## The Week’s Ending

A later post than usual for a weekend. I’ve been feeling a bit fragile all day after a very late night last night “playing Bridge” (i.e. drinking and gossiping into the early hours of the morning, with the occasional hand of cards thrown in for good measure). My broadband connection has also been playing up nearly as badly as the connections in my brain, although I don’t think there’s a causal relationship between the two. Anyway, just time for a round-up of, and some reflections on, the events of the past seven days.

This has been the first week of term, so has naturally been extremely busy. I got my first week’s second-year lectures, examples sheets and handouts together last Sunday for a 9am start on Monday morning. There were 104 students on the register, and I was delighted to find that 100 of them actually showed up bright and early for the first session. The lecture wasn’t brilliant unfortunately – I misjudged how many worked examples I could fit into an hour and got a bit rushed as a consequence. Still, at least nobody threw anything at me, and I survived. At the end of the week the students were asked to hand in solutions to some problems, which most of them seem to have done. Unfortunately, however, I neglected to ask for the key to the box in which they are posted before the support staff went home at 5pm, so the scripts are still all in the box. At least that gives me an excuse for not having started to mark them yet.

I gave another lecture this week to the 4-th year Cardiff students taking the *Quantum Field Theory* lectures from Swansea, to try and fill in a bit of background our lot won’t have learned in other lectures on relativistic quantum mechanics, chiefly the Dirac equation. I really love that sort of stuff, so didn’t mind stepping up to do an impromptu class on it. They seemed to find it reasonably useful, although I went on a bit longer than I should.

Two other events this week in the School were a colloquium by Dr Anupam Mazumdar from Lancaster on Wednesday and a seminar by Prof. Pedro Ferreira from Oxford yesterday (Friday), both of which were related to alternative theories of gravity (i.e. modifications of Einstein’s theory of general relativity). Pedro has co-authored a comprehensive review article on such things if anyone is interested in following up the details. The basic point, however, is that standard cosmology almost all develops from the assumption that gravity and space-time are described by general relativity. That theory is well tested on solar-system scales, but independent tests on the much larger scales involved in cosmology are hard to come by. It’s clearly therefore an important goal to work towards testing alternative theories, as is the case in any scientific discipline.

As well as these specific events there was a steady stream of problems and irritations to do with the teaching timetable: rooms too small, clashes, and so on. This is part of my responsibility as Director of Teaching and Learning in the School of Physics and Astronomy, and I don’t mind telling you that it’s a royal pain in the derrière. However, I think all the bugs have been ironed out and we can hopefully now carry on with a settled teaching programme into the new year.

Looking back on the week I can see so many things I would not long ago have found unbearably stressful, even going to the pub after Friday’s seminar. Such victories, however insignificant they may seem to others, have given me the confidence to face the greater challenges that I know the future has in store.

Follow @telescoper
October 6, 2012 at 7:06 pm

Wish they’d included the Cambridge gauge theory of gravity in that preprint. It predicts identically to GR in many cases (including all experiments to date) but is more general in one direction and more tightly constrained in another. It allows for non-zero torsion (which physically is due to lepton spin). It does not deal directly with the metric tensor (which in GR satisfies second order differential equations), but constructs it from two gauge fields, one relating to translation and one to rotation, which satisfy first order equations. Though there are consequently fewer constants of integration in the solutions, there are more scalar equations to start with than in GR. The main difference from GR lies in the global, topological nature of solutions to the equations; locally the theory predicts identically to GR in the absence of lepton spin. Like GR, the theory is easily generalised to allow for a cosmological constant. It is best (and traditionally) expressed mathematically using Clifford algebra.

October 6, 2012 at 9:41 pm

It seems strange to me that this hasn’t really entered the mainstream yet. Anyone interested in reading more about this would do well to have a look at:

http://arxiv.org/abs/gr-qc/0405033

October 6, 2012 at 9:55 pm

I think that’s because people don’t learn the Clifford Algebraic language and the theory, being more complicated than GR, is more unwieldy in the usual tensor formalism (although it’s not the first gauge theory of gravity). If a big prediction comes up that differentiates it from GR then it might get more attention.

October 8, 2012 at 7:22 am

In the first draft of the article there was no mention of Einstein-Cartan-Kibble-Sciama gravity. In the final draft there is some discussion of it, but its still

not comprehensive enough and ignores some of the recent applications of this to cosmology, including it been suggested as an alternative to inflation and it can avoid big-bang singularity.

See http://arxiv.org/abs/1111.4595 and http://arxiv.org/abs/1007.0587

October 8, 2012 at 7:51 am

I remember those ‘bridge playing’ days well ;-)