Saturday, November 19, 2011


Switched window manager to LXDE because the default Unity interface for ubuntu was getting really slow and possibly even somewhat buggy.

Love the fast performance! Blazingly quick and I should have done this long ago.

Thursday, November 10, 2011

Physics Pieces (Part 5)

Interesting set of seminars last week.

Claudio Castelnovo from Royal Holloway, who was a post-doc in Oxford, gave a talk about magnetic monopoles in spin ice, which was featured on the cover of Nature in 2008. He gave a brief theoretical introduction and described results by Morris et al. from neutron scattering experiments with an applied magnetic field to compare against this model of emergent electrodynamics in a 3D condensed matter system.

Daniel Khomskii from Koeln University, Germany spoke on frustrated Mott insulators. The virtual hopping of Hubbard spins around a triangle in a triangular lattice gives an orbital current in third order perturbation theory, which was a somewhat analogous result to magnetic monopoles in spin ice (electric charge instead of magnetic monopoles).

Dieter Jaksch, associated with the atomic and laser physics sub-department of Oxford, and with the Centre for Quantum Technologies in Singapore, gave a talk about strongly driven quantum systems. He described the application of tensor network and path sum approaches to their areas of research, on impurities in optical lattices, Rydberg lattices and tetrahertz pump-probes.

Martin Rees gave another talk, this time on real and counterfactual universes. This was the 8th Dennis Sciama memorial lecture, and Rees was Sciama's graduate student. Stephen Hawking had been Sciama's graduate student for about 2 years when Rees joined the research group. Interestingly, Roger Penrose, who made contributions to astrophysics during the 1960s, was at the talk as well.

Rees gave some of the history of the steady-state theory versus big bang theory in the 1940s and 50s, and spoke about the "tuning" problem of the cosmological constant and the amplitude of fluctuations during the big bang. To produce a universe like ours, there seem to be strong constraints on the allowed value of the cosmological constant (cosmic expansion rate), and some sensitivity also to the fluctuations - too much fluctuations and there are too many black holes, too little and there are too few stars. And gravity needs to be weak so the universe has enough time to become interesting.

Physics Pieces (Part 4)

Talks by two Princeton professors who visited Oxford last week. Dan Marlow gave a talk about luminosity measurements at the Large Hadron Collider, discussing the various technical issues involved when pushing equipment to its limits to test the limits of science. Duncan Haldane spoke about geometry and topological phases of matter, starting from the Gauss-Bonnet theorem and the generalisation by Chern. Interesting history about how Karplus and Luttinger's paper in 1954 (Phys. Rev. 95, 1154–1160) on the anomalous Hall effect was discredited and finally vindicated in 2005.

Fellow graduate student Curt von Keyserlingk gave a talk on the Toric Code too, a toy model involving plaquette and vertex terms in the hamiltonian for the spins. There's a nice pictorial representation of the states of the system, and similar models can lead to what are known as "anyon statistics" for quasiparticles that are neither fermions nor bosons.

Roser Valenti from Goethe University in Frankfurt gave a talk on frustration, using density functional theory to come up with effective models and studying them with quantum Monte Carlo and other methods. Interesting attempt to understand caesium copper chloride and caesium copper bromide by substituting the chlorine atoms with bromine atoms and vice versa.

Martin Rees from Cambridge delivered a public lecture on "The Limits of Science" last week too, and I took the kids to it. He had some encouragement for beginning scientists, who might feel that so many major advances have been made that it's hard to push further forward. His idea was that each advance leads to new questions, and the computational power we have at our disposal is a powerful tool that previous generations did not have. Yet there are likely to be things beyond our ability to comprehend, which require posthuman intelligence. There is a huge gulf between what we can do today and what we should do, whether in research or in public policy, and we need to choose wisely with a longer term view of leaving a fair inheritance for future generations.

Tuesday, November 8, 2011


The gNewSense 2.3 LiveCD boots my computer into a working state, which is great. Unfortunately the Ethernet adapter doesn't work out of the box with my laptop, so that's a bummer.

According to the FAQ, the current version is based on Ubuntu, but the next version (3.0) will be based on Debian.

Sunday, November 6, 2011


Richard Stallman came by to Oxford to give a talk ("A Free Digital Society") on Friday. As I was at another seminar, I didn't manage to attend even though it was relatively conveniently held at the physics department. As a result, I read up more about his life and work, after finding this very interesting piece that details his preferences and requests for anyone interested in getting him to speak.

The actual talk he gave was probably more or less along the lines of this earlier transcript. I agree that indeed, copyright and patents are relics of the past that now mainly benefit corporations only and stand in the way of progress. We do need to disentangle the issues to both encourage sharing and cooperation and also encourage content creation.

Reading up again about his life and cause reminded me of the ideals of freedom, choice and software. In many ways, universities embody the essence of freedom and cooperation - research published in open journals are analogous to "copyleft".

I'll end this post by pointing out that the story of his younger days is pretty interesting. He did physics at Harvard and spent weekends at the MIT Artificial Intelligence lab, where the "freedom" issue first reared its head in the form of a proprietary printer driver. He was a physics graduate student for a while and decided that he could make a greater contribution through computer code.

[On a slightly more technical/purist point, as I'm using Ubuntu GNU/Linux now with non-free drivers, I've sacrificed some "freedom" for the convenience of getting my laptop to work well. Just downloaded the fully free gNewSense which I'll test-drive.]

Tuesday, November 1, 2011


Visited London over the weekend with the family (photos). We went to the Natural History Museum. Plenty of dinosaur bones and other pieces from our past. Didn't have time for the Science Museum - maybe next time!

Physics Pieces (Part 3)

It's a new month!

This is going to be a short piece since I've already reported on some of the talks from last week. There was a talk by Jacques Laskar from IMCCE in Paris. Unfortunately I missed this one but there is a video that he showed at the end of the talk.

Joanna Haigh from Imperial College London gave a talk about how changes in the sun affect climate. The prevalence of sunspots has a 11-year cycle of fluctuations, and recent data has suggested a spectral distribution quite different from what is usually assumed.