Our galaxy consists of hundreds of billions
of stars and trillions of planets. There’s something deeply disturbing about
the idea that we might be the only ones living in it. So today we return to the Fermi Paradox series
for the first in a short series of episodes discussing all the possible factors which
might contribute to making technological civilizations like our own extraordinarily uncommon. We have looked at, and will discuss more in
the future, some possible ways in which we might be surrounded by advanced civilizations
and just not be aware of it. We can never safely discount the possibility
that they might drop by for a visit, if indeed they have not already done so. However, the Occam’s
Razor approach to the Fermi Paradox, the seeming contradiction between the immensity of the
Universe, and the apparent absence of any other advanced civilization than our own,
is that there just aren’t any close enough for us to detect. That’s really not
a big problem in and of itself. After all, we can’t even see most of the
equipment we left on our own Moon half a century ago, let alone buildings on other planets
around other stars, and we certainly haven’t built anything on other planets yet. No man has ever traveled further than our
own Moon, and except for those twelve and some hundreds who have traveled a couple hundred
kilometers over the planet to low orbit, nobody has yet left our own homeworld. We don’t broadcast
our signals very loudly and indeed they have gotten quieter as we’ve gotten more advanced,
since efficiency encourages us to make them ever quieter and harder to recognize as a
signal. We’d have problems hearing our own transmission
with our own detectors much further away than our immediate neighboring star systems. Taken at face value
then, it’s not much of a Paradox. So long as technological civilizations aren’t
so common that virtually every star hosts one, there could be a billion of them in our
galaxy alone. But this is not the
actual Fermi Paradox and never has been, people get lost in that a bit. The paradox arises from conversations and
speculation beginning around the mid-20th century, as we started getting an idea of
how truly old and huge the Universe is, and also with the growing recognition that there
was actually the possibility of reaching other planets and living on them. It is the awareness
of this possible expansion that creates the Paradox. If you believe we won’t colonize our own
solar system, let alone other ones, then there’s no real paradox. The Fermi Paradox is more properly known as
the Fermi-Hart Paradox because it was Michael Hart’s conjecture back in 1975 that fully
manifested the real paradox. We had landed on the
Moon and were discussing the creation of bases and colonies on other planets. The first tentative interstellar ships were
on the drawing table. Looking at that, he pointed out that we should
expect our civilization to generally seek to expand and make use of places with no life
on them as new homes for humans and their furry, feathered, scaly and other cousins. We do seem to want to do this and it does
appear possible under known science which is steadily improving. The basic nature of biology seems to imply
that other non terrestrial civilizations should tend to feel the same way. Any critters who have successfully clawed
their way up Darwin’s Ladder ought to be strongly inclined to want to spread out and
reproduce; this should hold for any natural alien biology as well. This is the paradox,
and it gets far worse when you come to realize that colonizing other planets is advantageous
and doable, but far less so than constructing vast swarms of artificial habitats to take
advantage of all the sun’s light that is not hitting planets, which is very nearly
all of it. Earth gets only a billionth of the light the
Sun makes. Access to such power levels makes interstellar
travel viable even without improved technology, as we’ve discussed elsewhere, and continuous
improvements in computers and robotics make that travel, or the construction of such swarms,
often called Dyson Swarms, far easier too. Now up until the day
we actually have a colony in another solar system that builds its own colony ship to
send folks further out, or have vast swarms of habitats whose combined living area grossly
exceeds that of Earth’s, it is an entirely valid objection to say we can’t be sure
if such expansion waves are possible from a practical standpoint. We’ve had the technology to land people
on Mars since we went to the Moon, or to establish a base on the Moon, yet we’ve done neither,
so capability doesn’t imply practicality. However, on this channel,
I’ve spent dozens of episodes talking about getting off of Earth, constructing habitats,
terraforming planets, and building interstellar starships. We’ve always vigorously confined ourselves
to known science when doing this, barring a few looks at concepts like warp drives or
wormholes. If you’re a channel regular, you probably
feel pretty confident that interstellar travel is within reach, and that we can overcome
those challenges to settle our own system and even our whole galaxy. So to restate our
problem, if we can see a clear path to soon achieving interstellar travel as a species…
a species that has evolved in a relatively short period of time on the cosmic time-scale,
and if there is similar life out there in the galaxy, then our galaxy should be saturated
with other evolved species who have already done so… so where the heck are they? Nor does the paradox
end at the galaxy’s edge, and later this summer we’ll look at intergalactic colonization,
and show that it is viable under known science as well, and we never know when some new Einstein
might emerge to show us easier and faster means of space travel. The point is if we can
do it, so could other civilizations, and even if some were disinclined, or blew themselves
up before doing it, the galaxy ought to be settled a thousand times over by now if such
civilizations are even slightly common. If just one planet per billion ever spawned
civilizations with the capability and desire to settle the galaxy, and if just one of those
did it even a few millions years before now, the galaxy should be as untamed and wild as
New York or London. And you can’t miss
such civilizations. You don’t need to see their homeworld, you
don’t need to hear their radio, they’re just all over the place and there’s dozens
of ways they’d be detectable, same as trying to detect intelligence in a major metropolis. Trying to hide all those blisteringly obvious
signs of civilization would seem both impossible and pointless, you don’t hide civilizations
you advertise them. Inside that framework
of ideas folks have come up with tons of possible explanations for why such civilizations might
not expand and build, or might hide, or might evolve in some way as to not wish to expand. Some seem a bit ludicrous on the surface,
others are more sound but still seem fatally flawed. We went through a ton of both types back in
the Fermi Paradox Compendium and we’ll give each one a more thorough going over in the
future. But getting back to
the topic for today, and this sub-series as well... since the reasoning on a lot of those
solutions tends to break down, a lot of folks figure that civilizations just aren’t too
common at all. Maybe planets that can host life, especially
complex life, are far rarer than we think. The Rare Earth hypothesis. Maybe they’re decently common but the pathway
to higher intelligence is a lot less likely than we think, with many hurdles filtering
out evolutionary improvements along the road to sentience and sapience, or diverting them
down different evolutionary paths. Maybe one of these filters is so strong, and
so unlikely to be passed through, that virtually no one does. This has become known as the Great Filter
Hypothesis. Now this intellectual
camp on the Fermi Paradox is a big and diverse one, with many different suggestions for what
causes technological civilizations to be rare, but that’s the shared view. The solution to the Fermi Paradox is that
we don’t see alien civilizations because there are none, or they are so far away that
we can’t see them yet... but not because they aren’t visible. You could see a galaxy sprawling Kardashev
3 civilization even billions of light years away, but the light from them wouldn’t have
reached us yet. There may be no civilizations within a billion
light years of us, but if one did arise 900 million light years away 800 million years
ago, we couldn’t see it yet, even if it had turned entire stars into giant broadcast
systems to say hello. There are many filters,
some stronger than others, and it is hard to evaluate their relative strengths as we
don’t know enough yet. However I generally classify them into 4 groups. Lesser Filters, those we’d be inclined to
think would be passed through by most, given enough time. Minor Filters, those which most wouldn’t
pass but we’d expect at least a small percentage to squeak through. Major Filters are ones which very few pass
through but given the scale of the galaxy and the universe, you’d still expect a decent
number of them overall. And lastly Great Filters, those which are
lottery-odds at best, one in a million or less kinds of filters. This is the kind of filter that singlehandedly
would shift civilizations from being so common you could hear each other's radio transmissions
easily to so rare there might only be a handful galaxy, or less. Now most filters can
be broken into many smaller ones. Earth might be quite rare but there’s a
lot of ways it might be rare, none of which by themselves is terribly improbable, yet
they might stack up to be such a Great Filter when assessed together. We showed an example of that in the aforementioned
Compendium episode, arbitrarily assigning 50/50 coin flip odds to each of 50 proposed
filters, and seeing how that stacked up to a probability so low that you’d have to
search thousands of galaxies and quadrillions of stars to find another civilization. But those were
not the only proposed filters by any means, and while many of them are demonstrably stronger
than 50%, others might not be filters at all, but simply delaying factors. In this episode and the rest of this short
series, we will be examining general categories of these filters in detail. Most discussions of this begin with the Rare
Earth filters, but there are a few Great Filters that folks tend to bypass along the way, and
we’ll be looking at some of those today. Some of you might be
nodding your heads now and thinking of things like supernovae and gamma ray bursts, or the
conditions and time spans necessary for heavy elements to collect, and indeed you are right
to do so, but we can go back even further. For us to examine all the reasons why civilizations
might be rare in this universe, we should not skip the rarity of our Universe itself,
nor the importance of time when regarding it. So that will be our focus for today. Later in the series we’ll talk about the
filters to get to intelligent life, of which we have many examples besides humans, and
from there we will discuss all of the hurdles and filters you must navigate in going from
high animal intelligence to launching rockets into space. These are all big topics which might need
further sub-division as we go but for now those will be our primary great filters, and
each will get its own episode. But today we are looking
at 3 which are not given much attention, largely because the Fermi Paradox has been phrased
rather poorly. A big problem in many
examinations of the Fermi Paradox, and what creates holes in various arguments concerning
it, is that it tends to focus on our galaxy alone. The Universe does not end there, and not only
might we detect civilizations further away than in our galaxy, we might have an easier
time in doing this if they colonize other galaxies. This does not even require faster than light
travel, though most folks tend to think we will achieve that one day. Personally I do not, both because known science
doesn’t permit it except under some dubious scenarios that are mathematically valid but
probably not physically valid, and because it tends to only exacerbate the problems in
the Fermi Paradox. If faster than light
(FTL) travel is possible, then you need to account for alien critters from civilizations
that emerged over a billion light years away but more recently than a billion years ago. Indeed what we often consider the Universe,
better known as the Observable Universe, are those parts that light has had time to reach
us from and which are not traveling away from us faster than light. If you have FTL, you have to consider running
into civilizations that do too and which originated in areas beyond our ability to see. And while we can’t be sure, the common thought
is that our Universe is much larger than the observable parts, possibly a little bigger,
possibly vastly bigger or even infinite. Part of the reason I
don’t expect us to ever discover a means of traveling faster than light is because
of the Fermi Paradox. A billion light years already seems a huge
volume to not find other civilizations in, but it’s only about a millionth of the Observable
Universe and the entire Universe might be much bigger, and even potentially infinite. If the latter is the case, an infinite universe
implies infinite civilizations, even if they are vastly far apart. You can review the various reasons for that
in the Infinite Improbability Issues episode, which are equally valid for an infinite or
super-large universe as well as alternate timelines. Surely if FTL were possible some of those
would have swung by here. But I just mentioned timelines and alternate
universes and that’s more of the problem. If time travel is possible
for instance, and if you have FTL travel, you should have time travel, fundamentally
they’re the same thing. We have to worry not just about civilizations
that might have popped up recently but are too far away to see yet, but also ones that
haven’t even existed yet. The joke about what year time travel gets
invented is ‘all of them’, and the ‘aliens’ you meet might even be folks from Earth far
in the future. We have this same problem
with alternate dimensions and realities, if they exist and you can travel to them, then
that is presumably a two way street, and folks should be showing up from them as well. There are very solid scientific reasons why
traveling through time, traveling to other realities, or traveling faster than light
should be impossible, but I consider the strongest evidence against them to be that we haven’t
run into any folks with this technology. We can reason that some aliens might
be very hesitant to show off such technology to a primitive species, for whatever reason,
but it’s quite a stretch to assume every single member of every species that exists
in the entire universe, or its entire future history, or in other Universes, all feels
that way. Nor is that in conflict with the idea that
no one seems to be doing sub-light speed interstellar travel either, since for the latter I only
need to establish that no one is doing it in our relatively small chunk of time and
space, not the sheer immensity of the entirety of all time and space or even in other possible
realities. Yet this does give us
our first Great Filter too, and it’s called the Fine Tuned Universe. You’ve probably heard of it before in discussion
of the Anthropic Principle. We’ve discussed that principle before, and
have done episodes on two of its more common examples, the Doomsday Argument and the Simulation
Hypothesis. But I intentionally avoided the Fine Tuned
Universe consideration because it wasn’t pertinent at the time and tends to make folks
get off onto heated theological discussions and attack each other, which I try to discourage
here. Let me explain it quickly
and simply though. The fundamental structure of our world and
our universe is based on various physical constants, the most obvious being gravity
which is strangely weaker than the other three known forces. Were it as strong as they, you wouldn’t
be able to put enough atoms in one place to make even single celled organisms without
their undergoing gravitational collapse into tiny black holes. So presumably any universe where gravity was
that strong could not host life, though we’ll beat on that notion later this summer when
we visit the concept of a Boltzmann Brain. Gravity is just one
such example, we have a number of physical factors and dimensionless physical constants,
that if they differed significantly from what they do in this Universe, would seem to prevent
life from being possible. Indeed even very tiny alterations to these
could make life impossible and if something has a value of 1,234,576, and can have any
value up to a billion, but only 1,234,566, 67, and 68 permit life, you’re really lucky
to live in a place where it has that value. In fact the odds against it are… well…
astronomical. That is what causes
the big theological arguments and why it is called Fine Tuning. One camp argues that it is so insanely improbable
that those constants can’t possibly be random and if they aren’t random then some Intelligent
Designer must have set them up that way. The other camp says that it can be random,
if we simply assume a ridiculously large number of other realities with different values in
which life doesn’t exist… and thus has no need to worry about how improbable their
existence is. Yet I’ve never personally
considered either argument particularly compelling. I could propose nearly exact copies of Earth
with minor variations in gravity or pressure or composition and how these variations would
prevent complex life from emerging, and indeed we’ll be discussing how such minor variations
might impact the development of complex life later in this series. Those variations will include versions of
Earth having less mass, different compositions, etc. A person living a few
hundred years back would have been entirely justified in wondering if near exact copies
of Earth, just with weaker gravity or thinner air, might exist. We now know though that these are not independent
variables. If you want stronger gravity you need a more
massive planet, or one that is denser. The surface gravity of Earth is that specific,
seemingly arbitrary value of 9.807 meters per second squared for a reason and can’t
just be 9.806 or 8, let alone 9,807 meters per second. If you head up from sea level a bit, climb
up a mountain, gravity drops in a clear and predictable fashion. The pressure of 101,325 Pascals could vary
from less than a Pascal to billions of them, but there is a reason why it is what it is
and it is directly linked to the surface gravity, change one and you change the other. As we’ll see later in the series, there
is more to atmospheric pressure than just that, but then none of those factors are random
in their effect either. So I don’t like
the Fine Tuning arguments just taking for a given that all of these physical constants
have values pulled out of a hat, be it random or by divine fiat. It may be so, but it is entirely possible
these things are connected. A man standing on a bunch of hexagonal cobblestones
might be justified in wondering if that’s a natural phenomena and find himself absorbed
in investigating how it could be so, until someone comes by and asks him to please stop
poking at the bricks in her garden path. But in neither scenario, natural or artificial,
would he be correct in simply assuming that the pattern was completely random. It could be that such
a pattern might emerge somewhere in a vast enough field of stones, but we know from places
like the Giant’s Causeway that such things can be the result of complex geological processes
making them much more likely. We also know that humans like to build paths,
generally out of clean geometric shapes that fit together and are of dimensions appropriate
to our own bodies, width, and footspan. Neither is actually random. Yet those values could
be random, or from a set that’s still quite large and in which very few combinations permit
life, so we see this as our first Great Filter. Projected numbers vary on this wildly, and
again we have no idea how random those constants are, if at all, but in most contemplations
of this concept the improbabilities of being in one that can support life are so huge that
they can only be meaningfully expressed in exponential notation. So it’s a pretty monumental Great Filter. You have to live in
a Universe where life is possible in order to contemplate how likely it is to encounter
aliens to chat with. There may be innumerable ones where the parameters
don’t permit it, or make it far less common than in ours, or even far more common. We’ll get to that more in the Boltzmann
Brain episode but a Universe truly fine-tuned for life should be one in which every drop
of matter is being utilized towards that purpose almost from the get go, and ours is clearly
not. That said, it actually
used to be. The Universe is about 14 billion years old,
but back when it was only 14 million years old, it was much closer together and about
the temperature of warm bathwater. This was a short period, only a few millions
years, perhaps decently longer if we assume life popped up then and was able to evolve
enough to survive in a few places where local phenomena like gravitational heating kept
things warm until stars emerged. Indeed it might have adapted enough to the
increasing cold to survive, much as we often consider comets as possible sources for life,
under the Panspermia hypothesis, as an alternative to shoreline tidal pools or deep sea thermal
vents. I don’t favor Panspermia myself, but we
don’t know how life started on Earth yet, and comets remain a viable scenario. We don’t know what conditions are required
for Earth-style carbon based life, let alone all the options. So we want to be very careful as we move forward
in the series from our geocentric perspective on life not to rule out that it might emerge
from a wide variety of environments and elemental compositions besides carbon and liquid water. We will also see however,
that when it comes to truly complex life, this situation is reversed, and there do not
appear to be many environments that would allow technological civilizations to arise
and flourish. It is that sort of advanced, intelligent life
that the Fermi Paradox is interested in, not more basic forms of life which are incapable
of space-travel or communicating with us. Simple life might be incredibly rare too,
or so common it has developed multiple times in our own solar system, but you need a lot
of biodiversity to spawn intelligence, excluding the Boltzmann Brain scenario, and for that
you need a lot of energy, time, and pretty ideal conditions. We’ll get more into
those as this series progresses, but that’s our second Great Filter. Earth is the only plausible place in our solar
system to host truly complex life sophisticated enough to build spaceships. We might find extinct or even extant microorganisms
elsewhere in the solar system. It might emerge wherever an appropriate chemical
soup exists that is churned around by some energy source, but there’s no place with
big animals and plants around that we can see. Even in a place like Europa, where you might
feasibly have hidden marine life beneath the ice, it wouldn’t seem terribly realistic
to expect to find civilizations. But even if life is
that common, Earth composes about a millionth of the solar system’s mass, most of which
is in the Sun or in the Gas Giants, neither of which seem hospitable places for life. All the other big moons and rocky planets
combined still only account for a tiny fraction of the available mass in our solar system
and most have no plausible energy source abundant enough to allow civilizations to have arisen
there. Additionally, only a
thin skin around the Earth, just the first several meters out of several million meters
of rock and magma on the way to the center, actually hosts life. There are several trillion tons of matter
on this planet that is incorporated into living tissues but the planet is around a billion
times that in total mass, and the solar system a million times more massive than that. So in our solar system only about a quadrillionth
of the matter is alive. Only a small portion of the matter in this
universe is going to have the right composition, right density, and right amount of energy
flux, an essential triad, to have any chance at all of being alive and a far smaller percentage
of that will be positioned to be intelligent. Only one quadrillionth
of our solar system’s matter is alive and not even a thousandth of that is actually
contained within humans. A billion billionth, just a quintillionth,
of this solar system is made of humans, not a bad Great Filter considering that’s in
the ballpark of how many stars are in the part of the Universe we can plausibly hope
to see recently enough in time for civilization to have arisen and be detectable. That takes us to our
third and final great filter for today, which is Time, though perhaps it's unfair to call
it a Great Filter. As I mentioned a moment ago the Universe used
to be the temperature of warm bathwater, and life might have evolved all over back then,
but the big hindrance to doing so was the lack of heavy elements. In astronomy and cosmology we usually refer
to all elements heavier than hydrogen and helium as metals, and for the most part only
hydrogen and helium were around right after the big bang. Some heavier elements in trace amounts were
around even then, but large quantities of them didn’t begin appearing till stars formed
and died. The biggest stars live the shortest time,
and make the heaviest elements, so those started appearing on the scene quite early in the
game, about a hundred million years in, and the biggest stars are often shorter-lived
than that. Yet it takes a while
to accumulate a lot of these, and as we’ll see next time there’s a lot of factors that
would have made the early universe inhospitable too, even in those lucky few places that might
have gotten enough metals for a decent planet to form. But this is where we see time as a Great Filter
and also see an important Fermi Paradox concept that people miss a lot. This Universe is still
quite young at 14 billion years old, check back in 14 trillion years and it will still
be quite ripe with stars, though appear far less massive and far bigger. Just one over-sized galaxy composed of the
handful of our nearest neighboring galaxies merged together, an island of stars surrounded
by an ocean of night trillions of light years across. Universal expansion will steal away virtually
every galaxy we can see now, even as time lets light from further and further away reach
us. Check back in 14 quadrillion years and it
will all be dark, lit only occasionally by the collision of dead stars with each other
or leftover planets. We’ve discussed how life might continue
on during that time and beyond, indeed even flourish, but it won’t be naturally occurring
anymore. No new planets spawning new civilizations. For the next several
trillion years there will be stars and planets forming continuously, and barring artificial
intervention life should be popping up a lot more often for most of that time. Our biggest constant filter is time not because
some filters are impassable, but rather because they each take time to pass and you only have
so much of it. Anything which delays development could make
civilizations not emerge until their star dies, but more importantly, the Universe is
young, and most of the stars in it are much younger. Most of them will live far longer than our
Sun, which is actually on the heavy and short-lived side of normal, so some planet around a sun
that will live 20 billion years might not host civilizations yet, but it’s still got
a lot of time to get that done. The Rare Earth and Great
Filter camps generally do not think life is all that rare, but as we’ll see in the series,
the focus is more that advanced life like ourselves is pretty rare so far. Given more time, given more metals in the
universe, we expect to see many more places host life and more of that develop intelligence. Check back in ten billion years and the galaxy
might be boiling over in life-bearing planets with intelligent critters roaming around them. If we checked back in
ten million years, we’d actually tend to expect life everywhere too, but originating
from Earth, with us colonizing outwards. This is our last point for today, and it is
what I call the Time Elapse Argument or (TEA). It comes up a lot in contemplating whether
or not some peculiar phenomena is natural or indicates artificiality. We expect that as the
universe gets older we would see more artificial aspects. More civilization arising and expanding and
manipulating matter and energy. It follows from that then that a younger Universe
would show less signs of all of the above. And since when we look far away in space we
are also looking far back in time, you would expect anything which is artificial in nature
to be less common the further away you look. So anytime we see some
phenomena that folks think might indicate intelligence, our quickest way to check is
to see if distant parts of the Universe have less of them. Ring galaxies for instance were often looked
at as signs of an emerging Kardashev 3 civilization. The problem is they don’t appear any less
common as you look further into the past... at least not until you look so far back that
galaxy formation itself was still pretty rudimentary. Quasars, on the other hand, were more common
in the past, with most galaxies having settled down since then, and so are clearly not a
sign of life. Now some folks will
point to the Supervoids, those huge areas of space absent of virtually all galaxies,
and say that could be artificial. This is flawed logic for a number of reasons. The voids are indeed bigger now than they
used to be, but they’re no bigger than the rate of expansion of the Universe would suggest. More importantly, they were there from the
beginning expanding along with everything else and seem to do that in every direction
we look. We wouldn’t expect civilizations springing
up all over the universe to be expanding in the same ways, at the same rates, or from
the same starting points. Especially ones predating any realistic timeline
for the development of Earth-like planets. A void expanding around an emerging civilization
as it begins converting stars into engines should have a starting point of at least a
few billion years after the galaxies began forming, not right from the very outset. It also ought to give off huge amounts of
Infrared radiation and exhibit measurable gravity in excess of the apparent matter present
in them, which the voids do not. They should actually be devoid of visible
stars entirely, which the voids also are not. There’s tons of stars and galaxies in those
voids, just way less than in other places. But that’s the Time
Elapse Argument in a nutshell, and it’s one that is important to keep in mind while
contemplating the Fermi Paradox, along with Exclusivity and statistics in general. You might have gotten a rocky planet forming
around a yellow sun as early as a couple hundred million years into the universe, possibly
even seeded with life by comets made up of frozen ice from the Bathwater Epoch, but these
ought to be very uncommon and the Fermi Paradox is all a statistics game. On the same note,
we can easily talk about civilizations that might be very different than ours in behavior. They may not be interested in expansion, or
may be going out of their way to hide, However we are operating on the assumption that intelligent
life that manifest technological civilizations will tend to favor that kind of behavior for
the same reasons we do. Evolution should favor growth-inclined species,
and a taste for exploration and challenges ought to come with the curiosity you’d expect
to be a prerequisite for developing technology. There may be exceptions to this, but they
ought not be too common, and in this context we only care if the reverse is true, that
such behavior is exceedingly rare. If expansion across
a galaxy is possible and practical, than the desire to do it has to manifest much less
often than the number of civilizations capable of it in a galaxy. If there is less than one such civ per galaxy,
no problem, but if you’re talking thousands or millions, it gets a bit ridiculous to assume
they all can but none choose too, so you either have to assume they can’t, because they
don’t exist, or they can’t because it isn’t practical, or you have to assume that
they don’t want to for some reason. As mentioned, we have talked about some reasons
not to before and will do so again in the future, and of course we talk about the practicality
of interstellar colonization all the time here. But our focus for the rest of this series
on Great Filters of the Fermi Paradox will center around why they might just be incredibly
rare, and we’ll pick that up in the next episode of the series by focusing on the Rare
Earth Hypothesis, but also discussing whether an Earth-like environment is really necessary
for life and why places with life but unlike Earth might not be able to evolve more sophisticated
life as well. Next week we will
be looking at ways to get a permanent foothold off of Earth, and closing out the Upward Bound
Series by looking at Orbital Rings, massive structures that don’t just give you a foothold
in space but rather a nice comfortable highway to the stars. To get alerts when
those and other episodes come out, make sure to subscribe to the channel, and you can visit
this channel’s website, IsaacArthur.net, or our Patreon page, to help donate and support future episodes. If you enjoyed this
episode, please like it and share it with others. Until next time, thanks
for watching, and have a great week!
Not a huge fan of the voiceover saying one thing, but the screen having other text. Specifically the notes on the screen about our moon.
Rest was good.
So, the TEA argument is one I've thought a lot about recently and never had a name for. The concept that the time involved with the creation of complex life would have a direct impact on our observation of complex life, especially in (but not limited to) the truly young galaxies that we can observe, just seemed fairly obvious to me. I'm glad Isaac covered that one. I'm going to go over my understanding of it, and if anyone can point out any flaws in my reasoning, I'd greatly appreciate it.
Specifically, my thoughts on this recently have been along the lines of truly metal poor systems. My first assumption, which I'm almost positive is correct, is that the creation of every element aside from hydrogen requires the fusion reaction of a star. My second assumption is that without a wide variety of elements, life would not form. Maybe that's a little less obvious, but if you only have, say, the first 8 elements to play with, then I then the possible chemical reactions are so low as to make complex life impossible. The third assumption was one I learned recently from cosmos, which was the progress of star formation in our universe. Apparently, our star is in the third wave of stars forming in our galaxy, hence it's metal content.
So, with all these as given, the first wave of stars certainly couldn't have held life (hence the TEA argument for really distance galaxies), and it's also possible that the second wave of stars also didn't have the capability for life due to its non hydrogen content being restricted both in mass quantity and elemental quantity. If this is the case, then the only possible planets in the surrounding area that would have a decent chance to visibly be hosting technological life would be in, say, a bubble around us between 1 and 0.5 billion light years distant. That was my estimate, though I honestly think it's a bit large.
So, to kinda spearhead this, is this basically the TEA argument? And is this one of the things that groups like SETI take into account when scanning stars for signs of technological life?