The Sciences

Practicality and the Universe

Cosmic VarianceBy Sean CarrollOct 6, 2009 12:46 PM

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This year's Nobel Prizes in Physics have been awarded to Charles Kao, for fiber optics, and Willard Boyle and George Smith, for charge-coupled devices (CCD's, which have replaced film as the go-to way to take pictures). Very worthy selections, which are being justly celebrated in certain quarters as a triumph of practicality. Can't argue with that -- as Chad says, things like the internet (brought to you in part by fiber-optic cables) and digital cameras (often based on CCD's) affect everyone's lives in tangible ways. But they are also important for lovely impractical uses! When I hear "fiber optics" and "CCD's" in the same breath, I am immediately going to think of the Sloan Digital Sky Survey (SDSS), which has provided us with the most detailed map we have of our neighborhood of the universe. Almost a million galaxies, and over 100,000 quasars, baby! How impractical is that?

The SDSS is a redshift survey, which means it's not sufficient to just snap a picture of all those galaxies; you also want to measure their spectra (i.e., break down their light into individual frequencies) to see how much they have been shifted to the red by the cosmological expansion. And you just want the spectra of the galaxies, not the blank parts of the sky in between them. The Sloan technique was to drill giant plates for each patch of sky, with one hole corresponding to the position of every galaxy to be surveyed. (There were a lot of plates.) This image from the Galaxy Zoo blog.

Then you want to bring that light down to the camera. You guessed it -- fiber-optic cables. Thanks, Dr. Kao.

The camera in question was possibly the most complex camera ever built -- thirty separate CCD's, combining for 120 megapixels in total, all cooled to -80 degrees Celsius. Thanks, Drs. Boyle and Smith.

And the result is -- well, it's pretty, but it doesn't materially affect your standard of living. It's a map of our local neighborhood in the universe. Extremely useful if you'd like to understand something about the evolution of large-scale structure, for example to pin down the properties of dark matter and dark energy.

Also useful for providing a bit of perspective. It's technological advances like those honored in this year's Prize that make it possible for we insignificant sacs of organic matter to stretch our senses out into the universe and understand the much bigger picture of which we are a part.

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