Losing Andrew Lange


Cosmology suffered a great loss yesterday with the passing of Andrew Lange, co-leader of the BOOMERang experiment, which provided the first experimental evidence that our universe is flat, and offered strong support to the supernova evidence for dark energy. Lang was a professor of physics at Caltech, and that tight-knit community is reeling from the news that Lange apparently took his own life. I only met Lange once, but my husband Sean, a Caltech colleague, knew him well and offers his own eulogy (of sorts) over at Cosmic Variance:

It’s hard to convey how unexpected and tragic this news is. Very few people combined Andrew’s brilliance as a scientist with his warmth as a person. He always had a sparkle in his eye, was enthusiastically in love with science and ideas, and was constantly doing his best to make Caltech the best possible place, not just for himself but for everyone else around him. He was one of the good guys. The last I spoke with him, Andrew was energetically raising funds for a new submillimeter telescope, organizing conferences, and helping plan for a new theoretical physics center. We are all walking around in shock, wondering how this could happen and whether we could have done anything to prevent it.

The only way I can think to honor Lange is to tell you a bit more about his most famous work. BOOMERang stands for Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics, and it's essentially a balloon-borne telescope designed to make measurements of the cosmic microwave background radiation — the "afterglow" of the Big Bang that still pervades our universe. The first flight, in 1997, concentrated on North America, while two subsequent flights in 1998 and 2003 circled the South Pole.

Based on this data, the BOOMERang team made the most detailed map of temperature fluctuations in the CMB — at least as of April 2000, when the first results were announced. (Science always marches on.) The CMB is pretty smooth, so those fluctuations are tiny, with differences of 1 part in 100,000, and hence very difficult to measure.

Those fluctuations provided the "seeds" that eventually grew into the gigantic galaxies, galaxy clusters and cosmic structures we see in the cosmos today. What BOOMERang did was to measure the size of those fluctuations in angular measure (degrees). I'll let these folks explain why that's significant:

f we know the angular size of something, and its actual size, we can measure its distance. We do this all the time; we know roughly how far away a hill is because the people on it look quite small. In curved space the sums are more difficult, but the principle is similar. The extra complication is that we have to make sure that the inferred distance to the "last scattering surface" fits in with its redshift, or age, which we know anyway. This means we have to choose the right curved space…. The conclusion is that space has to be "flat". This means it is just like the familiar space of high school geometry, where the area of a circle depends on the square of its radius, and parallel lines never meet. This is the only geometry in which the distance we measure to the last scattering, using the angular size, can match up with what we know about how long ago last scattering happened.

BOOMERang's exciting results were the first "to resolve the structures in the CMB, allowing us to 'see' structures that predate even the first star or galaxy in the universe," Lange said in an interview with the European Space Agency in 2001. But he was always looking forward to the next experiment — in this case, the Planck satellite that launched last spring. Planck's instruments have even better resolution than BOOMERang, capable of measuring many more frequencies in the CMB, and it will cover the entire night sky, instead of just select regions. "Planck will be revolutionary!" Lange declared in that 2001 ESA interview. It's a tragedy that he didn't live to see the revolution in action.

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