Estamos mesmo sozinhos, irra, porque os outros não serão nossos contemporâneos, ou estarão muito longe!

ECT: extra-terristerial civilization

Lost in Time and Lost in Space| Centauri Dreams

Foi assim que, provavelmente, aconteceu...

Supercomputers Allow First Detailed Milky Way Simulation - Staff - International Business Times - RichardDawkins.net

Excelente simulação. O processo de formação das galáxias foi tumultuoso e isso, conjecturo eu, poderá ser um motivos porque poderá ter sentido o que defendem alguns que os "outros" estão a emergir como civilizações estelares ao mesmo tempo (à escala galáctica) que nós, e por isso mesmo, não nos estão, ainda, a bater à porta, qualquer que seja o modo como o venham a fazer no futuro.

Não gosto da implicação, mas a ver vamos (ainda que não no meu tempo de vida)

Astrophysicists apply new logic to downplay the probability of extraterrestrial life

David Spiegel of Princeton University and Edwin Turner from the University of Tokyo have published a paper on arXiv that turns the Drake equation on its head. Instead of assuming that life would naturally evolve if conditions were similar to that found here on Earth, the two use Bayesian reasoning to show that just because we evolved in such conditions, doesn’t mean that the same occurrence would necessarily happen elsewhere; using evidence of our own existence doesn’t show anything they argue, other than that we are here.

Onde estamos, como podemos ir, e como poderá ser noutro lado

• Astronomy Without A Telescope – Don’t Make a Meal of It | Universe Today

•  Pushing Up Against Lightspeed|Centauri Dreams 

• Other Life in the Multiverse?: "What conditions would you say are ‘congenial to life’? For physicist Robert Jaffe and colleagues at MIT, the phrase refers to places where stable forms of hydrogen, carbon and oxygen can exist." e "Economist's View: "Life Beyond Our Universe"

De novo: porque razão, se existem, não aparecem, a visitar-nos?

• Notes & Queries 2/8/10| Centauri Dreams: (é um conjunto de notas, mas a maioria tem a ver com o tema dos extraterrestres) 
• If the Earth is Rare, We May Not Hear from ET | Universe Today

O paradoxo de Fermi revisitado [Com esta são 2000 as notas publicadas neste blogue]

The Allen Telescope Array in California. 

Photograph: Ho New/ Reuters 

Uma boa síntese da questão, e da história das tentativas de detecção dos nossos primos distantes [mais neste blogue, via motor de busca, sob "Fermi", "extraterrestres"; via etiqueta "ET"].

"It will soon be half a century since the American astronomer Frank Drake first pointed a radio telescope at the star Tau Ceti in the hope of picking up an extraterrestrial broadcast, and we still haven't heard anything. So is there anyone out there?" 

First contact: will we ever hear from aliens? | Feature | Culture | The Observer
 

Uma outra estratégia "henriquina", e mais sobre outras "Terras"

The Space Review: First stop for Flexible Path?: "[...] the White House and NASA are pondering the future of human space flight for the United States, one strategy for doing it that was proposed by that committee has garnered a lot of attention. The flexible path—or flexpath strategy, as it is more compactly known—is less a detailed plan and more a guiding philosophy for future work. Guided by this philosophy, humans would visit sites never visited before and extend our knowledge of how to operate in space, while traveling greater and greater distances from Earth, as opposed to efforts directed at a single solar system body, such as the Moon or Mars."

Superior Super Earths | Physorg.com
Super Earths are named for their size, but these planets - which range from about 2 to 10 Earth masses - could be superior to the Earth when it comes to sustaining life. They could also provide an answer to the ‘Fermi Paradox’: Why haven’t we been visited by aliens? 

Neste blogue, há muito mais sobre isto (pesquisar sob "henriquina", "paradoxo de fermi", etc.). 

Civilizações extraterrestres e o Paradoxo de Fermi revisitado (mais uma vez)

Technology Review: Blogs: Information Processing: Evolution, Design and the Fermi Paradox (via links for 2009-10-29 - J. Bradford DeLong's Grasping Reality with All Eight Tentacles.

Sobre os ET e o Paradoxo de Fermi pesquisar no blogue, através do motor de busca Google (ao cimo), sob a expressão "Paradoxo de Fermi"

Ainda sobre a classe de estrelas mais favorável ao aparecimento da vida

No seguimento desta nota, sugiro que continuem a ler no Universe Today:

In Praise of K-class Stars:

"When it comes to exoplanet speculations, we’re still in the era when data are few and dominated by selection effect, which is why we began by finding so many ‘hot Jupiters’ — such planets seem made to order for relatively short-term radial velocity detections. It’s a golden age for speculation, with the promise of new instrumentation and a boatload of information from missions like Kepler and CoRoT to be delivered within a few years. What an extraordinary time to be doing exoplanetary science.

The big questions can’t be answered yet, but it shouldn’t be long before we have an inkling about what kind of stars are most likely to produce terrestrial planets. And maybe a qualification is in order. M-dwarfs are so common in our galaxy — some estimates run to seventy percent of all stars and up — that finding habitable worlds around them would hugely increase the possible venues for life. But is there any way we could call planets around M-dwarfs ‘Earth-like?’ Maybe in terms of temperature in a specific habitable zone on the surface, but little else applies. [...]"

Afinal o par Sol Terra não é o mais favorável ao aparecimento da vida

Pode-se conjecturar soluções mais eficazes. Interessante. Ler em Sun, Earth Are Unlikely Pair to Support Life Universe Today. Sobre este assunto ver as notas com a etiqueta ET.

Mais sobre a possibilidade de vida extraterrestre

"Does complex life emerge at a gradual, uniform rate? If so, we can come up with one answer to the Fermi paradox: We have not detected signs of extraterrestrial life because the time needed for complex life to appear generally exceeds the life of a star on the main sequence. But the assumption that intelligence appears over time with a gradual inevitability — a key tenet of work by Brandon Carter, Frank Tipler and others in the 1980s, may not in fact be true. Solar system-wide events connect life with its stellar environment, while galaxy-wide events provide yet another context. [...]"

Continuar a ler em Galactic Life in Context, Centauri Dreams: muito interessante - mais sobre o assunto sob a etiqueta ET.

O paradoxo de Fermi revisitado...

"While having lunch with colleagues at Los Alamos National Labs in 1950, physicist Enrico Fermi mused about the likelihood of intelligent life existing elsewhere in the Universe. Fermi, one of the most astute scientists of his day, thought the size and age of the Universe means many advanced civilizations should have already colonized the galaxy, just as humans colonized and explored the Earth. But if such galaxy-wide extraterrestrial civilizations exist, he wondered, where are they?

Some believe this problem, called the Fermi Paradox, means advanced extraterrestrial societies are rare or nonexistent. Others suggest they must destroy themselves before they move on to the stars.

But this week, Jacob D. Haqq-Misra and Seth D. Baum at Penn State University proposed another solution to the Fermi Paradox: that extraterrestrial civilizations haven’t colonized the galaxy because the exponential growth of a civilization required to do so is unsustainable."

- continuar a ler em So Where Is ET, Anyway? Universe Today

Nota: Neste blogue podem encontrar mais informação sobre a problemática da vista extraterrestre (via a etiqueta ET, ou, fazendo uma pesquisa, por exemplo, pela palavra Fermi ).

Kepler

O observatório astrónómico Kepler foi, ou vai ser lançado para o espaço. Há algumas semanas atrás o blogue Centauri Dreams nesta sua nota: Kepler and the Odds, explicava a importância do que estava em causa:

"We just looked at Alan Boss’ remarkable statement that there could be 100 billion trillion Earth-like planets in the visible universe. It’s startling to think that a mission to be launched within weeks could so quickly give us a chance to size up the idea. The thinking is that dozens of planets like ours in the habitable zone should be visible to Kepler if such worlds are common, but if it comes up short, with few or none, we’re going to quickly re-evaluate how unusual a world we live on. A null result would be striking indeed. William Borucki, who is science principal investigator on the mission, has this to say: “Finding that most stars have Earths implies that the conditions that support the development of life could be common throughout our galaxy. Finding few or no Earths indicates that we might be alone.”

Sobre o Kepler, e a problemática mais geral da possibilidade de detectarmos vida (inteligente) extraterrestre, ver também estas ligações:

• 
  
  Centauri Dreams » Blog Archive » Kepler, SETI and Ancient Probes
  



• 
  
  Centauri Dreams » Blog Archive » One Hundred Billion Trillion Habitable Planets
  



• 
  
  Centauri Dreams » Blog Archive » 361 Civilizations in the Galaxy?
  



• 
  
  Centauri Dreams » Blog Archive » New Angles on the Drake Equation

PS: Sobre esta questão ver, neste blogue, as notas sob a epígrafe ET

Visto em Jupiter's Europa -The Water Moon

Mais sobre a possibilidade de vida extraterrestre inteligente

Mais artigos sobre a possibilidade de vida extraterrestre inteligente e civilizada (e sobre as razões que fazem com que, se existe, não dê sinais de vida).

• Centauri Dreams » Blog Archive » Rethinking Galactic Empire:

  "How much would an extraterrestrial civilization resemble our own? The question resonates because on the one hand, the signature of our activities is what we tend to translate into the SETI search. We look, for example, for the signs of civilizations that are like us but more advanced technologically, which means we apply human thinking and motivations to cultures that are by definition not human. This is natural enough, because we’re the only technological civilization we know about, but it leads to results that may mislead us and obscure the actual situation".

• Centauri Dreams » Blog Archive » First Contact Scenarios: How to Reply:

  "Assume we receive, at long last, a signal from the stars that is unmistakably an attempt to communicate. After long debate, we decide to respond, describing who we are as a species. Which of these statements, drawn from a class Lockwood teaches on the subject, offers the best ten-word summary of the human condition?"

• Open the Future: Pondering Fermi

  "The Fermi Paradox -- if there's other intelligent life in the galaxy, given how long the galaxy's been here, how come we haven't seen any indication of it? -- is an important puzzle for those of us who like to think ahead. Setting aside the mystical (we're all that was created by a higher being) and fundamentally unprovable (we're all living in a simulation), we're left with two unpalatable options: we're the first intelligent species to arise; or no civilization ever makes it long enough..."

• Centauri Dreams » Blog Archive » The ‘Great Filter’ Tackles Fermi:

  "Suppose for a moment that life really is rare in the universe. That when we are able to investigate the nearby stars in detail, we not only discover no civilizations but few living things of any kind. If all the elements for producing life are there, is there some kind of filter that prevents it from proceeding into advanced and intelligent stages that use artifacts, write poetry and build von Neumann probes to explore the stars? Nick Bostrom discusses the question in an article in Technology Review, with implications for our understanding of the past and future of civilization."

Vida e vida inteligente extra-terrestre

Mais sobre a probabilidade da existência de vida e de vida inteligente fora da Terra (ver também aqui): Centauri Dreams » Blog Archive » Life as Rarity in the Cosmos. Um excerto: "Although I suspect that intelligent life is rare in the cosmos, I’m playing little more than a hunch. So it’s interesting to see that Andrew Watson (University of East Anglia) has analyzed the chances for intelligence elsewhere in the universe by looking at the challenges life faced as it evolved. Watson believes that it took specific major steps for an intelligent civilization to develop on Earth, one of which, interestingly enough, is language. Identifying which steps are critical is tricky, but in the aggregate they reduce the chance of intelligence elsewhere."

Aditamento (08.04.20)

Sobre o mesmo ver Is there anybody out there? e The Odds of Intelligent Life in the Universe Universe Today.

Planetas extra-solares habitáveis

O The Daily Galaxy refere, em New Habitable Planets in Space, o que Francis Drake, o cientista da "Equação de Drake" (1), tem vindo a dizer, mais recentemente, sobre a revisão das probabilidade de haver planetas habitáveis, e nestes, de haver vida inteligente e civilizada. A nossa galáxia tem cerca de 400 mil milhões de estrelas; já se detectaram mais de 200 planetas extra-solares (277 - ver aqui) - o que melhorou a perspectiva de haver planetas com aquelas características . Francis Drake estima que haverão entre 1.000 a 100 milhões de civilizações avançadas na nossa galáxia.

Bem gostaria que essas estimativas se viessem a revelar como verdadeiras, mas não sei - existem cépticos que colocam em cima da mesa a possibilidade da vida, e, em particular, a vida inteligente, e, dentro desta, vida civilizada, serem extremamente raras. A Terra, o conjunto de factores que possibilitaram a ocorrência de vida e de vida inteligente nela, seria um caso que se verificaria poucas vezes: existe um livro expressando essa tese tendo como título exactamente esta designação, Rare Earth. A implicação desta tese é que, não negando a possibilidade da existência de vida extra-terrestre e extra-solar, a sua raridade, faria com que, em termos práticos, tendo em conta as dimensões da galáxia, para não falar do Universo, estivessemos sózinhos e isolados, ficando assim resolvido o "Paradoxo de Fermi" (ver também aqui) - se existem extra-terrestres civilizados porque é que não apareceram ainda?

Uma outra hipótese de solução, partilhada por alguns astrónomos, que conciliaria a ocorrência de civilizações extra-terrestres avançadas com o "Paradoxo de Fermi", seria da galáxia só há relativamente pouco tempo ter possibilitado as condições para o aparecimento daquelas - estaríamos na fase da emergência de civilizações solares e, por isso, nem seríamos os primeiros (evento de probabilidade reduzida), nem teríamos sido visitados, quer por não houve tempo para isso e/ou a densificação dessas ocorrências ser ainda reduzida (potenciando a importância das distâncias). Em alternativa a tudo isto, teríamos a hipótese de estarmos de quarentena galáxica - tema de muita FC - enquanto não atingirmos o nível adequado de civilização.

_______________________________________________________

(1) A Equação de Drake é formulada como segue: N= R* x fp x ne x fl x fi x fc x L

Onde:

N é o número de civilizações extraterrestres em nossa galáxia com as quais poderíamos ter chances de estabelecer comunicação.

e

R* é a taxa de formação de estrelas em nossa galáxia;
fp é a fração de tais estrelas que possuem planetas em órbita;
ne é o número médio de planetas que potencialmente permitem o desenvolvimento de vida por estrela que tem planetas;
fl é a fração dos planetas com potencial para vida que realmente desenvolvem vida;
fi é a fração dos planetas que desenvolvem vida que desenvolvem vida inteligente;
fc é a fração dos planetas que desenvolvem vida inteligente e que têm o desejo e os meios necessários para estabelecer comunicação;
L é o tempo esperado de vida de tal civilização.

Obituário - Arthur C. Clark

Do obituário de Arthur C. Clarke no Economist.com, alguns excertos:

"Did Sir Arthur believe in extra-terrestrials? The answer was given with a smile. “Two possibilities exist: either we are alone in the universe or we are not. Both are equally terrifying.” And UFOs? A broader smile. “They tell us absolutely nothing about intelligence elsewhere in the universe, but they do prove how rare it is on Earth.” For all his star-gazing, Sir Arthur's feet were firmly on the ground."

"He did not predict the future in his copious science fiction, he insisted. He simply extrapolated. ... The point was never to say what would happen for certain, but to ask what might happen; to prepare people painlessly for the future and to encourage flexible thinking. Politicians, he thought, ought to read his books rather than westerns or detective stories, because imagination could pave the way for revolutionary practical ideas."

"His notions of the future remained unswervingly radical. Sir Arthur knew that outlandish ideas often became reality. But they provoked, he wrote, three stages of reaction. First, “It's completely impossible.” Second, “It's possible but not worth doing.” Third, “I said it was a good idea all along.” ... “Any sufficiently advanced technology”, he declared, “is indistinguishable from magic.”

Não os ouvimos porque não usam as ondas de rádio

Enrico Fermi, nos anos quarenta, enunciou o paradoxo que tem o seu nome: "Se existem extra-terrestres, porque é que não aparecem?". Na verdade, podia argumentar-se que, dado o devido tempo, e com um nível tecnológico (não muito) superior ao nosso, haveriam soluções que possibilitariam qualquer espécie espalhar-se pela nossa galáxia. Uma outra versão dessa pergunta seria: "Se existem extra-terrestre, porque é que os não ouvimos?". A resposta é anunciada aqui: The Great Silence -Are We the Miss Lonely Hearts of the Milky Way? The Daily Galaxy: News from Planet Earth & Beyond. Um excerto:

"Drake goes on to point out that contrary to popular wisdom which believes that we could discover the existence of extraterrestrials from powerful beacons beamed our way from their vastly advanced civilizations, that if we use the Earth is an case study, that the more advanced the civilization, the less likely they are to emit powerful radio waves. With our evolution to cable and satellite transmissions, we are now leaking very little out to space. The earth is gradually becoming 'radio quiet' in a cosmic blink of the eye."

Ligações recomendadas: espaço

• As lições do asteróide 2007 TU24 - passou perto da Terra em 27/28 de Janeiro passado (Visual Astronomy).
• A tese da "Terra Infrequente" revisitada - quão incomum é a Terra? (The Space Review).
• Mundos similares à Terra podem ser mais comuns do que se pensava (Centauri Dreams).
• Mercúrio não é bem aquilo que se esperava (uma outra versão da Lua) (The Daily Galaxy).
• Centauri Dreams » Blog Archive » Fast Mover from the Large Magellanic Cloud How Did the Universe Start? (Cosmic Variance).
• Físico russo diz como se pode identificar um "buraco de verme" ("wormhole") (The Daily Galaxy).
• Matéria e energia escuras: podem ser a mesma coisa (The Daily Galaxy).
• No início houve inúmeros universos - as últimas elucubrações de Hawking (e Hertog) (The Daily Galaxy).