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03:00 - 18:0018:00 - 23:00

18:06
@Jim ok I have a project for you guys
figure out how explosive nital is
Necroing a 1995 thread
1
Q: Would it be theortically possible to use wormholes to travel short distances? i.e. UK to America

A.RaeThis being if Wormholes are possibly (which I know they're currently not possible). As wormholes as usually described to travel long distances across the galaxy or multiple galaxy's. Could wormholes be used to only travel around the Earth?

I like how specific this question is
Jim
Jim
@0celo7 Obituary: The university of Toronto: Mississauga physics club was killed in a massive explosion today because someone on the internet (who shall remain nameless) suggested they take on a stupidly dangerous physics experiment
18:21
You know I wonder how easy it would be to destroy the universe in a physics experiment
@0celo7 if you add more than 10 % HNO3 to methanol, you can get a runaway exothermic reaction
Like what energy levels are required to make vacuum collapse likely
Jim
Jim
@Slereah do you want a number?
I want the machine
Let's destroy the universe
Jim
Jim
then what?
18:23
Also how certain is the theory of vacuum collapse
What do you mean "then what"
What part of "destruction of the universe" do you not get
It's the kind of thing where you don't have to worry about "then"
Jim
Jim
@Slereah not with that attitude
Do we have any non-perturbative proof that the current vacuum isn't the actual vacuum
Jim
Jim
proof? No. The whole thing exists only in theory from the get go
What's a good heuristic argument for it
Jim
Jim
I have no idea. Is there something about the pure mathematics of the theory that you dislike?
18:30
I do not know the pure math of it, either
Jim
Jim
as in the math is above you? or just that you haven't taken the time to go through the math?
I have not looked too much into it
@Loong My prof was convinced a 2:1 ratio is ideal!
He's trying to kill me :<
The math is probably pretty awful, tho
@0celo7 According to the ASTM standard, nital is 1–5 ml HNO3 in 100 ml ethanol or methanol.
18:33
Ok good thing I didn't raid the chemical closet and make this :P
Jim
Jim
well, the explanation is basically just math, so I doubt you'll find another way to learn it
@Loong wtf!
What molarity are you talking about here
concentrated HNO3 is about 15 mol/l
@Loong what if I slowly pour in the acid
Like making mayonnaise
18:40
that would only delay the reaction
you could cool the flask in an ice bath; however, the resulting mixture wouldn't be stable
@Loong He said I should be doing the etching at around 0 degrees
As this is America, I don't know in which unit system that is.
@0celo7 sounds like 0 °C, i.e. ice/water bath
Jim
Jim
@0celo7 seeing as it's science, it won't be Fahrenheit
@Jim this is an old ass engineer, could be Rankine for all I know.
19:08
Hey, any recommendations on whether to take a graduate level algebra class or graduate level complex analysis class?
I'm leaning towards complex...
@NeuroFuzzy Although I like algebra, complex analysis will most likely be more useful to you.
I think complex + algebraic geometry (studying the prereqs [atiyah and mcdonald] this summer) + diff geo would be a nice triple of courses.
@ACuriousMind but, what I'm worried about: useful as in "can do contour integrals more quickly"?
@NeuroFuzzy If you want to learn how to compute things or do them "quickly", math courses will usually not be useful for that.
Oh, of course not, I don't want to take a class like that.
I meant "useful" as in - physicists are more likely to use complex analysis than algebra
@NeuroFuzzy If you're taking algebraic geometry then shouldn't you already know what is done in algebra?
Or are we talking about very classical alg. geo. here where not so much modern algebra is needed?
19:17
@ACuriousMind I've taken 2/3 of the undergraduate algebra sequence, and am trying to study through atiyah & mcdonald's commutative algebra over the summer.
Which I've heard should be okay.
What does the alg. geo course do? Follow Hartshorne?
I think "roughly the first chapter of hartshorne" was mentioned, yeah.
Yeah. From a previous year: "Some knowledge of modern algebra at the level of Math 200 is required. However, I will not assume background in commutative algebra. Familiarity with complex analysis, basic point set topology, differentiable manifolds is helpful, but not required. " math.ucsd.edu/~doprea/math203.pdf
I am really tempted to crash course it :)
Basically my next year is my last year and I get to spend the whole year doing (almost) nothing but mathematics.
Jim
Jim
isn't this question a chemistry thing, not really physics?
53
Q: Why does wet hair keep its shape when it dries?

Petr PudlákWhen I wash my hair and go to sleep, my hair is impossible to comb in the morning, stubbornly sticking to the shape it assumed during the night. The only way to get it right is to wet it again and comb it. What's the cause of this memory effect?

even the accepted answer gives a chemistry answer
how did this not get migrated?
19:34
@Jim By no one caring enough to cast a close vote on it? Like, right now, I'm out of votes and I'll certainly not remember to come back tomorrow and cast one.
Jim
Jim
I flagged it for migration to chemistry
that'll give them some more popular posts too. I feel like they need those more than we do
20:21
@acuriousmind I think I'm missing a point in this text. How does one use an isomorphism mapped between two groups to list subgroups of one group?
$Z_{48} = \langle x \rangle$ and $\mathbb{Z}/48\mathbb{Z}$ is isomorphic by $\bar{1} \to x$
okay screw it i'm just gonna write out all subgroups of $Z_{48}$ as I did $\mathbb{Z}/48\mathbb{Z}$
@Obliv I'm not sure what you mean
@ACuriousMind I don't really get it either.. If an isomorphism exists between groups how would that help list out subgroups?
@Obliv Assuming that with $Z_{48}$ you mean the cyclic group of order 48, these are indeed isomorphic - and therefore not really different. In particular, isomorphisms send subgroups to subgroups.
ohh
that doesn't really help list out the subgroups though.. One generates a set of equivalence classes and the other generates a bunch of powers of $x$. dangit
not writing this out
@Obliv ???
You use Lagrange's theorem to "list" the subgroups - it's just finding the divisors of 48.
20:35
$\bar{1} = \mathbb{Z}/48\mathbb{Z}$ whereas $\langle x \rangle = Z_{48}$ which are different sets ,no?
oh
what I'm saying is I'm not just supposed to list generators, I'm supposed to write out the entire sets
As you say, there's an isomorphism given by $\bar 1 \mapsto x$.
So the subgroup generated by $\bar n$ maps to that generated by $x^n$.
Why on earth would you write out the "entire sets"?
actually you're right. listing subgroups doesn't sound like it wants me to list the sets..
21:01
:( How can I choose $a$ for $\bar{1} \to x^a$ to be a well defined homomorphism between $\mathbb{Z}/48\mathbb{Z}$ and $Z_{36}$
I'm trying to use the definition $\varphi(a\star b) = \varphi(a) * \varphi(b)$ but I don't get what $a,b$ are supposed to be lol. Can they be any $\bar{a} \in \mathbb{Z}/48\mathbb{Z}$
@Obliv Hint: For the morphism to be well-defined, you need that $1 = \phi(\bar 1) = \phi(\bar 1^{48}) = \phi(\bar 1)^{48}$, so you need $x^{48a} = 1$.
21:22
well that narrows it down to multiples of 48..
21:51
@ACuriousMind Turns out my advisor is fluent in German
I'm in shock
@0celo7 Why does that shock you?
@ACuriousMind He's Brazilian
And I've mentioned before that I speak German and he didn't react
This time he just switched to German
22:21
@ACuriousMind I thought you guys loved crap :)
(I honestly think it's not that bad of a question)
One could wonder about changing the scale where quantum effects become relevant, and when it starts to matter
22:46
@Danu Lee is so good
I think I've convinced my adviser to pick up a copy ;)
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