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arXiv2018

The astronomical garden of Venus and Mars-NG915: the pivotal role of Astronomy in dating and deciphering Botticelli's masterpiece

This essay demonstrates the key role of Astronomy in Botticelli's "Venus and Mars-NG915" painting, to date only very partially understood. Worthwhile coincidences among the principles of the Ficinian philosophy, the historical characters involved and the compositional elements of the painting, show how the astronomical knowledge of that time strongly influenced this masterpiece. First, Astronomy provides its precise dating since the artist used the astronomical ephemerides of his time, albeit preserving a mythological meaning, and a clue for Botticelli's signature. Second, it allows the correlation among Botticelli's creative intention, the historical facts and the astronomical phenomena such as the heliacal rising of the planet Venus in conjunction with the Aquarius constellation dating back to the earliest representations of Venus in Mesopotamian culture. This work not only bears a significant value for the history of science and art, but, in the current era of three-dimensional mapping of billion stars about to be delivered by Gaia, states the role of astronomical heritage in Western culture. Finally, following the same method, a precise astronomical dating for the famous Primavera painting is suggested.

physics.hist-ph↗

arXiv2018

"First in, last out" 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 constitutes the Fermi Paradox. In this paper, I argue that the Paradox has a trivial solution, requiring no controversial assumptions, which is rarely suggested or discussed. However, that solution would be hard to accept, as it predicts a future for our own civilization that is even worse than extinction.

physics.pop-ph↗

arXiv2018

Super-Earths in need for Extremly Big Rockets

Many rocky exoplanets are heavier and larger than Earth, so-called "Super-Earths". Some of these may be habitable, and a few may be inhabited by Super-Earthlings. Due to the higher surface gravity on these worlds, space-flight is much more challenging. We find that chemical rockets still allow for escape velocities on Super-Earths up to 10x Earth mass. Much heavier rocky worlds, if they exist, will require using up most of the planet as chemical fuel for the (one) launch, a rather risky undertaking. We also briefly discuss launching rockets from water worlds, which requires Alien megastructures.

physics.pop-ph↗

arXiv2018

Closed periodic orbits in anomalous gravitation

Newton famously showed that a gravitational force inversely proportional to the square of the distance, $F \sim 1/r^2$, formally explains Kepler's three laws of planetary motion. But what happens to the familiar elliptical orbits if the force were to taper off with a different spatial exponent? Here we expand generic textbook treatments by a detailed geometric characterisation of the general solution to the equation of motion for a two-body `sun/planet' system under anomalous gravitation $F \sim 1/r^α (1 \leq α< 2)$. A subset of initial conditions induce closed self-intersecting periodic orbits resembling hypotrochoids with perihelia and aphelia forming regular polygons. We provide time-resolved trajectories for a variety of exponents $α$, and discuss conceptual connections of the case $α= 1$ to Modified Newtonian Dynamics and galactic rotation curves.

physics.pop-ph↗

arXiv2018

A Tether-Assisted Space Launch System for Super-Earths

Super-Earths are one of the most common types of extrasolar planets currently known. Hundreds of these planets have been discovered by the $Kepler$ spacecraft and other surveys, with masses up to 10 $M_\oplus$ and consequently higher surface gravity than Earth. These planets would have greater escape velocities than Earth, reaching as high as 27 km s$^{-1}$ for the largest super-Earths. To launch a spacecraft from the surface of such a world with chemical rockets would be cost-prohibitive or nearly so, while another commonly proposed launch system, the space elevator, would lack the necessary tensile strength to support its weight. However, we find that a hybrid launch system combining chemical rockets and a space-based momentum-exchange tether could reduce the $Δv$ to be provided by chemical rockets to reach escape velocity by 40\%, bringing it back into the realm of feasibility. Such a system could also function on Earth with considerably less exotic materials.

physics.pop-ph↗

arXiv2018

Monologue of a graviton in identity crisis. Or on Alternative Theories of Gravity. (In Spanish)

The era of high precision Cosmology has shown our ignorance about the composition of the Universe. In this context, there has been a renewed interest on Alternative Theories of Gravity. Through the experience of a graviton measured by the LIGO collaboration, we shall understand the conceptual framework of those theories. They provide us with a theoretical construction where we can contrast the predictions of General Relativity and a possible scenario to describe the accelerated expansion of our Universe without assuming the existence of dark components. During the dawn of gravitational wave astronomy, gravitation is already promising to be one of the most fascinating fields of research of the XXI century.

physics.pop-ph↗

arXiv2018

Locating Planets in Sky Using Manual Calculations

In this article, we describe a very simple technique to locate naked-eye planets in the sky, to an accuracy of $\sim 1^{\circ}$. The procedure, comprising just three steps, involves very simple manual calculations for planetary orbits around the Sun; all one needs are the initial specifications of planetary positions for some standard epoch and the time periods of their revolutions. After applying a small correction for the orbital ellipticity, appearance of a planet relative to Sun's position in sky, as seen by an observer from Earth, is found using a scale and a protractor (found inside a school geometry box).

physics.pop-ph↗

arXiv2018

Experimental Tests of Spirituality

We currently harness technologies that could shed new light on old philosophical questions, such as whether our mind entails anything beyond our body or whether our moral values reflect universal truth.

physics.pop-ph↗

arXiv2018

A Gravitational Wave Transmitter

We consider how an advanced civilization might build a radiator to send gravitational waves signals by using small black holes. Micro black holes on the scale of centimeters but with masses of asteroids to planets are manipulated with a super advanced instrumentality, possibly with very large electromagnetic fields. The machine envisioned emits gravitational waves in the GHz frequency range. If the source to receiver distance is a characteristic length in the galaxy, up to 10000 light years, the masses involved are at least planetary in magnitude. To provide the energy for this system we posit a very advanced civilization that has a Kerr black hole at its disposal and can extract energy by way of super-radiance. Background gravitational radiation sets a limit on the dimensionless amplitude that can be measured at interstellar distance using a LIGO like detector.

physics.pop-ph↗

arXiv2020

Role of Symmetry in Irrational Choice

Symmetry is a fundamental concept in modern physics and other related sciences. Being such a powerful tool, almost all physical theories can be derived from symmetry, and the effectiveness of such an approach is astonishing. Since many physicists do not actually believe that symmetry is a fundamental feature of nature, it seems more likely it is a fundamental feature of human cognition. According to evolutionary psychologists, humans have a sensory bias for symmetry. The unconscious quest for symmetrical patterns has developed as a solution to specific adaptive problems related to survival and reproduction. Therefore, it comes as no surprise that some fundamental concepts in psychology and behavioral economics necessarily involve symmetry. The purpose of this paper is to draw attention to the role of symmetry in decision-making and to illustrate how it can be algebraically operationalized through the use of mathematical group theory.

physics.pop-ph↗

arXiv2018

Securing Fuel for Our Frigid Cosmic Future

Advanced civilizations will likely migrate into rich clusters of galaxies, which host the largest reservoirs of matter bound by gravity against the accelerated cosmic expansion.

physics.pop-ph↗

arXiv2018

Heisenberg uncertainty principle and the strange physics of spaghetti

This is an article written in a popular science style, in which I will explain: (1) the famous Heisenberg uncertainty principle, expressing the experimental incompatibility of certain properties of micro-physical entities; (2) the Compton effect, describing the interaction of an electromagnetic wave with a particle; (3) the reasons of Bohr's complementarity principle, which will be understood as a principle of incompatibility; (4) the Einstein, Podolski and Rosen reality (or existence) criterion, and its subsequent revisitation by Piron and Aerts; (4) the mysterious non-spatiality of the quantum entities of a microscopic nature, usually referred to as non-locality. This didactical text requires no particular technical knowledge to be read and understood, although the reader will have to do her/his part, as conceptually speaking the discussion can become at times a little subtle. The text has been written having in mind one of the objectives of the Center Leo Apostel for Interdisciplinary Studies (CLEA): that of a broad dissemination of scientific knowledge. However, as it also presents notions that are not generally well-known, or well-understood, among professional physicists, its reading may also be beneficial to them.

physics.pop-ph↗

arXiv2018

Banjo Drum Physics -- sound experiments and simple acoustics demos

11" D mylar heads over a normal range of tensions (DrumDial 85 to 91) and "open-back" backed pots of depths 2", 2 3/4", and 5 5/8" are studied over the range 100 to 2000 Hz. Normal modes and resonant frequencies of the heads and of the pot air separately are easily identified and agree with simple expectations. The present focus is the head - pot air interaction. There is no "gold-plated" example of a pair of head-air interacting modes that are distant in frequency from all others. (Had there been such a pair, their interaction could have been isolated and studied in detail.) Nevertheless, there are a few cases where there are hints of the kind of interactions expected from a simple theory. The investigations also offer several examples of banjo physics, including aspects of bridge position and rim flexibility, and some dramatic examples of the perils of sound recording, including floor bounce and room sound.

physics.pop-ph↗

arXiv2019

Natural illumination solution for rotating space settlements

Cylindrical kilometre-scale artificial gravity space settlements were proposed by Gerard O'Neill in the 1970s. The early concept had two oppositely rotating cylinders and moving mirrors to simulate the diurnal cycle. Later, the Kalpana One concept exhibited passively stable rotation and no large moving parts. Here we propose and analyse a specific light transfer solution for Kalpana One type settlements. Our proposed solution is technically reliable because it avoids large moving parts that could be single failure points. The scheme has an array of cylindrical paraboloid concentrators in the outer wall and semi-toroidal reflectors at the equator which distribute the concentrated sunlight onto the living surface. The living cylinder is divided into a number of $φ$-sections (valleys) that are in different phases of the diurnal and seasonal cycles. To reduce the mass of nitrogen needed, a shallow atmosphere is used which is contained by a pressure-tight transparent roof. The only moving parts needed are local blinders installed below the roof of each valley. We also find that settlements of this class have a natural location at the equator where one can build multi-storey urban blocks. The location is optimal from the mass distribution (rotational stability) point of view. If maximally built, the amount of urban floorspace per person becomes large, up to 25,000 m$^2$, which is an order of magnitude larger than the food-producing rural biosphere area per person. Large urban floorspace area per person may increase the material standard of living much beyond Earth while increasing the total mass per person relatively little.

physics.pop-ph↗

arXiv2018

Boiling, steaming or rinsing? (physics of the Chinese cuisine)

Some physical aspects of Chinese cuisine are discussed. We start from the cultural and historical particularities of the Chinese cuisine and technologies of food production. What is the difference between raw and boiled meat? What is the difference in the physical processes of heat transfer during steaming of dumplings and their cooking in boiling water? Why is it possible to cook meat stripes in a "hot pot" in ten seconds, while baking a turkey requires several hours? This article is devoted to discussion of these questions.

physics.pop-ph↗

arXiv2018

Understanding quantum physics through simple experiments: from wave-particle duality to Bell's theorem

Quantum physics, which describes the strange behavior of light and matter at the smallest scales, is one of the most successful descriptions of reality, yet it is notoriously inaccessible. Here we provide an approachable explanation of quantum physics using simple thought experiments. We derive all relevant quantum predictions using minimal mathematics, without introducing the advanced calculations that are typically used to describe quantum physics. We focus on the two key surprises of quantum physics, namely wave-particle duality, a term that was introduced to capture the fact that single quantum particles in some respects behave like waves and in other respects like particles, and entanglement, which applies to two or more quantum particles and brings out the inherent contradiction between quantum physics and seemingly obvious assumptions regarding the nature of reality. Following arguments originally made by John Bell and Lucien Hardy, we show that the so-called local hidden variables are inadequate at explaining the behavior of entangled quantum particles. This means that one either has to give up on hidden variables, i.e., the idea that the outcomes of measurements on quantum particles are determined before an experiment is actually carried out, or one has to relinquish the principle of locality, which requires that no causal influences should be faster than the speed of light and is a cornerstone of Einstein's theory of relativity. Finally, we describe how these remarkable predictions of quantum physics have been confirmed in experiments. We have successfully used the present approach in a course that is open to all undergraduate students at the University of Calgary, without any prerequisites in mathematics or physics.

physics.ed-ph↗

arXiv2018

Radioactivity measurements of green tea leaves from Japan after the Fukushima incident

A series of 32 green tea leaves samples from different Asian producers were analyzed by direct γ-ray spectrometry at the PRISNA facility in Bordeaux. All the samples contain about 500 Bq/kg of 40K and 10 Bq/kg of 210Pb. As expected, most of the recent Japanese samples contain also the 137Cs and 134Cs radio-isotopes, whose activity distributions are studied as a function of the geographical origin in order to get an insight on the outspread and fallout of radionuclides stemming from the 2011 Fukushima Dai-ichi Nuclear Power Plant incident.

physics.pop-ph↗

arXiv2018

Where do ideas come from?

Ideas are nurtured by informal dialogues in environments where mistakes are tolerated and critical thinking is encouraged.

physics.pop-ph↗