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Piloto de Podcast

Ainda não temos nome. Ainda não temos formato. Nem assunto temos. Mas no último domingo, Antônio Carlos Roque, Luciano Bachmann, George Cardoso e eu fizemos um piloto, regado a muita comida e vinhos na casa do Roque.
Conversamos das 11h às 21h, Ufa! Mas só gravamos duas horas e meia. Vou colocar alguns pedaços para degustação. Se alguém tiver ideia para o nome do Podcast, deixe no comentário por favor!

Clat Farris Naff: Mais um adepto do Demiurgo

universo inteligenteA Secular Case for Intentional Creation

By Clay Farris Naff | November 18, 2011 |  Comments21

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“Does aught befall you? It is good. It is part of the destiny of the Universe ordained for you from the beginning.”

– Marcus Aurelius, Stoic Philosopher and Emperor of Rome, in Meditations, circa 170 CE

“’He said that, did he? … Well, you can tell him from me, he’s an ass!”

– Bertie Wooster, fictional P.G. Wodehouse character, in The Mating Season, 1949

People have been arguing about the fundamental nature of existence since, well, since people existed. Having lost exclusive claim to tools, culture, and self, one of the few remaining distinctions of our species is that we can argue about the fundamental nature of existence.

There are, however, two sets of people who want to shut the argument down. One is the drearily familiar set of religious fundamentalists. The other is the shiny new set of atheists who claim that science demonstrates beyond reasonable doubt that our existence is accidental, purposeless, and doomed. My intent is to show that both are wrong.

Read more [+]

Paradoxo de Fermi e ETs

Persistence solves Fermi Paradox but challenges SETI projects

Osame Kinouchi (DFM-FFCLRP-Usp)

Persistence phenomena in colonization processes could explain the negative results of SETI search preserving the possibility of a galactic civilization. However, persistence phenomena also indicates that search of technological civilizations in stars in the neighbourhood of Sun is a misdirected SETI strategy. This last conclusion is also suggested by a weaker form of the Fermi paradox. A simple model of a branching colonization which includes emergence, decay and branching of civilizations is proposed. The model could also be used in the context of ant nests diffusion.

Comments: 2 pages, no figures, v2 with corrected definition of branching ratio
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Cite as: arXiv:cond-mat/0112137 [cond-mat.dis-nn]
(or arXiv:cond-mat/0112137v1 [cond-mat.dis-nn] for this version)

Submission history

From: Osame Kinouchi [view email]

The exoplanets analogy to the Multiverse

kepler-planet-candidatesPrecisa dar uma melhorada. Pretendo enviar para o International Journal of Astrobiology.

The exoplanets analogy to the Multiverse

The idea of a Mutiverse is controversial, although it is a natural possible solution to particle physics and cosmological fine-tuning problems (FTPs). Here I explore the analogy between the Multiverse proposal and the proposal that there exist an infinite number of stellar systems with planets in a flat Universe, the Multiplanetverse. Although the measure problem is present in this scenario, the idea of a Multiplanetverse has predictive power, even in the absence of direct evidence for exoplanets that appeared since the 90s. We argue that the fine-tuning of Earth to life (and not only the fine-tuning of life to Earth) could predict with certainty the existence of exoplanets decades or even centuries before that direct evidence. Several other predictions can be made by studying only the Earth and the Sun, without any information about stars. The analogy also shows that theories that defend that the Earth is the unique existing planet and that, at the same time, is fine-tuned to life by pure chance (or pure physical necessity from a parameter free Theory of Everything) are misguided, and alike opinions about our Universe are similarly delusional.

Comments: 9 pages, 1 figure
Subjects: General Physics (physics.gen-ph); History and Philosophy of Physics (physics.hist-ph)
Cite as: arXiv:1506.08060 [physics.gen-ph]
(or arXiv:1506.08060v1 [physics.gen-ph] for this version)

Submission history

From: Osame Kinouchi [view email]
[v1] Tue, 16 Jun 2015 22:42:12 GMT (566kb)

 

Uma defesa secular para criação intencional do universo

What is the purpose of the Universe? Here is one possible answer.

A Secular Case for Intentional Creation

By Clay Farris Naff | November 18, 2011 |  Comments21

Scientific American Blog

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“Does aught befall you? It is good. It is part of the destiny of the Universe ordained for you from the beginning.”

– Marcus Aurelius, Stoic Philosopher and Emperor of Rome, in Meditations, circa 170 CE

“’He said that, did he? … Well, you can tell him from me, he’s an ass!”

– Bertie Wooster, fictional P.G. Wodehouse character, in The Mating Season, 1949

People have been arguing about the fundamental nature of existence since, well, since people existed. Having lost exclusive claim to tools, culture, and self, one of the few remaining distinctions of our species is that we can argue about the fundamental nature of existence.

There are, however, two sets of people who want to shut the argument down. One is the drearily familiar set of religious fundamentalists. The other is the shiny new set of atheists who claim that science demonstrates beyond reasonable doubt that our existence is accidental, purposeless, and doomed. My intent is to show that both are wrong.

I do not mean to imply a false equivalence here. Concerning the fundamentalist position, my work is done. Claims of a six-day Creation, a 6,000-year-old Earth, a global flood, and so forth have been demolished by science. It has not only amassed evidence against particular claims but has discovered laws of nature that exclude whole classes of claims. To the extent we can be certain about anything, we can rest assured that all supernatural claims are false.

The “New Atheist” position, by contrast, demands serious consideration. It has every advantage that science can provide, yet it overreaches for its conclusion. The trouble with the “New Atheist” position, as defined above, is this: it commits the fallacy of the excluded middle. I will explain.

But first, if you’ll pardon a brief diversion, I feel the need to hoist my flag. You may have inferred that I am a liberal religionist, attempting to unite the scientific narrative with some metaphorical interpretation of my creed. That is not so.

I am a secular humanist who is agnostic about many things — string theory, Many Worlds, the Theo-logical chances of a World Series win for the Cubs  – but the existence of a supernatural deity is not among them. What’s more, I am one of the lucky ones: I never struggled to let go of God. My parents put religion behind them before I was born.

I tell you this not to boast but in hopes that you’ll take in my argument through fresh eyes. The science-religion debate has bogged down in trench warfare, and anyone foolhardy enough to leap into the middle risks getting cut down with no questions asked. But here goes. Read more [+]

O Paradoxo de Fermi e Caminhadas do Turista

International Journal of Astrobiology

Research Article

Slingshot dynamics for self-replicating probes and the effect on exploration timescales

Arwen Nicholsona1 c1 and Duncan Forgana1

 

a1 Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK

 

Abstract

 

Interstellar probes can carry out slingshot manoeuvres around the stars they visit, gaining a boost in velocity by extracting energy from the star’s motion around the Galactic Centre. These manoeuvres carry little to no extra energy cost, and in previous work it has been shown that a single Voyager-like probe exploring the Galaxy does so 100 times faster when carrying out these slingshots than when navigating purely by powered flight (Forgan et al.2012). We expand on these results by repeating the experiment with self-replicating probes. The probes explore a box of stars representative of the local Solar neighbourhood, to investigate how self-replication affects exploration timescales when compared with a single non-replicating probe. We explore three different scenarios of probe behaviour: (i) standard powered flight to the nearest unvisited star (no slingshot techniques used), (ii) flight to the nearest unvisited star using slingshot techniques and (iii) flight to the next unvisited star that will give the maximum velocity boost under a slingshot trajectory. In all three scenarios, we find that as expected, using self-replicating probes greatly reduces the exploration time, by up to three orders of magnitude for scenarios (i) and (iii) and two orders of magnitude for (ii). The second case (i.e. nearest-star slingshots) remains the most time effective way to explore a population of stars. As the decision-making algorithms for the fleet are simple, unanticipated ‘race conditions’ among probes are set up, causing the exploration time of the final stars to become much longer than necessary. From the scaling of the probes’ performance with star number, we conclude that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time to warrant the existence of the Fermi Paradox.

(Received April 02 2013)  (Accepted May 24 2013)

 

Planetas extra-solares, Kepler 62 e o Paradoxo de Fermi local

Conforme aumentam o número de planetas extra-solares descobertos, também aumentamos vínculos sobre as previsões do modelo de percolação galática (Paradoxo de Fermi Local).
A previsão é que, se assumirmos que Biosferas Meméticas (Biosferas culturais ou Tecnosferas) são um resultado provável de Biosferas Genéticas, então devemos estar dentro de uma região com pucos planetas habitáveis. Pois se existirem planetas habitados (por seres inteligentes) por perto, com grande probabilidade eles são bem mais avançados do que nós, e já teriam nos colonizado.
Como isso ainda não ocorreu (a menos que se acredite nas teorias de conspiração dos ufólogos e nas teorias de Jesus ET, deuses astronautas etc.), segue que quanto mais os astronomos obtiverem dados, mais ficará evidente que nosso sistema solar é uma anomalia dentro de nossa vizinhança cósmica (1000 anos-luz?), ou seja, não podemos assumir o Princípio Copernicano em relação ao sistema solar: nosso sistema solar não é tipico em nossa vizinhança.  Bom, pelo menos, essa conclusão está batendo com os dados coletados até hoje…
Assim, é possível fazer a previsão de que uma maior análise dos planetas Kepler 62-e e Kepler 62-f revelará que eles não possuem uma atmosfera com oxigênio ou metano, sinais de um planeta com biosfera.

Persistence solves Fermi Paradox but challenges SETI projects

Osame Kinouchi (DFM-FFCLRP-Usp)
(Submitted on 8 Dec 2001)

Persistence phenomena in colonization processes could explain the negative results of SETI search preserving the possibility of a galactic civilization. However, persistence phenomena also indicates that search of technological civilizations in stars in the neighbourhood of Sun is a misdirected SETI strategy. This last conclusion is also suggested by a weaker form of the Fermi paradox. A simple model of a branching colonization which includes emergence, decay and branching of civilizations is proposed. The model could also be used in the context of ant nests diffusion.

03/05/2013 – 03h10

Possibilidade de vida não se resume a planetas similares à Terra, diz estudo

SALVADOR NOGUEIRA
COLABORAÇÃO PARA A FOLHA

Com as diferentes composições, massas e órbitas possíveis para os planetas fora do Sistema Solar, a vida talvez não esteja limitada a mundos similares à Terra em órbitas equivalentes à terrestre.

Editoria de arte/Folhapress

Essa é uma das conclusões apresentada por Sara Seager, do MIT (Instituto de Tecnologia de Massachusetts), nos EUA, em artigo de revisão publicado no periódico “Science“, com base na análise estatística dos cerca de 900 mundos já detectados ao redor de mais de 400 estrelas.

Seager destaca a possível existência de planetas cuja atmosfera seria tão densa a ponto de preservar água líquida na superfície mesmo a temperaturas bem mais baixas que a terrestre. Read more [+]

Os deuses de Richard Dawkins

File:NASA child bubble exploration.jpgMy personal theology is described in the Gifford lectures that I gave at Aberdeen in Scotland in 1985, published under the title, Infinite In All Directions. Here is a brief summary of my thinking. The universe shows evidence of the operations of mind on three levels. The first level is elementary physical processes, as we see them when we study atoms in the laboratory. The second level is our direct human experience of our own consciousness. The third level is the universe as a whole. Atoms in the laboratory are weird stuff, behaving like active agents rather than inert substances. They make unpredictable choices between alternative possibilities according to the laws of quantum mechanics. It appears that mind, as manifested by the capacity to make choices, is to some extent inherent in every atom. The universe as a whole is also weird, with laws of nature that make it hospitable to the growth of mind. I do not make any clear distinction between mind and God. God is what mind becomes when it has passed beyond the scale of our comprehension. God may be either a world-soul or a collection of world-souls. So I am thinking that atoms and humans and God may have minds that differ in degree but not in kind. We stand, in a manner of speaking, midway between the unpredictability of atoms and the unpredictability of God. Atoms are small pieces of our mental apparatus, and we are small pieces of God’s mental apparatus. Our minds may receive inputs equally from atoms and from God. This view of our place in the cosmos may not be true, but it is compatible with the active nature of atoms as revealed in the experiments of modern physics. I don’t say that this personal theology is supported or proved by scientific evidence. I only say that it is consistent with scientific evidence.  Freeman Dyson

Parece que Dawkins está rumando para uma posição similar à de Gardner, Clément Vidal e outros da comunidade Evo-Devo Universe.

Human Gods

After two hours of conversation, Professor Dawkins walks far afield. He talks of the possibility that we might co-evolve with computers, a silicon destiny. And he’s intrigued by the playful, even soul-stirring writings of Freeman Dyson, the theoretical physicist.

In one essay, Professor Dyson casts millions of speculative years into the future. Our galaxy is dying and humans have evolved into something like bolts of superpowerful intelligent and moral energy.

Doesn’t that description sound an awful lot like God?

“Certainly,” Professor Dawkins replies. “It’s highly plausible that in the universe there are God-like creatures.”

He raises his hand, just in case a reader thinks he’s gone around a religious bend. “It’s very important to understand that these Gods came into being by an explicable scientific progression of incremental evolution.”

Could they be immortal? The professor shrugs.

“Probably not.” He smiles and adds, “But I wouldn’t want to be too dogmatic about that.”

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Meio século atrás, os cientistas encaravam com ironia a possibilidade de existirem outros universos além deste que habitamos. Tal hipótese não passava de um delírio digno de Alice no País das Maravilhas – e que, de todo modo, jamais poderia ser comprovada experimentalmente. Os desafios propostos pela Teoria da Relatividade e pela física quântica para o entendimento de nosso próprio universo já eram suficientemente complexos para ocupar gerações e gerações de pesquisadores. Entretanto, diversos estudos independentes entre si, conduzidos por cientistas respeitados em suas áreas de atuação – teoria das cordas, eletrodinâmica quântica, teoria da informação -, começaram a convergir para o mesmo ponto: a existência de universos paralelos – o multiverso – não só é provável como passou a ser a explicação mais plausível para diversos enigmas cosmológicos.
Em A realidade oculta, Brian Greene – um dos maiores especialistas mundiais em cosmologia e física de partículas – expõe o fantástico desenvolvimento da física do multiverso ao longo das últimas décadas. O autor de O universo elegante passa em revista as diferentes teorias sobre os universos paralelos a partir dos fundamentos da relatividade e da mecânica quântica. Por meio de uma linguagem acessível e valendo-se de numerosas figuras explicativas, Greene orienta o leitor pelos labirintos da realidade mais profunda da matéria e do pensamento.

“Se extraterrestres aparecessem amanhã e pedissem para conhecer as capacidades da mente humana, não poderíamos fazer nada melhor que lhes oferecer um exemplar deste livro.” – Timothy Ferris, New York Times Book Review

Novo artigo sobre automata celulares e Paradoxo de Fermi

Saiu um novo artigo sobre a hipótese de percolação para o Paradoxo de Fermi, onde simulações de automata celulares em três dimensões são usadas.  Dessa vez, a conclusão dos autores é a de que as simulações não suportam a hipótese.

Bom, acho que isso não é o fim da história. Eu já sabia que, para a hipótese dar certo, a difusão deveria ser critica (ou seja, formando um cluster crítico ou levemente supercrítico de planetas ocupados).

Ou seja, a hipótese precisa ser complementada com algum argumento de porque a difusão deveria ser crítica. Bom, como sistemas críticos são abundantes nos processos sociais e biológicos, eu acho que basta encontrar esse fator de criticalidade para justificar o modelo. Minha heurística seria: Read more [+]

Kepler detecta 140 planetas similares à Terra?

Telescópio acha 140 planetas que podem ter vida
22 de julho de 2010 13h48 atualizado às 14h15

comentários
181

Kepler descobre planetas quando eles passam em frente a sua estrela Foto: Nasa/Divulgação

Kepler descobre planetas quando eles passam em frente a sua estrela, assim como registra Vênus ou Mercúrio ao passarem em frente ao Sol
Foto: Nasa/Divulgação

Cientistas anunciaram a descoberta de 140 novos planetas parecidos com a Terra encontrados nas últimas semanas. Com os novos dados, os cientistas acreditam que existam cerca de 100 milhões de planetas parecidos com o nosso e que possam abrigar vida apenas na Via Láctea. As informações são do Daily Mail.

Os achados foram feitos pelo telescópio espacial Kepler, que procura novos planetas desde que foi lançado, em janeiro de 2009. Segundo o astrônomo Dimitar Sasselov, os planetas têm tamanho parecido com o da Terra. O cientista descreveu a descoberta como a “realização do sonho de Copérnico”, em referência ao pai da astronomia moderna.

Novos planetas fora do sistema solar são descobertos quando eles passam em frente a sua estrela. O telescópio não capta uma imagem direta, mas registra a minúscula diminuição do brilho do astro quando o planeta passa em frente. Essa passagem causa “piscadas” na luz. Pelo cálculo da diminuição de brilho, do tempo entre as “piscadas” e da massa da estrela, os astrônomos conseguem descobrir o tamanho do planeta.

O Kepler continuará pesquisando o céu dia e noite, sem interrupção, pelos próximos quatro anos, segundo o cientista. Sasselov afirma que nos últimos 15 anos cerca de 500 exoplanetas foram descobertos, mas nenhum foi considerado parecido com a Terra, ou seja, com a possibilidade de abrigar vida.

“Vida é um sistema químico que realmente necessita de um planeta pequeno, água e pedras e uma grande quantidade de complexos químicos para surgir e sobreviver. (…) Tem um monte de trabalho para fazermos com isso, mas os resultados estatísticos são claros e planetas como a nossa Terra estão lá fora. (…) Nossa própria Via Láctea é rica nesse tipo de planetas”, disse o astrônomo durante a apresentação dos resultados do Kepler na conferência TEDGlobal, em Oxford, no Reino Unido.

Redação Terra

Twitter, SETI, ETs e Astrobiologia

Cientistas propõem abordagem ‘Twitter’ para contato com ETs

Farol contínuo seria muito caro para uma civilização avançada manter, especulam cientistas

21 de julho de 2010 | 14h 18

estadao.com.br

A busca por inteligência extraterrestre (SETI) baseada em radiotelescópios depende, para obter sucesso, de haver pelo menos uma raça alienígena transmitindo um sinal contínuo de alta potência para o espaço – o equivalente de um farol cósmico – que pudesse ser detectado na Terra. A manutenção de um farol do tipo consumiria muita energia, no entanto, e vários cientistas questionam se uma civilização qualquer estaria disposta a arcar com esse tipo de custo.

blog O tempo está acabando para a SETI?

Agora, em dois artigos publicados na revista Astrobiology, os irmãos gêmeos Gregory e James Benford – astrofísico e físico – analisam os custos do ponto de vista da espécie emissora e concluem que o meio mais eficiente de sinalizar a própria presença não seria a emissão de um farol contínuo, mas de pulsos intermitentes. “Essa abordagem é mais como o Twitter e menos como Guerra e Paz“, resume James, em nota.

“Qualquer que seja a forma de vida, a evolução favorece economia de recursos”, acrescenta Gregory. “Transmitir é caro, e transmitir sinais por anos-luz iria requerer recursos consideráveis”.

Supondo que a civilização alienígena busque otimizar os gastos, limitar desperdício e aumentar a eficiência da tecnologia, os Benfords propõem que, em vez de um sinal contínuo transmitido em todas as direções, os ETs usariam um sinal pulsado, direcionado e de banda larga na faixa de 1 a 10 Ghz.

Se os Benfords estiverem certos, o programa SETI atual, com seu foco na busca por sinais de banda estreita, pode estar procurando no lugar errado.

Os irmãos também propõem que as antenas sejam apontadas na direção do núcleo da galáxia, onde aglomeram-se 90% das estrelas da Via Láctea.

“As estrelas ali são um bilhão de anos mais velhas que o Sol, o que sugere uma maior possibilidade de contato com uma civilização avançada”, disse Gregory.



Mais um projeto SETI desafiado pelo Paradoxo de Fermi


A Failure of Serendipity: the Square Kilometre Array will struggle to eavesdrop on Human-like ETI

D.H. ForganR.C. Nichol
(Submitted on 6 Jul 2010)

The Square Kilometre Array (SKA) will operate in frequency ranges often used by military radar and other communications technology. It has been shown that if Extraterrestrial Intelligences (ETIs) communicate using similar technology, then the SKA should be able to detect such transmissions up to distances of ~100 pc (~300 light years) from Earth. However, Mankind has greatly improved its communications technology over the last century, dramatically reducing signal leakage and making the Earth “radio quiet”. If ETIs follow the same pattern as the human race, will we be able to detect their signal leakage before they become radio quiet? We investigate this question using Monte Carlo Realisation techniques to simulate the growth and evolution of intelligent life in the Galaxy. We show that if civilisations are “human” in nature (i.e. they are only “radio loud” for ~100 years, and can only detect each other with an SKA-like instrument out to 100 pc, within a maximum communication time of 100 years), then the probability for such civilisations accidentally detecting each other is low (~10^{-7}), much lower than if other, dedicated communication techniques are permissible (e.g. optical SETI or neutrino communication).

Comments: 8 pages, 2 figures, accepted for publication in the International Journal of Astrobiology
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1007.0850v1 [astro-ph.EP]

PS: Além do mais, se existissem civilizações tecnológicas (CTs) em um raio de 300 anos-luz, elas já teriam tido tempo de nos colonizar ou colonizar as CTs que estão nesta janela de 100 anos de radio loud (e que portanto, deixariam de ser radio loud). Parece desperdício de dinheiro, acho que outros projetos SETI seriam mais promissores… 
Ver a continuação do “Argumento de Fermi Local” aqui

Equilíbrio puntuado e Astrobiologia


Galactic Punctuated Equilibrium: How to Undermine Carter’s Anthropic Argument in Astrobiology

Milan M. Cirkovic, Branislav Vukotic, Ivana Dragicevic
(Submitted on 30 Dec 2009)

We investigate a new strategy which can defeat the (in)famous Carter’s “anthropic” argument against extraterrestrial life and intelligence. In contrast to those already considered by Wilson, Livio, and others, the present approach is based on relaxing hidden uniformitarian assumptions, considering instead a dynamical succession of evolutionary regimes governed by both global (Galaxy-wide) and local (planet- or planetary system-limited) regulation mechanisms. This is in accordance with recent developments in both astrophysics and evolutionary biology. Notably, our increased understanding of the nature of supernovae and gamma-ray bursts, as well as of strong coupling between the Solar System and the Galaxy on one hand, and the theories of “punctuated equilibria” of Eldredge and Gould and “macroevolutionary regimes” of Jablonski, Valentine, et al. on the other, are in full accordance with the regulation- mechanism picture. The application of this particular strategy highlights the limits of application of Carter’s argument, and indicates that in the real universe its applicability conditions are not satisfied. We conclude that drawing far-reaching conclusions about the scarcity of extraterrestrial intelligence and the prospects of our efforts to detect it on the basis of this argument is unwarranted.

Comments: 3 figures, 26 pages
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: Published in Astrobiology, 2009, Volume 9, Issue 5, pp. 491-501
DOI: 10.1089/ast.2007.0200
Cite as: arXiv:0912.4980v1 [astro-ph.EP]

Arqueologia Interestelar

Daqui a dez anos, a Astrobiologia será uma área quente. Comece já o seu mestrado nisso se desejar entrar nessa área no futuro.

Starry Messages: Searching for Signatures of Interstellar Archaeology

Authors: Richard A. Carrigan Jr (Fermi National Accelerator Laboratory)

(Submitted on 29 Jan 2010)

Abstract: Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. For example, the constraints of the anthropic principle would have to be loosened if a different type of intelligence was discovered elsewhere. A variety of interstellar archaeology signatures are discussed including non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is introduced in the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale. A modified Drake equation is used to evaluate the relative challenges of finding various sources. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.

Comments: 29 pages including 4 figures and 1 table
Subjects: Galaxy Astrophysics (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP)
Report number: FERMILAB-PUB-09-607-AD
Cite as: arXiv:1001.5455v1 [astro-ph.GA]

Marina Silva e a colonização galática


Bom, uma alternativa é uma expansão em forma de lei de potência: N(t) = c t^\theta. Talveza se possa demonstrar que tal expansão seria economicamente sustentável. Interessante que isso corresponderia a um processo de ramificação crítico, que criaria uma expansão fractal, de modo que haveria bolhas não colonizadas de todos os tamanhos dentro da galáxia. E a minha solução para o Paradoxo de Fermi (que estamos dentro de uma dessas bolhas, e portanto não adianta fazer pesquisa SETI nas estrelas vizinhas) seria compativel com esse vínculo de expansão economicamente sustentável… Quem sabe os ETs (e nós no futuro) têm a mesma opinião da Marina Silva?

The Sustainability Solution to the Fermi Paradox

Jacob D. Haqq-Misra, Seth D. Baum
(Submitted on 2 Jun 2009)

No present observations suggest a technologically advanced extraterrestrial intelligence (ETI) has spread through the galaxy. However, under commonplace assumptions about galactic civilization formation and expansion, this absence of observation is highly unlikely. This improbability is the heart of the Fermi Paradox. The Fermi Paradox leads some to conclude that humans have the only advanced civilization in this galaxy, either because civilization formation is very rare or because intelligent civilizations inevitably destroy themselves. In this paper, we argue that this conclusion is premature by introducing the “Sustainability Solution” to the Fermi Paradox, which questions the Paradox’s assumption of faster (e.g. exponential) civilization growth. Drawing on insights from the sustainability of human civilization on Earth, we propose that faster-growth may not be sustainable on the galactic scale. If this is the case, then there may exist ETI that have not expanded throughout the galaxy or have done so but collapsed. These possibilities have implications for both searches for ETI and for human civilization management.

Comments: 14 pages, PDF file
Subjects: Popular Physics (physics.pop-ph); Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: J.Br.Interplanet.Soc.62:47-51, 2009
Cite as: arXiv:0906.0568v1 [physics.pop-ph]

Persistence solves Fermi Paradox but challenges SETI projects

Osame Kinouchi (DFM-FFCLRP-Usp)
(Submitted on 8 Dec 2001)

Persistence phenomena in colonization processes could explain the negative results of SETI search preserving the possibility of a galactic civilization. However, persistence phenomena also indicates that search of technological civilizations in stars in the neighbourhood of Sun is a misdirected SETI strategy. This last conclusion is also suggested by a weaker form of the Fermi paradox. A simple model of a branching colonization which includes emergence, decay and branching of civilizations is proposed. The model could also be used in the context of ant nests diffusion.

Comments: 2 pages, no figures, v2 with corrected definition of branching ratio
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech)
Cite as: arXiv:cond-mat/0112137v1 [cond-mat.dis-nn]

Mais uma solução para o Paradoxo de Fermi…

Ainda não li, mas pelo que entendi do resumo, é uma espécie de problema de percolação com esferas.

Broadcasting but not receiving: density dependence considerations for SETI signals

Reginald D. Smith
(Submitted on 24 Jan 2009)
Abstract: This paper develops a detailed quantitative model which uses the Drake equation and an assumption of an average maximum radio broadcasting distance by an communicative civilization to derive a minimum civilization density for contact between two civilizations to be probable in a given volume of space under certain conditions, the amount of time it would take for a first contact, and whether reciprocal contact is possible. Results show that under certain assumptions, a galaxy can be teeming with civilizations yet not have a guarantee of communication between any of them given either short lifetimes or small maximum distances for communication.
Comments:
10 pages, 2 figures, submitted to the International Journal of Astrobiology
Subjects:
General Physics (physics.gen-ph); Popular Physics (physics.pop-ph)
Cite as:
arXiv:0901.3863v1 [physics.gen-ph]

Epidemiologia e o paradoxo de Fermi


Cirkovic me cita neste review. Acho que preciso dar a forma final no paper e tentar publicar. Entretanto, estou atraido por uma nova hipótese baseada no modelo SIRS com automata celulares: usando idéias de epidemiologia para tratar a dinamica de colonização galactica, mostra-se que a galaxia é um meio excitável. O modelo SIRS prediz uma sequencia de epidemias galacticas. Para explicar o paradoxo de Fermi, basta supor que estamos vivendo entre duas ondas epidemicas de colonização galactica.

Fermi’s Paradox – The Last Challenge for Copernicanism?

Milan M. Cirkovic
(Submitted on 20 Jul 2009)

We review Fermi’s paradox (or the “Great Silence” problem), not only arguably the oldest and crucial problem for the Search for ExtraTerrestrial Intelligence (SETI), but also a conundrum of profound scientific, philosophical and cultural importance. By a simple analysis of observation selection effects, the correct resolution of Fermi’s paradox is certain to tell us something about the future of humanity. Already a more than three quarters of a century old puzzle – and a quarter of century since the last major review paper in the field by G. David Brin – Fermi’s paradox has generated many ingenious discussions and hypotheses. We analyze the often tacit methodological assumptions built into various answers to this puzzle and attempt a new classification of the numerous solutions proposed in an already huge literature on the subject. Finally, we consider the ramifications of various classes of hypotheses for the practical SETI projects. Somewhat paradoxically, it seems that the class of (neo)catastrophic hypotheses gives, on balance, the strongest justification for guarded optimism regarding our current and near-future SETI efforts.

Comments: 39 pages, 3 figures, slightly expanded in comparison to the journal version
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: Serbian Astronomical Journal, vol. 178, pp. 1-20 (2009)
DOI: 10.2298/SAJ0978001C
Cite as: arXiv:0907.3432v1 [astro-ph.EP]

Cadê os monolitos negros?

Arthur C. Clark defende uma tese de Desígnio Inteligente na série 2001-2010-2061-3001. Mas é uma questão sem sentido perguntar se ele acreditava no DI. Afinal, a ficção científica hard tipo Clark brinca com “especulação científica”. Acho que a especulação científica, ou seja, a formulação de hipóteses (não necessariamente testáveis) compatíveis com a ciência é uma atividade normal de todo cientista. Como me respondeu uma vez o prof. Roland Koberle quando lhe perguntei se ele gostava de ficção científica:

– Mas eu faço ficção científica!

Roland trabalhava na época em Termodinâmica de Buracos Negros…

Fermi Paradox Points To Fewer Than Ten ET Civilisations

Posted: 29 Jul 2009 09:10 PM PDT

The absence of alien probes visiting the Solar System places severe limits on the number of advanced civlisations that could be exploring the galaxy.

The Fermi Paradox focuses on the existence of advanced civilisations elsewhere in the galaxy. If these civilisations are out there–and many analyses suggest the galaxy should be teaming with life–why haven’t we seen them?

Today Carlos Cotta and Álvaro Morales from the University of Malaga in Spain add an another angle to the discussion. One line of thought is the speed at which a sufficiently advanced civilisation could colonise the galaxy. Various analyses suggest that using spacecraft that travel at a tenth of the speed of light, the colonisation wavefront could take some 50 million years to sweep the galaxy. Others have calculated that it may be closer to 13 billion years, which may explain ET’s absence.

Cotta and Morales take a different tack by studying how automated probes sent ahead of the colonisation could explore the galaxy. Obviously, this could advance much faster than the colonisation wavefront. The scenario involves a civilisation sending out 8 probes, each equipped with smaller subprobes for studying regions that the host probe visits.

This is not a new scenario. One previous calculation suggests that in about 300 millions years these 8 probes could explore just 4 per cent of the galaxy. The question that Cotta and Morales ask is: what if several advanced civilisations were exploring the galaxy at the same time? Surely, if enough advanced civilisations were exploring simultaneously, one of their probes would end up visiting the solar system. So that fact we haven’t seen one places a limit on how many civilisations can be out there.

The numbers that Cotta and Morales come up with depend crucially on the lifetime of the probes doing the exploring (and obviously on the number of probes each civilisations ends out). They say that if each probe has a lifetime of 50 million years and that evidence of them visiting the solar system lasts for about a million years, there can be no more than about 1000 advanced civilisations out there now.

But if these probes can leave evidence of a visit that lasts for 100 million years, then there can be no more than about 10 civilisations out there.

Of course, we may not have discovered the evidence yet. And when we finally find the black obelisk on the Moon, the paradox will be resolved.

Ref: arxiv.org/abs/0907.0345: A Computational Analysis of Galactic Exploration with Space Probes: Implications for the Fermi Paradox

Paradoxo de Fermi: onde está todo mundo?

Figure 1. A slice from a percolation simulation on a simple cubic lattice in three dimensions. Here N=6 and P=1/3. Filled circles denote “colonizing” sites, open circles “non-colonizing” sites, and the absence of circles represents sites not visited. The irregular shape of the boundary and large voids in the percolation structure are clearly visible.


A Computational Analysis of Galactic Exploration with Space Probes: Implications for the Fermi Paradox

Carlos Cotta, Álvaro Morales
(Submitted on 2 Jul 2009)

Temporal explanations to the Fermi paradox state that the vast scale of the galaxy diminishes the chances of establishing contact with an extraterrestrial technological civilization (ETC) within a certain time window. This argument is tackled in this work in the context of exploration probes, whose propagation can be faster than that of a colonization wavefront. Extensive computational simulations have been done to build a numerical model of the dynamics of the exploration. A probabilistic analysis is subsequently conducted in order to obtain bounds on the number of ETCs that may be exploring the galaxy without establishing contact with Earth, depending on factors such as the number of probes they use, their lifetime and whether they leave some long-term imprint on explored systems or not. The results indicate that it is unlikely that more than ~10^2-10^3 ETCs are exploring the galaxy in a given Myr, if their probes have a lifetime of 50 Myr and contact evidence lasts for 1 Myr. This bound goes down to ~10 if contact evidence lasts for 100 Myr, and is also shown to be inversely proportional to the lifetime of probes. These results are interpreted in light of the Fermi paradox and are compatible with non-stationary astrobiological models in which a few ETCs have gradually appeared in the Fermi-Hart timescale.

Comments: 14 pages, 6 figures
Subjects: Popular Physics (physics.pop-ph); Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference: J.Br.Interplanet.Soc.62(3):82-88,2009
Cite as: arXiv:0907.0345v1 [physics.pop-ph]