Are we alone?
Recent amazing discoveries have given us
more hope than ever that our universe is full of life.
So why don't we see it?
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Why don't we see alien civilizations?
We've asked this question before here on "Space Time,"
and if you haven't seen that episode
you should check it out.
But today we'd like to go deeper because it really does seem
like there should be aliens.
The Kepler Space Observatory has told
us there are a couple of hundred billion nice,
watery planets in the Milky Way and probably billions of them
are Earth-sized planets around sun-like stars.
Many of them have been around long
enough to produce a civilization that
could have easily colonized the entire galaxy by now.
So why is the Milky Way so un "Star Warsy?"
This genuine oddity is referred to as the Fermi paradox
and the resolution for it has to be
that there's some sort of great filter
that either makes intelligent life extremely
rare in the first place or that wipes out, essentially,
all advanced civilizations before they
get to the galactic empire stage,
whether by a nuclear war, environmental catastrophe,
accidentally making a black hole that
swallows the planet, et cetera.
Personally, I'm not buying it.
I just don't think that there's an inevitable great filter
still ahead of us.
As we saw in a previous episode, we're
not so far from building starships ourselves.
Surely, some civilizations must make it
through these growing pains and manage to reach the stars.
So where are they?
Well, there's another deeply sad and deeply inspiring
possibility.
Humanity may be one of the very first interstellar species
in the history of the galaxy.
But before we get all emo, let's science this right.
We know of exactly one instance of intelligent life
happening, the case of Earth.
And as if it wasn't hard enough to do statistics
with a sample size of one, we also
have to deal with a massive selection bias.
Of course we're going to observe at least one instance
of intelligent life happening because we are that one
instance.
In a way, it doesn't matter how improbable sentience is.
As long as it happens once, it will
be there to observe itself.
Here we're touching on the anthropic principle, which
states that an observer will always
observe a universe that can make observers or a planet that can.
We'll talk about the cosmic implications
of this more in another episode, but for now we
need to acknowledge that this selection
bias allows that life could be extremely rare, or even unique.
Given that, can we even begin to assess the likelihood of life
out there?
Yeah, we can science anything.
So let's dig into whether we should really expect
to see a Salarian Empire.
Let's take the knowns.
Now, Earth certainly required a number
of very special conditions to build life
and it's hard to know how essential each of these was
or how frequently these conditions are
met through the galaxy.
I'm going to avoid details of the biology
here because we can say a lot just
based on how much time it took to get
through each step on the path to building technological life.
We can crudely summarize the big leaps that lead up
to intelligent life as one, assembly
of self replicating RNA from organic molecules;
two, RNA based proto-cells; three, DNA
and the first actual cell-- this is the moment of a biogenesis,
life from not life; four, increasingly complex
single cells; five, the first multicellular organisms so
plants, animals, et cetera; and six, the first intelligent life
form capable of counting to six on You Tube.
Now, the crazy thing, the thing that I
find the least intuitive, is that the first three
steps in that chain combined-- the appearance
of true cellular life-- happened faster
than any of those later steps.
so fast, in fact, that it seems hard to believe.
And in fact, so fast that our galaxy probably
should be brimming with at least simple life.
Let me explain.
See, around four billion years ago,
pretty much just after the Earth had first cooled down
from being a giant hellish magma bowl,
we think that it totally got pounded
by a meteor storm that lasted a couple of hundred
million years.
This is the late heavy bombardment,
and it probably obliterated the surface.
We think we know this because we flew to the moon
and found evidence of it.
Up until recently, the earliest known evidence
of life dated to roughly 3.5 billion years ago,
fossilized blue green algae beds-- stromatolites--
found in Western Australia.
The place was covered in this greenish-purple slime
that reeked of rotten eggs.
Yeah, the beach was horrible back then.
Basically, Earth was once a giant slimeball planet.
And it looks like Earth went from magma ball
to slimeball in less than 300 million years.
What?
That seems crazy fast.
But it also suggests that this first step,
the genesis of life, is not the great filter.
But wait, the abiogenesis thing gets even weirder.
See, nature has provided us with a perfect time
capsule for studying the very early Earth,
zircons-- super hard silicate crystals whose formation
can be dated precisely by the ratio of decaying uranium
versus lead decay product locked inside.
And get this, just recently a zircon
was found containing the possible signature of life
and dated at 4.1 billion years ago,
from before the late heavy bombardment.
That little crystal contains what
looks like biogenic carbon.
That's a fancy way of saying there's too little carbon
13 compared to carbon 12.
See, photosynthetic finds C12 a bit yummier,
and so it absorbs more of that than the heavier C13.
Pretty much all carbon enters the biosphere
from the photosynthesizing bottom of the food chain.
Any carbon that's been through living systems
will have the same C13 light isotopic ratio
that we see in this zircon.
Now, there are other nonbiogenic explanations,
but this is extremely suggestive that life was abundant on Earth
remarkably soon after it first coalesced from stardust
and that life either survived the late heavy bombardment
or formed again after that or the late heavy bombardment
never happened.
That's actually a possibility, too.
But either way, it looks like Earth
became a slimeball teeming with life in a crazy short amount
of time.
How on earth did this happen?
Two options.
One, given the right conditions the genesis of life
happens like that, and two, it didn't happen on Earth-- life
was seeded from space, an idea called panspermia.
Look, there's no question that lots of rock
gets ejected into space after meteor impacts
and can move between planets.
We've found plenty of meteorites originally from Mars.
A lot of the ejecta from Earth is
going to be swarming in bugs.
Could similar bacterial astronauts
have once survived an interstellar journey to Earth?
Some bacteria are certainly hardy enough
to survive launch and landing.
This has been tested.
If these bacteria were frozen solid,
they could plausibly survive a very, very long journey
and you only need one out of billions to make it.
Maybe the solar wind pushes infested material
into interstellar space so that tens
of thousands, even millions, of years later a single bug
winds up on a brand new planet and boom, instant slimeball.
Questionable, but it would mean that life only
needs to evolve once from scratch in any given galaxy.
Now, this should be very testable.
Earth was infested fast, so that means
this stuff should be out there.
Mars must have been hit when it had water.
Did it go slimeball?
There should be something like stromatolite fossils
on its ancient surface.
We haven't seen them yet, but they'd be hard to spot.
These cosmic cooties should be findable in space, too.
So either fast abiogenesis or panspermia, one of them
must be true.
However, both suggest that the galaxy
should be teeming with slimeball planets filled with life.
Now, that's exciting.
We don't have a telescope to find them yet,
but we could soon.
These planets will have atmospheres
driven by biotic processes.
If we could analyze light passing
through these atmospheres, we would
see signatures of oxygen, ozone, methane,
nitrous oxide at concentrations impossible without a biosphere.
Properly fund NASA and its terrestrial planet
finder and we could find extraterrestrial life
within 20 years.
So it's entirely possible that we'll soon
discover that the galaxy is filled with life.
But this just makes it weirder that the Milky
Way isn't swarming with ancient alien civilizations.
There is a filter, but it's not the genesis of life.
The clue might be that the Earth stayed a slimeball
for nearly three billion years.
The first multicellular organism turned up only 600 to 800
million years ago and life as we know
it quickly exploded after that.
Was this a random lucky event that we just had to wait for?
No, multicellular life evolved independently dozens of times.
It just took a really long time for those single cells
to become complex enough to form large collaborative
structures capable of collective reproduction, i.e.
plants, animals, a species capable of making the Kerbal
Space Program.
And speaking of space programs, technological life
took a little while longer, but not
really so long on the overall scale once we had complex life.
After the Cambrian Explosion, it was only around half a billion
years to go from jellyfish to moon landing.
Of course, maybe the emergence of intelligence
is a random and unlikely event, and this one
is the hardest to assess.
However, it's worth noting that we
do have other species on Earth that
seem to be moving down the same big brain path independently
of humans.
So what is the great filter?
Maybe it's just time.
If life is common, then of the billions of Earth-like planets
in the galaxy, only a tiny fraction
needed to have a small head start on us in order
to have produced the Federation of Planets
and Stargates and stuff by now.
So what if humanity started early?
Of all of the sun-like stars and Earth-like planets
that will ever form over the full past and future
history of star formation in our universe, Earth is early.
It's part of the first 8%, according
to recent Hubble Space Telescope based calculations.
We have emerged in the epoch of life in a universe
abundant in the rich resources of past supernova explosions,
but after the violence of the starburst and quasar epochs.
It strains believability to imagine
that life didn't or won't happen elsewhere,
but it is possible that we are a very early outlier
and that any other civilizations are so distant as to not yet be
apparent.
Is humanity a first generation intelligence,
one of the species that will watch and maybe guide
as other intelligent life emerges throughout the galaxy?
Well, there's something to work towards on the next episode
of "Space Time."
Last week we talked about Miguel Alcubierre's warp drive.
You guys had a lot to say.
Let's do it.
A lot if you noticed my mistake in saying
that Miguel Alcubierre is Spanish, rather than Mexican.
That was my mistake.
We cram a lot of details into each episode of "Space Time"
and sometimes things like this do slip through,
so thank you for catching it.
Miguel Alcubierre was, in fact, born in Mexico and, in fact,
educated up to master's level there.
Eric Vilas wonders what it would look
like seeing an Alcubierre warp bubble
race by from the outside.
This is tricky.
The bubble would definitely leave some sort
of light signature because light inside the bubble
can traverse the walls in any direction besides forwards
and our negative mass matter may also end up on the outside.
Because the bubble is superluminal,
any light that we see would trail the bubble just
like the sound of a supersonic jet.
Ahead of the bubble, you'd see nothing
unless it stopped, in which case all the photons and particles
that are captured on its journey would blast you into oblivion.
Now, a few of you took issue with my statement
that it's never aliens.
And fair enough, it's never aliens until it's aliens.
The point of this philosophy is that the alien hypothesis
is a bad place to start because you can explains almost
any weird natural phenomenon as having been produced
by a super intelligent, extremely high tech
civilization with inscrutable motives.
Really anything.
It's a week hypothesis until you've generally
ruled out everything else or you actually see the mother ship
and take an unsuspiciously blurry photo of it.
So Nate asks if we can please do another challenge episode.
Absolutely, we'll do one soon.
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