Transcript Life in the Galaxy

Life in the Galaxy
(old version: instead use 24Life
•
•
•
•
•
What is life, anyway?
The chemistry of life
The Drake Equation
How might we contact ET?
Puzzles regarding ET contacting us
• What Criteria Must Something
Have Before You Would Call
It “Alive”?
Here’s some…
• Must reproduce itself
• Must take in nutrients and energy from
environment to use for its own purposes
• Must fight for an ecological niche by outcompeting other life wanting to use those
resources
• Must be capable of evolving to keep its
competitive edge
Life: must reproduce, compete for a
niche, take in and process
matter/energy for its own use, and
must evolve to fit its environment
• To do all this, things called “alive” must have a large
number of degrees of freedom. Must require large
numbers of “information bits” to fully describe
• In other words - Living organisms are complex!
• Of the 92 chemical elements allowed by the Laws of
Physics, only one atom is capable of building
complex molecules – carbon
• But that’s just from the laws of physics we see
around us. Do these laws apply everywhere?
• Yes! Spectra of Quasars near the edge of the
Observable Universe show all 4 laws are exactly the
same as locally
• All life in our Universe is almost certainly
carbon-based – Carbon is the only atom
capable of building complex molecules.
• Life processes are mediated by proteins in all
known living organisms. And, proteins are
built out of amino acids.
• Miller-Urey experiment shows amino acids
are created naturally in the conditions of the
young Earth.
• Amino acids later were discovered in comets,
meteorites, and in interstellar clouds by
spectroscopy.
• Still, it’s a Big step from amino’s to proteins,
and then to living organisms.
Evolving Simplicity into
Complexity requires a Special
Environment
• Environment must be not too cold (frozen!) or
hot (stars destroy all molecules).
• Universe must collapse on smaller scales to
permit planets and stars and yet be long-lived
and therefore expand on big scales, giving time
• Laws must permit stable environments. Law of
gravity permits stable two-body orbits. Not all
conceivable gravity laws will do that.
Lucky? Or…
• Either we were incredibly lucky that the one and
only Universe happened to have the right laws
of physics to allow life, or…
• Maybe there’s a God - but then, where did
HE/SHE/IT come from? Circular reasoning and
doesn’t take us closer to a solution.
• And the notion of the western religion version of
God has other deep flaws too numerous to go
into here anyway.
• A Better Solution is…
A Multitude of Universes! – The
MultiVerse
• In fact, it’s pretty hard to find an Inflation scenario which
does NOT include creation events happening “all the
time”!
• “Universe” now means a particular instance in this “multiverse” with it’s own framework. Space, time, dimensions,
and force laws, which tumble out of symmetry-breaking
in a random way, subject only to the Quantum
Uncertainty Principle and laws of Quantum Mechanics,
which we believe is more deeply fundamental and
common to ALL universes)
• Inflation describes how Total Energy=0 Universes could
be created out of the the Vacuum. “Eternal inflation”
“Chaotic inflation”.
• Testing these ideas against reality…not so easy! But…
Testable or Not - It’s the Most Logically
Compelling and Observationally WellMotivated Idea We Have
• Quantum processes within a larger framework create
Universes, which through Inflation can create and
populate their own space, time, laws, all of which may be
unique to that particular Universe
• Analog; the laws of fluids are the same everywhere, but
yet every snowflake is different. Symmetry-breaking
includes randomness.
• We, OF COURSE, find ourselves in one of the rare,
wonderfully incredible universes with physics friendly to
life.
• Tons of other Universes could be out there which are
totally MESSED UP! But, no one lives in them to complain
about it!
• Now – next topic, finding other smart beings out
there
“ET Phone Home… ET Phone
Home” – Life Elsewhere in Our
Galaxy
• How many civilizations are in the Galaxy which are able
and willing to communicate with us?
• Frank Drake (at UCSC) took this seemly impossible
question and broke it into a series of more focused
questions we could hope to make progress on - The
Drake Equation…
• It’s really just freshman probability and statistics applied
to an interesting question
• How many interstellar-communicating civilizations,
N, are in the Milky Way Galaxy?
N=R* fp n fL fI fc L
• R* = rate of formation of suitable stars
• fp = fraction of these with solar systems
• n = number of life-suitable planets per solar
system
• fL = fraction of these planets with life
• fI = fraction of living planets with intelligent life
• fc = fraction of intelligent living planets which
choose to communicate across the stars
• L = average lifetime of a communicating
civilization
Let’s put some numbers to these…
• R* = rate of formation of suitable stars
• We need temperatures suitable for complex carbon
molecules and a liquid environment for chemistry to
happen. Not too hot (breaks them apart), not too cold
(hard to reproduce if you’re frozen solid). Stars are too
hot, we need planets orbiting stars!
• Life capable of interstellar communication took 4.6 billion
years to evolve on our planet. If that’s typical, it means
we need stars who are stable for at least that long.
• We need G & K main sequence stars. Rate of formation
of these is about 1 per year in our Galaxy. Stars hotter
than G & K have lifetimes too short to evolve intelligent
life, if we are any guide. Stars cooler (M,R,N,S spectral
type stars) have convection zones too deep and
resulting stellar luminosity instabilities which are too
large, at least in a large fraction of cases. Stellar flares
would be mass extinction events.
fp = fraction of these with solar
systems
• Till recently, we had no good idea of how
common solar systems were. Now, we do.
• Looks like this fraction is about 30%
• fp = .30
np = number of life-suitable planets
per solar system
• Still not enough other solar systems statistics to
judge np very well
• But in our solar system, we have 1-2 planets in
the “habitable zone”, where temperatures are
just right. Earth of course, but we’re “selfselected” so not clear if we can use it. But Mars
was suitable, and maybe Venus for a while.
Maybe just bad luck their fortunes went south?
• Let’s say….. np=1
fL = fraction of these planets
with life
• Life seems pretty tenacious, and bacteria
appeared on earth very soon after the Early
Bombardment period.
• We find life even buried inside rocks miles
beneath the surface.
• If life’s possible, it seems to happen. And quickly.
• So let’s say fL =1 In other words, life-suitable
planets WILL have life, at least most of the
time
fI = fraction of living planets
which, at some point, evolve
intelligent life (Interstellarcommunication-capable)
• Let’s kick this one around a bit, in class
• Should be expect life to always evolve towards
higher intelligence?
• What is the survival value of intelligence?
• Should intelligence in a survival value context
include the ability to be technological enough to
communicate with Galactic civilizations?
• I think that sooner or later, life will get
around to trying intelligence. It certainly
does have survival value.
• We don’t need to ask yet how LONG an
intelligent civilization will last; here we only
care whether interstellar-communicationcapable intelligent life will arise some day
on a living planet
• I say, let’s be optimistic….. fI=1
fc = fraction of intelligent living
planets which choose to communicate
across the stars
• Just because they CAN interstellar
communicate, doesn’t mean they will. So,
this one needs some kicking around the
classroom as well.
• We must psyche these ET’s out!
Dr. Rick’s Thoughts?
• My thoughts… I can’t imagine a mature
intelligence, an intelligence capable of
interstellar communication, which does not
also feel curiosity.
• Curiosity is the in-built motivation to use
intelligence,
• At least in our species. Is this a deal-killer
caveat? We have no idea!
Are We Too Pathetic and
Ridiculous to be Curious About?
• Hey wait – our species has also produced Albert
Einstein, Mozart, Rachmanninov…. not just George W.
Bush’s and the “Housewives of Orange County”. Yeah,
we’ve got plenty of pathetic individuals, but we’re not a
pathetic species.
• And even if we were pathetic, look at how many
intelligent and curious scientists are fascinated with
bloodworts and slime molds and doggy fleas!
• For me, it’s hard to imagine that they would NOT want to
talk to us, if only to help us figure out how not to de-spoil
the rest of our cosmic environment
• (but then…. Did you see “The Day the Earth Stood
Still”?
L = The average lifetime of a
Communicating Civilization
• So our Drake equation has a rate of formation,
and then a bunch of probabilities which pare
down to the suitable stars and get to real
civilizations we can talk to.
• To get a dimensionless pure number of
civilizations, we need something with time units.
We need the average lifetime of a civilization
• This one’s another tough one… let’s kick it
around some
We Really Don’t Know How Long a
High Tech Civilization Will Last
• So let’s just use The Principle of
Mediocrity
• I think the 21st century will be bad, but it
won’t kill EVERYbody
• We’ll survive (I think, but am not sure), and
learn
• What are the Big Bogie’s that we may not
be able to deal with?....
• Supernova explosion nearby (<35 light years away) –
maybe 100 million years between events
• Gamma ray burst aimed in our direction. Major bummer,
anywhere in the galaxy if it’s aimed at us. But extremely
rare we think.
• Planet Killer asteroid. We’ll almost certainly be able to
deal with any of these very soon, but if not…time scale
of about 50 million years
• Solar evolution (increasing luminosity) drives planet to
Venus-style climate… few hundred million years. This we
can deal with (for a while) too – thanks to UCSC
Astronomer Greg Laughlin’s idea.
• Our current climate change induces positive feedbacks
which acidify the oceans so drastically that they become
essentially sterile. Methane trapped in the Arctic and
methane hydrates in the ocean are released, causing a
“Hot House” climate. This would require geologically long
periods of time to heal, too late for us. This one is not so
easy to dismiss, although I still want to believe we will
wake up before this tipping point is passed.
So…
• Instead, let’s figure the Principle of Mediocrity,
for lack of any other guidance
• We’ve been a pretty intelligent species for
roughly for ~5 million years
• Figure we’re halfway through our time as a
species. Figure then, that we’ll survive with our
knowledge for another ~3 million years
• L = 3x106 yrs
• So now we can plug this in and calculate our
guesstimate of how many civilizations are out
there for us to talk to…
N = 1/yr x .3 x 1 x 1 x 1 x 1 x 3x106yrs
• = ~1 million civilizations in the Milky Way
Galaxy right now, today!
A More Interesting Question Is –
How Far Away is the Nearest One?
• We need population I stars, with rocky
material; exponential scale length 5 kpc,
scale height 200 pc, and we’re 25kpc from
the center of our Galaxy
• Throw some calculus at the problem, plug
and chug, and we arrive at what we’ll call
– the Nolthenius Equation
• Dnearest = 77,000 lyr / Sqrt(N)
• So, for N= 1 million civilizations…
• D = 77 light years; interestingly, about as
far as our first radio programs have
penetrated at the speed of light. Even
casual listeners should have picked up on
that.
• Are they preparing a “Welcome!” party for
us?
• Or are they arming the photon
torpedoes?
How Would We Contact Them??
•
•
•
•
•
•
EM radiation is fastest
UV?
Visible?
IR?
Microwave?
Radio?
Listening on What Wavelength Band?
• Gamma Rays, X-rays, UV are all too high energy –
they’d ionize every atom they hit and thereby scramble
any information encoded on those waves.
• Visible light – no problem, except you’d have a lot of
trouble picking out that visible light signal against the
glare of the parent star
• InfraRed light – same problem with glare, although
concentrating into extremely short pulses might work
• Microwaves – cosmic microwave background radiation is
99% of all photons; that’s a lot of noise to overcome.
• Radio – Ah, it’s nice and dark in this band! Yes!
Where in the Radio would You
Look?
• At the short wavelength end, the Cosmic Microwave
Background gets troublesome
• At the long end, radiation from electrons spiraling in the
magnetic field of the galaxy would add noise
• In the middle, roughly around 1420 Mhz, it’s quietest,
and also this is where H and OH (the ingredients for
water) have their key absorption bands.
• The water hole! Galactic civilizations would perhaps
congregate (and sing kumbaya?) around the Water Hole
in the electromagnetic spectrum. Or so we have decided.
• This is where SETI is concentrating their searches
So, where are they??!
• If civilizations last 5 million years, the typical Galactic
civilization has been around vastly longer than our paltry
80 years
• Technology advances at a blistering pace… an
acceleratingly blistering pace.
• Why? We have the ability to TEACH! That makes ALL
the difference
• We should be able to travel to the stars in maybe a 1000
years, tops. We can listen to civilizations even at our
infant stage, for thousands of nearby stars already
• So… where are they? This is Fermi’s Paradox
X-Files?
• The Area 51 nonsense has been debunked for a
long time.
• …You really believe ET is going to kidnap
Farmer John and his wife for their evil
experiments?
• We see no “2001”-style monoliths or equivalents
on the moon or anywhere else
• The radio waves… silent, says SETI, so far
• Point is – if they WANTED to talk to us, they
certainly could’ve arranged to have been found
by now, because most civilizations will be vastly
technologically more advanced than we are (we
are at the very beginning of our interstellarcapable communicating lifetime)
Maybe Our Earth is More Rare
and Special Than we Thought
• One astronomer calculates that if Jupiter
weren’t there, we’d have ~10,000 times
higher rate of comet impacts to the Earth
• A massive Moon needed to stabilize
rotation axis and therefore climate. We’re
the only inner planet with a real moon, and
it took an extraordinary collision to make it
Most of our Galaxy may Not Be
Good for Life.
• In closer to the galactic center, the rate of
nearby supernovae is much higher and
stars are closer together. Too far away, not
enough metals to make suitable planets.
• We live in the Galaxy’s “habitable zone”,
which may be narrower than we might like
to think?
Plate Tectonics May be Essential
• Carbonate cycling via subduction allows
removal of greenhouse gas (mostly CO2)
by converting it into calcium carbonate via
life forms, and prevent a Runaway
Greenhouse Effect.
• Only Earth clearly has plate tectonics and
the resulting carbon sequestration
Planetary Migration
• As computer power rises to the challenge, we’re
finding that over cosmic time scales that
planetary orbits can migrate substantially,
allowing the surprisingly common “hot Jupiters”
we see around dozens of nearby stars.
• But life requires billions of years to evolve to the
point of producing an intersteller-communicating
civilization. That requires very stable climate –
no wandering allowed!
And Need Circular Orbits
• We pointed out good reasons why orbits
would start out near-circular (fluid friction)
• Yet we have enough data now from nearby
solar systems to see that elliptical orbits
are much more common than we had
guessed…
Most Extra-Solar Planets Have Evolved Very Eccentric
orbits, unlike the circular orbits of our own Solar System. Very
Probably Goes Along with Planetary Migration
Need Jupiter and an Asteroid
Belt in the Right Position
• Jupiter acts to deflect or eliminate most but not
all comets from too-frequent impacts in the inner
solar system, at later times
• Jupiter needs to be just outside an asteroid belt,
so that rare impacts can stimulate evolution and
bring water, heavy elements to the surface of the
planet (see recent work (Martin et.al. 2012)
• Only seems to be true for a few percent or less
of planetary systems, based on observations
Fermi’s Paradox Persists
• Bottom line is that there may be more factors
than the original Drake equation considered,
• But still, we have to explain why 1 million
predicted civilizations turns into (maybe) just 1
actual civilization (ours) when we refigure the
math. That looks hard to accomplish, from what
we know.
• So again….. Why don’t we see / hear from
other Galactic Civilizations?...
1. Microbe life may be common, but
Intelligent life may be so rare that
we are perhaps unique
• Why? Does EVERY civilization commit suicide
during their adolescence, as we might be doing?
• I think we’ll survive, and it’s even less
reasonable to think that EVERY civilization kills
itself in the first few hundred years of its
existence. Do they survive, but become
Luddites?
2. Maybe they’re out there, and are
all in some Galactic Federation…
• and obeying the Star Trek “Prime
Directive” – Don’t disturb the natives
3. Maybe they think we’re not
worth mentoring, or talking to.
• I personally think this idea is ridiculously
self-denigrating. The more we learn, the
more know how incredibly rare are planets
which could harbor intelligent life. For ET’s
to sit by and watch us destroy so much of
our planet without trying to help with some
education, seems bizarre
4. Maybe Our Species was
Planted Here?
• Thing is, DNA analysis shows that all life we’ve
examined evolved from common ancestors, with DNA
changes happening over time completely in agreement
with the very long 4 billion year time scale since life
began
• Including us! All DNA here is left-handed (didn’t need to
be so, but is)
• If we’re planted here, and therefore ALL life here is a
transplant from another civilization, why did They let so
much time be wasted sitting around as lazy single-celled
organisms till just 500 Million years ago?
• “Life here was planted” may make for fun SciFi, but
doesn’t stand up very well to a close look.
• Or…. Any ideas from you fine people?
• Recent books: “Rare Earth” (but makes the big
mistake of assuming all life is very closely like
Earth life, and its creationist author makes
sloppy mistakes elsewhere as well)
• Better is “Here be Dragons”, which is more
agnostic on how rare intelligent life is