Explain xkcd: It's 'cause you're dumb.
Title text: Anyway, that's a common misconception. Geese live for a long time; all the ones we can see will probably keep flying around for billions of years before they explode.
Megan is commenting on a flock of geese passing overhead and says the light from the geese reaching their eyes now could have come from hundreds of years ago. This is a fact for the light from stars. Cueball points out the absurdity of Megan's statement by pointing out that the geese are only a few hundred yards away rather than a few hundred light years. She continues along the same lines when she implies to Cueball that he is observing a past version of her, despite them being only a few feet apart. (Technically he is viewing a past version of her, but not one from "long ago"; if someone is two feet away from you, you are seeing them as they were roughly 2 nanoseconds ago.)
In the title-text Megan continues to treat the geese as if they were stars, which "live" for a few billion years before exploding. Most stars visible with naked eye are within a thousand light-years of Earth, (as discussed in 1342: Ancient Stars), and it's unlikely that any star Megan currently sees actually exploded within the relatively short span of last few thousand years.
Megan's statement "You're hearing how they once sounded." is somewhat more justified -- sound from "a few hundred yards away" would take about one second to be heard (depending on the exact distance and the prevailing atmospheric conditions (which affect the speed of sound)). That said, the sound of a goose isn't likely to change enough over the course of a second or two to make this distinction particularly significant.
The strip may also take inspiration from Gamow's "Mr Tompkins" stories which were designed to help laymen understand some of the consequences of relativity and quantum mechanics. In one of the stories Mr Tompkins visits a town where the speed of light is 30 miles per hour. For the light to have taken hundreds of years to go from the geese to Megan and Cueball, the speed of light in this strip would have to be much slower than in Gamow's story.
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- [Geese fly in V-formation. Megan and Cueball are lying on the ground, watching them.]
- Megan: To think... we're seeing light that left those geese centuries ago.
- Megan: By now, they could be long dead.
- Cueball: ... What? They're a few hundred yards away. I hear them honking.
- Megan: Ah, yes. You're hearing how they once sounded.
- Cueball: You're very weird.
- Megan: Or I was, long ago...
The mere idea of geese spontaneously exploding mid-flight makes me giggle like a madman. 18.104.22.168 12:03, 29 October 2014 (UTC)
- 22.214.171.124, you're twisted. ... and now i can't stop thinking about it... and giggling. Iggynelix (talk) 16:27, 29 October 2014 (UTC)
- Wasn't it a goose going supernova that caused the Tunguska event? 126.96.36.199 16:40, 29 October 2014 (UTC)
Time Dilation? 188.8.131.52 09:16, 29 October 2014 (UTC)
The explanation should point out that the comic is referring to the common misconception that there is a high chance that a visible star is already dead. The facts are explained but the context is missing. This misconception was also mentioned in a what-if, but I cant find it right now.
The Milky Way is 120kly in diameter and most visible stars are much closer. With a lifetime of at least a couple millions of years the probability for a random star being dead is way below 1%. Given that there are 5000 stars visible to the naked eye (under best viewing conditions), this means that statistically there are maybe 5 stars in the entire night sky that are dead already. --184.108.40.206 09:10, 29 October 2014 (UTC)
- "With a lifetime of at least a couple millions of years" True only for the most massive stars. The average star in the Milky Way is around half a solar mass and will last around 50 billion years. So the probability of one of the 5000 stars visible to the naked eye having died in the last 1000 years is even smaller than "way below 1%". 220.127.116.11 16:45, 29 October 2014 (UTC)
- I first read the above as "... stars naked to the visible eye ...". --RenniePet (talk) 23:32, 29 October 2014 (UTC)
- Although you are overstating things a bit, because more massive stars are more likely to be naked eye visible. According to Wikipedia today, no M-class stars are naked eye visible at all. 18.104.22.168 18:00, 29 October 2014 (UTC)
- Almost all stars have a lifetime of at least a couple milions of years. However, some stars have lifetimes that extend on for billions of years after those few million. Mulan15262 (talk) 23:08, 29 October 2014 (UTC) Mulan15262
I think this relates to a previous XKCD 1342: Ancient Stars (http://xkcd.com/1342/) where he makes the same joke of how stars may not necessarily be that far away. 22.214.171.124 17:22, 29 October 2014 (UTC)
No! The moving V of the geese is reminiscent of a light cone! I think that's what triggered Megan's absurdist fantasy. And indeed, we're seeing the geese as they were in the past. By about a microsecond. If enough readers agree I think this belongs in the explanation. ExternalMonolog (talk) 20:49, 29 October 2014 (UTC)
- The light cone thing is important I think. I read the whole discussion in the comic as a play on the concept of abosolute time vs relativity. And I found it hilarious with that interpretation. --126.96.36.199 21:38, 29 October 2014 (UTC)
But Goose *is* dead. You fly jets long enough, something like this happens. DivePeak (talk) 21:07, 29 October 2014 (UTC)
There is an obscure linkage between wild geese and stars: http://www.connectingthreads.com/tutorials/Stars-Flying_Geese_Variable_Stars__D12.html 188.8.131.52 (talk) (please sign your comments with ~~~~)
I think this comic is extremely simple at heart and it is an example of a comedic style called transference. This style was first widely popularized by the 1950s BBC radio broadcasts of The Goon Show and it was immediately adopted by Beyond The Fringe, Monty Python's Flying Circus, and The Firesign Theater, and countless others. In this style one takes two different seemingly unrelated systems or regimes of action or behavior, finds a superficial resemblance, and then transfers the behavior of one regime into that of the other no matter how absurd the result. Megan sees a flock of geese flying by and the moving V shape sparks in her mind the idea of a light cone. The idea of a light cone sparks the ideas of space and astrophysics. This is the superficial resemblance. She then transfers the knowledge she has of astrophysics to the behavior of the formation of geese flying above and draws the most extreme and absurd conclusions she can imagine. As one can see, this style is hallmarked by an extreme dedication to an unsupportable premise and is best played as absolutely deadpan and utterly serious and is driven by a tight focus on details. Megan displays this unreasonable dedication to a preposterous premise through to the last line. I think this comic is nothing more than that. No time dilation no relativity required. Just the knowledge of both behaviors and the superficial resemblance! (By the way, I've been a big fan of The Goon Show since they first were broadcast in the US during the 60s. Wikipedia has a page on them and there is web site playing everyt remaining recording of theirs that is known to exist. It's here http://goons.fabcat.org/
and I highly recommend it!) ExternalMonolog
) 10:02, 30 October 2014 (UTC)