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In the vastness of empty space surrounding Earth, the Moon is our closest celestial neighbor. Its face, periodically filled with light and devoured by darkness, has an ever-changing, but dependable presence in our skies. In this article, we’ll learn about the Moon and its path around our planet, but to experience that journey first-hand, we have to enter the cosmos itself. This article has many interactive demonstrations which are best seen on the website.
The dream of soaring in the sky like a bird has captivated the human mind for ages. Although many failed, some eventually succeeded in achieving that goal. These days we take air transportation for granted, but the physics of flight can still be puzzling. In this article we’ll investigate what makes airplanes fly by looking at the forces generated by the flow of air around the aircraft’s wings. More specifically, we’ll focus on the cross section of those wings to reveal the shape of an airfoil – you can see it presented in yellow below: This article has many interactive demonstrations which are best seen on the website.
There is something delightful about riding a bicycle. Once mastered, the simple action of pedaling to move forward and turning the handlebars to steer makes bike riding an effortless activity. In the demonstration below, you can guide the rider with the slider, and you can also drag the view around to change the camera angle: Compared to internal combustion engines or mechanical watches, bicycles are fairly simple machines – most of their parts operate in plain sight. This article has many interactive demonstrations which are best seen on the website.
In the world of modern portable devices, it may be hard to believe that merely a few decades ago the most convenient way to keep track of time was a mechanical watch. Unlike their quartz and smart siblings, mechanical watches can run without using any batteries or other electronic components. Over the course of this article I’ll explain the workings of the mechanism seen in the demonstration below. You can drag the device around to change your viewing angle, and you can use the slider to peek at what’s going on inside: This article has many interactive demonstrations which are best seen on the website.
More in science
My post last week clearly stimulated some discussion. I know people don't come here for political news, but as a professional scientist it's hard to ignore the chaotic present situation, so here are some things to read, before I talk about a fun paper: Science reports on what is happening with NSF. The short version: As of Friday afternoon, panels are delayed and funds (salary) are still not accessible for NSF postdoctoral fellows. Here is NPR's take. As of Friday afternoon, there is a new court order that specifically names the agency heads (including the NSF director), saying to disburse already approved funds according to statute. Looks like on this and a variety of other issues, we will see whether court orders actually compel actions anymore. Now to distract ourselves with dreams of the future, this paper was published in Nature Photonics, measuring radiation pressure exerted by a laser on a 50 nm thick silicon nitride membrane. The motivation is a grand one: using laser-powered light sails to propel interstellar probes up to a decent fraction (say 10% or more) of the velocity of light. It's easy to sketch out the basic idea on a napkin, and it has been considered seriously for decades (see this 1984 paper). Imagine a reflective sail say 10 m\(^{2}\) and 100 nm thick. When photons at normal incidence bounce from a reflective surface, they transfer momentum \(2\hbar \omega/c) normal to the surface. If the reflective surface is very thin and low mass, and you can bounce enough photons off it, you can get decent accelerations. Part of the appeal is, this is a spacecraft where you effectively keep the engine (the whopping laser) here at home and don't have to carry it with you. There are braking schemes so that you could try to slow the craft down when it reaches your favorite target system. A laser-powered lightsail (image from CalTech) Of course, actually doing this on a scale where it would be useful faces enormous engineering challenges (beyond building whopping lasers and operating them for years at a time with outstanding collimation and positioning). Reflection won't be perfect, so there will be heating. Ideally, you'd want a light sail that passively stabilizes itself in the center of the beam. In this paper, the investigators implement a clever scheme to measure radiation forces, and they test ideas involving dielectric gratings etched into the sail to generate self-stabilization. Definitely more fun to think about such futuristic ideas than to read the news. (An old favorite science fiction story of mine is "The Fourth Profession", by Larry Niven. The imminent arrival of an alien ship at earth is heralded by the appearance of a bright point in the sky, whose emission turns out to be the highly blue-shifted, reflected spectrum of the sun, bouncing off an incoming alien light sail. The aliens really need humanity to build them a launching laser to get to their next destination.)
Recent results show that large language models struggle with compositional tasks, suggesting a hard limit to their abilities. The post Chatbot Software Begins to Face Fundamental Limitations first appeared on Quanta Magazine
A tour of interesting developments built in the last two decades
Is that immigrant high-skilled or do they just have a fancy degree?
Everything, apparently, has a second life on TikTok. At least this keeps us skeptics busy – we have to redebunk everything we have debunked over the last century because it is popping up again on social media, confusing and misinforming another generation. This video is a great example – a short video discussing the “incorruptibility’ […] The post Incorruptible Skepticism first appeared on NeuroLogica Blog.
