The h Bar

\o

user116211

@Secret The problem is Lanczos hasn't discussed Hamiltonian mechanics yet.

user116211

Meanwhile got a ps file; converting it to pdf...

user116211

6:13 AM

Okay, is he really talking about singular Lagrangian? I'm dubious:

@bl00 Where?!

user116211

user116211

What does he mean by singular case?

6:29 AM

He says what he means literally :P

user116211

Okay... re-reading

If $\dot q_k$ appears linearly in $L$

user116211

then it is a singular case?

He says so

user116211

okay.

6:34 AM

"Thanks" (<-Sarcasm) for deleting the comments below this; physics.stackexchange.com/questions/284717/… "But Why?"

user116211

@JokelaTurbine Comments are not permanent; you have to remember this.

user116211

Either they were obsolete with respect to the current version of the query or were not adding any important point to the query; in any case, comments are not permanent.

Yes, I do. I have no problem with that. But I am trying to figure out how to proceed with this question. I just get my question closed, but dont really have way to go forward with me theme.

with the theme.

Comments are intended only as a way for users to ask for clarification and make the post better. If a comment is chatty, obsolete, or off topic, it can be deleted.

@JokelaTurbine The close reason you got is completely unhelpful, as far as I can tell.

user116211

@JokelaTurbine This will be decided by the community as a whole. You have edited it many times; so I would say, wait.

6:38 AM

@ no problem. The mostly I miss the comment from John Forkosh, which was makeing the post better. I even edited the post accordingly.

@ACuriousMind See starred message above. This is a great example of why I keep harping on about how the close reasons should tell the user how to make the post better.

Oh wait, that post was edited five times...

@JokelaTurbine If you already edited the post based on the comment, then the comment is obsolete and should be deleted :)

Yes. first was spelling corrections from MAfia

@JokelaTurbine Your profile says you know many languages. Русский? Ελληνηκά?

then I added the "1/c" stuff for Forkosh, then the question got almost closed, and I re structured it majorly. and after it got closed, I made it "as acceptable as possibe" = deleted 90%

Espanol?

@JokelaTurbine Well, what is it you want to know?

Can you explain to us here?

6:41 AM

I can communicate= travel in these countries with

YEs, I can; The idea behind the question is not mainstream, but I can make this to work within the mainstram

@JokelaTurbine We're in chat. To hell with "mainstream" (it's a stupid word anyway).

@ACuriousMind Meeeehhhhhhhhhh, yeah ok fine.

Q: In Quantum mechanics, we take the wave function as $Ψ = Ae^{i(kx - \omega t)}$. Can anybody give the derivation of the equation?

-3

I just want the derivation of $Ψ = Ae^{i(kx - \omega t)}$

quantum-mechanics homework-and-exercises wavefunction schroedinger-equation

This = downvote

I feel really bad for the person who posted that.

OK, I want to know if my second area moment deflection calculation for Light gives understandable explanation to planck constant

They're just another poor student with a crappy teacher who doesn't actually explain stuff.

@JokelaTurbine What is a second moment deflection calculation?

6:45 AM

Second moment of area

This article is about the geometrical property of an area, termed the second moment of area. For the moment of inertia dealing with the rotation of an object with mass, see mass moment of inertia. For a list, see list of second moments of area. The second moment of area, also known as moment of inertia of plane area, area moment of inertia, or second area moment, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. The second moment of area is typically denoted with either an I {\displaystyle...

Well he will have to look up some stuff and then head to this chat, casue main SE don't allow no research effort questions

Have fun in the rabbit hole Daniel :)

user116211

@DanielSank no research efforts at all.

List of second moments of area

The following is a list of second moments of area of some shapes. The second moment of area, also known as area moment of inertia, is a geometrical property of an area which reflects how its points are distributed with regard to an arbitrary axis. The unit of dimension of the second moment of area is length to fourth power, L4, and should not be confused with the mass moment of inertia. If the piece is thin, however, the mass moment of inertia equals the area density times the area moment of inertia. == Second moments of area == == Parallel axis theorem == The parallel axis theorem can be used...

user116211

@danu, wait...

6:46 AM

@MAFIA36790 That's possible, but you and I have no idea what horrible teaching this person has been subjected to.

I used the I_z on the first pic of list, as the most logical, and I got it immidietly correct

user116211

@DanielSank When teaching doesn't help, books can help.

@Secret The rules say that, but I think we're not really consistent about how we judge whether or not a question has sufficient research effort.

@MAFIA36790 Point me to a good quantum textbook.

The list is:

1) Shankar

user116211

@DanielSank Introductory: Feynman.

\endoflist

6:47 AM

Hello everyone

@MAFIA36790 As a student, I found Feynman's writings completely useless.

user116211

Intermediate: Schiff/ Schwabl

user116211

@DanielSank ._.

@MAFIA36790 I can play that game too

._______________.

^ Whale face

@DanielSank Same. Do you respect it now?

6:48 AM

@DanielSank Besically I used common defelction calculations from structural engineering; en.wikipedia.org/wiki/Deflection_(engineering)

@SwapnilDas "Respect"? Sure.

I don't understand why it is useful.

@JokelaTurbine Please link to the full calculation/theory.

user228700

Hi everyone :-) @DanielSank: U're in a bad mood today :/

you mean my own paper? researchgate.net/publication/…

6:51 AM

@Kaumudi I am?

Q: How to derive Schrödinger equation?

2

How is the Schrödinger equation $$\frac {\partial }{\partial t}\psi=-\frac {i }{\hbar }H{\psi }$$ being derived?

quantum-mechanics schroedinger-equation

Meanwhile, this one is protected, but their nature are exactly the same

The most important is on page 6

I offered to read someone's personal theory. That seems generous to me.

user116211

@DanielSank: Advanced undergrad: no idea still

@DanielSank Could you tell me why is it worth that 'respect'? It is so boring.

user228700

6:51 AM

@DanielSank Yeah :-P U aren't?

user116211

@DanielSank oh lord ;D

@DanielSank Thanks I appreciate.

the most difficulties was to find a way to atom diameter. thus the paper uses so much to that discussion

@SwapnilDas Feynamn's writings point out some very simple principles that can be used to get a good intuition for subjects. However, I find that they are generally useless if you want to learn to actually calculate something.

user116211

@SwapnilDas okay; I have a special place for Feynman; only he enlightened me after months of confusions and bafflements; his writings is really lucid; no offence.

@DanielSank True. As a student, the latter is more important to me.

user116211

6:54 AM

@DanielSank Okay, I will agree with that.

user116211

Vol 2 is excellent; Vol 3 is really good; Vol 1? Haven't read that much.

@MAFIA36790 I agree with clarity

@JokelaTurbine near the beginning it says $$\frac{2h}{\pi} = \left( \frac{e}{2c} \right)^4 \, .$$

This equation does not have correct dimensions.

@MAFIA36790 I've Volume 1 , perhaps that makes me think so :P

@MAFIA36790 Feynman's lectures were known to be devoid of the undergraduates for whom the course was intended, and instead full of professors and graduate students.

6:56 AM

@DanielSank any particular reason?

@Kaumudi I don't think so.

@SwapnilDas Yes, he was a bad teacher.

user116211

:(

Rule #1 for teaching: know your audience.

@MAFIA36790 Oh come on, don't tell me you hero-worship physicists...

Good researchers are not always good teachers.

user116211

@DanielSank I don't worship him; not at all.

@SwapnilDas Well, this was the comment for John Forkosh in the chat. I understand why you have this opinion. But I am convinced that the dimension is correct.

6:58 AM

In my experience there is neither strongly positive nor negative correlation between good science researchers and good science teachers.

I am fine with a wide variety of teaching styles. Probably this had something to do with me always thinking abotu rosetta stone like concepts that kinda maps the teaching of one teacher to another

user116211

What I'm saying is that the lectures are really lucid and intuitive and have worked for me.

@MAFIA36790 There are some physicists whom I madly worship, though

user116211

@DanielSank I worship Bourbaki.

user116211

;P

6:58 AM

@MAFIA36790 Great!

NeuroFuzzy

@DanielSank Hah! That's good, and the first time I've ever heard that from anyone. You're probably right for the most part!

@DanielSank Sorry my answer was linked wrong

user116211

Although you should note that the lectures actually given and written are quite different.

@DanielSank do u worship any?

user116211

Not in content but in the style of presentation and language @DanielSank.

7:00 AM

@SwapnilDas Not really.

I admire Nyquist quite a lot.

The only book I am not very content of is Griffiths (when he skip steps) and Schutz (he skip step even worse than Griffiths)

@DanielSank I worship Ed Written, Dirac and Fermi madly

Many physicists are very admirable, but even the best had faults: Einstein didn't believe that quantum entanglement were correct.

@DanielSank Thanks for the contribution. Because of this. I will delete the question, and give more efford to explaining units. I think I must do a explaining drawing. --- Thanks. Witht this I gan get forward.

He's demonstrably wrong on that one ;)

user116211

7:01 AM

@Secret Griffiths is really skipping with ropes.

Having said that I only have read very few books, since most of my learning is from my professors, my peers and me doing massive googling

user116211

@DanielSank JD worships his digital papers; HORROR!!

@MAFIA36790 What the...? You're worried about Griffiths skipping steps?

What about how Feynman says (in QED) that you can do quantum mechanics by summing up little arrows? He's skipping all of how you actually do path integrals.

user116211

He starts the book with Schrödinger's Equation; that's it!

user116211

@DanielSank Can't comment; no idea.

7:03 AM

@MAFIA36790 Oh that book. Yes Griffiths's quantum book is terrible.

NeuroFuzzy

@DanielSank The one that really got to me was Landau. He worked a lot, he methodically raised loads of other solid physicists up (with his theoretical minimum and colloquia). I forget the exact quote, but, when asked "if he could have done more", he responded immediately "no, I did all I could." (I read this in anna livanova's biography of landau)

His electrodynamics book is ok.

I have read some of his electrodynamics book (It's the textbook of our EM undergrad course), I like how he conceptually explains something, but when he go to the maths for the first time, he skip steps like crazy

user116211

Dyson has also written Advanced Quantum Mechanics.

To Indians, Cengage is god for High School Electrodynamics.

user116211

7:06 AM

@SwapnilDas Cengage?

Yup. Company name, not author.

user116211

ohh.

Author is BM Sharma

https://arxiv.org/abs/1409.2912
-1-Phenomena for the pluri χy-genus and elliptic genus

(What it reads to me:
(What) for the (What) and (What)

@DanielSank Did you like Irodov as a student?

user116211

7:08 AM

I liked some of the problems. But that's it.

@MAFIA36790 It is easy, you think?

@SwapnilDas Never heard of it.

Lol

user116211

@SwapnilDas Some problems were easy but messy; others needed time; I had even taken an hour or more to solve two or three problems; the problems contain mixtures of problems in them.

@MAFIA36790 true. In which grade did you try?

user116211

7:11 AM

However, I had not much time to complete the whole book.

user116211

@SwapnilDas 11th.

@Danu What rabbit hole?

Of physics numerology :)

@Danu Looks like I dodged it.

@DanielSank Did you read his third book though (I'm talking about the famous Lectures, of course)? It's pretty nice

The first/second kinda suck

7:13 AM

It's particularly funny because I was just now working on my blog post about why we should not think of physics equations as relations between numbers.

@DanielSank is mathematical physics physics or math?

@SwapnilDas physics

note the adjective being mathematical, but the noun being physics :P

@SwapnilDas That's like asking if a blue rock is blue or a rock.

@Danu Nope.

But I do mean it when I say it's more physics than math :P

@DanielSank I like it because it avoids the naive classical questions that come up when you learn QM the Schroedinger way

Physical mathematics

The subject of physical mathematics is concerned with physically motivated mathematics and is different from mathematical physics. The Journal of Physical Mathematics is an important journal in the field. String theorist Greg Moore said this about physical mathematics in his vision talk at Strings 2014. "The use of the term “Physical Mathematics” in contrast to the more traditional “Mathematical Physics” by myself and others is not meant to detract from the venerable subject of Mathematical Physics but rather to delineate a smaller subfield characterized by questions and goals that are oft...

7:14 AM

I read some thing about the double slit experiment and decided it was crap. Then I tried reading some other part and it was ok, but neither part explained how to calculate anything, so I saw no point in continuing.

lol :P

@Danu I doubt that.

CALCULATE OR BUST

@Danu Could you name some mathematical physicists other than witten?

@Danu More like "cartoons are cute but I don't know what to do with this".

7:15 AM

@SwapnilDas In what area? Functional analysis stuff, I don't know so much. But I know some people working on mirror symmetry.

Joke: What is the value of [Physics,Maths]?

@Secret 0

explain

Mathematical physics .

Actually I think it's $i \hbar$.

user116211

7:16 AM

@danu, In the singular case, why doesn't the partial derivative $\frac{\partial L}{\partial \dot q_k}$ contain all other $\dot q_k\,?$

user116211

@SwapnilDas applied maths, you can say.

Yeah, it's either $i \hbar$ or 0, but those are the same in the classical limit anyway, so basically I'm right no matter what.

Mayr, Klemm, Cecotti, are some of the ones that are working on the stuff I recently attended a conference on. There are tons more.

@MAFIA36790 Try it for yourself

Gaiotto is very famous now

user116211

okay.

you can probably count most people working at the IAS

so Maldacena, Dijkgraaf, Seiberg

etc etc etc

7:18 AM

[physics,Maths]=Physical mathematics-Mathematical physics=I have no idea if this is a number or not, lol

user116211

@Danu yes, he thinks differently ;/

^he didn't read it

@DanielSank Meh, you can calculate some stuff with it.

@Danu IAS! I badly wanna visit it someday

@Secret Math and physics are conjugate, both meaningless without the other. Therefore, their commutator is $i \hbar$. However, classically, mathematicians and physicists were the same people, so the commutator would be zero. It all works out!

But it's not more efficient than the Schroedinger picture, that's why we teach that to undergrads first :)

7:19 AM

@Danu Lol, wut?

lol it actually makes sense

@DanielSank ...so they form an infinite-dimensional vector space? :P

@DanielSank I mean we teach the Schroedinger thing first

@Secret Of course. You think this is some kind of game?

I don't play around.

@Danu ...which is utterly retarded. We should teach Heisenberg picture first.

@Danu Another question. Which requires more math GR or string?

@DanielSank Bold claims

@SwapnilDas Strings easily

7:21 AM

@Danu What, haven't I ranted about that before?

@DanielSank Nope

Well I put that joke tag for a reason (next post will expand on this message)

I don't think the difference is significant.

@Danu That's because you're wrong, of course.

@Danu why do people think the theory is right?

7:22 AM

There is a huge difference.

The equivalence is trivial, you can teach it early on and make kids live with both at the same time

In classical mechanics, we have time dependent x and p.

Me when asking question is not very different from this spock meme. I can actually do many things with the same action: Asking questions

@DanielSank Just your mental idea is different.

user116211

@Secret His species is emotionless.

7:23 AM

@SwapnilDas Long story---no interest in re-telling it.

However, when we start with Griffiths's POS book, we get $$\left(-\hbar^2\left( \frac{d}{dx} \right)^2 + V(x) \right) \Psi(x,t) = i \hbar \frac{d \Psi(x,t)}{dt}$$ on page one.

1. Wtf is $\Psi$?

2. Why are we taking derivatives?

I never had any problems with it, to be honest.

3. What is that $i$ doing in there?

e.g. When I am angry, I ask questions, when I am worried I ask questions, When I want to learn something, I ask questions, when I am trying to suggest an idea or nudge someone, I ask questions. when I make jokes, I ask questions

It's not optimal, but it's just not that important

7:23 AM

@Danu That's because you're not a physicist ;)

@Danu is there anything unsolved in GR?

@DanielSank I was back then.

@Danu d00d, have you taught courses yet?

Also, I'm tutoring QM now.

@Danu great!

7:24 AM

@SwapnilDas Sure

user116211

@Danu Which book?

user116211

Are you using?

@DanielSank And no I'm not going to push your personal ideas on what's best :P I don't get to decide anyways... I'm just doing problems with 'em.

@Danu Example, if any?

Basically, nearly everything and every emotion of mine can be expressed by just asking questions

7:25 AM

@SwapnilDas Sorry, I'm not really in the mood for more questions, if you don't mind :)

@Danu I wasn't going to suggest you "push" anything.

@DanielSank I know, hence the ":P"

@Danu Sure, sorry I'm abnormally curious :P

However, I seriously question the wisdom of having undergraduates solve for the eigenstates of the hydrogen atom.

user116211

@DanielSank Why?

user116211

7:26 AM

We will be doing it in 3rd year.

"LOL here's quantum mechanics. It's a whole new set of ideas. Oh, and why don't you also learn differential equations, including power series methods, Laguerre polynomials, and spherical harmonics at the same time?! LOLOL"

It's f------ ridiculous.

@DanielSank Except that's not how it is in Europe :P

It winds up being an exercise in memorization for the students and they learn nothing.

We have a separate course for the diff. eqn stuff in parallel in most places, AFAIK

@Danu Oh really? You can speak for a whole continent?

Paging @BernardMeurer who is presently at university in Lisbon and will confirm everything I just said.

7:28 AM

@DanielSank I can speak for NL + GER :) Essentially everything, yeah :)

When spock has emotions

@Danu I am amused by the use of "we" for "all of Europe".

@Danu I dare you to ask @BernardMeurer about his experience so far :)

Also most (Western) countries went through a big effort to homogenize the curricula throughout Europe, though the outcome will of course not be close to perfect

I'm crying hard. Is this guy a mathematician or a physicist?williewong.wordpress.com

7:29 AM

@DanielSank I feel firstly European, yes :)

So I speak of it as my country :P

@SwapnilDas Well, he's not a graphic designer, I'll tell you that.

user116211

@Danu You are indeed.

@SwapnilDas mathematician

He seemed to be a black hole theorist

@Danu I wouldn't even pretend that we have a consistent way of teaching quantum mechanics at UCSB, let alone across an entire country.

7:32 AM

I still feel like this stuff is pretty homogenous across West-Europe.

user116211

@SwapnilDas He is in Maths.SE.

Q: My math students consider me a harsh grader. Is my teaching attitude wrong?

I just checked for ETH Zurich, also

@DanielSank That's not really the question though: All I claim is that in at least Western Europe, one has a course on differential equations during or before learning about QM.

user116211

63

I am a math major grad student at a big public school, and we need to do TA every semester. I got assigned to lower level classes last couple semesters, and it's been quite difficult for me. Even though I am a pretty nice person in general, I have so much trouble tolerating my students' sloppin...

mathematics teaching teaching-assistant

@Danu We also have that kind of structure in UNSW in australia, although for us it is concurrent. We also have numerical method courses

user116211

You are in South Wales, @Secret?

7:42 AM

yes, NSW

user116211

ah!

user116211

Do you mean numerical analysis by numerical methods?

yes, and also statistics

user116211

WTH, is with your phantom phone @0celo7?

user116211

Well, we are taking course on numerical analysis in the first semester,

user116211

7:44 AM

Scarborough is a beautiful book in numerical analysis.

@Danu @DanielSank I confirm everything DS said. My freshman Chemistry course is bananas

user228700

@MAFIA36790: Do u suggest learning Chemical Bonding first, before diving into organic chemistry..?

user116211

@Kaumudi yes.

user228700

@MAFIA36790 OK, will do. Thanks :-) How long did it take u to finish OC BTW?

user116211

@BernardMeurer You are majoring in chem?

7:46 AM

@MAFIA36790 No, but I'm not sure my prof is aware of that yet

user116211

@BernardMeurer WTF :'(

@BernardMeurer Chemistry?

user228700

@MAFIA36790: ?

@Danu Yes, it's unbelievable

So I don't think you're in a standard program if you're in chemistry courses :P

7:48 AM

We're learning Schrodinger in 3D with spherical coordinates without learning calculus

@Danu Engineering program?

user116211

@Kaumudi Frankly speaking I had somewhat hastily read the last chapters of organic chem like amides, carbohydrates; nevertheless it took two months or more to actually finish it.

@Danu I'm not a pesky physicist, nor mathematician; remember? :p

@BernardMeurer Oh, well I never said I'd vouch for the curriculum structuring of engineers @DanielSank

user116211

@BernardMeurer HORROR!

@MAFIA36790 Everytime I'm talking with DS about it he has minor convulsions

It's so fucking difficult

7:49 AM

@BernardMeurer I remember when I came to uni and the prof asked us if we knew what spherical coordinates were

user228700

@MAFIA36790 Oh, OK. Did u do anything to remember it? Write down every reaction in a separate book etc.?

I was so scared :P

I spend all my time studying it and yet I can barely get anything

@Danu I can't even do an integral ffs

user116211

@Kaumudi Not every but yeh had the practice of writing equations.

user116211

@BernardMeurer Why in the world would anyone frame such syllabus ?

user228700

7:51 AM

@MAFIA36790 OK. Did u learn it from ur school's textbook or were there any other good books that u followed?

@BernardMeurer Well... What kind of integral?

I assume you learned how to integrate polynomials in high school?

@MAFIA36790 Idk, he's like 70 or something and I'm fairly sure he escaped Willy Wonka's factory b/c he's a 1.30m tall little tan man

@Danu Nope

user116211

@Kaumudi Solomon Fryle; you need to skip many contents as they are not relevant to JEE or so.

user116211

@BernardMeurer Insane loompa.

@Danu You gotta remember I come from the underworld

user228700

7:52 AM

@MAFIA36790 Ohh. What about Morrison Boyd?

@MAFIA36790 Willy Wonka banned my chemistry professor from the factory after he attempted to teach QM to a chocolate mixer

user116211

@Kaumudi I have the book but they are not rigorous; also they have many topics untouched.

@Kaumudi Organic chemistry basically revolve around a few key ideas: Functional groups and their major reactions (carbonyls are in particular important such as its role as a nucleophile), various types of isomers, the techniques used in the lab (e.g. chromatography, various spectrosopic techniques), and molecular orbital theory to explain why some reaction pathways are more favourable than the other as well as selectivity on the products formed

user228700

@MAFIA36790 Oh, crap, it's the only book I have :/

@Secret I can operate a spectrometer fast as a lightning

user228700

7:54 AM

@Secret Hm, yes, OK...

Above all of that, (depending on the test requirements) you either have to memorise or lookup a lot of reaction conditions and reagents to synthesize a compound

user228700

@Secret Yes, I must memorize :-(

In more advanced settings, retrosynthesis is an important tool in helping you to break down the target compound into smaller bits to plan your synthesis

user116211

@Kaumudi Go with NCERT; although it is sometimes very much confusing and leave the most important query as a question. And solve practice papers you have; that's enough.

user228700

@Secret No, I don't think I have that in my syllabus.

user116211

7:56 AM

@Kaumudi Retrosynthesis is in Solomon Fryle.

user228700

@MAFIA36790 Yeah, no, NCERT doesn't compare to Morrison and Boyd tho. NCERT only gives us the most basic idea; I studied it in high school and it isn't amazing or anything.

For high school level organic chem, it's mainly the major reactions that functional groups can do. Amines, carbonyls and alcohols are the most important ones