NSCI 314LIFE IN THE COSMOS19 - THE FERMI PARADOXDr. Karen Kolehmainen Department of Physics, CSUSBhttp://physics.csusb.edu/~karen/THE FERMI PARADOXTHE DRAKE EQUATION LEADS US TO BELIEVE THAT THERE IS LIKELY TO BE A LARGE NUMBER OF TECHNOLOGICALLY ADVANCED CIVILIZATIONS IN OUR GALAXY (AND EVEN MORE IN THE UNIVERSE AS A WHOLE). BUT WE HAVE RECEIVED NO SIGNALS FROM THEM NOR HAD ANY KNOWN VISITS BY THEM.THEREFORE “WHERE ARE THEY?” (ASKED BY ENRICO FERMI, 1950)CHRONOLOGY OF THE UNIVERSE14 BYA BIG BANG12 - 13 BYA MW AND OTHER GALAXIES FORM4.6 BYA FORMATION OF EARTH4.0 BYA LIFE BEGINS ON EARTH600 MYA MULTICELLULAR LIFE FEW MYA FIRST HOMINIDS OTHER CIVILIZATIONS COULD HAVE A HEAD START OF SEVERAL BILLION YEARS ON US!COMPRESS 14 BILLION YEAR HISTORY OF UNIVERSE INTO ONE YEAR:JANUARY 1 – BIG BANGEARLY FEBRUARY – MILKY WAY AND OTHER GALAXIES FORMMID-AUGUST – OUR SOLAR SYSTEM FORMSEARLY SEPTEMBER – LIFE STARTS ON EARTHMID-DECEMBER – CAMBRIAN EXPLOSIONDEC 31 EVENING – FIRST HOMINIDSDEC 31 HALF MINUTE BEFORE MIDNIGHT – HUMAN CIVILIZATION BEGINSTECHNOLOGICAL LADDERARE ALIEN TECHNOLOGIES LIKELY TO BE MORE OR LESS ADVANCED THAN WE ARE? 1. DEFINE “TECHNOLOGICAL” AS HAVING THE ABILITY TO COMMUNICATE OVER INTERSTELLAR DISTANCES (AS IN OUR DISCUSSION OF THE DRAKE EQUATION).2. WE HAVE BEEN TECHNOLOGICAL FOR ABOUT 50 YEARS.3. ESTIMATE L (AS IN THE DRAKE EQUATION) – THE AVERAGE LIFETIME OF A TECHNOLOGICAL CIVILIZATION.4. THE “AVERAGE” CIVILIZATION WILL BE APPROXIMATELY HALFWAY THROUGH THE LIFETIME L, WITH APPROXIMATELY HALF OF ALL CIVILIZATIONS MORE ADVANCED AND APPROXIMATELY HALF OF ALL CIVILIZATIONS LESS ADVANCED.5. COMPARE THE TWO TIMES: OUR AGE AS A TECHNOLOGICAL CIVILIZATION (50 YEARS) AND THE AVERAGE AGE OF A CIVILIZATION(1/2 OF L).TECHNOLOGICAL LADDERRESULT:- IF L IS MORE THAN A FEW HUNDRED YEARS, THEN MOST CIVILIZATIONS WILL BE MORE TECHNOLOGICALLY ADVANCED THAN WE ARE, PERHAPS BY A LARGE AMOUNT- THE ONLY WAY OUR LEVEL OF TECHNOLOGY COULD BE AVERAGE IS FOR L TO BE ONLY 100 YEARS OR SO! IF L IS THIS SMALL, OUR CIVILIZATION PROBABLY WON’T LAST MUCH LONGER!THE FERMI PARADOXREASONING AND ASSUMPTIONS LEADING TO THE QUESTION:THE DRAKE EQUATION LEADS US TO BELIEVE THAT THERE IS PROBABLY A LARGE NUMBER OF TECHNOLOGICAL CIVILIZATIONS IN OUR GALAXY.UNLESS CIVILIZATIONS ARE VERY SHORT-LIVED, WE EXPECT MOST OF THESE CIVILIZATIONS TO BE MORE TECHNOLOGICALLY ADVANCED THAN WE ARE (PERHAPS BY MILLIONS OR BILLIONS OF YEARS).SOME FORM OF INTERSTELLAR SPACE TRAVEL IS PROBABLY INEVITABLE FOR A SUFFICIENTLY LONG-LIVED AND ADVANCED CIVILIZATION.GALACTIC COLONIZATIONAT v = c, COULD CROSS THE GALAXY IN 100,000 YEARS v = 0.1c 1 MILLION YEARS v = 0.001c 100 MILLION YEARSTHEREFORE, AN ADVANCED TECHNOLOGICAL CIVILIZATION SHOULD BE ABLE TO COLONIZE THE GALAXY IN A SHORT AMOUNT OF TIME COMPARED TO THE AGE OF THE GALAXY (10 BILLION YEARS).COLONIZATION: HOME PLANET ESTABLISHES COLONIES ON SUITABLE PLANETS IN NEARBY SOLAR SYSTEMS. AFTER A FEW HUNDRED TO A FEW THOUSAND YEARS TO “GET ON THEIR FEET,” THESE COLONIES ESTABLISH MORE COLONIES. SUCH A STRATEGY WOULD LEAD TO COLONIZATION OF THE ENTIRE GALAXY WITHIN A PERIOD OF A FEW MILLION YEARS TO A FEW HUNDRED MILLION YEARS.GALACTIC COLONIZATIONMAYBE ALIEN CIVILIZATIONS AREN’T INTERESTED IN COLONIZATION AND CONQUEST.IF HUMANS ARE TYPICAL, THIS ISN’T TRUE. WE’RE PRETTY EXPANSIONIST.BIOLOGICAL EVOLUTION MAY NATURALLY PRODUCE CREATURES THAT ARE SOMEWHAT AGGRESSIVE (ALTHOUGH THERE ALSO SEEM TO BE SOME EVOLUTIONARY ADVANTAGES TO BEING COOPERATIVE). MAYBE SPECIES THAT ARE OVERLY AGGRESSIVE TEND TO DESTROY THEMSELVES VIA INTERNAL WARS BEFORE DEVELOPING INTERSTELLAR SPACE TRAVEL. IN ORDER TO DEVELOP A SOCIETY THAT LIVES LONG ENOUGH TO DEVELOP INTERSTELLAR SPACE TRAVEL, MAYBE A SPECIES NEEDS TO LEARN TO CURB ITS AGGRESSIVE TENDENCIES. BUT EVEN IF THEY DON’T WANT TO COLONIZE, WOULDN’T THEY STILL WANT TO EXPLORE? CURIOSITY SEEMS TO GO ALONG WITH INTELLIGENCE.GALACTIC COLONIZATIONBUT EVEN IF THEY DON’T WANT TO COLONIZE, WOULDN’T THEY STILL WANT TO EXPLORE?–MAYBE THEY WOULD AVOID COLONIZING PLANETS THAT ALREADY HAVE LIFE, IN ORDER NOT TO CONTAMINATE IT OR INTERFERE WITH IT.–THEY COULD STILL SET UP OUTPOSTS ON LESS SUITABLE PLANETS THAT COULD THEN (PERHAPS WITH A LONGER TIME BETWEEN EXPANSIONS) SET UP ADDITIONAL OUTPOSTS.THEY’LL EVENTUALLY GO EXTINCT UNLESS THEY CAN MOVE TO ANOTHER SOLAR SYSTEM.–AS THEIR HOME STAR BRIGHTENS WITH AGE, ITS HABITABLE ZONE WILL MOVE OUTWARD, AND THEIR PLANET WILL BECOME TOO HOT.–EVENTUALLY THEIR HOME STAR WILL EVOLVE INTO A RED GIANT, MOST LIKELY VAPORIZING THEIT HOME PLANET.–THERE MAY NOT BE ANOTHER SUITABLE PLANET IN THEIR HOME SOLAR SYSTEM. (EVEN IF THERE IS, IT'S ONLY A TEMPORARY SOLUTION.)SO, “WHERE ARE THEY?”WE DON'T KNOW, BUT LET'S EXAMINE SOME POSSIBLE ANSWERS. SOME OF THESE ANSWERS ARE UNLIKELY, WHEREAS OTHERS ARE PLAUSIBLE.RESPONSES TO “WHERE ARE THEY?”THERE IS NO EXTRATERRESTRIAL LIFE AT ALL. –THIS SEEMS UNLIKELY. –WE THINK SUITABLE PLANETS ARE RELATIVELY COMMON, AND THAT LIFE ARISES EASILY WHEN THE CONDITIONS ARE APPROPRIATE. IT DID SO QUICKLY ON THE EARTH.RESPONSES TO “WHERE ARE THEY?”ALTHOUGH THERE MAY BE EXTRATERRESTRIAL LIFE, THERE ARE NO ALIEN CIVILIZATIONS. THE FACTORS ALLOWING COMPLEX, INTELLIGENT, OR TECHNOLOGICALLY-DEVELOPED LIFE FORMS TO EVOLVE ARE UNIQUE TO EARTH. –THIS COULD BE TRUE. SUPPORTING ARGUMENTS:•COMPLEX AND INTELLIGENT LIFE TOOK A LONG TIME TO EVOLVE ON EARTH.•SPECIAL FEATURES OF EARTH (PRESENCE OF A LARGE MOON, SPECIFIC CLIMATE CHANGES, ETC.) MAY HAVE BEEN CRUCIAL IN STIMULATING THE EVOLUTION OF COMPLEX AND/OR INTELLIGENT LIFE FORMS ON EARTH.RESPONSES TO “WHERE ARE THEY?”ALIEN CIVILIZATIONS HAVE DEVELOPED, BUT THEY TEND TO DESTROY THEMSELVES (OR ARE DESTROYED BY NATURAL DISASTERS) BEFORE DEVELOPING INTERSTELLAR SPACE TRAVEL OR COMMUNICATION. –EVEN IF L IS VERY SHORT, REMEMBER THAT L IS THE AVERAGE LIFETIME OF A TECHNOLOGICAL CIVILIZATION. SOME CIVILIZATIONS WILL BE SHORTER-LIVED THAN THE AVERAGE, AND SOME WILL BE LONGER-LIVED. IF THERE ARE AS MANY CIVILIZATIONS AS THE DRAKE EQUATION LEADS US TO BELIEVE, THERE SHOULD BE A FEW OF THEM THAT ARE SUFFICIENTLY LONG-LIVED TO EXPLORE THE UNIVERSE AND VISIT THE EARTH.RESPONSES TO “WHERE ARE THEY?”ALIEN CIVILIZATIONS EXIST, BUT THEY ARE ALL LESS TECHNOLOGICALLY ADVANCED THAN WE ARE. • MAYBE!• ON