• March Meeting Update – Days 2 & 3

    I knew when I posted the Day 1 update from the March Meeting that it would be pretty hard to keep up daily updates, and I was right!
    The students arrived on Tuesday morning, and Drew did a great job with his poster at the Tuesday afternoon poster session.

    Drew ready for visitors to his poster
    Drew ready for visitors to his poster

    We all had dinner together at Amicci’s in Little Italy which was amazing. Elliot Wainwright ’15 who is now at Johns Hopkins had recommended it and was able to join us for dinner.

    The Wooster crew at dinner on Tuesday night
    The Wooster crew at dinner on Tuesday night

    Day 3 – starting to get a little harder to get to those first sessions of the morning at 8 am! Avi and Justine had adjacent posters in the noon poster session and got lots of good traffic and had good conversations.

     

    Avi explaining his work
    Avi explaining his work
    Justine in action at her poster
    Justine in action at her poster

    It was also a beautiful sunny day for the first time, and people were absolutely clustered enjoying the day down by the inner harbor.

    Outside the convention center
    Outside the convention center

    In the evening, I ran into Justine at the Diversity Networking Reception. Before I bumped into her, she had been talking to another attendee who was a postdoc at Johns Hopkins. As I arrived, he asked her GPA and gave her his card and pretty much offered her a summer research job. That’s effective networking!

    The evening ended with the Rock-n-Roll Physics Sing-a-long, which was hilarious. Geeky? Yes, but in a fabulous way. And, the band was really good!

    I'm a LIGO believer!
    I’m a LIGO believer!
  • March Meeting 2016 – Day 1!

    I’m at the March Meeting in Baltimore this week — Day 1 was today, which is so appropriate since it is both Einstein’s birthday and Pi Day!  They were giving away pie at the APS booth in celebration.

    The March Meeting is the largest gathering of physicists in the world, so it’s always bursting with energy in a rather chaotic way.  When I first went to the March Meeting in the 1990s, I think there were around 30 simultaneous sessions.  This year, there are over 50 simultaneous sessions, and more than 10,000 attendees!

    IMG_0030
    Arriving at the Convention Center, just before 8 for the first session

    I spent most of the morning in the special sessions on Avalanches, which included my talk.  There were too many other great choices as well — I spent part of the midday session in the History of Electrical Science, including an interesting talk on how 19th century scientists tried to unify the theories of heat and electricity!

    IMG_0034
    Steven Weinberg

    The big talk of the afternoon was a session with theoretical physicist Steven Weinberg (Nobel Prize 1979, along with lots more awards) discussing his book “To Explain the World”. The talk was in a huge ball room with probably 600 chairs and there were still people standing in the aisles and packed four people deep standing in the doors.  It was an interesting discussion of some of the ideas in the book — about whether we can judge scientists of the past by the scientific knowledge we have now.

    Egg cooked at 61 degrees C. Photo courtesy of Lauren Aycock.
    Egg cooked at 61 degrees C. Photo courtesy of Lauren Aycock.

    Finally, an evening session on Science and Cooking was really interesting and fun.  Not only did they cook eggs in a constant temperature bath — comparing eggs cooked to 61, 63, and 65 C– but they also ‘cooked’ eggs in liquid nitrogen.  Yes, that’s right, even physicists who have been doing physics for a LOOONG time still get a thrill from seeing what they can freeze in liquid nitrogen.  We also got to see the science of different foams (specifically different types of whipped cream), and learned that the reason people don’t like either raw meat or overcooked meat is because of the elastic modulus, and saw an actual measurement of the modulus.  Direct quote: “We deform the chicken with a known weight…”

    So it was an amazing day 1 — tomorrow, four Wooster students will arrive at the meeting to present their work too!  Should be great!

  • Kelly Twin Paradox

    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 Earth’s most accomplished time travelers.

    As predicted by the theory of relativity, identical twins Mark and Scott Kelly aged differently during Scott's year in space. Photo credit: Robert Markowitz / NASA.
    As predicted by the theory of relativity, identical twins Mark and Scott Kelly aged differently during Scott’s year in space. Photo credit: Robert Markowitz / NASA.

    The familiar Pythagorean line element dl2 = dx2 + dy2 + dz2 (and corresponding metric) describes the geometry of Euclidean space. The Lorentzian line element – 2 = ds2 = – dt2 + dx2 + dy2 + dz2 = – dt2 + dl2 (and corresponding semimetric) describes the flat spacetime of special relativity, where space is measured in light-years and time in years. The Einsteinian line element 2 = gμνdxμdxν describes the curved spacetime of general relativity, with an implied sum over the indices. From third semester physics, in flat spacetime the proper time increment = √(dt2dl2) = dt√(1 – v2) = dt/γ, where the relativistic stretch γ ≥ 1 regulates the time dilation. More generally, the length Δτ = ∫ dτ of a spacetime worldline is the proper time or aging along it (which is most evident in the observer’s rest frame).

    In the curved, approximately Kerr spacetime of the rotating Earth, clocks tick faster with increasing altitude but slower with increasing speed. In low Earth orbit aboard the ISS, the speed effect dominates the altitude effect, sending Scott Kelly about 10 ms – 1 ms = 9 ms into the future. Furthermore, in curved spacetime, multiple free fall or geodesic paths between the same two events can have different lengths or aging, which can desynchronize clocks or twins without proper (as opposed to coordinate) acceleration — and without paradox.

  • A New Kind of Astronomy

    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 with Kip Thorne and Ron Drever on LIGO, perhaps making a career of it. I would be a small part of a large and long collaboration, but one that would probably make history. I chose a different path, but I never forgot LIGO, and I have closely followed its progress ever since. In 2007, I even co-advised Stephen Poprocki’s senior I.S. “Bayesian Source Direction Determination for Gravitational-Wave Bursts”, which was a small contribution to the LIGO effort.

    A packed crowd of Wooster physicists eagerly awaits the news from LIGO.
    A packed crowd of Wooster physicists eagerly awaits the news from LIGO.

     

    Last Thursday morning, I was thrilled to sit with the Wooster physics department in a crowded Taylor 111 watching the LIGO team announce the first direct detection of gravitational waves. I got goosebumps reading the discovery paper in Physical Review Letters. However, during a later replay of the press conference, I heard Kip say Ron Drever was too ill to be there, but his family sent their best wishes. Sadly, the New York Times reports that Ron is in a nursing home in Scotland suffering from dementia, this historic discovery apparently too late for him to savor.

    Audible chirps as proper distances between LIGO mirrors change by a few thousandths of a proton diameter in response to a binary black hole merger over a billion years ago
    Audible chirps as proper distances between LIGO mirrors change by a few thousandths of a proton diameter in response to a binary black hole merger over a billion years ago

    Gravitational waves are the analogue for gravity of what light is for electromagnetism but about 1040 times weaker. Over a billion years ago, two black holes spiraled together, merged, and rung down, radiating away the equivalent of about 3 solar masses of energy in a third of a second with more power than the luminosity of the entire observable universe. Last September 14th, gravity waves from the merger passed through Earth, stretching and expanding the 4-km long arms of the two LIGO interferometers, which were thousands of miles and several milliseconds apart, by a few thousandths of a proton’s width. The resulting chirps in strain were visible to the eye above the noisy backgrounds. History had been made, and a new era in astronomy had begun.

    The moment we first saw the now-famous plots of the gravitational wave signals.
    The moment we first saw the now-famous plots of the gravitational wave signals.
  • Hillary & Armstrong

    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 Mount Everest! You’re probably also familiar with the iconic photograph of Neil Armstrong in a pressure suit standing on the surface of Earth’s airless moon — but actually Armstrong carried the still camera for nearly the entire moonwalk, so  this photograph is by Armstrong of his companion Buzz Aldrin during 1969’s historic Apollo 11 moon landing!

    Iconic photos: Tenzing Norgay on Everest, 1953 May 29, and Buzz Aldrin on Moon, 1969 July 20. Photo credits: Edmund Hlllary and Neil Armstrong.
    Iconic photos: Tenzing Norgay on Everest, 1953 May 29, and Buzz Aldrin on Moon, 1969 July 20. Photo credits: Edmund Hlllary and Neil Armstrong.

    Hillary and Armstrong became friends later in life and even travelled together. In 1985, the pair flew from arctic Canada to the North Pole leaving the memorable logbook page reproduced below.

    Page from a logbook at an arctic inn where Hillary and Armstrong stayed during their July 1985 North Pole trip. Presumably the exclamation points were added later. Credit: Stephen Braham
    Page from a logbook at an arctic inn where Hillary and Armstrong stayed during their July 1985 North Pole trip. Presumably the exclamation points were added later. Credit: Stephen Braham
  • Ticktock Deadbeat Escapement

    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 frictional damping while periodically stopping (and escaping) to count the number of oscillations.

    Swinging pendulum (green) periodically locks escape wheel (red) interrupting fall of weight (brown) as escape well periodically nudges pendulum to compensate for frictional damping
    Swinging pendulum (green) periodically locks escape wheel (red) interrupting fall of weight (brown) as escape well periodically nudges pendulum to compensate for frictional damping

    The swinging pendulum (green) extends below each frame; a length of one meter provides a swing of about one second (and a period of about two seconds). The pallets attached to the pendulum periodically engage the teeth of the escape wheel (red) in two ways: near the extremes of the pendulum’s swings, the teeth hit the pallets’ curved faces concentric with the pendulum pivot with a torque-less “dead beat” and the wheel locks; near the pendulum’s equilibrium, the teeth hit the pallets’ angled faces clockwise or counter-clockwise to keep the pendulum swinging and the wheel rotates. The energy comes from a falling mass connected to the escape wheel by a rope (brown). This precision ballet provides the ticktock of mechanical clocks and watches.

  • The Falcon Has Landed

    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 supercooled to 66.5 K (or −340 °F) and the kerosene fuel RP-1 cooled to 266 K (or 20 °F) to store more energy per unit volume and help increase performance by about 1/3.

    The 48-m Falcon 9 first stage lands back at Cape Canaveral after launching the second stage and 11 satellites into Earth orbit, 2015 December 21
    The 48-m Falcon 9 first stage lands back at Cape Canaveral after launching the second stage and 11 satellites into Earth orbit, 2015 December 21

    Thanks SpaceX for this thrilling achievement and historic first, which may eventually radically lower space transportation costs, and thanks for sharing it with us live as it happened! If you missed the SpaceX broadcast, check out the landing excerpt, currently available on You Tube, for a great natural high.

  • ER = EPR?

    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 doubly connected. In the “wormhole” depicted below (using two different embeddings), the distance across the flat region may be large even if the distance through the tube is small. Traversable wormholes, like the one in the movie Interstellar, might be propped open by exotic matter of negative energy density and provide shortcuts across the universe. Such structures are sometimes called Einstein-Rosen bridges, after a 1935 paper by Einstein and Nathan Rosen.

    A wormhole is a geometry of four-dimensional spacetime in which two regions of the universe are connected by a "shortcut" consisting of two "mouths" connected by a short narrow “throat”
    A wormhole is a geometry of four-dimensional spacetime in which two regions of the universe are connected by a “shortcut” consisting of two “mouths” connected by a short narrow “throat”

    Also this month, several research teams reported the best yet experimental realizations of quantum entanglement, in which pairs of particles interact so that each particle cannot be described independently regardless of their separation. For example, an electron and positron in the ground state of positronium can annihilate into two oppositely traveling photons whose spins are completely correlated, so that measurement of one spin determines the other even if the measurements are spacelike (or so far apart that no signal could connect them). In the visual metaphor below, a Necker cube outline can be interpreted two ways, representing a photon in a superposition of two spins; similarly, a pair of Necker cubes can be interpreted two ways, representing measurements of its correlated parts. Such “spooky action at a distance” is sometimes called an EPR correlation after another 1935 paper by Einstein, Boris Podolski, and Rosen.

    Single ambiguous Necker cube is a metaphor for quantum superposition, while a pair of ambiguous Necker cubes is a metaphor for quantum entanglement
    Single ambiguous Necker cube is a metaphor for quantum superposition, while a pair of ambiguous Necker cubes is a metaphor for quantum entanglement

    Recent discussions of the black hole information paradox and the holographic principle in anti-de-Sitter-space model universes suggest a relationship between wormholes and quantum entanglement that may elucidate the nature of spacetime itself: Can Einstein-Rosen bridges explain Einstein-Podolski-Rosen correlations? Is ER = EPR?

  • The Martian

    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 skill of scientists and engineers in the celebrated tradition of the Apollo 13 rescue.

    Actor Matt Damon plays astronaut Mark Whatney marooned on a largely realistic Mars
    Actor Matt Damon plays astronaut Mark Whatney marooned on a largely realistic Mars

    I especially like the scenes of Whatney living, farming, walking, and driving on a mostly realistic Mars, with a near-terrestrial day-night cycle, authentic dust and sand and sky, including high wispy clouds and dust devils. I’d prefer less atmospheric pressure and sounds in Mars’ thin air (and space’s vacuum), more radiation protection and dust mitigation, and water from heating regolith (= soil) rather than catalyzing and burning hydrazine (= N2H4). I’d also like more accurate 0.38g surface gravity on Mars and more natural microgravity aboard the Hermes interplanetary spaceship (whose size and complexity I’d decrease while reducing the crew from 6 to 4).

    Indeed, The Martian makes me eager for more, especially for the real thing. I remember pausing one night to stare at the moon when people briefly lived on its surface during the Apollo program, and alongside that thrilling memory is the longing for another: to gaze at the ruddy dot of Mars amidst the stars while knowing other people live there — or to live there myself. As SpaceX founder Elon Musk said, it would be wonderful to be born on Earth and die on Mars*.
    —————–
    * But not in the landing.

  • 19th Century Foreground, 20th Century Background

    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, they went home to Dayton Ohio and built the successively better Flyer II and III and the Model A. Using those aircraft, Wilbur and Orville Wright became the first to fly for one minute, the first to fly for two minutes, for half an hour, for one hour, and for two hours. In fact, all world record flight times between 1903 and 1909 were set by the Wright brothers. They truly were first in flight.

    The Wrights became world famous when they demonstrated their flying machines in Europe in 1908-1909. Wilbur went first and was later joined by brother Orville and sister Katherine. Crowds came to watch them; even King George of England crossed the channel to France to see the modern miracle of flight. In the accompanying photo, farmers with an ox cart pause to watch Wilbur Wright and a passenger fly overhead, the 19th century foreground contrasting with the 20th century background.

    Wilbur Wright instructing a student pilot in Pau, France, passes over an ox cart in 1909
    Wilbur Wright instructing a student pilot in Pau, France, passes over an ox cart in 1909

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