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. Armstrong died in 2012 and Mitchell in 2016, so the current number is 7. The oldest living person to have landed on the moon is Aldrin, 86. There is one 86-year-old, one 85, two 83s, one 81 and two 80s.

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 civilisation which chooses to do this is doomed to go extinct fairly rapidly while those which do explore and colonise may last long enough to be safely established on multiple worlds and discover the remains of civilisations 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].
{| class="wikitable"
|+Table of men who walked the moon
|- style="background:#ccc;"
| style="width:20px;"|
| '''Name'''
| '''Born'''
| '''Died'''
| '''Age at<br>first step'''
| '''Mission'''
| '''Lunar dates'''
| '''Service'''
| '''Alma Mater'''
|- style="background:#def;"
| 1. || {{w|Neil Armstrong}}|| 1930-08-05 || 2012-08-25 || 38y&nbsp;11m&nbsp;15d
|rowspan="2"| {{w|Apollo&nbsp;11}} ||rowspan="2"| July&nbsp;21,&nbsp;1969 || {{w|NASA}} || {{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
|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 || || 37y 8m 4d || {{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
|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 || 40y 4m 19d || {{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 || {{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 || || 41y 6m 28d
|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 || || 38y 9m 7d
|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 || {{w|NASA}} || {{w|Caltech}}, {{w|University of Oslo}} (exchange), {{w|Harvard University}}
|}

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