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A Probabilistic Analysis of the Fermi Paradox

Evan Solomonides, Lisa Kaltenegger, Yervant Terzian
The fermi paradox uses an appeal to the mediocrity principle to make it seem counter-intuitive that humanity has not been contacted by extraterrestrial intelligence. A numerical, statistical analysis was conducted to determine whether this apparent loneliness is, in fact, unexpected.
An inequality was derived to relate the frequency of life arising and developing technology on a suitable planet in the galaxy, the average length of time since the first broadcast of such a civilization, and a constant term. An analysis of the sphere reached thus far by human communication was also conducted, considering our local neighborhood and planets of particular interest. We clearly show that human communication has not reached a number of stars and planets adequate to expect an answer.
These analyses both conclude that the Fermi paradox is not, in fact, unexpected. By the mediocrity principle and numerical modeling, it is actually unlikely that the Earth would have been reached by extraterrestrial communication at this point.
We predict that under 1 percent of the galaxy has been reached at all thus far, and we do not anticipate to be reached until approximately half of the stars/planets have been reached. We offer a prediction that we should not expect this until at least 1,500 years in the future. Thus the Fermi paradox is not a shocking observation, and humanity may very well be contacted within our species’ lifespan.
… Read more at https://arxiv.org/ftp/arxiv/papers/1604/1604.07687.pdf

Conformal cyclic cosmology and the Fermi paradox

CCCV. G. Gurzadyan, R. Penrose
Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the “Fermi paradox” and the SETI programme – of communication by remote civilizations – may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.
Read more at http://arxiv.org/pdf/1512.00554v1.pdf

Galactic exploration by directed Self-Replicating Probes

… and its implications for the Fermi paradox

Martin T. Barlow
This paper proposes a long term scheme for robotic exploration of the galaxy,and then considers the implications in terms of the `Fermi paradox’ and our search for ETI. We discuss the parameter space of the `galactic ecology’ of civilizations in terms of the parameters T (time between ET civilizations arising) and L, the lifetime of these civilizations. Six different regions are described….
(…)

Figure 1: Galactic ecology parameter space

(….)
Conclusion
Consideration of the points above, and Figure 1, leads to three broad categories of answer to Fermi’s question:
(F1) They have not visited us because they do not exist. (Regions R1 and R2.)
(F2) The ‘zoo hypothesis’: their probes are watching us now (Regions R3 and R4.)
(F3) They have not visited us because civilizations are all too short lived (Regions R5 and R6).
Of these, possibility (F3) relies all all civilizations being short lived, while the zoo hypothesis appears to be deeply unpopular (partly I suspect because it compromises human dignity.) The analysis above reduces the force of some of the objections that have been made to the zoo hypothesis, since in both cases R3 and R4(ii) we would lie in the zone of control of just one ETI.
If we exclude (F2) and (F3), then we are left with (F1), to which there are no objections except that it is uninteresting. It is worth noting that while astronomers have frequently given rather large values to fci – typically in the range 0.01–0.1, many evolutionary biologists have been much more pessimistic. Even if one is not convinced by all the arguments in [10], it seems very possible that the development of intelligent life requires evolution to pass through several gateways, and hence that fci is very small.

Read more: http://arxiv.org/pdf/1206.0953v1.pdf

The Fermi Paradox, Self-Replicating Probes …

… and the Interstellar Transportation Bandwidth

Keith B. Wiley
It has been widely acknowledged that self-replicating space-probes (SRPs) could explore the galaxy very quickly relative to the age of the galaxy. An obvious implication is that SRPs produced by extraterrestrial civilizations should have arrived in our solar system millions of years ago, and furthermore, that new probes from an ever-arising supply of civilizations ought to be arriving on a constant basis. The lack of observations of such probes underlies a frequently cited variation of the Fermi Paradox. We believe that a predilection for ETI-optimistic theories has deterred consideration of incompatible theories. Notably, SRPs have virtually disappeared from the literature. In this paper, we consider the most common arguments against SRPs and find those arguments lacking. By extension, we find recent models of galactic exploration which explicitly exclude SRPs to be unfairly handicapped and unlikely to represent natural scenarios.
We also consider several other models that seek to explain the Fermi Paradox, most notably percolation theory and two societal-collapse theories. In the former case, we find that it imposes unnatural assumptions which likely render it unrealistic. In the latter case, we present a new theory of interstellar transportation bandwidth which calls into question the validity of societal-collapse theories.
Finally, we offer our thoughts on how to design future SETI programs which take the conclusions of this paper into account to maximize the chance of detection….
Read more: http://arxiv.org/pdf

“The Undetectability Conjecture” — A Radical Theory for the ‘Great Silence’

The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations. As Enrico Fermi asked if the Universe is conducive to intelligent life, “Where is everybody?
A new answer proposed by Adrian Kent of the University of Cambridge and Perimeter Institute, is that extraterrestial life sufficiently advanced to be capable of interstellar travel or communication must be rare, since otherwise we would have seen evidence of it by now. This in turn is sometimes taken as indirect evidence for the improbability of life evolving at all in our universe.

“Intelligent species might reasonably worry about the possible dangers of self-advertisement and hence incline towards discretion” — the “Undetectability Conjecture,” put forth by Beatriz Gato-Rivera, a theoretical physicist at the Instituto de Fisica Fundamental (previously Instituto de Matematicas y Fisica Fundamental) of the CSIC (Spanish Scientific Research Council) in Madrid. According to Gato-Rivera, we may find ourselves in a universe in which there exist intelligent technological civilizations but they have chosen to be undetectable, camouflaging themselves mainly for security reasons (because advanced civilizations could also be aggressive).

“Evolutionary selection, acting on a cosmic scale,” Kent adds. “tends to extinguish species which conspicuously advertise themselves and their habitats.”

“It often seems, Kent concludes, “to be implicitly assumed, and sometimes is explicitly argued, that colonising or otherwise exploiting the resources of other planets and other solar systems will solve our problems when the Earth’s resources can no longer sustain our consumption. It might perhaps be worth contemplating more seriously the possibility that there may be limits to the territory we can safely colonise and to the resources we can safely exploit, and to consider whether and how it might be possible to evolve towards a way of living that can be sustained (almost) indefinitely on the resources of (say) our solar system alone.”

In another take on the “Fermi Paradox,” Stephen Hawking asks In his famous lecture on Life in the Universe: “What are the chances that we will encounter some alien form of life, as we explore the galaxy?”

If the argument about the time scale for the appearance of life on Earth is correct, Hawking says “there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before the Earth. So why is the galaxy not crawling with self-designing mechanical or biological life forms?”

Why hasn’t the Earth been visited, and even colonized? Hawking asks. “I discount suggestions that UFO’s contain beings from outer space. I think any visits by aliens, would be much more obvious, and probably also, much more unpleasant.”

Hawking continues: “What is the explanation of why we have not been visited? One possibility is that the argument, about the appearance of life on Earth, is wrong. Maybe the probability of life spontaneously appearing is so low, that Earth is the only planet in the galaxy, or in the observable universe, in which it happened. Another possibility is that there was a reasonable probability of forming self reproducing systems, like cells, but that most of these forms of life did not evolve intelligence.”

We are used to thinking of intelligent life, as an inevitable consequence of evolution, Hawking emphasized, but it is more likely that evolution is a random process, with intelligence as only one of a large number of possible outcomes.

Intelligence, Hawking believes contrary to our human-centric existece, may not have any long-term survival value. In comparison the microbial world, will live on, even if all other life on Earth is wiped out by our actions. Hawking’s main insight is that intelligence was an unlikely development for life on Earth, from the chronology of evolution: “It took a very long time, two and a half billion years, to go from single cells to multi-cell beings, which are a necessary precursor to intelligence. This is a good fraction of the total time available, before the Sun blows up. So it would be consistent with the hypothesis, that the probability for life to develop intelligence, is low. In this case, we might expect to find many other life forms in the galaxy, but we are unlikely to find intelligent life.”

Another possibility is that there is a reasonable probability for life to form, and to evolve to intelligent beings, but at some point in their technological development “the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion. I very much hope it isn’t true.”

Hawkling prefers another possibility: that there are other forms of intelligent life out there, but that we have been overlooked. If we should pick up signals from alien civilizations, Hawking warns,”we should have to be wary of answering back, until we have evolved” a bit further. Meeting a more advanced civilization, at our present stage, Hawking says, “might be a bit like the original inhabitants of America meeting Columbus. I don’t think they were better off for it.”
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