[ExI] Eternity in six hours: intergalactic spreading of intelligent life and sharpening the Fermi paradox

John Clark johnkclark at gmail.com
Mon Sep 9 20:54:59 UTC 2013

Stuart Armstrong and Anders Sandberg wrote:

> There are about 2. 5* 10^ 11 stars in the Milky Way and about 5*10^22
> stars in the visible universe. Planetary systems appear to be relatively
> common

Those are some big numbers, but I think biology may be able to come up with
numbers that are just as big as those that astronomy can and perhaps even

> Assuming the mediocrity principle [...]

That is quite an assumption! The average cubic meter in the universe
contains just one hydrogen atom and about 5 times that amount of mass in
the form of Dark Matter, whatever the hell that is. So the Earth
environment is very very very unusual.

> Even if a very small fraction such worlds developed intelligence, e.g.
> 10^-9 it would imply hundreds of intelligent species in the Milky Way.

But where did you come up with that 10^-9 figure? Why isn’t the probability
of evolving intelligent life in a given solar system 10^-30? I don’t think
astronomy has a monopoly on big numbers.

> the Earth is certainly not among the earliest terrestrial planets.

I don’t believe we know that to be the case, it could be that there are no
terrestrial planets significantly older than Earth's 4.5 billion years. And
if it had taken just 800 million years longer for intelligent beings to
evolve on the Earth humanity would have discovered fire just about the time
when life of any sort would no longer be possible because the sun would be
starting to get off the main sequence.

 > Indeed it has been indeed it has been estimated that of the stars that
> could have planets with complex life on them in the Milky Way, 75% of them
> are older than our sun

But we don’t know if any of those very old stars, such as those found in
globular clusters, have planets. We do know that today those very old stars
contain very little metal and when they were first formed long ago they had
even less. By “metals” astrophysicists  mean every element except hydrogen
helium and lithium, and you can’t make life with just that, or even make
planets except for gas giants.

> if the alien civilisations wished to remain undetectable,

It is very hard for me to believe that a super mega advanced civilization
would think we were even worth the bother of hiding from.

> it would be relatively easy for them to do so. We are unlikely to notice
> a single Dyson sphere in a distant galaxy.

I think we could probably detect a Dyson sphere with its distinctive
infrared signature if it were within several thousand light years of us,
and we could see a galaxy of Dyson spheres if there were one anywhere in
the observable universe. But we see nothing.

> it was possible for humans to launch the colonisation of the entire
> universe on scales of time and energy that are cosmically insigni cant
> only requiring about two replication stages to reach every star we could
> ever reach, with a rapid launch phase. If human civilisation could achieve
> this, then it is highly likely that any star-spanning alien civilisation
> would be capable of doing so as well.

And that is the key mystery right there, why doesn’t the universe look
engineered? I can think of 4 explanations:

1) Nonexistence.

Maybe we’re the first, after all somebody has to be.

2) Extinction.

Could every single civilization really engage in a war so brutal that it
didn’t leave any survivors at all? During the cold war that possibility
seemed somewhat more likely to me than it does now.

3) Unknown physical laws that prevent intelligence from performing large
scale engineering.

I can’t say anything about stuff that’s unknown except that at least so far
there is no hint of anything like that.

4) Stagnation.

ET may exist but he’s a couch potato. If you had complete control of your
emotional control panel you might not want to do anything but sit and
experience pleasure. I do see hints that this might be the case in the
increased difficulty humanity has had in dealing with drugs.

I think numbers1 and 4 are the most likely explanation for the Fermi

  John K Clark

> it could be that there exist some fundamental limitation
to what can be automated, whether macroscopic objects can be accelerated
to high speed, reliably sent over long distances, or function over very long
periods of time, making interstellar or intergalactic colonization
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