## Holmes, Sir Isaac Holmes

December 18, 2009

If you’re looking for some fun reading for the coming holidays, and like physics and detective stories, you’re in for a treat: Thomas Levenson‘s book Newton and the Counterfeiter. I’ll let Thomas himself tell you what it’s about. Here’s a short promotional video:

And, much more interestingly, this talk at MIT, where Levenson glosses over the story and offers some interesting thoughts on how scientific knowledge influenced society during the late seventeenth century and beyond. And all that by way of telling you a good and true detective story!

## Lectures on Classical and Quantum Physics

December 13, 2009

The Indian Institute of Technology Madras has some online collections of lectures. Among them, a Quantum Physics course imparted by Prof. V. Balakrishnan. You can see the first lecture below, devoted to an introduction to the conceptual underpinnings of quantum mechanics and, more specifically, Heisenberg’s principle. Prof. Balakrishnan does a remarkable job at explaining these horny issues, avoiding common pitfalls; and, as the students’ questions make him wax philosophical, he shows a very refreshing honesty in not trying to sell the theory as the end of the path, avoiding the “shut up and calculate” stance that was so common during the second half of the past century (and which i still suffered during my undergraduate and graduate years). The exposition doesn’t use any advanced mathematics and keeps at a conceptual level, and i think it should be understandable by anyone with a very modest background (perhaps some acquaintance with classical mechanics will help at some point, but it’s not a requirement to enjoy the lecture).

There’re are thirty more lectures in the course, all of them available for your learning pleasure. Although i haven’t had the time to watch them all, if Prof. Balakrishnan keeps their quality as high as in the first installment, i’m pretty sure they’ll make up for many hours of fun.

And, if you feel like learning classical physics, i’ve got good news for you too: there’s also a series by Balakrishnan on Classical Physics! Here’s the first lecture:

and here you can find 37 more!

## Atlas animated

December 11, 2009

## CERN lectures

December 4, 2009

CERN makes available at its web site a truly awesome collection of video lectures and courses. The whole set is browsable here and consists of almost 1500 entries. Naturally enough there’s a bias towards particle physics, but many other topics make cameo appearances. Here’s a list of some of the lectures that caught my attention:

Yeah, i’m too still trying to decide where to begin! :)

## Nobel gathering at CERN

December 3, 2009

Today and tomorrow, CERN is hosting a gathering of Nobel laureates in the particle physics field who are largely responsible for its development during the last 50 years. The program is available online, and i’m told that video streaming for the talks will be available from the same page later. In the meantime, some of the presentations are already available, including a retrospective on unification by Sheldon Lee Glashow:

Other questions cannot so “easily” be answered: What is the origin of neutrino mass? Why is the cosmological constant so tiny? But my own most vexing problem is that of flavor: At least 20 parameters are needed to describe the various masses and mixings of quarks and leptons. Most of these have been measured, but no plausible theoretical relation among them has ever been found. Are we likely to find such relations in the future? Or are these 20 numbers simply accidents of birth of the universe, just as the radii of planetary orbits are accidents of birth of the solar system. Some of my string-bound colleagues advocate just such a gloomy philosophy. For them I would pose one last question: How can we ever learn whether uperstrings are the correct approach to fundamental physics?

Read the whole article here (PDF).

## Inflated claims

December 2, 2009

The Institute of Physics’ Isaac Newton medal was awarded this year to Alan Guth, of inflation fame, and his talk is available at the IoP’s website. The talk is devoted to explaining how great and awesome the inflationary theory is, including the usual reasons it’s believed by many to be correct: it explains the large-scale homogeneity of the universe (by causally connecting in the past regions that are unconnected after the inflationary period) and supposedly predicts a smoothed out geometry with an average mass density close to its critical point (that is, a universe with flat spatial sections). There’s also some talk about eternal inflation and pocket universes, which i didn’t understand well enough to comment on: this article by Guth himself is a good way to learn more.

Dr Guth is extremely happy about the fact that estimates for the ratio of the observed over the critical density ($\Omega$) have jumped during the last decade from the 0.2-0.3 range to a value almost exactly equal to 1, which corresponds to the flat model. The correction comes from taking bringing dark energy into the picture, and the second half of the talk is devoted to some speculations as to its mysterious origin. To Guth, the most plausible explanation is that this dark energy corresponds to the vacuum energy density ($\Lambda$), but there’s this little problem that quantum field theory predicts an infinite value for it. Even if you try to introduce an (arbitrary) ultraviolet cut in the calculation at the usual Plank energy, the value obtained is some 120 orders of magnitude greater than the observed one. String theory and the landscape to the rescue! Which of course explains nothing, in my opinion.

Guth’s last resort is the anthropic principle, according to which $\Lambda$ is so low because it’s the only way intelligent (?) beings would be here to observe it, and then uses an analogy so broken that i’m sure i’m missing something obvious. It goes as follows: Kepler initially thought that the radius of the orbits of planets in the solar system should have values deducible from geometrical considerations alone, but, as we all know, that’s not the case: their concrete values could be different just by changing the initial conditions leading to the formation of the solar system. So it is with $\Lambda$: since we have no way of computing its unexpectedly low value, it must be that the reason for it is that we exist. This argument is so plainly wrong that, as i said, i’m sure i’m misunderstanding (perhaps one of my two or three readers will set the record straight in the comments).

Other than that, and the fact that it feels at times like a commercial (including some arguments pretty close to straw men when he shows the curves matching the observations of the microwave background (without any mention, by the way, to the possible discrepancies for low terms of the multipolar expansion)), the talk is entertaining and gives a good, if quick, overview of commonly accepted wisdom on the field these days. So, if you have a grain of salt handy and don’t mind a bit of hand-waving, just ignore my rants and go for it.

(While you’re at it, i’ll be giving a try to last year’s winner, Anton Zeilinger, and his talk on quantum information and the foundation of quantum mechanics).

## The shoulders of giants

November 30, 2009

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!

## World record

November 30, 2009

From 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, 2009

Some 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.