How close are we to finding alien life?

For me, I think what we're doing right now is a bit like being the map makers

If you go back 400, 500 years, we really didn't know what the shape of the globe was or where

the continents were. And people were voyaging out into the unknown and drawing the first maps of

what might be out there. And I think a lot of what we're doing right now is kind of similar

as astronomers. We are map makers, essentially. We are looking out and trying to draw not the

continents, but the maps of the exoplanets that our distant descendants might one day

visit and perhaps even build colonies on. And the question is why do we have this urge? I think deep

down the natural endpoint of this whole goal of looking for planets is to answer the question

are we alone? The fact that space is simply so large means this is a challenge that humanity

undertakes over not just centuries but maybe millennia into the future. In the similar way

that Galileo 400 years ago was first starting astronomy and couldn't have imagined how astronomy

and the discovery of exoplanets and cosmology would be born from his creation of the telescope

We have a long journey ahead of us in astronomy too to answering this question about life in the universe

but it is the great question and a question which I think many of our future descendants

will be inspired to continue studying. My name is David Kipping. I'm a professor of astronomy at Columbia University

and director of the Cool Worlds Lab. There's a long history of people claiming planets which look Earth-like, Earth 2.0

Earth twins. I think a famous example was Gliese 581 g. That got a lot of people very excited

but of course within I think two or three weeks, another independent team showed that this planet

was not real. And so we've already had several claims of not only Earth-like planets, but even

life. There's been claims of life on Venus, there's been claims of life on interstellar asteroids

and of course there's many UFOs that we often hear about. And so there is a sense of exhaustion

at this point. I think a lot of people probably naively assume that we have a whole bunch of

Earth twins at this point, and that's really not the case. One of the hardest scientific aspects of

this is that you can't prove a negative. So I can never prove to you that Mars does not have life

on it. I can look at the surface and claim on the surface, I am 99% sure there are no microbes

But then you could also say, well, what about underneath the surface? Have you checked there

What about underneath that rock over there or behind that canyon or behind that hill? And so

I can never totally prove, totally prove, even on the nearest planet to us, Mars, that it does not

have life on it. So there is a natural temptation to look at anything that seems anomalous, that

seems a little bit different, and immediately reach for aliens. And when we're looking for aliens

of course, the question is the Fermi paradox. Then Rico Fermi asked this question, look, if there's

so many good arguments as to why life should be out there, how come we don't see any evidence for

them? And Hart's Fact A, named after Michael Hart, points out that there are no aliens on Earth right

now. We don't see a civilization cohabiting the earth with us, we haven't been totally colonized

by an alien civilization, it appears to be a very lonely planet with just one civilization which is

us living on it right now. Now what I like about Fact A is it's kind of indisputable, it's one of

the hardest points we can really say in astronomy. I can't claim that a distant exoplanet doesn't have

an extraterrestrial civilization on it but I can be much more assured about the fact that we are

not currently cohabiting the Earth with another alien civilization. For it turns out that even

traveling the galaxy at sort of Voyager 1, Voyager 2 type speeds, the speeds of our current spacecraft

it should have been eminently possible to have colonized the entire galaxy many times over during

its 13 billion year history. And even that claim, as weak as that might seem, does put some

interesting limits upon the behavior of other civilizations. It means really that a galactic

civilization does not exist. That there is no instances of a marauding berserker type civilization

that just decided to gobble up every exoplanet, every real estate it could find and turn it into

another colony for itself. Because if that happened, the whole Milky Way would have been

colonized by now and we wouldn be here That is probably one of the strongest data points I think we have One of the primary tools that astronomers use to think about the abundance of life in the universe

is the famous Drake equation, first written down by Frank Drake. It is essentially the number of stars in the galaxy

multiplied by a long list of possible factors, such as how often do you have planets

how often are those planets Earth-like, how often does life begin on those planets, and so on and so on

Now, when we look at this, it's like a narrowing filter, And you can imagine with the rare earth hypothesis by Ward and Brownlee, adding on extra terms

such as having how often does the planet have a large moon? How often does it have the same mass as the earth

How often does it have the same land mass fraction the earth has? Or the same ocean salinity or chemistry, etc, etc

And you can imagine adding on hundreds, even thousands of extra parameters onto the Drake

equation, which get ever, ever narrower. And of course, if you multiply a very large number of fractions together, you'll eventually

get zero. Now, on each one of those criteria, you can make a good case as to why life on Earth indeed requires those conditions

However, we really don't know whether life elsewhere does or does not require the same conditions that we enjoy here on the Earth

So, for example, there's some thermophiles that can range from minus 25 degrees Celsius

and you have other extremophiles which can live at 125 degrees Celsius

But the fact that extremophiles today can survive in such an extreme range of temperatures

doesn't mean that life could begin under such an extreme range of temperatures

Maybe the nascent conditions for the birth pangs of life to begin with

the abigenesis event, the spark of life which created all life on the Earth

maybe that requires a very special and subtle temperature range that cannot be violated

These are questions we just don't know. what were the initial conditions on the Earth that led to the emergence of life

And if you just go another step further, even defining life is an incredibly difficult task

and there is definitely no consensus about how to call such a thing. Maybe it's actually better

to call it more like porn, like you will know it when you see it, rather than having a strict

textbook definition of it. NASA have certainly tried to have a definition. For a long time

we had a definition from NASA that said it is a self-replicating chemical system capable of

Darwinian evolution. And that's pretty good, but maybe chemistry isn't actually necessary

Maybe you could have an AI system or self-replicating technology that would still

resemble life in many ways, but wouldn't actually involve the kind of chemical systems that we're

familiar with. And I think this is one of my big problems with the rare earth hypothesis

is that it's a very narrow view of how life began and how life must survive on other planets

All of these factors have to be true. It is a singular path

And that is a path which has indeed led to success. But perhaps there are different paths parallel to us

which are completely different yet also lead to life. And so the Drake equation simply multiplies fractions by each other

But perhaps truly what is missing is an additive sign. There is a second path below it, a different way of getting to intelligent civilization

and a different way after that and a different way after that. And it is that addition that we just really can't do

without a lot of creativity and discovery because right now we only have this sole example to look at

So there are two basic strategies which we might attempt to search for life in the universe

One is with a so-called biosignature, that is a signature of biochemistry essentially

on another planet, and a second is a technosignature, the signature of technology. Now technology

obviously requires that not only do you have life, that an advanced civilization also developed on

those planets. And so that naturally seems like a smaller piece of the pie to look at. However

those technosignatures could be very, very loud, heard from millions of light years away potentially

and could also perhaps be very persistent. We can imagine a civilization maybe building

a beacon or something that could last for billions of years to perpetuate its knowledge

into the cosmos. So a simple balance is not so easy in weighing which of these options would be

most fruitful. The biosignature case certainly has had, I'd say, greater attention from entities like

NASA and government funding agencies, because after all, you don't require all this evolutionary

complexity. You can just have simple life and potentially still be able to see them

The way biosignatures work is to look for gases that are emitted into the atmosphere which are uniquely produced by life At least that the theory The problem is it very difficult to find gases which are indeed uniquely produced by life

Lots of gases can be produced through geological processes as a side product

and so that can become a false positive to our search efforts. A classic example of this is oxygen

Of course, plant-based life manufactures oxygen on the Earth through the process of photosynthesis

And so it would seem like oxygen would be a good thing to look for. But we could imagine different types of planets where oxygen is being manufactured without the need for life at all

One possible way this could happen is through a process called photolysis

So ultraviolet radiation from the sun strikes the upper atmosphere. and if there is water in the atmosphere, that water will be split into hydrogen and oxygen

generating a significant amount of oxygen in a planet without any life involved

And so that signature would be a false positive for us. If we're not careful, we would interpret that to be life, whereas in fact it is not

And so astronomers, chemists, biologists, we're involved in this game now of trying to imagine

all of the different signatures that life could produce and all of the different confounding factors that might trick us

and trying to find those unique combinations that we really trust as being the smoking gun that this has to be life

And once you have two starts to life in the solar system, that would essentially establish that life really would be everywhere in the universe

SETI, S-E-T-I, is the Search for Extraterrestrial Intelligence. It is essentially an effort to try to detect the radio signals

or possibly even more broad than that, laser signals, whatever signals you might want to look for

from another civilization out there in the galaxy. Now, there is a strange aspect for SETI

We have this kind of paradox that we are listening for radio signals

from beyond, from these other planets, but we don't really transmit much

In fact, when the field first began, it was actually called CETI, and that C stood for communication

Very quickly, they changed their minds and realized that the idea of a two-way communication was maybe a bit ambitious

and it might be better just to focus on searching for the signal rather than truly trying to have a dialogue

In the remote contingency that there are interstellar space-faring societies, We thought we would put a message on it to indicate a little bit of where we are, when we are, and who we are

So on the other side, we have the idea of METI, messaging extraterrestrial intelligence, also called Active SETI

So this is where we actually send out a message hoping to get a reply at some point in the distant future

Of course, that could be hundreds or even thousands of years, given the vast expanse of space beyond us

Now, METI is a little bit controversial. Stephen Hawking had the concern that, you know

maybe we should be very careful about communicating to the civilizations because whenever you've had a more advanced civilization

engage with a less advanced civilization on the Earth, that has usually ended very badly for the less advanced one

And so if you extend this out to the galaxy, maybe we should be careful about sending out our presence into deep space

And certainly this is a trope that has been played with in science fiction as well

If you look at Liu Xixin's three-body problem, That's where we get the idea of the dark forest hypothesis, the idea that civilizations could be out there, dangerous, marauding ones who want to take over and colonize your planet

And so it's much better to just be quiet. Don't let anybody know that you're here

I do have a bit of an issue with this idea of resistance to METI and resistance to communication

and that's that we humanity are already engaged in the activity of trying to build telescopes and

future facilities that can detect life whether they want to be detected or not. So you don't

have to send out a radio wave for me to be able to detect your civilization. We could potentially

detect their satellite systems, their star links, we could detect their solar panels on their surface

we could detect their industrial space presence, even the chemical pollutants in their atmosphere

from industrial processes. There are so many ways that we could imagine being able to tell

there was a planet that had advanced civilization on it without the need for a radio message

that it's a little bit archaic to assume that that's the only way that a civilization would

be able to know of another one presence I suspect if there is another advanced civilization out there in the galaxy they already know that we are here And so I think it would be difficult to argue

that we should be very, very quiet because otherwise they will never know we're here

I suspect they are well aware that this plant is inhabited with or without our radio signals

Communicating over large distances, and really we mean extremely large distances when we're

talking about the galaxy, requires a lot of energy. And so this is a real problem. If you

want to communicate your presence across the entire galaxy, you're going to need a transmitter

which is ultimately the size of a planet or even the size of a star, and it has to be turned

on all the time. For as soon as you turn that signal off, of course, the light wave will stop

And so you're going to have a finite time in which you could be detected. So an interesting question

is how could we build a communication system that would be much more long lived? There's an

interesting idea by Luke Arnold, he suggested that rather than trying to build a giant transmitter

be it radio or laser or whatever it is, instead, you do something passive. And so his idea was to

exploit the transit method of looking for exoplanets. We could build a giant structure

in space of a very elaborate shape that would transit in front of the star, maybe a giant

triangle for instance. And as this triangle transits in front of the star, it would create

a very remarkable and alien-looking transit signature, something which nature should never

produce that we would be able to tell from afar there must be a civilization who built that

And the beauty of this is that it requires no power system. The sun itself is powering that for billions of years

It requires no mechanical parts, no maintenance. It's just going to sit there for billions of years saying

hey, there is somebody around this. Another example is to leave something physical behind for them to find

And of course, this is an idea that was played with the film 2001 A Space Odyssey

where there's these monoliths which are left within the solar system, especially beneath the lunar surface

I think that is a really terrific place to leave something. The moon has no active geology

It has no atmosphere. It has no weathering. Think about Neil Armstrong's footprints

They're going to be there for at least a million years. So anything that you leave on the lunar surface is going to be preserved for a very, very long time, millions of years

We could potentially encode a message, maybe an LLM, an AI agent that can teach another civilization about who we were

And the extra benefit would be, of course, to bury it maybe a meter beneath the surface where you're now protected from micrometeorites as well

I think to some people this idea can be a little bit depressing. We maybe have the idea that we want to actually meet them on the White House lawn, shake their hand like we see in sci-fi films and have a communication, a dialogue in real time

But if we're being more realistic about it, maybe that's just never going to happen. And if we concede that that might be an improbable circumstance, perhaps the next best thing we can hope for is to communicate not in a simultaneous sense, but through time

We could leave something behind in the same way that our ancestors speak to us through the monuments they left

We too have an opportunity to build something on the moon, I would claim, that could last for billions of years and be a record

And perhaps, perhaps the most likely advanced civilization that is going to discover that relic that we leave behind will be a future descendant of the Earth

For the Earth has another billion years left to go in its evolutionary history

And think about all the advanced evolution that has occurred in just half a billion years

We've gone from single-celled organisms to us. What's going to happen in another billion years

We will probably disappear at some point. And I can imagine not just one, but perhaps multiple advanced civilizations re-arising on this planet, having their own space ages

And they will go to the moon, find this relic, and perhaps know something about who we were

To me, that is the most likely alien encounter we're going to have

Want to support the channel? Join the Big Think members community where you get access to videos early, ad-free