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where are you

发布时间:2013-11-19 12:01:38  

S.E.T.I.

ET, where are you?

Chapter 12

Day 27

Ch. 12 -HW

?Due Fri. 29 April

1, 2, 9, 25, 29, 32, 35, 43, 44, 47

Announcements

?

?

?Final Exam –Tuesday May 5 –0800Presentations –Wednesday, April 29Chapter 13 –HW –due exam time?1, 6, 11, 33, 34, 35, 49, 50, 51, 52, 55

The Drake Equation

?1961 –1stSETI conference, Green Bank, WV?Number of civilizations in our galaxy (or the Universe at large) from which we could potentially get a signal.

?Does NOT give a definitive answer.

?Rather, it lays out the factors that are important in determining this number.

The Drake Equation

?

?

?

?Number of Civilizations = NHPX flifeX fcivX fnowNHP -Number of habitable planets in galaxyflife -Number of habitable planets that have lifefciv -Fraction of life-bearing planets where a civilization capable of IS communication at some time has arisen.

?fnow -Fraction of habitable planets with civilization now, not in the past.

Cosmic Calculation #1

?What is the volume that civilizations could occupy in the galaxy?

–Assume limited to the disk. Why?

?Metallicity content

?Age of stars

Is Intelligence Widespread?

?If life is widespread, what about intelligence??SETI is only successful if THEY communicate.

?Homo sapienshave only started to understand the environment and explore the cosmos in the last <500 years.

–Suggests a long period of evolution is required to produce technologically intelligent creatures.

–Chance events

?body plans in Cambrian explosion

?K-T extinctor

Convergent Evolution

?The tendency of organisms of different

evolutionary backgrounds that occupy similar ecological niches to resemble each other.–Large marine predators –dolphins & sharks–Eyesight (eyes evolved eight times).

Encephalization Quotient (EQ)??

?

?

?

?Raw brain power based on brain mass.Simple measureEQ = 1 line –general intelligenceAbove line –capable of elaborate behaviorBelow line –less mentally agile

Evolution of Intelligence

?Humans don't have the largest brains.?Is the largest in relation to body mass.

Early SETI

?Marconi (1874-1937)?

?Tesla (1856-1943)?

?Both claimed to have heard aliens on the radio.–Probably “whistlers”

?Low frequencies which don't penetrate atmos.

Modern SETI -Origins

?1959 –Cocconi & Morrison –Cornell Univ.?Galaxy is older than solar system, so could be civilizations around linger than ours.

?Band –set of freqs receiver is sensitive to.?Bandwidth –a particular freq. in the band.?Governed by how much information is xmitted.

Announcements

?Final Exam –Tuesday May 5 –0800?Presentations –Wednesday, April 29?Dept. Spring picnic this afternoon –4:30pm, fairgrounds

?Chapter 13 –HW –due exam time–1, 6, 11, 33, 34, 35, 49, 50, 51, 52, 55

SETI -Today

?Categories of Signals

1.Local

communications on other world.Communications between home world & other site.Intentional signal beacons. (Project Ozma)

26m dish at NRAO-Green Bank2.3.?In theory, SETI can detect all three types.

Our Own Signals

?Broadcast in ~1950, just past 50 ly distance.

–High power, high-frequency TV> 2000 stars in this volume.

A Signal

Look?for:?repetition,?prime?numbers?…

1974 –signal sent to M13 (bad choice in hind sight). –21,000 ly distant.

SETI -Today

?

Current SETI projects

Radio –vs.–Optical

?Radio is a logical choice since we developed radio capability early (didn’t everyone?)

?Dust blocks light in the denser parts of the Galactic plane.

–Limits our view to a few hundred parsecs.–Not as big an issue today.

?But how?

–Laser pulses -doesn’t everyone know Morse code?–Lick –500 ly search distance

–Harvard also has a project going.

Artifacts

?2001: A Space Odyssey

?

The TMA is clearly not natural.

Artifacts

?Parking spaces –Lagrange points?Manufacturing plants.

Types of Civilizations

?Nikolai Kardashev –20thcentury

Planetary (Type I) –use resources of home planet.Stellar (Type II) –corral resources of home star.

Galactic (Type III) –employ resources of entire galaxy.?We’re in the first category.

?What would be the hallmark of the third?“Any sufficiently advanced technology is indistinguishable from magic.”

–Sir Arthur C. Clarke

Type II Civilizations?Dyson SphereFreeman Dyson?Could detect the IR radiation

Big Question

?What if we succeed in finding another civilization?–Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence

Sistilli NASA experience

Jill Tarter at

UFOs

?Project Bluebook

?Day the Earth Stood Still?War of the Worlds?Mars Attacks

Evidence of Visitation?Roswell, NM?July 8, 1947

?2009 Conference

Evidence of Visitation?Crop Circles?Abductions

“Extraordinary claimsrequire extraordinaryevidence.”

-Carl Sagan

Ancient Visitations??Nazca Line Drawings in Peru, ~2000 years ago.?Mayan pyramids?

Easter Island heads

Interstellar Travel

Fermi Paradox

If we find them, can we visit?Chapter 13

Challenges of Interstellar Travel

?Pioneer 10, 11; Voyager 1, 2; New Horizons ?All five are headed out of Solar System–No place in particular.

?

All carry messages.

Challenges of Interstellar Travel

?Pioneer 10 –headed to Aldebaran

?Pioneer 11 -Aquila

?At current average speed P10 will rqr 115,000 yrs to reach Alpha Centauri (if it was headed there), the closest star system to us –4.4 ly

?

Speed of Light –the Real Issue

?Special Theory of Relativity –Einstein

–Can't travel through space faster than speed of light.–Closest star system –8.8 years round trip?Not counting acceleration time.

?Energy –even at 10% speed of light, a ship that could carry 5000 people at 18,000 kg/person (Titanic) –100,000,000 kg.

222?Using ?mv= E ==> 4.5 X 10Joules

–100 times the world's annual energy use.

Rockets

?Cosmic Calculation 13.1 (pg 442).

??Rocketry began (in earnest) in the early 1900s–Tsiolkovsky, Goddard, Oberth

?The issue is mass ratio ~39 for the most efficient chemical system. Requires multi-stage vehicles to achieve Earth orbit.

?A 100-stage Saturn V –ignore all the other issues –could only achieve 0.1% of speed of light (0.001c).

Konstantin TsiolkovskyRobert

B.D.

B.Mass Ratio –23.113,300 kg to Moon

?What about non-chemical propulsion? Nuclear?Rockets?

?Fission is only 0.07% efficient, mass conversion. But, dwarfs chemical.Fusion, 0.7%.?Use reactor to heat

Exotic Nuclear Projects?Project Orion –good use of bombs?

?

?Not the current Orion~100 yrs to Alpha Centaurus

?Project Daedalus –BIS?Exotic Nuclear Projects?Deuterium pellets –fusion powered50 yrs to Barnard's Star.

?Ion engines

?Exotic Nuclear Projects?Low power (impulse) but long firing (years-decades)?Tested in space –ESA and NASA

?Very large. Probably limited to interplanetary.

Space?test?planned?“soon”.Lasers?Solar Sails?

?

?How about near the speed of Light?Relativity??????Time dilation –time slows down on board the ship as you approach c. Cosmic calculation 13.2 (pg 451)?Constant acceleration500ly in 12 yearsBut 500 yrs on Earth

?How about near the speed of Light?Matter –Antimatter propulsion

??100% conversion.But, how contain it??IS Ramjets

?Collisions

?Relativity

?Hyperspace

?If we can't go at or beyond the speed of light in space, what about bending or folding, spacetime?Einstein –General theory of relativity. Energy to create a mass to warp space.

Black Holes, Wormholes?

?

?How control a BH?Massive ones might be stableTorus in core?

Fermi Paradox

?If we're not special, then there should

be older civilizations in the galaxy. Where are they?

?Von Neumann machines –self

replicating.

Would other civilizations try to colonize the galaxy?

??

?

?Coral model10% c, 150 years to 5lyEntire galaxy in 10 Myr

Motives to Colonize?Humans want to explore. Are we

unique?

Extinction-proof civilization?

?Population control? -Not likely.

Fermi Paradox -Solutions

1. We are alone, therefore we are it.

2. Civilizations are common –but no one has colonized the galaxy.

A. Technological difficulties.

B. Sociological considerations.

C. Self-destruction.

3. There is a galactic civilization –they just don't want to deal with us.Zoo hypothesis

Sentinel hypothesis

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