GR21 @ Columbia + Workshop @ Caltech

In academia, summer is the period to attend conferences and workshops, since the term is over (typically between May and June, depending on the country) and researchers do not have teaching duties at this time. 

This year I attended the GR21 Conference at Columbia University in NYC, the biggest event (organized every 3 years) that brings together scientists working in all aspects of General Relativity. 

I was not super happy with attending this conference, since the conference fee (~$600) and the cost of staying in NYC were much higher than usual (GR20 was held in Warsaw and conference fee was about half the price). However, in this very special and exciting year for General Relativity, I couldn't miss this conference. Attending it, in fact, turned out to be a very good choice: the conference was great, I had the chance to discuss with a lot of colleagues and I've particularly enjoyed the talks at the parallel sessions. I gave two talks, one presenting the recent work discussed here at the Special Gravitational Wave Session, and another on tidal deformations at the Parallel Session on Perturbation Theory in General Relativity. 

The slides of my talks are available here and here, respectively, whereas some nice pics from the event can be found here; I'm not in any of them, though, so I took this one myself:

Heading to the morning plenary session (hence the sleepy face) at Columbia campus

The GR conferences are organized by The International Society on General Relativity and Gravitation, ISGRG. During the GR21 conference, Prof. Eric Poisson was elected new President of ISGRG and the venue for GR22 in 2019 was decided (it's going to be in Valencia).

After the conference, I went to Boston for a short visit and then flew to LA to attend the workshop "Unifying Tests of General Relativity", organized by Leo Stein and other members of the Caltech in Pasadena, CA.

After a conference like GR21 (where one passes most of the time scattering off the 600+ participants, chatting and discussing projects for which one usually doesn't even have the time to sit down and think about) attending a small workshop (~40 participants, most of which friends and long-standing colleagues) like the one at Caltech was really a relief. I've never been on the West Coast and Pasadena is a lovely town, everyone seems relaxed and I had time to sit down and talk to collaborators I usually see in person just a few times per year. Science-wise, the workshop was excellent in many aspects, and I left Caltech really excited and looking forwards to working again on some new projects (if any, this is probably the best outcome of a successful workshop!) Some pictures of the event can be found here and below:

Group photo next to the Keck Center at Caltech

Me discussing with Nico Yunes and Vitor Cardoso about our recent work on GW ringdown

I managed to break my glasses on the very first day of the workshop. The secretary was a a DIY-type lady and helped me fixing them. 
This was the result.... [pic taken by Thomas Sotiriou]

Meetings in Lisboa

Right before Christmas I visited Lisbon to attend a conference and a workshop held at the Instituto Superior Técnico. It was a great opportunity to come back to Portugal after almost one year and meet a lot of friends and colleagues there.

Visit to Shangai

Many things have happened in the last few weeks, including the Centenary of General Relativity. On November 25th, I wanted to write a post on this event, but I couldn't because I was visiting Cosimo Bambi's gravity group at Fudan University in Shangai and, as it is infamously known, Google products (including this webpage) are inaccessible from China. None of the standard workaround really worked for me so, as a part of my Chinese trip, I have experienced how one feels being without access to gmail, google maps, facebook, etc... (it turned out to be not that bad in fact..)

During the visit, we had a mini-workshop with astrophysicists Javier Garcia-Martinez (Harvard-Smithsonian CfA), Thomas Dauser (Erlangen-Nuremberg) and Matt Middleton (Cambridge) who are working on different aspects of the electromagnetic emission from accretion disks as a possible way to measure the black-hole spin.

Shangai's skyline as viewed from one of the skyscrapers of Fudan University. The city is simply ENORMOUS..

Visit to EGO-VIRGO

A meeting of the theoretical and experimental groups of the Italian Institute for Nuclear Physics (INFN) working on the detection of gravitational waves and on theoretical aspects related to them was held at the European Gravitational Observatory (EGO) in Cascina, near Pisa.

The site hosts Virgo, a detector of gravitational waves which -in one year from now- will be ready to join its U.S. cousin Ligo in the decade-long search of gravitational waves from compact objects.

Me standing in front of one of the 3-km long arms of Virgo. Is the motion due to the passage of a gravitational wave? Hope not since the detector is still offline...

What is a gravitational wave?

All roads lead to....

I didn't have much time to write lately. The reason is the map below, which shows the places i'll be visiting in the next 45 days... it's going to be a very busy period!

I'm flying tomorrow to Boston for 10 days, then I will attend 3 workshops (in Bremen, Toronto and Lisbon), a friend reunion in Barcelona, a wedding in my home town, Cagliari, and each time touching base in Rome (where all roads lead after all!). I am also co-organizing the NRHEP Meeting and will chair one parallel section at Marcel Grossman Meeting in July. Fortunately, these latter two will not involve any travel, since the venue will be Sapienza for both.

I'll try to report more or less constantly during this crazy schedule, especially from the conferences which looks very interesting and i'm pretty much looking forward to attend.

Running Citizenship

Today's historical referendum in Scotland gives me the opportunity to talk about something I have in mind since I came back from the U.S. earlier this year. It's actually a very trivial concept that originates from the fact that:

When outside Europe, I feel European. When within Europe, I feel Southern European/ Mediterranean. When in Southern Europe, I feel Italian and, finally, when in Italy I definitely feel Sardinian. 

There is actually no contradiction in this Matrioska-like sense of belonging and I'm sure most people who happen to live abroad (which is already a rather subjective concept....) share the same feeling.

Anyway, this is interesting because in physics there is a much deeper and far-reaching concept that is (vaguely) related to the one above: that of the running couplings. In a quantum field theory, the coupling "constants" that define the strength of the couplings among quantum fields are not really constant, but actually their values depend on the energy scales.

As an example, take the most famous coupling constant, Newton's gravitational constant G that appears in the gravitational force law

F= G*mass1*mass2 / distance^2

which simply means that the intensity of the gravitational force between two masses (mass1 and mass2) is proportional to the masses and inversely proportional to the square of the distance. The proportionality factor is nothing but what we use to call Newton's constant and its value is G~6.673×10^{-11} N·(m/kg)^2. Now, Newtonian gravity is a classical theory and there is no such thing like a running G (although the situation might be different in alternative theories of gravity, such as scalar-tensor theories, but this is another story...). Indeed, G is a constant no matter how close the two masses are or how massive the objects are. In a quantum field theory, G would depend on the energy involved, for example on the typical distance of the interaction.

If you think about that, this is a beautiful and elegant concept: it teaches us there's no such thing like "the ultimate theory", but each theory (if consistently quantized) would be different at different energy scales. For example, a theory like electromagnetism (or QED in its quantum version) becomes more strongly coupled as the energy increases. The QED coupling constant (the fine structure constant α) is about α ≈ 1/137 at low energies, whereas one measures α ≈ 1/127 at the scale of the Z boson, about 90 GeV. A theory like quantum chromodynamics (QCD) behaves exactly in the opposite way and it becomes more weakly coupled at high energies. This phenomenon is called asymptotic freedom (because the interaction between particles becomes zero at infinite energy) and its discovery  (by Frank Wilczek, David Gross and David Politzer) was worth the Nobel prize in 2004.

What does this have to do with Scotland? (if anything...) The idea that can be borrowed from particle physics is that of a "running citizenship". In other words, each person changes her/his sense of belonging to some country/community accordingly to the "characteristic scale of the problem". It's something that European people are already experiencing given that economy in Europe is mainly governed on European scales, whereas local regulations are governed by state laws. Something similar also happens for federal countries, although the idea of running citizenship that i'm trying to describe has more to do with sense of belonging than with politics (politics often tries to change the sense of belonging and to tailor it accordingly, though).

In physics, the theory that studies the running couplings is called renormalization group and the running is usually called "flow". In most theories, the coupling either grows or decreases with energy, but for some special theories it asymptotes a constant value, a "fixed point".

As for the running citizenship, my impression is that we better try to have a fixed point for that, because the other two cases are quite catastrophic. The analog of a theory like QED would be a sense of citizenship that becomes smaller and smaller as smaller scales are approached, eventually terminating in individuals that do not belong any community. This would imply a sort of total isolation for each individual. The other case would be funny: an individual would become more and more aware of the global nature of Mankind and would feel like more and more part of the entire Universe as smaller scales are approached (this sounds like a nice outcome but perhaps a bit too Hippie for these times....). The most natural solution would be approaching a limit, a minimum size of the community (which we can perhaps identify with the family or hopefully with something larger than that) and then having each person feeling as a part of a larger community dependending on the context and the environment.

In which category does the running citizenship flow of the Scottish people fall? We shall discover this quite soon and the outcome has probably very little to do with physics.....

Story of a moka pot

Sometimes i develop a kind of fetishistic attraction for apparently modest objects.
The one in the picture is my moka pot and it (she?) is leaving Lisbon together with me today.

It's just occurred to me that the moka and I are tightly connected since the dawn of my adventure in physics. It was 2007 when I bought it in a small mall close to Oxford, MS. At that time, I was there as a visiting student during the master thesis and spent the first weeks in the deep South of the U.S. trying to drink that horrible soluble coffee. The fact is, it was nearly impossible to buy a proper coffee machine in Oxford, specially for a poor student as I was, who didn't want to spend >50 bucks for a fancy machine.

The moka pot in Rua Ferreira Lapa, Lisbon. The kitchen might appear dirty, but i guarantee that it is even worst.

Tomorrow: Stockholm

There are two huge conferences on gravity: the GR series and the Marcel Grossmann meetings. Every three years, several communities working on gravity, astrophysics and related subjects join these events, with excellent plenary talks and an unbelievable number of parallel sections.

This year, the MG13 will be held in Stockholm, starting from next Sunday. I'm going there tomorrow and will try to keep you posted [not as other contributors of these blog did in the past :P] ....Many interesting events are planned!

more on the 13rd MG meeting here. Next GR conference will be held in Warsaw instead, in July 2013