Archive for May, 2009
The coming collapse of the middle class
As usual on Saturdays, discussion of physics is forbidden (why? check out Old Testament). Let us talk a bit about global financial crisis instead 
, namely about work of Elizabeth Warren, professor of Harvard Law School.
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Workshop on tests of gravity in Case Western – day 2: aether and modified gravity
Let me finally briefly review the reminder of the second day of the workshop.
Justin Khoury (whom I knew from Perimeter years and who is in Penn now) gave the first talk afternoon – titled “observational hints of IR modified gravity”. His talk followed Nima’s, and the latter almost completely blew me away, so I was somewhat unfocused during Justin’s presentation. Yet, I was able to capture that as such observational hints he wanted to present local bulk flow of matter within 50 
MPc scale, excess power in Lyman 
(about 30%) and small scale CMB anomalies (which I would hardly call anomalies due to lack of statistics there). According to him, all this shows that gravity should be stronger at larger scales – and that’s exactly what many models of modified gravity predict.
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Susskind’s general relativity – lecture 9
… where Leonard Susskind discusses spacetime – spacelike, timelike and lightlike directions, explains how one gets special relativity from general relativity (post-Newtonian approximation), non-relativistic limit of GR and finally … Einstein equations (hurray!)
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Workshop on tests of gravity in Case Western – day 2 and Arkani-Hamed’s talk
The second day of the Workshop on Tests of Gravity (and here is my blog post about the first day) was mostly devoted to analog models (Bill Unruh, Michael Uhlmann, George Pickett) and models of modified gravity (Nima Arkani-Hamed, Justin Khoury, Stacy McGaugh, Ted Jacobson, Levon Pogosyan and Mark Wyman).
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Susskind’s 8th lecture on general relativity
Leonard Susskind continues reading his lecture course on general relativity in U. of Stanford. Previous lectures can be found here: Lectures 1-5, Lecture 6 and Lecture 7.
Susskind continues to discuss covariant derivatives, parallel transport of vectors, Ricci and Riemann tensors. In the second part of the lecture he turns to geodesics. He is terrific lecturer but after the lecture N7 I start wondering whether it’s worth spending so much time discussing technicalities
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Workshop on tests of gravity at Case Western – day 1
Dear friends,
I am sorry for being rather quiet for a while. As many of you may already know, my laptop has decided to enter coma during the trip, as a result, I was left without appropriate internet access (sporadic use of Pascal Vaudrevange’s computer is not counted, thanks, Pascal!). Although the laptop tried to revive after we came back home, demonstrating some kind of “brain” activity, in a couple of days I understood that the growth of entropy is as inevitable as a finally victory of string theory over loop quantum gravity.
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Things that go bump in the CMB polarization
This post is written by Michael Mortonson, graduate student of Wayne Hu at the U. of Chicago. Michael has also asked me to thank Cora Dvorkin and Wayne Hu (U. of Chicago), and Hiranya Peiris (U. of Cambridge), who contributed to the post. Dmitry.
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Real-time gauge/gravity duality
Balt van Rees from the U. of Amsterdam continues the discussion of non-equilibrium AdS/CFT we have started not so long time ago. Since his recent paper with Skenderis was one of the major achievements in the field, I highly recommend going through his post. Dmitry.
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Correlator of Wilson and t’Hooft loops at strong coupling in N=4 SYM theory
Andrew Zayakin works at LMU, Munich and ITEP, Moscow. His interests include non-perturbative physics of QCD, string theory and AdS/CFT correspondence. Dmitry.
This post is about my recent paper with Alexander Gorsky and Alexander Monin about a correlator of a Wilson and a ‘t Hooft loop. Before I proceed, I should explain what these objects are and why they are important to be studied. QCD possesses a consistent description in terms of “dual variables” – charges and monopoles. Reader familiar with the systematics of particle-like solutions in different theories would stop me at this very moment by pointing out there are no monopoles in QCD. True, there are no monopoles in the sense of e.g. Georgi-Glashow model. However, effectively there is such a thing as monopole, which is widely observed on lattice as a non-zero Abelian flux through a closed lattice surface. A lot is known on “thermodynamics” and “phenomenology” of these quasiparticles. They do not exist in the sense of theory spectrum. Still, they are an important tool of describing QCD. The QCD phase transition, which is an element of common lore, can easily be understood in terms of monopoles (Fig.1).
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String theory and the diffusion equation
Gianluca Calcagni is a postdoc at Penn State working in the group of Martin Bojowald. His interests include string theory, string field theory and cosmology. Dmitry.
This post is based on arXiv:0904.3744, in collaboration with Giuseppe Nardelli. Check the links for references and introductory reviews on the subject.
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Vorticity generation in cosmological perturbation theory
Adam Christopherson is a PhD student at Queen Mary, U. of London working with Karim Malik on cosmological perturbation theory. Dmitry.
In this blog post, I will summarize recent work on vorticity generation in cosmological perturbation theory, undertaken by Karim Malik, David Matravers and myself. The main result of the paper this is based on, arxiv:0904.0940, is that at second order in perturbation theory, vorticity generation is sourced by entropy gradients.
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Correcting the initial vacuum state in quantum gravity
Emre Kahya is a postdoc at Koc University, Turkey (he is a former graduate student of Richard Woodard). Dmitry.
Cosmology is becoming the most active area of research in theoretical physics for the last 10 years. We now understand that initial quantum fluctuations are reasons of our existence with in the context of Inflation. This brings the following question: Can we make quantum gravity calculations and expect to test them by some means? Naively one would say no. One reason is the smallness of the coupling constant:
quantum gravity effects have the order of magnitude ![0^{\rm th}{\rm Order} [1+\alpha_1 G + \alpha_2G^2 + ...]](http://www.nonequilibrium.net/latexrender/pictures/99bb619d901560bc9c639f1c44ea6834.gif "0^{\rm th}{\rm Order} [1+\alpha_1 G + \alpha_2G^2 + ...]")
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One week to spend in US
At this very moment – when you are reading this – I am flying to US, where the final destination of my trip is Cleveland. The plan is to take part in the 3-day Workshop on tests of gravity and gravitational physics at Case Western Reserve U.
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On gun politics and culture in US
In Russia, any talk about personal weapons/gun policy gets immediately reduced to the question of how actually effective are guns for personal self-defence on the street. On the other hand, in US general attractor seems to be discussion of the statement that personal weapons is your defence against tyranny, i.e., “armed man=free man” etc. etc.
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Average life expectancy or more on data visualization
In continuation of my series of posts about data visualization (Dynamical maps and Gapminder), let me show you today another cool resource: interactive map of the world StatPlanet.
Here is for example a map showing average age in different countries (data from 2006):
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