Are we blinded by our desire to find extraterrestrial life?

Many astronomers are really driven by the search for Earth twins because I think deep down

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

are we alone? That is a burning itch that I think many of us have our entire lives wanted to answer

I'm sure many of you feel the same way as well. So I think that was what really drives us. But

you know, whenever you have a temptation, a goal, an aspiration that you're reaching for

It is so easy to get blindsided and drawn into dark avenues that aren't really true, especially in science

That can happen quite often. 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. So there is a natural temptation to look at anything that seems anomalous, that seems a little bit different, and immediately reach for aliens

because, of course, deep down, I think a lot of us really want that to be the answer

that we are not alone. This drives us, it inspires us, but it's always a risk that we could go too far into that temptation

and see aliens where there's none really there, and we have fallen prey to that trap many times in the past

The search for alien life. 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, adding on extra terms

So just having how often does the plant 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. And I think this is one of my big problems with the rare earth hypothesis, is that it's

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 so perhaps not only should we be multiplying all those things

but also adding up all those parallel tracks. 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

What is life, though? What are astronomers actually ultimately hoping to detect

Defining life is an incredibly difficult task, and there is definitely no consensus about how to cause 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

So whenever you come up with one of these definitions, it's really easy to poke holes in it and say, well, what about this

What about this? And I think it's just too hard for us to come up with a singular thing to say this is exclusively what life is until we've discovered more examples of it

That's the quest that we're on. We're going to look out. We're going to try and find examples of things which resemble properties of what life does

And then we'll do the hard work of truly trying to classify what actually is life in the first place and where do we draw our boundaries

The necessary conditions for life on a planet are still up for debate as well

We really don't know exactly where the limits of life are. When we look at life on Earth, there are some organisms, especially extremophiles

that can cope with fairly large ranges of conditions. 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

So 150 degrees Celsius range of diversity. 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. And perhaps things as cold as minus 25 degrees Celsius are just way outside of that range

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

Similarly, we can't assume that just because extremophiles on Earth can only survive from

minus 25 to plus 125, that means that life elsewhere could not survive under even more

extreme conditions because it could be based, of course, on different chemistry and use

different thermodynamic rules than the ones that our life currently uses. So there's a lot we don't know, but I think the idea of just narrowing in on the places

where liquid water could survive, which is from 0 to 100 degrees Celsius, that certainly

makes a lot of sense because even those extremophiles still require liquid water as some part in

their life cycle in order to survive. So I would be comfortable with that as an initial hunting ground with the idea that

we might perhaps extend that to more diverse environments as we go on. The Copernican Principle, named after Nicholas Copernicus, also goes by the name of the

mediocrity principle and sometimes in cosmology is an extension of it called the cosmological principle

And all of these ideas essentially say the same thing and that's that where we are, where

we live even when we live is typical Everything about us is normal and therefore we should expect that if we go to another part of the universe it would look basically the same as it does here And usually

this is a pretty good argument. Take for example the instance of Neptune. We have a Neptune, in fact

really two Neptunes in our solar system, Uranus and Neptune, and they don't seem to really play

any part in our own evolution out there in the distant part of the solar system. And so you might

reason, if we have two of them, perhaps other solar systems should have them too, by this mediocrity

principle, the idea that we are typical and normal. And indeed, that would be strikingly true. When you

look out at these exoplanets, that's what we find. We find Neptunes all over the place. They're indeed

a very common type of planet. But here's where it runs into problems. Let's imagine we use the

Copernican principle to argue that the Earth has an oxygen-rich atmosphere. Therefore, all of the

planets in the solar system should have an oxygen-rich atmosphere or liquid water, whatever

you want to choose. And of course many features of the earth are incredibly unique and special to the

earth itself and are not found on any of the solar system planets and perhaps not found elsewhere in

the universe too. We just don't know. And there's a good reason for that and it's called the weak

anthropic principle. And the weak anthropic principle basically points out that you can only

live in a place where conditions are suitable for you to live. So it's not surprising that we don't

live on Pluto. It's not surprising that we don't live on a moon of Neptune because those places are

so cold, they have very little atmosphere, that of course a human being could never have evolved

on such a world. We would of course live on the only the subset of exoplanets or planets in general

where the conditions were right for life and those conditions themselves could be very very rare

Maybe there is only three Earth-like planets in the entire universe as far as we know. It should

not be surprising that we find ourselves living on one of those three Earth-like exoplanets

because perhaps that is the only place where we could live. And all the other places are just

simply devoid of life. So when we use the Capernaum principle, my big caveat would be, look

it's okay to use it when it has nothing to do with our survival, our emergence. Neptune, fine. Neptune

has nothing to do with why we're here. There's no way which Neptune affects life on this planet

But the moment you use it in a case which is connected to our existence, which is predicated upon our existence

such as maybe the presence of a large moon or oceans on our planet, then we have to be very careful

I don't think in those cases we can reliably use the Copernican principle because if we do in the solar system, it clearly fails

So in that case, I think we should just take a beat and really yze how connected we are to the statements that we are making

And that's why I do not buy the argument that by the Copernican principle, life must be common

It's kind of a circular statement I would claim to make that argument

One way that we have attempted to classify hypothetical alien civilizations is with the

so-called Kardashev scale. So the Kardashev scale basically splits civilizations up by energy usage and maybe that's a somewhat

archaic way of thinking about it. Today I think maybe we might think about capabilities more than energy usage but this has still

remained a very persistent way in which astronomers think about how we might split up civilizations

So a Kardashev type 1 civilization is defined as a civilization which uses all of the energy

which is incident upon its planet. And we are not there yet

We do not have our planet covered in solar panels and use that amount of energy

That still greatly exceeds our current global energy consumption. A type 2 civilization would be one which not only uses all the energy on the planet, but

uses all the energy of the star. So you might imagine a type 1 civilization being able to control their weather and their

But a type 2 would be able to control the entire solar system. They have to move planets and moons around at will as they needed

And practically speaking, in order to harvest all the energy of a star, you probably need

to build some kind of giant shell around that star, often called a Dyson sphere, after Freeman

Dyson, who first proposed that idea. And that shell or swarm of material would absorb all of that starlight, which you could

use for whatever you want to do, computation, manufacturing, whatever. advanced purposes these civilizations might have for such an energy need

And if you just go another step further, you can do to Kardashev Type 3, and that's one

that not only controls their solar system and all of the energy output of their solar system, but now goes to the entire galaxy

I think most realistically, you might imagine a civilization like that living around Sagittarius A-star

That's the supermassive black hole that lives right in the center of our galaxy

And that thing spews out gigantic amounts of energy that you might imagine a very advanced

civilization, harvesting and using. And indeed, I think it's an interesting place that we should

consider looking for alien civilizations. Maybe not an intuitive place, but a place that I think

we have a good argument as to why they might end up in the center of a galaxy. Hart's fact A

named after Michael Hart, is connected to the Fermi paradox, the idea as to how come we don't

see aliens out there if it seems like they should be out there. And fact A in particular 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

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 Earth with another alien civilization. I feel much more confident making that claim

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't be here. This really connects

to the ideas of self probes also called von Neumann probes which have been argued for a long time to be a real problem for those thinking about life in the universe and especially life in the galaxy For it turns out that even though the galaxy is very

large, 100,000 light years across, 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 colonize

the entire galaxy many times over during its 13 billion year history. That's a long period of time

for all of that colonization to have taken place. And you really don't need to have fast rockets

to have colonized the entire galaxy by now. Yet clearly that hasn't happened as fact A

demonstrates. And so that's interesting. It means that maybe civilizations do emerge elsewhere in

the galaxy, but they never have the will or the capabilities to conduct such an expansion phase

such an aggressive expansion phase, where they take over the entire galaxy because, of course

we wouldn't be here had that had happened. That is probably one of the strongest data points I

think we have. We don't have any evidence for life outside of the solar system. And so when we talk

about the propensity of planets to form life, probably the only strong data point we have is

the fact that we're here, but also, more importantly, when life appears to have emerged on the Earth

And strikingly, it appears to have emerged very, very quickly in the Earth's history

Now this naively could be taken to say, well, therefore if life starts quickly

it must be an easy process. But we have to be careful when making such claims

Perhaps the evolutionary process to go from the simplest forms of life to something like us

as a self-aware entity which can do all of this paleontology, all the statistics and math

maybe that time scale takes 4 billion years, pretty much all the time on these types of planets

And if it consistently takes 4 billion years for that process to play out

life kind of has to get going pretty quickly, else there wouldn't be enough time for us to have emerged in the first place

I think a surprising fact about the Earth people don't realize is that it will likely become uninhabitable to complex life in less than a billion years' time

And so life really does have to get going quickly, else there just wouldn't be enough time in that evolutionary process to get to us

So we could naively look at that early start to life and say, therefore, life is easy

We add this complexity of evolution, say, maybe not so quickly. But eventually, if we push that early start to life further and further back

you eventually overwhelm even that evolutionary timescale. And you do end up with a genuine result that actually there's no way around it

life actually is an easy process, despite all the nuance of that evolutionary argument

And indeed, I think for the first time, we are seeing signs that we are crossing that threshold

There was a recent result that we are able to date the emergence of life on the Earth

to 4.2 billion years ago. And for context, the oceans formed 4.4 billion years ago

So within 200 million years, really a cosmic snapshot, we had the conditions ready for

emerging and we went all the way from there to the first organisms on our planet within 200 million

years. That is such a short period of time that it overwhelms that evolutionary argument and you have

for the first time I would claim strong evidence, not definitive evidence, but strong evidence that

life is indeed an easy process to get going at least under the conditions that the earth enjoyed

So based off the early start to life on the earth we might genuinely think that simple microbial life

could be quite common, at least assuming that Earth-like conditions are common in the universe

So we'd have lots of planets out there with simple life on Earth. Now the interesting question then

is how often do those simple life forms develop and evolve all the way up to something that is

like us? Here it took four billion years, perhaps it takes a little bit less or a little bit longer

on other planets. And so we might look forward to the future and say if it takes four billion years

for this process to happen, surely as the universe ages there should be an emergence of more and more

civilizations into the future. But we actually have to be a little bit careful with that argument too

because stars and planets have finite lifetimes. They don't last forever. They eventually die. Our

own earth will die as a habitable biosphere in less than a billion years due to the evolution

of our star. As the star evolves, it grows in luminosity and will eventually make the earth

too warm for liquid water and thus life on our planet. So there'll be a collapse point in less

than a billion years when that happens. So this sets a time constraint for life in the universe

Not only do you have to have life get going fairly quickly, then you also have to have enough time

for that evolutionary process to play out and get to something like us

And this immediately rules out a large swath of stars as possible places where a civilization might live

For example, stars which are more massive than the stun have shorter lifetimes

They burn through their nuclear fuel much faster. And so perhaps those stars wouldn't have enough time

for a civilization to develop on them. Vice versa, we have the M-dwarf stars

stars which can last for trillions of years in some cases. And so potentially there, that might be the place

in the far future, we can imagine civilizations emerging and we would be the first, the weirdos of the universe

who lived around a sun-like star early in its history and civilizations emerged much later on

around these M-dwarf stars. 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 buyer signature case certainly has had I say greater attention from entities like NASA and government funding agencies because after all you don 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's the theory. The problem is it's 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, especially because oxygen is a very reactive molecule that really doesn't want to hang around in an atmosphere

Something has to be making it because otherwise it just reacts with stuff and oxidizes and so quickly disappears

The fact that our planet has a sustained level of oxygen proves essentially that life is here

At least that's true on the Earth. 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 that atmosphere, H2O, the H2O will be split up into the hydrogen and the oxygen separately

Now hydrogen is very, very light. It's the lightest element you can have

And so it's very easy for it to escape into space and simply be lost, like letting go of a helium balloon

that disappears into the sky. But the oxygen is heavier and it sinks

And so you can end up with just ultraviolet radiation plus water in the atmosphere

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. So it's a very complex chemical

field that we're involved in but ultimately a tractable question but a question that we still

need to work really hard on. From a scientific perspective the question we really care about is

looking for life on these exoplanets and indeed planets in the solar system as well. So for example

Mars is a good case study. We have sent robots there which have attempted to look for life

and a big question has always been are we accidentally carrying life with us to that

planet and thus when we do the experiment to look for life are we maybe accidentally detecting just

life which hitchhiked a ride and joined us on that journey and arrived at Mars without really

that being the intention. It's actually very very difficult to totally sterilize a spacecraft and

eradicate every single spore on the surface of that thing. There is essentially always going to

be a little passenger which hitches a ride with you but we of course want to minimize that as much

as possible to reduce the chance of that being a false positive. And so this raises some interesting

ideas about where is the best place to look for life because Mars has had a lot of contamination

not only from spacecraft from the Earth, but also asteroids. Even before we had a space program

there was still material being constantly swapped between the Earth and Mars just by meteorites

being knocked off one and landing on the other. So perhaps life has long contaminated Mars even

before humans were around. But there are places in the solar system where that shouldn't have

happened. You look at the icy moons of Europa and Enceladus, for example. Those are protected

by a thick ice shell, many kilometers thick, which should really prevent any material being

able to penetrate through the ice and get into that subsurface ocean

So for me, I think those are the most interesting places to look. We could drill down through, hopefully be very careful about contamination, and we would

have a pristine location where if we detected life there, I think we could be pretty assured

that was not a contamination from the Earth. This was a genuine second abiogenesis event

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

I think we have to accept the possibility that even though we're on this quest

to look for life in the universe, we may never get a conclusive answer either way

I certainly hope that we can find an answer, but it is possible we never will

For the truth is that space is just a very, very huge expanse to try and explore

and have conclusive answers on. 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 what hope is there in that sense of ever proving that we are alone

It's impossible to prove we are alone. We will always wonder about that

We can get a series of null results, of negative results, but it's never going to establish true loneliness

The fact that space is simply so large means this is a challenge that maybe we should be patient

I mean, I hope we can get an answer in my lifetime. I would love to know the answer in my lifetime

But this may be a journey 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 want to support the channel join the big think

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