"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
The world-renowned physicist Lee Smolin author of Life of the Cosmos says that what we should look for to confirm the existence of intelligent life in the Milky Way is a message left for us some time in the last several hundred million years.
Smolin suggests that one such message might have been left in the genetic code of some living creature in the language of nucleic acid bases in the DNA, confident that the ability of living creatures to replicate DNA would keep the message relatively uncontaminated for the time scales of this order. There is a great deal of DNA in most species that does not play any biological role and varies enormously from species to species without apparent cause. The existence of this DNA is one of the puzzles of molecular biology.
The unsolved question of the existence of extraterrestrial intelligence is one of the greatest scientific challenges that currently confronts humanity.
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
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 rocky planets like Earth orbiting around small yellow stars are typical, intelligent life should be common. Using NASA's Spitzer Space Telescope, a team of scientists found that at least 20 percent, and possibly the majority (as many as 60 percent) of stars similar to the sun are candidates for forming rocky planets. The Legacy Science Program set out to determine whether planetary systems like ours are common or rare in the Milky Way. What they found is that many, perhaps even most, of the sun-like stars in our galaxy could well harbor Earth-like planets.
The ideal stars to support planets suitable for life for tens of billions of years may be a smaller slower burning ‘orange dwarf’ with a longer lifetime than the Sun ― about 20-40 billion years. These stars, called K stars, are stable stars with a habitable zone that remains in the same place for tens of billions of years. They are 10 times more numerous than Sun G-class stars, and may provide the best potential habitat for life in the long run.
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 in the New Scientist, "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.
Posted by Casey Kazan.
Related Galaxy posts:
James Cameron & Arthur C Clarke on 2001 A Space Odyssey
New Technologies & the Search for -A Galaxy Insight
Lonely Hearts of the Cosmos Revisited -NASA's Phoenix Probe & the Search for
Eyes on the Cosmos -European Space Agency's Hawk 1 & Hubble's Successor
New Phoenix Mission Technology to Search for Life
Cruising the Goldilocks Zone -The Search for "Super-Earths"
Adventures of a Planet Hunter
Non-Carbon Lifeforms -Why We May Overlook
The Milky Way Enigma -How Galactic Forces May Control Life on Earth
Astro-Engineering Artifacts as Evidence of
The Biological Universe -A New Copernican Revolution?
Jupiter's Europa & the Search for
Earth's Twin Habitable?
Search for Extraterrestrial Genomes
TrackBack URL for this entry:
Listed below are links to weblogs that reference "The Great Silence": Why Haven't Signs of Intelligent Extraterrestrial Life Been Discovered? :