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Life in the Galaxy

Life in the Galaxy. 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 take in nutrients and energy from environment

katelyn-vaughan
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Life in the Galaxy

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  1. Life in the Galaxy • What is life, anyway? • The chemistry of life • The Drake Equation • How might we contact ET? • Puzzles regarding ET contacting us

  2. What criteria must something have before you would call it “alive”?

  3. Here’s some… • Must take in nutrients and energy from environment • Must reproduce itself • 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

  4. These actions are complicated! • They require a large number of “degrees of freedom” in the entity doing them, in the jargon of information theory • In plain English – Life is Complex • There are 92 chemical elements allowed by the laws of physics in this Universe. There is only one which is capable of making complex molecules – carbon • We see no way that any conceivable life could be based on any other chemistry than carbon. Life is Carbon-based. • Finding life elsewhere means finding environments where carbon can assemble complex molecules – organic molecules

  5. How would be Contact Them?? • EM radiation is fastest • UV? • Visible? • IR? • Microwave? • Radio?

  6. 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!

  7. 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, around 1440 Mhz, it’s quietest, and also this is where Water has it’s 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

  8. “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

  9. 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

  10. 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 1 per year in our Galaxy.

  11. 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 20% • fp = .20

  12. n = number of life-suitable planets per solar system • Still not enough other solar systems statistics to judge n 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….. n=1

  13. 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

  14. fI = fraction of living planets with intelligent life • 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?

  15. 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 • I say, lets be optimistic….. fI=1

  16. fc = fraction of intelligent living planets which choose to communicate across the stars • This one needs some kicking around the class too…

  17. 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

  18. Are we too pathetic and ridiculous to be curious about? • Hey wait – our species has produced more than just George W. Bush’s, it’s also produced Einstein, Mozart, Bob Dylan…. Yeah, we’ve got plenty of pathetic individuals, but we’re not a pathetic species. • And even if we were, look at how many intelligent and curious people 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

  19. L = The average lifetime of a Communicating Civilization • So our Drake equation has a rate of formation, and then a bunch of probabilities meant to pare down 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. Clearly this is the lifetime of the civilization • This one’s another toughy… let’s kick it around some

  20. We really don’t know • So let’s just use The Principle of Mediocrity • I think the 21st century will be very bad, but it won’t kill EVERYbody (but maybe most) • We’ll muddle through, and learn • What are the Big Bogie’s that we may not be able to deal with?....

  21. We’ve been a species roughly for ~5-10 million years • Supernova explosion nearby (<35 light years away) – maybe 100 million years • Gamma ray burst aimed in our direction. Major bummer, anywhere in the galaxy if it’s aimed at us. • Planet Killer asteroid. We’ll probably be able to deal with any of these, but if not…time scale of about 100 million years • Solar evolution drives planet to Venus-style climate… few hundred million years. • We could wait till one of these Big Bogies gets us, but

  22. Instead, let’s figure the Principle of Mediocrity, for lack of any other guidance • Figure we’re halfway through our time as a species. Figure then, that we’ll survive with our knowledge for another 5 million years • L = 5x106 yrs • So now we can plug this in and calculate our guesstimate of how many civilizations are out there for us to talk to…

  23. N = 1/yr x .2 x 1 x 1 x 1 x 1 x 5x106yrs • = 1 million civilizations!

  24. 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)

  25. 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 accelerating blistering pace. • 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

  26. The Area 51 nonsense has been debunked. • You really believe ET is going to kidnap Farmer John and his wife? • We see no monoliths on the moon or anywhere else • The radio waves… silent (so far) • Point is – if they WANTED to talk to us, they certainly would’ve been found by now

  27. 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 • 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

  28. Most of our Galaxy may be no good for life. In closer, the rate of nearby supernovae is much higher. Too far away, not enough metals to make suitable planets. We live in the Galaxy’s perhaps narrow “habitable zone”?

  29. Plate Tectonics May be Essential • Carbonate cycling via subduction allows removal of greenhouse gas (mostly CO2) and prevent the Venus syndrome • Only Earth clearly has plate tectonics, and maybe Europa in a different watery sort of way.

  30. Bottom line is that there may be more factors than the original Drake equation considered, and all it takes is one or two very low probability numbers to zap your N • So again….. Why don’t we see / hear from other Galactic Civilizations?...

  31. 1. Microbe life may be common, but intelligent life may be so rare that we are almost unique

  32. 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

  33. 3. Maybe they think we’re not worth mentoring or talking to. (I personally think this idea is ridiculously self-denigrating)

  34. 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

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