Author: John F. Lindner

  • An academic in industry

    John F. Lindner

    Recently, with members of NCSU’s Nonlinear Artificial Intelligence Lab, I completed a 3.5-year project as a subcontractor working on an industrial project. As an academic, this was a novel experience. Unlike most of my research, this work will not result in a journal article or conference presentation, although it might one day contribute to an…

  • Does a charge in gravity radiate?

    John F. Lindner

    Caltech, Saturday night, grad student pizza. The conversation turns to a famous general relativity puzzle: does an electric charge at rest in a gravitational field radiate? According to Einstein’s equivalence principle, a static homogeneous gravitational field is indistinguishable from constant acceleration in empty space, and as is well known, accelerating charges radiate. Does that mean…

  • The Longest Flight

    John F. Lindner

    As a kid pouring over the Guinness Book of World Records, I was astonished by the record longest flight, which lasted not just a few hours – as I would have guessed – but more than two months! Today, nearly 65 years later, that amazing achievement remains one of aviation’s most enduring records. For over…

  • Where Are the Stars?

    John F. Lindner

    When viewing space photography, such as Apollo or International Space Station photos, people often ask, “Where are the stars?” Typically such photos properly expose the bright lunar or space station surfaces and consequently underexpose the dim background stars, rendering space as featureless black. Current ISS astronaut Matthew Dominick has been experimenting with photography, and his…

  • Bertrand’s Postulate

    John F. Lindner

    When searching for prime numbers, the next prime number is no larger than twice the current number. Postulated by Joseph Bertrand, first proved by Pafnuty Chebyshev, I present an elementary proof based on one by the teenage Paul Erdős. Erdős was one of the most prolific twentieth century mathematicians, publishing about 1500 articles with more…

  • Aero thermo dynamics

    John F. Lindner

    Up early this morning to watch the spectacular fourth integrated flight test of SpaceX’s Superheavy Starship, the largest rocket ever built. Each IFT has greatly improved on the previous one, and the fourth was no exception. For the first time, both the booster and the ship softly splashed down in the ocean! Especially impressive was…

  • Stegosaurus Tiling

    John F. Lindner

    John Chase, the head of the Walter Johnson High School Math Department, in Maryland, near Washington DC, liked my Stegosaurus variation of the Spectre monotile so much that he had his students paint it on the wall of their math office! Attached are a couple of photos he shared. Smith, Myers, Kaplan, and Goodman-Strauss recently discovered an infinite…

  • A Better Alphabet

    John F. Lindner

    I still retain the episodic memory of my first encounter with the spelling of people. I was learning to read, and I got cat, mat, pat; I got lot, pot, dot; but I did not get people. Why the o, and why the le instead of el? Soon after I balked at Wednesday; surely that should be something like Wensday (or even Wenzday)? I had…

  • Measuring the Solar System

    John F. Lindner

    Thousands of years ago, ancient astronomers like Aristarchus and Eratosthenes combined careful observations with simple mathematics to measure the solar system, especially the diameters D of Earth, Luna (Earth’s moon), Sol (Earth’s star, the sun), and the radii r of their orbits. You too can do this, but it helps to observe an eclipse or two.…

  • Wooster’s Time Crystals

    John F. Lindner

    Saturday, March 8, 2008. A heavy snow, one of the heaviest I remember, shuts down the city of Wooster. Streets are undriveable, so I walk to Taylor Hall, getting snow in my boots. Taylor is deserted, as the College has begun Spring Break, but like yesterday, Kelly and I work all afternoon and evening in…

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