Relativistic spring-mass system

Rodrigo Andrade e Silva, Andre G. S. Landulfo, George E. A. Matsas, Daniel A. T. Vanzella

The harmonic oscillator plays a central role in physics describing the dynamics of a wide range of systems close to stable equilibrium points. The nonrelativistic one-dimensional spring-mass system is considered a prototype representative of it. It is usually assumed and galvanized in textbooks that the equation of motion of a relativistic harmonic oscillator is given by the same equation as the nonrelativistic one with the mass M at the tip multiplied by the relativistic factor 1/(1−v2/c2)1/2. Although the solution of such an equation may depict some physical systems, it does not describe, in general, one-dimensional relativistic spring-mass oscillators under the influence of elastic forces. In recognition to the importance of such a system to physics, we fill a gap in the literature and offer a full relativistic treatment for a system composed of a spring attached to an inertial wall, holding a mass M at the end.

Read more at https://arxiv.org/pdf/1810.13365.pdf

The Science and Legacy of Richard Feynman

Avinash Dhar, Apoorva D. Patel, Spenta R. Wadia
This year is the 100th birth anniversary of Richard Philips Feynman. This article commemorates his scientific contributions and lasting legacy.

… He influenced the way physicists think about physics, especially physical processes whose description requires the quantum theory. Feynman’s approach to physics was to show how the solution to a problem unravels, aided by a visual language that encapsulates complicated mathematical expressions. James Gleick put this very succinctly, “Feynman’s reinvention of quantum mechanics did not so much explain how the world was, or why it was that way, as to tell how to confront the world. It was not knowledge of or knowledge about. It was knowledge how to.” He went to the heart of the problem he was working on, built up the solutions from simple ground rules in a step by step nuts and bolts way, articulating the steps as he built up the solution, keeping in mind that science is highly constrained by the fact that it is a description of the natural world. He laid bare the strategy of the solution, and was explicit about the various difficulties that need to be surmounted, perhaps now or in the next attempt to solve the problem: “In physics the truth is rarely perfectly clear.” Feynman’s attitude to ‘fundamental physics’ is well put in the collection, ‘The Pleasure of Finding Things Out’: “People say to me, ‘Are you looking for the ultimate laws of physics?’ No, I’m not, I’m just looking to find out more about the world, and if it turns out there is a simple ultimate law which explains everything, so be it, that would be very nice to discover.” …

Read more at https://arxiv.org/pdf/1810.07409.pdf

Who discovered positron annihilation?

Positron annihilatioTim Dunker
In the early 1930s, the positron, pair production, and, at last, positron annihilation were discovered. Over the years, several scientists have been credited with the discovery of the annihilation radiation. Commonly, Thibaud and Joliot have received credit for the discovery of positron annihilation. A conversation between Werner Heisenberg and Theodor Heiting prompted me to examine relevant publications, when these were submitted and published, and how experimental results were interpreted in the relevant articles. I argue that it was Theodor Heiting – usually not mentioned at all in relevant publications – who discovered positron annihilation, and that he should receive proper credit.
Read more at https://arxiv.org/pdf/1809.04815.pdf

Is our universe one of many?

BY KER THAN
As physicists have delved deeper and deeper into nature’s mysteries, they have been forced to accept the unsettling fact that our universe is suspiciously fine-tuned to support life. The amount of matter in the universe, the mass of the electron, the strength of gravity – if the value of any of these deviated only a tiny bit from what they actually are, then galaxies and stars could not form and biological life could not exist. The best theory that physicists have come up with to explain this cosmic coincidence is called the String Theory Landscape.

The String Theory Landscape combines elements from two of the strangest and most enduring ideas in modern physics – string theory and cosmic inflation – to argue that we live in a multiverse made up of infinitely many “pocket universes,” of which our perfectly calibrated universe is just one. This five-part series tells the story of how theoretical physicists at Stanford helped develop the String Theory Landscape – and in the process sparked a fierce and still ongoing debate about what science is and what it should be…

Read more at https://news.stanford.edu/2018/09/10/landscape-theory/

Snellius meets Schwarzschild

Refraction of brachistochrones and time-like geodesics
snellHeinz-Jürgen Schmidt
The brachistochrone problem can be solved either by variational calculus or by a skillful application of the Snellius’ law of refraction. This suggests the question whether also other variational problems can be solved by an analogue of the refraction law. In this paper we investigate the physically interesting case of free fall in General Relativity that can be formulated as a variational problem w. r. t. proper time. We state and discuss the corresponding refraction law for a special class of spacetime metrics including the Schwarzschild metric…
Read more at https://arxiv.org/pdf/1809.00355.pdf

Analogy between thermal emission of nano objects and Hawking’s radiation

cavity
Karl Joulain
We analyze in this work some analogies between thermal emission of nano objects and Hawking’s radiation. We first focus on the famous expression of the black hole radiating temperature derived by Hawking in 1974 and consider the case of thermal emission of a small aperture made into a cavity (Ideal Blackbody). We show that an expression very similar to Hawking’s temperature determines a temperature below which an aperture in a cavity cannot be considered as standard blackbody radiating like T^4. Hawking’s radiation therefore appear as a radiation at a typical wavelength which is of the size of the horizon radius. In a second part, we make the analogy between the emission of particle-anti particle pairs near the black hole horizon and the scattering and coupling of thermally populated evanescent waves by a nano objects. We show here again that a temperature similar to the Hawking temperature determines the regimes where the scattering occur or where it is negligible.
Read more at https://arxiv.org/pdf/1808.08037.pdf

Effects of exoplanetary gravity on human locomotor ability


Nikola Poljak, Dora Klindzic, Mateo Kruljac
At some point in the future, if mankind hopes to settle planets outside the Solar System, it will be crucial to determine the range of planetary conditions under which human beings could survive and function. In this article, we apply physical considerations to future exoplanetary biology to determine the limitations which gravity imposes on several systems governing the human body. Initially, we examine the ultimate limits at which the human skeleton breaks and muscles become unable to lift the body from the ground. We also produce a new model for the energetic expenditure of walking, by modelling the leg as an inverted pendulum. Both approaches conclude that, with rigorous training, humans could perform normal locomotion at gravity no higher than 4 gEarth.
Read more at https://arxiv.org/pdf/1808.07417.pdf