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arXiv2014

Dynamics of the Universe in Problems

To our best knowledge, there are no problem books on cosmology yet, that would include its spectacular recent achievements. We believe there is a strong need for such now, when cosmology is swiftly becoming a strict and vast science, and the book would be extremely useful for the youth pouring in this area of research. Indeed, the only way to rise over the popular level in any science is to master its alphabet, that is, to learn to solve problems. Of course, most of modern textbooks on cosmology include problems. However, a reader, exhausted by high theory, may often be thwarted by the lack of time and strength to solve them. Might it be worth sometimes to change the tactics and just throw those who wish to learn to swim into the water? We present an updated version of the "Dynamics of the Universe in Problems" We have the following new sections, 'Gravitational Waves', "Interactions in the Dark Sector", "Horizons" and "Quantum Cosmology" . A number of new problems have been added to almost every section. The total number of problems exceeds fifteen hundred. Solutions to all the problems can be found at www.universeinproblems.com

astro-ph.CO↗

arXiv2009

Computational Physics and Reality: Looking for Some Overlap at the Blacksmith Shop

The paper describes two general problems encountered in computational assignments at the introductory level. First, novice students often treat computer code as almost magic incantations, and like novices in many fields, have trouble creating new algorithms or procedures to solve novel problems. Second, the nature of computational studies often means that the results generated are interpreted via theoretically devised quantities, which may not meet a student's internal standards for proof when compared to an experimental measurement. The paper then offers a lab/programming assignment, used in a calculus-based physics course, which was devised to address these problems. In the assignment, students created a computational model of the heat flow involved in heating an iron rod in a blacksmith's forge. After creating the simulation, students attended a blacksmithing seminar and had a chance to work with iron and take data on its heating in a coke-fueled forge. On their return to campus, students revised their computational models in light of their experimental data.

physics.ed-ph↗

arXiv2013

One world versus many: the inadequacy of Everettian accounts of evolution, probability, and scientific confirmation

There is a compelling intellectual case for exploring whether purely unitary quantum theory defines a sensible and scientifically adequate theory, as Everett originally proposed. Many different and incompatible attempts to define a coherent Everettian quantum theory have been made over the past fifty years. However, no known version of the theory (unadorned by extra ad hoc postulates) can account for the appearance of probabilities and explain why the theory it was meant to replace, Copenhagen quantum theory, appears to be confirmed, or more generally why our evolutionary history appears to be Born-rule typical. This article reviews some ingenious and interesting recent attempts in this direction by Wallace, Greaves, Myrvold and others, and explains why they don't work. An account of one-world randomness, which appears scientifically satisfactory, and has no many-worlds analogue, is proposed. A fundamental obstacle to confirming many-worlds theories is illustrated by considering some toy many-worlds models. These models show that branch weights can exist without having any role in either rational decision-making or theory confirmation, and also that the latter two roles are logically separate. Wallace's proposed decision theoretic axioms for rational agents in a multiverse and claimed derivation of the Born rule are examined. It is argued that Wallace's strategy of axiomatizing a mathematically precise decision theory within a fuzzy Everettian quasiclassical ontology is incoherent. Moreover, Wallace's axioms are not constitutive of rationality either in Everettian quantum theory or in theories in which branchings and branch weights are precisely defined. In both cases, there exist coherent rational strategies that violate some of the axioms.

quant-ph↗

arXiv2010

Many Worlds in Context

Everett's Many-Worlds Interpretation of quantum mechanics is discussed in the context of other physics disputes and other proposed kinds of parallel universes. We find that only a small fraction of the usual objections to Everett's theory are specific to quantum mechanics, and that all of the most controversial issues crop up also in settings that have nothing to do with quantum mechanics.

quant-ph↗

arXiv2009

The Sustainability Solution to the Fermi Paradox

No present observations suggest a technologically advanced extraterrestrial intelligence (ETI) has spread through the galaxy. However, under commonplace assumptions about galactic civilization formation and expansion, this absence of observation is highly unlikely. This improbability is the heart of the Fermi Paradox. The Fermi Paradox leads some to conclude that humans have the only advanced civilization in this galaxy, either because civilization formation is very rare or because intelligent civilizations inevitably destroy themselves. In this paper, we argue that this conclusion is premature by introducing the "Sustainability Solution" to the Fermi Paradox, which questions the Paradox's assumption of faster (e.g. exponential) civilization growth. Drawing on insights from the sustainability of human civilization on Earth, we propose that faster-growth may not be sustainable on the galactic scale. If this is the case, then there may exist ETI that have not expanded throughout the galaxy or have done so but collapsed. These possibilities have implications for both searches for ETI and for human civilization management.

physics.pop-ph↗

arXiv2010

The Quantum Liar Experiment in Cramer's Transactional Interpretation

Cramer's Transactional Interpretation (TI) is applied to the "Quantum Liar Experiment" (QLE). It is shown how some apparently paradoxical features can be explained naturally, albeit nonlocally (since TI is an explicitly nonlocal interpretation, at least from the vantage point of ordinary spacetime). At the same time, it is proposed that in order to preserve the elegance and economy of the interpretation, it may be necessary to consider offer and confirmation waves as propagating in a "higher space" of possibilities.

quant-ph↗

arXiv2009

At the root of things

Modern theories of fundamental interactions describe strong, electromagnetic and weak interactions as quantum field theories with certain kinds of embedded internal symmetries called `gauge symmetries'. This article introduces quantum field theories and gauge symmetries to the uninitiated.

physics.pop-ph↗

arXiv2009

A Computational Analysis of Galactic Exploration with Space Probes: Implications for the Fermi Paradox

Temporal explanations to the Fermi paradox state that the vast scale of the galaxy diminishes the chances of establishing contact with an extraterrestrial technological civilization (ETC) within a certain time window. This argument is tackled in this work in the context of exploration probes, whose propagation can be faster than that of a colonization wavefront. Extensive computational simulations have been done to build a numerical model of the dynamics of the exploration. A probabilistic analysis is subsequently conducted in order to obtain bounds on the number of ETCs that may be exploring the galaxy without establishing contact with Earth, depending on factors such as the number of probes they use, their lifetime and whether they leave some long-term imprint on explored systems or not. The results indicate that it is unlikely that more than ~10^2-10^3 ETCs are exploring the galaxy in a given Myr, if their probes have a lifetime of 50 Myr and contact evidence lasts for 1 Myr. This bound goes down to ~10 if contact evidence lasts for 100 Myr, and is also shown to be inversely proportional to the lifetime of probes. These results are interpreted in light of the Fermi paradox and are compatible with non-stationary astrobiological models in which a few ETCs have gradually appeared in the Fermi-Hart timescale.

physics.pop-ph↗

arXiv2016

The Peace Mediator Effect

Statistical mechanics has proven to be able to capture the fundamental rules underlying phenomena of social aggregation and opinion dynamics, well studied in disciplines like sociology and psychology. This approach is based on the underlying paradigm that the interesting dynamics of multi-agent systems emerge from the correct definition of few parameters governing the evolution of each individual. Into this context, we propose a new model of opinion dynamics based on the psychological construct named "cognitive dissonance". Our system is made of interacting individuals, the agents, each bearing only two dynamical variables (respectively "opinion" and "affinity") self-consistently adjusted during time evolution. We also define two special classes of interacting entities, both acting for a peace mediation process but via different course of action: "diplomats" and "auctoritates". The behaviour of the system with and without peace mediators (PMs) is investigated and discussed with reference to corresponding psychological and social implications.

physics.soc-ph↗

arXiv2009

Other-regarding preferences and altruistic punishment: A Darwinian perspective

This article examines the effect of different other-regarding preference types on the emergence of altruistic punishment behavior from an evolutionary perspective. Our findings corroborate, complement, and interlink the experimental and theoretical literature that has shown the importance of other-regarding behavior in various decision settings. We find that a selfish variant of inequity aversion is sufficient to quantitatively explain the level of punishment observed in contemporary experiments: If disadvantageous inequity aversion is the predominant preference type, altruistic punishment emerges in our model to a level that precisely matches the empirical observations. We use a new approach that closely combines empirical results from a public goods experiment together with an evolutionary simulation model. Hereby we apply ideas from behavioral economics, complex system science, and evolutionary biology.

physics.soc-ph↗

arXiv2010

Nuclear Reactions

Nuclear reactions generate energy in nuclear reactors, in stars, and are responsible for the existence of all elements heavier than hydrogen in the universe. Nuclear reactions denote reactions between nuclei, and between nuclei and other fundamental particles, such as electrons and photons. A short description of the conservation laws and the definition of basic physical quantities is presented, followed by a more detailed account of specific cases: (a) formation and decay of compound nuclei; (b)direct reactions; (c) photon and electron scattering; (d) heavy ion collisions; (e) formation of a quark-gluon plasma; (f) thermonuclear reactions; (g) and reactions with radioactive beams. Whenever necessary, basic equations are introduced to help understand general properties of these reactions. Published in Wiley Encyclopedia of Physics, ISBN-13: 978-3-527-40691-3 - Wiley-VCH, Berlin, 2009.

nucl-th↗

arXiv2009

Atoms as perfect oscillators?

By using Supersymmetric Quantum Mechanics and Semiclassical Quantization, one may argue that the low-lying excited states of any quantum system can be modeled by a set of harmonic oscillators. In the present paper, we fit the experimental excitation spectra of atoms with atomic number 2< Z< 36 to a simple harmonic oscillator model with two parameters: the number of degrees of freedom, d, and the effective frequency, ω. The obtained \hbarωtakes values around 0.03 (in atomic units), whereas d shows clear shell filling effects, that is, takes high values for the noble gases, suggesting collective oscillations of the electrons occupying the last shell.

physics.atom-ph↗

arXiv2009

Models of the World human population growth- critical analysis

We analyze mathematical models of the global human population growth and compare them to actual dynamics of the world population and of the world surplus product. We consider a possibility that the so-called world's demographic transition is not a dynamic crossover but a phase transition that affects all aspects of our life.

physics.soc-ph↗

arXiv2009

Naming the extrasolar planets

Extrasolar planets are not named and are referred to only by their assigned scientific designation. The reason given by the IAU to not name the planets is that it is considered impractical as planets are expected to be common. I advance some reasons as to why this logic is flawed, and suggest names for the 403 extrasolar planet candidates known as of Oct 2009. The names follow a scheme of association with the constellation that the host star pertains to, and therefore are mostly drawn from Roman-Greek mythology. Other mythologies may also be used given that a suitable association is established.

astro-ph.EP↗

arXiv2010

Terrorism: Mechanisms of Radicalization Processes, Control of Contagion and Counter-Terrorist Measures

The spread of radical ideologies is a key to fanaticism, recruitment and terrorist activities. Hence, preventing such activities requires predictive models capable of identifying areas and agents before occurrence of catastrophic terrorist act. In this paper, we develop a model that captures a radicalization mechanism through several intermediate stages of individuals. We propose a radicalizatiom mechanism using individual-based approach constructed from epidemiological model of contagion. Our model builds on insights from contagion models used in theoretical epidemiology and entails a mechanism for controlling the spread of radical ideologies on social spatial networks by identifying suspicious individuals and monitoring them, and taking action when necessary. We show how our model can combat the development of terrorist networks even with limited information on a target terrorist network.

physics.soc-ph↗

arXiv2010

ETTORE MAJORANA: Introduzione a vita & opere (ETTORE MAJORANA: An introduction to his life and work)

This agile small "book" (in Italian) is an introduction to the life and work of Ettore Majorana, the brightest Italian theoretical physicist of the XX century, regarded by Enrico Fermi as the best theoretician of his time in the world. It consists of ten smooth chapters, only few of them being moderately technical, and of three Appendices: (i) about his inaugural lecture on physics at the University of Naples; (ii) about some notes of his, on the role of the statistical laws in physics and in the social sciences; and (iii) with a recapitulatory biographic outline. The present material is mainly taken from our previous book "Il Caso Majorana: Epistolario, Documenti, Testimonianze", first published (1987, 1991) by Mondadori, Milan, and recently (2000, 2002, 2008) published by Di Renzo Editore, Rome. That book presented practically all the serious documents existing on Majorana's life & work [indeed, almost all the biographical documents have been discovered or collected, during a few decades, by the present author, who was the first to publish them]. Actually, we might address to such a book (c/o www.direnzo.it, "Arcobaleno" series) all the readers interested in more and deeper information.

physics.pop-ph↗

arXiv2009

Phenomenological Quantum Gravity

If the history of science has taught us anything, it's that persistence and creativity makes the once impossible possible. It has long been thought experimental tests of quantum gravity are impossible. But during the last decade, several different approaches have been proposed that allow us to test, if not the fundamental theory of quantum gravity itself, so at least characteristic features this theory can have. For the first time we can probe experimentally domains in which quantum physics and gravity cohabit, in spite of our failure so far to make a convincing marriage of them on a theoretical level.

physics.pop-ph↗

arXiv2009

Testing SETI Message Designs

Much work in SETI has focused on detecting radio broadcasts due to extraterrestrial intelligence, but there have been limited efforts to transmit messages over interstellar distances. As a check if such messages can be interpreted once received, we conducted a blind test. One of us coded a 75-kilobit message, which the other then attempted to decipher. The decryption was accurate, supporting the message design as a general structure for communicating with aliens capable of detecting narrow-band radio transmissions.

astro-ph.IM↗