# Difference between revisions of "Talk:2034: Equations"

Is the joke that all of the equations are actually wrong/malformed/meaningless but they sort of look like typical equations for that field? 172.68.133.66 (talk) (please sign your comments with ~~~~)

Sort of. A bit of dimensional analysis would have helped. ;-) --162.158.91.221 07:28, 17 August 2018 (UTC)

Should we add a column with examples of similar correct equations from the respective fields? Sebastian --172.68.110.4 09:33, 17 August 2018 (UTC)

That would definitely tidy up my attempts to provide context for Randall's versions. The challenge then is working in explanations for the correct equations as well as arguing over which examples should be used. Exxi (talk) 09:45, 17 August 2018 (UTC)

I don't think the part in parentheses about OH in the Chemistry equation explanation is correct. OH- would mean that it's negatively charged and has nothing to do with unpaired electrons of Oxygen. It would add another horror to the equation, though, as it wouldn't be charge preserving anymore. 162.158.88.230 09:58, 17 August 2018 (UTC)

"Redshit". Best typo ever. Please keep it. 172.69.54.177 10:13, 17 August 2018 (UTC)

Deep physics equations

The transcript is wrong here, the last letter is not a $\mu$, but a "u" with a cedilla: u̧. The math parser refuses to render it, though. 162.158.88.230 05:54, 17 August 2018 (UTC)

Looks like it. But I don't think that letter exists even. --162.158.91.221 07:28, 17 August 2018 (UTC)
Is this equation a sort of nod to a Theory Of Everything which unifies quantum mechanics and gravity... H-hat (a Hamiltonian, which in quantum mechanics describes the total energy of a system, and usually runs in to problems describing large systems - such as the entire universe - where gravity or spacetime curvature effects matter) *minus* u0 (the relativistic mass of the whole system at time zero ie. the big bang) gives 0 (no energy everywhere always). Since mass is energy (e=mc^2) and mass is also the sole cause of gravity the two theories cleanly collapse together when mass is zero, and figuring out how to extend the theory to other less clean points on the mass axis is obviously a job for less profound physics? I've no ideas to explain the cedilla. 141.101.98.28 08:49, 17 August 2018 (UTC)
It looks to me a little like a parody of the Wheeler-DeWitt equation which (in theory) describes a wavefunction for the entire Universe. Exxi (talk) 09:06, 17 August 2018 (UTC)一
I'm just thrilled someone found the right character for it. I spent 20 minutes looking for the right u symbol without any luck at all. 172.68.143.132 (talk) (please sign your comments with ~~~~)

Is this poking fun at equation-filled blackboards in movies and cartoons? 172.68.254.42 (talk) (please sign your comments with ~~~~)

Doesn't seem like it. These equations actually do look like the kinds of equations you would see in these fields. On blackboards in movies you tend to get equations that are pure nonsense. 172.68.143.132 (talk) (please sign your comments with ~~~~)

I think this may also be a reference to Feynman's unworldliness equation, http://www.feynmanlectures.caltech.edu/II_25.html#Ch25-S6 . 108.162.219.220 17:02, 17 August 2018 (UTC)

Table layout at the explanation

That oversized table is really bad layout. We've had this discussion many times before - tables should only be used for small contents. Right now I would run into too many edit conflicts but I'll change it to a proper floating text with small headers for each section. --Dgbrt (talk) 11:51, 17 August 2018 (UTC)

Done, looks much more like a real paper... --Dgbrt (talk) 12:58, 17 August 2018 (UTC)
All number theory equation

The explanation for math doesn't seem entirely correct. You can in fact extend the ring of integers (as well as rational and real numbers) with positive and negative infinity, but it won't be a ring anymore. Specifically, the infinities don't have an additive or multiplicative inverse (but 1/infinity = 0); and addition of positive and negative infinity, as well as the product of 0 and either infinity is undefined. However, these properties are not used in the above equation. What we can use is that $\forall n < \infty: n - \infty= -\infty$. We would thus have $K_n = \sum_{i=0}^{\infty}\sum_{\pi=0}^{\infty}(n-\pi)(i-e^{\pi-\infty}) = \sum_{i=0}^{\infty}\sum_{\pi=0}^{\infty}(n-\pi)(i-0) = \sum_{i=0}^{\infty}\sum_{\pi=0}^{\infty}(n-\pi)i= \sum_{i=0}^{\infty}i\sum_{\pi=n}^{\infty}-\pi= \sum_{i=0}^{\infty}i\cdot(-\infty)=-\infty$. Also, how often does one use e and pi in number theory? --Ycthiognass (talk) 12:11, 17 August 2018 (UTC)

Pi (or any other number) minus infinite is just absurd. You can use the infinite symbol only as a limit but NOT as number in calculations. --Dgbrt (talk) 12:33, 17 August 2018 (UTC)
It is not absurd. Adding the rules $n+\infty=\infty\text{ for }n>-\infty,n-\infty=-\infty\text{ for }n<\infty, \pm n\cdot\infty = \pm\infty\text{ for }n>0, \pm n\cdot(-\infty) = \mp\infty\text{ for }n>0,\frac1{\pm\infty}=0$ gives you a consistent theory that is especially useful when talking about infinite sums and integrals. Would you say the term $n-\sum_{i=1}^\infty i$ is absurd? --Ycthiognass (talk) 14:35, 17 August 2018 (UTC)
Of course it's absurd. It is $\infty-\infty \neq 0$ because it could be everything between $\infty$ and $-\infty$. Infinity is a concept describing something without any bound... And, as you can't divide by zero you can't do the same for infinity. --Dgbrt (talk) 17:24, 17 August 2018 (UTC)
One more: It is
$\sum_{i=1}^\infty a_i = \lim_{n\to\infty} \sum_{i=1}^n a_i.$
When this limit exists, one says that the series is convergent or summable. Otherwise it's called divergent and has no solution like this one:
$\sum_{i=1}^\infty i$
Infinite is NO number! --Dgbrt (talk) 17:33, 17 August 2018 (UTC)

Completely separate from the above, it's probably worth noting that i is also a constant, and as such has the same misconception as $\pi$. Computer scientists are happy using i for loops/summations, but mathematicians prefer using n. Based off that, it's probably another misconception/joke that n is treated as a constant, while known-constants are used as variables. 108.162.246.149 17:28, 17 August 2018 (UTC)

There is nothing non-standard about using i as an index variable. Often as part of the series i,j,k.

Searching for summation convention will give plenty of examples.

There are fewer letters than mathematical concepts in need of letters, so most letters are used for multiple purposes. Occasionally this causes difficulty. You can be halfway through a linear algebra problem before you discover you need i for an imaginary number despite already using it as an index. Hilarity ensues. 162.158.74.105 19:57, 17 August 2018 (UTC)

Chemistry equation

OH should have a charge symbol: OH-. The actual reaction would be:

CH4 + OH- + heat -> CH3- + H2O

The methyl group can dissolve in water, and this is presumably happening in water, so this equation can work, just not the one provided by Randell. Reacting longer alkanes with bases is a way to make soaps, but the methyl group would be too reactive to be used this way. Nutster (talk) 13:13, 17 August 2018 (UTC)

Fluid Dynamics equation

I believe the fraction 8/23 in the Fluid Dynamics equation is a Randallesque reference to the fractional approximation of pi = 22/7. It's probably not a coincidence that you get 8/23 from 22/7 if you invert it and add 1 to both the numerator and denominator. Ianrbibtitlht (talk) 15:19, 17 August 2018 (UTC)

Gauge theory equation

I think the transcript is missing a left superscript 0 before the turned xi. 172.68.226.16 16:50, 17 August 2018 (UTC) Ah no, sorry. False alarm. It's just that Randall writes the xi with a funny tail. The same tail is on the non-turned xi earlier. 172.68.226.10 16:52, 17 August 2018 (UTC)

If explainxkcd.com is to make XKCD comics more understandable then this explanation is failing that. I assumed from the beginning that the joke was about the equations being wrong, but the description of the joke is making my head hurt.

All truly deep physics equations
In the description paragraph, the last sentence starting "The principle of least action says allows..." does not scan. If someone can fix this (copy&paste?) error, please delete this comment. 162.158.58.171 19:33, 17 August 2018 (UTC)


Note that this comics also emphasizes that Randall is more familiar with physics than with chemistry : while most of the equations here require college-level education to grok, the chemistry one is at the very most high-scool-grade.20:14, 17 August 2018 (UTC) -unsigned

“Nobody knows if Randall references a horse here” - what?! Because the expression lacks an equal sign; doesn’t represent an equality, it might mean Randall is referencing equines, aka horses?! Is this vandalism, an attempt at a joke, or what? This explanation clearly still needs quite a bit of work! PotatoGod (talk) 20:14, 17 August 2018 (UTC)