The Probability of Extra-Terrestrial Intelligence

Is there any good reason to think there is intelligent life in the
universe that is not from Earth?

There have been UFO sightings, and an organization dedicated to
looking for extra-terrestrial communications (SETI), but nothing very
convincing has come out of this line of evidence, scientifically
speaking. That is, it is not reasonable to believe we have been
visited or contacted in any way by an extra-terrestrial intelligence
(ETI). If you need convincing of this, please, please, read the
relevant chapter of Shermar's Why People Believe Weird
. In fact, read the whole book.


So maybe there are ETIs out there we just haven't heard from yet. What
is the probability of this? One attempt to estimate the number of ETIs
in our galaxy is the Drake equation:

number = N x f x n x f x f x f x f

p e l i c l

The lower letters are my attempt to do subscripts in HTML.

This means that the number of radio-communicating ETIs is the number
of stars in the milky way times the fraction with orbiting planets
times the average number capable of supporting life, times the number
fraction on which life actually evolves, times the fraction that
evolves intelligent life, times the fraction of the universe's life
during which the ETI communicates with radio waves.

Depending on what numbers you put in these variables (have any good
idea of the fraction of planets on which life actually evolves?) you
can get widely differing numbers, but most people who do end up with
high numbers (obviously there could be a biased sample effect
here). For example, Carl Sagan estimates a million; Drake estimates
ten thousand.

How encouraging! (i.e. if you don't think they would be out to destroy

Then why has SETI failed to hear from them? Why haven't they shown up
on our doorsteps and made us welcome to the galactic community? There
are a few answers for this.

SETI's answer is that we haven't been looking at enough wavelenghts of
enough portions of sky to see the signal.

An answer from science fiction is that we are not ready. That is,
perhaps evolving worlds are left alone until they reach a certain
level of technological competence. This is the "prime directive" idea
from Star Trek. In the film Star Trek: First Contact, as soon
as the first warp drive is tested on earth, the Vulcans just... show
up. It's exciting to think this might be the case. What tech are they
waiting for?

I don't find it very convincing, though, because you'd think that,
even if they'd come up with new forms of communication, they'd
still be communicating with light waves (radio, gamma, etc.) and we'd
"hear" it. Or if they stopped, it still takes a while for light to get
to us, and those communications would still be propogating.

And as Ray Kurzweil points out, it seems unlikely that all of
the civilizations would follow this rule to the letter.

There are so many variables in the Drake equation. And we don't have
very good estimates of, well, any of them. Other reasonable numbers
make N = 1, which would be... us.


Ray Kurzweil, in his book The Singularity Is Near, presents an
interesting take on this debate, which I will outline below.

Astronomer N. S. Kardashev introduced the idea of Type II and Type III
civilizations. Type II civilizations have harnassed the power of their
own star for use in communications. Type III have done so with their
own galaxy. According to current trends, our civilization will become
a Type II in the twenty-second century.

If there are billions of civilizations ahead of us in the galaxy,
there should be many Type IIs out there, and some Type IIIs as
well. But even one Type II would be sending out enough communications
to be picked up by SETI.

Therefore, it's unlikely that there are other ETIs in the galaxy.


This is not to say there is no other life. It could be that there is
other life out there but it's not that smart. We might find
single-celled organisms or something. Right now, though, Kurzweil's
argument seems pretty convincing to me. If there were a few planets
with life, why not many? And if many, why did no others become
intelligent? Sad as it makes me, we just might be all there is out

This back and forth is a great example of how our opinions on
mysterious things can switch around based on new arguments that relate
to things we never even thought relevant. I would not be the least bit
surprised if my mind changed again at some point, based on some new
argument that involves some information about something I can't
predict now.
Pictured is a view I took from an airplane with my cell phone.


Kurzweil, R. (2005). The Singularity Is Near. Penguin Books.

Shermer, M. (1997) Why People Believe Weird Things. Freeman.


Anonymous said…
This comment has been removed by a blog administrator.
Anonymous said…
Is outbound communication a necessary premise for ETI? Maybe they're just introverts.

I don't have a problem with the idea that we're the only sentient creatures in the universe.

But I have read enough science fiction to be glad nobody's "done unto us what we would do unto them," yet!

Anywhom. Nice photo!
jowdjbrown said…
If you need convincing of this, please, please, read the relevant chapter of Shermar's Why People Believe Weird Things. In fact, read the whole virtual assistant

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