Greetings from sunny Palo Alto, California, where we’re having the 2005 incarnation of the SLAC Summer Institute, Gravity in the Quantum World and the Cosmos. It’s an annual two-week school, aimed primarily at graduate students in physics, covering topics of interest to SLAC (the Stanford Linear Accelerator Center). Until recently, gravity didn’t qualify as something of interest to anyone working at a particle accelerator, but times have changed — gravity was the subject of SSI in 1998, and again this year. These days, considerations of dark energy, extra dimensions, and string theory are of direct interest to particle physicists.
I got to speak first, giving a three-hour General Relativity Primer. For lecture notes, we handed out my No-Nonsense Introduction to General Relativity that’s been on the web for a while; the online transparencies were scanned in from the actual lectures I gave. The idea was to give a complete intro to GR (metrics, geodesics, tensors, covariant derivatives, curvature, Einstein’s equation, some solutions), aimed at physics graduate students who hadn’t been exposed to GR. (Sadly, there are still plenty of physics grad students who have never been exposed to GR.)
I really wanted to give a blackboard talk, but the organizers talked me out of it, claiming (correctly, as it turns out) that blackboard in SLAC’s lecture hall is practically unreadable. But I didn’t want to use powerpoint, as it’s nearly impossible to move at a pedagogically appropriate pace when you speak from pre-made slides. As a compromise, I wrote the transparencies in real time as I lectured. It worked okay, although I realized that the main test of endurance wasn’t talking for three hours, but rather staring into the light of an overhead projector for three hours as I was writing the transparencies. In the afternoon I fielded questions for another two hours at a discussion section, so the organizers squeezed their money’s worth from me.
Yesterday morning we heard from Alessandra Buonnano on gravitational waves and Gabriella Gonzalez on actual gravitational-wave detectors, such as the LIGO observatory. All seems to be going well at LIGO, and Gabriella mentioned that they’ve even detected something — but it turned out to be an airplane flying overhead. We’re still waiting for the direct detection of an honest gravitational wave.
In the afternoon, we had Ken Nordtvedt talking about testing GR by bouncing lasers and radar signals around the solar system, and Shane Larson talking about the LISA mission. LISA will (assuming all goes according to plan) consist of three satellites flying in formation five million kilometers apart, measuring passing ripples in the geometry of spacetime by bouncing lasers back and forth. What’s that you say? You think the satellites should feature more powerful lasers, and be located twenty million kilometers from each other? Shane has set up a sensitivity curve generator, allowing you to determine how the noise limits of the satellite will change as a function of such parameters. Once you’ve hit on your favorites, it’s up to you to convince NASA to go along.
“All seems to be going well at LIGO” which could also be read as “getting ready to get more money to build advanced LIGO” followed by “but what we really want was really REALLY super-duper A+ advanced LIGO….on the moon……operated by robots made of pure platinum.”
“All seems to be going well at LIGO, and Gabriella mentioned that they’ve even detected something — but it turned out to be an airplane flying overhead.”
Give the folks a break… That’s not all they’ve detected.
It’s also worth pointing out that Sean’s lectures were impressively clear and coherent and were well received by the attendees… Wish I’d had him teach me GR as an undergrad. Thanks, Sean!
Hopefully the videos of the lectures will be appearing soon. SSI posted RealVideo links to last years seminars on “Nature’s Greatest Puzzles,” which were excellent. Helped me start studying for my oral qualifier! 🙂
Sean – Could you explain to us non-physicists what questions the
detection of gravitational waves – assuming it all works swimingly –
might help you answer?
Listening to Sarah Church’s talk on the CMB, it occurs to me that none of you have a post explaining what Cosmic Variance is. That would certainly make a good physics post.
Ben, there’s a short definition on the about page. We should go more deeply into later.
TM, there are a lot of things, starting with making sure that gravitational waves actually exist and do what we think they do. (Nobody doubts it, but in science it’s always nice to check.) Then there is honest astrophysics — learning about binary stars and supernovae and black holes and gamma-ray bursts and whatnot. Especially the “whatnot” — as a rule, any time we look at the sky in some different waveband, we discover new phenomena. Finally, there’s more speculative things we can check about black holes or the early universe. But the real fun in doing an experiment is that we don’t know ahead of time what we will see.
Now why would I do something silly like reading the “about” page, especially if I wanted to know about the title of the blog? 🙂
(As soon as I posted I knew it would be there)
Sean – Thanks. I do recall from Kip Thorpe’s book him mentioning that,
in principle, one should be able to detect gravitational waves from the big
bang since they don’t interact strongly with other particles and that was what
particularly intrigued me, but I don’t recall him saying what one might discover,
whether one might be able to say something about inflation, say.
Anyways, don’t want to waste your time. The blog’s terrific; the string theory
post and thread were really interesting.
Sean,
On their website you provided, under ther participants section, your research area is “gravitational Radiation.” Did you recently changed your area of research? 🙂
Hey Sean, which books have a good proof of Birkhoff’s theorem? I thought I just heard Scott say… 😉 (Heckling from 6 rows behind you.)
I’m going to have to give Hughes a hard time. Nice Hawaiian shirt, Scott.
And no, I haven’t changed my research specialty. It’s California, they don’t sweat the details.
Sean and others ,
does anyone know when the recorded video of the talks be up on the web?
I agree with Stan. They are a great resource.
Thanks
Shantanu
No idea when they’ll be up on the web, or even if they will be; I’ll post a pointer if I find out that they are.
Thanks Sean for the update. To Joanne and other members of the SSI organizing committee, a sincere request I have, which is to upload real videos of the talks on the web. From the slides itself I can see that all of them were great talks and I am curious to watch them