The Great Filter and Intelligent Life Elsewhere in the Universe
I had roughly this idea myself a few years ago: The Great Filter.
Not 1996, though... Probably closer to 2004. Ah well.
Not 1996, though... Probably closer to 2004. Ah well.
posted by Winston Smith at
9:43 PM
6 Comments:
Seems kinda presumptuous of me. I mean, even if intelligent life is only occurring at the rate of one species per galaxy at any given moment, there are still billions of instances of intelligent life in the universe at any given moment.
And it ain't like it's unlikely that we wouldn't run into each other if separated in that fashion.
The sheer size of the universe and the staggering number of potential homes makes me think we're just those ancient Greeks, thinking Greece was the center of the world.
We live in the middle of an expanding sphere almost 100 light years in radius of radio transmission. As it says in the Hitchhikers' Guide to the Galaxy, space is really big. We've barely taken baby steps outside our own planet, so I think it premature to say that we're the only life in the Universe, or even the Milky Way Galaxy.
From archy and mehitable, by the writer Don Marquis.
warty bliggens, the toad
i met a toad
the other day by the name
of warty bliggens
he was sitting under
a toadstool
feeling contented
he explained that when the cosmos
was created
that toadstool was especially
planned for his personal
shelter from sun and rain
thought out and prepared
for him
do not tell me
said warty bliggens
that there is not a purpose
in the universe
the thought is blasphemy
a little more
conversation revealed
that warty bliggens
considers himself to be
the center of the said
universe
the earth exists
to grow toadstools for him
to sit under
the sun to give him light
by day and the moon
and wheeling constellations
to make beautiful
the night for the sake of
warty bliggens
to what act of yours
do you impute
this interest on the part
of the creator
of the universe
i asked him
why is it that you
are so greatly favored
ask rather
said warty bliggens
what the universe
has done to deserve me
One problem with the filter concept is that it doesn't really consider the issue of timing. The fact that humans have not seen evidence of interstellar civilization in our neighbourhood might not mean that interstellar civilization is an improbable phenomenon. We might in fact simply be a very early expression of a common one. The earth is about four billion years old. For most of the earth's history, it was inhospitable to life. A great deal of planetary evolution had to take place before any biological process could take place, and there is little reason to think that the evolution of the earth was unusually slow. Can't rush cooling. So too with biological evolution. Dinosaur men not withstanding, it looks like the intelligent life evolved just about as early as it reasonably could. Stellar evolution also tells in favor of the earth and its creatures being about as fast on the scene as plausible. From my understanding, a star such as ours, with rocky planets, is third generation star at minimum. The galaxy itself is estimated to be eight billion years old, so that gives us only four billion years in which to run through two generations of metal free and metal poor stars going nova to the material for a sun with a rocky planet. Granted, these prior generations of stars would burn a great deal faster than ours, but their material also has form from the nebulae, which is a slow process. All in all, it looks like human life formed with very little delay relative to what is possible.
Civilization is the result of a terrifically long sequence of chance events. Put aside the likelihood of each individual chance event coming to pass, and focus on timing. The past history of an interstellar civilization will represent a portfolio, so to speak, geological, biological, and technological developments, each of which could only take place in a limited number of sequences. The timing of events on that sequence may largely be a matter of chance: ie, given that the are multi-celled organisms, how long will it take for some of them to develop nervous systems? Given that a civilization has discovered electro-magentism, how long will it take to develop radio communication? Even so, since there are so many milestones, the chancyness of their timing can be expected to smooth out, the lateness of one compensating the earliness of another. We can expect the lengths of the histories of interstellar civilizations to be very, very similar. And, since we're all evolving in a galaxy with a homogenous generation of metal heavy stars, the result could be an almost freakish level of synchronicity. We could all be poking our heads out at roughly the same time.
Yo, as a generic response to everybody...
I was under the impression that we're still basically using a version of the Drake equation to estimate the prevalence of technologically-advanced civilizations... And I'm also under the impression that our best estimates predict that we ought to have detected some by now. This is basically the Fermi paradox.
Now, of course there's lots of speculation built into the Drake equation, and there are disagreements about how likely it is that SETI would have found anything by now even if we got the Drake stuff right...
But, anyway, there's at least some reason to think that we need an explanation...
What I was trying to get across is that the Drake equation and theories that try to supply values for its terms, like the filter theory, are problematically unindexed to time. They treat star systems like balls in an urn, already black or white, just waiting to be examined. This causes us to illicitly infer from the present infrequency of interstellar civilizations to improbability.
The output of the Drake equation confuses me. Going with the values given in the original estimates, we have:
R = 1/year (1 star formed per year, on the average over the life of the
galaxy; this was regarded as conservative)
fp = 0.2-0.5 (one fifth to one half of all stars formed will have planets)
ne = 1-5 (stars with planets will have between 1 and 5 planets capable of
developing life)
fl = 1 (100% of these planets will develop life)
fi = 1 (100% of which will develop intelligent life)
fc = 0.1-0.2 (10-20% of which will be able to communicate)
L = 1000-100,000,000 years (which will last somewhere between 1000 and
100,000,000 years)
Multiply all that together and we have N, which is described by Drake as "the
number of detectable civilizations in our galaxy." But that doesn't seem
right, given that the value should be expressed in years, right? Say I choose the values as:
R = 1
fp = 0.5
ne = 1
fl = 1
fi = 1
fc = 0.2
L = 10,000
If I try to express the equation verbally, I find myself saying something like: on average, every twenty years a star is formed with a planet which develops intelligent life that can communicate for a duration of 10,000 years.
That seems incomplete, no? Don't we need to figure out how many civilizations ought to be simultaneously coexisting with us, not just how many develop per
year which can communicate for a duration of 10,000 years?
Anyway, the point is that it seems reasonable estimates include figures such as 1,000 per galaxy at any given moment. There are 400 billion stars in our galaxy. So that means one of every 400 million stars has a planet with communicating intelligent life? I
guess you have to factor in the expansion of these civilizations, but
approximating such a thing would be difficult and regardless, that's a very
broad search area.
Do we really have the capabilities sufficient to warrant the expectation that, were an intragalactic neighbor somewhere in the closest 400,000,000 star systems that we would surely know about it? Asking "where is everybody" seems fairly non-paradoxical to me.
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