Kip Thorne Talks Geometrodynamics (And Other Words To Impress Your Astrophysicist Father)
Written by Riva Weinstein
This Monday, Columbia hosted a colloquium with Dr. Kip Thorne, recipient of the 2017 Nobel Prize in Physics for co-founding the LIGO project. Arts Editor Riva Weinstein, who previously showed you how to one-up your cousin with Yugoslavian film trivia, hopes you too can use her newfound physics knowledge to impress your brilliant father even though you’re a humanities major and couldn’t tell a pulse wave from a periodic.
When Dr. Kip Thorne received a call at 2:15 A.M. one October morning with the news that he had been nominated for the Nobel Prize in Physics, the secretary general asked if he was surprised. “It doesn’t surprise me at all,” Dr. Thorne responded; “but I’m highly disappointed. It should have gone to the entire LIGO team.”
LIGO – the Laser Interferometer Gravitational Wave Observatory – is a pair of huge detectors which use laser interferometry to detect gravitational waves. Gravitational waves are ripples in space-time caused by the collision of incredibly distant, massive bodies (such as black holes). Their existence was prophesied by the great sage Albert Einstein in his 1916 general theory of relativity, but it wasn’t until 2015 that LIGO finally detected one.
Dr. Thorne is correct. LIGO is not the work of one, albeit brilliant, man. It is the project of hundreds of professors, grad students, postdocs and researchers. One of them is my father: Dr. Alan Weinstein, head of the LIGO data analysis group. Well, maybe Dr. Thorne was just jealous – for his own 20-year contribution to the project, my dad got a box of commemorative Nobel-shaped chocolate coins. Try chewing on that gold!
My father has always been highly supportive of my endeavors, including but not limited to drawing comics about Crime and Punishment and teaching Shakespearean actors to play the kazoo. Nonetheless, a time might never again come for me to impress him; and so, instead of doing something sensible, like composing choral Russian folk music, I headed down to Pupin on a Monday to listen to his old friend Dr. Thorne.
In addition to designing the LIGO project and performing cutting-edge research in gravitational waves and curved spacetime, Dr. Thorne was the science consultant for the Oscar-winning 2014 film Interstellar, which depicts the inside of a black hole. (All very impressive, but is it as great an achievement as my father, who graduated from Harvard at age 20, betraying no sign of disappointment when his daughter announced her intent to go to a women’s college and major in Anthropology?)
If we had expected him to talk about LIGO and Interstellar, however, we were disappointed. “If you were expecting me to talk about LIGO and Interstellar, you’ll be disappointed,” said Dr. Thorne. “I would prefer to talk to a physics audience about something that was a major motivation for me… one of the most interesting areas in science for the future.”
This area is geometrodynamics, a way to calculate the non-linear dynamics of curved spacetime. Geometrodynamics becomes useful wherever the fabric of spacetime is massively warped. Thorne studies three instances of spacetime warping: 1. At singularities; 2. When multiple large gravitational waves collide; and 3. When black holes collide. His current project involves using numerical analysis to create 3D simulations of these events. Then, the simulation is measured against real LIGO data.
A singularity, in addition to being a really cool Star Trek plot device, occurs at the center of a black hole when gravitational forces grow apparently infinite. As you approach a singularity, gravity operates like Earth’s tidal forces, stretching and squeezing you along perpendicular axes. This stretching and squeezing effect oscillates along a waveform, which is made even more complicated by what Dr. Thorne refers to as Mixmaster dynamics – essentially, gravitational chaos. Mixmaster dynamics refers to the theory that the early universe underwent an oscillatory phase, expanding and contracting in different sections as it developed. I would explain this in further detail, but unfortunately I spent 12th grade Physics thinking up strongly-worded letters to send my college advisor for forcing me to take 12th grade Physics.
The interaction between two gravitational waves can also produce an effect large enough to be detected by LIGO. One wave generates spacetime curvature, and another interacts with the curvature. If the combined amplitude of the wave is greater than the critical amplitude, a black hole forms; if it is less, the wave disperses. Little is known about this phenomenon, since numerical studies are still in their infancy. “There is a great richness to be uncovered,” says Dr. Thorne – much like the richness my parents hoped I would have, before I was majoring in Underpaid with a concentration in Unemployed.
The most dramatic astronomical event of all – and the one most often detected by LIGO – is a collision between two black holes. Matter behaves very strangely around these bodies. In addition to the stretching and squeezing effects, the two poles of a rapidly spinning black hole will cause matter to twist in a clockwise or counterclockwise vortex. When two black holes begin to merge, they briefly have four vortices. Then, as the merged black hole wobbles into shape like a rubber ball, the vortices rapidly exchange polarity until they assume two fixed poles. The integration of the two black holes sends out ripples in space-time, which eventually reach Earth, causing a blip in LIGO’s interferometers.
I, the only member of my immediate family who did not go to Harvard, found all of this extremely interesting and totally comprehensible. But Dr. Thorne wasn’t done yet. He discussed how his predictions in geometrodynamic simulation matched up with real LIGO results – and sometimes didn’t. His 1984 speculation on a black hole collision waveform was far more complex than the waveform recorded in 2015. He had accounted for perturbations which, though they did originate deep in the neck of the black hole, disappeared quickly once they left the black hole. The real waveform was relatively simple.
LIGO measurements of gravitational waves give us information about the mass, distance and source of the events which produced the waves. But as Dr. Thorne reminds us, scientists have “barely scratched the surface” in their understanding of black holes. Only a handful of events have been recorded so far, and gravitational waves can tell us nothing about the singularity. Perhaps only Matthew McConaughey will ever know its secrets.
When the lecture was over, I worked up the courage to introduce myself to the amiable Dr. Thorne. I asked him a question about neutron stars, to which he responded eloquently, but I can’t explain the answer since I wrote my last academic term paper on the Orientalist dynamics of Tintin. Then I asked him the more important question: did he get a box of the Nobel chocolates, too?
He looked surprised for a second, and then he laughed. “Yes, I did.”
God damn it.