## Archive for the ‘**PHYSICS**’ Category

## What We’ve Learned from New Kind of Science Chapter 9: Fundamental Physics

In this episode of “What We’ve Learned from NKS”, Stephen Wolfram is counting down to the 20th anniversary of A New Kind of Science with [another] chapter retrospective. Read all of NKS here: https://www.wolframscience.com/nks/

00:00 Stream Begins 2:28 Stephen begins talking 6:16 Section 1: The Problems of Physics 8:18 Section 2: The Notion of Reversibility 14:58 Section 3: Irreversibility and the Second Law of Thermodynamics 30:15 Notes 42:33 Section 4: Conserved Quantities and Continuum Phenomena 50:09 Section 5: Ultimate Models for the Universe 53:15 Section 6: The Nature of Space 54:00 Section 7: Space as a Network 57:54 Section 8: The Relationship of Space and Time 1:01:40 Section 9: Time and Causal Networks 1:06:08 Section 10: The Sequencing of Events in the Universe 1:09:00 Section 11: Uniqueness and Branching in Time 1:12:50 Section 12: Evolution of Networks 1:17:47 Section 13: Space, Time and Relativity 1:20:54 Section 14: Elementary Particles 1:22:16 Notes 1:34:06 Section 15: The Phenomenon of Gravity 1:43:22 Section 16: Quantum Phenomena 1:50:54 Wrap up of Chapter 9 1:56:30 Is measurement a time irreversible process? Is it the case that in order to gain information about a system the system must have an arrow of time? Or is the flow of time itself the generation of information? 1:57:12 Does this mean the universe is perhaps on a trajectory to reverse to it’s initial state or will the rule expand randomly forever. if the former will time run backwards or will everything that “exists” be organically destroyed in the reversal? 1:57:45 Is there a network defined by a few simple rules, implying that the monster group and the 6 pariah groups give rise to the Standard Model with 6 basic quarks? 1:58:30 Has anyone ever run two rules in a combined computational space, could the rules “procreate” in this instance at connecting points to combine and create new rules? 1:58:46 Is there any evidence of higher complexity classes of connections in regions of branchial space that are contained in finite spaces of physical space? E.g, planets 1:59:33 It seems like half integer spin particles are only observed because the universe is 3 dimensional. If your model implies that the universe is not exactly 3 dimensional, does this mean that we can observe fractional spin particles? 2:01:30 Farewell Remarks

## Modeling Transport of SARS-CoV-2 Inside a Charlotte Area Transit System (CATS) Bus

**Gregory McGowan, Jeffrey Feaster, Andy Jones, Lucas Agricola, Matthew Goodson, William Timms, Mesbah Uddin**

We present in this paper a model of the transport of human respiratory particles on a Charlotte Area Transit System (CATS) bus to examine the efficacy of interventions to limit exposure to SARS-CoV-2, the virus that causes COVID-19. The methods discussed here utilize a commercial Navier-Stokes flow solver, RavenCFD, run using a massively parallel supercomputer to model the flow of air through the bus under varying conditions, such as windows being open or the HVAC flow settings. Lagrangian particles are injected into the RavenCFD predicted flow fields to simulate the respiratory droplets from speaking, coughing, or sneezing. These particles are then traced over time and space until they interact with a surface or are removed via the HVAC system. Finally, a volumetric Viral Mean Exposure Time (VMET) is computed to quantify the risk of exposure to the SARS-CoV-2 under various environmental and occupancy scenarios. Comparing the VMET under varying conditions should help identify viable methods to reduce the risk of viral exposure of CATS bus passengers during the COVID-19 pandemic.

read more at

## Applying physics to mathematics

**by Tadashi Tokieda**

abstract : Humans tend to be better at physics than at mathematics. When an apple falls from a tree, there are more people who can catch it—we know physically how the apple moves—than people who can compute its trajectory from a differential equation. Applying physical ideas to discover and establish mathematical results is therefore natural, even if it has seldom been tried in the history of science. (The exceptions include Archimedes, some old Russian sources, a recent book by Mark Levi, as well as my articles and lectures.) This TMC Distinguished Lecture presents a diversity of examples, and tries to make them easy for imaginative beginners and difficult for seasoned researchers.

## Chirality Through Classical Physics

**Chris L. Lin**

Chirality, or handedness, is a topic that is common in biology and chemistry, yet is rarely discussed in physics courses. We provide a way of introducing the topic in classical physics, and demonstrate the merits of its inclusion – such as a simple way to visually introduce the concept of symmetries in physical law – along with giving some simple proofs using only basic matrix operations, thereby avoiding the full formalism of the three-dimensional point group.

Read also https://arxiv.org/pdf/2004.08236.pdf

## Memory and entropy

**Carlo Rovelli**

I study the physical nature of traces (or memories). Surprisingly, (i) systems separation with (ii) temperature differences and (iii) long thermalization times, are sufficient conditions to produce macroscopic traces. Traces of the past are ubiquitous because these conditions are largely satisfied in our universe. I quantify these thermodynamical conditions for memory and derive an expression for the maximum amount of information stored in such memories, as a function of the relevant thermodynamical parameters. This mechanism transforms low entropy into available information.

Read more at https://arxiv.org/pdf/2003.06687.pdf

## Graphic Talk about the Universe: Clifford V. Johnson

In his public lecture webcast at Perimeter on February 7, Clifford V. Johnson discussed the process of turning complex scientific topics into compelling visual narratives.

## 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 g_{Earth}.

Read more at https://arxiv.org/pdf/1808.07417.pdf