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