Okay, I get some of the jokes or references. Like Pi and Phi. I know .999[…] might spiral out into a sore spot here (and considering many say .999… is equal to 1, what is meant by his comment?). But, I’d like to see this one teased out into all its glory as those more learned, practiced and enlightened than I in math can (and should, dammit!) eek out the more subtle aspects.
I’ll sort of remain in the background as an observer on this one, if anyone would like to indulge me?
Well, math does prove that .999… = 1.
x = 0.999…
10x = 9.99…
10x - x = 9.99… - 0.999…
9x = 9
x=1
thus
1 = 0.999…
I got most of it, but the comment about “if you encounter a number higher than this, you’re not doing real math” went over my head.
I’m a math major, and I don’t find this funny at all, so you’re definitely not alone. The only two that I may be able to help you with are the “observed” bit, which makes fun of the tendency for governments to group multiple important dates into a single “observed” holiday, and the “real math” comment, which is entirely true. The work done by research mathematicians involves very few numbers, as there is very little computation involved. The numbers that are used just indicate things like what dimension a particular sphere lies in, and thus they are very small. The largest number I’ve ever heard used in an actual math discussion was 7.
What about 8 being the largest even prime? I thought 2 held that honor?
8 ÷ 4 = 2 
Well, 2.9299372 ≈ (π + e)/2, i.e. halfway in between them. While I understand the words, I don’t really get anything special about the rest of them.
+1.000…
flees
I have to guess at most of these.
The phi comment: you sometimes see people invoking the “Golden Ratio” whenever they want to make some sort of floofy New Age=y sort of point that involves numbers.
The 2.922… comment probably has to do something with people coming up with pretty bad estimates for pi and e?
Gird… I have no idea, though I imagine it is some sort of Orthodox Jewish thing?
4 through 7: when was the last time you saw some sort of constant or, really, anything interesting about this area? I thought this one was pretty funny.
7: this one should be self-explanatory, I think.
8: I don’t know what he’s trying to get at with this one. Obviously, as cmyk remarked, it’s not prime. I wonder if he’s trying to pull the old “engineering” joke where the engineer says, “2 is prime, 4 is prime…”
“If you encounter…” This was the only one I thought was laugh-out-loud funny. What Cryptic C62 said.
I thought the joke was in the mouse-over, which was a reference to the wiki “List of Numbers” having a tag saying “This list is incomplete; you can help by expanding it.” So he expanded it with fake numbers.
The joke there is that any list of numbers will of necessity be incomplete.
Yeh, GIRD, I have no idea. It’s at 3.5 on the line. Hrmm.
I’m still not clear on the “unexplored” 4–7 region. Care to explain the funny?
I thought the gag in that mouse-over was in that, of course the list of numbers is incomplete… as it’s infinite. No?
Never heard that joke. Do tell…
That particular joke is just making fun of the fact that numbers are infinite, so the list on Wikipedia will never be exhaustive.
I don’t see what’s not to get about the actual graph, though. It’s Troll Mathematics. I mean, negative “imitator” numbers? Site of battle of 4.108? Largest even prime? None of those have any basis in truth, he’s just making up vaguely plausible but non-existent “facts”.
I googled 8 as the largest prime, and the only reference is the XKCD forum thread. No real answer for that one, but they did give answers for the others, other than “imitator” numbers and the battle of 4.108.
Also, one person claims the entire thing is a reference to the screwed up Creationist timelines used to predict the end of the world.
ETA: Randal doesn’t tend to just make up crap. He tends to have some esoteric reason behind everything. That’s kinda the point of XKCD.
The way I’ve heard it is:
Proofs that all odd numbers are prime:
Physicist: 1 is prime[li], 3 is prime, 5 is prime, 7 is prime, 9 is experimental error, 11 is prime…[/li]
Mathematician: 1 is prime, 3 is prime, 5 is prime. Therefore all numbers by extension are prime.
Engineer: 1 is prime, 3 is prime, 5 is prime, 7 is prime, 9 is prime, 11 is prime…
[*] yes, I know that 1 is a special case and not really prime.
Tends to, not always. Troll science is funny enough on its own.
As I said, the largest number I’ve heard used in a real discussion of mathematics was 7. The key words are “heard”, meaning I actually listened to mathematicians speaking with their mouths, and “real”, meaning that it had some basis in legitimate mathematical research, not trivial nonsense or computer science problems.
I think the bottom line is that this particular XKCD strip just isn’t funny. You can’t win 'em all.
De gustibus. You don’t think it’s funny. I chuckled.
Thanks all. I just wanted to be sure I wasn’t missing anything, as I found some of it amusing, but didn’t know if the rest was reaching into esoteric realms or what.