Explain xkcd: It's 'cause you're dumb.
Title text: 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.
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 actuarial tables 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 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 Apollo astronauts who landed on the Moon between 1969 and 1972.
In particular, Neil Armstrong and Buzz Aldrin landed in July 1969. Pete Conrad and Alan Bean landed in November. Alan Shepard and Edgar Mitchell: February 1971. David Scott and James Irwin: July 1971. John W. Young and Charles Duke: April 1972. Eugene Cernan and 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, so the current number is 8. The oldest living person to have landed on the moon is Aldrin, 83. There are two 82-year-olds, two 80s, one 78 and two 77s.
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. High five for exoplanet archaeology.
- [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.']
- The theme of actuarial projections was explored earlier in 493: Actuarial; Randall's morbid python script for both was given in the blag.
Table of men who walked the moon
|| Age at
|| Lunar dates
|| Alma Mater
|| Neil Armstrong
|| 38y 11m 15d
|| Apollo 11
|| July 21, 1969
|| Purdue University, University of Southern California
|| Buzz Aldrin
|| 39y 6m 0d
|| Air Force
|| United States Military Academy, MIT
|| Pete Conrad
|| 39y 5m 17d
|| Apollo 12
|| November 19–20, 1969
|| Princeton University
|| Alan Bean
|| 37y 8m 4d
|| University of Texas, Austin
|| Alan Shepard
|| 47y 2m 18d
|| Apollo 14
|| February 5–6, 1971
|| United States Naval Academy
|| Edgar Mitchell
|| 40y 4m 19d
|| Carnegie Mellon University, Naval Postgraduate School, MIT
|| David Scott
|| 39y 1m 25d
|| Apollo 15
|| July 31 - August 2, 1971
|| Air Force
|| University of Michigan (freshman year, and later, an honorary doctorate), United States Military Academy, MIT
|| James Irwin
|| 41y 4m 14d
|| Air Force
|| United States Naval Academy, University of Michigan
|| John W. Young
|| 41y 6m 28d
|| Apollo 16
|| April 21–23, 1972
|| Georgia Institute of Technology
|| Charles Duke
|| 36y 6m 18d
|| Air Force
|| United States Naval Academy, MIT
|| Eugene Cernan
|| 38y 9m 7d
|| Apollo 17
|| December 11–14, 1972
|| Purdue University, Naval Postgraduate School
|| Harrison Schmitt
|| 37y 5m 8d
|| Caltech, University of Oslo (exchange), Harvard University
add a comment! ⋅ refresh comments!
I wonder if it would be possible to identify individual people who are behind those vertical jumps in the graph (in the not projected part)... --JakubNarebski (talk) 19:18, 14 December 2012 (UTC)
- Glad you asked! </Information Hen> Neil Armstrong and Buzz Aldrin landed in July 1969; that's two. Pete Conrad and Alan Bean joined the group that November; that's four. Alan Shepard and Edgar Mitchell in February '71; that's six. David Scott and James Irwin in July '71; that's eight. John W. Young and Charles Duke in April '72; that's ten. Eugene Cernan and Harrison Schmitt in December '72; that's twelve. Irwin died in '91, dropping it to 11. Shepard and Conrad died in '98 and '99 respectively, making it 9 as of the date this comic was published. Armstrong died in '12, so our current number is 8. The oldest living person to have landed on the moon is Aldrin, 83. There are two 82-year-olds, two 80s, one 78 and two 77s. Ekedolphin (talk) 13:28, 27 January 2013 (UTC)
Almost prophetic and very, very sad. RIP Neil Armstrong ------
Can we add the 5% and 95% columns to the table? Spongebog (talk)
- i dont feel like this would add to the explanation of the comic and would require us to know a great deal about the author's calculations. rather than attempt to redo the actuarial calculations performed to make the chart and assign this to the individuals in the table we should rather explain the concepts behind the 5% and 95% and preserve the intention of actuarial information as applying to demographic groups. 5% of people in the demographic the author selected live to _ age 95% of those people live to _ age and how this affects our subject population. Mrarch (talk) 21:43, 6 December 2013 (UTC)
Why is this explanation incomplete? The second paragraph does a good job explaining what the 5th percentile and 95th percentile are referring to. String userName = new String(); (talk) 23:35, 19 June 2015 (UTC)
I prefer to think of the inhabitable planets as extensions to earth reserved for when we have learned not to kill all the inhabitants of the only inhabited planet in the universe.
I used Google News BEFORE it was clickbait (talk) 22:39, 23 January 2015 (UTC)
I see no reason this is marked as incomplete; I've tidied up the percentile explanations, but haven't really added much more. I think it's fine, and will remove the incomplete tag in a few days if nobody objects. Cosmogoblin
) 13:53, 24 June 2015 (UTC)