Days of Summer

by Shane L. Larson

As a father, I watch my daughter scoot off to summer camp with a vaguely unsettled sense of longing for those by-gone days of my youth. As grown-ups, we don’t go to “summer camp” any more. Instead, we sometimes have “vacation,” but vacation never has quite the same care-free, no-holds barred, reckless sense of fun, adventure and freedom that summer camp always had. There’s just too much of the trappings of being a grown-up tied up in “vacation.”  Too much “enjoying the morning paper by the pool” instead of “dodge-ball.”  Too much “eating a salad with this fancy dinner” instead of “let’s blow every last penny I have in this candy store.”  Too much “looking for the Museum of Historical Art” instead of “standing on our heads to find the Zowie Rock so our cabin wins the giant popsicle tonight!”

But sometimes I find myself in a kayak on a still mountain lake, my phone forgotten (or dropped overboard), and nothing on my mind except that serene fugue state of thought that whispers, “if you keep paddling, there is no telling what’s on the other shore…”

As a scientist, I have the immense good fortune of doing something I love every day — probing the mysteries of the Cosmos, mentoring young (and old!) minds on their own voyages of self-discovery, and adding to the collective knowledge of our species. But a job as a scientist is still just like every job, and it has its share of interruptions and stresses. There is always another telecon to be on; there is always another deadline for book orders and class website requests; there is always a student who needs some career advice; there is always another midterm exam to write or grade; there is always another grant you should write a proposal for to support your next student on their path to knowledge. Like every job, there are good days and bad days, and many days that make you long for those by-gone days of summer camp!

This year I was able to spend three weeks in a workshop at the Aspen Center for Physics. Founded in 1962 by George Stranahan and Michael Cohen, the Aspen Center for Physics is located on a small, 3 building campus in Aspen, Colorado. It shares this idyllic setting with two other world-renowned intellectual organizations: the Aspen Institute, and the Aspen Music Festival and School. The idea of the Aspen Center for Physics is simple — bring scientists together, away from the demands of every day life, and give them freedom and opportunity to think and interact. Isolation combined with creative intellectual colleagues can and will spawn remarkable and ingenious moments of progress at the forefronts of science.

Let me tell you some tales about my few, short weeks at the Aspen Center for Physics.  If my third grade teacher (Mimi Martin) is out there reading this, you might call this my “What I Did This Summer” essay!

My office at the Aspen Center for Physics

The Setting: The Aspen Center for Physics is set on a small campus with three buildings that are, for the most part, comprised entirely of offices for scientists, and small meeting “alcoves” where groups of us can gather to hash out mysteries and plot to win Nobel Prizes.  We share offices, kind of like when we were students, usually with a complete stranger, and often with someone who is not in our same discipline. This mixing of minds is an essential part of the Aspen Center for Physics’ recipe for success — exposure to new ideas and learning new things about other subjects always generates new and interesting approaches to science (I’ve written about that before).

The campus itself is pastoral and idyllic, replete with gathering spaces and benches conducive to quiet contemplation and speculation about the inner workings of the Cosmos. Again, the setting is purposeful — intended to produce an isolated and minimally distracting environment, free of the normal trappings of everyday life, in an effort to allow the mind the freedom to explore new ideas and discover new approaches to science.  All things being equal, it is a model that has succeeded admirably — over 10,000 physicists have visited the Aspen Center for Physics since its founding, including 52 Nobel Laureates. Over the years, more than 10,000 scientific publications have emerged as a result of time spent at the Center.

Campus of the Aspen Center for Physics.

The Workshop: The workshop I came to the Center for was about “ultra-compact binary star systems.” That’s a mouthful — the kind of thing you like to tell your mother you work on because it sounds important. Whatever does it mean? Most stars you see in the sky, possibly as many as 50%, have a companion star that orbits them, like the planets orbit our Sun. We call these systems “binary stars.”

When stars reach the ends of their lives, they typically evolve into one of three different kinds of skeletons that mass as much as the Sun or more. These three stellar skeletons are called white dwarfs (something about the size of the Earth, made by low mass stars), neutron stars (something the size of a small city, made by medium mass stars), or a black hole (also about the size of a city, but made by much more massive stars).  Given the menu of stellar skeletons, you can imagine that long after binary stars are born, you can (and do!) end up with a binary made up of TWO stellar skeletons!

Evolutionary pathways from stellar life into the graveyard after stellar death. The three end states are white dwarfs, neutron stars, or black holes, depending on the mass of the star in its life. [Image by NASA/CXC/M.Weiss]

Over time, the orbits of these skeletal star systems shrink smaller and smaller and smaller, until the stars are so close together they orbit at phenomenal speeds. For a pair of white dwarfs that orbit once every 15 minutes, they are separated by about half the Earth-Moon distance, and are travelling at a speed of 1 million meters per second (about 2.4 million miles per hour)!  These are “ultra-compact binary star systems.”

Ultra-compact binary systems have stellar mass objects, like two white dwarfs, orbiting in extremely small, short period orbits at extreme speeds.

My office chalkboard after just a couple of days at the Aspen Center for Physics.

What Happens: We talk. A LOT. There are chalkboards all over the Center — in the offices, in the hallways, and outside on the patios.  There are always clusters of physicists around them — debating, deriving, teaching, learning. I know it sounds funny, but this is where a lot of science is born.

For instance, my graduate student and I have been working on a project where we need to know something about the number of neutron stars in the galaxy.  We need to know how many there might be, because we are thinking about an interesting way to observe them. If there aren’t very many neutron stars, we should abandon the idea, but if there are a lot of neutron stars, it could be important. I promised her that I would ask around at the workshop to see if anyone knew anything that could help us out.

(L to R) Me with my colleagues, Matt Benacquista and Melvyn Davies.

So one day I was talking about this to my colleagues, Melvyn Davies (Lund University, Sweden) and Matt Benacquista (University of Texas-Brownsville) — they’re both experts in this sort of thing. They told me some very useful stuff, which I’ve passed on to my student. But at one point Melvyn asked me from how far away we could detect the gravitational waves from systems with a neutron star and a white dwarf together. I sketched out a quick calculation that suggested this was a very interesting idea to think about, and soon the three of us will publish a paper about how to study these systems with gravity, not light. It’s perhaps surprising that no one has thought about this before, but it’s a big Cosmos — there is a lot to think about! This is what the Aspen Center for Physics was designed to do — put scientists together, and let their brains roam free to make new discoveries.

And it’s not just at the Center that this stuff goes on. We are together all the time, which means we are always thinking and talking about science, usually intermixed with other enjoyable life activities.  We segue in and out of science and life the way you often segue in and out of sports and life or weather and life.  For instance, on any given evening if you are in Aspen, hanging out, eating dinner at the famous Hickory House, you might find us sitting next to you. You might be engaged in pleasant conversation about a nice hike you took earlier that day; we of course were hiking earlier that day too, but are still debating the question that occupied us on that hike, namely whether or not star systems with highly elliptical (oval shaped) orbits can be detected farther away in the Universe by LIGO than star systems with circular orbits.

When two stars orbit one another, the orbits can be perfect circles, or they can be elongated ellipses; we say these orbits are “eccentric.”

Fun and Games. While it is all science all the time, it’s not all high-brow esoteric research. Physicists, as a rule, love to talk about what they do, as most of you who have a physicist neighbor or relative know. The Aspen Center for Physics hosts a regular public lecture series, intended to explain for a popular audience what physics is all about, and why and how we do physics. This summer I had the good fortune to hear K.C. Huang from Stanford talk about the evolutionary life cycles of bacterial cells and colonies, and also a talk about the dark energy in the Universe from my colleague, Bob Kirshner of Harvard (Bob has written a very nice book on this topic).

Bob Kirshner (Harvard) during his 2014 Heinz Pagels Public Lecture about Dark Energy and the Accelerating Universe.

I also got to put my public game on, when I was asked if I could do a half-hour chat at the “Physics for Kids” picnic, hosted by the Aspen Science Center at the Center for Physics. This was a crowd of about 20 or 30 9-10 year olds and their parents, so I decided to talk to them about energy, which is and will continue to be a crucial topic of conversation during their lives.  So we talked a bit about how scientists think about energy, and then I did three demonstrations. First, we made craters in a tray of flour, showing how the size of the crater depends on the energy of the impactor — the biggest crater was made with a hollow shell shot from a paint-ball gun.

Impact crater made by a paintball shell from a distance of about 1.5 meters. Typical speed for a paintball shell is about 90 m/s (~200 mph!). Crater size is about 7 cm across. (Click to enlarge!)

Second, we showed how energy is stored and converted using the famous “Bowling Ball of Doom” demo. You mount a bowling ball to a long cable, then hold it against your chin. When you release it, the bowling ball swings out across the room, then comes right back at your head but stops at the precise point you released it! It really looks like it is going to smash you in your face, but that is an impossibility because that would require it to obtain some energy from nowhere.

First person views of the Bowling Ball of Doom Demo. (L) The bowling ball is initially held touching your chin. (C) After release, the bowling ball swings away, then right back at you! (R) If you tie a camera to the bowling ball, you see it is moving pretty fast (about 3.5 m/s, or 8 mph!). (Click to enlarge!)

The last demo, as any of my students can tell you, is the Number One Physics Demo of All Time: the Bed of Nails. I lay on a bed of nails. A second bed of nails is laid on my chest. A cinder block is placed on top of that. A volunteer (in this case, my colleague, Stephan Rosswog, from Stockholm University) takes a 10 pound sledgehammer and smashes the cinder block. Obviously I survive (otherwise I wouldn’t be writing this blog!). How? The cinder block dissipates the energy of the hammer by breaking, thus sparing my life. You can see some videos of this demo: slow motion view; low, ground level view; first person head-mounted GoPro view.

(L) My Bed of Nails hammer weilder, Stephan “Thor” Rosswog (C) Matt Benacquista makes sure the GoPro is ready to capture the action! (R) Stephan works out some of the day’s frustrations… 🙂 (Click to enlarge!)

Me and J. Craig Wheeler. He’s one of the reasons you’re reading this blog right now!

But probably the most important thing that happened this summer at Aspen, was I closed a loop in my career. When I was a young man, just starting out in college at Oregon State University, I was a mechanical engineering major. The reason for this was I was going to be an astronaut, and the way to become an astronaut (during the shuttle era) was to become a mission specialist, and one way to become a mission specialist was to design experiments that flew on the shuttle. At Oregon State during this time, there was a general science class taught called “Rocks and Stars,” and during my first year there they brought to campus a guest speaker: Dr. J. Craig Wheeler, from the University of Texas at Austin. Wheeler gave a great public lecture about black holes, which made me start seriously thinking about this whole astronomy business. This, of course, ultimately culminated in me becoming a physicist (a story I have written about before). As it turns out, he was at the Aspen Center for Physics this summer. We got to chat and hang out, I got to tell him the story that I just told you, and got a selfie of the two of us. 🙂

My colleague, Enrico Ramirez-Ruiz, a professor in the Department of Astronomy and Astrophysics at the University of California – Santa Cruz, summarized a sojourn at the Aspen Center for Physics very succinctly: “It’s like summer camp for physicists.”

And so it is. It clears the mind, it rejuvenates the soul, it connects you with people of like mind and like spirit. We argue, we debate, we eat, we laugh, we play, and we try to push science a little bit farther forward.  And like those summer camps from our youth, it is over far too soon. But you go home with new friends, with new ambitions, and a burning desire to come back again soon.

 

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This post was written during, and after, a summer residency at the Aspen Center for Physics.