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Despite decades of concerted effort by radio astronomers working on the project
known as SETI, the Search for Extraterrestrial Intelligence, we've had no sign
of beings elsewhere in the universe that match or exceed us in smarts. That's
just one of many pieces of evidence that paleontologist Peter Ward, coauthor of
Rare Earth: Why Complex Life is Uncommon in the Universe, points to when
claiming that intelligent life beyond Earth must be exceedingly rare. Since
many other scientists believe advanced life is common out there—Carl
Sagan estimated a million intelligent civilizations in our galaxy
alone—NOVA eavesdropped on astrophysicist and "Origins" host Neil
deGrasse Tyson playing devil's advocate in a conversation with Ward about
extraterrestrial intelligence. Here's what they had to say to each other:
Time is of the essence
Neil deGrasse Tyson: Peter, when you combine the fossil record on Earth with all that we
know of biology and evolution, what can we expect as we look for intelligence
elsewhere in the cosmos?
Peter Ward: There are maybe 30 million species on the planet today—10 to
30 million. If we look at the fossils, there are hundreds of millions of
species in the past. And one time on Earth has intelligence arisen to the point
where we can build a radio telescope (which is the definition of intelligence
to a radio astronomer). One time out of hundreds of millions of possibilities.
That's an astronomically small number of intelligences that have
arisen—just one.
Tyson: At last tally, there are several hundred billion stars in the Milky Way
galaxy and perhaps 100 billion galaxies in the universe. Yet according to your
book, we're just cold, dark, and alone.
Ward: No, we're not alone; we're lonely. There's a big difference between being
alone and being lonesome.
Tyson: But in this big galaxy of ours—hundreds of billions of
stars—surely Earth is repeated many places, many times.
Ward: We got to intelligent organisms on this planet after 500 million years of
animal life. Now, that doesn't say you couldn't get it sooner at other places,
but you still need long periods of time. And to me that is the major argument
against there being intelligent civilizations. We are on a planet that's very
safe, a planet that has not been repeatedly bombarded by the thing that killed
the dinosaurs—asteroids. How many other planets are going to have such
long periods of time? Not many, I think.
Tyson: But suppose life is common in our galaxy. We are now asking, of all the
planets with life, isn't intelligence surely going to show up?
Ward: I still think it's a question of time, Neil. I agree with you, I think
life is pervasive in the galaxy. I think that the way the Earth has
extremophiles [organisms that thrive in extreme hot or cold habitats], the fact
that we can have life living in so many bad environments, suggests that you can
have life in really nasty, nasty places.
But it takes time to evolve into a T. rex or an Allosaurus,
whatever; it takes a long period of time. Now, our planet has had a very low
record of large asteroid impacts. Jupiter is the major reason for that. One of
the great studies of the 20th century showed that if we did not have a Jupiter,
the impact rate on Earth would be 10,000 times higher than it is.
Location is everything
Tyson: It's not hard for me to imagine a solar system that forms when the
vacuuming up of the debris in the early phases happened more efficiently than
here. For you to base a whole idea about the likelihood of intelligence in the
galaxy on the fact that we had some extra bombardment seems kind of thin.
Ward: No, that's only a piece of the puzzle. But let's stay on that one. "Oort
Cloud" is the name of the big bunch of comets around us. There are many studies
suggesting that Oort clouds will be bigger and denser the closer you get to the
center of the galaxy. So it could be that we are in a section of the galaxy
real estate-wise that's great for life, and that as you head more centrally,
where there's more and more stars that form, it gets worse. You know the nature
of galaxies' centers. They are very dangerous places.
Tyson: They're nasty places.
Ward: And it's not just asteroids. It's gamma ray bursts, it's supernovae.
You've got black holes, you've got energetics, you've got sterilization events.
So the centers of galaxies aren't going to work. And perhaps half the stars in
the galaxy are in the center. So now we have to move off to the suburbs, where
things start getting spread out. If we go too far out, we run out of the heavy
elements necessary to make a habitable planet.
“I think life is almost everywhere in the universe. But you’re
asking about intelligent life, and that’s a whole different ball game.”
So we've got a portion of the galaxy that is no good, and another portion that
is no good. We're looking at narrow real estate areas. How narrow that is is
debatable. But this debate we're having would not have taken place 10 years
ago. We have new information just coming in that seems to be narrowing the
areas where habitability can take place.
Enter geologists
Tyson: Alright, so you're an intelligence pessimist. But clearly people who
professionally look for intelligence in the galaxy—the SETI
people—don't share that pessimism. What gives them the confidence that
you don't have?
Ward: They're not geologists. I think what astronomers have missed is the
record of our own planet. Geology tells us a couple of very important things.
First of all, you need a long period of temperature stability. That's a
geological phenomenon. A very finite set of conditions on this planet has
allowed us to have liquid water for four billion years. We never went above
100°C. We never went below 0°C for long periods of time. That, for
four billion years, is a rare thing, I think.
Secondly, the impact rate is also something that causes species to go extinct.
Sixty-five million years ago, millions of dinosaurs were suddenly wiped out by
an impact.
Tyson: Yeah, but that same incident enabled mammals to become something more
ambitious than a tree shrew.
Ward: Sure, maybe that was an instigator towards intelligence.
Tyson: But you just said it was bad for intelligence.
Ward: Well, what if such a cataclysmic event happens 100 times, 1,000 times, or
10,000 times, and you're looking at things being knocked out? It took 65
million years after the knockout to get to the level of intelligence that we
have.
Tyson: But as a geologist, is it possible that you're a little close to the
problem? You see Earth in such detail as a planet that sustains intelligent
life, that it's inconceivable to you how many different kinds of planets could
give you intelligence. You're kind of stuck in a geological paradigm. Maybe
it's as much a handcuff as a liberator of ideas.
Ward: But you astronomers never even considered it.
Tyson: No, we didn't.
Ward: You've been so far out in space. I never heard the term "plate tectonics"
ever used; it's not even in your lexicon. And this is where I think a whole new
view comes from biologists and geologists and paleontologists to add to the
great work you astronomers are doing. It's not simply a function of how many
planets are out there.
There's an enormous amount of new information coming from planetary geologists.
We know so much more now about how planets form and how habitable planets work.
We have this entire new science called "Earth System Science" that examines how
the life systems of Earth continue, the carbon cycle, how we have water, how we
have temperature changes, the weather patterns. But all of this in sum brings
together Earth as a planet, which over long periods of time is able to stay
alive. It's like the life of an individual. It's born, it grows, and it has
these systems that allow it to maintain life.
Animals are rare
Tyson: I don't hear you exploring exotic models for what a solar system or
planet can be. For instance, maybe there are planets where the water is frozen
on the surface, but deep down there's a place where it's liquid. And wherever
it happens to be liquid life goes to that.
Ward: That's a great idea, and I agree with you entirely. I think there are so
many places in the universe that allow life that I think life is almost
everywhere in the universe. But you're asking about intelligent life, and
that's a whole different ball game. I think that even animals are rare. The
lowest animals on this planet, worms or snails or whatever, are far from
intelligent. Even they are rare, I think, because it takes a long time for a
planet to allow them to evolve.
Tyson: It took a long time for Earth to do it. Now, when you say "a planet,"
you just generalize this single case that you know for all possible cases that
could exist in the galaxy. That's kind of bold.
Ward: It is bold, but I think time is still the constant. You need a certain
amount of time for evolution to take things from inorganic to organic, from
organic to a cell that combines with another cell, to eventually
intelligence.
Tyson: You're accusing Earth of being rare. But history is filled with cases of
people asserting that our place in the cosmos is rare. And the march of science
has continuously demonstrated the opposite of that. So here you are now making
cogent arguments, but I see you as one in a long series of people who have come
before you trying to claim that we are the product of something special. So
what makes you the only one in that history of scientists who's correct?
Ward: Luckily, it's not just me. I'm really cutting short a lot of my
colleagues. This has not been just my work, of course.
Tyson: When I look at the variation in the kinds of planets there might be,
it's not hard for me to imagine that you could have a planet where all the
conditions of that planet promote intelligence, rather than here on Earth where
it's kind of a special case, or a peculiar branch that happened to eke it out
of the variation in the biosphere. It might be that there are planets out there
where intelligence is rampant.
Ward: There might be. It's a big galaxy. I'll give you that.
Intelligence is rare
Tyson: Suppose that as we start looking for planets around stars in the galaxy
we find out that planets are common, which appears to be happening. Does that
up your estimates a little bit?
Ward: No. Let me use an analogy. Every once in a while a musical genius arises,
and great symphonies come out. Now, this is one in a million, one in ten
million—a really rare happenstance. But still it takes a long time, even
for a prodigy, a musical genius, to get to the point where he or she can write
that symphony.
“Where are the intelligent martians? They never had a chance.”
Now, what happens if you change the rules, and all of these kids die at two
years of age, none gets even to 10 years. Maybe once in a while you've got one
rare case. You've cut down the possibilities to near zero. And our point is,
it's probably hard for a planet to exist long enough as a habitable planet for
animals to arise. A few do, and of those few that do, you then need another
long period of time for intelligence to arise. The numbers get so small.
And by the way, let's get rid of the word "special." Special denotes that
there's some moral force or something. We don't need to think special; all we
need to think is numbers. And we talk about rarity. We're asking in this huge
Milky Way, how many intelligent civilizations are there? Carl Sagan estimated a
million. We know there's one.
Tyson: It could be zero [laughs].
Ward: So the number is somewhere between one and a million; maybe it's more
than a million. I think the most important point is, if it's not one, is it
two? Is it ten? Is it a hundred? Even if it were a hundred, there are 500
billion stars. That's pretty rare.
Being Earth-like
Tyson: Suppose we come to learn that solar systems that look like ours are
everywhere. Will that up your confidence in finding intelligent life?
Ward: Let's examine the concept of an Earth-like planet. This is the most
commonly used phrase, "Earth-like planet." Well, Earth-like planet is a moment
in time. Earth-like planet is Earth as we know it now. If we went back four
billion years, our planet would be the most hostile-looking place you can
imagine; it would not be an Earth-like planet. An Earth-like planet is not only
geography, it is time, because planets start as uninhabitable. They become
habitable if they're lucky. And they go uninhabitable again. So we are looking
again not just at the number out there. It's where they are in the whole time
frame of things.
Tyson: In principle then, Mars might have had its time in the sun as an
Earth-like planet, when now it's clearly completely hostile to life as we know
it, as is Venus.
Ward: Mars is one of the best examples. Mars probably had water to begin with.
Mars surely had early plate tectonics. It had everything necessary for life as
we know it. And it only lasted maybe 100 million years or less. Where are the
intelligent martians? They never had a chance. Mars maybe had bacteria and then
they died out. I think that's the fate of most planets. Mars' fate is the fate
of most Earth-like planets. They don't stay Earth-like very long; they die.
Tyson: If you look at when the dinosaurs went extinct, 65 million years ago,
out of the four and a half billion years of Earth, that's not very long. Yet in
that period of time, intelligence as we know it rose up from whatever existed;
animals went from tree shrews to modern humans.
Ward: But that's not right, Neil, because you needed all the time that came
before. You have to go all the way back to trilobites and flatworms and
everything that came before. You just can't start 65 million years ago and say,
"We're starting from scratch. Here's 65 million years to intelligence." What
about all that genomic construction that was necessary over the hundreds of
millions of years prior?
The right recipe
Tyson: What, then, is your recipe for a planet that will breed intelligence?
Just go down the list, what do you need?
Ward: Let me answer by saying, What do I need to breed animals, which is our
complex life; intelligence is a whole other ball game. Obviously, you have to
have a sun that's large enough to give a constant amount of energy over time,
and yet a sun that is not so large that it burns out quickly. As you know, our
sun is getting brighter, brighter, brighter. A billion years from now, this
planet will no longer be habitable for intelligence, because our sun will be
too bright. So you have to have something that gives you enough time. Now, the
small stars, of course, let you go for a long time—20 or 30 billion
years.
Tyson: They live longer.
Ward: They live longer, but as a planet you would have to be so close to them
as to become totally locked—just like our moon, the same face all the
time. Well, you've got one side that's really hot, and one side that's really
cold. That's not going to work either.
Tyson: Well, then everyone lives along the border between the hot and the
cold.
Ward: I don't think so. People are studying that right now. It does not seem to
be an option. Now, you know and I know that three-fifths of the stars in this
galaxy—correct me if I'm wrong—are those tiny stars.
Tyson: Yeah, the majority.
Ward: So we've just thrown out more than half of all the stars in the galaxy.
The big stars, they're gone. The double stars, they're probably gone because
the orbits of the planets get so irregular that you start throwing things
around. You throw out all those. Now you're really cutting down the number. The
centers of galaxies, they're gone. So we have really cut down to maybe 10
percent of the stars in the galaxy. That's still a huge number, so let's think
about planets.
“I stand by the great Enrico Fermi’s question, ‘Where are
they?’”
Earth maintains constant temperature because of the strangest circumstance. It
turns out that plate tectonics causes carbon to recirculate in such a way that
when we get too hot, we pull greenhouse gases out of the atmosphere and turn
them into coral reefs. When we get too cold, the coral reefs die. Volcanoes put
more carbon dioxide in the atmosphere. This only works because of plate
tectonics. One of the most interesting aspects of studying the geology of
planets is asking the question, How common will plate tectonics be? We don't
know, but all indications are it's rare. It takes very specific geological
conditions to allow it.
Where are they?
Tyson: Getting back to intelligence, if we're not alone, you're telling me
there's other intelligence out there in the cosmos?
Ward: I cannot believe that we're the single intelligence in the universe. What
I can believe is maybe there's one per galaxy. We are really scattered,
lonesome, very lonesome.
Tyson: So what you're saying is, if we're going to try to find other
intelligence...
Ward: Good luck!
Tyson: ...we need to broaden that search to go well beyond the Milky Way to the
rest of the galaxies in the cosmos.
Ward: There are probably so few intelligences in our galaxy that to find any of
them could be a remote, remote chance.
Tyson: So we should just give up.
Ward: I don't think we should give up. SETI is an interesting intellectual
endeavor. Why not continue it? I just don't think they'll ever find anything.
Or if they do, the separation is so great, you could never signal back and
forth.
Tyson: So in practice we're alone because they're not coming to us, and we're
not going to them?
Ward: I stand by the great physicist Enrico Fermi's question, "Where are they?" If there
were so many, we would have had a signal, we would have seen somebody, there
would have been a visitation. That's not happened.
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