The Search for Extra-Terrestrial Intelligence (SETI) seeks to answer one of the most basic questions of human identity - whether we are alone in the universe, or merely one civilization among many.  It is perhaps the biggest question that any human can ponder. 

The Drake Equation, created by astronomer Frank Drake in 1960, calculates the number of advanced extra-terrestrial civilizations in the Milky Way galaxy in existence at this time.  Watch this 8-minute clip of Carl Sagan in 1980 walking the audience through the parameters of the Drake Equation.  The Drake equation manages to educate people on the deductive steps needed to understand the basic probability of finding another civilization in the galaxy, but as the final result varies so greatly based on even slight adjustments to the parameters, it is hard to make a strong argument for or against the existence of extra-terrestrial intelligence via the Drake equation.  The most speculative parameter is the last one, fL, which is an estimation of the total lifespan of an advanced civilization.  Again, this video clip is from 1980, and thus only 42 years after the advent of radio astronomy in 1938.  Another 29 years, or 70%, have since been added to the age of our radio-astronomy capabilities, and the prospect of nuclear annihilation of our civilization is far lower today than in was in 1980.  No matter how ambitious or conservative of a stance you take on the other parameters, the value of fL in terms of our own civilization, continues to rise.  This leads us to our first postulate :

The expected lifespan of an intelligent civilization is rising.       

Carl Sagan himself believed that in such a vast cosmos, that intelligent life would have to emerge in multiple locations, and the cosmos was thus 'brimming over' with intelligent life.  On the other side are various explanations for why intelligent life will be rare.  The Rare Earth Hypothesis argues that the combination of conditions that enabled life to emerge on Earth are extremely rare.  The Fermi Paradox, originating back in 1950, questions the contradiction between the supposed high incidence of intelligent life, and the continued lack of evidence of it.  The Great Filter theory suggests that many intelligent civilizations self-destruct at some point, explaining their apparent scarcity.  This leads to the conclusion that the easier it is for civilization to advance to our present stage, the bleaker our prospects for long-term survival, since the 'filter' that other civilizations collide with has yet to face us.  A contrarian case can thus be made that the longer we go without detecting another civilization, the better. 

But one dimension that is conspicuously absent from all of these theories is an accounting for the accelerating rate of change.  I have previously provided evidence that telescopic power is also an accelerating technology.  After the invention of the telescope by Galileo in 1609, major discoveries used to be several decades apart, but now are only separated by years.  An extrapolation of various discoveries enabled me to crudely estimate that our observational power is currently rising at 26% per year, even though the first 300 years after the invention of the telescope only saw an improvement of 1% a year.  At the time of the 1980 Cosmos television series, it was not remotely possible to confirm the existence of any extrasolar planet or to resolve any star aside from the sun into a disk.  Yet, both were accomplished by the mid-1990s.  As of May 2009, we have now confirmed a total of 347 extrasolar planets, with the rate of discovery rising quickly.  While the first confirmation was not until 1995, we now are discovering new planets at a rate of 1 per week.  With a number of new telescope programs being launched, this rate will rise further still.  Furthermore, most of the planets we have found so far are large.  Soon, we will be able to detect planets much smaller in size, including Earth-sized planets.  This leads us to our second postulate :

Telescopic power is rising quickly, possibly at 26% a year.  

This Jet Propulsion Laboratory chart of exoplanet discoveries through 2004 is very overdue for an update, but is still instructive.  The x-axis is the distance of the planet from the star, and the y-axis is the mass of the planet.  All blue, red, and yellow dots are exoplanets, while the larger circles with letters in them are our own local planets, with the 'E' being Earth.  Most exoplanet discoveries up to that time were of Jupiter-sized planets that were closer to their stars than Jupiter is to the sun.  The green zone, or 'life zone' is the area within which a planet is a candidate to support life within our current understanding of what life is.  Even then, this chart does not capture the full possibilities for life, as a gas giant like Jupiter or Saturn, at the correct distance from a Sun-type star, might have rocky satellites that would thus also be in the life zone.  In other words, if Saturn were as close to the Sun as Earth is, Titan would also be in the life zone, and thus the green area should extend vertically higher to capture the possibility of such large satellites of gas giants.  The chart shows that telescopes commissioned in the near future will enable the detection of planets in the life zone.  If this chart were updated, a few would already be recorded here.  Some of the missions and telescopes that will soon be sending over a torrent of new discoveries are :

Kepler Mission : Launched in March 2009, the Kepler Mission will continuously monitor a field of 100,000 stars for the transit of planets in front of them.  This method has a far higher chance of detecting Earth-sized planets than prior methods, and we will see many discovered by 2010-11.

COROT : This European mission was launched in December 2006, and uses a similar method as the Kepler Mission, but is not as powerful.  COROT has discovered a handful of planets thus far. 

New Worlds Mission : This 2013 mission will build a large sunflower-shaped occulter in space to block the light of nearby stars to aid the observation of extrasolar planets.  A large number of planets close to their stars will become visible through this method. 

Allen Telescope Array : Funded by Microsoft co-founder Paul Allen, the ATA will survey 1,000,000 stars for radio astronomy evidence of intelligent life.  The ATA is sensitive enough to discover a large radio telescope such as the Arecibo Observatory up to a distance of 1000 light years.  Many of the ATA components are electronics that decline in price in accordance with Moore's Law, which will subsequently lead to the development of the..... 

Square Kilometer Array : Far larger and more powerful than the Allen Telescope Array, the SKA will be in full operation by 2020, and will be the most sensitive radio telescope ever.  The continual decline in the price of processing technology will enable the SKA to scour the sky thousands of times faster than existing radio telescopes. 

These are merely the missions that are already under development or even under operation.  Several others are in the conceptual phase, and could be launched within the next 15 years.  So many methods of observation used at once, combined with the cost improvements of Moore's Law, leads us to our third postulate, which few would have agreed with at the time of 'Cosmos' in 1980 :

Thousands of planets in the 'life zone' will be confirmed by 2025. 

Now, we will revisit the under-discussed factor of accelerating change.  Out of 4.5 billion years of Earth's existence, it has only hosted a civilization capable of radio astronomy for 71 years. But as our own technology is advancing on a multitude of fronts, through the accelerating rate of change and the Impact of Computing, each year, the power of our telescopes increases and the signals of intelligence (radio and TV) emitted from Earth move out one more light year.  Thus, the probability for us to detect someone, and for us to be detected by them, however small, is now rising quickly.  Our civilization gained far more in both detectability, and detection-capability, in the 30 years between 1980 and 2010, relative to the 30 years between 1610 and 1640, when Galileo was persecuted for his discoveries and support of heliocentrism, and certainly relative to the 30 years between 70,000,030 and 70,000,000 BC, when no advanced civilization existed on Earth, and the dominant life form was Tyrannosaurus. 

Nikolai Kardashev has devised a scale to measure the level of advancement that a technological civilization has achieved, based on their energy technology.  This simple scale can be summarized as follows :

Type I : A civilization capable of harnessing all the energy available on their planet.

Type II : A civilization capable of harnessing all the energy available from their star.

Type III : A civilization capable of harnessing all the energy available in their galaxy.

The scale is logarithmic, and our civilization currently would receive a Kardashev score of 0.72.  We could potentially achieve full Type I status by the mid-21st century due to a technological singularity.  Some have estimated that our exponential growth could elevate us to Type II status by the late 22nd century.  

This has given rise to another faction in the speculative debate on extra-terrestrial intelligence, a view held by Ray Kurzweil, among others.  The theory is that it takes such a short time (a few hundred years) for a civilization to go from the earliest mechanical technology to reach a technological singularity where artificial intelligence saturates surrounding matter, relative to the lifetime of the home planet (a few billion years), that we are the first civilization to come this far.  Given the rate of advancement, a civilization would have to be just 100 years ahead of us to be so advanced that they would be easy to detect within 100 light years, despite 100 years being such a short fraction of a planet's life.  In other words, where a 19th century Earth would be undetectable to us today, an Earth of the 22nd century would be extremely conspicuous to us from 100 light years away, emitting countless signals across a variety of mediums. 

A Type I civilization within 100 light years would be readily detected by our instruments today.  A Type II civilization within 1000 light years will be visible to the Allen or the Square Kilometer Array.  A Type III would be the only type of civilization that we probably could not detect, as we might have already been within one all along.  We do not have a way of knowing if the current structure of the Milky Way galaxy is artificially designed by a Type III civilization.  Thus, the fourth and final postulate becomes :

A civilization slightly more advanced than us will soon be easy for us to detect.

The Carl Sagan view of plentiful advanced civilizations is the generally accepted wisdom, and a view that I held for a long time.  On the other hand, the Kurzweil view is understood by very few, for even in the SETI community, not that many participants are truly acceleration aware.  The accelerating nature of progress, which existed long before humans even evolved, as shown in Carl Sagan's cosmic calendar concept, also from the 1980 'Cosmos' series, simply has to be considered as one of the most critical forces in any estimation of extra-terrestrial life.  I have not yet migrated fully to the Kurzweil view, but let us list our four postulates out all at once :

The expected lifespan of an intelligent civilization is rising.  

Telescopic power is rising quickly, possibly at 26% a year. 

Thousands of planets in the 'life zone' will be confirmed by 2025. 

A civilization slightly more advanced than us will soon be easy for us to detect.

As the Impact of Computing will ensure that computational power rises 16,000X between 2009 and 2030, and that our radio astronomy experience will be 92 years old by 2030, there are just too many forces that are increasing our probabilities of finding a civilization if one does indeed exist nearby.  It is one thing to know of no extrasolar planets, or of any civilizations.  It is quite another to know about thousands of planets, yet still not detect any civilizations after years of searching.  This would greatly strengthen the case against the existence of such civilizations, and the case would grow stronger by year.  Thus, these four postulates in combination lead me to conclude that :

Most of the 'realistic' science fiction regarding first contact with another extra-terrestrial civilization portrays that civilization being domiciled relatively nearby.  In Carl Sagan's 'Contact', the civilization was from the Vega star system, just 26 light years away.  In the film 'Star Trek : First Contact', humans come in contact with Vulcans in 2063, but the Vulcan homeworld is also just 16 light years from Earth.  The possibility of any civilization this near to us would be effectively ruled out by 2030 if we do not find any favorable evidence.  SETI should still be given the highest priority, of course, as the lack of a discovery is just as important as making a discovery of extra-terrestrial intelligence. 

If we do detect evidence of an extra-terrestrial civilization, everything about life on Earth will change.  Both 'Contact' and 'Star Trek : First Contact' depicted how an unprecedented wave of human unity swept across the globe upon evidence that humans were, after all, one intelligent species among many.  In Star Trek, this led to what essentially became a techno-economic singularity for the human race.  As shown in 'Contact', many of the world's religions were turned upside down upon this discovery, and had to revise their doctrines accordingly.  Various new cults devoted to the worship of the new civilization formed almost immediately. 

If, however, we are alone, then according to many Singularitarians, we will be the ones to determine the destiny of the cosmos.  After a technological singularity in the mid-21st century that merges our biology with our technology, we would proceed to convert all matter into artificial intelligence, make use of all the elementary particles in our vicinity, and expand outward at speeds that eventually exceed the speed of light, ultimately saturating the entire universe with out intelligence in just a few centuries.  That, however, is a topic for another day.