NSCI 314LIFE IN THE COSMOS15 - THE DRAKE EQUATION:HOW COMMON ARE EXTRATERRESTRIAL CIVILIZATIONS THAT ARE SUFFICIENTLY TECHNOLOGICALLY ADVANCED THAT WE MIGHT BE ABLE TO COMMUNICATE WITH THEM? Dr. Karen KolehmainenDepartment of Physics,CSUSB http://physics.csusb.edu/~karen/THE DRAKE EQUATIONTHIS EQUATION IS USED TO ESTIMATE THE NUMBER OF “TECHNOLOGICAL” CIVILIZATIONS IN THE MILKY WAY GALAXY. –WE DEFINE A “TECHNOLOGICAL” CIVILIZATION AS ONE THAT IS CAPABLE OF (AND INTERESTED IN) ENGAGING IN INTERSTELLAR COMMUNICATIONS WITH OTHER CIVILIZATIONS.–NOTE: WE ARE ONLY MAKING THIS ESTIMATE FOR OUR GALAXY, BUT THE NUMBER SHOULD BE SIMILAR FOR ANY SIMILAR SPIRAL GALAXY.THIS IS THE NUMBER OF CIVILIZATIONS THAT COULD BE SENDING OUT RADIO (OR OTHER) SIGNALS THAT WE MIGHT BE ABLE TO RECEIVE.THE DRAKE EQUATIONWHY TRY TO ESTIMATE THE NUMBER OF TECHNOLOGICAL CIVILIZATIONS?–IF THE ESTIMATED NUMBER IS VERY SMALL, SEARCHES FOR SIGNALS FROM ALIEN CIVILIZATIONS MIGHT NOT BE WORTH THE TIME, EFFORT, AND EXPENSE.–IF THE ESTIMATED NUMBER IS LARGE, SEARCHES ARE MORE LIKELY TO BE SUCCESSFUL. THEREFORE IT’S EASIER TO ARGUE THAT THE TIME, MONEY, AND EFFORT ARE WORTH IT.KEEP IN MIND THAT:– WE CAN’T MAKE AN EXACT CALCULATION OF THE NUMBER OF CIVILIZATIONS, ONLY A VERY ROUGH ESTIMATE.–OUR ESTIMATE WILL APPLY ONLY TO LIFE THAT IS SIMILAR TO TERRESTRIAL LIFE. IF EXOTIC LIFE EXISTS, CIVILIZATIONS MAY BE MORE COMMON.DRAKE EQUATIONN = N*fsnpflfifcfLN = Number of civilizations in the MW galaxy capable of communication(what we'd like to find)N* = Number of stars in the MW galaxy = approximately 400 billionSUITABLE STARSN = N*fsnpflfifcfLfs = fraction of stars that are suitable stars(result of N*fs is number of suitable stars in MW galaxy)fs = 0.1 = 1/10 (optimistic case)fs = 0.001 = 1/1000 (pessimistic case)fs = 0.05 = 1/20 (my best estimate)SUITABLE PLANETSDrake Equation: N = N*fsnpflfifcfLnp = average number of planets that are suitable for life per each suitable star np = 2 (optimistic case)np = 0.1 = 1/10 (pessimistic case)np = 0.5 = 1/2 (my best estimate)DEVELOPMENT OF LIFEDrake Equation: N = N*fsnpflfifcfLfl = fraction of suitable planets on which life actually originatesfl = 1 (optimistic case - life will always arise if the planet is suitable)fl = 0.005 = 1/200 (pessimistic case)fl = 1 (my best estimate)DEVELOPMENT OF INTELLIGENCEDrake Equation: N = N*fsnpflfifcfLfi = fraction of planets with life on which intelligent life evolvesfi = 1 (optimistic case) fi = 0.001 = 1/1000 (pessimistic case) fi = 0.01 = 1/100 (my best estimate)DEVELOPMENT OF TECHNOLOGYDrake Equation: N = N*fsnpflfifcfLfc= fraction of planets with intelligent life on which technology sufficient for interstellar communication developsfc = 1 (optimistic case)fc = 0.01 = 1/100 (pessimistic case)fc = 0.5 = 1/2 (my best estimate)DO THEY EXIST NOW?Drake Equation: N = N*fsnpflfifcfLfL= Probability that they’re around NOW (as opposed to civilizations that existed in the past, but don’t exist any more) = L/tt = Age of MW galaxy = 10 billion yearsL = Average lifetime of a technological civilization (measured in years) = Average lifetime of civilization with ability and desire to communicateLIFETIMES OF CIVILIZATIONSL = Average lifetime of a technological civilization L = 10 billion years (optimistic case) = Age of galaxyL = 100 years (pessimistic case) Civilizations destroy themselves or lose interest in communication!NOTE: L is the least well-known factor in the Drake equation!DRAKE EQUATIONEXTREME OPTIMISTIC CASE(Use optimistic values of all factors except L)N = 400 billion x 0.1 x 2 x 1 x 1 x 1 x L/10 billionRESULT: N = 8 LNow look at different values of L:IF L = 100 YEARS (pessimistic case for L), THEN N = 800IF L = 10 BILLION YRS (optimistic case for L), THEN N = 80 BILLIONDRAKE EQUATIONMY BEST ESTIMATEN = 400 billion x 0.05 x 0.5 x 1 x 0.01 x 0.5 x L/10 billionRESULT: N = 0.005 L = L/200Now look at different values of L:IF L = 100 YEARS (pessimistic case for L), THEN N = 0.5IF L = 10 BILLION YRS (optimistic case for L), THEN N = 50 MILLIONDRAKE EQUATIONEXTREME PESSIMISTIC CASE(Use pessimistic values of all factors except L)N = 400 billion x 0.001 x 0.1 x 0.005 x 0.001 x 0.01 x L/10 billionRESULT: N = 0.0000000002 L = 2 X 10-10 LNow look at different values of L:IF L = 100 YEARS (pessimistic case for L), THEN N = 0.00000002IF L = 10 BILLION YRS (optimistic case for L) THEN N = 2DRAKE EQUATIONWE KNOW THAT N MUST BE AT LEAST 1 BECAUSE WE EXIST!THEREFORE:IF THE EXTREME PESSIMISTIC CASE IS CORRECT (N = 2 X 10-10 L),WE WOULD CONCLUDE THAT L > 5 BILLION YEARS.THIS WOULD MEAN THAT CIVILIZATIONS ARE LONG-LIVED!DRAKE EQUATIONWE KNOW THAT N MUST BE AT LEAST 1 BECAUSE WE EXIST!THEREFORE:IF THE EXTREME OPTIMISTIC CASE IS CORRECT (N = 8L),WE CONCLUDE THAT L > 1/8 YEAR.BUT WE ALREADY KNOW THIS!(WE’VE HAD THE RELEVANT TECHNOLOGY FOR ABOUT 50 YEARS SO FAR.)DRAKE EQUATIONWE KNOW THAT N MUST BE AT LEAST 1 BECAUSE WE EXIST!THEREFORE:IF MY BEST ESTIMATE IS CORRECT(N = 0.005 L),WE CONCLUDE THAT L > 200 YEARS.DRAKE EQUATIONCONCLUSIONS BASED ON THE FACT THAT WE EXIST2. EITHER N = L IS VERY ROUGHLY CORRECT (TO WITHIN A FACTOR OF A FEW HUNDRED OR A FEW THOUSAND), AS IN THE EXTREMELY OPTIMISTIC CASE OR MY BEST ESTIMATE OR2. IF THE EXTREMELY PESSIMISTIC VALUES OF VARIOUS FACTORS ARE CLOSE TO CORRECT, THEN L MUST BE VERY LARGEDRAKE EQUATIONBUTWE SUSPECT FROM HUMAN EXPERIENCE THAT L COULD EASILY BE SMALL! (MORE ON THIS LATER)THEREFORE WE CAN PROBABLY EXCLUDE THE EXTREMELY PESSIMISTIC CASE.REALITY IS PROBABLY CLOSER TO THE OPTIMISTIC CASE (N ~ L) OR TO MY BEST ESTIMATE (N ~ L/200).DRAKE EQUATIONN = # OF CIVILIZATIONS IN MW GALAXY CAPABLE OF INTERSTELLAR COMMUNICATIONL = AVERAGE LIFETIME OF SUCH A CIVILIZATION IN YEARSRESULT: N ~ LVERY ROUGHLY,(TO WITHIN A FACTOR OF A FEW 100 OR FEW 1000)BUT HOW LARGE IS L??(BIGGEST SOURCE OF UNCERTAINTY)MILKY WAY GALAXYN=1*THIS IS USMILKY WAY GALAXYDISTRIBUTION OF CIVILIZATIONSN=10*THIS IS US********WHY ISN’T THIS REALISTIC?*MILKY WAY GALAXYDISTRIBUTION OF CIVILIZATIONSN=10THIS IS US*********RANDOM DISTRIBUTION*MILKY WAY GALAXYDISTRIBUTION OF CIVILIZATIONSN=50*THIS IS US**********HOW HAVE THE DISTANCES BETWEEN CIVILIZATIONS CHANGED FROM N=10?**************************************MILKY WAY GALAXYDISTRIBUTION OF CIVILIZATIONSTHE LARGER THE NUMBER OF CIVILIZATIONS, THE SMALLER THE AVERAGE DISTANCE BETWEEN THEM,THE MORE FEASIBLE INTERSTELLAR COMMUNICATION