
The Great Filter – Are We Almost Past It? (1998) - gwern
http://mason.gmu.edu/~rhanson/greatfilter.html
======
exratione
Two things to bear in mind when thinking about the Fermi paradox:

1) The more important observation is that everything we see is a wilderness of
apparently natural origins and processes, not that we have apparently not been
visited.

2) No hypothesis involving choice that leads to failure to carry out self-
replicating colonization can explain (1). All it takes is one small group in
one sufficiently advanced species. This rules out wolves, berserkers,
relinquishment, self-destruction, and so on and so forth.

Clearly something is missing or incorrect in how the pieces of the various
sciences fit together to explain what we see. Some of the best reading on the
subject is speculation on what it is that we don't know or the relative odds
on where the present consensus is incorrect.

~~~
chevman
Can you suggest some of your favorite speculations? Or links to other
material?

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sgt101
There is a review in the FT today of "The Future of Violence" a book in which
the authors apparently (I haven't read it) assert that as technology improves
the risk of a violent individual to society increases (because that person has
more leverage).

This raises an interesting problem : to make it as a society may require a
high level of dynamism and aggression. To cope as a society (as technology
becomes more potent) passivity and sensitivity may be necessary. It may be
that there is no balance, and that if you have enough vim to create a
technical society you will reach a point where progress becomes impossible due
to progress so far.

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Udo
There is a disconnect between these two statements:

" _No alien civilizations have substantially colonized our solar system or
systems nearby. Thus among the billion trillion stars in our past universe,
none has reached the level of technology and growth that we may soon reach._ "

While the article is in a way all about exploring that disconnect, it's a bit
strange to find it written down so explicitly in the conclusion. We can
ascribe a very high level of confidence to hypothesis that neither our own nor
any of the directly neighboring star systems have been colonized. But to
postulate that therefore the universe has not yet produced a civilization as
technologically sophisticated as our own is still a non-sequitur, at least in
my opinion. The article also makes a lot of assumptions (it has to!), some
plausible, some seemingly arbitrary, which might in the end not be important
factors at all. For example, any consideration about radio communication must
be on very shaky grounds, in particular when charting the absence of it.

The reason why we're not seeing alien neighbors or predecessors (which would
be "neighbors" in time), might well be a combination of factors. While we can
exclude certain scenarios, such as a cloud of Von Neuman Probes eating the
galaxy, it still leaves room for a lot of little factors that can change the
galactic stage for us in a fundamental way - especially if they work in
conjunction.

For example, the average duration of the technologically recognizable phase a
civilization goes through may be smaller, and there may well be less of them
than expected. In addition, willful avoidance or isolation may well play a
role; the zoo hypothesis is an extreme example of this, but in a sparse cosmos
the measures you have to undertake in order to isolate an emerging
civilizations become less heroic.

It's also worth mentioning that we ourselves are not past the Filter by any
means. In fact, as time progresses, it seems to become less likely we'll ever
move off the Earth as an exclusive habitat. Part of this is due to psychology,
we could have made it happen by now but didn't. The best bet at becoming an
interstellar civilization right now seems to be to wait until we're pure
computer systems, unburdened by aging and the passage of time, but that
development, too, might end up being something we never elect to actually
pursue.

Luckily, this whole thing is a mystery we can solve over time, just by
gathering data about what's out there.

~~~
exratione
The problem is that if you exclude the scenarios that obviously didn't happen
you are still left with no likely scenarios given the present consensus
understanding of biology and physics.

The timescale for megascale engineering to occur throughout our galaxy as the
result of the launch of one megascale engineering minded self replicating
probe is small (1 million years) in comparison to the age of the galaxy (13
billion years). It is unlikely that we are sitting here while someone else is
in the process of doing it; that's not the scenario to focus on.

All it takes, remember, is one small group in one sufficiently advanced
culture to start this going. Some (post)human group will clearly do it at some
point if we as a species continue. Why hasn't someone already done it, where
"it" is visibly engineer the totality of the future light cone?

The problem is less one of why don't we see Dyson spheres and other similar
type II projects within a few hundred light years of our position, and more
one of why do we see no obviously altered galaxies among the hundreds of
thousands cataloged to date. At this scale the zoo hypothesis looks stretched,
and the simulation argument begins to look more plausible.

~~~
Udo
Good points, but I'd like to offer some counter arguments to the megascale
engineering idea, hopefully without sounding too pedantic.

The need for megascale projects is not as obvious as it's sometimes made out
to be. There might well be reasonable limits beyond which the maximizing of
habitat space and energy consumption tapers off in utility. Even if our
civilization continues on its present course, it's not certain that we will
get to the point where we (or some of us) feel the need to change the face of
the galaxy. If you go one step down from the galactic stage, the detectability
of solar system-scale megatech is also open to debate, especially as you move
beyond a couple hundred light years from here.

You're right of course when you say all it takes is one civilization (or even
one member of a sufficiently advanced society) to undertake projects that are
liable to make all kinds of strange phenomena appear in our night sky. But the
number if beings capable of doing so on a whim, multiplied by the chance
they'd be interested in such things, might be very very small without breaking
any of our current expectations about biology and physics.

Finally, I'd like to address the simulation argument. There are two extreme
ends of the simulation scenario spectrum.

At the one extreme, we're talking about an artificial reality made especially
for us, humans. This would be the popular "Matrix"-style simulation. No
scientific argument I've heard so far makes it a convincing model for the
reality we live in, _except_ as a possible explanation for the Fermi paradox.

At the other end of the spectrum, we have a full simulated universe. It's hard
to argue for or against that notion, simply because either way it fits with
our observable reality. The catch is of course that it's a neutral proposition
with no impact on us at all. This variant does not offer _any_ explanation for
the Fermi paradox.

As I see it, the simulation argument as pertinent to the Fermi problem offers
two options, neither of which are intellectually appealing: one is a
borderline-untenable just-so make-believe world where all rules are an
illusion and anything can happen, and the other one is virtually
undistinguishable from our "normal" world, up to and including an absence of
any obvious explanation for the Fermi paradox.

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Zigurd
There remain some big tests, among them: Can we accumulate and release enough
energy to take us to the stars without having a civilization-ending war with
ultra-destructive directed energy weapons? Can we avoid mistakes in modifying
life, and in nanotech, that would cover the planet in goo? Can we master
germline modifications of humans without doing something that ends with no
humans, and no post-humans? So plenty of filter to go yet. Never mind the
smaller-scale "do we have way too many humans already to not overheat the
planet we're on?" questions.

~~~
wyager
>Can we accumulate and release enough energy to take us to the stars without
having a civilization-ending war

This is why, if I invented antimatter production, I would absolutely demand
that it not be used on Earth until it had been used to send hundreds of human-
bearing seed ships to other solar systems. The risk is too great.

~~~
im2w1l
Imo, we should be sending out seed ships with hardy microorganisms already
now.

------
PeterWhittaker
We suffer from hubris when we label it the "Fermi _paradox_ ": It implies that
somehow we are interesting, worth visiting. If we are, it may well be as a
cautionary tale or for tourism.

Consider the energy and material engineering necessary to achieve long-
distance space transport of any sizable amount of people, equipment, and
supplies. Regardless of whether the transport is subluminal or FTL, the energy
requirements are tremendous and the engineering requirements for a durable
vessel astounding.

My guess is that by the time our materials science and our energy production
are up to the task, our interests may well have changed - because (and here I
speculate wildly) science at engineering at that level will reveal so much
about the fundamental nature of the universe and give us so much interesting
practical technology that biochemical life clinging desperately to lucky rocks
in the lucky zone won't be near so interesting anymore.

No one comes near because we have nothing to offer those able to come near and
get home again to report what they found.

As to simply detecting signals, we have to consider how lucky we are to have
so much ore so close to the surface: Metallurgy and eventually radiated
communications were a natural for us.

Other civilizations may well start with fantastically engineered wood and
eventually plastics, and go all-fibre, all line-of-sight, and have very, very
different communications systems, systems undetectable at any remove.

~~~
thesteamboat
"No one wants to talk to us" is not a sufficient explanation. We need to be
able to explain why we don't observe any stellar engineering. Assuming alien
civilizations they either 1) can't make use of the most prominent energy
sources around, 2) choose not to for some reason, or 3) we can't detect what
they're doing.

1 and 2 don't make sense if you assume that there are many alien civilizations
older and more advanced than us. 3 implies that we're fundamentally
misunderstanding a lot about (astro)physics.

~~~
exratione
Astrophysics is as solid as particle physics and plasma physics; it's the
other laboratory used to confirm fundamental theory. The models are very good.
There is a natural explanation for every well observed phenomenon that fits
all known physics, and wherein the models match up to the observations.
Astrophysics really isn't the place to be looking first for issues, I'd say.

~~~
thesteamboat
I don't really know enough about physics to be able to judge, but what you say
is nicely in accordance with my priors. I think we're in agreement here. I
wouldn't argue that 3 was the place the argument most likely fails, merely
that there is something here that we don't fully understand and which may be
rather important -- hence it's reasonable to call it a paradox.

------
tomjen3
I forgot who came up with the idea, but the great filter may not exist - it is
just that an intergalactic civilisation wouldn't be using radio communication
(due to the lag because of the slow speed of light).

Or the put it a bit different: unless the Culture want us to see it, we won't.

~~~
jeremyjh
Why aren't they building Dyson spheres?

~~~
krapp
Maybe it turns out Dyson spheres are a bad idea for some reason? Maybe Dyson
spheres are out there, but constructed in such a way that they don't look
obvious to a distant observer? Maybe the idea that advanced civilizations
exponentially consuming energy as per the Kardashev Scale is a flawed and
anthropocentric premise based entirely on what we know of our own
civilization, and a lack of observable stellar engineering doesn't necessarily
mean a lack of advanced life?

------
Mahn
Another argument against the great filter, and one I'm surprised it's not
considered more often, is the relativity of the space and time. We assume,
long story short, that the colonization explosion is rare because we can't see
it, but what if all that we can observe in terms of space and time is a
incredibly "microscopic" slice compared to all that there is/has been/will be
out there? The way I see it it looks like we've concluded water must be
commonplace on earth, but then we act puzzled when we can't find a lake down
the street and assume water must be rarer than we thought.

~~~
jeremyjh
We're only talking about what we can observe. Just a few dozen billions of
stars. That is sufficient for the Fermi paradox.

~~~
Mahn
> That is sufficient for the Fermi paradox.

Is it? How do we know it is?

~~~
taygetea
The terms we know in the Drake equation make it very difficult to say it is
unlikely for intelligence to arise more than once. ~100 billion stars * ~100
billion galaxies in the observable universe. Exoplanet surveys seem to be
suggesting at least one planet per star on average. In addition, chemical self
replication seems to happen fairly easily given the right chemical conditions,
which don't appear to require much more than liquid water.

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je_bailey
Among other comments here, there is the question of why? Why does a
civilization need to expand? Why should it? We can already see in our world
where the birthrates start to decline in societies that have a certain level
of technology and quality of live. When we reach a point where our whims are
catered for and energy is cheap. Reproduction doesn't seem very cost
effective.

~~~
has2k1
Expansion can be due to a lot more than mere birthrates. First and foremost
expansion will happen only when there is means to do so. And, 'means' can be
driven by a combination of curiosity and necessity. On earth people have gone
somewhere far off (migrated), because there was the place to go and the means
to get there. In many cases that (migration) was the option over having to
fight (or find some form of accommodation) within the local social & political
system.

If this is why an intelligence can spread out on a planet, couldn't other
intelligences (if they exist) spread out for similar reasons in the galaxy.

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api
We are provably not beyond the great filter. At least one great filter lies
tangibly in front of us: ecological sustainability.

Barring several fairly large changes to our energy and resource systems, our
civilization is mathematically and physically guaranteed to collapse within
the next 200 years at most.

That's not a hypothetical filter. It's a real one that we can see, and we are
not past it.

~~~
privong
> We are provably not beyond the great filter. At least one great filter lies
> tangibly in front of us: ecological sustainability.

> Barring several fairly large changes to our energy and resource systems, our
> civilization is mathematically and physically guaranteed to collapse within
> the next 200 years at most.

Would you mind elaborating on this or posting some links with more evidence
for this? As stated, your claim seems reminiscent to previous claims that
humanity would soon not be able to grow enough food for the projected
population. So far, unexpected scientific advances have managed to increase
food yields substantially, and we can now effectively produce more than enough
food to feed people (though we clearly have issues ensuring that food gets to
everyone who needs it). So I wonder what is different now, that makes this
looming catastrophe "provable" and "mathematically and physically guaranteed".

I agree that humanity is facing significant challenges (e.g., climate change),
but I think the claim of "guaranteed collapse" is not as well established.

~~~
avn2109
>> "Would you mind elaborating on this or posting some links with more
evidence for this?"

I'm not the GP, but I suspect api has in mind something like this [0]. The
money quote from that article is this:

 _" At that 2.3% growth rate, we would be using energy at a rate corresponding
to the total solar input striking Earth in a little over 400 years."_

The obvious first-order thermodynamic consequences of that fact for the
temperature of the surface of the earth are pretty undeniable.

[0] [http://physics.ucsd.edu/do-the-math/2012/04/economist-
meets-...](http://physics.ucsd.edu/do-the-math/2012/04/economist-meets-
physicist/)

~~~
privong
Thanks. I had seen that calculation before, but had forgotten about it. It is
good to remember that we will eventually come up against limits from basic
physics.

Though, to be a bit picky, showing that we can't indefinitely sustain our
current trajectory is a different argument than saying a collapse is
inevitable.

