations are more prolific of new predictions and applications than non-understandable explanations. Disunification in physics can be remedied only by discovering an understandable ontology and applying it as the basis of unifying explanations of phenomena that were earlier explained by different theories. Due to disunified physics and the nature of traditional analysis in philosophy, there is no consensus about central concepts such as time, possibility and truth. It is suggested that philosophical analysis would be more prolific of understandable and applicable concepts, were it complemented by a method of unification.

What’s the Problem with the Cosmological Constant?

The “Cosmological Constant Problem” (CCP) is widely considered a crisis in contemporary theoretical physics. Unfortunately, the search for its resolution is hampered by open disagreement about what is, strictly, the problem. This disagreement stems from the observation that the CCP is not a problem within any of our current theories, and nearly all of the details of those future theories for which the CCP could be made a problem are up for grabs. Given this state of affairs, I discuss how one ought to make sense of the role of the CCP in physics and generalize some lessons from it.

Analysis in Noncommutative Algebras and Modules

In a previous paper, we developed an analysis in associative commutative algebras and in modules over them, which may be useful in problems of contemporary mathematical and theoretical physics. Here we work out similar methods in the noncommutative case.

Beyond Boltzmann-Gibbs-Shannon in Physics and Elsewhere.

The pillars of contemporary theoretical physics are classical mechanics, Maxwell electromagnetism, relativity, quantum mechanics, and Boltzmann–Gibbs (BG) statistical mechanics –including its connection with thermodynamics. The BG theory describes amazingly well the thermal equilibrium of a plethora of so-called simple systems. However, BG statistical mechanics and its basic additive entropy started, in recent decades, to exhibit failures or inadequacies in an increasing number of complex systems. The emergence of such intriguing features became apparent in quantum systems as well, such as black holes and other area-law-like scenarios for the von Neumann entropy. In a different arena, the efficiency of the Shannon entropy—as the BG functional is currently called in engineering and communication theory—started to be perceived as not necessarily optimal in the processing of images (e.g., medical ones) and time series (e.g., economic ones). Such is the case in the presence of generic long-range space correlations, long memory, sub-exponential sensitivity to the initial conditions (hence vanishing largest Lyapunov exponents), and similar features. Finally, we witnessed, during the last two decades, an explosion of asymptotically scale-free complex networks. This wide range of important systems eventually gave support, since 1988, to the generalization of the BG theory. Nonadditive entropies generalizing the BG one and their consequences have been introduced and intensively studied worldwide. The present review focuses on these concepts and their predictions, verifications, and applications in physics and elsewhere. Some selected examples (in quantum information, high- and low-energy physics, low-dimensional nonlinear dynamical systems, earthquakes, turbulence, long-range interacting systems, and scale-free networks) illustrate successful applications. The grounding thermodynamical framework is briefly described as well.

Black hole thermodynamics: general relativity and beyond

Black holes have often provided profound insights into the nature of gravity and the structure of space-time. The study of the mathematical properties of black objects is a major research theme of contemporary theoretical physics. This review presents a comprehensive survey of the various versions of the first law and second law of black hole mechanics in general relativity and beyond. The emphasis is to understand how these laws can constrain the physics beyond general relativity.

Elementary Errors in Contemporary Theoretical Physics

The paper discusses two cases showing crucial effects of error correction. It proves that contrary to the common belief, the electronic state of atoms having more than one electron has a multiconfiguration structure and that the central field approximati...

Fluid Mechanics in Sommerfeld's School

Sommerfeld's affiliation with fluid mechanics started when he began his career as an assistant of the mathematician Felix Klein at Göttingen. He always regarded fluid mechanics as a particular challenge. In 1904, he published a theory of hydrodynamic lubrication. Four years later, he conceived an approach for the analysis of flow instability (the Orr-Sommerfeld approach) as an attempt to account for the transition from laminar to turbulent flow. The onset of turbulence also became a major challenge for some of his pupils, in particular Ludwig Hopf and Fritz Noether. Both contributed considerably to elaborate the Orr-Sommerfeld theory. Heisenberg's doctoral work was another attempt in this quest. When Sommerfeld published his lectures on theoretical physics during World War II, he dedicated one of the six volumes to the mechanics of continuous media. With chapters on boundary layer theory and turbulence, it exceeded the scope of contemporary theoretical physics—revealing Sommerfeld's persistent appreciation of fluid mechanics. He resorted to Prandtl's Göttingen school of fluid mechanics in order to stay abreast of the rapid development of these specialties.

Nuclear Structure of Light Nuclei Near Threshold

Moving toward an understanding of nuclei at the threshold of nuclear binding is a major theme of contemporary experimental and theoretical nuclear physics. The challenge to the former is to probe nuclei at the limits of existence requiring a variety of different techniques such as nucleon transfer, nucleon knockout, and Coulomb dissociation, and so on. And to the latter, a question of framing the problem: What role does finite binding play? What role does the continuum play? How can the action of these effects be isolated when interpreting the experimental data? Is it even possible to disentangle these?

Reflections on the four facets of symmetry: how physics exemplifies rational thinking

In contemporary theoretical physics, the powerful notion of symmetry stands for a web of intricate meanings among which I identify four clusters associated with the notion of transformation, comprehension, invariance and projection. While their interrelations are examined closely, these four facets of symmetry are scrutinised one after the other in great detail. This decomposition allows us to examine closely the multiple different roles symmetry plays in many places in physics. Furthermore, some connections with others disciplines like neurobiology, epistemology, cognitive sciences and, not least, philosophy are proposed in an attempt to show that symmetry can be an organising principle also in these fields.

Enanas blancas, agujeros negros y la tesis filosófica de la inconmensurabilidad

La inconmensurabilidad ha sido durante unos cuarenta años una de las cuestiones más discutidas de la filosofía contemporánea de la ciencia. Para abordarla asumo la caracterización de Howard Sankey (1997: 425) de la misma como “la tesis de que el contenido de algunas teorías científicas alternativas es incomparable debido a fallos de traducción en el vocabulario que emplean las teorías”. Este tipo de incomparabilidad debería impedir, por ejemplo, la derivación de la mecánica newtoniana a partir de la teoría de la relatividad, según mantiene Thomas Kuhn (1970a y 1970b). Como yo mismo me he ocupado de la comparación de los conceptos newtoniano y einsteiniano de masa en Rivadulla (2004), en este artículo breve me centro en la comparabilidad de teorías de la física teórica contemporánea.Así, en lugar de tratar la cuestión de si las teorías de la física contemporánea son decididamente inconmensurables entre sí, el objeto principal de este artículo es proporcionar una respuesta al problema de si tiene sentido pensar sobre la inconmensurabilidad entre teorías físicas contemporáneas, dada su obvia comparabilidad.

Stereotypes That Help Define Who We Are

The research Fay Fransella undertook with stereotypes is reviewed in this article. It concentrates on her lesser-known articles dealing with relations between the self and stereotypes in certain “symptom groups” (stutterers, arsonists, alcoholics, and heroin addicts) as well as in wider social groups, such as students and scientists. In these articles, Fransella voiced important insights that have appeared in more recent writings of social constructionism, at the same time being strikingly similar to the position of thinkers in contemporary theoretical physics.

Science and theory in modern physics and psychoanalysis

Today, much of psychoanalysis has moved beyond Freud, both methodologically and theoretically. I understand Freud to have been always either explicitly or implicitly committed to the view that psychoanalysis is a science, if only at times as an aspirational goal. The question I intend to raise in this article is not whether psychoanalysis is scientific, but rather whether it should still consider itself so in the light of contemporary theoretical physics' ever greater dependence on mathematical assertions that have not to date been validated by experimental conformation. Bestowing the appellation of science to superstring theory, “the theory of everything,” is at present a self-crowing by its adherents taken as a hereditary birthright. I view the relation between psychoanalytic theory and contemporary theoretical physics as a parallelism – a parallelism between approaches to conceptualisation rather than a reduction of disciplines.

Quantum Gravity and Phenomenological Philosophy

The central thesis of this paper is that contemporary theoretical physics is grounded in philosophical presuppositions that make it difficult to effectively address the problems of subject-object interaction and discontinuity inherent to quantum gravity. The core objectivist assumption implicit in relativity theory and quantum mechanics is uncovered and we see that, in string theory, this assumption leads into contradiction. To address this challenge, a new philosophical foundation is proposed based on the phenomenology of Maurice Merleau-Ponty and Martin Heidegger. Then, through the application of qualitative topology and hypernumbers, phenomenological ideas about space, time, and dimension are brought into focus so as to provide specific solutions to the problems of force-field generation and unification. The phenomenological string theory that results speaks to the inconclusiveness of conventional string theory and resolves its core contradiction.