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"The idea that we are the only intelligent creatures in a cosmos of a hundred billion galaxies is so preposterous that there are very few astronomers today who would take it seriously. It is safest to assume therefore, that they are out there and to consider the manner in which this may impinge upon human society." -- Arthur C. Clarke, physicist and author of 2001: A Space Odyssey
Source: New Scientist, via The Daily Galaxy
One of the greatest philosophical and scientific challenges that currently confronts humanity is the unsolved question of the existence of extraterrestrial intelligence.
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.
The 14-billion-year age of the universe and its 130 billion galaxies and a Milky Way Galaxy with some 400 billion stars suggest that if the Earth is typical, should be common. Nobel laureate Enrico Fermi, discussing this observation with colleagues over lunch in 1950, asked, logically: "Where are they?" Why, if advanced extraterrestrial civilizations exist in our Milky Way galaxy, hasn't evidence such as probes, spacecraft, or radio transmissions been found?
As our technologies become ever more sophisticated and the search for extraterrestrial intelligence continues to fail, the "Great Silence" becomes louder than ever. The seemingly empty cosmos is screaming out to us that something is amiss. Or is it?
Using a computer simulation of our own galaxy, the Milky Way, Rasmus Bjork, a physicist at the Niels Bohr Institute in Copenhagen, proposed an answer to the Fermi Paradox. Bjork proposed that an alien civilization might build intergalactic probes and launch them on missions to search for life.
He found, however, that even if the alien ships could hurtle through space at a tenth of the speed of light, or 30,000km a second, - NASA's current Cassini mission to Saturn is gliding along at 32km a second - it would take 10 billion years, roughly half the age of the universe, to explore a mere four percent of the galaxy.
Like humans, alien civilizations could shorten the time to find extra-terrestrials by picking up television and radio broadcasts that might leak from colonized planets. "Even then," he reported, "unless they can develop an exotic form of transport that gets them across the galaxy in two weeks it's still going to take millions of years to find us. There are so many stars in the galaxy that probably life could exist elsewhere, but will we ever get in contact with them? Not in our lifetime."
The problem of distance is compounded by the fact that timescales that provide a "window of opportunity" for detection or contact might be quite small. Advanced civilizations may periodically arise and fall throughout our galaxy as they do here, on Earth, but this may be such a rare event, relatively speaking, that the odds of two or more such civilizations existing at the same time are low.
In short, there may have been intelligent civilizations in the galaxy before the emergence of intelligence on Earth, and there may be intelligent civilizations after its extinction, but it is possible that human beings are the only intelligent civilization in existence "now." "Now" assumes that an extraterrestrial intelligence is not able to travel to our vicinity at faster-than-light speeds, in order to detect an intelligence 1,000 light-years distant, that intelligence will need to have been active 1,000 years ago.
There is also a possibility that archaeological evidence of past civilizations may be detected through deep space observations — especially if they left behind large artifacts such as Dyson spheres.
Perhaps... but in our search for life and intelligence we have to keep in mind that the Milky Way Galaxy is two or three times the age of our Solar System, so there are going to be some societies out there that are millions of years, maybe more, beyond ours, which may have proceeded beyond biology—that have invented intelligent, self-replicating machines and it could be that what we first find is something that's artificially constructed if we have the ability to recognize it as such. It may very well be that our greatest discovery will be that the very nature of alien communication will prevent our being able to communicate with it.
In his famous lecture on Life in the Universe, Stephen Hawking asks: "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 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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Michio Kaku and much of the civilian scientific community think that alien life should be top secret, even if it's found light years away in outer space. Imagine if they were here already. Do you think the governments and the scientists would tell us?