The Royal Society is commemorating its 350th anniversary next year and, as part of the celebrations, has put together a very nice site called Trailblazing. The site presents an interactive time-line highlighting some of the events and publications that have made history during those three and a half centuries. The best part is that one can download, in PDF, a bunch of jewels. Among them: Newton’s letter on light and colors, Faraday’s musings on gravity and electricity, Maxwell’s article presenting his field equations, Bayes’ essay on chance, Eddington’s report on his famous expedition, or Hawking and Penrose’s work on singularities. Talk about the shoulders of giants!

## Archive for November, 2009

### The shoulders of giants

November 30, 2009### World record

November 30, 2009From this press release:

CERN’s Large Hadron Collider has today become the world’s highest energy particle accelerator, having accelerated its twin beams of protons to an energy of 1.18 TeV in the early hours of the morning. This exceeds the previous world record of 0.98 TeV, which had been held by the US Fermi National Accelerator Laboratory’s Tevatron collider since 2001.

There’s also a photographic report.

### Time

November 30, 2009Some months ago, the FQXi ran a contest on essays on the nature of time. Many interesting articles were submitted, and most if not all of the awarded ones are worth reading. Perhaps my favourite among them is Carlo Rovelli’s Forget time (PDF). You can read an abstract and some reader comments here.

Rovelli’s a thought-provoking and quite fun to read article (i happen to like Rovelli’s writing quite a bit). The main idea is to get rid of a singled out time variable in the Hamiltonian formulation of general relativistic mechanics and, by extension, quantum mechanics. It is argued that our usual time parameter, as it is used in Newtonian and quantum mechanics, as well as in special relativity, is not well-defined in a general relativistic context. Therefore, it must be replaced by a notion of coordinated events that conform a configuration space. Physical systems follow special orbits in the configuration space. often parametrizable by a finite set of state variables (think for instance of the amplitude and phase of a pendulum), so that we can pair events and describe the evolution of one in terms of another. These special orbits are obtained from a variational principle, derived from a Hamiltonian function. When the latter has a separable time we’re in a classical, non-relativistic regime. But this is not usually the case. It is then shown how our everyday notion of time can be given a statistical interpretation, and derived in terms of the Gibbs theorem and the postulate of a Gibbs distribution for equilibrium states.

While i don’t feel really qualified to properly criticise Rovelli’s approach, i must say that it sounds reasonable and quite beautiful. Julian Barbour’s The nature of time also seeks to get rid of time as a fundamental concept by defining it as a (quite different) derived quantity, although i don’t find his arguments as compelling; the same happened to me with his book The end of time. And of course there are other physicists with some serious arguments on the opposite camp: Sean Carroll’s essay What if time does really exist? in the same contest, and Lee Smolin’s survey article The present moment in quantum cosmology: Challenges to the arguments for the elimination of time are some of the readings that could help making up your mind (or, if you’re like me, increase your incertitude!).

Or you can also watch all the talks in the seminar held at the Perimeter Institute last year, The Clock and the Quantum. Although i haven’t had time to do much more than skimming over a couple or three videos (for instance, Barbour’s and Roger Penrose’s), it looks like a pretty interesting set for those of you wondering what’s this queer thing we call time.

### Quick video links

November 28, 2009A couple of interesting links for those of you with a penchant for videos.

MIT World is a free and open site that provides on demand video of significant public events at MIT, including some physics lectures, like this very fun series by Walter Lewin on electromagnetism, music and light; or this one where Robert Laughlin and Steven Weinberg talk about the social aspects of physics.

ScienceDump is a new site devoted to “popular science, technology & digital lifestyle videos”, contributed by its users. Although the site is brand new, it already contains some interesting bits.

The Lindau Nobel Laureate homepage contains lots of videos of this annual gathering in the Constance Lake that brings together consecrated scientists and young researchers. You can find both lectures and short documentaries. In particular, 2008 was devoted to physics: the list of lectures is here, and there’s also a collection of short films featuring Gerardus `t Hooft and David Gross, among others, interviewed by young students. These Lindau meetings have been taking place since the 1950s, and one can find some funny stuff in there: for instance, there’s the recording of a talk by P.A.M Dirac himself, from 1979.