Fermat's Library | Where is everybody? An account of Fermi's question annotated/explained version.

There are **100,000 Earth-like planets capable of intelligent life ...

Here's a couple of recent links, somewhat zany, in different direct...

Enrico Fermi was an Italian-American physicist. He was awarded the ...

Travelling to distant Galaxies to meet other intelligent civili...

**Fermi is famous for his guesstimations** and his impressive abili...

### Where is everybody? *"So there are 100 Earth-like planets in...

The Drake equation provides an estimate of the number of communicat...

“WHERE

I EVERYBODY

A NACCOUNTO FERMI

QUESTI

EriM Jon

ABSTR

Fermi’s

famouquestion ocentrt debaa bt prev

o fextraterrestriacivilizatioaroduria luncconve

withEm iKonopinskiEdwaTellea nHerbY oi t s u

o f1950Fermi’companioo thad ah aprovaccoo t

incident.

Parto fthecurrentdebateabouttheexistencea nprevaleno extraterre

conc

interstellartravelandsettlement.

1-3I n1975MichaeH aargut h

interst

traw o

b efeasiblefora technologicallyadvancedcivilizatioa nthaa migratwouf it G a

i na fewmillionyears.4Sincethatintervali shorcomparewitt ha go t hGalh t h

concludedthattheabsenceo fsettIerso revidenco theiengineerprojei t S o

Systemmeantthattherearen ocxtraterrestrials.

Newman,Sagan,andShklovski2”5recallthaa legeno scien

say

t hEnrF ea s

thequestion,“Wherearethey?”duringa visit L oAlamodurit hSecW oW o

shortlythereafter.Fermi’squestionhasbeenmentionei severothrecpublicb

historicalbasisfortheattributionhasnotbee

established

Thant t hexcelmemo

HansMark,whohadhearda retellinga t

Los

Alamoi t hearl1950w nowlmoF e

didmaketheremarkduringa lunchtime

conversation

abou195H icompanw e

E m

Konopinski,EdwardTeller,andHerbertYorkA lthrehavprovidaccouo t inci

W ebeginwithKonopinski:“ Ihaveonlyfragmentarrecollectiabot hocca. . . I

d ohavea fairlyclearmemoryo fhowthediscussioo extra-terrestrg ostarted

Enrico,Edward,HerbYork,andI werewalkingt Iunca FullLodg

“WhenI joinedtheparty,I foundbeingdiscusseevidenaboflyisaucT h

immediatelybroughtt om yminda cartoonI h arecentlseei t hN eYork

expla

whypublictrashcansweredisappearing

from

t hstreeto N e

Yor

CitT hN Y op a

weremakinga fussaboutthat.Thecartoonshowewhaw aevidena flysausiti

thebackgroundand,streamingtowardit,‘littlgreemen(endoww iantencar

thetrashcans.MoreamusingwasFermi’scommentthai w aa verreasonthes ii

accountedfortwoseparatephenomena:t hreporto flyinsaucea w ea

t h

disapp

o fthetrashcans.Thereensueda discussiona t whethet hsaucecousome

exc

speedo flight.”

w..,,... ,

~,,..:.f..

:..$;.>:...

, ..:.;*

. ’..---.--,-:,-. ....

. .-

●. . ....

, !.:..*aA*,*:

%..:.

Drawib A lDunQ i951 9

=@,

T hN eYorkMagazI n

— --

Tellerremembers:“Myrecollectiono ft heveninvolviFer. . . i cleb o npar

T obeginwith,I wasthereattheincident.I believi occurrshortaftt he o t w o

a visito fFermit otheLaboratory,which

quite

possiblmighhavb edura sum

“ IrememberhavingwalkedoverwithFerma nothert t hFullLod

f o

lunW h

w ewalkedover,therewasa conversationwhicI believt hav

bee

quibria supe

o na subjectonlyvaguelyconnectedwithspactravelI hava vagrecollecw hm

notb eaccurate,thatw etalkedaboutflyingsaucera nt hobviostatemt ht

fly

saucersarenotreal.I alsorememberthatFermexplicitlraist hquesti

a n

I t hh

directedi ta tme,‘Edward,whatd oyouthink?H oprobabi i

tha

witht hn et y e

w eshallhaveclearevidenceo fa materialobjecmovinfastthalighI remet hm

answerwas10-6.’Fermisaid,‘Thisi smucht olowT hprobabili m ol it per

(thewellknownfigurefora Fermimiracle.)”

Konopinskisaysthath edoesnotrecallt hnumericavalue“excet ht hcha

rapidlya sEdwardandFermibouncedargumentso feacothe”

Tellercontinues:“Theconversation,

according

t m memorw ao nvaguconn

withastronauticspartlyo naccounto fflyingsaucermighb d ut extraterrepeo

(hereI believetheremarkswerepurelynegative)partlbecauexceedligvelow o

makeinterstellartravelonedegreemorereal

“WethentalkedaboutotherthingswhichI d n orememba nmayapproxie i

o fu ssatdowntogetherforlunch.”

Konopinskia nYora rquicertt ht hw e

o n

fouro fthem.

“Itwasafterw ewerea ttheluncheon

table,”Konopinsk

recall“thFersurpu

withthequestion‘butwherei severybody?’I w ah iw ao puttii t hd rlauf ru

York,whodoesnotrecallthepreliminaryconversatioo t h

wal

t FulLodd o

rememberthat“virtuallyaproposo fnothingFermsaid‘Dony oe vwonw h

everybodyis?’Somehow. . .

w eallknewh meanextra-terrestria”

Tellerremembersthequestioni nmucht hsamway“Thdiscussh a

noth

t d w

astronomyo rwithextraterrestrialbeings.I thini w asomdown-to-etopT hi t

middleo fthisconversation,Fermicameo uwitt hquitunexpecquest‘Whi

everybody?’. . .

Theresulto fhisquestionw ageneraIaughterbecao t h

stra

f a

t h

spiteo fFermi’squestioncomingfromthecleablueeveryboarout htabseet

understanda toncethath ewastalkingabout

extraterrestria

lif

“ Id onotbelievethatmuchcameo fthisconversationexceperhaa statet ht

distancest othenextlocationo flivingbeingsmaybvergreaa nthaindea f a o

galaxyi sconcerned,w earelivingsomewherei t h

sticks

f aremovf rt h

metrop

areao fthegalacticcenter.”

YorkbelievesthatFermiwassomewhatmorexpansiva n“follou w ia sero

calculationso ntheprobabilityo fearthlikeplanetst h

probabili

o l igiva eart

probabilityo fhumansgivenlife,thelikelyrisa n

duratio

o higtechnola s o H

concludedo nthebasiso fsuchcalculationsthaw ought hav

bee

visil oa a m

timesover.A SI recall,h ewento nt oconcludethat hreasow hadnb evisim ib

thatinterstellarflighti simpossible,or,

i f

i i possible

alway

judgt b n ow ot eff

o rtechnologicalcivilizationdoesn’tlastlonenougf oi t happe” Y oconfet b e

hazyabouttheselastremarks.

I nsummary,Fermididaskthequestion,a nperhapn osurprisinisss tdeb

todaywereparto fthediscussion.Certainly,t hlino argume

tha

Y orememb e

familiara decadelatera stheDrake-Greenbank

Equation.6’

A finalpoint:thedateo ftheconversation.Yori cleareo t hdat“ Tconverw

eitheri nthesummero f1950,1951,o r

1952,

ver

probabl

195a nt opla. . . w hI

wasvisitingIASLi nconnectionwiththe

forthcoming

Greenhoutests—specift

Georgeshot.” TheGeorgetestoccurred

o n

M a8 1951suggesti1 9datSurv

correspondencefromthetimeindicatesthaFermw aa annusummvisidurt y e

i nquestion.Unfortunately,attendanceandtraverecordf othoyeah ab edest

However,w ehavetheevidenceo fthecartoonKonopinsk

mention

Drab A lD ui w

publishedi ntheMay20,1950,issueo f

TheNewYorkerI

seem

qui

proba

t ht

incidento fFermi’squestionoccurredi nt hsummeo 1950

I a mgratefult oHansMarkandt othethreesurvivinparticipaf otheaccouT h

accounts,togetherwithm yletterso finquiry,a r

reproduce

i t hfollowpag

A nEqualOpporlunllyEmploywlOperatodb yUnlvarsllyo f

C M

fOrn1

Loala

LosAlaNatio

Labor

LosAlamosMexic

DAT

Sep2 1

I NREPLYREFERT O

E S:84

MAILSTO

TELEPHONE( 56 6

( F8 4

D rE mKonopi

IndiUniver

Departo Phys

SwaW e- R o

1 1

BloominT 474

D eD rKonopi

recen

g oa letf rH eY oconft h w

preaa a luncconverinvohimF eT e

a ny oa

convers

t hh beca f ai t S ( s

f oextraterrintellcomma “ Na t A p

Accort a popuvert hw a odiso f l

sauca nt hlikF ebecengri a

calc

suddeaskWeli y a rigt hw hi eveT

modimplici t hi intert ri

fea

t hSolSysougt h ab eviaa a em t i

t hpassometw s n convevio

D y oremet inciI s I w og rappa

writaccowhiI w ou a lw iY oa T e( c

encloi compoa “trvero t F eS t

T c

uosiw iamei t Droceo a confc a“In

,–—–

. .

Migraa nt h

Hum

Exper‘ b pub

CalifoPrei Sept1 9B F i(

t hUnivero

Hawa

a 1 a t edi

Thay of oy oh e

b t Unio

antha

Siny o

E M J o

EMJ:

E N-

als

C TCRM( 2w /E nM A I

E M JonESSM F 6

ESSF i( 2

DEPAO P H

S wHal1

BIeemington,I n4 7

( 8335

Oct1 1

D r

E rM Jon

L oAlaaNatiLabor

M F 6

L oAlamN eMex

8 7

DearD rJon

I h ao nfragmerecolla bt o c

t hy oletreft

I @ ha f ac lm eo

b ot hdiscuso extra-teg

start

EnriEdwaH eY o

a I w ewalt l ua

FullLod

W hI joi

t b

p aI f ob edise v

aboflysauc

T himmed

bro

t m m a

cartI h a

recentlyseeni t hN eYorkeexplaiw

publictrashcansweredisappearingfrot hatreo N

Y oCitT hN eY opapw em aa f

a b

T hcartshow hw evida f ls as i

i t hbackgra natret oi “ lg m

(endow iantencarrt t rc aM a m

w aFermcomm

t hi w a v e

reas

t hs

i accouf ot wsepaphent r eo f l

sauca w ea t disappo t t rc a

Theensa discua t whet s ac

someexct hs po l ia i w a fw w a

t hlunchtabt hF esurpu w t q u

“ Bwhei everyb

I w h w o p ui t

d r

laug

f ru aI t ht hwero t f o u

j ua H eY o

remem

I b a

absolu

n recolo t num

estimat hEdwment

e xt ht c h

rapia Edw

a n

F ebouargo e o t

Sinc

E m

Kono

EK:d

Losm

LosAlaNatioLabora

l-&s$;6m#Mex875

ESS-5:84-O

J u1 31 9

D rEdwaTell

PhysiDepart

Universo Califo

BerkelC 947

DeaD rTell

Thei a stoaboFerd ai L A lt i m a

t hrouni t hS E(seaf extrateinte

communiwhih aunfortulits ob aI w S

w hfiru si i h ib ow iShklb

C a

h for

wheo f rw hh heai

AlthH aM ah g im a

secondhaccof ra

retel

h h ei t e af tI

havfoun o nw icloknowo t t aS ep e

havsuggest hy omigb a sou

T hw at hstoi

bei

t ot hd ai t t lun

conversaturt t hpossio intert ra n

signaliFerbecengroi a q ucalca t

announ“Ifya rrigt hw hi everT imp

o t hquesti t hi inters

tra

i feat t

Galaxywouh ab efill oa b b ew oris

wheels

D y oh aa nfirstinfora bt hl it aI

s oy oh e

anda writdescro t e va y k t

woub o grehelT hs ti slit r ai l e

a nchanw ie aretel

I a curredit pro

o a confercal“IntersMigra t H uExp

whiw ah eh el ayeaT b ow ib pubb t

Universo Califopren ey ea I w ov m l t

inclua accuraccoo t F eS t

Thay of oy ohel

EMJ/

C yCRM( 2M A 1

E M JoneESSM F 6

ESSF i( 2

MEqualOppodunlWEmployer/Owa!edb yUnNarallyofCdilOrnla

Siny o

E M

J o

wreLive N aLab

A u1 1

Dr.EricM .Jones

LosAlamosNationalLaboratory

M SF665

LasAlamos,NewMexico87545

DearErie

M yrecollectiono ftheeventinvolvingFermithay owrott m aboi cleb

onlypartial.

T obeginwith,I wastherea ttheincident.I believi occurr

short

aftt e

o fthewaro na visito fFermit otheLaboratory,whicquitpossibmigh ab e

duringa summer.

1 rememhavingwalkedoverwithFermia nothert t hFullLodf o

lunch.Whilew ewalkedover,therewasa conversationwhicI beliet h ab eq u

briefandsuperficialo na subjectonlyvaguelyconnectewitspac

trave

I h aa

vaguerecollection,whichmaynotb eaccurate,thaw talkeaboflyisauca

theobviousstatementthattheflyingsaucersa rn orealI als

rememb

t h

Fer

explicitlyraisedthequestion,andI thinkh e

directed

i a m e~~Edwaw hd

y o

think.Howprobablei si tthatwithinthenextt eyearw shalhavcle

evide

a materialobjectmovingfasterthanlight?!tI remembetham answw a~llO

Fermisaid,“Thisi smuchtoolow.Theprobabilityi morlikt epercen( tw e

knownfigurefora Fermimiracle).

ThisincidentI haveclearlyi nmindandI believi w ao t hsamoccasw h

theotherquestionarosewhichyouhavementioned.ThilattepoinhowevI a n

certainof.

A tanyrate,theconversation,accordingt m memoryw aonlvagucome

withastronauticspertlyo naccounto fflyingsaucermighb d ut extraterre

people(hereI believetheremarkswerepurelynegative)partlbecauexceel i

velocitywouldmakeinterstellartravelone

degree

morreal

W e

t htalkabooththiwhichI d n oremembea nmay

approxim

eighto fu ssatdowntogetherforlunch.Thediscussioh anothit d w iastro

o rwithextraterrestrialbeings.I thinki twassomdown-to~artopi

Then,i nthemiddleo fthisconversation,Fermcamo uwitt hqui

unexpe

question“Wherei severybody?llWhatI a msureo i thayouquot‘ Ty oa rrig

thenwherei severybody?”,i swrong.Fermi

did

n ot ih iquestit a nconvers

whichwasthengoingon.Theresulto fhisquestionw a

genera

laughtbecao t

strangefactthati nspiteo fFermi%questioncominfrot h

clea

bluevery

aroundthetableseemedt ounderstanda toncethah w atalkiabo

extraterre

An.EquslQqwtmua-wdc.afmns.~ammuiwm

~945W*Tde@ins(415)422-110●Twx910-3WS3391L

Dr.EricM .Jones

Page2

August13,1984

life.I

d n obelit hm uc ao t h

conver

e xp ea s t

that hdistant t hn eloca

o flivinbeingm ab vergrea n

tha

indeed,a sfara sourgalaxyi sconcerned,w a rlivinsomewhei t hsticf

removedfromthemetropolitanareao fthegalacticenter

I canfullyconfirmthatthequestionw abroughu b Fermi FullLoda

lunch,probablybefore1950.

Hopingthatthisi stheinformationyouwanted

Witbesregar

Edwar

Tell

P.S.Goodo fyout oaska

quesIc ansThesdayi happea lt orar

140mw

LosAlaNatioLabora

L oAlamos,

Mex!co8

EarthandSpaceSciencesDivision

GeoanelysisGroup

D rHerbY o

PhysDepsrt

Univero Califa S D i

L JollC 920

D eD rYor

Sep

4 1

ESS-5:84-O

MsiS tF 6

(50667-6

@TS843-6

Therei a storyaboutFermi’s

days

i L oAlsmothai makt

roundsi ntheSETI(searchforextraterrestrialintelligencommun

whichhas,unfortunately,littleaolidbasis

I w aSagw hfiru s

i ti nhisbookwithShklovski,butCarlh a

forgotte

wheo f rw hh

heardit.

HansMarkhasgivenm ea

secondhand

accoufroa retel

h eheardi ntheearlyfifties;EdwardTelleh aalsprovidh ir e

ollectiono ftheevent.

Severalpeoplehavsuggestthay omigb

a source.

T hw at hstoi b et ot hd ai t t lun

conversturt t possio

inter

t rpar

faster-thantravF ebecengri a q ucala

t hannou“ Iy oa rigt hw hi everT imp

o t hquesti thati finterstellart ri feat t

G a

wouh ab efill oa b beiw origaome

Tella at ht hconverh m oo

w h

F ea s“ Wi

everybo

o uo t hb la witt qual

H s t

w agenelaug

beca

everrea

t h

F ew t a

aboextraterre( enca c oo Tellet

D y oh aa nfirsinfora bt l it I s

y oh ea na writdescro t e va y k t w b

o grehel

l %

sto

i slipt rapi l ea c h

w ie aretellI a curredit proco a c o

call

“InterstMigra

a t H uExpew hw h h

l ayea

T hb ow ib publb t Univo Calp

n eyeaa nI wouv em ul it inca acca co t

FerSto

Thay of oy oh e

EMJ:

E N-

a l

C T

CRM( 2w iEncM A 1

E M JonESSM F 6

ESSF i( 2

Sinceryou

E M J

A nEqualOpwnunlWtiployw/OptiatdWUnMwollyofCalifOmla

UNIVERSITYO CALIFORN

INSTITUTEO NGLOBALCONFLICTA NCOOPERATI

BSSKSIZY. DAVIS. mvmc. LosANCEI.I!.9. SNESSIDE. SAWDIECO. SANFSANCISCO

SASTn

. SANCSU

HerbertF .York

Director

E rM Jon

Eara nSpaScieDivi

GeoanalGro

L oAlaNatiLabor

M aS tF665

LosAlamoa,New

DearEric:

M yrecollection

f Ollows:

Mex87545

o Ferrem

IGCCCENTRALOFFICEQ.06

UNIVERSITYO FCALIFORNIAS ADIE

L AJOLLA,CALIFORNIA92093

(619)452.3352

Sept

1 1

a b“ wevei i a

A ta lunchi t hL ow hincj uf p eF eT e

E mKonopia nmysF es avira po n o

‘Dony oe vwonw heveri s

Som

( p ei

w aconnet t hp rconvei t w y dese

thouI d n oremet hw a k nh m eextra-

H t hfollu w ia sero calcuo t pro

o earthplant probao l ig ia e at

probabio humg il it l i

r i

a d uo h

technola na o H conco t b ao s cal

t hw ougt h ab evisl oa a m t io A

I recah w eo t conct ht r ew h ab

viaimigb t hintersf li impoo i i

i poaaialwjudt b n w ot e fo

tech

civilizdoesl al oenof i t h a

I a m

haziabothel arem

a o

The

conversw aeiti t

proba195a nt op la a

i connecw it forth

t hGeosho

y s hprod it

s uo 1 91 o 1 v

t iw hI w visL

Greet e(spe

HFY:

1 0

INDIANAUNIVERSITY

DEPAO P H

S wHal1

BloomI n4 7

( 8335

Februar1 1

D . E rM Jones

EarthandSpaScieDiv

Geoanal

Gro

L oAla

L oAlaNati

Labor

L oAlamN M

8 7

De a rD rJon

T hcarty f oi i nt o I

refert oI a ls et d ao t

discuss

sinI a n cer

t h

i t

plai t hsumo 1950t c aw

stiquifrei m m i

M yb ew i

- - 2

ifiL

E rKono

EK:d

REFERENCES

1 .M .H .HartandB .Zuckerman(eds.),

Ext ra t errest ri

Wbe

A r

T b(PergP r

Inc.,NewYork,1982),p .182.

2 .W .T .NewmanandC .Sagan,Ic a r u4 6293-3(1 9 8

3 .E .M .Jones,Ic a r t z s 4 6 ,328-336(1981).

4 .M .H .Hart,

Qua rterly Journa l

oftbeRoyalAstronomicaZSo

1 6128-(19

5 .I .S .ShklovskiandC .Sagan,

In t e l l ig eLz Yi t bUnive(Holden-

Inc

S Fran

1968),p .448.

6 .W .Sullivan,

WeAreNotAlone(Mc G r a w -HBooCo.NewYor196

7 .F .D .Drake,“TheRadioSearchforIntelligentExtraterrestriLifei Cur

Asp

Exobiology,G

MamikunianandM .H Brigg(eds.,JePropulsLaboratech

report32-428(1965),pp.323-346.

Discussion

### Where is everybody? *"So there are 100 Earth-like planets in the Universe for every grain of sand in the world. Think about that next time you’re on the beach."* There are 100,000 Earth-like planets capable of intelligent life in our Galaxy, the Milky Way. How come we have never made an "encounter" with extraterrestrial life? Any ideas? *(feel free to comment below)* Enrico Fermi was an Italian-American physicist. He was awarded the Nobel Prize in Physics in 1938. He is the creator of the world's first nuclear reactor and worked on the Manhattan project during WW II. Fermi is famous for his back of the envelope calculations and his impressive ability to estimate the magnitude of answers to complex problems. A great example of this ability is this article he wrote guesstimating the power dissipated by the explosion of the first atomic bomb with simple sheets of paper: **[My observations during the explosion at Trinity](http://fermatslibrary.com/s/my-observations-during-the-explosion-at-trinity)** ![Fermi Teller](https://i.imgur.com/16Spiv9.jpg) *Edward Teller (left) with Enrico Fermi in 1951.* You can learn more about Fermi here: [Enrico Fermi](https://en.wikipedia.org/wiki/Enrico_Fermi) **Fermi is famous for his guesstimations** and his impressive ability to estimate the magnitude of answers to complex problems. He had an uncanny ability to take problems apart and describe them in simple terms. Fermi tried to inculcate this facility in his students. Some famous Fermi questions: - How many grains of sand are there on the world’s beaches? - How many piano tuners are there in Chicago? - How far can a crow fly without stopping? - How many atoms of Caesar's last breath do you inhale with each lungful of air? The Drake equation provides an estimate of the number of communicating civilizations in the Milky Way. The equation is composed of 7 terms. The first 6 are used to compute the rate at which intelligent civilizations are being created and the final term identifies how long each lasts on average as a broadcasting civilization. The Drake equations can be written as: $$ N = R × f_p × n_e × f_l × f_i × f_c × L $$ where: - N is the number intelligent civilizations that are broadcasting their presence - $R$ is the yearly rate at which stars form in the Galaxy - $f_p$ is the fraction of stars that possess planets - $n_e$ is the number of planets with environments suitable for life - $f_l$ is the fraction of suitable planets on which life actually develops - $f_i$ is the fraction of these planets on which life develops intelligence - $f_c$ is the fraction of intelligent life-forms that develop a culture capable of interstellar communication - $L$ is the time that such a culture will devote to communication There is a lot of uncertainty associated with the parameters and the Drake equation can give a very wide range of values, depending on the assumptions and the values. To learn more about the Drake equation: - [Drake equation tutorial](http://www.astrodigital.org/astronomy/drake_equation.html) - [SETI - The Drake Equation](http://www.seti.org/drakeequation) - [Drake equation](https://en.wikipedia.org/wiki/Drake_equation) Here's a couple of recent links, somewhat zany, in different directions regarding Fermi's paradox: Dissolving the Fermi Paradox (Future of Humanity Institute, Oxford) https://spectrum.ieee.org/tech-talk/computing/hardware/computing-and-the-fermi-paradox-a-new-idea-emergestheyre-all-asleep Runaway consumerism explains the Fermi Paradox https://www.edge.org/q2007/q07_print.html#miller What Donald Trump Teaches Us About the Fermi Paradox http://nautil.us/blog/what-donald-trump-teaches-us-about-the-fermi-paradox There are **100,000 Earth-like planets capable of intelligent life in our Galaxy**, the Milky Way. (*see guestimations below*) ### Where is everybody? How come we have never made an "encounter" with extraterrestrial life? Any ideas? 🤓 🤔 (*Feel free to comment below*) --------------------- In this matter I tend to go with the hypothesis that there's extraterrestrial life in other places in the Universe but we just haven't been able to detect it. It's also very unlikely that we are the most developed civilization out there so I agree with Freeman Dyson's theory that a sufficiently developed species will try to harness a large part of the energy produced by a star by enclosing it in some sort of shell - [a Dyson Sphere](https://en.wikipedia.org/wiki/Dyson_sphere). This will shift the energy emission spectrum around the star towards infrared which in theory should be detectable at a relatively long distance. We just need to map a large portion of sky for a long enough time to capture the signals from these spheres :) Most likely because there's a more advanced civilization that is able to simulate a Universe where we are the single intelligent species (also called the Planetarium hypothesis). This grew stronger in me after reading [Nick Bostrom's paper](http://fermatslibrary.com/s/are-you-living-in-a-computer-simulation) that has been featured a few months ago. It seems to depend a lot on how mobile everyone is, or how long they've been sending out messages. Are all 100,000 civilizations whizzing around in FTL ships or just sending signals out at *only* the speed of light? Assuming the latter makes the situation a lot harder. If we imagine sending ships in all directions looking for a planet with intelligent life, we can estimate the number of planets we would need to visit as a binomial random variable. If we visit N planets, where we expect $\lambda = \frac{1e5}{1e11}$ planets to harbour intelligent life, the probability of finding intelligent life is: $p = 1 - Bino[0,N,\lambda] = 1-(1-\lambda)^N$ Alternatively, $N = \frac{\text{log}(1-p)}{\text{log}(1-\lambda)}$ So now we know how many planets we have to visit, how far do we have to travel? If the Milky Way is approximately a 150k-light year diameter disk, with all the planets equally spaced out and us in the center (all not true, so our number may be generous to us), then the radius of our search from Earth must be: $R\approx\sqrt{\frac{N}{N_{total}}}\frac{150}{2}\text{kly} = \sqrt{\frac{\frac{log(1-p)}{log(1-\lambda)}}{1e11}}75\text{kly}$ $R\approx\frac{0.75}{\sqrt{10}}\sqrt{\frac{log(1-p)}{log(1-\lambda)}}$light years You can plot this to see how the distance changes with your confidence of finding life. Searching in all directions is pretty similar to sending a message into space. The earliest man-made radio signals from about 150 years ago have a 1-in-3 chance of reaching an intelligent civilization (if they're still strong enough). You need to travel 200 light years in all directions to have a 50/50 likelihood. Being 99% sure requires a 510 light year search radius. Unless our neighborhood aliens are mobile and able to come find us, or very old and have been transmitting information for a long time (which isn't so crazy), it seems pretty unlikely that we'll find them soon. Travelling to distant Galaxies to meet other intelligent civilization would take billions of years and is practically impossible. So let's focus on our home Galaxy, the Milky Way. **How many intelligent civilizations are there in our Galaxy?** We can *guesstimate* the number of planets harboring intelligent life in the Milky Way: - there are **$100 \times 10^{9}$ Stars in our Galaxy** ⭐️ - if 5% of all stars are Sun-like then there are **$5 \times 10^{9}$ Sun-like stars in our Galaxy** ☀️ - if 20% of all Sun-like stars are orbited by an Earth-like planet then there **$10^{9}$ Earth-like planets** 🌎 - if only 1% of these Earth-like planets harbor life then there would be **$10\times 10^{6}$ planets with life in the Milky Way** 🐋 - if 1% of those develop intelligent life then **there are 100,000 intelligent civilizations in our Galaxy** 🤓 If there are 100,000 intelligent civilization in the Milky Way, then the question arises **where are all the Aliens?** This is the **Fermi Paradox**. You can learn more about the Fermi Paradox: - [Fermi Paradox](https://en.wikipedia.org/wiki/Fermi_paradox) - [SETI - The Fermi Paradox](https://www.seti.org/seti-institute/project/details/fermi-paradox) - [Wait But Why - The Fermi Paradox](https://waitbutwhy.com/2014/05/fermi-paradox.html)

Comments

Products

Project