- (unknown speaker) I've wondered almost every single day
of my life, what else could be out there?
Haven't you?
- Space is a vast ocean of truly gargantuan scale
amongst that immense darkness peppered
with billions of stars, trillions of worlds.
We wonder, could there be others out there?
But knowing where, when, and how to listen alludes us.
There could be thousands of messages
washing over our planet right now.
Unimaginable wealth of knowledge
drifting between our fingertips
but we simply haven't figured out
what we should be looking for.
Are we doomed to never truly hear?
Are we fated to always be alone?
Provocatively, the solution to our dilemma might lie
in a thought experiment from game theory.
Consider the following problem.
You are instructed to meet
with a total stranger somewhere in the US.
You are not given the time, the date, not even the location
and your life depends upon successfully making this meeting.
And indeed their life too, also depends on this.
It seems like an almost hopeless task,
but remarkably there is some hope.
You know that this person is presumably
another rational entity who doesn't want to die
and so will do their best to succeed in this task.
Since we're in the US, they're presumably familiar
with American culture and geography.
Now there's no single answer to this puzzle
but a reasonable guess might be
to pick New York City as a meeting point,
being the most populous economically active
and famous city in the country.
Now, let's think about time.
Rather than picking some arbitrary calendar date or time,
you might want to pick a moment that stands out.
The most obvious choice would be New Year's Eve at midnight
but exactly where should you meet in New York?
There's a few possible options.
You could meet right here in Times Square
but it's pretty busy.
It'd be very difficult to find that stranger.
Perhaps, a better option might be the Empire State Building.
Yes, there's a lot of flaws to cover and plenty of people
but it's one of the most well known landmarks in the city.
Or maybe you might try Grand Central Station,
right by the famous clock
because this point in time and space is special.
And in game theory, it's known as a Schelling point.
The ABC network actually did a modified versions experiment.
No one's lives are at risk and they had multiple chances
but remarkably after just a few hours,
strangers did successfully meet at the Empire State Building
- Are you looking for two people from ABC News.
- Yes.
- So are we.
(people laugh)
- Whilst game theory might at first seem rather irrelevant
to the field of astronomy,
these Schelling points have become the subject
of increasing discussion within the community.
In particular astronomers attempting
to detect the communications from alien civilizations,
often dubbed SETI, realized just how crucial
these focal points are in their search.
It was economist Thomas Schelling, who first described these
in his 1960 book, The Strategy of Conflict,
writing that people can often concert their intentions
or expectations with others if each knows
that the other is trying to do the same.
Now, I don't think that Schelling had aliens in mind
but the same philosophy actually holds true.
Because if we are gonna try and search
for alien transmissions and it helps if both parties
have a central focus to hone in.
Or else, the search area is simply too vast.
The idea of a focal point like this,
is actually not new to SETI.
Indeed, even what it's arguably the first serious SETI paper
by Morrison and Cocconi in 1959,
they suggested radio searches should focus their efforts
on one frequency in particular.
To quote, "There lies a unique,
objective standard of frequency
which must be known to every observer in the Universe:
the outstanding radio emission line
at 1,420 megahertz of neutral hydrogen.
This was later coined the radio water hole
but it's really a radio frequency Schelling point.
Why so?
Well, hydrogen is the simplest element possible
and it is the most common element in the universe.
Yet more, it's a mission line caused by the spin flip
of it's single electron, lives almost exactly
where the universe is naturally quietest in the radio.
So this really does seem like a perfect choice.
Of course, the problem here is that how can one be sure
that aliens would arrive at the same conclusion?
Well, one modification to this, it's not just search
at that one hydrogen line, but to search all
of the integer multiples of that hydrogen frequency.
And indeed, that has become a fairly common strategy
in modern setting, but maybe aliens don't think
of hydrogen as fundamental at all.
As strange as that might sound to us.
- One alternative radio shelling point
was recently suggested by a friend
of the channel, Professor Jason Wright.
Wright suggests that Planck units might be the key.
Planck units are combinations of the fundamental constants
of the universe that give the various basic dimensions
like distance, time, and energy.
Max Planck himself, called them natural units since,
and I quote "they remain meaningful for all time
and for all extra terrestrial and nonhuman cultures."
If aliens know about the fundamental constants,
then they should also know about the Planck frequency.
Energy and frequency are interchangeable
when we are talking about light because the energy
of a photon is simply the Planck's constant H
multiplied by the frequency of light.
And it's here that we see the problem
because the Planck frequency or correspondingly,
the Planck energy is rather extreme.
It corresponds to an energy
of 10 to the power 28 electron volts.
That's far more energetic
than the most energetic photons known, let alone detectable.
To get around this, Wright suggests
that they would multiply this energy
by the fine structure constant repeatedly,
creating a kind of comb of Planck frequencies
to search through.
Now that's not a totally arbitrary choice.
The fine structure constant with a value
of about one over 137 is a constant that is fundamental
to electromagnetic radiation, such as radio emissions.
You can see here, the final list of possible frequencies.
Many of which fall the range of various existing detectors.
Crucially, you'll notice that none of these
are particularly close to the hydrogen line
used by SETI for decades at 1420 megahertz.
So perhaps we've been looking
at the wrong shelling point all along.
Choosing the right radio frequency is really
just the tip of the iceberg
when it comes to Schelling points in SETI.
After all, one might question whether radio
is really the right part of the spectrum to be looking at.
What bandwidth they might use.
And even whether electro magnetic radiation
is the right medium to be considering at all.
And going further. what about Schelling points in space
and in time?
The actual method of transmission is a topic
which we have identified no clear Schelling point.
Or should I say Schelling method?
There's a general consensus that transmission
should use something which propagates as fast as possible,
that is at or close to the speed of light.
So this gives us electromagnetic radiation,
IE, light as a natural contender,
but that's not the only option.
What about gravitational waves or neutrinos?
These two have certainly aroused interest
within the SETI community,
but add difficulty in detecting these means
that they've largely been a fringe topic.
It's a bit like suggesting that the peak
of the highest US mountain, Denali in Alaska,
as a meeting point to our initial stranger problem.
Sure, it's a special place being the highest peak
but it's highly inaccessible to most humans.
But perhaps, to a highly advanced civilization
that peak isn't particularly challenging nor is
using neutrinos any more challenging than using light.
Plus, it would have the added advantage
of filtering out those less advanced species
that they might not be interested in talking to anyway.
And of course, one could even go further than this
and imagine a hyper-advanced civilization
embedding their messages
into something even more fundamental.
Could they inscribe their messages
into the cosmic microwave background?
Or arrange the core size around us
into a particular pattern?
Or even codify their messages
within the fundamental constants of the universe itself.
It's easy to fall down the rabbit hole here
and muse on ever more speculative ideas.
But if we come back to the original Schelling idea,
then I think we can largely discard these more exotic ideas.
If the other parties modus operandi
is one of vastly greater capabilities to that of ourselves,
then a meter may be frankly unlikely, to ever happen.
It would be a bit like taking that original example
of meeting a total stranger in the US
but replacing that person with, let's say a pigeon.
It's pretty unlikely that we're gonna have any agreement
about what an obvious time
or place to meet up would be.
Yet more, they are plausibly far less interested
in us anyway nor would we have the ability
to reply to them in the same way.
I'm skeptical that we can even define a Schelling point
if the other party is assumed to be far more advanced
than that of ourselves.
No.
Better, I think to focus
on communicating with a less advanced party.
One that has a greater intuition about our own abilities
and thus, would choose a point
that we too would naturally consider
to be a Schelling point.
And on that basis,
electromagnetic radiation is the clear winner.
It's a technology we've been using for communication
for more than a century.
Yet, it travels at the speed of light
largely unimpeded through space.
A final topic I want to discuss here is space and time.
Let's start with space.
Schelling points in space
are perhaps most naturally the stars.
Yes, there's a lot of them
but we can at least hone into specific locations on the sky.
One might consider looking towards the galactic center,
the Times Square of the galaxy.
But this raises a practical problem of how the other party
would move their transmitter into that line of sight
unless they just happen to live there.
Whilst this is perhaps
within the realms of a highly advanced species,
it's certainly not something
that we could ever imagine doing for a very long time.
So if we just return to the stars then,
is there anything else that we could do here
to focus in on an interesting sub sample of them?
Several groups have suggested that stars
which have the correct position in the sky,
such that they can see the earth eclipse
or transit in front of the sun, could be just that.
These stars essentially lie within about half degree
of the ecliptic plane,
the plane in which the earth orbits the sun.
Professors Lisa Kaltenegger and Jackie Faherty,
recently calculated that there are 1,715 stars
that are within a hundred parsecs
and that have been in that zone long enough
to have witnessed the beginnings of human civilization.
Yet more 75 of these
have already had human radio leakage wash over them.
So they may already know about our technology.
Professor Evan Karens takes this a step further.
Higher lighting that some of these earth transit zones
will not only see earth transit
but we could see them transit too.
This happens if their alignment in space happens
to be coincidental with our own.
Like a geometrical bridge, they can see us
and we can see them.
So in principle,
both parties could detect life on each other.
Karens has even suggested that this setup
disarms the usual resistance to broadcasting one's presence.
Since now both parties
can quite easily find each other regardless.
With methodology and space covered,
we are now finally ready
to get into Schelling points in time.
Now sure, an obvious strategy
is that one could just broadcast your signal
out into the universe continuously
but that would be a rather expensive enterprise.
Perhaps instead, civilizations save up their resources
for one loud bang into the dark
that would be much more easily detected.
But then, that raises the obvious problem.
How do we synchronize the transmitter
and the receiver to have a chance
of actually catching that signal?
In our example of meeting a stranger New Year's Eve worked
because we all know the calendar
but there's no such calendar for the galaxy.
For example, each star has a different location
and thus, orbital period around the galactic center.
One suggestion in the literature is
to use high energy astrophysics events
as synchronization times.
Gamma ray bursts are a great example of this.
Since they're fairly common.
They have short durations.
Are bright and appear all over the sky.
In principle, they may be predictable too
since several merging black holes observed by LIGO
were subsequently found to produce such bursts.
Another suggestion is to come back
to the earth transit zone idea.
Here, there is a special moment in time
when the planet passes in front, transits its star.
We have such a special moment, such a Schelling point.
I've even built upon this idea myself
by suggesting that even if the geometry
of that system is not crefort transit,
we can still measure and predict the planetary motion
around that star and those defining special orbital moments
when we could search for these signals.
For example, the moment of inferior conjunction
is when the planet is physically closest to us in space.
Which is where transits would occur,
if the alignment were correct.
Another suggestion might be the quadrature points
of the orbit or perhaps even times related to the orbit
of a possible moon around that planet.
So as hopefully you've been able to see then
whether we're discussing the how, the where, or the when,
there is no one singular, unambiguous, clear Schelling point
but then if we think about it, going back
to that earlier example of meeting a stranger
somewhere in the US, that also wasn't true there either.
But unlike our meeting, the stranger case
we don't have to risk it all on a single bet.
We can lay down several hedges on the board
watching multiple locations at multiple times
in multiple ways.
Still a focused search but one that gives us a better chance
of picking the right Schelling point.
But I wanna hear what you think.
Do you think that aliens would indeed use Schelling points
to transmit to us?
And indeed, which of these do you think
has the best chance of success?
Perhaps a fun question for the comments is,
can you think of a Schelling point on the internet?
For me, Schelling points have a certain romanticism
about them like two long, last lovers, trying to reconnect.
Not sure where they move to or even how long it's been
but perhaps visiting their old haunts,
the street that they grew up on,
the burst they used to ride in desperate hope of trying
to catch them once more.
Despite the enormous challenge,
the seemingly slim chance of success,
we're compelled to try because as hard
and as hopeless as this journey may sometimes feel,
there may very well be someone out there right now,
desperately trying to make contact with us
and like so many things in life,
the moment that we decide to stop,
is the moment that we've committed to failure.
So until next time, stay thoughtful and stay curious.
(upbeat music)
Thank you so much for watching everybody.
We actually have a couple of SETI projects
ongoing in our research team right now.
If you wanna help us out, you click the link up above
and become a supporter to the Cool Worlds Lab right here
at Columbia University
just like one of our latest donors.
I wanna thank Ian Atar.
Thank you so much for your support, Ian.
All right, have a cosmically awesome day out there.
Now, see you in the next video.