Editing 893: 65 Years

{{comic
| number    = 893
| date      = May 2, 2011
| title     = 65 Years
| image     = 65 years.png
| titletext = The universe is probably littered with the one-planet graves of cultures which made the sensible economic decision that there's no good reason to go into space--each discovered, studied, and remembered by the ones who made the irrational decision.
}}
==Explanation==
[[Randall]] is showing the number of still living humans who have walked on another world for the 65-year period that begins in 1969 (when a human first walked on the Moon). Up to 2011 (when the comic was drawn), he has drawn a single line for the actual figures.

For the subsequent years, he has drawn three lines using {{w|actuarial table}}s or life tables (such tables show, for each age, the probability that a certain person will die within the next year).

The line marked "5th Percentile" indicates that there is a 95% probability that the number alive in a given year will be above that line and a 5% probability that the number alive will be below that line.  For example, this line indicates a 5% chance that all Apollo moon-walkers will be dead by 2023, and a 95% chance that at least one will still be alive by that year.

The line marked "95th Percentile" indicates that there is a 5% probability that the number alive in a given year will be above that line and a 95% probability that the number alive will be below that line.  For example, this line indicates a 95% chance that all Apollo moon-walkers will be dead by 2035, and a 5% chance that at least one will still be alive by that year.

The middle line is not identified, but is probably the "50th Percentile" (see [http://blog.xkcd.com/2012/07/12/a-morbid-python-script/ these tables]).  If so, it indicates that there is a 50% probability that the number alive in a given year will be above that line and a 50% probability that the number alive will be below that line.  For example, this line indicates a 50% chance that all Apollo moon-walkers will be dead by 2028 (see previous link), and a 50% chance that at least one will still be alive by that year.

Although the term ''other world'' would include all other worlds on which humans have walked, there is currently only one other world on which humans have walked, which is the Moon.  The humans that have walked there are the 12 {{w|List of Apollo astronauts#Apollo astronauts who walked on the Moon|Apollo astronauts}} who landed on the Moon between 1969 and 1972.

In particular, {{w|Neil Armstrong}} and {{w|Buzz Aldrin}} landed in July 1969. {{w|Pete Conrad}} and {{w|Alan Bean}} landed in November. {{w|Alan Shepard}} and {{w|Edgar Mitchell}}: February 1971. {{w|David Scott}} and {{w|James Irwin}}: July 1971. {{w|John Young (astronaut)|John Young}} and {{w|Charles Duke}}: April 1972. {{w|Eugene Cernan}} and {{w|Harrison Schmitt}}: December 1972.

Irwin died in 1991. Shepard and Conrad died in 1998 and 1999 respectively, making the total 9 as of the date this comic was published. Since then, Armstrong died in 2012, Mitchell in 2016, Cernan in 2017, Young on January 6, 2018, and Bean on May 26, 2018. The death of Bean kept the actual line almost in line with the 50% 'arctuarial line', though it had generally been at least slightly higher prior to that. The situation by January 2025 sees the factual line stay at 4, taking it again beyond the 95% for at least the time being.<!-- Not wishing to tempt fate, just updating... Also deliberately removing the awkward "as of" phrase, 20/Jan/2025--> The oldest living person to have landed on the Moon is Aldrin at 95<!--b. January 20, 1930-->. Also living are Scott at 92<!--June 6, 1932-->, Schmitt at 89<!--July 3, 1935-->, and Duke at 89<!--October 3, 1935-->.

The chart assumes that no other humans will go to walk on another world within the time-frame plotted and the title text implies that this is primarily an economically determined decision. While noting that not exploring space is a justifiable and sensible decision which may also be made by many hypothetical cultures on other worlds, the text implies a grandness to a civilization that would be given the opportunity to discover, study and memorialize the 'one-world graves' of other civilizations by choosing to explore space despite the economic difficulty. This also implies that the likely consequence of not exploring space is that a civilization which chooses to do this is doomed to go extinct eventually while those which do explore and colonize may last long enough to be safely established on multiple worlds and discover the remains of civilizations which acted on a purely economic basis and hence ensured their own collapse. High five for exoplanet archaeology.

==Transcript==
:[A graph titled 'Number of Living Humans Who Have Walked on Another World' - its y-axis is numbered 5, 10, 15, its x-axis increments every ten years from 1960-2040. The line of the graph has a bracket above it that says '65 Years', starting at 1969, ending in 2034.
:The line starts at 1969 and increases steeply to 12 by 1972. It then plateaus until the early nineties, declines gradually to 9 between 1991-1999, and then plateaus again.
:From 2011-2035, which is labeled 'Projected Actuarial Tables', the line branches into three and begins to decline more steeply to zero. The area between the first and second branch is shaded and labeled '5th percentile' and the area between the second and third branch is shaded and labeled '95th percentile.']

==Trivia==
*The theme of actuarial projections was explored earlier in [[493: Actuarial]]; Randall's morbid python script for both was given in [http://blog.xkcd.com/2012/07/12/a-morbid-python-script/ the blag].

[[File:65_years_actual.png|none|thumb|800px|Version extended to 2025]]

{| class="wikitable"
|+Table of men who walked the moon
|- style="background:#ccc;"
| style="width:20px;"|
| '''Name'''
| '''Born'''
| '''Died'''
| '''Age at<br>first step'''
| '''Age at death'''
| '''Mission'''
| '''Lunar dates'''
| '''Service'''
| '''Alma Mater'''
|- style="background:#def;"
| 1. || {{w|Neil Armstrong}}|| 1930-08-05 || 2012-08-25<br/>(after&nbsp;comic) || 38y&nbsp;11m&nbsp;15d || 82y 0m 20d
|rowspan="2"| {{w|Apollo&nbsp;11}} ||rowspan="2"| July&nbsp;21,&nbsp;1969 || {{w|United States Navy|Navy}} || {{w|Purdue University}}, {{w|University of Southern California}}
|- style="background:#def;"
| 2. || {{w|Buzz Aldrin}}|| 1930-01-20 || || 39y 6m 0d || || {{w|United States Air Force|Air Force}} || {{w|United States Military Academy}}, {{w|MIT}}
|- style="background:#ffe8e8;"
| 3. || {{w|Pete Conrad}} || 1930-06-02 || 1999-07-08 || 39y 5m 17d || 69y 1m 6d
|rowspan="2"| {{w|Apollo 12}} ||rowspan="2"| November&nbsp;19–20,&nbsp;1969 || {{w|United States Navy|Navy}} || {{w|Princeton University}}
|- style="background:#ffe8e8;"
| 4. || {{w|Alan Bean}}|| 1932-03-15 || 2018-05-26<br/>(after&nbsp;comic) || 37y 8m 4d || 86y 2m 11d || {{w|United States Navy|Navy}} || {{w|University of Texas, Austin}}
|- style="background:#def;"
| 5. || {{w|Alan Shepard}} || 1923-11-18 || 1998-07-21 || 47y 2m 18d || 74y 8m 3d
|rowspan="2"| {{w|Apollo 14}} ||rowspan="2"| February 5–6, 1971 || {{w|United States Navy|Navy}} || {{w|United States Naval Academy}}
|- style="background:#def;"
| 6. || {{w|Edgar Mitchell}}|| 1930-09-07 || 2016-02-04<br/>(after&nbsp;comic) || 40y 4m 19d || 85y 4m 28d || {{w|United States Navy|Navy}} || {{w|Carnegie Mellon University}}, {{w|Naval Postgraduate School}}, {{w|MIT}}
|- style="background:#ffe8e8;"
| 7. || {{w|David Scott}} || 1932-06-06 || || 39y 1m 25d ||
|rowspan="2"| {{w|Apollo 15}} ||rowspan="2"| July&nbsp;31&nbsp;-&nbsp;August&nbsp;2,&nbsp;1971 || {{w|United States Air Force|Air Force}} || {{w|University of Michigan}} (freshman year, and later, an honorary doctorate), {{w|United States Military Academy}}, {{w|MIT}}
|- style="background:#ffe8e8;"
| 8. || {{w|James Irwin}} || 1930-03-17 || 1991-08-08 || 41y 4m 14d || 61y 4m 22d || {{w|United States Air Force|Air Force}} || {{w|United States Naval Academy}}, {{w|University of Michigan}}
|- style="background:#def;"
| 9. || {{w|John Young (astronaut)|John W. Young}}|| 1930-09-24 || 2018-01-06<br/>(after&nbsp;comic) || 41y 6m 28d || 87y 3m 13d
|rowspan="2"| {{w|Apollo 16}} ||rowspan="2"| April 21–23, 1972 || {{w|United States Navy|Navy}} || {{w|Georgia Institute of Technology}}
|- style="background:#def;"
| 10. || {{w|Charles Duke}} || 1935-10-03 || || 36y 6m 18d || || {{w|United States Air Force|Air Force}} || {{w|United States Naval Academy}}, {{w|MIT}}
|- style="background:#ffe8e8;"
| 11. || {{w|Eugene Cernan}} || 1934-03-14 || 2017-01-16<br/>(after&nbsp;comic) || 38y 9m 7d || 82y 10m 2d
|rowspan="2"| {{w|Apollo 17}} ||rowspan="2"| December 11–14, 1972 || {{w|United States Navy|Navy}} || {{w|Purdue University}}, {{w|Naval Postgraduate School}}
|- style="background:#ffe8e8;"
| 12. || {{w|Harrison Schmitt}} || 1935-07-03 || || 37y 5m 8d || || None (civillian) || {{w|Caltech}}, {{w|University of Oslo}} (exchange), {{w|Harvard University}}
|}

{{comic discussion}}
[[Category:Line graphs]]
[[Category:Math]]
[[Category:Statistics]]
[[Category:Science]]
[[Category:Space]]
[[Category:Comics to make one feel old]]