Tudomány: Megvan, hogy mitől olyan speciális a Föld és az emberiség

Úgy tűnik, hogy az emberiséget csak pár találmány és/vagy fejlesztés választja el attól, hogy elindulhasson először a Naprendszer majd galaxisunk, a Tejútrendszer meghódítására.

De ha ez a helyzet, vajon miért nem nyüzsögnek az idegenek a környéken? Vagy legalábbis miért nem hallunk róluk? http://hu.wikipedia.org/wiki/Fermi-paradoxon

Lakható bolygóból egy csomó lehet: http://kepler.nasa.gov/Mission/discoveries/candidates/

De akkor mi lehet az a Nagy Filter http://en.wikipedia.org/wiki/Great_Filter , ami megakadályozza, hogy a lakható bolygókon élet alakuljon ki? Hol akadtak el a többiek? Nm volt elég különleges a bolygójuk? Vagy nem állt össze a DNSük? Vagy […] Vagy a mi fejlettségi szintünktől a galaktikus terjedésig tartó időszakban történt velük valami baj?

A probléma részletesen http://hanson.gmu.edu/greatfilter.html :

Humanity seems to have a bright future, i.e., a non-trivial chance of expanding to fill the universe with lasting life. But the fact that space near us seems dead now tells us that any given piece of dead matter faces an astronomically low chance of begating such a future. There thus exists a great filter between death and expanding lasting life, and humanity faces the ominous question: how far along this filter are we? […]

Combining standard stories of biologists, astronomers, physicists, and social scientists would lead us to expect a much smaller filter than we observe. Thus one of these stories must be wrong. To find out who is wrong, and to inform our choices, we should study and reconsider all these areas. For example, we should seek evidence of extraterrestrials, such as via signals, fossils, or astronomy. But contrary to common expectations, evidence of extraterrestrials is likely bad (though valuable) news. The easier it was for life to evolve to our stage, the bleaker our future chances probably are. […]

So far, life on earth seems to have adapted its technology to fill every ecological niche it could. Previously stable populations and species have consistently expanded into newly-opened frontiers. All known life seems to have a “dispersal phase” to encourage colonization, with non-trivial mutations and sexual mixing to encourage exploration of new technologies.

Similarly, humanity has continued to advance technologically, and to fill new geographic and economic niches as they become technologically feasible. For example, while imperial China closed itself to exploration for a time, other competing peoples, such as in Europe, eventually filled the gap.

This phenomena is easily understood from an evolutionary perspective. In general, it only takes a few individuals of one species to try to fill an ecological niche, even if all other life is uninterested. And mutations that encourage such trials can be richly rewarded. Similarly, we expect internally-competitive populations of our surviving descendants to continue to advance technologically, and to fill new niches as they become technologically and economically feasible. […]

No alien civilizations have substantially colonized our solar system or systems nearby. Thus among the billion trillion stars in our past universe, none has reached the level of technology and growth that we may soon reach. This one data point implies that a Great Filter stands between ordinary dead matter and advanced exploding lasting life. […]

To support optimism regarding our future, we must find especially improbable past evolutionary steps. And in fact we can find a number of plausible candidates for groups of hard trial-and-error biological steps: life, complexity, sex, society, cradle and language. Presuming there are about nine hard steps total here, the Great Filter could be explained if the expected time for each of these steps averaged (logarithmically) to about thirty billion years, if only one percent of stars could support such steps, and if we have only about a one percent chance of not destroying ourselves soon (or permanently banning colonization).

[…] the Great Filter is so very large that it is not enough to just find some improbable steps; they must be improbable enough. Even if life only evolves once per galaxy, that still leaves the problem of explaining the rest of the filter: why we haven’t seen an explosion arriving here from any other galaxies in our past universe? And if we can’t find the Great Filter in our past, we’ll have to fear it in our future.

A válasz nem triviális, és mint a fentiekből látszik, a mi jövőnkre nézve is nagy jelentősége van.

Úgy tűnik, hogy Dave Waltham megtalálta a megoldást http://www.liebertonline.com/doi/pdf/10.1089/ast.2010.0475 (vagy legalábbi a megoldás nagy részét) a problémára, hogy mitől olyan különleges a Föld:

Planetary anthropic selection, the idea that Earth has unusual properties since, otherwise, we would not be here to observe it, is a controversial idea. This paper proposes a methodology by which to test anthropic proposals by comparison of Earth to synthetic populations of Earth-like planets. The paper illustrates this approach by investigating possible anthropic selection for high (or low) rates of Milankovitch-driven climate change. Three separate tests are investigated: (1) Earth-Moon properties and their effect on obliquity; (2) Individual planet locations and their effect on eccentricity variation; (3) The overall structure of the Solar System and its effect on eccentricity variation. In all three cases, the actual Earth/Solar System has unusually low Milankovitch frequencies compared to similar alternative systems. All three results are statistically significant at the 5% or better level, and the probability of all three occurring by chance is less than 10−5. It therefore appears that there has been anthropic selection for slow Milankovitch cycles [that is, the periodic variations in Earth’s climate that are induced by changes in Earth’s orbit and orientation in space. The key factors here are axial precession (time varying axis orientation), orbital precession (time varying orbital orientation), and time variation in orbital eccentricity (circularity of the orbit)]. This implies possible selection for a stable climate, which, if true, undermines the Gaia hypothesis [that
is, that life modifies the environment in ways which are beneficial to itself] and also suggests that planets with Earth-like levels of biodiversity are likely to be very rare. […]

It is widely recognized that regions of Earth that have stable temperatures (e.g., tropical rainforests) have high levels of biodiversity (see review by Wilson, 2001). The hypothesis that this link is direct and causal is reinforced by the observation that the deep ocean seafloor also has high biodiversity (Sanders, 1968), even though the conditions are, stability excepted, poor and biological productivity therefore low. Further evidence of a link between rapid climate change and loss of species richness has been gleaned from studies of Earth’s glacial-interglacial cycles. The most recent ice ages have resulted in reduced biodiversity within the temperate zones where the greatest changes in climate occurred (see review by Hewitt, 2004). There are, therefore, two independent lines of evidence that support the proposition that biodiversity is, in general, lower when climate change is significant. […]

Tehát nem kell csúnya katasztrófa a jelenlegi fejlettségünk és a galaktikus terjeszkedésünk között ahhoz, hogy megmagyarázza, miért vagyunk látszólag olyan kevesen (konrétan: egyedül) a környéken. A többiekkel nem történt semmi rossz azt leszámítva, hogy a bolygójuk pályája miatt nem alakult ki náluk stabil éghajlat, és a stabil éghajlat hiánya miatt létre sem jöttek.

Ez jó hír. Ma este kicsit jobban alszom:)