Alien Contact Forthcoming?

There seems to be a great deal of optimism amongst scientists regarding the existence of life in the cosmos. Some astronomers argue for the ubiquity of extraterrestrial civilizations and suggest that we will likely receive a communication in the upcoming decades. 

World famous physicist Stephen Hawking thinks that we should avoid advertising our existence to any aliens that might be listening. Many others agree with him.

Even the astronomers at the Vatican have hopped onto the alien bandwagon.

Youtube Video: Vatican Astronomer on Aliens

With all the talk about aliens and the search for extraterrestrial intelligence of late, I decided to revisit the equation for predicting the number of civilizations in our galaxy; the Drake equation.

To quote Wikipedia:

The Drake equation states that:

where:

N = the number of civilizations in our galaxy with which communication might be possible;

and

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 such civilizations release detectable signals into space

Here are my estimates of those variables:

R* - There are about 100 billion stars in our galaxy and the galaxy is thought to be on the order of 10 billion years old. Dividing those numbers we get an average of about 10 stars per year.

fp - Planet formation seems to be a common part of star formation. However, many star systems contain multiple suns that will cause any planets have chaotic unstable orbits and result in their destruction. Given that, I think 1/4 is a generous estimate.

ne - Since there are roughly 200 planets and moons in the solar system and maybe 4 that might have conditions for life (Earth, Mars, Europa, Titan) 1/50 is a reasonable estimate. This assumes that the solar system is an average planetary system. The real number is probably much smaller. Chaotic stable orbits in multi-star systems likely result in planetary environments too extreme for the development of life. Stars near the galactic core would probably be unsuitable for the formation of life bearing planets. Its also possible that there is some unusual feature of Earth (our giant moon perhaps?) or the Sun that make life more of a freak occurance.

fℓ - Earth's fossil history shows that life started very shortly after the planet cooled. This suggests that when the conditions for life are met, its easy to get it started. So this is probably a number pretty close to 1.

fi - Since complex life appeared somewhere between 1-0.5 billion years ago and life was apparently around for about 4-3.5 billion years, I'd divide 0.75 billion by 3.75 billion and say complex life only appears about 1/5 of the time. Because intelligence is a useful evolutionary advantage I would think that it almost certainly evolves whenever complex life arises, so 1/5 is a reasonable estimate for intelligent life.

fc - There are other intelligent life forms on Earth besides humans, but they lack things like long life spans, manipulative appendages, abstract language, and social structure that are needed to create culture and technology. I'd say given cephalopods, dolphins, social insect colonies, apes, elephants (which I think are the non primate organism most likely to form an intelligent civilization), and man. I'd say 1/6 isn't a bad projection. Although, one could alternatively examine human history to arrive at an estimate. We've only had technology for about the last 10,000 years and fossil evidence dates humans back to about 50,000-100,000 years, so looking at that ratio we still get around 1/5 to 1/10 so I stand with my 1/6 estimate from earlier.

L - Since technology has been around for about 10,000 years, it doesn't seem unreasonable to think that "broadcasting" technology will subsist for at least another 10,000 years...I think thats a decent estimate

Multiply it all out and you get around 16 or 17 civilizations in our galaxy. However that was with an extremely generous estimate of planets around stars that can support life I think. You have to remember that stars near the galactic core will probably be unsuitable for life and that would probably reduce our estimate quite a bit.

This is not very promising for humanity’s alien search. The galaxy’s radius is around 100,000 light years. If you assume that the civilizations are evenly spaced on the outskirts of the galaxy’s circumference, then the spacing between us and E.T. would be around 20,000 light years. This means that it would take us about 40,000 years to send and receive a message.