In 1961, Frank Drake formulated his famous equation to predict the likelihood of intelligent, technological life in the galaxy. Since that time we have made numerous scientific advances. In 1961 we had not found any extra-solar planets, and were not even sure if they existed. Today we have found hundreds of extra-solar planets and now believe that there are planets surrounding most stars.
Drake made his calculation and came up with the number 10. His answer was that there were ten civilizations in our galaxy with intelligent, technological societies with which we could communicate.
A technological civilization simply means a society capable of building radio telescopes to scan the heavens, for without such instruments any extraterrestrial contact is simply impossible. It should be noted that the first radio telescope on the earth was built in 1931. So, by this definition, we have been a technological society for less than one hundred years, a brief moment in the history of the cosmos.
The Drake equation states that:
N = the number of civilizations in our galaxy with which communication might be possible;
R* = the average rate of star formation per year in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fℓ = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space.
But now it would appear that Frank Drake was an optimist. Steven Hawking has predicted that we might be alone in the Universe as the only technological society.
The nearest star to us is a red dwarf star named Proxima Centauri at a distance of 4.24 light years. This is our nearest neighbor in interstellar space, but getting there would take us some 80,000 years traveling at space shuttle speed. Just beyond Proxima Centauri is the binary star system Alpha Centauri A and B at 4.37 light years from our sun. And, what if we went there and found nothing? What would be our next destination and how long would it take to get there?
We are learning how hard and slow the process is to evolve from primitive life forms to advanced, technological civilizations. On earth this process took some four billion years. This means that a planetary nursery must be maintained in a relatively steady state for billions of years in order for an intelligent, technological society to emerge.
Humanity went almost extinct 73,000 years ago from the great Toba super-volcano in Sumatra. Some sources say that only around 10,000 humans were left on the planet, while other sources say that the human population dwindled down to a few hundred or even a few dozen. After millions of years of evolution we almost died out, but a few survived and our species went on to build a radio telescope.
There are new factors, not found in the Drake Equation, that may set earth off as the sole technological society:
The earth is big enough to sustain its magnetic field and the shielding that it produces for billions of years. Because the earth’s core is still molten, we have a magnetic shield that protects us from harmful radiation, coronal mass ejections, and the solar wind that could strip our planet of its atmosphere and water. When Mars lost its magnetic shield that planet died of these effects.
The earth has plate tectonics that continuously recycle the continents and continuously bring new minerals to the surface.
The earth has a large moon that provides gyroscopic stability and prevents our axis from wobbling too much. This provided for climactic stability over millennium in order that civilization may develop and thrive in one place without disruption or dislocation. Imagine, for example, if the earth’s axis tilted so that Europe dropped down to the latitude of the Sahara Desert. Any such civilization at that latitude would be doomed.
The moon was originally much closer to the earth than it is now. In the early days the moons tidal pull upon the earth was much larger. The effect of this tidal pool was to stir the waters in the inter tidal zone. This tidal stirring, this mixing of nutrients, proteins, and amino acids may well have aided in the formation of life.
The earth has big brother Jupiter that protects us from asteroid bombardment by corralling many errant space rocks and ice balls before they hit the earth. This was recently demonstrated by the Jovian capture and destruction of the Shumaker-Levi 9 comet.
The earth orbits a single star. Any planets in multiple star systems would be at a distinct disadvantage. It would be very difficult for a planet in a multiple star system, such as Alpha Centauri, to find a stable orbit in the “Goldilocks” zone where it is neither too hot nor too cold. Also, it is likely that at some point in time the planet would be either torn apart by gravitational forces or slung out into the interstellar void.
Our sun will shine for another five billion years. Our technological civilization is flourishing as our sun is in the middle of its useful life. Scientists believe that the world will be habitable for at least the next billion years or so, unless we destroy ourselves earlier. After the next five billion years we know that the sun will swell up into its red giant phase, with its outer edged touching the earth’s orbit. Long before the sun reaches its full expansion the earth will become a scorched, lifeless cinder.
Other planets in our galaxy may not be so lucky.
Carl Sagan worried that we might have reached the required level of technological development (i.e. radio telescopes) just in time to destroy ourselves with nuclear weapons. For today’s generation our main worry might be global warming. It is sad, but it seems that achieving the technological pinnacle of a radio telescope gives us power over nature to destroy ourselves and our habitat.
Steven Hawking said that since we might be the only intelligent, technological society in the galaxy, we may want to survive and continue.