
Originally Posted by
pauln
Well, there you've done it - opened a most crawly can of worms.
It begins with the Drake equation, estimating the number of intelligent life forms within our galaxy where communications might happen. The equation multiplies a series of terms:
average rate of star formation
fraction of those stars with planets
average number of those planets potentially supporting life
fraction of those planets that actually develop life
fraction of those planets that develop intelligent life
fraction that develop a technology, detectable signs of their existence
length of time the send detectable signals
The insidious thing about the Drake equation is that if you feed in the current best estimates and then reduce each of them by 50% or even 90% just to be real conservative, the resulting number of stars hosting intelligent life is huge, and the subsequent galactic density estimate to figure where the nearest might be is pretty close. That is why Fermi asked, "Where is everybody?"
There is a pretty good possible answer, but people don't see it in the same way that people imagining space travel a few hundred years ago might have imagined they would need to take horses with them to the Moon.
First, review how we got to today.
4.6 billion years ago
the Earth forms
4 billion years ago
self replicating, organic molecules, structure without cell walls
3.4 billion years ago
prokaryotic organisms, microscopic, single-cell with cell walls, single chromosome, no nucleus
1.4 billion years ago
eukaryotic organisms. larger microscopic, single-cell, with a nucleus, other inclusions like mitochondria
560 million years ago
soft-bodied organisms, fairly to barely microscopic. first multicellular (worms and plants)
So, in short
replicating molecule to microscopic worn in 3.5 billion years
microscopic worm to man with just another 0.5 billion years
Now, we look at distant galaxies to find the earliest indication of high metalicity stars (cosmologists call all elements beyond hydrogen and helium as "metals") for the formation of rocky planets and... opps! We find them to be 11.2 billion years old, a little too soon to have formed after the Big Bang in the current theories.
The presumed rocky planets hosting life might be early or late in their development of life - we might be observing them as the Earth was 4.6B years ago (or as the Earth is now if the age of the universe is extended from current 13.8B to 15.8B), so the intelligent life there could be between 6.6 to 11.2 billion years ahead of us... lets go with a conservative 6B years ahead of us.
We saw that 3.5B years got from molecule to worm and 0.5B years more got to man. It is time to think about what intelligent life as we know it (us) might become after another 6 billion years of development - what the aliens might be right now...
If you're still with me, let's look at the ancients, who believed that the fundamental particles had agency rather than being dead matter (earth, water, air, and fire). The modern view it to consider the fundamental particles as dead and shift the agency to fields, which are invisible and immeasurable without placing a test particle and attributing its motion to the field (this is considered an improvement).
So let's replace fire with light; they thought of the Sun and stars as fire, but light seems to be a better description, and now we can examine the levels of life schematically as we know it on the Earth.
Level 1
Modern view is that earth, water, air, and light have no agency, know nothing, are dead matter.
Level 2
Plants, which display some agency - they grow roots down into earth and branches up, actively seek water and light, exchange light and air for energy, etc.
Level 2 has some "awareness" of level 1, is all about and around level 1, reside on it and in it, and consumes it for its own purposes, and level 1 knows nothing of this.
Level 3
Animals live in and around and about level 2, make their homes in it, consume it, and display strong agency and awareness of level 2 (and level 1). Level 2 has no knowledge of level 3.
What can be said as a level 3 (us!) about the nature of level 4, whatever that might be. We might guess that the hierarchical relationship and its asymmetries might continue in form:
Level 4 would be
- totally aware of us and all levels below 4
- invisible, inaudible, untouchable, totally imperceptible to us
- about, around, and within us all the time, unknown to us
- live in us, consume us in some fashion for their own purposes
There may likely be more levels. Douglas Adams described an advanced intelligence as "a super-intelligent shade of the color blue.” Those that have studied the extremely long term future of the universe will recognize a resemblance to the time when only cold black holes remain encircled by orbiting light.
As far as problems of long distance space travel and other things we have not even thought of, I believe that with billions of years to work on it, there is no problem that can't be solved. Whatever the level 4 folks are, I tend to think they may travel from one galaxy to another with about the same effort as Samantha used to wiggle her nose (Bewitched). All of our protestations that something can't be done are echos of needing horses on the Moon... as are all the ideas of "people" visiting in space craft. Basically, we may probably not be in any position to imagine, recognize, or perceive whatever other intelligence forms are out there (statistically they must be ahead of us on the order of our regard for the microscopic multicellular worm).
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