Home

 Astronomy

 Seti

 Gallery

 Wallpaper

 Downloads

 Links

 About Us

The Chances

 
"The probability of success is difficult to estimate, but if we never search, the chance of success is zero. "

These words were written by the physicists Giuseppe Cocconi and Philip Morrison in their 1959 NATURE article "Searching for Interstellar Communications", which marks the beginning of the modern SETI era. The difficulty or more likely the impossibility to predict the chances of the Search for Extraterrestrial Intelligence has launched a polarizing, theoretical SETI debate among scientists as well as the general public. While pessimists tend to say that SETI is a vaste of time, optimists believe that the universe is teeming with life and that the detection of an artifical ETI signal from outer space is only a question of time.

Radio Astronomer Frank Drake, who carried out the first systematic search for such a signal, set up the equation that put the SETI research on a scientific basis. The Drake or Green Bank equation, as it has come to be known, is the attempt to estimate the number of communicative civilizations in our galaxy and so also the attempt to define the chances of detecting other technologies.

N = R x fp x ne x fl x fi x fc x L

The number (N) of observable civilizations in the Milky Way is calculated by multiplying specific factors thought to play a role in the development of advanced intelligences:

Astronomers and biologists alike have tried to "solve" the equation. The problem is that after all at least three variables remain very unknown.
R, the number of stars born in the Milky Way each year, has been known for decades and is approximately 1.

The second factor fp could be as high as 50 or even 100 percent. Recent discoveries that many young stars are surrounded by planet-forming disks, along with detections of actual planets, confirm what astronomers had already suspected: planets are common.
But not every planet has an environment suitable for the origin of life (liquid water etc.) and so the next question has to be: How frequent are habitable planets?
Indeed the number of earthlike worlds in a solar system, ne, is the first term in the equation where scientist’s opinions begin to vary. A few say that our solar system, including the materials necessary for making rocky planets or the many worlds and moons in nice, circular, stable orbits, might be the exception rather than the rule. However a lot of scientists have an optimistic view concerning ne and estimate the number at 1 – 5.

Today biologists are also optimistic about the value of fl, the fraction of habitable planets on which life actually evolves. They have discovered that the raw material for life is abundant in the universe and that microorganisms appeared on Earth very early, only moments after the last devastating impacts about 3.8 billion years ago. The origin of life seems to be a rather straightforward process, which happens easily when given the right conditions. So if life does form wherever it can, then fl is probably 1.
The last three terms are the most discussed factors of the Drake equation.
Particularly fi, the fraction of worlds where intelligent life arises, has caused a scientific debate dividing researchers into optimists and pessimists. Some scientists believe fi is almost certainly next to zero, others are convinced it's close to one.

Pessimists argue that evolution is unpredictable and chaotic. They say there is no overall pattern, no preferred direction and no firm indication that increased intelligence is inevitable in the evolution of life.
Beside the biological factors fi strongly depends on the stability of solar systems and planetary climates. Extreme or frequent planetary crisis keep life beaten down to a low level, but biologists believe in some cases change and stress actually promote the emergence of new, adaptable species. Indeed the human species itself - arised during an unusual run of ice ages - is sometimes cited as a possible example of stress-driven evolution leading to adaptability and intelligence.
Optimists often emphasize that greater intelligence improves the chance of survival. They also point out the early emergence of intelligent creatures on Earth and that it seems likely that other, entirely different, advanced species will emerge in the coming billion years, of course only if Earth remains stable and suitable for life...........

This and other open questions along with contrary scientific opinions lead to a lot of speculations regarding fi, evidently the most controversial factor in the equation today.
However the next term fc, the fraction of intelligent species that become capable of interstellar communication, isn't easier to determine. Here also, the value depends on a number of unanswered questions leading to different views among scientists.
For example, we don't know, if extraterrestrials broadcast in a way we can detect at all. So as for fi, the valuations of fc range from zero to one.
In the most optimistic case, the Drake equation is reduced to N = L, the lifetime of technological civilizations and the last term in the equation. As fi and fc it belongs to the factors, which are practically unknown. Extreme optimists believe that a stable, intelligent society could last for tens of millions of years, but a more realistic view would be about 10 000 years. Of course, pessimists estimate the number much lower.

All these speculations and attempts to solve the equation have led to one certain conclusion:
Success can't be predicted!
N obviously isn't zero..........otherwise you wouldn't read these lines ;-))........but it's anyone's guess whether N is 1, 10, 100, 1000, 10 000 or higher.
Though or perhaps just because the chances of SETI remain indeterminable the search for an artifical signal from outer space should go on, 'cause when we don't search, the ancient question "Are we alone?" will probably never be answered.

Mirella