
Dissolving the Fermi Paradox [pdf] - davidrpugh
http://www.jodrellbank.manchester.ac.uk/media/eps/jodrell-bank-centre-for-astrophysics/news-and-events/2017/uksrn-slides/Anders-Sandberg---Dissolving-Fermi-Paradox-UKSRN.pdf
======
kaj_sotala
My summary of the link:

Possible solution to the Fermi paradox: there is no paradox. The normal
approaches find that there should be a very large number of civilizations by
plugging point estimates into the Drake Equation, but multiplying point
estimates (as opposed to probability distributions) with each other gives you
misleading results.

As a toy example, if you multiply nine factors together to get a probability
of life per star, each of the factors a random real number drawn uniformly
from [0, 0.2] and the point estimate for each being 0.1, then the product of
the point estimates is 1 in a billion. This would translate to an expected 100
life-bearing stars, given 100 billion stars. But if you instead combine the
probability distributions, you get a median number of 8.7 life-bearing stars
(the mean is still 100).

Going through the literature to estimate reasonable prior distributions for
different values in the Drake Equation, you get much more pessimistic
estimates for the probability of life in the universe; the priors chosen by
the authors suggest a 40% a priori chance for life only emerging once. We
really might just be alone.

~~~
svachalek
Thanks for the summary - the slides were a little hard to follow.

In a universe that's practically if not actually infinite in size, it seems to
me that no species is ever big or strong enough to be safe from a bigger,
stronger one. And thus any rational species interested in self-preservation (I
hope this includes us) simply MUST hide. Forever. We're not very quiet but
we're also extremely harmless at a galactic scale so I imagine if I were an
alien species that noticed us, I'd just leave us alone as bait to reveal any
less cautious species.

Following that line of thought, I'd be much happier to believe we're simply
alone. :-)

~~~
sillysaurus3
Another explanation, possibly unrelated to the slides:

It's hubris to (a) know the universe is probably infinite and (b) assume that
life evolved anywhere within our slice of it.

Infinite! The universe seems to be infinite. If that's true, it seems just as
likely that all intelligent life in the universe is completely alone.

~~~
smilliken
Consensus in physics is that the universe is finite[1]. Even if it weren't
finite, it's likely still a moot question because the speed of light will
inhibit us from every seeing outside a finite radius.

[1]
[https://en.m.wikipedia.org/wiki/Observable_universe](https://en.m.wikipedia.org/wiki/Observable_universe)

~~~
sillysaurus3
That's likely our observable portion of the infinite universe. It doesn't mean
the universe is finite.

~~~
oceanswave
If your definition of infinite is also includes that the portion of the
universe that actually has energy in it is 1/∞ then sure

------
gmuslera
Dealing with unknown unknowns is bad for "precise" math. The great filter may
be the point where civilizations realize that spreading around the galaxy is
not feasible nor necessary, and as we didn't reached that point, we assume
that everyone should be spreading around like crazy. Or anything else, that in
our current stage and culture we couldn't consider as a possibility.

Assuming things based in our lack of knowledge, and deducing that there are no
keys because we can't find yet any under this narrow streetlight are my
biggest concerns on the paradox. Why "insufficient data for meaningful answer"
is not an option?

And this paper takes the paradox hypothesis as granted and just tune for the
worse some variables.

~~~
mikeash
Where does anyone deduce that there are no keys?

The point of the Fermi Paradox is simple: according to our best knowledge, the
sky should be full of alien civilization. It's not. Therefore, something we
know is wrong.

The point of the linked document is likewise simple: if you properly account
for the unknowns in our knowledge, it's actually consistent with a lack of
alien civilizations in the sky.

There's nothing wrong with declaring "insufficient data" and moving on. But
there's also nothing wrong with analyzing the data that's available and coming
up with the best answer you can.

~~~
Chathamization
> The point of the Fermi Paradox is simple: according to our best knowledge,
> the sky should be full of alien civilization. It's not.

But this statement isn't true. We've looked at a tiny fraction of the galaxy
for radio signals and didn't find any in that small area that looked like they
came from an intelligent origin (actually, we found one, the Wow! signal). But
from what I've read - using the equivalent of the Arecibo dish, even the
closest star to earth wouldn't be able to pick up our general transmissions.
So first we have to assume that civilizations use radio transmissions for a
very, very long period of time, and don't replace it with some other tech (so
the earth wasn't only receiving them from, say 200,000 BC to 150,000 BC or
1200 BC - 200 AD before the civilization moved on to gamma burst
communication). Then we need to assume that these signals are much stronger
than the ones we're currently emitting. And then hope we get lucky and look in
the right spot for them.

So after a small amount of searching we haven't yet been able to find one
specific type of civilization using one specific type of technology in a very
particular way (not even in the way we use it). Even if the universe is
teaming with life, there's nothing paradoxical about that.

~~~
ralfd
It is not radio alone. We also didn't find any alien megastructures dimming
stars. Though Tabby's star is strange.

[http://www.popularmechanics.com/space/deep-
space/a26575/some...](http://www.popularmechanics.com/space/deep-
space/a26575/something-weird-is-happening-to-the-alien-megastructure-star/)

Subreddit devoted to the star:
[https://www.reddit.com/r/KIC8462852/](https://www.reddit.com/r/KIC8462852/)

------
lawless123
>When our uncertainty is properly accounted for in the model, we find a
substantial a priori chance that there is no other intelligent life in our
observable universe

:(

~~~
avian
But on the brighter side:

> Conclusion 2: the great filter is likely in the past

Is there an article to go with these slides? I'm somewhat competent with
probability theory and I found it hard to follow with all the unmarked graphs
and unexplained parameters.

~~~
reubenswartz
I'd say " _a_ great filter is likely in the past." There could be more than
one...

~~~
DiThi
What's why it says it doesn't imply our safety. It's called _the_ great filter
because affects pretty much any attempt of intelligent life, and not because
it's the only one.

~~~
reubenswartz
I agree with what you're saying, I've just never liked the naming convention.
;-) There are probably lots of great filters that we've passed through
already, and I imagine there are lots more "in front" of us, if we are good
and lucky.

~~~
jerf
The reason it is called "the" great filter is similar to the sort of thinking
that this PDF is attempting to debunk. If you optimistically assumed that the
early Fermi terms are likely to be high, that therefore many civilizations
must have gotten at least as far as ours, but there are still no aliens in the
stars, then the logical conclusion is that there must be something standing
between where we are now and galactic civilization, hence, the Great Filter.

If on the other hand the early terms are much lower than expected, as this PDF
is discussing, then the sum total of them could be considered the "Great
Filter" and we could be past it. It's fine to just lump them together from our
point of view, since at the moment we don't have the data to figure out which
gate is "really" the determinative one.

Wandering down my own thoughts here: The Copernican Principle, or perhaps
better termed in modern parlance the Copernican Heuristic, that we are nothing
particularly special, has had a good run. But it _is_ just a heuristic, and
one whose adherence has arguably been driven more by a science v. religion
feud than logic or data, and whose underlying logic in the past 50ish years
has metastasized into "Some religious people I don't like think Man is unique,
they're wrong about everything, therefore Man is not unique in any way." But
lately the Copernican Heuristic has been showing a lot of strain. Our solar
system may not be _unique_ , but it is increasingly looking like it may indeed
be _unusual_ , for instance. The Rare Earth arguments have never gone away and
I think a lot of the dismissal of that idea has also come from "Religious
people like the idea of the Rare Earth and some of them are arguing for it,
religious people are wrong about everything, therefore Earth is not rare."
[1], because scientifically they look as good as anything else on the subject
(namely "those arguments seem to fit our lack of data as well as anything
else", which is a pretty weak endorsement). And per the PDF under discussion,
a lot of the universe really starts to make more sense when you start to
seriously consider the possibility that, yes, we may in fact be very unusual,
if not perhaps truly unique.

[1]: Those are not the only arguments here, nor are they the best; I'm just
saying that it is my subjective sense that the debate over the past few
decades has often been very skewed by the underlying presence of this
argument, even when not necessarily spoken. It is my perception that this
debate has often been had under unspoken ground rules where all the discussion
must occur in such a way as to ensure that the religious people are unable to
point to anything as evidence for their side. It... doesn't make for the best
conditions to do science under.

------
yk
> Also similar to Tegmark’s argument, but with more process

So basically Uber for aliens. (General reminder, Bayesian statistics is math
not magic, one can move a few percent of uncertainty to somewhere else, or get
nicely interpretable parameters if it happens to be the right tool, but it is
not some kind of general reasoning mechanism, its a tool.)

------
mihaifm
I was hoping the article touched other aspects of the Fermi Paradox, such as
the potential explanations listed on Wikipedia
([https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_exp...](https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_explanations_for_the_paradox)
)

One troubling fact for example is that radio signals might disintegrate into
noise after large periods of time, making detection via this method
impossible.

~~~
Analemma_
I find that to be one of the _less_ troubling solutions to the Fermi paradox,
to be honest. Try pondering the ones where one stealthy galactic superpredator
has already taken over the galaxy, and is just waiting until we reach a
certain level of technological advancement to exterminate us because it's
currently not worth the trouble.

------
SCAQTony
What we do know know is that the Kepler mission has accomplished the
following: Candidate exoplanets: 4,034 Confirmed exoplanets: 2,335

Confirmed exoplanets less than twice Earth-size in the habitable zone: 30

K2 mission: Candidate exoplanets: 520 Confirmed exoplanets: 148

[https://www.nasa.gov/kepler/discoveries](https://www.nasa.gov/kepler/discoveries)

These are anemic numbers; even those in the "habitable zone are either tidal
locked, their solar year are weeks or days long and we don't really know what
their surface is.

The James Webb Telescope will help a lot but if you look at all the species
and forms of life that lived on this planet in last 4-billion years (billions
and trillions) only one has evolved intelligence to the degree that it can
contemplate the universe and investigate it. I think it is plausible that we
could be it...or at best so far and so few in between.

Link to explanet archive: [https://exoplanetarchive.ipac.caltech.edu/cgi-
bin/TblView/np...](https://exoplanetarchive.ipac.caltech.edu/cgi-
bin/TblView/nph-tblView?app=ExoTbls&config=planets)

~~~
InclinedPlane
Only about one in a hundred planetary systems would be properly aligned to be
detected by Kepler. The purpose of Kepler is to gather statistics on the
frequency of occurrence of different kinds of planets.

2700 confirmed planets out of 145k monitored stars indicates that planets are
very common, around most stars, since there are an estimated 270,000 planets
of similar type in that sample that just have inconveniently aligned orbits.

Similarly, 30 confirmed near-Earth mass planets translates to 3000 per 145k
stars (nearly 2%!), and thus literally billions in our galaxy alone.

~~~
PaulHoule
In our own solar system most of the liquid water is outside the frost line;
most of the "possibly habitable places" are not terrestrial such as several
moons of Jupiter, Saturn and beyond as well as possibly Kuiper Belt Objects.

If life that evolved in that sort of environment managed to work its way up to
the surface it could keep its lifestyle living on Kuiper Belt Objects and
probably other lumps of rock and ice between the stars and possibly not have
that much interest in anything that happens on our side of the frost line.

------
vivekd
My answer to the Fermi Paradox is that it seems to be human conceit that alien
life intelligent enough for space travel would want to contact us. If our
species really is typical, there is no reason for them to contact us above the
many other species. We don't go out of our way to make contact with every band
of chimps in the wild, so why would species much more advanced than us be
interested in contacting us?

~~~
Diederich
I don't think it's just about whether they WANT to contact us. It's about us
detecting them in some way, whether that detection is part of them contacting
us or not.

There's all the questions around how we would know what to look for, of
course.

------
placebo
I honestly don't understand how this issue is even arguable - I mean given
that: a) We haven't seen any evidence of life outside this planet b) We
haven't been able to reproduce life from scratch in a lab so we don't know the
odds needed for it to occur, then Isn't it obvious that: c) We have absolutely
no evidence whatsoever on which to base any range of probability regarding the
existence of life outside this planet ? I'm not saying I think there isn't
life outside this planet nor that I think there is - what I'm saying is that
so long as points a) and b) stand, any statement on the matter is just wishful
thinking, personal faith etc. It has nothing to do with scientific thinking.
If you think it isn't obvious, I'm interested (seriously) to understand where
the flaw in my logic is.

------
the6threplicant
Does the Drake equation include us, that is, Earth? In other words do we know
that N > 0 (since we exist) or can N = 0 (since we're not included).

~~~
maze-le
If one parameter of drakes equation is 0, then the whole equation is 0,
because it is just a series of multiplications. And we know for sure it cannot
be 0, since we live, and we can theoretically be detected by the
electromagnetic waves we emit -- and far less likeley by artifacts such as the
voyager 2 probe. So the likelyhood of a planet, capable of supporting life is
not 0, but at least 1*10^-11 (100 billion stars exist in our galaxy, and at
least one [the sun] has a habitable planet [the earth]).

That said, this particular parameter will likeley be higher, since we have
found several exoplanets, that are estimated to be habitable.

------
shmageggy
Anyone have a source for a paper? This is good material but hard to follow in
such a sparse format.

------
chicob
Isn't it intuitive that there is a strong chance we are alone, or is it just
me?

I've always found the Fermi paradox quite unconvincing. And the Drake equation
makes it even more obvious.

~~~
hvidgaard
Why is it intuitive?

To me, it's more intuitive that we cannot expect to be alone in this galaxy.
Perhaps we're the first advanced civilization, but in that case we will not be
the last. The vastness of the universe make the chance of us being one-of-a-
kind thing really low. If we accept that laws of physics created us, then they
can happen else where. And the Drake equation gives an estimate, albeit we
have no idea if the variables are reasonable.

~~~
DiThi
> The vastness of the universe make the chance of us being one-of-a-kind thing
> really low.

But it also means the chance of ever communicating with a different life form
is really low.

~~~
roywiggins
All it takes is some egotistical civilization that builds von Neumann
replicators to build KILROY WAS HERE monuments made of diamond on every moon
in the galaxy (it's a big galaxy, but there's millions of years to play with).
It's at least _mildly_ surprising that there's no evidence of any extrasolar
visitors in our solar system's past.

~~~
titzer
I don't find it mildly surprising the space-fairing aliens practice leave-no-
trace.

------
petraeus
The problem with the fermi paradox is that it assumes advanced civs will exist
on the same dimensional plane as we currently inhabit.

------
jackylee0424
It'd be informative if there was some kind of simulation for the origin of
life. Think about LHC for observing protein evolution to cell.

~~~
kleer001
We have Tierra and an understanding of the RNA world.

------
yourapostasy
A possibility I haven't seen really discussed seriously yet is physics as we
know it for FTL travel and mass lifting (in other words, how to lift mass on
the order of hundreds of millions of tons---the sheer literal mass of humans
and the paraphernalia brought with us [1]---out of our gravity well, without
devastating side effects) really is pretty close to the limit for the
foreseeable future, or it takes far more dedication and united effort than we
are currently putting forth to achieve even modest advances towards those
goals. If it takes planet-wide coordination to develop the massive array of
technologies to reach 0.01c for a generation ship and materials science to
make possible a 1 metric ton space elevator, and 1000 years of sustained
effort to get there, because the physics and engineering are just that hard,
it is debatable that we will start Year 1 of those 1000 years anytime soon.

Another possibility I do not see discussed at length yet is the soft factors
override the technological feasibility. The Great Filter could simply be
intelligent life cannot so far get its act together enough to cooperate long
enough to make it out of their cradle worlds. We ourselves simply do not have
the soft tooling, not to speak of the hard engineering, to sustain consistent
multi-hundred year and multi-millenia efforts, and none are even remotely on
the horizon as yet. Consider: our vocabulary in major world languages simply
do not have a word expressing tens or hundreds of thousands of years as a
discrete quantity like "millenium" expresses a thousand years [2].

The very fastest human-made object ever is Helios 2 at 221,232 mph [3]. An
order of magnitude and a tripling will get us close to 0.01c [4]. The closest
rocky planet in the habitable zone we know of is Proxima Centauri b [5], 4.2
light years away. Assume we can accelerate to 0.01c in the same time it took
Helios 2 from launch to its fastest point, 13 years, and it takes the same
amount of time to decelerate, so 26 years total just to boost and brake.
That's nothing compared to the _400+ years_ in between.

Okay, make it two orders of magnitude and we're talking roughly a single human
generation to make the trip one-way. We still don't possess the accuracy and
precision in leadership science, not to speak of governance, to say we can
cram enough people into a generation ship to be self-sufficient forever, and
with the certainty that they don't detonate themselves along the way. If we
can't get our act together enough as a species to work out how to co-exist
with Romanis for example, or mitigate externalizing/rentier behavior in
management in companies (think Romani-lite behavior) around the world for
another example, then we sure as hell can't even comprehend what kind of
social structures it takes to spread across the nearest exoplanets for
hundreds or thousands of years, not to speak of the galaxy in hundreds of
millions of years.

The best we can say at this point is even if we can solve the daunting soft
and hard problems of terraforming, and cramming millions of people into
generation ships, and countless other goals required to envision colonization,
it is a one-way trip, and the civilizations set up away from our home system
are separate-but-maybe-familiar. The closest experience we have to that are
the old colonial periods of the Western European powers, and even then, they
had one to two orders of magnitude time delays _less_ than we are going to
experience in the foreseeable future with generation ship tech.

I'm a huge Iain Banks _The Culture_ fan. But I recognize how paramecium-level
we are in so many sectors of knowledge, craft, and skills, to reach even the
first rung towards that kind of vision. I don't want us to kid ourselves on
the work we must put in for our future generations to plant the seeds towards
that first rung of the long ladder.

[1] [https://www.quora.com/Approximately-how-much-does-
humanity-w...](https://www.quora.com/Approximately-how-much-does-humanity-
weigh)

[2] [https://english.stackexchange.com/questions/331988/is-
there-...](https://english.stackexchange.com/questions/331988/is-there-an-
english-word-for-a-period-of-10000-years)

[3]
[http://www.guinnessworldrecords.com/news/2016/7/nasa%E2%80%9...](http://www.guinnessworldrecords.com/news/2016/7/nasa%E2%80%99s-juno-
probe-recognised-by-guinness-world-records-as-fastest-ever-spacecraft)

[4]
[http://www.wolframalpha.com/input/?i=0.01c%2F221,232+mph](http://www.wolframalpha.com/input/?i=0.01c%2F221,232+mph)

[5]
[https://en.wikipedia.org/wiki/List_of_nearest_terrestrial_ex...](https://en.wikipedia.org/wiki/List_of_nearest_terrestrial_exoplanet_candidates)

------
rpmcmurphy
As Mark Twain said "There are three types of lies: lies, damned lies, and
statistics". An honest answer to the question of whether communicative aliens
exist is "we just don't know".

~~~
lisper
That's true, but misleading. What matters is not whether they exist, but
whether enough of them exist close enough that we could some day receive one
of their communications (or other evidence of their existence). And the answer
to _that_ seems more and more likely to be "no".

------
TekMol
Maybe we are in a simulation. And to save processing power, only the stuff
near the solar system is actually simulated. The light from other stars is
just approximated. Like in a render program, where ambient light often is not
raytraced but just approximated.

Then there might be no other stars and habitable planets out there. What we
see is just the ambient light approximation of the simulation.

