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awesome update
A view of about half of the Alpine Club's Bouldering Cave
It turns out that in the battlements of Caltech's gym, there is an awesome bouldering cave, maintained by the Alpine club. It's a plywood palace of rock climbing holds. Very fun. The summer students (Sonya in particular) are awesome for finding all of these activities and cajoling me into participating. On Tuesday they went skydiving--solo, not even tandem!--but I did not join them for that. It was very apropos, however, for our research group, which is, after all, researching gravity.
Tomorrow I am cooking dinner with the summer students. I'm not sure what. Crepes? Tabouli? It makes me so rampant-nostalgic for Camp CERN cooking in my former life as a professional summerstudent.
Last night (July 4th) I attended Rob's 30th birthday party, held at an awesome house in some hills above Huntington Blvd, from which vantage we took in several hours of awesome (illegal) fireworks, courtesy the various neighbors.
Today some summer science program for supergifted highschool kids came through our lab for a tour. I gave a tour for half of them and Alan Weinstein the other half. They were pretty awesome, and even sported awesome accents--I guess they were gathered from world-round--with which they asked me numerous questions, some of which I couldn't begin to answer (clearly they had heard some things about string theory) but about the LIGO stuff they caught on immediately. For instance, I told them about optical cavities and how they can be used to build up power, stabilize length, and filter frequencies, and they nodded enthusiastically and scribbled down notes. One girl found a screw on the floor and asked if she could keep it as a souvineer (baffled, I just took it away); one guy asked if we could keep in contact and got out a piece of paper to write down my email address, but their program leader person ushered them out the door so fast I wasn't able to give it to him--I felt bad about that. Overall their program was kind of ridiculous in trying to shove them through our lab so fast for a tour--I had like 10 minutes to explain all of LIGO, and they were very interested. I walked with their group as they went to their next destination, answering more questions. These kids could have spent a week at Caltech but they only had an afternoon. Apparently last year one of them asked, "With so much optical power, don't you have a problem with radiation pressure?" Rana beams when he tells this story. He says, he wanted to say, "quit high school and be my grad student." (Instead he has me!)
I kind of want to write "the cartoon guide to LIGO". (As my thesis?!)
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LIGO
The theory of general relativity predicts that the gravitational field exhibits "gravitational radiation" (gravitational waves) just as the electromagnetic field exhibits electromagnetic radiation (light!). However, these waves have never been directly detected. LIGO, which stands for "Laser Interferometer Gravitational-wave Observatory," is a 1/2-billion-dollar, 400+-person project to detect gravitational waves.
Gravitational waves are expected to manifest themselves as a stretching and compressing of space. LIGO uses laser interferometers to look for this stretching and compressing, just as Michelson and Morley used an interferometer to look for a variation in the speed of light in different directions due to the then-hypothesized ether. We take a laser beam, split it into two parts, send them down two four-kilometer arms at right angles to each other. At the end of the arms, the light reflects back, and is ultimately recombined. Differential length changes (one arm stretching and the other arm compressing) will change the interference of the returned laser beams, resulting in a detectable signal. That's LIGO in a nutshell. LIGO claims to be able to detect periodic stretching and compressing of space of an amazingly small magnitude--less than 1/1000 the diameter of a proton!
In addition to the two large observatories (in Washington and Louisiana), there is a prototype here at Caltech, where I'm currently working.
wikipedia entry: http://en.wikipedia.org/wiki/LIGO