1856: "Existence Proof"
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Re: 1856: "Existence Proof"
Raidri wrote:PS: That last quote definitely needs an exclamation mark instead of a period: "I'm finally in the right one!"
I couldn't agree more.
Re: 1856: "Existence Proof"
Is she suffering from existential angst?
xtifr wrote:... and orthogon merely sounds undecided.
Re: 1856: "Existence Proof"
Of course, in that dream everyone always has, I didn't read the syllabus and now I have to go home and get my sword, and by the time I get back, the whole class will be gone.
P.S. I like the period better than the exclamation point.
P.S. I like the period better than the exclamation point.
Re: 1856: "Existence Proof"
I want to be in this math class.
Re: 1856: "Existence Proof"
Is that the same sword used when she was on the thesis defense committee?
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"The Planck length is 3.81779e33 picas."  keithl
" Earth weighs almost exactly π milliJupiters"  whatif #146, note 7
Re: 1856: "Existence Proof"
Raidri wrote:Looks more like complex analysis to me. And I'm not sure which part is real and which is imaginary ...
Find its conjugate, bring them together and the real part comes out twice. It's a happy little family.
Or find Euler's constant (probably buried with him) and raise it to an x. Once it's grown up, its size will be proportional to x's real part and it will be oriented at x's imaginary part. That only really works if x isn't too imaginary, though.
Does an x with x^2=1 really exist?
Re: 1856: "Existence Proof"
orthogon wrote:Is she suffering from existential angst?
Looks to me like she is successfully dealing with it.
And thus is born the category of destructive proofs.
ETA:
Flumble wrote:Does an x with x^2=1 really exist?
That, of course, depends on how you define "really exist"...
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Re: 1856: "Existence Proof"
Flumble wrote:Does an x with x^2=1 really exist?
Does "2" really exist?
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"The Planck length is 3.81779e33 picas."  keithl
" Earth weighs almost exactly π milliJupiters"  whatif #146, note 7
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"The Planck length is 3.81779e33 picas."  keithl
" Earth weighs almost exactly π milliJupiters"  whatif #146, note 7
Re: 1856: "Existence Proof"
cellocgw wrote:Does "2" really exist?
Of course it does, and 2+2=5... for sufficiently large values of 2.
Re: 1856: "Existence Proof"
Kim Kardashian possesses sufficiently large values of 2, as does Jenny McCarthy, et all.

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Re: 1856: "Existence Proof"
That number's name is bleem. You will not find it so easy to defeat, I am afraid. It has learned to hide itself from those who would do it harm, and fight back against those who persist in hunting it.
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Re: 1856: "Existence Proof"
orthogon wrote:Is she suffering from existential angst?
You'd expect that to be an occupational hazard of mathematicians. After all, their work deals mostly with things that have no actual physical existence, in this universe or any other.
OTOH, there are a number of common jokes among mathematicians about a colleague who thinks his entire life work has been destroyed by a scientists or (even worse) an engineer that just announced a practical application for his theorems.
I've seen claims that George Boole had a bit of a reaction like this when his "purely theoretical" system like the real numbers except for having two operators that each distribute over the other was found to have actual applications. Dunno if it's true, though, or someone was just having a bit of fun with the idea.
 JohnTheWysard
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Re: 1856: "Existence Proof"
Shouldn't that be
"Grab your surds, students; we ride!"
"Grab your surds, students; we ride!"
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Re: 1856: "Existence Proof"
I like that "I think I'm in the wrong class" wasn't the last line in the comic. Once upon a time it might have been, but Randall knows his audience very well at this point, and knows that there would inevitably be someone like us in that class.
cephalopod9 wrote:Only on Xkcd can you start a topic involving Hitler and people spend the better part of half a dozen pages arguing about the quality of Operating Systems.
Baige.
Re: 1856: "Existence Proof"
JohnTheWysard wrote:Shouldn't that be
"Grab your surds, students; we ride!"
Yes!
Re: 1856: "Existence Proof"
She should be careful. There exists f such that there are infinitely many values of x that meet that condition. We wouldn’t want to ride out against those, now would we?
Re: 1856: "Existence Proof"
Calculators, mount up!
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Re: 1856: "Existence Proof"
...why does my number line have a hole between 1 and 3? Why is there no integer between them, but two integers' worth of noninteger numbers?
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mittfh wrote:I wish this post was very quotable...
Re: 1856: "Existence Proof"
chridd wrote:...why does my number line have a hole between 1 and 3? Why is there no integer between them, but two integers' worth of noninteger numbers?
What do you mean? I count R nonintegers between 1 and 3, just like between any two consecutive integers.
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Re: 1856: "Existence Proof"
Really? I count 2ℝ integers in that interval. And why is there both 1½ and 1 3/2 (which is different from 3½)? Why is the number of fractions with any particular denominator on the interval [1,3) about twice what it is on intervals [0,1), [3,4), [4,5), etc.?
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mittfh wrote:I wish this post was very quotable...
Re: 1856: "Existence Proof"
2R = R (that's the joke)
The rest of those are good questions, though.
The rest of those are good questions, though.
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Re: 1856: "Existence Proof"
svenman wrote:Flumble wrote:Does an x with x^2=1 really exist?
That, of course, depends on how you define "really exist"...
I once had to take an incomplete in a philosophy class. I made a mistake in a homework assignment and accidentally proved my professor didn't exist.
Re: 1856: "Existence Proof"
da Doctah wrote:I once had to take an incomplete in a philosophy class. I made a mistake in a homework assignment and accidentally proved my professor didn't exist.
That sounds like another thing that could have been fixed by judicious application of a sword.
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Re: 1856: "Existence Proof"
da Doctah wrote:I once had to take an incomplete in a philosophy class. I made a mistake in a homework assignment and accidentally proved my professor didn't exist.
As long as the proof is consistent, everything is all right.
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Re: 1856: "Existence Proof"
Flumble wrote:Does an x with x^2=1 really exist?
Yeah, but it's not unique.
Re: 1856: "Existence Proof"
Xenomortis wrote:Flumble wrote:Does an x with x^2=1 really exist?
Yeah, but it's not unique.
Breaking News: mathematicians have just discovered that the number they thought was i may in fact have been i's evil twin, −i, all along. The two are not identical, although at the time of writing, nobody can tell which is which.
A spokesperson for the IEEE was relaxed about the possible case of mistaken identity. "We've been using j anyway," they said, "so we can simply define j=−i if the flatfooted mathematicians decide they'd had the wrong guy all this time."
xtifr wrote:... and orthogon merely sounds undecided.
Re: 1856: "Existence Proof"
Xenomortis wrote:Flumble wrote:Does an x with x^2=1 really exist?
Yeah, but it's not unique.
What do we have? i, i, j, j, k, and k ?
Or x could be 1 in the field of integers modulo 2.
orthogon wrote:Breaking News: mathematicians have just discovered that the number they thought was i may in fact have been i's evil twin, −i, all along. The two are not identical, although at the time of writing, nobody can tell which is which.
A spokesperson for the IEEE was relaxed about the possible case of mistaken identity. "We've been using j anyway," they said, "so we can simply define j=−i if the flatfooted mathematicians decide they'd had the wrong guy all this time."
But that would set ij = 1, while we know ij = k.

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Re: 1856: "Existence Proof"
She should have been wielding the Axe of Choice.
Re: 1856: "Existence Proof"
DavidSh wrote:Xenomortis wrote:Flumble wrote:Does an x with x^2=1 really exist?
Yeah, but it's not unique.
What do we have? i, i, j, j, k, and k ?
We can do better than that.
orthogon wrote:mathematicians have just discovered that the number they thought was i may in fact have been i's evil twin, −i, all along.
Oh no! Not emdash i!
Re: 1856: "Existence Proof"
Flumble wrote:orthogon wrote:mathematicians have just discovered that the number they thought was i may in fact have been i's evil twin, −i, all along.
Oh no! Not emdash i!
Anticipating such a comment, I deliberately copied and pasted it from the Wikipedia page for "Plus and minus signs".
xtifr wrote:... and orthogon merely sounds undecided.
Re: 1856: "Existence Proof"
orthogon wrote:Flumble wrote:orthogon wrote:mathematicians have just discovered that the number they thought was i may in fact have been i's evil twin, −i, all along.
Oh no! Not emdash i!
Anticipating such a comment, I deliberately copied and pasted it from the Wikipedia page for "Plus and minus signs".
I shouldn't have assumed a long horizontal line is an em or endash in this context.
Today I learned there are quite a few of them ﹣᠆‐–‑−‒﹘—―─
Re: 1856: "Existence Proof"
So math me up... She's saying that there should be a number x that simultaneously equals 0 and 1 when the gravitational constant and this mystery function are involved?
Re: 1856: "Existence Proof"
Darkhand wrote:So math me up... She's saying that there should be a number x that simultaneously equals 0 and 1 when the gravitational constant and this mystery function are involved?
Really they're two separate equations: f(x)=1 and G(f(0))=1. However, only the former says anything about x. The latter isn't itself a condition that can be satisfied or not depending on the value of x. It's presumably simply being asserted as true, perhaps as a result of the earlier parts of the derivation, or by definition, in the manner that one might say "f(x)=√81=9".
Using capital letters to denote functions isn't unusual, but there's normally something different about them: e.g. in Fourier analysis, capital letters are used for frequencydomain functions and lower case for time domain.
xtifr wrote:... and orthogon merely sounds undecided.
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Re: 1856: "Existence Proof"
The way I have read it, "eff of x and Gee of <whatever the eff of zero is> both equals one". In and of itself, this is an openended equation that is easily satisfied by any f() or G() functions you might wish^{1}. We just don't know how we got to this point in the lesson, with prior equations... And it looks like some of the students absolutely weren't too sure where it was going, either...
(Different fields of mathematics/sciences have different reasons to use capitalised functionletters, another unknown. But <constant G> times a function something would normally be G.f(x), give or take order preferences and maybe other fieldspecific uses of the dotmultiplier that might encourage or discourage another mark or perhaps allow none.)
More esoteric mathematical fields may understand it totally differently, though. People do all kinds of strange things to represent the odder algebras.
^{1} Try G(x)=x or G(x)=x² (amongst many others, including plain …=1), and any of various f()s and x values that happen to make f(x)=f(0)=1, regardless of what else it does (such as f(x)=1x itself for the ultraspecial case x=0).
(Different fields of mathematics/sciences have different reasons to use capitalised functionletters, another unknown. But <constant G> times a function something would normally be G.f(x), give or take order preferences and maybe other fieldspecific uses of the dotmultiplier that might encourage or discourage another mark or perhaps allow none.)
More esoteric mathematical fields may understand it totally differently, though. People do all kinds of strange things to represent the odder algebras.
^{1} Try G(x)=x or G(x)=x² (amongst many others, including plain …=1), and any of various f()s and x values that happen to make f(x)=f(0)=1, regardless of what else it does (such as f(x)=1x itself for the ultraspecial case x=0).
Re: 1856: "Existence Proof"
Soupspoon wrote:The way I have read it, "eff of x and Gee of <whatever the eff of zero is> both equals one". In and of itself, this is an openended equation that is easily satisfied by any f() or G() functions you might wish^{1}. We just don't know how we got to this point in the lesson, with prior equations... And it looks like some of the students absolutely weren't too sure where it was going, either...
Me too; when I said there were two equations, I meant that both were simultaneously true. However, the claim is that there exists some x that satisfies them both, and since G(f(0)) is not a function of x, G(f(0))=1 must simply be gnomically true.
Mathematical notation is highly ambiguous, and heavily dependent on some very arbitrary conventions. A lowercase letter followed by something in parentheses would normally be a function, e.g. f(x+1), but if you see a lowercase x or y, it probably is multiplying the contents of the parentheses, e.g. x(y+1). So it depends on which letter is used, with f,g and h the goto letters for functions and x,y and z for variables. When these conventions are violated it can really mess with the reader's ability to follow the mathematics, in the way that prose written in an unfamiliar dialect might be hard to follow. My personal dislikes are using superscripts for indices as opposed to exponentiation (Einstein apparently came up with this for his tensor notation, but he, unlike me, was clever enough to handle it) and reversing the role of main symbol and subscript, e.g. A_{T} to mean "absolute time" instead of T_{A}. I can see the temptation for speakers of adjnoun languages, but it's just wrong.
Mathematical notation is quite an interesting phenomenon in linguistic terms, since it has elements of natural language about it.
xtifr wrote:... and orthogon merely sounds undecided.
 chridd
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Re: 1856: "Existence Proof"
I initially read that as "whatever the f*** zero is".Soupspoon wrote:"eff of x and Gee of <whatever the eff of zero is> both equals one"
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mittfh wrote:I wish this post was very quotable...
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Re: 1856: "Existence Proof"
chridd wrote:I initially read that as "whatever the f*** zero is".Soupspoon wrote:"eff of x and Gee of <whatever the eff of zero is> both equals one"
And so you might! Have you never tried dividing by it? There's something odd about nothing, for sure! (Except that it's definitely even... Gah!)
Re: 1856: "Existence Proof"
Soupspoon wrote:chridd wrote:I initially read that as "whatever the f*** zero is".Soupspoon wrote:"eff of x and Gee of <whatever the eff of zero is> both equals one"
And so you might! Have you never tried dividing by it? There's something odd about nothing, for sure! (Except that it's definitely even... Gah!)
And then there's one, which is definitely odd  how can it be a number with no multiplicity to it? And it's neither prime nor composite, more evidence of it not really being a number...
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