Extra-terrestrial Civilizations

Are we alone? Contact … Direct contact through traveling to the stars and their planets Will be a challenge because of the vast distances involved and the (slow) speeds we can travel

Are we alone? Contact … Radio communication more likely possibility for contact Electromagnetic radiation travels at the speed of light.

Civilizations Will life always develop technology? Some societies on Earth have not developed the means to communicate with ETs. Will a society want to communicate? A society may develop the means to search for ET but elect not to attempt to reach out.

Consider... How many intelligent civilizations exist? How long on average do they last? How does communication proceed?

Drake Equation One possible way to estimate the number, N, of civilizations. N = N s x f s x p s x l s x l c x L

Stars in the Galaxy, N s The number of stars in the Milky Way galaxy … about 300 billion.

Suitable stars (fraction), f s Star must be old enough to allow life to develop: spectral types F, G, K Star must have enough heavy elements to form planets … 0.005

Suitable planets in a Solar System, p s To date, extra-solar planets have been ‘hot Jupiters’ Planets to sustain life need to be in the habitable zone around a star … 1.0

Fraction of planets suitable for life, l s Very speculative … sample of 1 only to date (Earth) If a planet is suitable for life, good reason to think life will develop Conservative approach suggest: Earth and Mars could produce life … 0.5

Life develops a civilization, l c Again, very speculative. Simple life started on Earth nearly 3.5 billion years ago. Extinction level events common … for example 250 and 65 million years ago.

Life develops a civilization, l c As long as some form of life exists after an extinction event occurs, natural selection should continue and life redevelops. Assuming life develops then a case can be made that a form of civilization is inevitable … 0.33

Lifetime of a civilization, L Firstly, the age of our Milky Way galaxy is 10 billion years. How long have we had the ability to communicate with ET … about 50 years. How many times have we sent a communication … not many! Radio telescope, Pioneer and Voyager

Drake Equation Result Substituting into N = N s x f s x p s x l s x l c x L N = 300x10 9 x0.005x1x0.5x0.33xL/10x10 9 = L/40 Large numbers top and bottom tend to cancel out.

Range of answers … Depending upon your optimism or pessimism, N can vary significantly … From 10L (Carl Sagan,1978) to a very optimistic 120L to a pessimistic L/10 billion If civilization survives for 100s or 1,000s of years then N could be very large indeed.

Survival lifetimes Dinosaurs lived for 150 million years … can we survive for longer thus increasing L substantially? Some species of life have lived for over 200 million years on Earth. Humans are living ‘outside’ the laws of Natural Selection … may well reduce L. Upper limit based upon life of a star … 10 billion years.

More than the Milky Way … Ours is not the only galaxy in the universe

Why communicate at all? Curiosity The urge to talk and listen! The hope to learn/gain knowledge The need for resources and/or living space Because we can!

Why not? Fear (enslavement, destruction, etc) Inertia … happy as we are Economics … expensive to try and need to deploy resources appropriately. Of course, contact may happen by accident … leakage of radio and TV signals.

How far away is a civilization? Even assuming optimistic values for the Drake Equation, the closest civilization maybe 100s of light years away! Average stellar separation in the outskirts of a galaxy … 5 to 10 light years. Two way communication then becomes a problem.

The urge to explore … In our Solar System, we seem keen to explore and colonize …

Types of civilizations Kardashev spawned the following classification scheme: Type 0 … inability to communicate with ET Type 1 … like us with limited technology Type II … almost 100% utilization of parent star’s energy (Dyson spheres) Type III … utilization of a galaxy of stars’ energy!