Friday, January 22, 2010

The last scattering horizon

(In memory of Andrew Lange)

In cosmology, the surface of last scattering is the "wall of light", the last horizon from which the CMB, the cosmic microwave background we measure today comes to us from the depth of cosmic time, when the photons of the microwave background radiation decouple from matter. In more metaphorical terms, people too have their own last horizon, a boundary of the observable universe, beyond which one cannot directly probe and which represents that external surface from which all information we can access is collected, shielding away a core destined to remain forever out of reach. One tries to guess shapes and structures hidden beyond the horizon through the feeble signs that emerge, inscribed on that last scattering surface.

Some of the most exciting discoveries that brought cosmology to a central role at the frontier of science have come from probing the cosmic microwave background. We recently learned that the global geometry of the Universe is flat, or nearly so. A natural question that scientists and philosophers have pondered about at least since the times of Giordano Bruno, but which, until so very recently, appeared to be completely out of reach of any experimental verification. Now, for the first time in history, we know. This amazing piece of knowledge came to us through the so called Boomerang experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics, that is). The suborbital balloon flights of the telescope in the Boomerang experiment provided a precise measurement of the angular diameter distance to the surface of last scattering. Combined with data on the Hubble constant, these sufficed to pin down the constraints on the geometry of the Universe. A most beautiful story.

I have never known much about cosmology. It was only in the past year that I made a first attempt at wandering about this glorious landscape, with small uncertain steps. A case of peer pressure probably, given where I am now working. I still know very little, naturally, I am just a silly mathematician borrowing other people's toys and foolishly playing around with them. I enjoyed it, though: it gave me an excuse to begin to learn something completely new to me, and also a way to begin to feel somewhat more at home in my new surroundings, to start creating that sense of belonging I had missed so much for so long. On a more personal level, engaging in the act of learning something new and different from anything I had been doing before was also a way for me to try to get out of a creepy depression I have been trying to come to terms with for several months.

When I first got here last year, to my new job, to the tragic beauty of California and its morbidly sensuous breathtaking landscapes, one of the first people to welcome me into the local scientific community was that same cosmologist responsible for the Boomerang experiment and the discovery of the flat geometry of the Universe: Andrew Lange was also the head of our division, in charge of the Physics, Mathematics, and Astronomy section of Caltech. I was not a close friend of Andrew's, I did not have the time to get to know him well enough, but we exchanged thoughts several times, on mathematics and theoretical physics, on mundane matters of everyday concern, hiring, such things. I told him one day that I was thinking of submitting a grant proposal on some admittedly very weird mathematical thoughts about cosmology: I felt awkward about it, as if I had been in the process of trespassing on someone else's territory. There is always that fear we carry around in our work, of publicly exposing our inadequacy. And yet, he listened to me and he was very encouraging. Not much came of my work, one new paper, big deal. No major breakthrough to write home about, I know, but the encouragement that he offered at that time did matter a lot to me, when so many things had seemed suddenly so difficult to cope with. It helped.

Andrew killed himself last night. We were all informed today during an emergency faculty meeting. He, we learned, had been struggling with mood disorder and a severe depression. And yet, all along, he was always there: for his research group, for the pressing demands of his administrative job, for all the needs and duties. He had nice words to offer, thoughtful scientific comments to make. Helpful, considerate, understanding. How much did it cost him, I wonder, to maintain all that intact until the very last? I know something about those dark psychological spaces, of what it feels like inside: it is the growing weight of the soul that drags you down, the endless pain that keeps exploding in the mind and never stops, the shadow that walks with you, and yet every day one needs to find the strength to live another day, to appear as the world expects you to appear. To act as your role demands. To live up to all the expectations, to be better and more efficient than ever until all the inner strength and resilience is consumed. In truth, I know nothing about what happened to him, I was not close enough to know. We only ever saw the smooth reassuring appearance of his last scattering surface, beyond which we could not probe. Perhaps, we should have paid closer attention to the feeble warning signs inscribed on that horizon: we should have searched it for clues to the inner core of suffering, to the hidden geometry of that very personal universe.

Andrew Lange's Segre Lecture: How did the universe begin? Berkeley, November 9, 2009.