A few days after my birthday last year, the LIGO (Laser Interferometer Gravitational-wave Observatory) project detected its first ever signal from the collision of two black holes. For a brief moment, the gravitational waves (GWs) emitted by this cosmic crash put out 50 times more power than all the light from all of the stars in the universe combined.
The detection of this signal has been the implausible goal of generations of scientists. It resoundingly confirms a grand prediction of Einstein's theory of Relativity and has given humanity a new way in which to understand the universe - in addition to light, we can now use the vibrations of spacetime to 'feel' whats happening throughout the universe.
Every scientist bit by the GW bug seems to have some screwy story for why they got involved in this far-fetched hunt; this one is mine.
The gas station that I was working at was just a block away from the town's public library. During a lunch break, I went to find some light reading material. I got Albert Einstein's 'Relativity' - its only 80 pages long.
I didn't spend much time reading it until Hurricane Erin rolled through town. When the power went out, we lost the pleasures of AC and television. To pass the time, I sat out on the porch with my dad in the mortifying Florida heat and tried to relate to him what Einstein's book seemed to be saying. "Things get heavier when they go faster.", and "If I get on a fast rocket ship, I won't age so fast". We both agreed it was bogus. I personally felt it was scandalous that scientists thought that nature was so strange and were keeping this hidden from us. I thought that maybe I could get serious about studying physics and blow the lid off of the whole thing.
I imagine that everyone has those few moments in their life when everything changes. A slight pivot of circumstance forks off into a drastically different life. Reading 'Relativity' was one of those for me. The next one happened in 1997.
At the University of Florida, there's a lab course offered to seniors where they let you do all kinds of 'modern' physics experiments, to get a feel for how real experimental physics works and you get to switch projects every couple of weeks. That experience blew the top off of my head; I knew physics was interesting, but I didn't know until then that real world physics meant tinkering with gadgets and discovering new things about the universe. I knew that I had to convince someone to let me do this for a living.
Then luck struck. I hit the grad school jackpot, advisor-wise. Without the effect Rai Weiss had on me, I'd probably be arranging test tubes or cleaning oscilloscope screens today. Our first encounter was such an energizing experience for me that I can still tell you what we had for lunch (roast beef sandwich at Au Bon Pain) and all the questions he asked me ("Have you ever really looked at that 'bending of starlight' data?" and "You know how to weld a muffler?"). I got an inkling that this hunt for gravitational waves could be a fun adventure that might eventually lead to the first cracks in Einsteinian gravity.
Uh huh. Not so fast hotshot. In attempting to pass the doctoral qualifying exams, I spent too many Saturday mornings fumbling through physics problems on Rai's chalkboard. The combination of his sharp glare and creative profanity worked like a laser beam (wielded with a saintly patience) to sear the problem solving techniques into my mind. What kind of advisor comes into campus on the weekend to help his grad student learn to tie his own shoes?
After I passed, Rai hauled me down to Louisiana. We spent two years working on one of the early LIGO interferometers. It was very rare to get a professorial lecture from Rai. Most of those I can't write about since they lose a lot after removing the swearing and spittle. I don't know if it's always been his teaching style, but I learned everything just by working alongside him. I cannot explain how great this experience was; it must be something like what the grad students of Michael Faraday or Bob Dicke got to experience. It has been the greatest privilege of my life.
Rai also told me that we had a 50/50 chance of finding the black holes in those first few years...that was 17 years ago. We kept chipping away, getting those giant interferometers to be as sensitive as Nature would allow, but Nature was not sympathetic. The message I received had two parts: "If you don't understand the noise in your apparatus, you're an amateur." and "If your measurement is not limited by fundamental physics, go back to the sandbox where you belong."
The strategy from the beginning was to upgrade the machines after we had gained experience with the first giant interferometers. After over a decade of design and planning, the Advanced LIGO interferometers were assembled. The expertise built up over all that time meant that the scientific teams in Washington and Louisiana were much more powerful than the last time around. They got their machines working in a breathtakingly short period of time.
The upgraded system is beautiful: powerful, ultra-stable lasers, the smoothest mirrors ever made, and very clever vibration isolation. And it has even cleverer young scientists adept at the delicate art of interferometry. The price of so much gain is that the system is much, much more complicated than before. There are now hundreds of active feedback controls and many thousands of monitoring channels. The system must conform to the tightest specifications. So many places where something can go wrong.
Luckily, we had a person sitting in the middle of all of this, making it all fit together. I imagine him sometimes as a large brain at the center of a neural spider-web filling the world with strands entering every lab where we work on GW experiments. Among the core group of people who worked on the interferometer integration, we know that everything works so well because Peter Fritschel (Chief Scientist for Advanced LIGO) spent countless hours analyzing the whole thing, subtly guiding us for years, and making the right scientific decisions when needed.
Over a billion years ago, two black holes, each 10,000,000 times the mass of the earth, crashed into each other. Their gravitational ripples traveled through space for a billion years and recently passed through the earth, changing the distance between the LIGO mirrors by less than a millionth the size of an atom.
And our fantastic machine captured this signal.
I know that might sound like magic, but I wasn't so surprised. I've known for awhile that we had a wizard on our team.