Author: John F. Lindner

  • Continental Bridge

    John F. Lindner

    I remember looking at a classroom map of Earth and thinking the continents seem like puzzle pieces, especially north and south America in the west and Europe and Africa in the east. I mentally fit them together. Later I learned about continental drift and plate tectonics, driven by gravity and mantle convection, with newborn crust…

  • Table of Nuclides

    John F. Lindner

    As of 2019, we have identified or synthesized 118 distinct elements with Z protons, but about 2900 distinct nuclides with N neutrons (where atom is to element as nucleus is to nuclide). The start of my version of the table of nuclides is below, where number of protons Z increases toward 2 o’clock, number of…

  • Intrepid-Surveyor

    John F. Lindner

    Fifty years ago, Apollo 12 landed within sight of another spacecraft, a dramatic demonstration of pinpoint landing capability. While Dick Gordon orbited Luna in the command module Yankee Clipper, Pete Conrad and Al Bean left the lunar module Intrepid and walked over to the robotic Surveyor, which had landed over two years earlier. They retrieved…

  • Relaxing Fermat

    John F. Lindner

    In 1637, while reading a copy of Diophantus’s Arithmetica, Pierre de Fermat famously scribbled “Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos & generaliter nullam in infinitum ultra quadratum potestatem in duos eiusdem nominis fas est dividere cuius rei demonstrationem mirabilem sane detexi. Hanc marginis exiguitas non caperet.” which roughly translates to “It…

  • Stainless Steel Starship

    John F. Lindner

    Welders in a Texas swamp have built a starship. But don’t bet against SpaceX. Starship is a prototype upper stage for a next-generation, fully reusable, two-stage-to-orbit launch vehicle designed to enable the human exploration of the solar system and the colonization of Mars. It’s made from stainless steel. (A little carbon converts iron to hard steel;…

  • After the Moonwalk

    John F. Lindner

    Iconic is Neil Armstrong’s photograph of Buzz Aldrin during the first moon walk, with Armstrong reflected in Aldrin’s visor. Much less well-known is this pair of photographs taken just after the moon walk. To my eyes, Armstrong seems exhausted but happy; Aldrin seems satisfied … and over his shoulder, almost casually, is a window, and…

  • “Contact Light”

    John F. Lindner

    Our TV is broken, so Aunt Nora invites us to her apartment. (Aunt Nora isn’t really our aunt, but she introduced our parents to each other, so that’s what we call her.) My brother Jim and I lie on the floor close to the TV, while the adults sit on the couch. We watch NBC…

  • Wooster Epicycles

    John F. Lindner

    A vector is the sum of its components, a mechanical vibration is a combination of its normal mode motions, a quantum state is a superposition of its eigenstates, and any “nice” function is a Fourier sum of real or complex sinusoids, . The animation below traces the Wooster W in epicycles of 100 circles-moving-on-circles in the…

  • Redefining SI

    John F. Lindner

    Today the SI (Système international d’unités) base units are redefined. The following are now exact. Memorize these numbers! Cs-133 transition frequency constant  defines the second. Then light speed constant  defines the meter. Then Planck’s constant  defines the kilogram. Then electron charge constant  defines the Ampere. Then Boltzmann’s constant  defines the Kelvin. And Avogadro’s constant  defines the mole. And luminous efficacy constant  defines…

  • Black Hole Radii

    John F. Lindner

    I set the alarm for 8:55 AM. Brutal, but I wanted to watch live the National Science Foundation Event Horizon Telescope news conference. I was expecting the first image of a black hole, and the EHT team did not disappoint. But the black hole was not the Milky Way’s Sgr A*, but M87*, a thousand…

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