I was honoured to attend the APS meeting in Baltimore between 14-19 March. The meeting was amazing—though I found myself oscillating between: “I get this” to “Umm… I think I understand some of what they are talking about” to “Really? What are they talking about?”. Overall, a five star rating, if you ask me!
A researcher from LIGO spoke to us about Gravitational Waves and explained how the advanced LIGO works.This massive book contained all the titles of the various talks/posters being presented.
There were over 9000 physicists+students at the conference and the topics ranged from the predictability of lightning, details behind the advanced LIGO project, progress in bio inspired robotics, to the bead-pile theory (Dr Lehman’s group!)! And these were from the sessions I attended—there were dozens of simultaneous sessions and much as we wanted to attend many, our physicality permitted only one session at a time. Given an opportunity, I would love to be back for more—hopefully, in a year, some of the esoteric subjects may seem a little more comprehensible.
This slide shows the diagram of a graduate student’s model of a mosquito’s proboscis (the mosquitos mouth part), which he implemented in a robot.This slide shows how gold nanoparticles inside water can help generate steam with light! Amazing!
I would strongly recommend this conference to any aspiring physicist, engineer, or, well, any curious student interested in all kinds of fun stuff!
Whew! It’s been a while since I have been at the March Meeting for the full week, and I definitely reached information overload. But before signing off, I wanted to summarize Day 5, Friday!
There were a number of interesting choices in the morning, but I chose to go hear Miles Padgett of the University of Glasgow give a talk on Ghost Imaging with Entangled Photons. He does really cool things with light, and his job title is officially the Kelvin Chair of Natural Philosophy, which is a title with wonderful history embedded in it. The talk was about using entangled photons, which are thus correlated in terms of where they came from within a down-conversion crystal, to image an object. One photon passes through an object of some sort and is just collected in a ‘bucket’, and when there is a photon in that bucket, there must be a correlated photon in the other leg of the optical system. That correlated photon can be collected on a CCD to create an image of the object, even though that photon never interacted with the object. Very interesting talk, and comprehensible even to me as a total non-expert in the area!
The main item on the agenda for the day was Catherine Tieman’s oral presentation in one of the afternoon sessions. It’s relatively unusual for one of our students to choose to give an oral presentation because the March Meeting is a pretty high stress situation. So, we definitely had some tension beforehand, but Catherine did a great job. It helped that the presenter immediately preceding her was an engaging and very funny speaker, so he warmed up the room a bit. Catherine even did a very nice job answering questions, which anyone who has done it knows is the hardest part of the March Meeting presentation.
Explaining some of the key points of the workCatherine prepares to answer questions.The leap of triumph after the talk!
I spent only part of Day 4 at the meeting in Baltimore. After some sessions in the morning, I got to tour some of the Johns Hopkins engineering facilities and hear more about the research that Elliot Wainwright is doing there.
Then I took the train down to Washington DC in the afternoon so that I could see an art exhibit I really wanted to catch, and also have dinner with my sister.
Both my walk in to the meeting and the art exhibit reminded me how amazing physics (especially optics) are all around us, if we just take the time to notice.
Reflection in the Harbor
As I crossed one of the bridges connecting the piers at the Inner Harbor, I noticed the reflection of a building in the water. Waves of light, waves of water — loads of physics.
Gabriel Dawe’s Plexus A1
The exhibit I traveled to DC to see is the Wonder exhibit at the Renwick Gallery. I was drawn there to see Gabriel Dawe’s Plexus A1, but all nine exhibits were amazing. In terms of optics, I was especially drawn to the dots of light that were created under each marble in Maya Lin’s installation Folding the Chesapeake. For the marbles on the wall, the light almost looks like another marble below the physical marbles.
A portion of Maya Lin’s Folding the ChesapeakeDetail of Folding the Chesapeake
Effects like this are why I love physics so much. It makes me notice the world around me so much more.
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
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
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 workJustine 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
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 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!
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!
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.
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!
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.
The familiar Pythagorean line element dl2 = dx2 + dy2 + dz2 (and corresponding metric) describes the geometry of Euclidean space. The Lorentzian line element – dτ2 = 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 dτ2 = 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 dτ = √(dt2 – dl2) = 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.
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.
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
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.
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.
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
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
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.
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
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.
Recent Comments
Thanks, Mark! I enjoy reading your posts as well.
Nice post, John! Thanks for writing these. I always enjoy them.
Thanks, Mark! I enjoy reading your posts as well.