LIFE IN THE UNIVERSE
LIFE IN THE UNIVERSE AST 2037
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This 22 page Class Notes was uploaded by Ms. Adrian Buckridge on Friday September 18, 2015. The Class Notes belongs to AST 2037 at University of Florida taught by Staff in Fall. Since its upload, it has received 17 views. For similar materials see /class/206978/ast-2037-university-of-florida in Astronomy at University of Florida.
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Date Created: 09/18/15
Interstellar Travel Stephen Eikenberry 15 April 2008 AST 2037 The Drake Equation Nciv N f ne f ft Lciv Lgal Nciv number of current civilizations in the Galaxy N 3 x 1011 stars fP 1200 fraction of suitable stars nc 1 suitable planets per suitable stars fl fraction of these planets where life forms fi fraction of lifebearing planets where intelligence evolves ft fraction ofintelligencebearing planets where technology develops for communication L6 average lifetime of a civilization Lgal lifetime of Galaxy Q Intelligence Fraction This is an endless debate But does the outcome REALLY matter Even ifintelligence is NOT inevitable it happened once out of two tries us dinosaurs would estimate fraction at 392 or 13 Permian extinction ended another try In short 1 out ofa few so this is not a huge factor it is close to 1 not 00 not 0000001 Technology amp Evolution Technological life reproducessurvives preferentially Eventually leads to dominant life being technological The more technol0gy the more likely it is to survive even if it does not directly kill off the others contrary to all of human history Theory of Neanderthal extinction Peaceful non technological Neanderthals were victims of CroMagnon genocide So technology fraction is about 1 Civilization Lifetime Why is this critical Do the math so far Nciv N fP ne f ft Lciv Lgal 3x10 0005 1111 Lci 13x10 0yrs 01 Lm LC 10 Carl Sagan estimated this as 10 LC in 1974 Pessimistic case would be Lciv 10 billion a BIG difference Number of Civilizations So estimates range from L 80 years to L 1000 years 100000 years Longer Mass extinctions seem to happen every 50 100 million years A realistic estimate is NC Lciv 10 So anywhere from 8 civilizations to 1000 to millions 3 A pessimistic estimate is LC 10 billion which gives ZERO even for long lifetimes limited by mass extinction timescale Distance amp Communication Lven for an optimistic case average distance is 10 pc away This Is 30 light years Play the Contact game We start broadcasts around 1936 Message arrives then in 1966 The send a return messak e to us within 1 year Would only have reached us In 1997 So just bmly possible in the most optimistic scenario 394 Summarv from Last Time Drake Equation guides estimate of number of civilizations in the Galaxy right now Depends on many unknowns One of the most important is lifetime of civilizations We can estimate that this is at least 80 100 years Could be as long as 100 million years 2 but depends on ecological collapse natural extinction or violent self destruction Realistic estimates of number of civilizations ranges from about 8 to as many as 1 million Pessimistic estimates would say zero Even for optimistic estimates we would just BARELY be at the threshold of being able to communicate with other civilizations d Interstellar Travel Why Bother It is already hard enough just to send messages to other civilizations VV IIJ 6U IU Ill 1 10le Ul IIJIIIE thrL Soft fuzzy answers Humans have always felt the need to explore in person Even today world leaders forgo telecoms for important deals travel in person instead for face to face meeting faceto tentacles here Real answer If you can t actually GO there it is rett hard to kill them and take their stuff it Interstellar Travel Shuttle OK let s Just hop on a space shuttle and go Problem Space shuttles are designed for short orbital missions around Earth Wltll shuttletype speeds even reaching Mars takes f V months Le Mars rovers 39 mam engines Wm quarters They are not up to the task star irackey anks wing engm lamam control mmstavs wwwimnviua mm orbilal rendez vous light Interstellar Travel Rockets Fine we ll pony up lots of to build a ship custom designed to get us to other destinations tar away Assume we have the same rocket technology as now How much food do we need to pack to take with us No known turnpike service areas along the way Just consider the CLOSEST star Alpha Lentaurl and the Lentaurl cluster Enormous Journeys as a hip limes to leach Centauri Cluster V5 55 mph 7 50000000 3 days Io moon 900030 37000 mph alum Conclusion we need a Light Speed Breakthrough 1 Interstellar Travel Time Current technology moves at about 0004 of light speed But we know from our message calculations that even at light speed 25000 times faster than this roundtrip times can be very long 60 years minimum to thousands of years or more for even CLOSEST civilizations This puts a crimp in our plans Maybe when we get there we can gum them to death and take their stewed prunes Our Friend Time Dilation Une enect 01 Linsteln 39s 1 neory 01 bpeClal Kelatmty Moving clocks tick slower We can actually see this with cosmic ray articles muons fastmoving muons live longer than slow moving ones 1 mm dilation t tl v2c2l2 y ll vzcz 2 is the Lorentz F actor for relativistic near lightspeed velocities Al v mac 7 14 ish At v 09c 39y 2ish At v 099c y 25ish Q Our Frlend Tlme Dilatlon bo at v 036 we on Earth see a trip to on Len take 0 years each way But the astronaut on the ship sees it take about 5 years each way 2 Now try v099c We see it takes 3 years each way Astronaut sees it take about 6 weeks each way Twin paradox one twin on Earth ages 6 years during the roundtrip the other twin ages only 3 months Interstellar Travel Light Speed DO mterstelalr travel 18 WCII U But at near lightspeed journeys are of tenable time for the travelers if not Earthbound folks An extra problem Humans can only handle a few Gs of acceleration before we die So to get to 099c takes a long time even at maximum survivable acceleration Light Speed Rocket Trouble hnergy 01 Ilying mass is ymcz To deliver payload mass 111 need enough fuel to slowdown and stop it For nuclear fusion VERY ef cient this is 0007 mfuel c2 So mass of fuel needed to stop m1 is mfuel ym10007 This means you need about 3500x as much fuel as payload just to stop not to mention the fuel to get started in the rst place Light Speed Antimatter Rockets Even more ef cient than nuclear fusion is matterantimatter annihilation Converts 100 of mass into energy For argument s sake let s assume that we can be 100 ef cient in harnessing the energy released for space travel gt a perfect rocket 100 of fuel rest mass converted into usable energy For the return trip still need ymc2 of stopping energy so mfuel yml total return trip in ight mass is m2 mfuel m1 71 m1 or about 26 times the payload mass But need fuel to start return trip of y1 m2 yl2 m1 or about 650 times the payload mass Similar thing for the way there 2 even a perlect rocket needs about 400000 times as much fuel mass as payload mass l So rockets are not a great idea for interstellar travel need to carry HUGE amount f fuel with you m Light Speed Other Techniques Other ideas solar sails Capture light pressure from star to accelerate the payload No fuel mass only extra sail mass could be very small Problems Once you leave the Vicmlty ot bunstar not much acceleration As you get closer to the speed oflight redshift decreases ef ciency So nice idea but looks tricky 4 Light Speed Other Techniques 30 rockets are not a great Idea tor interstellar travel need to carry HUGE amounts of fuel with you Other ideas Solar sails Bussard Ramjets M V H 4 quotI H mf li39av x 4 k g v a 1 x419 39quot39 J quotT WA a H 1m iii ax Era J Summary Stars are VERY far apart Travel times with current rockets are CRAZY long Even at light sl eed travel times are HUGE thouoh not for the traveler Rockets are very massinef cient for these trips though even matterantimatter drive Best bet nd a way to tunnel through space via wormholes probably not as easy as it sounds and it sounds hard