
The Fermi Paradox - itamarb
http://waitbutwhy.com/2014/05/fermi-paradox.html
======
maaku
The "we are the first" argument seemed less convincing than it could have
been. A better argument from that perspective is the observation that Type III
civilizations expand at an alarming rate. Whatever the motivation for
expansion[1], basic simulations and back of the envelope calculations show
that even with technology we could imagine building in the not so distant
future, humans could expand into the cosmos at >0.9c. We must assume the same
of ET.

Now information only reaches us at the speed of light; we are only capable of
looking for ET in our own past light cone. That means that any Type I or Type
II civilization like us should _expect_ to see an empty sky for most of their
existence, until all of a sudden the most distant stars go dim (Dyson sphere,
or whatever energy capturing device). And the darkness spreads in a wavefront
travelling at _almost_ the speed of light, until it hits and ... the
unpredictable happens.

We see an empty sky because if the sky wasn't empty, the planet we call Earth
and our Sun would already be consumed by some extraterrestrial Type III
civilization and Fermi would never have existed.

[1] An inflationary universe provides incentive for a hypothetical Type III
civilization to spread throughout the cosmos as quickly as possible, as idle
time means regions of the universe becoming permanently inaccessible. Or maybe
just resource competition and a desire for some elements of a population to
remain on the frontier.

~~~
bdamm
This model assumes that interstellar travel is profitable. There is no
evidence that this is the case, even if we had Star Trek technology.

If it isn't profitable, then it turns into a drain on the home planet. That
isn't sustainable.

~~~
dmix
Curious: What would make interstellar travel not possible? Do you mean for
humans or machines as well?

~~~
jacquesm
At scale it would not only have to be technologically possible but also
economically feasible. If you can't afford it you can't do it even if you have
the tech.

------
gpsx
This article does a good job of covering a lot of different ideas on this
paradox. I have a problem with the idea of "big numbers" in it though, like
where it implies 500 billion billion is nearly infinite, or that one-in-a-
billion is a freak occurrence. There is a saying that if enough monkeys pound
on a keyboard, one will type Hamlet. This would take a lot of monkeys. If we
take the odds of hitting one character to be 1 in 40 (which doesn't account
for properly hitting the shift key to make a capital), factoring in the
130,000 letters in Hamlet (according to Wikipedia), we get the odds of a
monkey typing it at 6x10^208267. This number comes from 40 keys and 130,000
letters. How about when we start taking molecular numbers of items (6x10^23)
and start raising that to a large power? I don't think it is a given that the
number of planets out there infer there should be other life.

~~~
_greim_
We can't calculate the probability of life arising though because even if we
did know how it arose here—which we don't exactly—we don't know all the
possible different ways it can arise, which may or may not also be a number
raised to a large power.

~~~
gpsx
That is a good point. I agree with you. And people do have suggestions as to
how life can be more probable than naively expected. But this answers the
question why there is life at all as opposed to why we don't see more of it.

My bias is that life is highly improbable and that we will not find any other
life in our universe. But I also think it is no miracle that we exist, as I
will describe. Given that I am trying to say this in one paragraph, it may not
sound well justified, but it is how I view the problem. I'll start with
Schrodinger's cat. A cat is in a box with some radioactive source that can
decay and kill the cat. You can ask if the cat is alive or dead - and the
answer is both. I will ignore the next part (Schrodinger's whole point) about
what happens when the human observes it. There are different interpretations
about why the human thinks the cat is definitely in one of the two states as
opposed to both. This has to do with the human's observation and is not
important for now. The point is that the cat is in both states. The universe
can be in multiple states, some with life on earth and some without. Every
possible state that can exist, does. So no matter how improbable we are, we
will exist in some version of the universe. And there would be lots of other
life too, just maybe not in our version of the universe. So the probability of
life existing doesn't impact whether or not we should exist, but it does
impact whether or not we see other life. I don't think we will. But as
correctly pointed out, we don't know the answer to this right now.

~~~
jacquesm
> My bias is that life is highly improbable and that we will not find any
> other life in our universe.

It's probable enough for you to be writing this. The only options are 0, one
and many. We can rule out '0'. That leaves us to decide whether the chances of
us being the only one are larger than the chances that we are one of many.
Obviously the second one has more chance of being true the one where there is
only one. But we like to consider ourselves to be special so most people will
believe the 'one'. Just like the sun used to revolve around the earth, now
we're essentially seeing the universe as revolving around us. The alternative,
that we're not special is not compatible with a lot of our collective culture.

~~~
gpsx
The point is that there are multiple universes, according to the quantum
mechanics interpretation I subscribe to. So all of your options are true: 0, 1
and many. My position, which is admittedly no better than a guess, is that
most universes by a far majority have 0. By virtue of me writing this, among
other things, we live in a universe with at least 1. Again, my position would
be that it is unlikely we have more than 1 in our universe.

What you are saying it true under the assumption there is a single universe.

~~~
darkmighty
I think you're trying to articulate is the Anthropic principle [1].

It basically states that the probability that "some" life exists is 1.

I'm not sure what the name of this next one is, but I believe it's a widely
defended scientific principle that we're "typical" in some sense. This
principle gets hard to justify cosmologically (it reduces to Occam's Razor
locally), but it makes sense to me. It rejects very clearly some quirks like
the Bolztmann Brain [2] argument.

[1]
[http://en.wikipedia.org/wiki/Anthropic_principle](http://en.wikipedia.org/wiki/Anthropic_principle)

[2]
[http://en.wikipedia.org/wiki/Boltzmann_brain](http://en.wikipedia.org/wiki/Boltzmann_brain)

------
mda
I think Authors is way way optimistic with these numbers:

"Let’s imagine that after billions of years in existence, 1% of Earth-like
planets develop life" and "

"And imagine that on 1% of those planets, the life advances to an intelligent
level like it did here on Earth"

Why 1% and not 10^-10%?

~~~
Coincoin
Agreed. It's a common error to think that the smallest fraction of something
is 1%.

------
arikrak
The estimates of stars seem reasonable; the estimates of Earth seem a bit ill-
defined. (The study he links to discuses Earth-size planets, but there are
many other factors that go into Earth's suitability for life.) The real issue
though is in the "speculative" part:

> Let’s imagine that after billions of years in existence, 1% of Earth-like
> planets develop life... And imagine that on 1% of those planets, the life
> advances to an intelligent level like it did here on Earth. "

1% sounds like a small number, but it's a bit ridiculous to just throw it out
there and assume it's reasonable. It's a little bit like when a startup does a
top-down estimate of revenue - "If we only capture 1% of the e-commerce
market, we'll be worth billions!"

I think if you do a "bottom-up" style analysis of the likelihood of atoms
forming a replicating growing organism, or that organism evolving to think
intelligently, you would get a far smaller number, say in the range of
0.00001% to 10^-20 for each one.

------
equil
I've always wondered at what distance it would be impossible for current
technology to detect life on earth.

~~~
maaku
A very short distance. IIRC something like 20 or so light years, but I'm
having trouble finding the citation. That's for radio waves (and the number is
getting smaller as the technology is getting better -- EM radiation blasted
into the universe is considered waste by hardware engineers).

For direct detection of life, that's still an open question. I remember a
poster done by a grad student who looked at whether life would be detectable
from the Moon, looking at the Earth. This was tested with data from one of the
outer solar system probes which did a lunar flyby on its way out (Cassini?).
The result, IIRC, was inconclusive -- you could see signs of life, but not
anything that was absolutely definitive proof.

Indirect evidence might be provided by spectra of the atmosphere observed via
solar transit. A biome is likely to have different spectra than would be
predicted by inorganic atmospheric physics. Still, that's making some
assumptions about what extraterrestrial life would be like, and only only
visible along the elliptic plane.

~~~
sampo
The chemical composition of Earth's atmosphere (21% O2) is so far away from a
long term chemical equilibrium, that any current astrobiologist would
interpret it as a sign of planetary scale life. (And correctly so: the oxygen
was produced by life.)

So life on Earth is pretty visible from the other planets in our solar system.

And spectroscopy to observe the composition of atmospheres of planets orbiting
the nearest stars will probably happen in not-too-distant future.

~~~
maaku
Meh, it's a long way from saying that "we don't know how the O2 could have
been produced except by life" to "the O2 was produced by life." Just look at
the current debate about methane on Mars.

~~~
sampo
In a 1993 article, Carl Sagan considered the atmospheric oxygen content "at
least suggestive of biology" (Conclusions, 3rd paragraph).

[http://www-pw.physics.uiowa.edu/~dag/publications/1993_ASear...](http://www-
pw.physics.uiowa.edu/~dag/publications/1993_ASearchForLifeOnEarthFromTheGalileoSpacecraft_NATURE.pdf)

~~~
maaku
Am I supposed to disagree with that? High atmospheric oxygen content is
suggestive of biology. So is seasonal blooms of methane on a planet like Mars.
Is that suggestive that there is life on Mars? Yes! Can we definitively infer
that there is presently life on Mars? Not yet.

------
wavesum
I think the biggest fallacy in this rationalization is when it is assumed that
advanced civilizations would want to expand like yeast; consuming everything,
building dyson spheres... Why would they want that much energy, and why
extract it from the sun? Trying to picture myself as one of these
superlifeforms, I think would like to have the sun visible... For sunbathing
and sh __ __... plants to grow etc... Maybe they have built little fusion
reactors wherever they need energy?

~~~
fernly
The SUN is visible everywhere within a Dyson sphere; it's the STARS that you
can't see any more. The idea isn't that a civilization wants to do this; the
idea is that it needs that much energy to continue with whatever industrial or
infrastructure processes it requires to support a very large population. Dyson
reasoned, we need steadily increasing amounts of energy input to support what
we are doing; if the trend continues, what's the limit? (Typical physicist
question, no?) The limit is to harvest all the energy emitted from your star.
The only way to do that is to build a spherical collector, so that every
photon can be captured. Then where do you live? On the sphere's inner surface.
Of what material could you build a stable sphere one AU in radius? Where would
that bulk of material come from and how be processed and positioned? How would
you provide gravity on its inner surface? We have no fucking idea -- but we
are not a Type-whatever civilization.

~~~
JoeAltmaier
I always thought that was a primitive notion. We can build the sphere, but not
control the star? Imagine a caveman - "Limit to civilization when all energy
from campfire captured - most people warm, most meat cooked" Clearly one can
do better than a campfire.

Instead, imagine harvesting energy from the star asymmetrically - from flares
or from the inside out. Or get your energy from a neighboring star. Or make
your own star. Or whatever a Type-whatever civilization decides to do.

------
Xcelerate
I am surprised a more common argument was not mentioned: other life exists but
the laws of physics limit our interaction. Maybe there is undiscovered physics
like wormholes or time travel, or maybe there isn't and the speed of light
really is a fundamental limit that cannot be surpassed. In that case, no
matter how advanced another civilization becomes, they still can't violate
natural law and are thus unable to reach us.

~~~
joe_the_user
The laws of any potential biology and the messiness of the world could
together effectively limit a civilization's energy usage to much lower than
indicated by the easily deducible laws of physic (the explicit laws of physics
might limit the output of an internal combustion engine to a certain but the
effective maximum winds up less than that. Human biological systems experience
serious damage by being weightless for significant periods, etc).

I only recently realized that this "paradox" looking at the possibility not of
"earth advanced" civilization but supposed advanced civilizations that would
put out much more energy than humans put out.

The whole thing seems to rest on false-extrapolations of mid 20th century
hard-science fiction authors. Our Western Civilization has experienced an
exponential growth of some things, has expanded it's "frontiers" quickly in a
variety of ways, conquering the rest of the globe and then labeling space "the
final frontier".

But all this has been low-hanging fruit. We're reaching the end of population
expansion, space is fundamentally hostile to human life in a way that would
take tremendous progress to overcome and we're facing longer term consequences
of the rapid expansions we have achieved (global warming is just one of the
consequences). If humans survive this, we'll have to have somehow achieve a
steady-state for energy consumption and related things. But once we do achieve
that steady state, why would we want or need to suddenly start using the
energy of an entire star (after the thousand years of scientific progress we'd
need to under how to do that)?

~~~
vorg
Humans can build large sealed cities on the Earth-facing side of the Moon
using solar-propelled remote-controlled "drone" technology. The response time
is only about 1 or 2 seconds so the human operators on Earth wouldn't need the
equipment to have much of its own AI (unlike later on when humans repeat the
process on Mars). Once enough such specialized machinery is on the Moon,
entire "cities" the size of an apartment building could be built, funded in
the same way Ordos in China was. The hard part would be experimenting with
different biochemical processes afterwards in each city so one of them could
provide enough oxygen, water, and food for humans who'd arrive much later on.

------
dennisgorelik
How about the theory that we are the way super-civilization spreads?

If physical space travel is extremely expensive (as it should be, considering
the distance), then may be it is better to send a signal that would trigger
creation of life (in our case on Earth).

Then when Earth civilization is advanced enough, it would be able to receive
complete boot sequence and then fully advanced alien civilization would be
replicated on Earth.

~~~
fernly
... or, how about the hypothesis that we were intended to be a seed package
(a.k.a. "biological rootkit") but due to a bug in the programming, we failed
to develop properly. Just a mistake playing itself out...

------
iopq
Possibility 5) There’s only one instance of higher-intelligent life—a
“superpredator” civilization (like humans are here on Earth)—who is far more
advanced than everyone else and keeps it that way by exterminating any
intelligent civilization once they get past a certain level.

If we're the most advanced civilization right now, that will be us in a few
million years. We're kind of dicks.

~~~
sebastialonso
Exciting for a movie plot I guess. But, what could they win from exterminating
another inferior intelligence? By your context, they are already inferior, and
thus, no threat to the apex civilization.

~~~
danielweber
It's been suggested by Robin Hanson (who coined the name "Great Filter") that
an ethical super-civ would see a galactic war with another super-civ as the
worst thing possible, and so wipe out other civs to stop that worst thing
possible,

I don't buy it, FWIW, because "ethical" doesn't overlap with "wipe out all
other life" in my book. (Although you could certainly, say, have some system
that stops any civ from leaving their planet by dropping rocks on them each
time they launch something into orbit.)

But you can search Hanson's blog for more talk about this if you want to see
more discussion.

------
dedward
In that great expanse and time, there may also have been ample time for
civilizations to rise, then fall. We might have just missed them on such grand
scales. Nobody says we'll be hanging around for a billion years trying to
communicate with others... if we even last that long.

------
kowdermeister
We are not even listening hard. SETI covers an incredibly tiny range of
possible spectrum and possibilities of intelligent life. Are there any other
attempts to find alien communication via data mining?

If I were a galactic artist, I would use pulsars to modulate their signals and
create a statue that broadcasts the existence of life.

[http://www.technology.org/2013/11/20/extraterrestrial-
civili...](http://www.technology.org/2013/11/20/extraterrestrial-
civilizations-modulate-pulsar-signals/)

------
drjesusphd
I personally find the "we are first" solution to be the scariest scenario. We
are not suited for the responsibility of being the only intelligent life in
the universe.

~~~
adventured
What responsibility? I can see absolutely zero responsibility attached to that
scenario.

Humans also may be the most responsible intelligent life that ever exists in
the universe. What's the basis to judge such things to begin with?

There's an exceptionally low probability that human survival has any bearing
on whether other intelligent life comes to exist (in the we're first
scenario). Being first bears no responsibility because future life in the
galaxy or universe is not inherently dependent on what we do.

~~~
sebastialonso
I guess parent was implying an inherent responsibility about being the first
intelligence, or conciousness.

As such, should we nurture, protect, and by all means spread the intelligence
sickness? I'd think yes.

------
mangecoeur
I don't see why a "Great Filter" is needed to justify there being no other
highly evolved lifeforms - all it needs is for there to need to be a
reasonably large number of key evolutionary steps and environmental conditions
with a sufficiently low probability. Multiply those and you end up with some
pretty tiny chances of observing life as we know it.

~~~
keule
I had the same thought and agree with what you wrote. But when you think about
this set of evolutionary steps you still end up with the same scenarios: you
are rare, you are first, you are fucked. So in that regard, you can subsume
all of these steps into a filter.

------
rdc12
Would discovering the fossils of some complex species on Mars (or any where
else in the solar system) be any worse for getting past the great filter then
the discovery of fossils of dinosours on earth. We allready know that mass
extinction events on Earth are possible, and should expect them to occur on
other planents with life too

------
DougN7
The idea that maybe aliens visited before humans could record what they
experienced struck me. Even if they did record it, we wouldn't believe it.
Need proof? See the Bible or virtually any other ancient religious text. Our
modern society believes if we can't prove it today, it didn't happen.

------
zw123456
I think they sort of cover this but here is my simple explanation. Think about
how many slugs there are on Earth. How many of them have never seen a human?
If we are slugs in comparison to advanced beings that have a billion years of
evolution on us then it is no surprise we have not seen them.

------
ScottBurson
How about this possibility: the Great Filter is now! We entered it, perhaps,
when we developed sufficient collective nuclear weapons capability to wipe out
most or all human life; we won't be out of it until the major threats our
civilization poses to the biosphere have been resolved.

~~~
Lrigikithumer
A lot of people consider nuclear annihilation a big threat but I'm not too
worried about tbh. I mean if you think about it, every major player has got a
trigger to end all life at any given point, doesn't it seem reasonable that at
some point you invest a lot of money into systems that can safeguard and
prevent this type of catastrophe. I know a lot of people may consider the
governments dangerous and selfish but they aren't stupid, major players have
definitely got systems in place to neutralise these threats.

At least they do in my optimistic viewpoint.

~~~
rwallace
I would like to share your optimism. But then I read about things like the US
nuclear launch codes being set to 00000000 for quite a few years, or an
incident when survival versus Armageddon depended on the judgment of one man
[1], and I have to conclude that human governments should not be in possession
of nuclear weapons.

[1]
[http://en.wikipedia.org/wiki/Stanislav_Petrov](http://en.wikipedia.org/wiki/Stanislav_Petrov)

------
ZanyProgrammer
My solution to the Fermi Paradox: Who the hell knows, who the hell _can_ know,
when all we have is a sample size of 1 to extrapolate from. The solutions to
the FP seem to be representative of the personal beliefs of whomever is
discussing it.

~~~
Udo
Of course no one can now _right now_ , it's not one of these things that can
be solved by theoretical work alone. At some point - assuming we don't go
extinct before reaching it - we _will_ know.

But it's still open to useful speculation, as there might be something we
still need to consider in order to avoid said extinction.

The Fermi Paradox is one of the more thought-provoking signs that something
might be amiss (at least in our part of the galaxy), and especially because
our culture is predisposed to _not_ take anything happening on the
interstellar stage very seriously this provides an impetus for reflection that
would otherwise not happen.

One of the most benign (but ultimately depressing) possibilities is that
biogenesis is somehow extremely unlikely. There is no reason to assume this is
true, given that we know even the more complex building blocks of life are
actually very prevalent throughout the universe - but it may still be
statistically unlikely that cells form from them. On the footsteps of that
possibility follows the hypothesis that technological intelligence is rare.
Again, that's not exactly in line with what we can observe on Earth, but it
might still be the case.

Most of the other options should be positively troubling, though.

~~~
ZanyProgrammer
"The Fermi Paradox is one of the more thought-provoking signs that something
might be amiss (at least in our part of the galaxy), and especially because
our culture is predisposed to not take anything happening on the interstellar
stage very seriously this provides an impetus for reflection that would
otherwise not happen."

A hypothetical observer in North America, circa 1500, would have no idea that
Asia and Europe existed. Perhaps we're not too far from some interstellar
space empire, but since they use some exotic means of FTL communication, we
can't detect them?

~~~
Udo
I'm not sure how your argument applies to what you cited of my post, but you
are not wrong. You don't even need to consider exotic FTL communication, it
could just be low-power directional radio traffic.

In fact, if a full clone of Earth with exactly the same culture and technology
as ours was located just a dozen light years from here, chances are we would
not be able to detect that civilization.

The media is always talking about our expanding radio sphere, but in reality
this signal gets very weak and jumbled, very fast, with increasing distance.
The means all the misinformed derps who believe aliens are coming to take our
resources (a group which includes Stephen Hawking for some reason) can sleep
pretty well at night knowing that we have not really advertised our existence
yet.

------
MrBra
Thanks for letting me find out about this article and this whole awesome
website!

------
ccvannorman
i love this puzzle. here are some theories:

1\. simulation argument

2\. civilizations have a high or inevitable chance to self destruct after <1M
years of language

3\. civilizations transcend our observable universe after <1m years [1]

4\. due to the single observer problem, humans fail to grok some very
important feature of larger scale space that prevents detection/increases
isolation

[1]
[http://accelerating.org/articles/transcensionhypothesis.html](http://accelerating.org/articles/transcensionhypothesis.html)

~~~
Pxtl
4 seems likeliest. Interstellar colonization is simply impossible because of
the vastness of the distance that must be covered. It requires more energy
than can be summoned to get a useful amount of hardware across multiple
lightyears.

~~~
ericb
At a certain point, if you can make a self-replicating machine, with harvested
solar energy for travel, you would expect that machine's descendants to slowly
get everywhere intended.

------
MrBra
Think of something like the "Human Brain Project" [1] scaled to what it could
become after evolving/improving/growing for 3.2 billion years..

[1] humanbrainproject.eu

------
kowdermeister
I'm a bit surprised nobody mentioned AI-s taking over as the Great Filter. I'm
sure every technical civilization attempts to do that because it's very
tempting to accelerate your intelligence by computation.

I've also read an interesting article that why probably machine life is more
abundant than biological: [http://www.popularmechanics.com/how-to/blog/robot-
universe-d...](http://www.popularmechanics.com/how-to/blog/robot-universe-
dominant-lifeform-17549081)

~~~
pilaf
If AIs were taking over left and right we'd still expect to see some kind of
evidence of their existence. Since they'd only be replacing biological
civilizations I don't think it would count as the Great Filter, not in the
context of Fermi's Paradox at least, as you'd end up with roughly the same
number of technologically capable civilizations after the filter.

~~~
kowdermeister
We can't comprehend intelligence million times beyond us, so speculating about
their intention is very wild. Who knows, maybe an universal law of super-
intelligence is to keep a low profile.

~~~
sebastialonso
Yes, but I like my sci-fi like I like my Minecraft worlds. With at least a
tiny layer of solid bedrock.

If you're going to propose a crazy but interesting possibility, you cannot
pull the 'can't speculate, they're to superior' card. You already speculate by
sharing the idea!

------
cdelsolar
We might be very close to finding life on Mars. If we did and it was different
than us that would answer a lot of questions.

------
fxj
when the question is: "where are they?" and the answer is: "there is nobody
here." then all long living civilisations must have left. so we should answer
the question "why did they leave?"

~~~
Lrigikithumer
Or maybe the long living civilisations never existed, or we aren't knocking on
the right doors, or in the right areas?

------
pigboy
Out of all those advanced civilizations in the universe, what fraction use
electromagnetic radiation for communication? We are like ants waiting for
other civilizations to communicate with us using pheromones.

~~~
danielweber
There are humans that try to talk with ants (and bees, and dolphins) using
those creatures' own methods. Unless there were strongly-enforced no-contact
laws, then _some_ alien researcher would want to inspect those Terrans and see
if we can talk. Even if they are way smarter, they'll use that smarts to talk
with us in a way we can understand.

------
thelollies
Another possibility... there are plenty of civilisations within broadcasting
distance from us that are all listening but not broadcasting for fear of
predatory civilisations.

~~~
thefreeman
that exact possibility was listed in the article.

~~~
thelollies
That's funny! I read the article and then had that thought five minutes later
and thought I'd come up with it. Thanks for pointing that out :)

~~~
chatmasta
I often wonder how many of my opinions derive from this same mistaken
originality... Quite scary, actually.

