The h Bar

download mathematica

user218912

I don't like programming.

user218912

and it's too expensive for me.

Bernard Meurer

@IceLord You'll have to learn it

user218912

12:01 AM

maybe when I'm a researcher.

your school gives you a subscription

Bernard Meurer

@IceLord It's your only way to defend Canada against Potatolypse. Think of that

I read that as prolapse.

user218912

@0celo7 I didn't know that.

user218912

what can mathematica do than wolfram alpha can't?

12:03 AM

Huh. Birds cannibalize prolapsed vaginas.

Good to know.

HDE 226868

@IceLord Check out some of the demos on Wolfram's website.

@IceLord it's free and faster

user218912

@0celo7 hmm

user218912

but idk how to use it

user218912

no time to learn right now

12:04 AM

@IceLord What do you need it for anyway? The point of the equations and integrals on your homework is not to have a program solve them for you

@0celo7 wtf. You can't google most things you want to know but you managed to find that?

@ACuriousMind Morbid curiosity got ahold of me.

Pigs do the same, btw.

user218912

@ACuriousMind prof said you will need mathematica to compute some integrals in qft. so I thought wolfram alpha could do the job too.

let's see the integrals

wonder if I can do them

@IceLord Well, if he says you need it, then it's reasonable for the school to provide it, no?

user218912

@ACuriousMind which it does apparently.

12:07 AM

@ACuriousMind I NEED this $300 E&M book that I had to buy and have not opened once.

user218912

@0celo7 we didn't get any yet.

user218912

the integral I asked about earlier was from a poisson distribution and I was being retarded.

user218912

it was a basic integral.

I had to do one of those on my QM homework

I gave up :/

I wrote "it is well known"

user218912

xD

12:09 AM

I could just cite my probability book probably

user218912

acm did it in his head in 1 second.

ACM is an AI

user218912

faster than wolfram alpha.

fine

I will edit my homework

let's see what the integral is

uhhh

I have no clue how to do this

I give up again

user218912

what is the integral?

12:15 AM

I'm not sure

hang on

@ACuriousMind I really like your singing on Empire State of Mind.

I think it's $$\int_0^\infty d\sigma\,\frac{\sigma^n e^{-\sigma}}{n!}$$

PhD level integral :(

user218912

wow

user218912

that's hardcore because of the exponent on the $\sigma$.

Yes

Looks like $n$-fold integration by parts should get you a solution there

@ACuriousMind Sure. But I don't remember how to integrate by parts.

user218912

12:18 AM

you know you're a mathematician when... you don't remember how to integrate by parts.

when you're doing math every day?

oh

no I think any good mathematician can do it

but I'm an engineer

@0celo7 And what hinders you to look it up?

user218912

@0celo7 even worse?

@ACuriousMind I hadn't thought about it.

...

user218912

12:19 AM

engineers are supposed to be able to do integrals like it's cake.

no

certainly not

ok how do integrate by parts

let's think

$$\int u'v=uv-\int uv'$$

user218912

tbh you can integrate by parts anything. right?

user218912

as long as there are parts

Sure, but it's not always gonna get you somewhere

Uh, I think there are some reasonable technical conditions (in $\Bbb R^n$)

Ok, let's do this integral.

wait

that's not it

user218912

12:23 AM

@ACuriousMind how did you figure out that integral was 1 so fast? it took me like 5 minutes to do it and I made a mistake so I had to redo it.

it might be $$\int_1^\infty \frac{\sigma^ne^{-\sigma}}{\Gamma(n+1)}dn$$

user218912

okay I have no idea whatsoever how to do that.

user218912

this is when wolfram alpha is your friend.

user218912

shows all the steps too

@IceLord The integrand is just $-\frac{\mathrm{d}}{\mathrm{d}t} \exp(-t/\tau)$, so one application of the fundamental theorem gives the result.

12:24 AM

yes, it's that second integral lol

@ACuriousMind halp

Ugh, that looks horrible

user218912

@ACuriousMind how would you do 0celo7's integral?

The second? No idea

well, I have a Poisson dist. $|f(n)|^2=\frac{e^{-\sigma}\sigma^n}{n!}$

Maybe it's a sum from $n=0$ to $\infty$

user218912

@ACuriousMind is it okay to use wolfram alpha in that case?

12:26 AM

Hmm

$n$ is an oscillator mode

I'm not the arbiter of when using WA is "okay"

user218912

what

...that's an exponential.

user218912

isn't that divergent af?

@ACuriousMind I know you saw it.

12:27 AM

Or not :D

I saw it as soon as I wrote it lol

its an exponential

wait, what is the mean of a PDF again

user218912

oh right

oh wait

if $f(n)$ is my PDF, then the mean is $\sum nf(n)$, right?

Sure

ok, so the mean is $\sigma$

Yes! Wiki agrees!

user218912

12:32 AM

wolfram alpha won't do that integral 0.o

user218912

it just stops loading after a while.

the human mind is superior to any machine @IceLord

user218912

I lost faith in wolfram.

(crap)

(Wiki uses a different definition and I made a mistake)

(why are you talking in brackets?)

user218912

12:34 AM

would mathematica be able to do it?

ah

I did not make a mistake

$n|_{n=0}=0$.

wunderbar

user218912

@0celo7 wow really?

no not really

that's wrong too :/

user218912

my condensed matter prof didn't teach us any of this ._.

user218912

the homework is like ph.d level but the lectures are high school level.

12:44 AM

I hate PhD level stuff

user218912

we're supposed to review a published paper from a journal in condensed matter theory and present it some day in november but we didn't learn a fucking thing.

user218912

and the class assumes 0 previous knowledge so idk how ppl are gonna do this.

DanielSank

1:24 AM

@0celo7 ?

user218912

3:06 AM

@NeuroFuzzy have you done a course with ashcroft and mermin as a book?

NeuroFuzzy

3:42 AM

@IceLord Nope! Never heard of it

you call yourself a physicist

NeuroFuzzy

@0celo7 Yes, I'm an expert on blocks sliding on ramps. Or at least theoretical models of them.

@NeuroFuzzy I doubt actual blocks follow the laws of physics

textbook laws of physics

4:05 AM

I did wonder if Crothers had changed his spots when he asked an apparently sane question. But no, it was just an excuse to tell us we're all stupid and GR is wrong. Oh well.

user116211

@JohnRennie Oh! It's Crothers. He is a pseudo-scientist, I think.

Crothers is a well known nutcase.

Delete that.

user116211

@0celo7 why?

I'm about to flag it.

user116211

4:09 AM

hmm.

There is no reason to insult the man.

@JohnRennie Should know better.

user218912

but it's behind his back.

@0celo7 that wasn't an insult, it was a statement of fact.

It's Not Nice and you know it.

user116211

@JohnRennie He might have come earlier also; this maybe his new but not the first account here.

4:12 AM

He's been in and out of the PSE. Every now and then he reappears to ask some loaded question. I just don't understand the mentality. I think it's basically a form of religious zealotry.

@JohnRennie So you stand by the comment? Are room owners immune from suspensions?

@MAFIA36790 !!!

user116211

What?

@0celo7 Yes. No.

@MAFIA36790 That's an insult.

Ah that's interesting. I get notified when my own comments are flagged but I can't counterflag them.

user116211

4:14 AM

@0celo7 Of course it is; but it is the fact.

@MAFIA36790 Then I have to flag...

user116211

hmm.

bwDraco

No personal attacks, please.

Hi bwDraco.

user116211

As a scientist, you must be prepared to face criticism - that's the truth.

4:16 AM

@MAFIA36790 Calling someone a douche is not criticism, it's an insult.

user218912

^

I must admit I would avoid terms like douche

user116211

@0celo7 He doesn't hear his own criticism; but well okay; I wouldn't use it further.

@JohnRennie I would avoid terms like nutcase.

user116211

@0celo7 ;/

4:17 AM

Everyone is entitled to their views

user218912

you can call him dumb because it's not an insult I think. xD

You're wrong.

user116211

New Discussion, please

user116211

Let's talk physics.

user218912

omg you're like JD

user116211

4:18 AM

@IceLord ;P

He's JD in disguise O.O

user116211

@0celo7 NOOOOO!!!

Quick, block him

user116211

stares angrily at 0celo

omg wtf JD has been among us this whole time

user116211

4:19 AM

T__T

user218912

I don't even block the real JD though, I find him really funny.

user218912

can be annoying at times with his evidence.

user116211

How should I prove I'm not JD....

user116211

I haven't read Einstein Digital Papers!!

lie

user116211

4:21 AM

._.

you're JD, and he worships them

user116211

@0celo7 I worship Bourbaki.

user218912

okay what is spin in qm?

user116211

@IceLord I don't know.

user218912

is the electron really spinning?

user116211

4:22 AM

@IceLord No idea.

user218912

JD would know.

@MAFIA36790 is Hawking a respectable physicist

@IceLord he could by lying

user116211

C'mon ask me from Classical Mech; Set Theory; Analysis; abstract Algebra; Order Theory.

Aha, I know.

user116211

@0celo7 I have not read any of his books; so it would not be good to share a view on him.

4:23 AM

Prove the fundamental lemma of Riemannian geometry

user116211

@0celo7 O.o

user218912

@0celo7 if you do a quick search you'll see he uses equations in his messages.

user218912

not JD confirmed.

user116211

@IceLord \o/

good point

@MAFIA36790 ok, you're in the clear -- for now

I'll be keeping my eye on you.

user116211

4:24 AM

I know Numerical Analysis too!!

user116211

@0celo7 \o/

user116211

@0celo7 ._.

user218912

I'm getting rekt by ashcroft and mermin problems.

that's an undergraduate level book.

user218912

no...

user218912

4:27 AM

it's hardcore graduate.

One of the headaches of learning a new math thing is how they like to pack a lot of things in one word, layer by layer
For example: A compact set is closed and bound
A closed set is one whoose complement is open
A bound set is one which is finite in size and has no infinite elments
A complement is any elements that is outside the set in question

user116211

@Secret Ah! You are learning topology!

user218912

there's no solid state physics book above the level of ashcroft and mermin as far as I know, unless you're talking about field theory approach.

@IceLord of course there are

user218912

@0celo7 tell me.

4:29 AM

This is why I often need to draw the words out else I lost track because of unpacking too many layers

take any book on specialized topics

user218912

@0celo7 I mean a general book that covers a large part of solid state physics in a single book.

then maybe not

user218912

can you do the problems in a&m? @0celo7

I don't have the book

4:30 AM

Abstract algebra is not as bad, because the concepts usually end up self contained, and not too much in a layered structure compared to topology

(although it is also another branch of maths that like to layer words)

What is so hard about topology?

user218912

@0celo7 try this

user218912

I did that problem btw.

user116211

@Secret You should start with metric space is a topological space.

user218912

you don't need to know anything other than what it tells you @0celo7

user116211

4:31 AM

Try introductory literatures like Kreyszig.

I don't know what a Drude model is.

user218912

you don't need to know.

user218912

this is purely a stats problem.

no clue how to do it

user218912

exactly

4:32 AM

so?

user218912

it's hard

I'm not taking the class

user218912

we didn't learn how to do it in the class.

then how do you do it?

user218912

creative problem solving skills

4:33 AM

either show it to me, or be quiet

user218912

okay so how I did it was

user218912

the probability of a collision not occuring is just 1 minus that.

user218912

so

user218912

choose an interval $t$ and divide it into infinitesimal intervals $dt$

user218912

the total probability is the probability of it not colliding in each of the infinitesimal intervals

user218912

4:35 AM

there are $t/dt$ intervals

Well, to start with, I don't really know what I am really doing to the set when I am defining a topology (other than following a rule book)
e.g. consider the set $S=\{a,b,c\}$ you can define different topoogies for it e.g. $\tau_1=\{\{a\},\{b\},\{a,b,\},\{c\},\{a,c\},\{b,c\},\{a,b,c\},\emptyset\}$ and $\tau_2=\{\{a,b,c\},\emptyset\}$. It is easy to see that $\tau_1$ and $\tau_2$ have very different notion of which sets are open (wrt $S$) and other topological invariants, but what exactly I am doing to the elements when I group them together in one subset e.g. $\{a,c\}$ vs $\{a\},\{c\}$.?

user218912

so do $(1 - dt/\tau)^{t/dt}$

user218912

limit as dt goes to 0.

good

user218912

that's all I can do tbh.

user116211

4:36 AM

@0celo7: Could you tell what the difference between a group and semigroup is?

No.

user218912

the other problems require ph.d level skills in physics.

user116211

I think I got it.

@MAFIA36790 the only time I've heard about semigroups was in the context of heat flow PDEs but I don't know any specifics

user218912

I love how whenever JD is losing an argument he says "I'm afraid I have to leave now."

user218912

4:38 AM

and leaves.

user116211

From $\mathsf{Pr}\infty\mathsf{fWiki}$ I got:

user116211

> A group is a semi-group with an identity in which every element has an inverse.

ok, looking at the semigroup stuff in Evans

user116211

@0celo7 Semi-group is an associative magma.

ok this is unrelated to set theory

it's about diff operators on Banach spaces

user116211

4:41 AM

@0celo7 No idea till now.

4:59 AM

Make positrons from strong lasers

user116211

Are you a die-hard fan of Sciencedaily, @Secret?

Kinda (except when they misreport about physics and regurgutating old articles)

They are otherwise pretty accurate, as most of my friends have checked. Most of the stuff on there will often appear in NewScientist, and the journal in relevant fields

user116211

okay.

Therefore, in most cases, as they claimed, they are really the resources for the latest news

However Sciencedaily is US based, thus it tend to slightly crowd with more USA researches

Nevertheless it is diverse enough to cover most things reported in other outlets in all fields of science

user116211

ohh, I see.

5:10 AM

This one is from molecular chemistry, never thought about one can inhibit the nonradiative pathways. Hmm, I wonder how we can impose this on other molecules so that by tuning its vibration manifold, we might be able to channel the reaction flux to other decay channels...?

What happens when a huge black hole collide with a tiny one

Preliminary investigation of the positive mass anomrlaly at Pluto's heart suggest it might be an ocean, more analysis need to confirm or refute this

user116211

Hey @yuggib o/

user116211

Guess what I'm reading...

user116211

@Secret I like it.

yuggib

Bourbaki?

user116211

Well, i'm studying order-theory.

user116211

5:19 AM

@yuggib It is implied ;P

user116211

Did you notice one thing @yuggib?

user116211

Bourbaki never mentioned binary operation.

user116211

They defined Law of composition and the algebraic structure as magma.

user116211

I really loved that.

user228700

Hello everyone :-)

5:21 AM

magmas are what other algebraic structures based on

user228700

@MAFIA36790: Are u a movie buff?

user116211

It's much less duller than the Set theory treatise @yuggib.

yuggib

It called it $R\{X,Y\} $ in set theory

user116211

@KaumudiHarikumar not very much that of a buff.

user116211

@yuggib yes! yes!!

5:22 AM

You first have a set, then define an operator for this set, if the operator is associative, you have a magma. Now if you sprinkle things like identities, inverses etc., you start to build semigroups, groups, rings and then fields

user116211

@Secret yes.

user228700

@MAFIA36790 Hm, OK. Was just wondering if u'll be watching "M.S. Dhoni, the untold story".

Abstract algebra is kinda like cooking. Everthing is step by step, unlike analysis where too many things happened at the same time to keep track of

user116211

@KaumudiHarikumar Would very much like to; I'm his fan; but I never watch movies in cinema/theatres. It's a wastage of time and money. I'm not into Bollywood that much though.

The irony is that analysis is actually prettier because many things happening at the same time

and make complicated shapes

user116211

5:24 AM

I'm now reading about Well-Ordering Principle.

@KaumudiHarikumar are you a cricket fan?

user228700

@MAFIA36790 Oh, I'd very much like to understand why you believe that movies are a wastage of time, some other time. And yes, the trailer looks great! I'm going to watch it this Sunday :D Will tell you how it is afterward. (I'm not into Bollywood either)

user116211

Also, @yuggib; I'm following Kelley where there is a good discussion on order-theory.

user116211

@KaumudiHarikumar Not movies; but watching them in cinema is a wastage of money and time.

user116211

@KaumudiHarikumar NOOO!!! No spoilers!!

user228700

5:26 AM

@MAFIA36790 Oh, yes, maybe.

user228700

@MAFIA36790 Dude. You can read about his life on Wikipedia now!

user116211

@KaumudiHarikumar Why should I ;P

user228700

@JohnRennie No, not really. Like every other Indian, it is the one major sport I watched, growing up. I do enjoy it once in awhile :-) I am a fan of M.S.Dhoni though.

user116211

you follow cricket @JohnRennie?

user116211

Yo mentioned earlier about that... lemme check.

5:29 AM

@MAFIA36790 not really. When there's a test match or one day series on I'll check the scores from time to time, but I'm not a fanatic.

user228700

@MAFIA36790 Am I not allowed to tell you if the movie is good, at least?

user116211

@JohnRennie ohh; good.

user228700

@JohnRennie Was just about to ask :-)

user116211

@JohnRennie I follow ball-to-ball of Ashes; they are exciting ;))

user116211

@KaumudiHarikumar sure.

user228700

5:30 AM

@MAFIA36790 OK :P I'll tell u on Sunday. I'm looking forward to it :D

user116211

@KaumudiHarikumar very well.

In the days of my youth we used to go and watch Somerset playing at home. That was in the days when we had Ian Botham, Viv Richards and Joel Garner in the team. But to be honest it was more of an excuse for a day out with friends rather than a fanatical interest in cricket.

user116211

@JohnRennie Botham is in commentary now; Richards is a supporting coach of WI cricket team (on and off); not sure of Garner. I do follow the scores of County; but they don't broadcast the matches here :(

user228700

@JohnRennie I don't follow cricket at all, so Idk who all those players are, but I see :-) I've only ever watched like 4 whole matches in my life thus far so I dunno if I qualify to be called a "fan", but almost everybody watches at least a little bit of cricket in India and I guess I do too, that's all...

user228700

But I'm definitely a fan of Dhoni, both as the captain who won us the world cup and as a person, which is why I'm looking forward to the movie! :-)

user228700

5:38 AM

@JohnRennie: I've got a quick chemistry question. Do u have the time?

@KaumudiHarikumar yes, of course. Shall we switch to the CSE?

user228700

@JohnRennie OK. I have already asked my question there so that would be convinent :-)

7:23 AM

To quantum guys: A PSE question incoming from me in a few seconds

Bass

Drumrolls please

Q: Why is the electron magnetic moment always parallel to the spin for an electron?

0

Consider the Hamiltonian $$\hat{H}=\frac{1}{2}\omega\vec{B}\cdot \vec{\sigma}$$ where $\vec{\sigma}$ is the Pauli vector $=\begin{pmatrix}\sigma_x & \sigma_y & \sigma_z \end{pmatrix}$, $\omega$ is the frequency of the magnetic field $\vec{B}=\begin{pmatrix}B_x & B_y & B_z \end{pmatrix}$ The el...

(Hopefully no unfixable false premise, or better: Hopefully I have not made any false premise)

Q: Destroy a Planet inside a blackhole?

8:02 AM

@Slereah: this seems an excellent use for home brewed cider! :-)

user116211

5

Imagine a race whom have mastered the knowledge of black-holes, at least a bit. They've found a way survive, with their planet intact, inside the gravitation of the black-hole without getting destroyed by it. (I know it is not possible for humans but in my fictional universe there are species whi...

science-based planets weapons science-fiction black-holes

user116211

How do they get such insane idea ;P

Got this idea from comparing between solving $\frac{d\vec{y}}{dx}=\vec{y}$ vs $\frac{dy}{dx}=y$. Note the former can have nontrivial kernal

Typo: $h\neq 0$

Typo: and also from my friend's explanation that classical state space is basically a space of pointer states

Flushing 240lbs of Mercury

9:16 AM

►

9:47 AM

Don't use chat flags except for seriously inappropriate messages. We've had a problem with inappropriate chat flagging for a while, and more so recently.

12

Q: Could a nearby black hole allow escape from the event horizon of a black hole?

0

My understanding is that the reason for the impossibility for escape from beyond the event horizon of a black hole is merely that the escape velocity is greater than c, and therefore unattainable. Given that, it seems obvious that it should be possible for two black holes, in orbit of one another...

physics black-holes

?

10:03 AM

16 mins ago, by David Z

Don't use chat flags except for seriously inappropriate messages. We've had a problem with inappropriate chat flagging for a while, and more so recently.

That means you 0celo7. Calling someone a nutcase is not seriously inappropriate you nutcase :-)

10:19 AM

It's a lot of people

For context: in the past week there have been 45 flags cast in the entire SE chat system, 12 of which came from this room. And 10 of those 12 are fairly obviously invalid - they should never have been cast. (The other 2 are maybe debatable, but probably not valid either.)

@DavidZ are there specific users involved or is it twelve different users? Obviously name no names.

@JohnRennie That I don't know yet.

Collecting this information is not exactly trivial.

"yet" - that sounds ominous for the people involved :-)

If we (mods) find out that there is a specific user casting a lot of invalid flags, we'll probably pull them into a private chat room to have a talk about their flagging standards. But for now, we're hoping a general notice will do well enough.

user116211

10:41 AM

Rehab centre for what David Z is saying ;))

10:56 AM

→ 1 message moved to Trash

Q: Why is the electron magnetic moment always parallel to the spin for an electron?

11:22 AM

2

Consider the Hamiltonian $$\hat{H}=\frac{1}{2}\omega\vec{B}\cdot \vec{\sigma}$$ where $\vec{\sigma}$ is the Pauli vector $=\begin{pmatrix}\sigma_x & \sigma_y & \sigma_z \end{pmatrix}$, $\omega$ is the frequency of the magnetic field $\vec{B}=\begin{pmatrix}B_x & B_y & B_z \end{pmatrix}$ The el...

quantum-mechanics electrons quantum-spin

I am experimentally convinced, now I just need to wait to be theoretically convinced

Fatima

Hey !
I'm from Pakistan and I want to be a researcher in Physics . I want to continue my studies in US . What should I study for that ? And what procedure should I follow ? I have completed my 12th grade this time.

user116211

@Fatima First take SAT and have a strong recommendation list; show your extracurricular activities; scholarships are very limited; so prepare keeping the expenses in mind.

Fatima

Oh, actually I want to get the scholarship . Studying without scholarship will be somewhere difficult for me . I have good grip in subjects also. From where I can get the application form of SAT ?

user116211

11:40 AM

They are available online. Go here: collegeboard.org

Fatima

Yeah I had seen there but there are alot of test dates there and I'm discombobulated which SAT test should I choose .

Can I enroll to Harvard in Physics department by giving this test ?

John Duffield

@peterh : yes, the acceleration will be zero, but not because of time dilation.

John Duffield

12:31 PM

@JohnRennie : you've been "not nice" a little too much recently.

@0celo7 : I don't worship the Einstein digital papers. I just refer to them to try to stop people lapping up woo. There's an awful lot of popscience pseudoscience out there.

@IceLord : yes, the Einstein-de Haas effect demonstrates that "spin angular momentum is indeed of the same nature as the angular momentum of rotating bodies as conceived in classical mechanics".

@IceLord : you need experimental evidence for this kind of thing, not equations.

@IceLord : I never lose. Because if I don't know something, I don't talk about it.

John Duffield

12:52 PM

@Secret : it's antiparallel, and I know why, but I prefer not to say at the moment. Sorry.

Gosh, it's quiet here. OK I'm off to write about monopoles.

user116211

Just say your iconic words @JD Let's talk physics .... everyone would be enchanted ;)

@JohnRennie I happen to think it is seriously inappropriate.

user116211

He trashed my comment; so chill @0celo.

I didn't flag your comment, against my better judgement.

user116211

@0celo7 I didn't say; but since it was inappropriate to call someone douche; it is good that it has been removed.

user116211

1:08 PM

And as I said earlier, I am sorry for using that.

user116211

Would Kip Throne win the Nobel Prize, btw?

user116211

Rainer Weiss' birthday: from Slovakia to circuits, vinyl in Manhattan to LIGO

user116211

Hmm, lately Lumo is writing more political stuffs ;/

@slereah what is the name of that Spivak topology book, cause all I found via googlign is his 5 volume diff geom books?

user228700

1:44 PM

Hello everyone :-)

user228700

Oh, shucks, nobody's here :P I was wondering if any of you have attended a TED conference..?