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Yay! The long awaited book 11 of Robert Jordan's Wheel of Time series has been released! Chris pre-ordered a signed copy online and we can't wait for it to be delivered. We've got the whole series so far, and I've just finished re-reading all the previous books in anticipation of book 11. For those of you who haven't read the series, I strongly suggest you do, it's amazing!
(pic from Dragonmount)
So just for fun I've been going to the 4th year's General Relativity lectures, held on Monday and Friday mornings. Why? Cause it's interesting, and it's amazing how much you forget between one year and the next. Also, the syllabus is slightly different this year; last year we looked a lot at geodesics and descriptions of different types of curved spacetimes, but we never actually got to deriving the field equations. This year they are doing that, another reason for me to want to attend the lectures.
Anyway, up till now we've been covering pretty much the same stuff as we did last year, only in different orders and different ways. Today, though, we got to something new that made me really excited in a completely nerdy way.
But first, a little bit of GR and personal history... In differential geometry there's this thing called the Riemann Curvature Tensor
(if it's hard to see, those indices are the greek letters mu, nu, rho and sigma)
which basically describes the curvature of a manifold, and is used in GR to describe the curvature of space.
Now, in third year Computational and Applied Maths, we had a course on tensor analysis. We didn't really understand what was going on, to tell the truth, but we just learnt all the rules for index notation and worked from there. One hot stuffy afternoon we were semiconsciously making our way through a lecture, when our lecturer threw in what was probably supposed to inspire us that what we were learning was so cool... He went (something along the lines of):
"And what Einstein did was take the Riemann tensor R mu nu rho sigma and changed the third index to mu, so it was R mu nu mu sigma, and hence got his field equations!"
Needless to say, there was no resounding "wow!". In fact, it was more like a resounding "Huh???"
Okay, back to this morning's lecture. R.... as it's shown above, for a 4-dimensional spacetime, has 256 components. This is rather nasty, so we'd want to reduce the number of components to make things easier for us. The way we do this is by "contracting" the tensor - summing over identical indices a la Einstein.
So after quite a bit of maths, obtaining and using R....'s (anti)symmetry relations and it's other properties, it turns out that the only non-trivial way to contract the tensor is exactly the way we "huh?"-ed about two years ago. Only now, after going through the math, I (think I) understand why. I was so excited, it made my day. Can you say NERD?!
Oh yes, the new tensor you get from contracting R.... in just the way we did above is called the Ricci tensor. And after a bit more mathematical fun on this one, you can define the aptly-named Einstein tensor, which appears in ... ta-da! ... the Einstein Field Equation.
But we're not there yet.
Every week (usually on a monday) Mark and I have a collaboration meeting on our projects via a conference call from the people at JLab. This week, however, Mark and Anthony (the other PhD student - who lives in the US - working on the same project as Mark) couldn't make it, so the meeting was pushed off to Thursday. The reason Mark couldn't make it on Monday was because he was flying down to iThemba LABS in Cape Town to help with an experiment, but he would be back on Thursday.
Anyway, the meeting was supposed to be at 4pm. At 3pm I get an sms from Mark saying please call me on some weird number. So I do. Turns out, he's stuck at the airport - the lab gave him a lift out there on Monday but couldn't pick him up for some reason - and his cellphone is dying. So I rush out to the airport in lovely pre-rush hour traffic, which is still bad anyway, get pushed off the arrivals onramp and onto the departures onramp by some idiot with attitude in a merc, have to go round the whole airport again to get back to arrivals, and pick Mark up. Then we race back to the lab, miraculously find parking by the front door, and race into the office just as the phone is ringing! Talk about getting there just in time :)
Hey, optics fans... Congrats to Roy J. Glauber, John L. Hall, and Theodor W. Hänsch, the winners of this year's Nobel Prize in Physics!
Roy Glauber was awarded half the prize for "his contribution to the quantum theory of optical coherence" and John Hall and Theodor Hänsch were each awarded a quarter for "their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique".
Read the press release here or a more advanced (interesting) document (pdf) on the laureates work.
(above pic comes from nobelprize.org)
