Van Gogh esconde Van Gogh

High-tech study reveals early Van Gogh work beneath another painting - Los Angeles Times

University of Antwerp/Deutsches Elektronen-Synchrotron

Researchers
used X-rays from a particle accelerator to reconstruct the portrait of
a woman Vincent van Gogh had painted over before composing his
landscape "Patch of Grass," completed in 1887. Conventional X-rays used
in previous analyses had produced only rough outlines of the portrait.
The image, unveiled in a scientific journal published this week, bears
a striking resemblance to a series of somber portraits the artist
produced in the Dutch town of Nuenen, where he composed “The Potato
Eaters,” completed in 1885 and regarded as his first major work.

High-tech study reveals early Van Gogh work beneath another painting
University of Antwerp/Deutsches Elektronen-Synchrotron
Researchers used X-rays from a particle accelerator to reconstruct the portrait of a woman Vincent van Gogh had painted over before composing his landscape "Patch of Grass," completed in 1887. Conventional X-rays used in previous analyses had produced only rough outlines of the portrait. The image, unveiled in a scientific journal published this week, bears a striking resemblance to a series of somber portraits the artist produced in the Dutch town of Nuenen, where he composed “The Potato Eaters,” completed in 1885 and regarded as his first major work.
X-rays from a particle accelerator help scientists reconstruct a portrait the artist had covered up to paint his 'Patch of Grass' in 1887.
By Karen Kaplan, Los Angeles Times Staff Writer
July 30, 2008
Using a thin beam of synchrotron X-rays generated by a particle accelerator, European scientists have reconstructed a portrait of a peasant woman painted by Vincent van Gogh that had been concealed beneath another painting for 121 years.

The image, unveiled in a scientific journal published today, bears a striking resemblance to a series of somber portraits the artist produced in the Dutch town of Nuenen, where he composed "The Potato Eaters," completed in 1885 and regarded as his first major work.

Conventional X-rays had revealed the rough outlines of the portrait, which Van Gogh covered 2 1/2 years later with a vibrant landscape of a flowering meadow after he moved to Paris and was influenced by Impressionism. But those X-rays weren't good at distinguishing between the many layers of paint on the single canvas, and pigments made from heavy metals obscured colors derived from other elements.

"We get a very partial, fragmentary, color-blind view," said Joris Dik, a materials scientist and art historian at the Technical University of Delft in the Netherlands.

So Dik and his colleagues took the painting, "Patch of Grass," which was completed in 1887, to a particle accelerator in Hamburg, Germany. The intense X-ray beam excited the atoms on the canvas, causing them to emit X-rays of their own that were captured by a florescence detector. It took two days to scan the roughly 7-by-7-inch portion of the meadow that masked the portrait.

Since each element in the painting had its own X-ray signature, the scientists were able to identify the distribution of metals in the various layers of paint and construct a three-dimensional model of the work. Then the team peeled off the layers one by one.

The top layer consisted of paints made with zinc, barium, sulfur and other elements. Behind that they found a uniform distribution of lead, which was used as a primer to hide the portrait and prepare the canvas for a new painting. Once that was removed, they combined the distributions of two more elements -- mercury and antimony -- to produce the outlines of the hidden portrait.

Then, with the help of computer software, the team embarked on an elaborate version of painting by numbers.

"We colorized those two distributions according to the color that the pigment would have had," Dik said.

Chemical analysis revealed that the mercury was an ingredient of vermilion, the red pigment used to color the woman's lips, cheeks and forehead. Antimony was a component of Naples yellow, which was mixed with zinc white paint to highlight certain areas of the woman's face, according to the report in the August issue of Analytical Chemistry.

Van Gogh often recycled his canvases. Art experts estimate that one-third of his early paintings hide others, which may be ripe for new analysis.

karen.kaplan@latimes.com

Dispositivo de Anticitera

:: Agência FAPESP :: Divulgação Científica - Calendário olímpico

Divulgação Científica
Calendário olímpico

31/7/2008

Agência FAPESP – Já se sabia que o Mecanismo de Anticítera, resultado da engenhosidade dos gregos antigos, era mais sofisticado tecnologicamente do que qualquer outro mecanismo inventado pelo menos nos mil anos seguintes. Agora, um novo estudo indica uma complexidade ainda maior.

O grupo liderado por Tony Freeth, do Projeto de Pesquisa do Mecanismo de Anticítera, conseguiu reconstituir inscrições que revelam que o mecanismo, construído por volta do ano 100 a.C., não era usado apenas para operações científicas.

Em estudo publicado na edição de 31 de julho da revista Nature, os pesquisadores usaram imagens feitas em raio X em três dimensões para mostrar que o mecanismo, utilizado principalmente para cálculos astronômicos, também armazenava dados de eventos esportivos, como se fosse um computador portátil.

Segundo eles, um dos discos, até então considerado um calendário de um ciclo de 76 anos, era usado para seguir outro ciclo, o de quatro anos das Olimpíadas e de outros jogos pan-helênicos. Entre as inscrições recuperadas nos fragmentos estão as palavras “olympia” e “nemea”, esta última referente aos Jogos de Neméia.

Os cientistas também identificaram no mecanismo 12 nomes de meses que consideraram de origem coríntia, da Siracusa, e sugerem que o conceito do mecanismo pode ser estendido a Arquimedes (c. 287 a.C. – c. 212 a.C.). Os meses integravam um sofisticado calendário de 19 anos.

O Mecanismo de Anticítera foi descoberto em 1901 por um grupo de mergulhadores que apanhavam esponjas próximo à ilha de Anticítera. As 82 partes hoje disponíveis e que são usadas para os estudos foram retiradas de um naufrágio a 42 metros de profundidade. A data estimada do naufrágio é 65 a.C.

O artigo Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism, de Tony Freeth e outros, pode ser lido por assinantes da Nature em www.nature.com.

Leonard Susskind

Hawking nemesis Leonard Susskind speaks - Los Angeles Times

Leonard Susskind


Matthew Black / For The Times

Stanford University physicist Leonard Susskind
went from a being a plumber in the South Bronx
to becoming an authority on black holes.


Hawking nemesis Leonard Susskind speaks

In 'The Black Hole War,' Stanford University physicist Susskind recounts his long history of scientific conflict with famed cosmologist Stephen Hawking (whose concession letter he prints).

By John Johnson Jr., Los Angeles Times Staff Writer
July 26, 2008


For two decades, Stanford University physicist Leonard Susskind battled cosmologist Stephen Hawking over the behavior of black holes. Hawking said that when black holes eat their fill, they disappear, taking with them everything they consumed over their billions of years of existence. Susskind found this idea so disturbing that he publicly declared war -- a conflict he describes in his new book, "The Black Hole War." In a conversation before a recent appearance at the Los Angeles Public Library, Susskind recounted his long struggle to "make the world safe for quantum mechanics."


How did this war with Stephen Hawking come about?


I was a particle physicist when I was invited to an event at Werner Erhard's house in 1981. Erhard [founder of the est self-awareness movement] admired scientists and liked to listen to them debate. At one of his events, I met Stephen Hawking. Stephen discovered an amazing fact, which is that black holes evaporate. It's like a puddle of water out in the sun.

OK.

So the question is, What happens to the information trapped in the black hole? Stephen said it was lost forever. Stephen didn't just say it, he proved it. At least he convinced himself and everybody else mathematically that it was true.

And you felt that was wrong.

It violates one of the fundamental principles of physics, which says nothing is ever lost completely. You may say, "How can you say information isn't lost? I can erase information on my computer." But every time a bit of information is erased, we know it doesn't disappear. It goes out into the environment. It may be horribly scrambled and confused, but it never really gets lost. It's just converted into a different form.

In your book, you compare Stephen Hawking to the White Whale and yourself to Ahab.

I obsessed over this. This was never a matter of personal animosity. But he couldn't see how damaging this would be to the rest of physics. And he didn't see what a great resolution might come out of it if thought about in the right way. I love the man, but I wanted to grab him by the neck and shake him a little bit. Stephen would just smile and say, "I'm right and you're wrong."

That's a pretty heady debate for someone who started out as a plumber.

I was from a poor Jewish family in the South Bronx. My father was a plumber, but when I was 16 he got sick and I had to take over. Being a plumber in the South Bronx wasn't fun.

When did physics come along?

I was going to engineering school but fell in love with physics. When I told my father I wanted to be a physicist, he said, "Hell, no, you ain't going to work in a drugstore." I said, No, not a pharmacist. I said, "Like Einstein." He poked me in the chest with a piece of plumbing pipe. "You ain't going to be no engineer," he said. "You're going to be Einstein."

What is the great resolution you referred to?

One result is something called Black Hole Complementarity. Let's say Alice falls into a black hole while Bob stays on the outside and watches. Nothing drastic happens to her when she crosses the event horizon [the point of no return around a black hole]. Of course she's eventually going to get it. On the other hand, there is another picture of the black hole, where every bit of information that you throw onto the horizon of a black hole gets sort of stuck on the horizon and builds up a soup of information bits. And this soup is hot, about a 100 billion billion billion degrees.

So Alice would get burned up?

We have a dilemma. One theory, based on general relativity, simply says Alice just floats past the horizon. That would be Alice's view of things. But Bob's view of things, if he believes in quantum mechanics, is that Alice falls into this soup of hot bits and her molecules are ripped apart. So, which one is correct? Alice can't both be killed at the horizon and not killed at the horizon. The answer is they are both correct.

How can that be?

These two ideas are not in conflict because to be in conflict, there has to be a contradiction. Well, nobody can see a contradiction for the simple reason that nobody can send a message from the inside of a black hole. Alice can't send a message saying, "Bob, I'm OK, don't worry about me," because the message can't get out of the black hole. Yet everything Bob sees is consistent with saying that Alice was thermalized.

It's difficult to see how both can be true.

We've had these things before in Einstein's thought experiments. Einstein, in the special theory of relativity, proved that different observers, in different states of motion, see different realities.

There's another strange theory that's come out of this battle, isn't there?

Yes, the Holographic Principle. A hologram is a two-dimensional sheet, such as film, which codes three-dimensional information. A simple way to say it is that the black hole horizon is like a hologram. The horizon of the black hole is like the film, and the image is the stuff that falls into the black hole. It's extremely unintuitive. According to this theory, the exact description of a region of space -- no matter how big -- is like a film on the boundary, where complicated and extremely scrambled versions of that space are going on. So in that sense, the universe is like a hologram.

Stephen now agrees that the information is not lost when a black hole evaporates.

Yes, he's seen the light. When he sees the light, he's very magnanimous.

[Susskind pointed to a page in his book, where a concession letter from Hawking is printed.]

Are there are any evaporating black holes in our region of the universe?

No. They are all accreting [still eating]. Black holes are much, much colder than their surroundings in space. That means heat flows from the surrounding space into the black hole. If we wait for a long, long time, the universe will expand, it'll cool, and eventually empty space will become colder than the black holes. When that happens, they will start to evaporate. But don't hold your breath.

john.johnson@latimes.com

Píon

P:: Agência FAPESP :: Notícias - Professores de física ganham página na internet

Professores de física ganham página na internet

28/7/2008

Agência FAPESP – Os professores de física de todo o país, em especial os do ensino médio, ganharam uma página na internet que fornecerá material instrucional de apoio à atividade docente, visando a melhorar o processo de ensino aprendizagem.

Trata-se do portal Píon, desenvolvido pela Sociedade Brasileira de Física (SBF) com o apoio financeiro do Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), que já está no ar para livre consulta. O site também pretende servir como um meio de divulgação da física para todos os interessados no assunto.

O nome do portal é uma homenagem ao físico brasileiro Cesar Lattes, co-descobridor da partícula elementar conhecida por Méson pi ou Píon. Nele estão disponíveis conteúdos como simulações, aulas prontas, textos, imagens e links.

A página tem uma sessão de artigos que contém adaptações de textos originalmente publicados na revista Física na Escola, da SBF, além de artigos escritos por internautas e colaboradores. Já a sessão “Você sabia” oferecerá uma seleção de desafios em física, elaborados especialmente para professores e estudantes.

Notícias relevantes sobre o ensino de física, um blog com comentários e dicas e uma sessão com informações sobre eventos também estão no portal. Há ainda um fórum de discussões para ampliar o relacionamento e a troca de experiências entre o público, os físicos e os professores.

O idealizador e coordenador do portal é o físico Nelson Studart, professor do Departamento de Física da Universidade Federal de São Carlos (UFSCar).

Mais informações: www.pion.sbfisica.org.br

Entropia e Tempo

Mysteries of time, and the multiverse - Los Angeles Times

Q & A

Mysteries of time, and the multiverse


Gary Friedman / Los Angeles Times

Sean Carroll is a physicist at Caltech in Pasadena. His recent article in Scientific American is called "The Arrow of Time."

In his studies of entropy and the irreversibility of time, Caltech physicist Sean Carroll is exploring the idea that our universe is part of a larger structure.

By John Johnson Jr., Los Angeles Times Staff Writer
June 28, 2008

Caltech physicist Sean M. Carroll has been wrestling with the mystery of time. Most physical laws work equally well going backward or forward, yet time flows only in one direction. Writing in this month’s Scientific American, Carroll suggests that entropy, the tendency of physical systems to become more disordered over time, plays a crucial role. Carroll sat down recently at Caltech to explain his theory.

What's the problem with time?

The irreversibility of time is sort of the most obvious unanswered question in cosmology.

Time has been talked about in cosmology for many years, but we have a toolbox now we didn't used to have.

We have general relativity, string theory, discoveries in particle physics that we can use to help us find the right answer.

What does entropy have to do with all this?

The most obvious fact about the history of the universe is the growth of entropy from the early times to the late times.

The fact that you can turn eggs into omelets but not vice versa is a thing we know from our kitchens.

You don't need to spend millions of dollars on telescopes to discover it.

Can you give me a simple explanation of entropy?

One way of explaining entropy is to say it's the number of ways you can rearrange the constituents of a system so that you don't notice the change macroscopically.

If you mix milk into a cup of coffee, the more mixing that occurs, the more disordered the milk molecules become and the more entropy builds.

If all the milk was somehow separated from the coffee, that would be low entropy.

So what's the problem?

If you really believed the conventional story that the Big Bang was the beginning, that there was nothing before the Big Bang, I think that's a very difficult fact to explain. . . .

There's no law of physics that says it should start at a low-entropy state. But the actual universe did that.

From a layman's standpoint, it seems perfectly rational that things would start small and grow apart. You're saying that's wrong.

Many of my very smart colleagues say exactly the same thing. They say, "Why are you thinking about this? It just makes sense that the early universe was small and low-entropy."

But I think that is just a prejudice: . . . Because it is like that in our universe, we tend to think it is naturally like that.

I don't think there is an explanation for that in terms of our current understanding of physics. I'm just saying it's not a fact that we should take for granted.

So you think the way the universe began is unnatural?

Low-entropy configurations are rare.

If you take a deck of cards and you open it up, it's true that they're in order. But if you randomly chose a configuration of a deck of cards it would be very, very unlikely that they would be in perfect order.

That's exactly low entropy versus high entropy.

The universe is more than what we see?

The reason why you are not surprised when you open a deck of cards and it's in perfect order is not because it's just easy and natural to find it in perfect order, it's because the deck of cards is not a closed system. It came from a bigger system in which there is a card factory somewhere that arranged it. So I think there is a previous universe somewhere that made us and we came out.

We're part of a bigger structure.

Are you saying that our universe came from some other universe?

Right. It came from a bigger space-time that we don't observe. Our universe came from a tiny little bit of a larger high-entropy space.

I'm not saying this is true; I'm saying this is an idea worth thinking about.

You're saying that in some universes there could be a person like you drinking coffee, but out of a blue cup rather than a red one.

If our local, observable universe is embedded in a larger structure, a multiverse, then there's other places in this larger structure that have denizens in them that call their local environs the universe. And conditions in those other places could be very different. Or they could be pretty similar to what we have here.

How many of them are there? The number could well be infinity. So it is possible that somewhere else in this larger structure that we call the multiverse there are people like us, writing for newspapers like the L.A. Times and thinking about similar questions.

So how does the arrow of time fit into this?

Our experience of time depends upon the growth of entropy. You can't imagine a person looking around and saying, "Time is flowing in the wrong direction," because your sense of time is due to entropy increasing. . . . This feeling that we're moving through time has to do with the fact that as we live, we feed on entropy. . . . Time exists without entropy, but entropy is what gives time its special character.

Entropy gives time its appearance of forward motion?

Yeah, its directionality. The distinction between past and future. If you're floating in outer space, in a spacesuit, there would be no difference between one direction and another. However, nowhere in the universe would you confuse yesterday and tomorrow. That's all because of entropy, and that's the arrow of time.

Does God exist in a multiverse?

I don't want to give advice to people about their religious beliefs, but I do think that it's not smart to bet against the power of science to figure out the natural world. It used to be, a thousand years ago, that if you wanted to explain why the moon moved through the sky, you needed to invoke God.

And then Galileo and Newton came along and realized that there was conservation of momentum, so things tend to keep moving.

Nowadays people say, "Well, you certainly can't explain the creation of the universe without invoking God," and I want to say, "Don't bet against it."

Designers Chineses

Computer Arts - China inspired

China inspired

A bold new generation of creative talent is about to burst onto the global scene. Craig Grannell talks to the designers and illustrators who are at the forefront of China’s revolution in graphic design

China is credited with two mainstays of graphic design – paper and movable type – yet the concept of ‘graphic design’ barely existed there 30 years ago. With China’s government beginning to replace the insular thinking of old with a more outward-reaching approach, and the Olympics making the country the focus of global attention, a new generation of Chinese creative talent has emerged, marrying traditional Oriental aesthetics with contemporary methodology and style. An entire nation’s design industry is being forged, and there’s the potential to tap into a massive and lucrative new market. But beware: many Chinese designers are starting to look outwards and thinking exactly the same thing.

Independent thinking
The West’s rich background in design stretches back many decades. So it’s hard to imagine a country where graphic design barely existed a generation ago. But in China, the words for ‘design’ or ‘designer’ only started being used in the early 1990s, and creative graphic design didn’t exist at all before the 1980s. Although the country has a strong history in calligraphy, its long period of being a centrally planned economy meant there was little demand for truly creative design. Output was generally functional, aiming to advertise products in the most basic and brutal sense. Even during periods of great political reform, craftsmanship prevailed over creativity, and only recently has this started to change.

Now aiming to become a major player in the global economy, China is beginning to understand the value of independent thinking when it comes to design and branding, particularly relating to products for export. “However, despite rapid development, China needs to catch up with the world in the field of design,” says designer Han Jiaying, whose classic poster series ‘Mouth’ and ‘Beauty’ for Frontier effortlessly blended the old and new in Chinese design. A good starting point, he thinks, would be for China’s design world to fully integrate with the international community: “We must broaden our vision to an international scale, with our thousands of years of historical and cultural background as a foundation.”

It’s clear that some Chinese designers already think along those lines. The Victoria & Albert’s China Design Now exhibition (open until 13 July) showcases contemporary Chinese design works, including those by relatively old hands Han, Chen Shaohua and Wang Xu. What’s interesting is how many of the posters on show were intended for international exhibitions. It’s through these international forums that many Chinese designers discovered an audience interested in Chinese characters and imagery, and became informed by outside interest.

A new generation of Chinese designers is keen to capitalise on pioneering work by the likes of Chen and Han, and one notable success is Ji Ji. Arguably a superstar of Chinese design, he’s graced TIME, been interviewed by numerous publications, and his iconic Hi Panda figures are conspicuous throughout much of the V&A show.

Despite fronting Poledesign, Ji Ji is almost becoming a brand himself – a marketing machine with a desire to take on the world, selling toys, T-shirts and more. Crucially, while his work appeals to China’s new urban youth, it also strikes a chord worldwide.

Design by type
While Ji Ji’s most celebrated current project embraces China’s most popular animal, the panda, it’s Chinese lettering that most resonates with Western audiences, albeit often in stereotypical fashion. Chinese characters are popular with designers aiming towards the exotic, and the tattoo industry seems to thrive on them.

Within China, too, traditional elements remain fairly popular. Chinese calligraphy continues to inform contemporary art and design, partly because those heading government organisations and large companies are slow to adapt and embrace design reform, and partly because of historical reasons. Designer and illustrator Zhang Jing notes that calligraphy was once considered a very important skill. She adds: “Although it’s no longer necessary, it’s still valued because it reveals one’s personality.”

Zhang notes that other elements of Chinese culture remain apparent in some modern work: “Chinese art was mainly influenced by Buddhism and nature, with elements being similar across many paintings. There’s more emphasis on curves and lines, rather than colour, which sets the Chinese aesthetic apart from that of the West.” Illustrator Xi He also considers a sense of underlying harmony intrinsic to the Chinese aesthetic: “The thinking of Taoism combines opposites to form balance, and this still influences Chinese creative output. As per Taoism’s yin-yang symbol, objects represented in Chinese design are often carefully combined and harmonised.”

Other designers argue that ancient concerns no longer fully apply to contemporary work. New York-based art director Qian Qian uses modern design methods to reinterpret traditional aesthetics, or as he describes it, “revisiting traditional culture from the ruins”. In a sense, the China of old is considered little more than a toy box, akin to a musician’s bank of samples, rather than offering methodology to be revered and adhered to.

This home-made spirit almost mirrors the UK’s punk movement during the late 1970s, and perhaps points to a time when the old will be trashed entirely. “I don’t really think there’s a particular ‘Chineseness’ that makes Chinese art unique,” reveals designer Gary Chen, founder of webzine Pigstyle.net and head of creative group Design By Guangzhou. “I can already see the ‘exotic’ elements fading from the Chinese design scene, and much outstanding Chinese design today has no apparent Oriental features.”

Imports and exports
Chen argues that several factors instigated a shift from traditional imagery, most of which are grounded in a desire to experiment and evolve. “The Chinese are becoming more concerned about the world we live in, and the prevailing ideologies in society,” he says. “Perhaps this awareness and consciousness now build our identity.” Han Jiaying reckons this is merely a symptom of the country’s late entry to the world of graphic design. It’s only natural that many modern Chinese designers are heavily influenced by the West – not just in terms of design, but also its values and culture.

However, there are pros and cons to this. Tommy Yen, a commercial graphic designer and instigator of his own T&Y brand, says: “On the one hand, this is a good thing because it enables Chinese designers to think in a more liberated way, and to find the means to go beyond what they already have. But from another perspective, there’s the danger of Chinese art and design becoming Westernised.” However, he adds that new graduates are more aware of originality as well as the importance of traditional culture.

The constant desire to make something new and unique means trends come and go with alarming speed, removing any doubts that Chinese design is stifled by a desire to be functional rather than creative. Shanghai-based illustrator Chun Guan thinks that Chinese design is transitioning away from its roots towards a more creative and unique conclusion.

The struggle ahead
Passion and rampant creativity are fantastic for design, but China is still plagued by output, industry and political issues. John Millichap’s 3030 Press imprint is dedicated to profiling the new generation of Chinese creatives, and he’s discovered that although young designers take risks, their brands and projects rarely impact on the international scene. “Large domestic companies remain cautious about how they present their products, and as a result often imitate successful foreign brands, rather than ask a designer to come up with something new,” he explains.

Additionally, there are rights issues, with plagiarism and theft still rife. There’s also a language barrier that stops Westerners truly appreciating Chinese output and hampers many Chinese when communicating with the outside world. “The infrastructure is weak,” says Zhang Hongxing, curator of China Design Now. “There’s little living space for young people, and a huge volume of graphic designers graduating. Many are forced to work in advertising, with little space for creativity, and competition is increasingly fierce, which reduces the value of work.”

Without the government undergoing a major shift in attitude, Zhang reckons most Chinese designers will continue to struggle: “Until the whole platform, including education, infrastructure and manufacturing, becomes more supportive of independently minded people and the value of independent design, I think the language and style of Chinese design won’t be very distinct, dominate or even be on a par with Japan.”

Despite this negative prediction, it’s clear that changes are happening, and only relatively small adjustments are required for China to become a design powerhouse. Its designers have the impetus, the skills, the desire and the drive. Even with his misgivings, Zhang concedes that within the next ten years Chinese graphic design will likely be a part of global design culture, even if it’s not entirely distinct.

But once a number of shifts occur – the Chinese government investing in infrastructure, more Chinese designers becoming conversant in English, the gradual replacement of today’s cautious generation – there’s a good chance the design landscape could change forever. While China’s creative explosion inspires Western designers with its brashness, stark colours and recycled propaganda, a future China might pose stiff competition when countless hungry, educated, skilled designers start looking outwards, rather than in.

Massa de Buracos Negros Supermassivos

:: Agência FAPESP :: Divulgação Científica - Como pesar buracos negros

Divulgação Científica
Como pesar buracos negros

24/7/2008

Agência FAPESP – Como pesar os maiores buracos negros do Universo? Certamente não dá para usar uma balança, mas uma nova resposta foi conseguida por um grupo de pesquisadores com ajuda de dados obtidos pelo Chandra, o observatório de raio X da Nasa, agência espacial norte-americana.

Ao medir a elevação de temperatura do gás no centro da galáxia elíptica NGC 4649, os cientistas foram capazes de determinar a massa do buraco negro supermassivo da galáxia. O método, usado pela primeira vez, trouxe resultados consistentes com técnicas tradicionais.

A nova técnica aproveita a influência gravitacional que um buraco negro tem no gás quente no centro da galáxia. À medida que o gás de desloca lentamente em direção ao buraco negro, ele se torna mais comprimido e ainda mais quente. O resultado é um pico na temperatura, que é detectado pelo Chandra. Quanto mais massivo o buraco negro, maior o pico.

O efeito foi preciso por Fabrizio Brighenti, da Universidade de Bolonha, na Itália, e por William Mathews, da Universidade da Califórnia em Santa Cruz, há quase dez anos, mas nunca havia sido observado.

Há tempos os astrônomos têm buscado novas formas de medir com precisão os buracos negros supermassivos, cujas massas são milhões de vezes a do Sol. Até agora tem sido usados métodos baseados nas observações dos movimentos de estrelas ou de gases em discos próximos a tais formações.

“O novo trabalho é muito importante, uma vez que buracos negros podem ser elusivos e quanto mais formas de medir suas massas, melhor”, disse Philip Humphrey, da Universidade da Califórnia em Irvine, nos Estados Unidos, que coordenou o estudo. Os resultados serão publicados em breve em artigo na revista The Astrophysical Journal.

A NGC 4649 é agora uma das únicas que teve a massa de um buraco negro supermassivo medida por dois métodos diferentes. Segundo a pesquisa, a formação tem cerca de 3,4 bilhões de vezes a massa do Sol e mil vezes a massa do buraco negro no centro da Via Láctea.

The Black Hole War

'The Black Hole War' by Leonard Susskind - Los Angeles Times

BOOK REVIEW

'The Black Hole War' by Leonard Susskind

Stephen Hawking and Susskind, two titans of theoretical physics, slug it out over whether or not information is lost forever once it enters a black hole.

By Jesse Cohen
July 13, 2008

The Black Hole War

My Battle With Stephen Hawking to Make the World Safe for Quantum Mechanics

Leonard Susskind

Little, Brown: 480 pp., $27.99

In a packed lecture hall at Columbia University in 1958 -- or so the story goes -- the eminent physicist Wolfgang Pauli was presenting a radical new theory. In the audience was Niels Bohr, another eminent physicist, who, at lecture's end, stood up and announced: "We are all agreed that your theory is crazy. The question that divides us is whether it is crazy enough to have a chance of being correct."

"Crazy enough" is no doubt a thought that occurred to Stanford theoretical physicist Leonard Susskind when he came up with his holographic principle -- an idea that has recently gained traction in the physics community. The principle, which states that our universe is a three-dimensional projection of information stored in two dimensions at the boundary of space, certainly ranks as crazy. But is it crazy enough?

After reading Susskind's entertaining new book, "The Black Hole War," you may decide that, yes, the holographic principle may well be on the good side of crazy. But before he gets to the holographic principle, Susskind gives an explanation, both lucid and enjoyable, of why black holes are so crucial to the future of physics and to any eventual reconciliation of relativity and quantum mechanics.

Einstein's general theory of relativity describes the world of the very large: planets, stars, galaxies, black holes, the warped curvature of space. Quantum mechanics describes the world of the very small, the bizarre precincts of subatomic particles, where gravity is trivial. General relativity is "classical," in that it can be used to make definite predictions about reality. Quantum mechanics is not: One can predict outcomes only in terms of their probability. The dream of many physicists is to find a way to unify these two seemingly antagonistic conceptions of reality.

It turns out, though, that black holes may have just the right ingredients for a unification recipe. A black hole is a region of space at whose center is the remnant of a collapsed star. But "remnant" isn't really the right word: Because of intense gravitational pressure, that star has become what physicists call a singularity -- an infinitesimal point of infinite density. Black holes suck up everything in their vicinity; gravity in a black hole's interior is so strong that nothing can escape, not even light.

In the 1970s, Cambridge theoretical physicist Stephen Hawking made the brilliant deduction that black holes dissipate their energy the way everything else in the universe does, through the radiation of heat -- a process known now as Hawking radiation. Gradually, that is, black holes evaporate. In 1983, Hawking also claimed that, along with everything else a black hole has gobbled up, "information is lost in black hole evaporation." ("Information" means the same thing as it does in computer science: data that can be measured in bits -- 0's or 1's. The "information" is what the bits encode.)

For Susskind, this was a declaration of war. Susskind is a quantum theorist, and a central principle of quantum mechanics is that information is conserved; it can never be annihilated. If Hawking was right, "the foundations of [quantum mechanics] were destroyed."

"War" may seem an overblown word to describe the debate between Susskind and Hawking, especially since the two are friends and Susskind's admiration for Hawking is boundless -- he considers him a "truly heroic figure" and "the first to enter a remote country and bring back gold." At Hawking's 60th birthday celebration, Susskind declared that "of all the physicists I have known he has had the strongest influence on me and my thinking." But perhaps "war" has the right emotional tone to convey his near-panic about Hawking's conjecture.

So how did Susskind -- and several others -- save quantum mechanics? It has to do with the peculiar nature of singularities at the heart of black holes. Infinitesimally small, infinitely dense, they are macroworld objects that behave with the quantum weirdness of the microworld.

In the quantum world, particles behave like particles or like waves, depending on what experiment is being performed; it's as though there were two separate realities. Within black holes, there's a similar duality. Susskind asks us to imagine two space travelers: Alice, who drifts toward a black hole, and Bob, who stays behind on the space station: "To Bob . . . it takes an eternity for Alice to reach the point of no return, but to Alice it may take no more than the blink of an eye." As Alice reaches that point -- the black hole's invisible, spherical "horizon" -- she appears to Bob to be frozen in time. From Alice's point of view, though, she passes through the horizon "without any sense of slowing down or speeding up." Her reality is completely different from Bob's.

Alice's fate isn't kind. The tidal forces of the black hole will tear her apart. According to the Hawking version, that's the end of her and her bits -- the information she's made up of. But, as Susskind and his colleagues discovered, that's not the case. The black hole's heat is a shredded and scrambled version of the information Hawking thought was lost, and "[i]nformation leaks out in the Hawking radiation in the same way that it escapes from an evaporating pot of water."

It gets weirder. That heat -- comprising the information that fell into the black hole -- exists as a thin layer coating the black hole's horizon. It's as though the black hole were a three-dimensional projection of that two-dimensional layer of information -- in short, a hologram.

As black holes go, so goes the universe: "The most notable inhabitants of the universe -- the galaxies -- are built around giant black holes that are continually gobbling up stars and planets. Out of every 10,000,000,000 bits of information in the universe, 9,999,999,999 are associated with the horizons of black holes." And consider this: As the universe's expansion accelerates, the light from faraway galaxies, the most distant of which are receding at light speed, will cease to reach us. Yet, to our eyes, nothing will look any different; this "cosmic horizon" will simply seem frozen, much as Alice appears to Bob when she enters a black hole. "It is as if we all live in our own private inside-out black hole," says Susskind. Could that ultimate, visible layer of the universe contain the information we experience as our three-dimensional reality?

This necessarily skeletal account may suggest the flavor of Susskind's bold thinking but does little justice to his book. Unlike his first book for a general audience, "The Cosmic Landscape," which was more didactic in tone, "The Black Hole War" is a gregarious narrative of intellectual brinkmanship. Although the narrative has a tendency to meander -- a chapter in which Susskind fails to meet Hawking in Cambridge is unnecessary -- it glows with the warmth of conversation. It's as though he has joined us for dinner, regaling us with tales of genius. Hawking and Richard Feynman make appearances, living up to their legends. There are also loving portraits of Susskind's fellow physicists, colorful characters who meticulously draw fanciful menageries or fight South American dictators or even profess evangelical Christianity. Susskind celebrates them all.

Like the best teachers, Susskind makes it fun to learn. With a deft use of analogy and a flair for language, he tames the most ferocious concepts. In his hands, a D-brane in anti de Sitter space seems like the most natural thing in the world. He has also come up with the best visual metaphor for the multidimensionality of string theory that I've yet come across, one that alone is worth the price of the book.

The holographic principle is dependent on string theory, and string theory is still controversial: It makes big claims that are unconfirmable by experiment. Susskind, one of the founders of string theory, is aware of its limitations and doesn't expect a solution anytime soon. But he does leave us with a glimmer of hope. It turns out that particles in the atomic nucleus act in ways that are similar to the behavior predicted for higher-dimensional strings. It's as if the 10-dimensional world of string theory were a -- dare one say it? -- holographic projection of the information contained in three-dimensional atoms. It's nothing less than the holographic principle, crazy like a fox. *

Jesse Cohen is the series editor of "The Best American Science Writing."

Sistema Solar é amassado

:: Agência FAPESP - Divulgando a cultura científica ::

Divulgação Científica

Sistema Solar é amassado


03/07/2008

Agência FAPESP – O Sistema Solar não é arredondado como se achava. Ele tem uma forma assimétrica, pois é amassado pelo campo magnético interestelar. A comprovação vem de um estudo feito a partir de dados enviados pela sonda Voyager 2, que está na fronteira final do Sistema Solar.

A Voyager 2 foi lançada em 20 de agosto de 1977, seguida alguns dias depois por sua nave irmã, a Voyager 1. Percorrendo mais de 1,6 milhão de quilômetros por dia, ambas estão em uma região turbulenta que começa a cerca de 14 bilhões de quilômetros do Sol e na qual o vento solar é reduzido ao encontrar o meio interestelar, o fino gás que preenche o espaço entre as estrelas.

Entretanto, a Voyager 2 tomou um rumo diferente ao cruzar, em agosto do ano passado, a fronteira da região conhecida como heliosheath, região da heliosfera que fica entre a heliopausa e o choque de terminação do vento solar.

Em artigo publicado na edição de 3 de julho da revista Nature, ao lado de outros quatro sobre resultados de observações recentes a respeito dos limites do Sistema Solar, Linghua Wang, da Universidade da Califórnia em Berkeley, nos Estados Unidos, e colegas confirmam o formato “amassado”, ou seja, que a bolha formada no espaço interestelar pelo vento solar não é redonda.

O motivo é que a bolha é empurrada de volta em direção ao Sol pelo campo magnético interestelar, o que faz com que se deforme. A sonda cruzou a heliosheath em um ponto mais próximo do Sol do que seria esperado se a bolha fosse arredondada, indicando um “dente” irregular no local.

O vento solar, formado por partículas carregadas eletricamente, é soprado pelo Sol em todas as direções, formando uma bolha que se estende pelo espaço além da órbita de Plutão. Essa bolha é a heliosfera, e teve sua camada externa explorada pela primeira vez em 2004, com a Voyager 1, quando então a nave encontrou a onda de choque que envolve o Sistema Solar.

Embora a Voyager 1 tenha cruzado antes a zona de choque de terminação, seu instrumento de ciência de plasma, capaz de medir diretamente a velocidade, densidade e temperatura do vento solar, não estava mais funcionando.

O instrumento similar a bordo da sua nave irmã está operando perfeitamente, o que permitiu os novos estudos. Outra diferença é que a Voyager 1 cruzou essa fronteira uma vez, quando dados não foram enviados, enquanto a outra o fez por diversas vezes.

O resultado das medições feitas pela Voyager 2 também apontam uma onda de choque incomum. Em uma onda normal, o material que se move rapidamente diminui a velocidade e forma uma região densa, mais quente, à medida que encontra um obstáculo.

Entretanto, a sonda encontrou uma temperatura além da zona de terminação cinco vezes inferior à esperada. Segundo os cientistas, isso indica que a energia está sendo transferida para partículas de raios cósmicos que se aceleram a altas velocidades com o choque.


Companhia após décadas

Por muitos anos as duas Voyager serão a única fonte de observação local da fronteira final do Sistema Solar, mas a Nasa, agência espacial norte-americana, pretende lançar ainda este ano uma missão com o objetivo específico de estudar a região. O Explorador da Fronteira Interestelar (Ibex) usará átomos energéticos neutros para produzir mapas da interação da heliosfera com o espaço interestelar.

As Voyager estão longe demais do Sol para poder usar energia solar. Elas empregam geradores termelétricos radioisotópicos para garantir o funcionamento de seus instrumentos que, em cada uma, tem consumo menor de 300 watts. A Nasa estima que a energia interna seja suficiente para que as sondas continuem operando até por volta de 2020.

As duas se comunicam com os cientistas da Nasa por meio da rede Deep Space, um sistema de antenas instalado em diversos países. Elas estão tão distantes que comandos enviados da Terra precisam de 12 horas para chegar à Voyager 1 e 14 horas para serem recebidos pela outra nave.

As espaçonaves carregam mensagens, para o caso de serem encontradas por alguma outra forma de vida. Um disco de cobre e ouro de 12 polegadas contém dados selecionados para mostrar a diversidade da vida, da sociedade e da cultura da Terra.

O conteúdo do disco foi selecionado por um comitê então liderado pelo astrônomo e escritor Carl Sagan (1934-1996). Estão gravadas 117 imagens e diversos sons obtidos na natureza, além de seleções musicais de diferentes culturas e períodos e saudações em 54 línguas.

O artigo Domination of heliosheath pressure by shock accelerated pickup ions from observations of neutral atoms, de Linghua Wang e colegas, e os demais a respeito dos dados enviados pela Voyager 2 podem ser lido por assinantes da Nature em www.nature.com.