Cosmic Knowledge & the Long-term Strategy of the Human Race: Sackler Lecture ’17


(ethereal music) My name is Eugene Chiang,
and it’s my privilege as Chair of the Department
of Astronomy to welcome you to this year’s 2017
Raymond and Beverly Sackler Distinguished Public Lecture. Since 1993, the Sackler
family has provided funding for an annual public lecture in astronomy as part of their effort
to further the arts and sciences at Berkeley. The Sackler family is
unable to attend today but they will be given a
video of today’s lecture and so on behalf of everyone here, thank you from across time and space. (audience clapping) So the Sacklers have given to astronomy, and astronomy has always
been about the big picture. And in this regard, I think
there’s really no other astronomer I can think
of who has done more to widen our field of view and
to take the biggest possible picture on the largest possible scales than our speaker tonight, Sandra Faber, Professor Emerita of UC Santa
Cruz, Astronomer Emerita of UC Observatories and
one of the most influential extragalactic astronomers
and cosmologists of our time. The difficulty in taking
the big picture in astronomy is actually twofold. It’s not just a matter
of taking the picture, that is it is not just a
matter, a difficult work of designing the instrumentation
and the equipment that enables you to
actually snap the picture. But after you’ve taken
it, there is the equally challenging part of deciding
just how big the picture it is that you’ve taken. And the second problem is the
classic astronomer’s problem of calculating distances to objects. Sandy has made fundamental
contributions to both problems and to many more. In the instrumentation side,
she pioneered the development of the Keck 10-meter telescopes and the Hubble Space Telescope and the associated
cameras and spectrographs. And on the distance problem,
she and her graduate student, Robert Jackson, discovered a relation between the luminosities of galaxies, and by luminosities I mean
their total power light output, so the total wattages of these
galactic scale light bulbs; a connection between
luminosities of galaxies and how fast their
component stars are moving. So when you take a picture
of a galaxy, right, and for the most part they
look like sort of fuzzy spots, you don’t know how far
away the galaxy is, right? Because you can measure how bright it is, but for a given apparent brightness, you don’t know whether that
object is very close to you and just contains the light
of a few thousand stars, or whether it’s really, really far away and burns with the light
of billions of stars. You can’t distinguish
between those possibilities. But Sandy could. And the way she did that was
by establishing a connection between the luminosities,
the total power outputs of galaxies, whether
they contain thousands or millions or billions of stars, and she connected luminosities
to another property of the galaxy that she could
measure that was independent of the distance, namely how
fast the stars were moving relative to one another. These stars and galaxies,
they’re like bees in a swarm. So she could measure how fast the bees were buzzing around, whizzing
about relative to one another by virtue of their Doppler shifts. So the faster the stars move,
the more luminous the galaxy. And what has come to be known
to generations of astronomers as the Faber-Jackson relation,
succeeded in calibrating the luminosities of
galaxies and by extension, their distances; and literally put galaxies on the cosmic map. So this put us on the road to
understanding their masses, their internal dynamics and the formation histories of galaxies. Now a lot of people, they
would be more than happy just to sit back and enjoy
the fruits of their labors, especially a landmark discovery like this. I’ve heard it said that
if your work makes it into a textbook, then it’s time to retire. And I defy you to find
an astronomy textbook that does not feature the Faber-Jackson relation prominently. But not Sandy. She published this paper
just four years after her PhD and has since gone on to
make really fundamental contributions to our
understanding of galaxies and the universe. She led the community to
appreciate that most of the matter in the universe is dark. That not only is it dark, but it’s cold. That is, it’s lumbering
along at speeds much less than the speed of light. She led a team of seven
astronomers that were dubbed the Seven Samurai to map out galaxies in the largest possible scales. So mapping super clusters of galaxies. And she established,
through her leadership of the Nuker collaboration, so she has a real knack for names, they sound very intimidating. In her leadership of
the Nuker collaboration, she established that in
the cores of every galaxy, there lies a supermassive black hole. And not only that, but the
properties of that hole, namely its mass, is intimately connected to the properties of the host galaxy. So her awards really are
too numerous to list. I’ll just mention a couple. In the lifetime achievement category, she was awarded a
University Professorship. This is the highest honor
accorded a faculty member by the University of California. And she was also awarded a
National Medal of Science, which was bestowed upon
her by President Obama. Sandy’s lecture today, you can see, it’s entitled Cosmic Knowledge
and the Long-Term Strategy of the Human Race, in one
sense is perfectly in keeping with her career-long insistence on asking the biggest questions framed in the biggest possible pictures. But another sense is
just really out there, in a sort of X-Files kind of way. Sandy has been quoted as saying, this is a direct quote,
“Astronomical knowledge is probably “the most important single
discipline that you need to know “in order to be an
informed citizen of Earth.” And I have to confess when I
read that I wasn’t quite sure if I agreed. You know, in our troubled
age, I might have pointed to a few other subjects. Energy policy, environmental
studies, computing biology. So I am very curious to learn what Sandy is going to teach us today. In this, as with so many other questions, we have looked to her, and
we continue to look to her, for intellectual leadership. So please join me in
welcoming Sandy Faber. (audience clapping) That was probably the nicest introduction I ever got, Eugene, so
that was just classic. Thank you so much. So maybe this is the kind of
thing that you think about in the waning years of a career. Why is what you’ve been doing important? And I’m convinced that
astronomy is important, I’m partially convinced just because everybody wants to know about it. It’s such a privilege to be an astronomer. You walk into a cocktail party,
people say what do you do and you say, I’m an astronomer, man, you are nailed to the
wall for the rest of the party while everybody comes by and asks their favorite cosmic question. So people, at least a
large fraction of people, really care about this. And I’m trying now to
ask myself, and you too, why do we care about this? And not only why do we care,
but why might it really be very important? So Eugene stated my thesis,
this quote which I was rash enough to make, it’s
the most important thing that we could possibly
understand right now; and I’m gonna try to defend that. You’re probably gonna
be a little disappointed by my success in defending that, but at least it’s provocative. And I expect that it will create a lot, stimulate a lot of questions,
and maybe we’ll have some time for discussions. And please, don’t be afraid
to nail me to the wall and make me feel uncomfortable trying to defend this proposition. Now here is the title I really
wish I had for this talk. Coming of Age in the Milky Way. But unfortunately, another famous person thought of that before me. But the premise, as you will
see as the talk develops, what happens when you come of age? You become not only self-aware, but you see yourself in a larger context and you try to make sense of that. So my premise is that, that’s
where our civilization, our human culture today, is. That’s where we are,
we are on the threshold of having just become cosmically aware. And what does that mean for us? So having set the stage,
I will now proceed to develop these thoughts. The first part of my talk is
going to be a quick resume of the history of the universe
and how it makes planets. And then the next part of the
talk is going to be devoted to whether or not our planet is rare and the evidence for or against. I happen to think it is
rare, but that’s not proven. Then I’ll talk about the
prospects for our planets, cosmically speaking; and
the conclusion will be that we have a great planet here. And we have the prospect
of long time periods that we can now play with. We have been given the
gift of cosmic time. And that is part of our problem today. What are we going to do with it? We’re cosmically aware,
we have this opportunity, we have a challenge,
what, as we as a species, do we have a species,
enterprise, a destiny? We’re the first generation to be able to even think
these thoughts, I believe. And then finally, I’m going to
end with some thoughts about our current trajectory and
how it’s really unsustainable on the timescales that are
of interest to an astronomer and what we need to do about that. So lots of pieces in this
talk, I better get going, otherwise I’m never gonna get through it. Okay, so the the next starting point here is how the universe began. It was extremely hot at an early time, and its physics was such
that it expanded faster than the speed of light. This is the famous inflationary paradigm. And just when things fall into black holes faster than the speed of light,
they emit Hawking radiation. In the same way, our universe
when it expanded faster than the speed of light,
generated radiation, ripples, density ripples, whatever you
wanna call them, fluctuations, and those fluctuations,
they weren’t very big. About a part in a hundred thousand. They acted as the seeds for
gravitational clustering several hundred thousand years later. And so that’s where galaxies come from. And I am so pleased to
have been an astronomer, even if I had never discovered anything, just to be able to say and semi understand what I just told you. Isn’t that the most amazing thing, that our Milky Way galaxy, a hundred thousand light
years across started out as a quantum fluctuation? I mean, if you would ask me
in graduate school, Sandy, would you ever be figuring this out or watching other people figure it out? I couldn’t, it would be
beyond my wildest dreams. I think it’s one of the
most subtle, deepest things ever discovered by our species. Okay, so anyway we’ve now got fluctuations. And as the universe expands, that generates a
gravitational instability. A peak draws in matter around it, and a valley loses matter
to the surrounding peaks. And so we develop clumpy
galaxies separated by voids. And I’m particularly fond of this video of what the Milky Way might
have looked like long ago. You will see that it started with sort of low-level fluctuations. They grow and they merge in a sort of a hierarchical clustering way. The blue is primordial
gas, hydrogen and helium, coming out of the Big Bang. And then the makers of the simulation turned that gas into stars. And gradually, we have proto galaxies here that are turning original cosmic proto primeval gas into stars. And so a cycle for these
galaxies, a life cycle emerges. We developed these dense cores where the star density is highest. Look, see, individual groups of stars, those are the little points
that you see, the yellow points. And it’s quite violent,
especially at early times, when these proto galaxies
collide with one another. And every time they collide,
they throw existing stars into a sort of a halo. But then more gas falls
in and they kind of regrow this rotating gaseous disc. And this process keeps repeating itself. And with time, the
collisions die down because things are spreading
apart in the universe, the collision rate goes down, and we wind up with more or less stable undisturbed
galaxies with a structure that looks like this, a
dense core, a halo of stars and a disc of gas, of residual gas, that has more recently fallen
in and hasn’t yet made stars. Okay? So that’s the model. And the wonderful thing is that actually, the model seems to match
galaxies rather well. So I’ll show you a few
pictures of this type of galaxy called a spiral or a disc galaxy. And you can see they all
have these dense centers and they’re surrounded by discs of gas that are still forming stars. And sometimes, we see them
edge-on, as in this picture, and we can see really they
are flattened objects, just as the model predicts. And of course we live in one of these. We know because we can take
pictures with fly’s eye cameras. This is a beautiful one from
Victoria, British Columbia, and we see the plane of our
Milky Way arcing across the sky, and this is the center of our galaxy here. So chapter one, we now understand
where galaxies came from. Galaxies are the building
blocks of the universe. Once you’ve made them, you can think about making stars and planets. So let’s turn to that. We know a lot about that as well. Oh, excuse me, I’m a
little ahead of myself. There are a lot of galaxies. This is a picture taken with
the Hubble Space Telescope, the Hubble Deep Field. There are about 10,000
galaxies in this picture. The bright ones are in the foreground. The faint ones in
general are farther away. And you might be sort of
depressed by this picture, right? Our galaxy is just one of many. We think, on the plane of the sky, if we could photograph the whole sky, we’d see a hundred billion of them. We don’t seem very special at all, and so maybe astronomy is really
a very depressing subject. And that reminds me of
a company that I love, I’m sure you’ve seen it. You know the Despair company? And they have these wonderful posters with a picture and then
a saying underneath them, guaranteed to make you
feel really horrible. So I made a despair
poster out of astronomy. (audience laughing) Okay. All right, so when I get
to the end of my talk, you’ll see I don’t really
believe this at all. So I’m setting up my premise. All right, now we’ve made galaxies, let’s think about how galaxies make stars. Here’s a nearby galaxy that’s full of gas, has lots of raw material for making stars, has a region in it that
is a stellar nursery. Let’s blow it up and look at the picture with the Hubble Space
Telescope, beautiful detail. We see many regions like this. These are a bunch of young stars in here that have just turned on. They’re extremely hot, very luminous, and their energy has
ionized the birth cloud and caused it to glow. So this is the typical
structure of a stellar nursery. Some of the most beautiful
pictures with Hubble are of regions like this. This is called The Jewel Box. The young cluster
illuminating the birth clouds from which it was born. Perhaps my most favorite Hubble picture is this one though, I love this one. This is a little bit more complicated. Here’s some bright stars
that are sending out rain of photons, like Bryce Canyon. And here’s a denser region that shields the gas underneath
from the rain of photons. It’s like Bryce Canyon, a rock shield. The rock underneath it and
you get these pinnacles. These are the Bryce Canyons of the galaxy. And in addition, very cute,
here is a little star cave. Here’s a young star whose
photons have excavated a volume around it, and it’s
just sort of peeping out and you can see it through
the hole that it has made. Beautiful, absolutely beautiful. Now in regions like this,
we actually see evidence of solar system formation. Here are four objects
from the Orion Nebula, which is one of the nearest star forming nurseries that we have,
and you can see these are proto solar discs. These are making planets here again. These are planets. And there are big bright
stars not far away whose photon rain is trying
to blow off the gas here in a kind of stellar fratricide. So it’s a race against time. Will the star form or
will it be evaporated by its big brother? Some of them make it through. These are the more developed ones. And here’s a protostar and
its disc of proto stellar, proto solar nebula. And here are four examples. We know that they’re
flattened rotating discs with the morphology of our solar system because one of them
providentially is seen edge-on, and we can see the light of its star peeping up above the disc. So you’ll notice that these
proto solar nebulae are dark. And that’s because they’re
populated with dust grains. And dust grains are the
seed of planet formation. They’re kind of sticky. This interstellar dust is
made in supernova explosions and also in the atmospheres of aging stars blown out into interstellar space where you can see it as dark clouds. And it’s really kind of
like cigarette smoke. It’s about the same size as
cigarette smoke particles. And when you have a lot of
it along the line of sight for many light years, it’s
quite opaque and absorptive. When it falls into a solar nebula, the particles stick just
from surface activity. And then they grow and gradually they come to form rocky cores and the
rocky cores bring in more gas. And that’s how Jupiter formed. The rocky core by itself
is our Earth all alone. So here is a sort of picture of a rotating proto solar nebula. I won’t try to start it. It rotates and it makes asteroids, and the asteroids get together
and make rocky planets. So I love this particular picture taken by a very gifted
photographer, Wellie Pocolca. And here he claims that this
is an actual photograph, no touching up or anything like that and it’s taken in New Mexico
looking out of a cave. And I love it because there
are all these terrestrial rocks in the foreground, and here’s the material of the rocks right out
there in the galaxy. That’s how we got rocks on our planet, was putting this stuff together. So we really are truly
made of of stardust. There’s a beautiful completed
cycle in this picture. Let’s now consider we’ve made planets. You see I’m going along at a
good clip, I made galaxies, now we’ve made planets. Let’s consider the question
of whether our Earth is a rare kind of planet or not. We now know that there are
planets all over the place. The question is not planets
but Earth-like planets. So astronomers and physicists in general have made a huge amount of mileage with something called
the Copernican principle. The Copernican principle simply
means, the way we use it, that the rest of the
universe is like we are. There’s nothing special about us. And this has worked over and over again. Other stars are like the Sun. Other galaxies are like our galaxy. Other atoms are like our atoms. The laws of physics are
the same everywhere, we don’t have special
laws of physics here. You get the idea. And in fact, this is such
a wonderful principle, we can study events here
and then we can assume, if something is true here,
like a law of physics, then it’s true throughout
the entire universe. Very powerful. Sometimes called the
principle of mediocrity, which I think is kind of a bad
name but some people like it; or the conclusion if we now
apply it to our planet Earth, would be that Earths are common. And you can do some arithmetic to show that, that might be true. There’s something called
the Drake Equation, which was invented by Frank
Drake, oh hmmm let’s see, in the 60s I think, so sometime ago now. He was curious with Shklovsky from Russia, they were curious about the number of detectable civilizations in the galaxy, and they have this equation, the number of civilizations
that you will see is proportional to some number of stars together with a bunch of factors. And there are six factors there. And supposing you just assume that each factor is 10% and then you apply that
to the number of stars in the galaxy, which is a
hundred billion, 10 to the 10th, that leaves you with a prediction
of 10,000 civilizations. So that looks like a rather
fecund fertile number of civilizations to think about. And it’s very inspiring, you might go off and actually try to find them. And Jill Tarter is in the audience here, who has made her lifetime performing and perfecting that technology. A contrasting view might
be that the Earth is rare, and that was developed in this book here, Rare Earth: Why Complex Life
is Uncommon in the Universe. And the basic reason is that
Earth-like planets are rare, according to these authors. This would be the
principle of singularity, or Earths are exceptional. So how does that work? They have an equation too. And they have 10 terms. So if each one of those terms is 10% and we multiply by a
hundred billion stars, we have one Earth in the galaxy. So this is the crux. I’m not taking a stand here. We don’t actually know the answer to this. The only way to do it
is to go out and observe the way Jill is doing it and others. But I’m going to entertain,
just for the fun of it, the notion that maybe we are
rare and why might that be. So let me talk about a few factors that were discussed by these authors. In order to have an Earth-like planet, you have to start with a good star. So let’s skip over this rapidly. It’s well known, the star can’t be too hot because it has ionizing radiation and hot stars have short lifetimes. It’s taken four billion
years of Sun radiation to get to the point where we are. So we can’t have a star that
lives only a few million years. It can’t though be too
cool because cool stars have dangerous flares on them and they have a habitable
zone that’s rather narrow. What do we mean by habitable zone? The habitable zone is only
actually one of many factors that you need to be habitable, but it is defined more or less officially as the region from a star
in which liquid water on the surface of the
planet, water on the surface, would be liquid. And so here you are too
hot, here you are too cold for this star right about
there, you have liquid water, you’re in the habitable zone. So why are little stars a problem? Here is a picture of
bright stars, solar stars and these dim stars called M dwarfs. So now I’m talking about the
problem with the M dwarf star. It has a very narrow habitable
zone close to its star, and it’s thought that
planets actually become tidally locked to the
star the way our moon is locked to the Earth with
always one face facing Earth. In the same way, this
planet would have one face always facing the star. And actually, we found
some planets like this. And it is noted that, that
would be a very strange planet to live on because you
always have day on one side and night on the other
side, which would generate enormous winds and a very strange climate. Whether or not that’s
good enough to preclude intelligent life, we don’t
know, but it certainly is not a favorable situation
based on our experience. Okay, more about the star. You need a stable solar system. You don’t want to turn
on the radio one day and news flash from CNN, astronomers have found that planet Earth is headed for outer space at a speed of around
30 kilometers a second. It’s been ejected by a
gravitational instability in the solar system. We’ve seen this coming but we
just didn’t tell you about it. And at the rate we’re going,
we have maybe a month or two of warm weather left,
and then write your will but don’t bother because
nobody will read it. (audience laughing) Okay, so we don’t want that to happen and it’s very nice that our solar system actually is a very stable thing. This was a question that
was posed a long time ago by Laplace, and we didn’t know
anything about its stability. It’s a complicated system
with Jupiter and Saturn pulling on other planets and so on. It couldn’t really be studied
until you had a very fast and accurate computer. That has now been done. And it’s been shown that our solar system is very stable for at
least a billion years. So that’s something that we can rely on. And the reason it is, is that it has a lot of circular orbits that are well spaced away from each other. And by the way, parenthetically,
many of the solar systems that we’re finding from extrasolar planets are not like this. They they have eccentric orbits in them, and their orbital structure
is wildly different from ours. Okay, the Sun. Making this planet has to be metal-rich because we need rocks in order
to make terrestrial planets. That’s heavy elements. And you should not be too close
to the center of the galaxy because there’s a flaring
black hole there periodically and you don’t want to be too close to it when it chooses to go off. So we’re safely located
in the boring suburbs of the Milky Way. All right, now you’ve got
to have a good planet. You can’t be too big because you’ll have the wrong composition and you
won’t have a solid surface. You can’t be too small though,
I’ll say more about that in a minute, because
your atmosphere escapes. Mars is an example of that. And if you’re small, you cool off too fast and the iron core, which drives the dynamo that makes our magnetic
field, you don’t have any magnetic field to shield
you from the onslaught of the solar wind. And that solar wind
constantly blowing on you for billions of years
blows away your atmosphere. And that’s also happened to Mars. Okay, so let’s say more
about the Earth’s interior because in our solar system at least, it is extremely special. We have something on our
planet called plate tectonics, and what is this? We have a hot core here
heated by radioactive decay. So energy wants to flow
out and that creates these convection cells. The convection cells
are not enough though. You need the right kind of crust in order to have a convection
cell pulldown material so that it subducts. The net result is that our
crust is constantly being recycled on our planet on a timescale of several hundred million years, and this cools the surface
causing the core to convect and powers the dynamo. This is the amazing thing
not known for that long. This is actually our
thermostat, this process, because if we generate too
much CO2 in the atmosphere, then it actually joins with
the rocks and gets subducted. At higher temperature, it’s
called rock weathering. Goes into the rocks and gets subducted, pulled out of the atmosphere. And this, over the course of
our history of our planet, has kept us thermally regulated. When we get too cold, the
cycle goes in one direction. When we get too hot, it
goes in the other direction. This is probably what
President Trump is relying on. (audience laughing) I haven’t had a conversation
with him on this, but he’s up to date with
the latest findings. I think somebody forgot to tell him though that it’s a cycle of several
hundred million years and it’s not going to do us any good. Good over cosmic time,
but not on shorter time. The last thing that this
does is it builds continents. It creates land. Some people have claimed
that in the beginning we had an ocean and there
were just a few volcanoes like Hawaii sticking up over it, and we actually built
the continents over time. That happens because as
the subduction occurs, some land scrapes off here on the edge of that other continent
and builds its mass. So all together, plate
tectonics is absolutely crucial for the world as we know it. Let’s talk about water for a minute. Water, hard to get and
even harder to keep. Important for life, but here’s something you might not have realized. You’ve got to have water hydrated
in the rocks of the crust in order to make this
subduction process work. So if you don’t have water
hydrating these rocks at the boundaries here, you
don’t have plate tectonics. So that’s gonna have
consequences in a minute. We have quite a lot of water. We don’t know where it comes from. It’s controversial. Did it come from comets? Was it older, did it come
from Vesta-like asteroids? We were not sure. But in general, there’s
probably less water close to the Sun and
more water farther out because closer to the Sun is hotter and the water would vaporize. An example is Venus. It lost its water. Too close to the Sun, too hot. Mars also lost its water
because it was too small and it didn’t have this
protective magnetic field. Think about a couple of coincidences here. The Earth has just the
right amount of water to fill our ocean basins. Have you ever thought about that? I just thought about that
about six months ago. I don’t think anybody could predict that, and yet that is a major,
major feature of our climate because ocean circulation is a huge factor in distributing heat around the planet. By the same token, I
didn’t put it on the slide, have you ever thought about
the size of our atmosphere? It’s very thin, but it’s not zero. If it were much thicker, we’d probably have a
greenhouse effect of some kind. And if it were thinner,
we wouldn’t be able to have life on Earth, we wouldn’t have an oxygen
atmosphere, et cetera. So on the subject of rare earth,
those are two coincidences that, as far as I know, are unexplained and yet very, very
important to the history and evolution of Earth as we know it. Alright, let’s talk about
Venus, a cautionary note. A study in tipping points,
almost the same mass and radius as the Earth, but just slightly closer to the Sun. Today, it has a whopping
atmosphere 90 times Earth’s pressure, mostly CO2. The CO2 came out of the rocks. Very hot there, no oceans, no continents. Why, what actually happened on Venus? Well, being closer to the
Sun, it stayed hotter longer. It probably got less
water in the beginning, and what water it had
it was just hot enough to vaporize the water out of the rocks. Now something they’re
not teaching us in school is that water is actually a more powerful greenhouse gas than CO2 is. And so when the water went
out, there was an initial phase one greenhouse effect on Venus, and it started to get hot. And it got even hotter,
and the CO2 outgassed out of the rocks and that was
a total greenhouse runaway. And that’s why Venus
is the way it is today. No water makes the crust rigid. That means that there
are no plate tectonics, trapped all the heat inside a planet, has massive volcanoes that
are sort of stuck in place that are just building
these big shield volcanoes because they don’t move around because the plates don’t move, and they repeatedly resurface the planet, altogether a completely
different kind of planet, no water, plate tectonics,
no magnetic dynamo, magnetic field, no continents,
no mountain chains, all just due to being
slightly closer to the Sun. All right. My last point about a
rare earth hinges around our potentially crucial moon. This is controversial, but
it’s something to think about. So it’s generally
acknowledged now that the moon formed in a giant impact
about 30 million years after the Earth itself formed. And the impact had some consequences. It gave angular momentum to the planet. Not only an amount, but a direction. Presumably that was kind of random. And as it happens, the axis
tilt is about 23 degrees relative to the ecliptic, not straight up and not in the ecliptic
but a moderate tilt. That gives us our seasons. And we get moderate seasons. If we were in the plane
when we went around the Sun, winter, the pole would
get all of its sunlight and then on the other side of the Sun, the summer, during the summer,
the other pole would get. And so it’d be a radically
different climate. It is thought by people who model climates that a moderate tilt like this is good. Seasons may promote genetic diversity, but too strong seasons
would really be very bad for higher life. Okay, so the scene was set
by for moderate seasons, dependable, gentle forcing function because of a point I haven’t mentioned, the moon also preserves
that tilt of 23 degrees. If you took the moon away,
the tilt would change, influenced by the gravity of Jupiter. So the moon has a one-two punch force. The angle of our axis and
preserving that over time. Finally, it also gave us a short day because it imparted rotation to the Earth. And a short day is also a good thing. It moderates the day-night
temperature variations, and that facilitates photosynthesis. So altogether, the moon did a lot for us according to this argument. And how often would another
planet in another solar system suffer a giant impact
from a Mars-like body to produce a moon? So you can see that the factors
now are sort of piling up, and that’s why some authors like to say that the Earth is rare. Okay, let’s talk about planets
in other solar systems. Don’t those solar systems look like ours? Planet discovery started by discovering these very massive Jupiters
close to their star, and that’s because they
were easy to discover using the radial velocity technique. But as we’ve gone on
to study solar systems, we found that yes, there
are a lot of hot Jupiters but solar systems kind of planets tend to group themselves into families. Here is a plot, this
is the mass of a planet in units of Earth mass,
and this is the period of a planet in days. So there appear to be three families that we’ve discovered so far. These are the original hot
Jupiters close to their star with short periods and quite massive. And we’re now discovering
lots of long period gas giants that look like Jupiter and Saturn. We’ve put those planets on this graph. And then completely surprising
everyone is the discovery of these so-called close-in super-Earths, which here’s the Earth here
with a period of 365 days, so these folks have days of periods of more like 10 days or so. They’re really quite close to their stars. So to a great extent, the fact that we haven’t
found anything here may reflect the fact that
those objects are hard to see. So this is where we would
find Earth-like analogs. They’re not very massive,
they’re far from their stars. Hard to see using the
radial velocity technique. So there are folks here
who are worrying about this trying to estimate from the
tenuous discoveries here on the edge of the known region trying to extrapolate,
trying to figure out how many planets there might be in this pretty much basically
unexplored region thus far. And it’s thought that there
could be a lot of planets there the claim is maybe 20, 25% of stars have Earth-like planets in this region. I’d just point out though
that we have three planets in that region and we’ve
just seen that only one of them is any good. And so just merely, when
you read in future articles about discovering planets here, just remember this argument
that just merely being in this part of a diagram
doesn’t necessarily mean that you’re going to be
a good planet for life. Let me pause there for just a second, and I’m clearly not
answering this question is Earth rare or not. I tend to think it is just because of all those arguments including
the moon and all of that. But let me return to
the premise of my talk that this is very important
information for our species. So in a hundred years
or so, if not before, I believe we will have
answered this question. And we will know what’s
here, and we’ll know more about what they’re like. So envision two outcomes. One outcome is that there are a lot of Earth-like planets here. How will we respond? I think we’ll be energized
because we have an explorer gene and this will be encouragement to us to preserve our
civilization, our planet here so that we will have the
wherewithal in future, when technology develops,
to go out and find those other planets and
see what they’re like. So there’s going to be a big incentive. That’s what I mean by important knowledge, knowing something in astronomy and then doing something
about it, planning for it here on Earth. Consider the other alternative, that further work shows
that this is an arid desert and Earth is extremely rare. What’s the reaction? It seems to me that we will, in this case, be motivated by our admiration and love for rarity. I think we also have this in our genome. We admire and appreciate
things that are rare. We regard them as precious. And in the same way, we will
have the same motivation, I believe, to go forward and protect our Earth environmentally, just as we would have
had in the other case. So either message is
going to be very important for the future of our species and I think will provoke
a great deal of discussion from the standpoint of do
we have now a joint mission that we should engage in to exploit the potential of our own planet or to visit other planets? Well, in order to do those
things, we have to have a future. So let’s consider for
some short period of time the questions of the things
that might threaten us. Dangerous cosmic disasters. Did you know by the way that
disaster is Latin for bad star? Dis-aster, okay. Alright, so the first
disaster that will occur and is inevitable, the Sun
is aging, it’s brightening, and this is going to slowly
heat up our atmosphere. And paradoxically, you would think that at the rate this happens,
that we would have more CO2 in the atmosphere. No, it’s going to increase
the chemical processes of weathering, and weathering
puts CO2 into the rocks. And so it’s estimated that
600 million years from now, there won’t be enough
CO2 in the atmosphere to have photosynthesis. And this will be the end of
agriculture and green plants as we know it. So the conclusion from this
disaster, which is unavoidable, is that we have a few
hundred million years to a loss of habitability on the Earth from this cause. Another kind of cosmic
disaster is that we might have a supernova explosion. Well, we know the rate what they go off. If it’s within 30
light-years, we’re in trouble. The frequency is such-and-such, and you can calculate
that we’re gonna get one every few hundred million years. Again, conclusion, few
hundred million years to loss of habitability. Same number. All right, cosmic impacts. We know about the famous
Chicxulub asteroid, which killed the dinosaur, and people now calculate
the effect of these impacts. A 10-kilometer collision
destroys all higher life, and one kilometer wipes out agriculture by putting a great cloud
into the atmosphere and blocking the surface. So the frequency is about one kilometer, lands about every million years. 10 kilometers, every 500 million years. Now the good thing about asteroids
is we can see them coming and we’re already searching for them. We’re finding all objects that
are bigger than a kilometer. And diversion is possible
now to 140 meters. So if part of our
project is to thrive here for several hundred million
years, it is inevitable that we’ve got to have a
better diversionary strategy. So I’m assuming we can do that, and they’re going to be
a major inconvenience but we’ll have the technology
to divert up to a kilometer. And that gives us again something like a few hundred million years. Then we have ice ages. Ice ages are not understood. Multiple factors having to
do with the Earth’s orbit, small changes in the Earth’s
axis, et cetera, et cetera. The continents move around,
the ocean circulation changes. But the conclusion is that mammals have gotten through
many, many ice ages. We’re going to have troubles with this. We’re going to have to
move around on the planet to adjust our agriculture and so on, but major inconvenience but does not affect our habitability. And then the last disaster
is actually the most serious, and that is supervolcanoes. There are two kinds. There are kinds that put
a lot of ejecta and ash into the atmosphere. They’re not so horrible. The really bad ones are the slow ones that put huge areas of
lava out onto the planet. And the biggest extinction
in the history of the planet was the Permian extinction, which was thought to, that’s
250 million years ago, and that was thought to be caused by one of these volcanic
episodes on the Asian continent. So we get massive explosion
every million years or so, but modern mammals have clearly suffered through those and survived. It’s not clear whether
or not we could survive one of these large igneous lava eruptions. We don’t know how often they occur. Could start tomorrow, but let’s estimate a hundred million years
to loss of habitability. And that’s the shortest
number actually in my list. The others were all several
hundred million years. But the net result is that we have a good place to exploit here for quite a large number
of years going forward. And there’s some lessons that we’ve learned here from cosmology. The first lesson is that we got here according to the laws of
physics and we’re subject to those laws and must live within them. Obviously, what’s hidden in my mind here is that there are no miracles. No miracles were required to get us here. You might think that this
is somewhat limiting. We are subject to these laws
and must live within them, but actually it gives us a
certain degree of predictability because the laws are predictable
and we don’t have to worry about some angry God
striking us with lightning and obliterating the planet. We can predict our
future precisely because we are subject to these physical laws. So I consider that a great benefit. Lesson number two is that
the Earth will provide a livable home for at
least 100 million years and maybe even longer,
and so we have been given the gift of cosmic time. What will we do with it? And as I was saying earlier in the talk, I believe we’re really the
first generation of human beings to be confronted with this major challenge to even think about it. Now I’d like to talk about
the thing that we’re doing these days, which clearly has no future, and that is our habit of growing. You know you read in
the Wall Street Journal that if we’re not growing
at three-and-a-half percent per year, we’re actually falling behind. I’d like to have a discussion
with you of why it is so ingrained in people’s thinking
that a moderate growth is like standing still, and not growing is like falling behind? How did we fall into that notion? I have some theories
myself but I’m just gonna leave it there as a fact for the moment. So as I say, three-and-a-half
percent is a target growth for our economy. And what happens if you’d
put those factors together year after year? Then you have a doubling time of 20 years. And over a lifetime, 80 years, the factor grows by 16. I’m verging on 80 now. Well, I wasn’t even
noticing our GDP has grown by a factor of 16. Do we really think, as
we look around our planet and limitations today, that it can grow by another factor of 16? I’m very pessimistic about that. And I note that now we’re struggling around a growth in our
country of about 2%. So could it be that we
are actually finding, beginning to sense the
end of the glory days of exponential growth on Earth? And let me just point out,
this is very important. This is what your pension depends on. I wanna talk to economists and learn more about really how the economy works. I suspect that the fact that
you put money in the bank, you used to be able to do this by the way, you can’t do it now. You could put money in the
bank and get 3% per year. Now we’re lucky if we
get a 10th of a percent. Is that temporary or will
we return to “normal”? I don’t know. But I do know that people
who are running endowments are pretty convinced that
they can’t depend on that good old 5% return per year anymore. So anything that depends
on depositing money now and getting more in the future
is potentially very risky. And this might be the first cataclysm to affect society as a
result of hitting the limits of what the Earth can support. If I were a young person today, I’d be thinking a lot about that. All right, so supposing this
miracle of compound interest goes on for cosmic time, 3.5% every year for a hundred million years, what happens? Okay, so that’s the number. Okay, so as a result I don’t have to turn the
equation around and tell you what the growth rate can be. Effectively, zero growth
if we are going to be in equilibrium with our
planet for any length of time, that means astronomically meaningful. So all this talk about sustainability, really, people have not confronted this. And that’s one of the
messages I wanted to bring to your attention in this talk and maybe we can talk about
it more in a few minutes. All right. So what is sustainable
growth on cosmic time? The answer is zero growth. So what’s the solution here? Here’s one solution, okay? I pulled this out of the air. I really have no justification for it. I call it the 1% solution. And what do I mean by this? It’s a society that is not growing. Somehow it’s replaced capitalism
in our economic system with something else, maybe more like Eskimos. Eskimos don’t grow economically, right? Or they didn’t historically. Okay, so everything we get
that’s interesting today comes from having lots of people. People are interesting,
they think up new stuff, they produce novelty. So in my scenario, I want
as many people as possible. And here’s why I pull it out of the air, I really think the environmental impact has to be much, much
less than we have today. We have to rely on the Earth to recycle things for us. And that includes absorbing waste. So I just say that this society is going to produce 1% of the current level of waste while maintaining an
adequate standard of living. Now how many people
will be in that society? Standard of living is really set by energy consumption per capita. If we assume a factor of
two gain and efficiency over what they’re doing
in Europe these days, which is a factor of two better than here, then we come up with a world
population in this scenario of only 50 million people. And that corresponds to
the start of the Iron Age, which was 1,000 BC. It’s like two Californias
or something like that. It’s not big, not big. But you see, most of
the planet is unmolested and it can do its thing
and maintain the biosphere and we’re not stressing it so much. Now is this a good place to live? Well clearly, the index of
whether it’s a good place to live is the number of astronomers that it has. (audience laughing) So astronomers live at the top
of the technological pyramid, and I’m assuming that
this society will have a similar technological pyramid. So if I just take per
capita the same fraction, this society has 100 astronomers. Okay, I’m making a point though. I’m making the point that
it’s all very well to say that we need fewer people. But there’s a price to that. A really severe price. And the reason why we got
into this fix here was it was a sustainable society
assuming the current, current human genome. So I know that genetic
engineering is difficult, I know that it’s not
obvious that our descendants are going to be machines
instead of people, but I do think in order
to preserve novelty, we have to have a better
way of using energy to complete, to create complexity. And whether or not we
create little human beings who think great thoughts
with smaller brains, or whether or not our
descendants are quantum computers that can compute 10 to the
30th times more efficiently than IBM can today, I don’t
know what the avenue is but I really think that the solution is going to be something
along those directions. Okay, I’m nearing the end here. Remember this famous film,
it’s a wonderful film, okay? So clearly, this cartoon
dates from Bush-Gore election and it speaks for itself. That was his film, An Inconvenient Truth. It’s true as far as it goes,
but this is the reality. That’s what I’ve been seeing. If we’re really thinking about
a long-term future on Earth, cosmic reality has pressure,
puts pressures on us that we haven’t even
begun to dream about yet and taken into account. And as I say, we’re really
the first generation of people to do that. So that’s kind of my ending message. Let me point out that we are now faced with a suite of new and thorny moral issues. What are our obligations
to future generations? Do we have a custodial
responsibility for the Earth? If the Earth is rare, maybe we should make a galactic planetary park out of it, the way we make a park out of Yosemite. Maybe the Earth will
turn out to be a planet of special worth. Is there any intrinsic
value in our activities? If the universe is pointless in the large, which is what Steven Weinberg has said, how do we, our intelligent
beings, find meaning? Do we have a destiny? And depending on what we
think about these things, I personally think that our value system is bound up in our genetic code. Some people think it comes from God. I think it comes from our genetic code. Either way, these are not
easy things to change. And our value system right now is pushing us in the direction of growth. Everybody wants to start a company, and why do they do? They want it to get
bigger, it’s reflexive. It’s built into us and we
have to get beyond that if we’re going to have a
sustainable society on cosmic time. I’ll end with a couple of pictures. So this is, I think, one of
the most stunning pictures ever taken by astronomers. This is a picture of Saturn and it was taken by the Cassini spacecraft from behind Saturn so that
the Sun is in Eclipse. It’s somewhere here behind the disc. But I’m not showing it to you because it’s a picture of Saturn. I’m showing it to you because
it’s a picture of Earth. Here’s Earth as seen from Saturn, okay? So this is perfect material
for a despair poster, okay? (audience laughing) And so many people have said this looking at this picture, you know? It it does seem to say that. But I’d like to encourage
us in another direction. There’s another picture we
should be thinking about. Okay, this was a picture
taken by Apollo 17. This is the picture that triggered the environmental movement. For years I saw this when
I went to my car dealer. It was on the wall and
it was encouraging me to recycle my oil. And it was trying to remind me
that I had a duty to do that and I was supposed to
be saving the planet. Let’s focus on that. That’s what astronomy is all about. That’s why astronomy is important. And the message of astronomy
is laying the groundwork for the future of Earth. Thank you.
(audience clapping) – [Man] Thank you, Sandy. I might mention the word
catastrophe also means bad star. (laughter drowns out dialog) As to the importance of the moon, I mean, (distant indistinct muttering) that using ourselves as the
model is kind of dangerous. Yes, I will agree. – [Man] Even Mars, after
all, is a 23-degree tilt in a one-day rotation period. That doesn’t mean it’s fixed for life. But who knows what will
happen when you discover the first exoplanet living system? They’re likely to be very
different, more expectation. I think that’s a clear prediction. So I don’t disagree with you really but I’m just reminding us
of the wide, wide variety of possibilities beyond
what we may imagine now. I agree with what you’re saying. I would say though that I’m not claiming that an excess of liquidy of 23 degrees means you have a good planet. You have to have a lot of other things, all those other nine factors. But I think you did bring up
a very good historical point. I remember when I was a
graduate school at Harvard and I heard an astronomer, I won’t name his name,
but he was making models of the solar system and
they were perfect models. They made little rocky
planets in the middle and then they made gas
giants at the ice line and then they made smaller planets. And it was all presented
that this is the way we make a solar system. We had one example and he made that. So I guess I would take your argument and turn it around on myself and say I would apply it to life. Is this the only way that we
can make intelligent life? And it’s very hard to do
science with one example. And these are both in that category. (distant indistinct muttering) Can we consider? (distant indistinct muttering) I don’t think we consider living on them as the beings that we are now, but it’s a perfectly good
question to imagine, ask, whether there are other
beings on those planets. And particular, Europa
has a subsurface ocean with probable hydrodynamic vents. And maybe that’s where
life started on Earth. Maybe there are organisms
under the surface in Europa. – [Man] I’m actually
studying architecture, so… (distant indistinct muttering) I think we need to think about this. A very good question
is where in our genomes does our personality reside? Rather than coding in cosmic time, what I think we need to do is we need to code in a sense of value and enjoyment that is not associated with growth or the acquisition of more stuff or controlling larger and larger forces. And you see, that is so antithetical to all the evolutionary
pressures of the past, that it’s a profound genetic change. And I don’t know if we can do that or not. – [Man] I’m wondering
what you think about, you mentioned that the
solution is no growth, but isn’t it possible, or
do you think it’s possible for mankind to make it into
space in a meaningful way? I think it might be possible eventually, but everybody would agree
that we’re going through some sort of nexus in the
next 100 to 200 years. And I don’t believe that
we’ll be meaningfully in space on a time scale to help
the population problem or the resource problem
on that time scale. – [Man] Do you think it’s
a genetic recoding, or… (distant indistinct muttering) Excellent question. I mentioned the Eskimos
as people who didn’t seem to be so concerned with,
and I picked them at random, I really don’t know
anything about Eskimos. (audience laughing) If there are Eskimos here who
are insulted, I apologize. I was just thinking that more, less advanced cultures where
life moved more slowly, maybe this tendency was not as pronounced as we see it today. Maybe it’s brought out
because the possibilities of growing a lot within
a single human lifetime are bigger for the average
person than they are now. So I think you’ve raised
a really great question. What is our human nature? And how malleable is it? And I don’t know. It’s one of the many
questions I’ve raised here. – [Woman] A 100-million-year
timescale is pretty comforting, but I’m from the environment
science discipline. We’re gonna kill our own
species in like 300 years if we don’t get our act together so how do you go about
making people care about an astronomical timescale or
like a planetary timescale when day-to-day life is
just not that (mumbles). Right, so I say two things about this. First of all, I think you’ve
made a wonderful point. How are these points even relevant? And surely, they are not very relevant to people who are just
looking for their next meal. To think thoughts like this
and actually maybe take some action in that direction is a luxury of people who have already
met their basic needs. So that’s a wonderful question, and I just don’t know
what to say about it. But we have all kinds of
decisions facing our planet, and if the attitude always is well, most people will never have
the luxury to think about it, we won’t be able to
make very much progress. – [Woman] I guess my question
was how do you go about trying to make people
care about this topic, cosmic timescale
(audience member coughing) I’m trying to help people here. So I gave you two arguments. They were both astronomical
and they both revolve around whether or not we find that
there are other planets. And if we find that
there are other planets, I think we have a great
motivation as a species to go to exploit that. By the same token, if we find
out that there’s only one, I think we have great
motivation to solve our problems on this planet. So I think either way we need some way of inducing people today to think that there is a future that they would sacrifice for. And so telling people that
this is a wonderful planet and our species could have a
collective goal and destiny is a way of sweetening that argument. How do we get people to
do less in their own lives in order to save more for future lives? (distant indistinct muttering) No, it’s a question of how the
water got on to the planet. And so there are two schools of thought. One is that it came in, mixed in with the rocks
of the asteroidal-like proto planetesimals that coalesced. Another school of thought
is that it came later from comet bombardment. And the moon impact is important here because the moon heats the
Earth to a very high temperature and it has been argued by
some that a lot of the water, had it existed, would have
gotten driven off in that time. In which case, we needed
a secondary source, and that secondary source just happened to have the right amount. So it’s an amount question, which you try to argue with
imponderables and histories that have different avenues. – [Man] Relating to the
question the lady in the back mentioned about 300 years from now, the problems we’re gonna
confront 300 years from now, do you ever think that
maybe it’s part our destiny to be gone?
(laughter) Many people say that, right, mm-hmm. I find that very sad, right. And the question is do we
collectively feel sad enough to do something about it? (audience laughing) – [Man] One last question. – [Man] This sort of relates
to the 300-year question in a sense. It’s hard to imagine an equilibrium that lasts for 100 million years. So I wonder if there’s
a dynamical solution. Think about your comment about the mammals surviving multiple ice ages? Maybe our future is a
series of catastrophes which basically thin out the population and then there’s a
period of recovery again. Right. Sometimes I think that maybe pandemics are not such a bad idea. (audience laughing) – [Man] I’ll just say that might be another poster of despair. (audience laughing) Yeah, right. But really, if you look at
the history of pandemics, there’s never been anything that big. – [Man] Well I think our time is up, so let’s thank Sandy. Thank you, thank you. (audience clapping) (upbeat music)

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