Author: John F. Lindner

  • Kelly Twin Paradox

    John F. Lindner

    Yesterday astronaut Scott Kelly returned from nearly a year in free fall aboard the International Space Station to join his identical twin brother Mark back on Earth. Due to their different spacetime paths, I estimate that Scott aged about 9 ms less than his brother, and therefore travelled about 9 ms into the future, becoming one of…

  • A New Kind of Astronomy

    John F. Lindner

    One of the first things I did as a grad student in 1982 was tour the Laser Interferometer Gravitational Wave Observatory (LIGO) prototype on the Caltech campus about a block from my dorm. It was housed in a utilitarian L-shaped building wrapped around the corner of another building. I toyed with the idea of working…

  • Hillary & Armstrong

    John F. Lindner

    You’re probably familiar with the iconic photograph of Edmund Hillary standing atop Earth’s highest mountain wearing an oxygen mask in air so thin the sky is almost black as space — but apparently Hillary declined to be photographed and instead this photograph is by Hillary of his companion Tenzing Norgay during 1953’s first successful ascent of…

  • Ticktock Deadbeat Escapement

    John F. Lindner

    The escapement is one of history’s greatest inventions; it enables a collection of wood or metal to tell time. The animation below illustrates a pendulum clock’s deadbeat escapement, apparently introduced by Richard Townseley, Thomas Tompion, and George Graham in the late 1600s and early 1700s. The escapement wheel transfers energy to the pendulum to overcome…

  • The Falcon Has Landed

    John F. Lindner

    Monday evening, the first of SpaceX’s 70 m (or 230 ft) Falcon 9 full thrust launch vehicles successfully deployed 11 satellites to low Earth orbit — and performed reversal, supersonic retrograde, and landing burns to return the first stage to Cape Canaveral. Recent upgrades to the Falcon 9 include densified oxidizer and fuel, with liquid oxygen…

  • ER = EPR?

    John F. Lindner

    This month is the 100th anniversary of Albert Einstein’s November 1915 discovery of the gravitational field equations of General Relativity, in which test masses move along the straightest possible paths (called geodesics) in spacetime curved by the density and flux of energy and momentum (including mass and pressure). General Relativity allows spacetime to be topologically…

  • The Martian

    John F. Lindner

    Ridley Scott’s The Martian (2015) is the best Mars movie I have yet seen. Genuinely faithful to Andy Weir’s popular novel, The Martian chronicles astronaut Mark Whatney’s struggle to survive on Mars, after being accidentally stranded there, and the efforts by NASA and Whatney’s crew to rescue him. The story emphasizes the problem-solving character and…

  • 19th Century Foreground, 20th Century Background

    John F. Lindner

    Although some early aviation aficionados allege other flights (or hops) preceding the Wright brothers’ experiments at Kitty Hawk on 1903 December 17, the Wright Flyer did fly four times that day, including a final flight nearly one minute long, with the Wrights famously photo documenting their progress. They never flew that first aircraft again. Instead,…

  • On the Shore of the Arctic Ocean

    John F. Lindner

    It was a privilege to spend the 2014-2015 academic year and summer on sabbatical at the University of Hawai’i in Honolulu. During the last week of July, I stood on the spectacular beach at Kailua near sunset and said to myself “wow, wow, wow”. A week later, on my way home, I stood on the…

  • Rubik’s Cube Puzzles

    John F. Lindner

    As a kid, I enjoyed solving the “15 puzzle”, a sliding puzzle consisting of a 4×4 grid of 15 squares. However, I was amazed by a kind of 3D analogue of the 15 puzzle: Ernö Rubik’s 1974 masterpiece, which is both a seemingly impossible mechanism (how does it not fall apart?) and a silent challenge (one…

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