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A brief introduction to gravitational waves, addressing those questions that nowadays more and more frequently arise within a large audience (not only of insiders): what is a gravity wave, how can it be detected and, above all, what impact on modern physical theories may have their recent discovery? Interested readers can also find a few simple technical details and insights in the final Appendices.
We discuss three rainbow theories created by Descartes, Newton and Young. The note is written primary for school students.
This is a brief, popular (non-technical) introduction (in Italian language) to the problem of quantum gravity, to the recent perspective of emergent spacetime and to its (potential) realization in the context of group field theories, in which the universe emerges as a condensate of non-spatiotemporal constituents.
It is seldom acknowledged the tremendous burden that the Nuclear Age leaves on future generations, and the environment, for an extremely long time. Nuclear processes, and products, are activated at energies millions of times higher than the energies of chemical processes, and consequently they cannot be eliminated by the natural environment on Earth. So it turns out that hundreds of nuclear tests performed in the atmosphere left a huge radioactive contamination; Rosalie Bertell estimated 1,300 millions victims of the Nuclear Age; civil nuclear programs have produced enormous quantities of radioactive waste, whose final disposal has not been solved by any country; decommissioning of tens of shut down nuclear plants shall involve costs which were underestimated in the past; spent nuclear fuel accumulates in decontamination pools, or in dry cask storage, but no final storage has been carried out yet; radioactivity of spent fuel will last for tens of thousand years; military nuclear programs leave, besides almost 15,000 nuclear warheads, approximately 1,300 metric tons of plutonium; even mining of natural uranium was, and is, carried out mainly by poor and exploited populations, which suffer serious health consequences; paradoxically enough (or maybe not), French territory itself is widely contaminated. All these facts have been downplayed during the whole history of the Nuclear Age. Future generations shall not be grateful.
In this paper we present a simple mathematical theory of carving turns in alpine skiing and snowboarding. The theory captures the basic dynamics of carving runs and thus provides a useful tool for assessing the potential and limitations of the carving technique. We also apply the model to simulate runs on slopes of constant gradient and describe the results. We find that pure carving is possible only on relatively flat slopes, with the critical slope angle in the range of 8-20 degrees. The exact value depends mostly on the coefficient of snow friction and to a lesser degree on the sidecut radius of the skis. In wiggly carving runs on slopes of subcritical gradient, the aerodynamic drag force remains relatively unimportant and the speed stops growing well below the one achieved in fall-line gliding. This is because the increased g-force of carving turns leads to enhanced snow friction which can significantly exceed the one found in the gliding. At the critical gradient, the g-force of carving turns becomes excessive. For such and even steeper slopes only hybrid turns, where at least some part of the turn is skidded, are possible. The carving turns of all alpine racing disciplines are approximately similar. This is because in the dimensionless equations of the model the sidecut radius of skis enters only via the coefficient of the aerodynamic drag term, which always remains relatively small. Simple modifications to the model are made to probe the roles of skier angulation and skidding at the transition phase of hybrid turns. As expected the angulation gives certain control over the turn trajectory, but does not remove the slope limitations.
This report is the product of the NASA Technosignatures Workshop held at the Lunar and Planetary Institute in Houston, Texas, in September 2018. This workshop was convened by NASA for the organization to learn more about the current field and state of the art of searches for technosignatures, and what role NASA might play in these searches in the future. The report, written by the workshop participants, summarizes the material presented at the workshop and incorporates additional inputs from the participants. Section 1 explains the scope and purpose of the document, provides general background about the search for technosignatures, and gives context for the rest of the report. Section 2 discusses which experiments have occurred, along with current limits on technosignatures. Section 3 addresses the current state of the technosignature field as well as the state-of-the-art for technosignature detection. Section 4 addresses near-term searches for technosignatures, and Section 5 discusses emerging and future opportunities in technosignature detection.
This essay gives a very general introduction to Schwarzschild black holes. First, it focuses on some of its classical features as solutions to Einstein's theory of gravity. In the second part it discusses briefly some specific quantum aspects and how a black hole processes quantum information. No previous knowledge about black holes, gravity or quantum mechanics is required.
The black hole information paradox is a contradiction between fundamental principles which has puzzled physicists for over forty years. The crux of the problem lies in an assumption about the structure of entanglement across the event horizon, namely, that the Hilbert space factorizes. While valid in quantum mechanics, this fails drastically in quantum field theory, and hence a deeper understanding of entanglement is required if further progress is to be made. Recently, ideas from algebraic quantum field theory have provided new insight into this issue, and show promise for elucidating the connection between entropy and horizons that underlies black hole thermodynamics.
Long range observations in the field of astronomy have opened up our understanding of the Solar System, the Galaxy and the wider Universe. In this paper we discuss the idea of direct in-situ reconnaissance of nearby stellar systems, using robotic probes. In particular, we consider what additional knowledge can be learned that can only be obtained by such close encounters. This may include calibration of existing measurements, detailed observations of stellar winds, astrometry measurements of stellar parallax, refinement of our understanding of physics through the use of long baseline interferometers. In addition, getting close to an exoplanet will enable detailed knowledge of planetary interiors, surface processes, geological evolution, atmospheric composition and climate, internal seismology, detailed surface morphology and even the speculative possibility of detecting the presence of microbial life, detailed palaeontology or even indigenous life-forms. We argue that astronomical remote sensing should be pursued in parallel with in-situ reconnaissance missions by robotic probes, so that both can enhance the discoveries and performance of the other. This work is in support of Project Starshot; an effort to send a Gram-scale probe towards another star at 0.2c within the next two decades, and return images and other data to the Earth. Presented at the 47th IAA Symposium on Future Space Astronomy and Solar System Science Missions. Session on Space Agency Strategies and Plans.
We show here how to create from digital films using the well-known software Tracker stroboscopic photos in order to analyze different types of movements. The advantage of this procedure is that it is possible to analyze the printed photo or on a computer screen in an intuitive way for the students. After presenting a historical perspective of the use of stroboscopic photos in secondary education we discuss several examples: the movement of a remote control car, an elastic planar collision, the movement of a projectile and also an experiment in electromagnetism, more specifically, the discharge of a capacitor measured using an analog multimeter.
Despite the legislation in force in most countries and the discourse on gender equality, the observed reality, still today, shows a clear picture of inequality and restrictions for women, particularly when the issue is the choice of a career and the subsequent promotions. In many professions, although women represent the majority in the entrance to undergraduate courses, their participation is dramatically reduced as the career progresses to the highest levels. While the participation of men increases, that of women decreases as the academic levels move towards the top ranks. This kind of evolution of two groups in opposed directions is usually referred as the "scissors effect". This effect with respect to sexes also occurs in the area of physics, both in Brazil and in the rest of the world. But at what age does this effect begin? What is its intensity in the different stages of women's lives? In this article we aim to shed some light on these questions by analyzing data of the Brazilian Olympiad of Physics and of fellowships for physicists in Brazil. We observe the systematic occurrence of scissors effect throughout the full studied data, ranging from the first years of participation in the Olympiads (13 years old) to the highest stages of the scientific career.
In the first papers of our series on interstellar generation ships we have demonstrated that the numerical code HERITAGE is able to calculate the success rate of multi-generational space missions. Thanks to the social and breeding constraints we examined, a multi-generational crew can safely reach an exoplanet after centuries of deep space travel without risks of consanguinity or genetic disorders. We now turn to addressing an equally important question : how to feed the crew? Dried food stocks are not a viable option due to the deterioration of vitamins with time and the tremendous quantities that would be required for long-term storage. The best option relies on farming aboard the spaceship. Using an updated version of HERITAGE that now accounts for age-dependent biological characteristics such as height and weight, and features related to the varying number of colonists, such as infertility, pregnancy and miscarriage rates, we can estimate the annual caloric requirements aboard using the Harris-Benedict principle. By comparing those numbers with conventional and modern farming techniques we are able to predict the size of artificial land to be allocated in the vessel for agricultural purposes. We find that, for an heterogeneous crew of 500 people living on an omnivorous, balanced diet, 0.45 km2 of artificial land would suffice in order to grow all the necessary food using a combination of aeroponics (for fruits, vegetables, starch, sugar, and oil) and conventional farming (for meat, fish, dairy, and honey).
The Search for Extraterrestrial Intelligence (SETI) makes certain assumptions which guide all current search programs. To illustrate some, this includes (1) that interstellar flight is not possible (2) that the motivations of interstellar cultures are based largely on anthropomorphic understandings of homo sapiens (3) that the Fermi Paradox and the Drake equation are the starting point (axioms) of all reasoning (4) that definitions of 'life' are based largely on our understanding of homeostasis (5) that radio waves are the most likely method of interstellar communications (6) that unknown single event source signatures detected in space are not amenable to scrutiny due to the demands of the scientific method to be reproducible (7) that such anomalous signatures are either astronomical or communications based in type with no consideration for emissions from advanced industrialisation or propulsion and power technology. These assumptions, and others, have guided the SETI community towards a constrained level of thinking that is equivalent to philosophical dogma. In this paper, we unpack these assumptions, and others, and argue that the potential for life and intelligent life in the Cosmos may be much greater than the SETI community currently appears to conclude. It is also argued that more progress in our underanding of our place in the Cosmos can be made, if the separate disciplines of astronomy, interstellar spacecraft design, SETI, biology and philosophy can work together in a complementary way. Presented at the 47th IAA Symposium on the Search for Extraterrestrial Intelligence. SETI and Society.
An essential component of the long-term success of scientific research is communicating the methodology and significance of new results to the wider public. Utilising various social media platforms is a vital tool for this endeavour. Over the years, there have been a number of important results on top physics released by the ATLAS Collaboration. These have been communicated through audience-tailored content, including ATLAS physics briefings, videos, and press statements, amongst others. The ATLAS Collaboration has continued to adapt its communication strategy to match the social media evolution, producing content specifically targeting this emerging audience, the effect of which has been explored.
Vincent van Gogh's painting, The Starry Night, is an iconic piece of art and cultural history. The painting portrays a night sky full of stars, with eddies (spirals) both large and small. \cite{Kolmogorov1941}'s description of subsonic, incompressible turbulence gives a model for turbulence that involves eddies interacting on many length scales, and so the question has been asked: is The Starry Night turbulent? To answer this question, we calculate the azimuthally averaged power spectrum of a square region ($1165 \times 1165$ pixels) of night sky in The Starry Night. We find a power spectrum, $\mathcal{P}(k)$, where $k$ is the wavevector, that shares the same features as supersonic turbulence. It has a power-law $\mathcal{P}(k) \propto k^{-2.1\pm0.3}$ in the scaling range, $34 \leq k \leq 80$. We identify a driving scale, $k_\text{D} = 3$, dissipation scale, $k_ν= 220$ and a bottleneck. This leads us to believe that van Gogh's depiction of the starry night closely resembles the turbulence found in real molecular clouds, the birthplace of stars in the Universe.
A proposed design for radiation shielding in interplanetary travel is presented with primary shielding created by a superconducting split toroid magnetic field and unconfined magnetic fields created by two deployable superconducting loops. The split toroid's shielding effectiveness is analyzed with calculations of mass, field, particle path, and synchrotron radiation provided. The creation of plasma regions is also taken into consideration. The design has a wire mass of 8.08x10^4 kg, which creates a 0.47 T shielding field, and a field less than 2.17x10^-4 T in the crew area. Calculations show the shielding field deflects concerning particles of solar wind, solar flares, and high energy high atomic number particles found in galactic cosmic radiation. This design might also be used to generate power and thrust from the radiation to create a potentially self-sufficient mobile station.
Indigenous peoples across the world observe the motions and positions of stars to develop seasonal calendars. Additionally, changing properties of stars, such as their brightness and colour, are also used for predicting weather. Combining archival studies with ethnographic fieldwork in Australia's Torres Strait, we explore the various ways Indigenous peoples utilise stellar scintillation (twinkling) as an indicator for predicting weather and seasonal change, discussing the scientific underpinnings of this knowledge. By observing subtle changes in the ways the stars twinkle, Meriam people gauge changing trade winds, approaching wet weather, and temperature changes. We then explore how the Northern Dene of Arctic North America utilise stellar scintillation to forecast weather.
Parameters of a shot of an ice hockey player are mostly determined by the capabilities of the player and the physical properties of the stick used. To reach better performance, every hockey player uses also a hockey tape for an adjustment of the stick blade, that changes both the damping properties as well as the friction coefficient of the blade surface. To show the unexpected extent to which these physical properties of the blade affect the shot, we compared two types of blade cover: traditional tape (rolled onto the blade) and a blade sticker that adheres to both sides of the hockey stick blade. We analysed high-speed recordings of two types of shots by 13 players, ranging from amateurs and junior players to NHL superstars. The two covers differ greatly in friction coefficient and stiffness, which results in significantly (more than $99\%$ confidence) greater speed, rotation and energy when using the stiffer and rougher sticker.