Gravitational waves and cosmic magnetic fields

One more report from LIGO collaboration came up saying that no stochastic background gravitational waves were detected in the fourth science run. It is expected the existence of a background of gravitational waves, due to a large number of unresolved sources, coming from all directions in the sky. There are constraints on the spectrum of such waves coming from CMB, millisecond pulsars and other resonant detectors. It seems LIGO is sensitive enough to probe some models, like cosmic strings and pre-big bang models, for stochastic background gravitational waves. Unfortunatly no positive results were found.

Another interesting article appeared in New Scientist (subscription required) telling the history of the cosmic magnetic field. There is an intergalactic magnetic field whose origin is unknown. The known mechanisms to produce magnetic fields can not explain them. One possibility is that they were created long ago possibly during the inflation period . If this is true this primordial magnetic fields could provide a lot of information about the early universe. As it is explained in the article some experiments are now being set up to study this cosmic magnetic fields.

Loop quantum gravity: a resposta

Em 2004 Helling e Policastro, que trabalham em cordas, analisaram criticamente a técnica de quantização utilizada pelos pesquisadores de loop quantum gravity. Mostraram que se aplicarmos a técnica ao oscilador harmônico não obtemos os resultados usuais da mecânica quântica. No ano passado apareceu um paper de Nicolai, Peeters e Zamaklar sobre loop quantum gravity. Esses autores também trabalham em teoria de cordas e estudaram os papers de loop quantum gravity encontrando sérios problemas. Um deles, por exemplo, é o fato de haver algo parecido com a não-renormalizabilidade da relatividade geral, quando se torna necessário adicionar um número infinito de novos termos à teoria original. Este ano, apareceu um novo paper, desta vez de Nicolai e Peeters com críticas ao modêlo de spin foam na loop quantum gravity. Estes resultados foram apresentados na Eurostrings'06, um seminário de loop quantum gravity numa reunião de cordas!

Hoje, apareceu uma resposta à essas críticas num paper de Thiemann. Imediatamente Helling rejeitou a resposta de Thiemann em seu blog e a coisa ficou feia indo ao nível do oscilador harmônico. Lubos aproveitou a oportunidade e já escreveu seu post. Há uma parte interessante onde menciona a história de Feynman e a teoria de tudo e como Thiemann tenta usar isso em seu paper.

UPDATE: Aaron Bergman escreveu um post onde detalha o tratamento do oscilador harmônico usando a proposta de Thiemann. Num outro post ele inicia uma discussão sobre o vínculo mestre usado pelo pessoal de LQG. No blog da Christine Dantas também há um espaço para a discussão do paper.

Matéria Escura

A descoberta espetacular da existência da matéria escura ocorrida na semana passada leva agora a uma nova questão. O que é a matéria escura? Existem vários candidatos e um post de Mark Trodden traz uma discussão muito boa. Como sempre, a Wikipedia também tem um bom artigo sobre o assunto.

The Tao of Mathematics

Terence Tao, aged 31, professor of mathematics at UCLA, got this year Fields Medal. He gave a long interview available in a press release of UCLA News. There he gives the recipe for success. Quantum Pontiff selected the main parts of the interview where he explains how to do research.

Fields Medal

Via Scott Aaronson, the winners of the Fields Medal are Andrei Okounkov, Grigory Perelman, Terence Tao and Wendelin Werner. The Nevanlinna Prize goes to Jon Kleinberg and the Gauss Prize to Kiyoshi Itô. The press release can be found here. It seems that Perelman declined the prize. There is an article in the Telegraph and in BBC News claiming that he can not afford the trip to collect the award. Peter Woit has some references to the works done by the winners. Lubos also has a post.

Dark matter is out there

The press conference to announce the discover of dark matter has just happened. You can read the news release and look at some pictures. Sean Carroll has a very detailed post about it. It seems now that MOND is dead. Long live dark matter.

Debate sobre a teoria de cordas

A teoria de cordas vem sendo duramente criticada, já por algum tempo, por diversos motivos. Isso levou à publicação de dois livros, um de Peter Woit, com o título "Not Even Wrong", o mesmo título de seu blog, e mais recentemente um novo livro apareceu, de Lee Smolin, chamado " The Trouble with Physics". Li uma versão preliminar do livro do Woit e ainda não vi o livro do Smolin.

É claro que esses livros levaram a um debate acalorado nos blogs. Muitos comentários foram feitos, a grande maioria de forma pessoal, o que não considero muito útil. Entretanto, Aaron Bergman recebeu o livro de Woit para uma resenha e o que ele escreveu é bastante equilibrado. Apesar de trabalhar em teoria de cordas, Bergman faz um balanço da área, e reconhece tanto os pontos positivos quanto os negativos. A resenha pode ser encontrada aqui. A resposta de Peter aos comentários de Bergman podem ser encontrados aqui.

A publicação desses livros levou a discussão para o grande público. Isso fez com que a NPR, National Public Radio, uma rede de rádio não comercial americana, promovesse um debate entre Lee Smolin e Brian Greene. A discussão é muito boa. Clique em "listen" para ouvir o debate. Lubos Motl fez um resumo do debate de forma tendenciosa, como sempre . Entretanto, ele escreveu um post bastante interessante sobre uma forma figurada que o Lee Smolin usou durante a entrevista. Lee comparou a busca de uma teoria quântica da gravitação com a escalada da montanha mais alta que existe. Só que ele se esqueceu que o caminho para a atingir o topo é para cima.

O fato da teoria de cordas estar sendo criticada por tantos anos e ainda assim conseguir atrair os estudantes mais talentosos e fazer com que o número de pesquisadores na área continue a crescer é bastante curioso. De fato, é preciso trabalhar em cordas para compreender o que acontece. Entrar na área é difícil pois não há um roteiro bem definido. Para estudar loop quantum gravity tudo o que se precisa saber é relatividade geral, mecânica Hamiltoniana e teoria quântica de campos. Isso é o básico. Em teoria de cordas o básico não é tão claro. Voce deve saber relatividade geral e teoria quântica de campos, mas dependendo do rumo que voce quer tomar, precisa saber também teoria de campos conforme, integrais de trajetória, quantização à la BRST, anomalias, topologia em duas dimensões, supersimetria, spinores em diversas dimensões, teoria de campos supersimétrica, BPS, QCD, o modêlo padrão, Calabi-Yau, topologia em dimensões superiores a dois, geometria algébrica, anti De Sitter, sólitons, instantons, teoria quântica de campos não perturbativa, ... Muita coisa mesmo. Pode-se ficar sem rumo nesse emaranhado e sem dúvida loop quantum gravity é mais direto. Porisso não é surpreendente que apenas estudantes capazes de encarar grandes desafios decidam entrar na área. Porque a teoria de cordas continua a crescer? Quem trabalha em cordas sabe, como descrito no review de Bergman , que a teoria não é "the only game in town", ela é "the best game in town". Nenhuma outra teoria que estende o modêlo padrão e que contém a relatividade geral produziu tantos resultados novos quanto a teoria de cordas. Os inúmeros testes de consistência a que a teoria foi submetida e o fato de ter passado em todos eles é o mais forte indicativo que estamos na direção correta.

Medalha Fields: o ganhador vai aparecer?

A Medalha Fields, o equivalente a um premio Nobel em matemática, será entregue no próximo dia 22 de agosto pelo rei da Espanha. Um dos prováveis ganhadores é o russo Gregori Perelman pelo seu trabalho sobre a conjectura da geometrização e a conjectura de Poincaré. Entretanto, ele demitiu-se do Steklov Institute of Mathematics em São Petesburgo e ninguém sabe por onde ele anda. Um caso semelhante aconteceu em 1966 quando um matemático alemão recusou-se a receber a medalha em Moscou devido à intervenção soviética no Europa oriental. Ele recebeu a medalha mais tarde. Mais detalhes no New Scientist.

Dark matter discovered

NASA site is announcing that dark matter was discovered by Chandra X-ray Observatory. A teleconference will be held on August 21 at 1 pm EDT (2 pm in Brasil). Sean Carroll is going to participate so the first question is: why wait for one week? Can anyone provide us with more information?

UPDATE: Imagine the collision between two galaxies. The ordinary matter in them collides and gets interlocked due to the mutual gravitational attraction. Dark matter, however, just keeps its momentum and keeps going on leaving behind the colliding galaxies. It seems that something like this has been detected by the Chandra X-Ray Observatory. Collisions of ordinary matter produces a lot of X-rays and the dark matter outside the galaxies acts as a gravitational lens. More details can be found in John Baez.

Extra dimensions in the lab and landscape

Since string theory predicted the existence of extra dimensions many Cavendish type experiments with improved technology were done. Up to now no deviations of Newton's gravitational law were detected. Now there is a proposal to optically trap supercold strontium atoms a few microns apart and measure the gravitational attraction. It would provide an alternative way to detect extra dimensions without the use of torsion balances and accelerators.

There is also a nice article on the landscape in Science Magazine. It gives a balanced view of the anthropic principle and its use in string theory landscape.

Loop quantum gravity in New Scientist

The last issue of New Scientist has an editorial and a full article dedicated to loop quantum gravity. The editorial mentions string theory and says:

"The rivalry between the two theories may turn out to be false. It is driven in part by the different backgrounds and prejudices of their practitioners, with string theorists mainly coming from particle physics and the loop camp from general relativity."

Well, we know that is not the reason. Anyway the editorial says that now loop quantum gravity can describe matter. The article has the title "You are made of space-time", and you can imagine how matter is supposed to be represented in LQG. It has nice pictures of braided space-time, which looks like an octopus, claiming to represent elementary particles. The article is based on two papers: gr-qc/0604044, hep-th/0603022 and hep-ph/0503213.To have a balanced view you should also read some trackbacks to these papers: here, here, and here.

ICMP 2006 - Day 2

Monday evening Lisa Randall gave a public talk on extra dimensions. She was tired but the talk was good. Even though it was announced as a public lecture it was really addressed only to the participants. After Lisa's talk there was an opening ceremony for the conference. Representatives of the main Brazilian sponsors of the conference were there and possibly that is the reason the opening was not in the morning as it should be. In Brazil formal aspects are more important than its contents.

Yesterday (Tuesday) there were three plenary lectures but only one with some interest to me. It was given by Bruce Kleiner and he talked about Perelman's work on Ricci flows and the geometrization conjecture. I was not aware that there are many papers explaining Perelman's work and that mathematicians like to write explaining other people works. The parallel session on string theory started with Sergei Gukov talking on categories and its application to link homologies and generalizations based on topological field theories. Hard stuff with the usual cartoons. Then Anton Kapustin gave a very clear talk on topological reduction of supersymmetric gauge theories. He explained in some detail the twisting procedure and how it can be used to get a topological or semi-topological field theories. The last string talk was given Marcos Marino on phase transitions in topological string theories. Again too mathematical.

Then I went to the parallel session on general relativity. The Brazilian GR community must be angry with its contents. The first talk was given by Gabriel Cardoso about entropy in supergravity and string theory where he proposes a modified OSV (Ooguri-Strominger-Vafa) relation to take into account subleading corrections to the entropy. The OSV proposal was discussed by Lubos. The second was a talk on loop quantum gravity. In fact, loop quantum cosmology, by Martin Bojowald, where the use of difference equations is claimed to allow the study of the singularity problems. Great if true. The last talk was given by Axel Kleinschmidt on the attempts to understand M theory looking at the symmetry structures hidden in D=11 supergravity. It is nice to see that there are signs of integrability there too.

I didn't see the end of the last talk because I had to catch my flight back to Sao Paulo. I went to Rio just for the string theory sessions. After I left, the Poincare Award ceremony took place. It was awarded to Ed Witten, Ludvig Faddeev and David Ruelle. All of them gave a talk on the Young Researchers Symposium held on Saturday and Monday.

The conference goes until Friday but I will not be there. Today there are only plenary talks and the afternoon is free. At night there is the conference dinner at Porcao, a very good barbecue restaurant in Rio. I will miss Zarembo's talk on Friday. Hope somebody can tell me later on.

ICMP 2006

The ICMP started today in Rio de Janeiro. I was surprised by the first talk given by W. Werner. It was about critical phenomena in 2D. He illustrated very well what he was saying by using percolation of hexagonal cells. He also talked about Brownian loops and mentioned the theorems he is associated with. Of course, everything has conformal invariance, so life is a bit easier. The second talk was about the classification of the irreducible representations of chiral conformal theories with c<1 using algebraic quantum field theory. It was given by Y. Kawahigashi. A very impressive piece of work.

There was a parallel session on strings theory. Chris Hull gave a very clear talk on nongeometrical string backgrounds. It is a clever way of implementing dualities. Pierre Vanhove talked about hypermultiplet couplings in N=2 sugra and Mina Aganagic on topological strings, monodromy and modular forms.

Tonight Lisa Randall is supposed to give a public lecture. The presentations will be online only after the conference is over. As usual because mathematicians are slower.

Colóquio do DFMA

Depois de organizar os colóquios do departamento por três anos seguidos passo a coordenação para o Gustavo Burdman. No início de cada semestre eu enviava aos professores e alunos do departamento um e-mail enfatizando a importância dos colóquios. O texto é endereçado principalmente aos estudantes novos. Acho muito importante alertar os estudantes acerca da importância dos seminários, mesmo que o exemplo do orientador seja contrário.

Se voce quer saber porque os seminários são importantes leia o texto aqui.

Se voce acha que dá muito trabalho estudar e assistir seminários talvez seja melhor ler o meu post aqui.

Young Researchers Symposium

Today is the second and last day of the YRS. The first talks were in areas of mathematical physics that I am not informed enough to comment on. One was on some sort of random walks, the second on entanglement and the third was too mathematical. You may see the program here.

The most expected talk was given by Witten and was about the Langlands program. He started giving an elementary introduction to electric-magnetic duality, magnetic monoples, Dirac strings and the quantization condition to arrive at the Montonen-Olive duality. He then explained the goal of the Langlands program, that is, to study number theory using geometry, and ended mentioning his work, that the Langlands program can be interpreted in terms of physical ingredients. Since the audience was very heterogeneous it seems he did it well.

International Congress on Mathematical Physics 2006

The ICMP 2006 will start in Rio de Janeiro tomorrow. It is a traditional meeting which began in Moscow in 1972 and is held each three years. During the conference the Poincare Medal is awarded and this year I heard it will go to Ludvig Faddeev. There are several other satellite meetings going on or ending now, like the Workshop on Pure Spinors organized by Nathan Berkovits in Sao Paulo.

yesterday and today it is happening the Young Researchers Symposium, a meeting promoted by the ICMP to attract younger people and where a Field medalist gives a talk. This year this seminar will be delivered by E. Witten.

The symposium started yesterday with a very nice talk by Faddeev on quantum groups. As he explained quantum groups are neither quantum nor groups. They are deformations of the phase space and the group structure. He started with spin chains using the XXX Heisenberg model along the lines of his well known review. He went on to the XXZ model and its connection with deformed algebras, Yang-Baxter, braid groups, and so on. During the talk he gave many historical accounts related to the subject and distributed a copy of a new preprint "History and Perspectives of Quantum Groups". Very interesting.

Berkovits gave a talk about string amplitudes and pure spinors. Too technical for an audience of mathematicians and physicists from several areas. Anyway it is too hard to explain his goal without going into the technical details. At the end he said that it is possible to extend his pure spinor formalism to 11 dimensions and maybe get more information on M theory. The talk of David Ruelle went the other way. Almost no equations. Too difficult to understand many of his statements and the line of reasoning. Maybe for people working in the area it was easier. He talked about dynamical systems, chaos, turbulence and nonequilibrium statistical mechanics. He told that the solar system is not stable and some guys in the audience seemed very worried about that! Many historical notes were told mainly about Poincare. Like the butterfly effect that had in fact begin with a seagull and not with a butterfly.

There were other sessions where younger people presented their work. The day ended with a reception and Brazilian music, chorinho and samba. Very good.

Why progress in science is so slow around here

Lubos Motl wrote a post trying to understand why Germany, and more generally Central Europe, after giving so many contributions to physics in the early XX century lost the leadership. He identifies three causes:

1. The American financial attractor that has caused some brain drain
2. The working American free market of ideas and its less viable European counterpart
3. The relative inability of European scholars to allow their younger colleagues to get further

It is interesting to realize that all this holds also for Brazil and possibly for Latin America. Maldacena is by far the most clear example of the first point. Even if he wanted to go back to Argentina it would be very difficult for the other reasons.

Lubos also details the other two points:

In the American system, new ideas are actively looked for and they are appreciated, together with their happy authors. In the Central European context, it is more important to be compatible with the old ideas - let us call them "perfectly balanced ideas" - that are currently dominating the intellectual landscape and in which the old myths and pre-conceptions play a comparable role to the newest developments.

and,

The third difference between America and Central Europe that I mentioned is the insufficient desire of the Central European scholars to support their students and younger colleagues in getting further than the previous generations. A particularly bad habit is to penalize students and others for being interested in and working on new ideas.

Reading this brings recollections from many years ago. When I was a MSc student, in the 70's, the preprints I read were saying that quantum field theory was the framework for elementary particle physics. The researchers I talked to said that it was just a fashion and it would go away. I could not understand why. After all there were experimental evidence supporting QFT. So I had to study QFT by myself and I did so. After the PhD in London I came back to Brazil at the beginning of the 80's. I recall giving several talks on supersymmetry. It was usual to hear comments like this:
- You should do research in supersymmetry only after it is found, not now.
I usually replied saying that when supersymmetry is found it will no longer be the subject of research but of textbooks. As we all know susy is likely to be found at LHC and even before its discovery it is already in textbooks! A colleague of mine already deceased, P.P.Srivastava, was one of the first people to work in conformal supersymmetry. He was in Europe when he did his work but had to return to Brazil. Here he was convinced by many Brazilian researchers that supersymmetry was just a fashion which would go away soon. Unfortunately he gave credit to this argument and stopped working in susy. Being out of scene people started to stop citing his works. Some years later he realized how wrong his decision was, went back to susy and wrote a book Supersymmetry, Superfields and Supergravity in an attempt to get credit for having worked in conformal susy. His book was one of the few available at that time and is quite good.

Things like this happened in other areas as well. Still in the 80's, when the inflationary theory was born, people working in general relativity in Brazil started to despise the idea. They used to compare the researchers of inflation with those old Hollywood western movies where an old guy in the back of his wagon sells a miracle medicine fooling everybody! That is how it works in many places. If you do not have sound scientific arguments you convince people in this way. Mainly if you live in an economically or militarily oppressed country. It works! I had a bad time explaining to young students the distinction between scientific ideas and political ideologies.

Of course, string theory was also a target for these people. Take Nathan Berkovits for instance. He applied for a position in my institute in the 90's. We discussed the CV and recommendation letters of all candidates. Nathan had a very strong recommendation letter from Witten. After some harsh discussions an influent professor said:
- Who is this Witten anyway?
I immediately said
- The same who just won the Fields Medal!
And he replied in a waggish way
- But his work was in geometry not in analysis!
That was the feeling against string theory at that time! A committee was chosen to select one of the candidates and obviously Nathan did not get the position. Very soon, another university in Sao Paulo, run by younger and smarter people, hired him so he got a good position and is well now. But we lost Berkovits!

Another tactics that is often used consists in bringing foreign people to say the last word against new ideas. There is a well known retired German professor who thinks that we all should do field theory like in 60's and forget everything about string theory. Fortunately almost nobody takes this sort of foreign authority seriously nowadays.

It has to be said that this kind of people is no longer representative of physics in Latin America. As the time goes by their proportion is diminishing in Brazil and they are loosing any decision power they had before. There are many serious researchers who appreciate new ideas and work on them. Some may not work on modern topics but accept that others do so. Without any embarrassment or any mocking. Students now can choose their area without being oppressed. And more than that, they are free to do better than their former teachers did.

A warning to the students. Some of this people are still around. You can easily recognized them. Do not trust those who attack a subject without any solid scientific argument. Never accept political or sociological arguments. They were wrong in the past. And they will be always wrong.

We are slowly finding our way to do leading science.

Why do you work so hard?

The answer from a student. Think about it!