#+title: A Universe of Human Experience

 #+author: Robert McIntyre

 #+email: rlm@mit.edu

 #+description: How many man-years are in a year?

 #+keywords: man-year man-month man-hour universe human experience philosophy

 #+setupfile: ../../aurellem/org/setup.org

 #+include: ../../aurellem/org/level-0.org

 

 * What is a Man-Hour?

 A [[http://en.wikipedia.org/wiki/Man-hour][/Man-Hour/]] is a term from the field of Management.  It is one hour

 of work by one person for a certain task. 

 

 For example, if I have a nine-to-five programming job at [[http://www.imdb.com/title/tt0151804/quotes][Initrode]], but

 I slack off most of the time and only /actually/ work from

 10:00-11:00, then I only put in one man-hour of work a day.

 

 If my task is simply existing, then I put in 24 man-hours of work

 every day.

 

 * Experience

 I've often wondered what it would feel like to have more than one

 body, and to experience the same day from different perspectives. 

 

 For example, there are around twenty different majors available at

 MIT. If you had ten different bodies, and each of them double-majored

 in different subjects, then in only four short years you would

 graduate with a degree in every field MIT has to offer. You would have

 experienced forty man-years of college in the process.

 

 How many man-years does the entire MIT class experience every year?

 [[http://web.mit.edu/fnl/volume/192/century.html][There were around]] $4585$ undergraduates at MIT in the fall of 1982.

 

 $4585$ students $\times$ $1$ year $=$ $4585$ man-years.

 

 One person could help lay the first blocks of [[http://en.wikipedia.org/wiki/Great_Pyramid_of_Giza][great Pharaoh Khufu's

 tomb]] and live to see [[http://www.burjkhalifa.ae/][Burj Khalifa]] and they would accrue the same

 amount of experience as the MIT class of '82 did in one year.

 

 * Forever in a Day

 How many man-years does everyone experience in a day? There are almost

 7 billion people around today, according to [[http://www.census.gov/main/www/popclock.html][www.census.gov]]. 

 

 #+begin_src clojure :results output :exports both

 (ns lifespan)

 (use '[clojure [pprint :only [cl-format]]])

 

 (cl-format *out* "Man-years per day: \n ~R"

            (* 6969492979 ;; people on Earth

               (/ 1 365)  ;; years-per-day

               ))

 #+end_src

 

 #+results:

 : Man-years per day: 

 :  nineteen million, ninety-four thousand, five hundred one

 

 Together, we experience almost 20 million years every day!

 

 A week in the lives of the people of Earth is enough to reach back to

 the age of the dinosaurs.

 

 * The Infinite Stories of Humanity

 How many man-years is the sum total of human experience? That is, how

 many man-years has every human who has ever lived experienced?  

 

 Using a very rough calculation involving the table from [[http://www.prb.org/Articles/2002/HowManyPeopleHaveEverLivedonEarth.aspx][here]] and the

 average human lifespans through the ages found [[http://en.wikipedia.org/wiki/Life_expectancy][here]], I get the

 following:

 

 #+begin_src clojure :results output :exports both

 (in-ns 'lifespan)

 

 (def

   time-periods

   "The time periods under question.

     'start' here is taken to be 50,000BC"

   [:start-8000BC

    :8000BC-1    

    :1-1200      

    :1200-1650   

    :1650-1750   

    :1750-1850   

    :1850-1900   

    :1900-1950   

    :1950-1995   

    :1995-2011])

 

 (def births

   "number of people who existed in the given time periods"

   (zipmap

    time-periods

    [ 1137789769  ;; \

     46025332354  ;;  | 

     26591343000  ;;  |

     12782002453  ;;  |

     3171931513   ;;  | -- from the video at:

     4046240009   ;;  | http://www.prb.org/Articles/2002/

     2900237856   ;;  |    HowManyPeopleHaveEverLivedonEarth.aspx

     3390198215   ;;  |

     5427305000   ;;  |

     2130327622]));; /

   

 

 ;; Confirm that the sum of people agrees with that in the video.

 (assert (= 107602707791 (reduce + (vals births))))

 

 (def lifespans

   "lifespans in years from birth for the various time periods"

   (zipmap

    time-periods

    [33   ;; start-8000BC  \

     22   ;; 8000BC-1      | -- from: 

     30   ;; 1-1200        | http://en.wikipedia.org/wiki/

     32   ;; 1200-1650     /    Life_expectancy

     35   ;; 1650-1750 \

     35   ;; 1750-1850  |-- from:

     45   ;; 1850-1900  | http://www.deathreference.com/

     66   ;; 1900-1950  |    Ke-Ma/Life-Expectancy.html

     66   ;; 1950-1995 /

     70   ;; 1995-2011-------> form:  

          ;;   http://www.prb.org/DataFinder/Topic/

          ;;      Rankings.aspx?ind=6&loc=241

     ]))

 

 

 ;;; ----------------------------------------

 ;;;         And now for the result!

 

 ;; This section is just here to make the result look pretty.

 (dorun

  (map println

       (clojure.string/split

        (cl-format 

         nil "years of human experience: \n ~R years"

         ;; Multiply each time-period's total number of people

         ;;  by those peoples' average lifespan in years to get

         ;;  the total number of man-years experienced during

         ;;  that period, then add them together.

         (reduce + 

                 (map *

                      (map births time-periods)

                      (map lifespans time-periods))))

        #",")))

 

 #+end_src

 

 #+results:

 : years of human experience: 

 :  three trillion

 :  three hundred seventy-one billion

 :  ninety-three million

 :  five hundred ninety-five thousand

 :  one hundred eighty-one years

 

 Humans have already collectively lived about two-hundred times longer

 than the age of the universe.