Life in the Galaxy(old version: instead use

24-Life

• 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 out-

competing 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 “multi-verse” 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 Well-

Motivated 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 “self-selected” 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 (Interstellar-communication-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-communication-capable 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 interstellar-capable 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