Intelligent Life in the Universe
Intelligent Life in the Universe?
A Statistical Estimate for the How Many Are Out there
We can write down a statistical equation to estimate the
number of civilizations which currently exist in our Galaxy .
This equation has three parts:
- An astronomical part which basically predicts the number
of planets that exist in the galaxy which have a liquid surface
- A biological part which basically estimates the probability
that intelligent life will evolve on those planets which have a liquid
- A socio-economic part which determines the survivability of the
civilization on that planet
Remember, we seem to be part of this Process
Our choice now is which divergent path do we choose? - the long term one
or the short term one?
So, here is the equation:
- The Astronomical part is the first three terms
- The Biological part is the next two
- The socio-economic part are the final two terms
- The uncertainty associated with each term grows as you move
down the right hand side of the equation
So what should the estimates be? In class we arrived at a
bunch of different numbers.
Remember, that if you want the
final answer to be 1 then you have to identify which term is
unique (that is, it only happened here). Here are my estimates
which are then explained below:
- The Astronomical Part: Basically, observations suggest
that planetary formation is a natural consequence of star formation. Nearby
stars exhibit dusty disks in orbit about them which are likely solar systems
in the process of formation. For every star of some temperature, there is
a zone around it called the habitable zone in which the temperature is
right for the condensation of water vapor. The width of the habitable
zone depends on the temperature of the star. If you make planets via
the acretion of small grains then it is likely that one of the acreting
planets will land in this habitable zone. In our case, if the sun were
a cooler star we would have this class on the second planet from the
sun, if it were hotter, we would be Martians. Hence, I regard the formation
of planets with a liquid surface as ubiquitous.
- The Biological Part: I believe that given enough time, chemistry,
mixing in the liquid surface, local concentration of organic molecules,
etc, will eventually lead to a self-replicating system. That process took
a billion years to happen on the earth so maybe all you need is time.
But, since the planet is subject to random catastrophe, there are all
kinds of problems that species have to overcome, I rate the probability
of reaching intelligence as only 10% (of course it could be much smaller!).
- The Socio-Economic Part: Okay, does intelligence begat Technology?
Is it the manifestation or the asshole of Intelligence? Does the capacity
to destroy our planet mean that we can never really be Intelligent?
And what about our lifetime as a technical civilization, will it be
short or long? I assume again only a 10% probability of intelligent
civilizations becoming technological (maybe most are smarter than US?).
So overall, I have assumed that on only 1% of all planets with a liquid
surface does a civilization which builds radio telescopes arise.
For the lifetime I adopt the following argument:
- 99% of all technological civilizations extinct themselves
after 100 years
- The remainin 1% survive, in harmony with their planetary resources
for 1 billion years.
- This leads to an average lifetime of 10 million years (1% of
- Notice, that the number of civilizations which currently exist is strongly
correlated with your estimate of the average lifetime.
- Multiply it all together to get one million civilizations which
now exist. This is actually a small number.
Why one million is a small number
- What is the Moral: Life, All Life is Rare whether its
yours, your neighbors or your neighbors pet slug.
- Yes but what about colonization? The argument why N must
Implications of the above argument:
- We are it we are suppose to colonize
- Multi-generational committment to this scheme is impossible
and therefore it is always doomed to failure
- Why would the blue dots choose to colonize?