Thanks to curiosity stream for supporting PBS Digital Studios. The Silence of the galaxy and the resulting Fermi paradox
Has perplexed us for over half a century
But our most recent surveys of the Milky Way
Finally allow us to draw scientific conclusions about this depressingly persistent absence of aliens
When Enrico Fermi uttered the words
"Where is everybody?"
He was succinctly summarizing what has become known as the Fermi paradox in short in a galaxy of hundreds of billions of stars
Each of which having billions of years to spawn life and civilization, isn't it odd that none have made themselves apparent to us
Enrico Fermi was supposedly using this as an argument against the plausibility of
Interstellar travel. If aliens can travel between the stars why haven't they visited?
But the paradox is much broader than this
There are several ways that an advanced civilization could give away their presence
radio transmissions, robotic probes, or star blotting solar arrays.
A series of very recent surveys of our galaxy reveal none of the above while at the same time
proving the abundance of potentially habitable worlds. The Fermi paradox has become only more
paradoxical and these surveys are finally powerful enough to draw some serious conclusions about the rarity of advanced civilizations
and about the chance of us ever becoming one.
Before we get to that
Let's see what the state of the art in astronomical surveys is telling us
Nasa's Kepler telescope has discovered
2652 alien worlds to date
Spotted as they marched across the face of their parent star in chance transit alignments
This number allows us to figure out the fraction of stars that have planets
Essentially all the stars do.
It also allows us to figure out that there are something like 40 billion habitable planets in the Milky Way
By habitable. I mean rocky planets the right distance from their star to have liquid water
TESS, the Transiting Exoplanet Survey Satellite, is now in orbit and taking over from Kepler
It'll find something like 20,000 new worlds telling us once and for all how common earth-like planets really are
And how many of these planets have life?
We have absolutely no idea
We have no way to even start to guess that yet
To answer this question
We'll need to look at the composition of their atmospheres
We talked about this before. Life is expected to massively alter the chemical composition of its home world's atmosphere
We can't see this effect on earth-like planets yet
But the James Webb Space Telescope - launched in a year or so will get close to doing so
There is a good chance we'll have found hard evidence of extraterrestrial life in the next decade or so,
but that's regular old non technological life
Surely a high-tech civilization would be easier to spot
We've been actively watching for radio transmissions from other worlds for half a century. We've seen nothing
Even the famous Wow signal has likely been explained as a mission from a pair of comets
That said our search hasn't even been sensitive enough to see human level transmission in the nearest star system
we're probably only sensitive to deliberate beamed communication of which there are none, but
Radio transmissions may not be our most likely first encounter with et
Assuming any of those guys are like us at all
they'll want to expand into and alter their galactic environment and
Because they almost certainly have a head start on us of at least thousands of years that galactic gentrification
Might be visible to us you might remember
Tabby's star - the strange star in the kepler field that showed these bizarre dips in brightness
some very large collection of
Something is passing in front of the star
Thrillingly, one proposed explanation was an alien mega-structure
perhaps a vast fleet of solar collectors built by the local inhabitants
Sadly, this is not the case
follow-up observations revealed that the wavelength dependence of the dips is consistent with
Dust so likely natural space junk not any type of artificial structure as we like to say on space time
It's never aliens
Until it is for example you these alien solar collectors may be our best shot at spotting other civilizations an
Advanced civilization may launch so many solar satellites that they substantially block the light from their own star
Let's call such a solar fleet a Dyson swarm after the Dyson Sphere
which is the next level up a structure that completely encases a star a
Dyson swarm would cause an
Unusual dimming of its parent star and also cause an unusual increase in infrared light due to waste heat shed by the structure
These are things we can look for. Kepler saw none of this
but actually the best instrument for finding Dyson swarms is the European Space Agency's Gaia mission a
team of astronomers
Scoured the Gaia data looking for stars that were unusually faint for their stellar type
They looked at 8,000 stars and exactly one of those stars had a brightness significantly lower than expected
however
They also figured out that the offending star has a binary companion
Which may have caused a wobble in the Stars position and that in turn may have messed with the Stars parallax distance
determination and the determination of its power output
I.e. the star may just be further away than expected not wreathed in a swarm
But Gaia's upcoming third data release will expand this study from 8,000 to a million stars
If they're out there, we'll find them
Eventually, it's still early days now hunt for ET
But maybe we can at least agree that if there are any technological civilizations in our neighborhood of the Milky Way
They are keeping to themselves
That still seems surprising given those 40 billion possible starting points for life in the Milky Way
After all would only take one of these worlds to spawn an expansionist species
Or even a single individual among that species to launch a single self-replicating probe
give them a million year head start on us just one ten thousandth of the age of the Milky Way and
Someone should have colonized the galaxy by now. Yet we see nothing but detecting nothing is still data
Give astronomers data and they will write papers a number of attempts have been made to address the Fermi paradox based on this new data
This is often done in terms of the famous Drake Equation
Which tries to estimate the current number of communicative civilizations?
by combining a series of factors, there are
Astrophysical factors like the rate of star formation and the fraction of these stars that form habitable worlds
biological factors like the frequency of the appearance of simple life and the proportion of those that lead to intelligent life and
sociological factors like the fraction of intelligent life that transmits radio signals
and how long that communicative civilization lasts
The biological and sociological factors are so poorly understood
That estimates of the number of civilization vary between none to tens of thousands
but now that we have a much better understanding of the
Astrophysical factors and are also pretty sure that there aren't tens of thousands of advanced civilizations
We can actually start to constrain those biological and sociological factors
Astronomers Adam Frank and WT Sullivan did this in 2015
They found that as long as the odds of any given how tall planet spawning a technological species is greater than
one in sixty billion
Then humanity is not the first to appear in the Milky Way
Let's take us even further
Assuming there aren't tens of thousands of civilizations existing before us we must have beaten some steep odds
it must be harder than one in a million to from damp rock to rocketship
Luis Anchordoqui and
collaborators found a less stringent limit on this likelihood by assuming that a lot of life gets wiped out
by gamma-ray bursts a type of cataclysmic exploding star
We covered those before also
These researchers estimate that in order for us not to see any aliens the chance of going from space rock to high-tech
Society must be less than half a percent
Now that sounds high
But remember it's only for the planets not wiped clean by gamma-ray bursts
whether it's gamma-ray bursts or something else our failure to find aliens tells us there must be a
developmental bottleneck or colloquially a great filter that seriously limits the milky way's production of
highly visible Galactic Civilizations
Optimists like to think that humanity has already passed the great filter
That is perhaps it's one of the biological factors of the Drake Equation that keeps the number of aliens low
So watery planets may be abundant
But maybe there's a step in that slow
Evolutionary crawl from primordial chemical soup to techno monkey that makes advanced
civilizations hellishly unlikely
This is something we can come back to but you can look into the rare earth
hypothesis or the gaian bottleneck hypothesis for some plausible proposals
If the great filter is behind us, that's good. It means we made it
It also means we have a long lonely future as one of the galaxy's only advanced species
But hey one is better than none, right?
But our modern understanding of the Fermi paradox
Permits a second interpretation
To wrap up
let's consider the possibility that lots of planets produce civilizations at around our level and
They wipe themselves out with such thorough
Reliability that literally none ever leave a mark on the galaxy
Some scientists have been inspired by the persistent absence of evidence for aliens to investigate this possibility
Statistically, how likely is it that we wipe ourselves out?
Some scientists argue that deliberate annihilation of all humans isn't just possible. It's likely
Joshua cooper and John Sotos point out that the technology needed to create an extinction-level event
will inevitably fall into the hands of many individuals
over time one whack job or
Impulse-control challenged individual will push the metaphorical big red button
Now these researchers focus on genetically engineered viruses
But the principle applies to any doomsday tech
nuclear weapons, genocidal nanobots, willful or negligent environmental destruction, you name it
the researchers argue that all emerging technological civilizations will go through this phase of
massive access to potentially cataclysmic technology
Depending on the destruction probability. Let's call it the wacko factor
You might expect civilizations to last from decades to thousands of years
But even thousands of years is brief enough to help explain the Fermi paradox
Well, that's a nice sobering thought to end on but I should also point out that this same massive access to technology
that could kill us may also get humanity off the earth and on to other planets
So which will come first spreading human civilization across the galaxy or humanity's doom.
I guess it depends on the relative probabilities
Are we more inclined to acts of self-destruction and planetary sabotage
or to acts of preservation and exploration
Well, perhaps more importantly can we actually choose between these?
Well, we sure can try the alternative may be
eternal quiet across the lifeless reaches of space-time
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Last week we dipped our toes into string theory. You guys had a lot to say
Sam Pollard asks, how does adding more particles require fewer dimensions?
well, the answer is supersymmetry
Now this is a type of gauge symmetry that in principle unifies fermions and bosons
Add it to string theory and you get super string theory. Adding the symmetry gives you fermions
But it also shaves off dimensions
Now the details are way beyond a comment response
But look into super string theory and supersymmetry
In response to me saying that string theory has only one tunable parameter
Michael Murphy sarcastically points out that 10 to the power of 500 is a little larger than 1
Now he's referring to the number of Calabi-Yau manifolds that string theorists need to search through to find the geometry of our
universe's extra dimensions
To be fair, it's not 10 to the power 500 different tunable dials
There's only one dial with 10 to the power of 500 different settings on it. So that's just one free parameter
It's not even the 19-ish free parameters of the standard model
Now some string theorists would say that there are zero free parameters all of those 10 to the power of 500 different
possibilities exist somewhere in the multiverse
We just happen to be in the one that makes people
Korbis Barkly and some others ask
Whether if string theory makes no testable predictions shouldn't it be just called string hypothesis?
Well, I'm going to quote vacuum diagrams on this one
Scientists don't actually use the nomenclature that some popularizers of science often insist on
Now that popular definition is expressed reasonably well on Wikipedia.
A scientific theory is an explanation of an aspect of the natural world that can be repeatedly tested and verified in
Accordance with scientific method using accepted protocols of observation measurement and valuation of results
But actually we've always used the word theory to mean again quoting doctor diagrams
Some framework that loosely described allows you to understand some aspect of the natural world
while a hypothesis most often refers to a single claim rather than a
coherent framework that typically comprises many claims
Or to put another way. In colloquial science speak,
a scientific theory is a well-developed suite of ideas laws models and
predictive tools that attempts to explain an aspect of the natural world
It should also have the possibility of making predictions even if they aren't verified yet
There's no separate word for a theory that's not well accepted
but there's still a huge difference between such a scientific theory and say the theory of intelligent design a
Scientific theory is self-consistent and well developed
Eduardo Martinez makes an interesting point
does not the idea of shut up and calculate and we don't care what strings are made of sound a lot like the flaws that
science finds in religion
I guess by that you mean that people in science sometimes accuse religion of promoting belief without
Analysis and evidence. Does science do the same? Surely sometimes
But in the case of shut up and calculate I think science is going in the opposite direction
promoting analysis without belief or rather
valuing the capacity of science to make concrete
observable predictions based on evidence based models and that any
Interpretation beyond these observables is beyond the realm of science.
I personally don't agree with that. I think being able to predict doesn't mean that you understand. I think understanding comes from
interpretation of your models ,not the models themselves
Archie Wahwah wonders why M theory is represented by five interlocking pringles
Well rumor has it that Ed Witten came up with M theory while he was eating Pringles late one night
He was struck by the potential of multi-dimensional Pringles to unify string theory
M is for munchies