LIGO to Collaboration Members: There Is No Santa Claus

By Sean Carroll | March 15, 2011 11:59 am

Ah, the life of an experimental physicist. Long hours of mind-bending labor, all in service of those few precious moments in which you glimpse one of Nature’s true secrets for the very first time. Followed by the moment when your bosses tell you it was all just a trick.

Not that you didn’t see it coming. As we know, the LIGO experiment and its friend the Virgo experiment are hot on the trail of gravitational waves. They haven’t found any yet, but given the current sensitivity, that’s not too much of a surprise. Advanced LIGO is moving forward, and when that is up and running the situation is expected to change.

But who knows? We could be surprised. It’s certainly necessary to comb through the data looking for signals, even if they’re not expected at this level of sensitivity.

Of course, there is something of a bias at work: scientists are human beings, and they want to find a signal, no matter how sincerely they may rhapsodize about the satisfaction of a solid null result. (Do the words “life on a meteorite” mean anything to you?) So, to keep themselves honest and make sure the data-analysis pipeline is working correctly, the LIGO collaboration does something sneaky: they inject false signals into the data. This is done by a select committee of higher-ups; the people actually analyzing the data don’t know whether a purported signal they identify is real, or fake. It’s their job to analyze things carefully and carry the whole process through, right up to the point where you have written a paper about your results. Only then is the truth revealed.

Yesterday kicked off the LIGO-Virgo collaboration meeting here in sunny Southern California. I had been hearing rumors that LIGO had found something, although everyone knew perfectly well that it might be fake — that doesn’t prevent the excitement from building up. Papers were ready to be submitted, and the supposed event even had a colorful name — “Big Dog.” (The source was located in Canis Major, if you must know.)

Steinn SigurĂ°sson broke the news, and there’s a great detailed post by Amber Stuver, a member of the collaboration. And the answer is: it was fake. Just a drill, folks, nothing to see here. That’s science for you.

When the real thing comes along, they’ll be ready. Can’t wait.

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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