O Prêmio Nobel de Física de 2006

Este ano o prêmio Nobel de física foi concedido para John Mather, do Centro Espacial de Goddard da NASA, e George Smoot, da Universidade da Califórnia em Berkeley, pelo trabalho de ambos no satélite COBE (Cosmic Background Explorer) que mediu a radiação cósmica de fundo.

COBE

Uma das previsões da cosmologia baseada no Big Bang é que logo após a explosão inicial o universo era constituído de um plasma muito quente de fótons, eletrons e bárions. Os fótons interagiam constantemente com o plasma. A medida que o universo expandia-se o plasma esfriava até permitir que os eletrons se combinassem com os prótons formando átomos de hidrogênio. Isso aconteceu a cerca de 380 mil anos após o big bang quando a temperatura do universo era de cerca de 3.000 K. Então, na ausência do plasma, os fótons começaram a viajar livremente pelo espaço, esfriando a medida que o universo expandia-se até atingir a temperatura atual de 2,725 K. Esses fótons remanscentes daquela época formam a chamada radiação cósmica de fundo. A previsão do modêlo do big bang é que essa radiação é quase perfeitamente isotrópica e apresenta o mesmo espectro de um corpo negro. As pequenas anisotropias são causadas por diversos fatores e o estudo das mesmas leva a determinação dos vários parâmetros do modêlo do big bang.

Essa radiação foi detectada pela primeira por Arno Penzias e Robert Wilson em 1960 e eles ganharam o prêmio Nobel por essa descoberta. O satélite COBE, lançado em 1998, mediu a radiação cósmica de fundo e obteve uma concordância impressionante com a radiação do corpo negro. As pequenas anisotropias também foram medidas e resultam no famoso mapa do COBE.

Esse prêmio Nobel também tem um valor simbólico muito forte. A cosmologia experimental, antes da década de 90, não era levada muito a sério devido as grandes incertezas observacionais. A mudança do valor constante de Hubble a cada nova medida era tão grande que se costumava dizer que era a constante da física que mais variava com o tempo. A partir do COBE a cosmologia entrou numa outra era, de medidas extremamente precisas, que mostraram, e ainda mostram, um universo cheio de surpresas. Hoje em dia a cosmologia experimental é respeitada por todas as áreas. Esse progresso continua até hoje e para verificar isso basta comparar o mapa de anisotropias do WMAP, o satélite sucessor do COBE lançado em 2002.

WMAP

Mais notícias do prêmio Nobel podem ser encontradas aqui e aqui (em portugues), e aqui e aqui (em ingles).

System of units and coordinates

There is nice post by John Baez on system of units and coordinates:

"... systems of units are like coordinates. They’re both systems of arbitrary choices that let us describe reality using numbers. In both cases, we’re ultimately interested in learning things that don’t depend on these arbitrary choices."

The discussion is quite good and interesting.

Brazilian Meeting in Particles and Fields

This year the Brazilian Meeting in Particles and Fields was held in Águas de Lindóia, a small town near São Paulo. Every year we have a meeting of experimental and theoretical physicists working in high energy physics and field theory in Brazil. The audience is very broad. There are plenary talks which are supposed to be non technical and also more technical parallel talks, besides short oral presentations and panels. Approximately 300 physicists and students were present. The program can be found here. Wireless was available but the connection was poor. On Monday we spent almost all day without internet but in the following days the situation got better.

The meeting started on Sunday night when David Gross was awarded with the title of Doctor Honoris Causa given by the São Paulo State University. He gave a talk, The Future of Physics, where he discussed his favorite 25 problems. It seemed to be an updated version of the talk he delivered during the celebration of the 25 years of the KITP two years ago.

On Monday there were two good talks, one about cosmic inflation by Viatcheslav Mukhanov and another on astroparticle physics given by Angela Olinto. Angela is a Brazilian physicist and the chair of the Department of Astronomy and Astrophysics at Chicago University. She also works in the Auger Observatory, the biggest cosmic ray laboratory now in operation. Then Nathan Berkovits gave a parallel talk on string amplitudes. It is always difficult to talk on technical stuff to a large audience.

In the evening we had a round table on the anthropic principle. Originally Susskind had been invited and it seemed natural to have such a round table. But then he cancelled his participation and the round table was kept in the program. It was something surreal. Nobody in the table was in favor of the anthropic principle. Hitoshi Murayama presented some points pro the anthropic principle and then everybody, including Murayama , talked against it.

On Tuesday we had a very good talk on the physics beyond the standard model given by Murayama. He presented many usual topics like the hierarchy problem from a new perspective. In the afternoon Burt Ovrut talked on the heterotic string, the standard model and cosmology. Again, too technical and it was very hard to follow him.

On Wednesday we had an experimental plenary talk given by Guenakh Mitselmakher on the LHC. It seems they will start to collect data only in the spring of 2008. In the afternoon David Gross gave a talk on string theory, The Coming Revolutions in Fundamental Physics. I think it is the first time the experimentalists in Brazil have been subject to such an exposition of string theory. It must have been frightening to them but I have to talk to some of them to find out.

There were many short oral and panel presentations. My feeling is that there was more work done in string theory than last year. This is good news.

The talks are already available in the homepage.

O universo elegante na Google video

No Google video voce pode encontrar uma versão reduzida da série de tres filmes O Universo Elegante, de B. Greene. No site da PBS a série está disponível em vários capítulos. No Google video a série foi compactada em tres episódios:

Einstein's Dream

Strings the Thing

Welcome to the 11th Dimension

Banda larga é realmente necessária. (Via blog do L. Motl)

Last solar eclipse in 2006

It starts tomorrow, Friday 22, at 9:48 GMT (6:48 in Brazil). It is an annular eclipse which will be seen in South America, Caribbe, western Africa and Antarctica. Maps and more details can be found at NASA. Wake up early!!!