“The Great Silence”: Why Haven’t Signs of Intelligent Extraterrestrial Life Been Discovered?
“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 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 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.
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Paul Young
22 Aug 09 at 10:42 am
Historically, it has been very difficult for physicists to acknowledge that some means of traveling vast distances “faster than light speed” is possible. A very few, such as Michio Kaku, Professor of Theoretical Physics, New York University, postulate that such achievement may indeed be feasible. “Kaku takes a serious look at what our current understanding of the universes physical laws may permit in the near and distant future.” This ‘space-time relativity’ thing cannot be discounted!
Interstellar Bill
22 Aug 09 at 11:28 pm
We have seen no IR stars with the unique signature of a Type II Dyson Swarm, the interception of most of a star’s light by millions of orbiting habitats. This is something we’ll be starting to do in another thousand years, after which we’ll take over the Milky Way in only a million years, resulting in a Type III civilization, with Dyson Swarms around every last star in our Galaxy. That this hasn’t happened is a strong indication that nobody in the Galaxy has yet reached space, in spite of its being nine billion years older than the Earth. But it gets worse.
No galaxies near our age (all those within a few billion light years) show any indication of Type III, which should be able to take over an entire cluster of galaxies in a mere billion years, so why don’t we see them? Fermi’s paradox is Universe-wide.
Only if space-faring intelligent life is cosmically rare to a degree extreme beyond our wildest pessemism could we see not even one galaxy ‘going dark’, as a triumphant Type-III-to-be settles huge swaths of its interstellar space.
Nate D.
6 Sep 09 at 12:04 am
A couple arguing points on the article and comments. First our failure to have yet heard radio signals from ET. The RF waves that we constantly transmit from our planet are not like polarized laser light. Over interstellar distances these signals degrade. Trying to pick up such a signal from far off stars or especially another galaxy may not be possible. A slightly more far-out hypothesis: Who says ET’s communications work the way ours do at all? It may be possibly that a developing civilizations period of rampant RF transmission may be short. It’s been less than two hundred years since mankind first began waving around antennas. There is mounting evidence that the complete saturation of our environment by these RF waves is harmful to life. It may be that within another century or two we may be using a global communications system that works differently and is a little more “closed-circuit” if you will. Advanced ETs may have evolved beyond the need for technologically assisted communication. They may use what we would call telepathy and are basically on a cosmic bandwidth we haven’t learned to tune in yet. We could be surrounded by such stray messages at all times and be oblivious to them. In this theory each developing races period of RF pollution is only a few centuries maybe a thousand years or so long. Which is not a long time compared to the history of the human race and especially not long in the case of a much older race. That’s a pretty slim window of opportunity for us to receive it even if it hasn’t been completely distorted by the vast distance. Considering we’ve only been listening hard for less than a century it’s no big surprise that we haven’t heard one yet. Perhaps a nearby civilization came to the end of their RF period a few centuries ago. The last of their noise may have passed us by mere decades before we raised our antennas.
As far as the failure to detect Dyson Spheres…the idea of them existing at all is completely theoretical. We have not encountered class II or III civilizations so we don’t really know how they work. It may be that encasing a star like that kills it for all we know about the Universe! I do not see the great silence as significant evidence for the lack of other civilizations in the universe.
There is one remaining possibility yet not discussed. The possibility that they have received messages from ET and just haven’t gotten around to telling YOU about it!!!