2000 April 25, SPS 1020 (Introduction to Space Sciences) - Reading: today was TNSS Ch. 27, and PBD 5 & 20. That's it! - Papers due Thursday, April 27. No late papers will be accepted. - Review readings, work on review problems, be ready with questions for the review session on Thursday. Remember also: the Final Exam will be cumulative (in other words, it'll test the whole course). --------------- SETI = The Search for Extraterrestrial Intelligence --------------------------------------------------- The rationale: we have radios, and have inadvertently been broadcasting powerful signals into space for a long time. We also have very sensitive radio receivers: radio telescopes. If intelligent extraterrestrial beings exists, might they also have the same? First paper in a refereed scientific journal: Giuseppe Cocconi & Phillip Morrison, 1959, Nature, vol. 184, p. 844 "Detection of Extra- Terrestrial Civilizations by Radio Signals" "The probabiliy of success is difficult to estimate, but if we never search, the chance of success is zero." Tell the joke about the prisoners: this is what happens when theory gets so far ahead of experiment. => THERE HAS NEVER BEEN A claimed SETI DETECTION that has stood up! => First SETI search with a radio telescope was carried out by Frank Drake in 1960: "Project Ozma" Looked at 2 Sun-like stars, tau Ceti and epsilon Eridani: At first, Drake thought he had something! Turned out to be just local two-way radios... The Drake Equation ------------------ N = R x f(planets) x n(Earths) x f(life) x f(intelligence) x f (comm) x L where: N = Number of planets with intelligent life we can detect, or in other words, have radio telescopes R = rate of star formation in the Milky Way Galaxy = 1 star/year (This is well known.) f(planets) = fraction of these stars that have planets ~ 1 (We're presently working on this one.) n(Earths) = number of habitable planets/star ~ 1 (?) (Might know this within your working lifetime.) f(life) = fraction of these planets on which life does arise (Working on this one, too...) f(intelligence) = fraction of these planets on which intelligent species arise (Who knows?) f (comm) = fraction of these planets on which the intelligent species develops radio telescopes (How should I know?) L = transmitting lifetime of each civilization, in years. (What are you, nuts? How can we tell this, in advance?) The way Frank Drake works it, N = L The number of civilizations in the Galaxy is about equal to their average transmitting lifetime, in years. Make of this what you will! MAJOR PROBLEM: this mixes well-known science (R) with things we're still working on (f(planets)) with complete wild guesses, e.g. f(comm). Toothpaste commercials do this, too. The public might be fooled, but don't you be! Another problem: The Fermi Paradox. Where is Everybody? --------------------------------------- If the Universe is so old, and it's teaming with intelligent life, why do we not see them here? This is a non-trivial question. They've had plenty of time: should take about 10 million years for a civilization to diffuse across the Milky Way. The Galaxy is > 10 billion years old. Many explanations have been offered: - Frank Tipler (Tulane): Extraterrestrial Beings Do Not Exist (!) - The Flying Saucer Hypothesis: We are being visited, and we see them (!) - The Zoo Hypothesis: We are being avoided on purpose (!) - Carl Sagan (late of Cornell): We've been missed by Dumb Luck: Diffusion won't happen so fast. - Richard Gott (Princeton): Interstellar travel Never Happens (!) It's strange to hear this after Apollo 11! Also: although difficult with present technology, interstellar flight _isn't_ theoretically impossible. He also later retracted this, saying that he just wanted to make a point: Humanity will be making a BIG mistake if it doesn't move out into space. What he really meant was: Do technological civilizations, all founded by creatures who evolved by natural selection (and hence had to have had a competitive, aggressive nature in order to have survived, at least at first), ever last long enough to produce starships? This was a concern during the Cold War! - Mario Livio (STScI): We are among the first, ever in the Galaxy (!!) Argument based on stellar physics: it would have taken the stars in the Galaxy this long to have cooked up the heavy elements that make up our bodies. Has Uncle Mario been working too hard lately? -> No matter how you slice it, the implications are hard to believe! The Cosmic Haystack ------------------- The problem isn't just that the sky has billions of stars to search. There are also billions of frequencies. Current searches, happening now: Sky surveys: - Serendip IV (U.C. Berkeley, Stu Bowyer) (eavesdrops on radio telescopes) - BETA (Harvard, Paul Horowitz; funded by Steven Spielberg & Planetary Society) - META II (same, but southern [Argentina]) - South Serendip (on Parkes Telescope, Australia) - Project Argus (OSU amateurs: _many_ small radio telescopes) Targeted searches: - Project Phoenix (Jill Tarter's own, privately funded) - 10-micron infrared (Steward Kingsley, amateur: watching for CO_2 laser flashes) - Harvard optical (Charles Townes: watching for pulsed optical signals) - Columbus OSETI (again, organizing many amateurs for optical SETI) Project Phoenix: began as 10-year, $100M NASA project, in 1992. --------------- U.S. government funding was killed in 1993, after more than half the money was spent (on equipment). by the same Senator Richard Bryan who voted to designate "the extraterrestrial highway" in his home state (Nevada). Now being done with private funding, much like the movie, "Contact". Several characters in this movie were based on real people: Jill Tarter = Eleanor Arroway (played by Jodie Foster) (Jill says: "We *don't* use the headphones...") David Packard = industrialist who funds her. In real life, he's sane. Kent Cullers = blind programmer, who helps her Amateur SETI: watching for optical/near-IR laser flashes SETI at Home project: occupy those idle CPU cycles! Do We Know What a Needle Looks Like, If We Find One? ---------------------------------------------------- Frank Drake says it would probably be easy: narrow-band signals, used in radio communications, are not found anywhere in nature. (It still worries me, though: Farside Comic.) But How Do We Communicate? -------------------------- Mathematics is universal. If they have radio telescopes, surely they must know mathematics? (Perhaps this is an anthropomorphic assumption: An interstellar whale, singing for its own amusement, might not.) Famous false alarms: ------------------- 1) First pulsar discovered in 1967 by Jocelyn Bell. Initially called LGM-1 = Little Green Men-1. Turned out to be a natural phenomenon, a rotating neutron star (like a lighthouse). 2) CTA-102 (also CTA-21): Soviets had press release in 1965, announcing a Kardashev Type III Civilization (powered by a whole galaxy!), but quickly retracted, embarrassed. Turned out to be an active galaxy with a (not really) periodic signal. 3) Ohio State's "Big Ear": the 1977 August 15 "Wow" signal - Undergraduate assistant scribbled "Wow!" on the chart recorder paper; apparently a very powerful, narrow-band signal. BUT: that part of the sky has been observed carefully since, nothing obvious has turned up. => BUT: intermittency, caused by scintillation in the interstellar medium (much as stellar images twinkle in Earth's turbulent atmosphere), may be a _serious_ problem, necessitating _much_ larger searches, with _much_ more thorough follow-up! (Cordes, Lazio, & Sagan 1997 Astrophysical Journal paper) Finding Extraterrestrial Artifacts: ---------------------------------- Pioneer 10 and 11 plaques: Pioneer 11 should reach lambda Aquilae in 4 million years... Also Voyager 1 and 2 LP records (Send More Chuck Berry!) - Nothing obvious (highly refined metal, plastic) has turned up in archaeological, geological finds. Then again, if they've visited Earth 10,000 times, the last time would have been 450,000 years ago! - Search for artifacts in Earth-Moon L4/L5 points by Frank Valdes and Robert Freitas in 1980: Nothing there larger than 1-3 m in diameter with lunar albedo (7%) or brighter (e.g., spacecraft just like Pioneers 10 & 11, Voyagers 1 & 2). - Still, we may consider looking farther afield: Classification scheme proposed by Kardashev, Soviet theorist, in 1963: Kardashev Type I Civilizations - distributed over whole planets. We're there now! Kardashev Type II Civilizations - distributed over whole planetary systems Dyson Spheres (spheres built around stars, to trap all the light: proposed by Freeman Dyson in 1960.) => Will look like what? Sun-like stars, with infrared excess R. Zubrin, in Entering Space, casts grave doubt on the feasibility of Dyson spheres: it would take 260 times the mass of all the planets. Perhaps we might look for something more modest: Praesodymium (short-lived radioactive element) in Sun-like stars, indicating nuclear waste disposal there? Kardashev Type III Civilizations - distributed over whole galaxies Clearly not in our own, the Milky Way Galaxy; also not in the Local Group, nor nearby. But again, what would this look like? Perhaps we might detect radio waves, from the screeching of the brakes of a starship, using a magnetic sail? Problem with all of this: can't judge the significance of negative results. --------------- There can be no thought of finishing, for "aiming at the stars," both literally and figuratively, is a problem to occupy generations, so that no matter how much progress one makes, there is always the thrill of just beginning. -- Robert Goddard, 1932, in a letter to his hero, H. G. Wells