The h Bar

"Hey is this John Martinis?"
"Ehm, yeah, who is this??"
"I'm a young Brazilian man, would you take 5% of my soul for an explanation on Shor's algorithm?"
"What?"
"A solid investment, better than the housing market"

How to get banned from a research group

but, @DanielSank, I started reading this but then I got befuddled and went for this and this but that befuddled² me

DanielSank

Oh yeah... @BernardMeurer do you know quantum mechanics yet?

Bernard Meurer

@DanielSank I'm Jon Snow

Did you get that reference?

no? :(

"You know nothing Jon Snow"

I know nothing

DanielSank

4:21 AM

@BernardMeurer GoT or some such.

Bernard Meurer

Yeah :)

But no, I don't know QM yet

DanielSank

@BernardMeurer Then don't try to understand Shor.

I mean, you could try to use Shor as a motivator and center piece of learning quantum, but you need to learn quantum first.

Bernard Meurer

@DanielSank The problem is this crap is dominoes

to learn Shor you gotta learn QM

to learn QM you need Linear algebra and Calc II/III

and EM

and to learn Calc II you need Calc I

and to learn EM you probably need something

DanielSank

You don't need E&M to learn quantum.

Bernard Meurer

No? I was sure someone told me to the other day

DanielSank

4:30 AM

You also don't really need calculus. Well... you need just a tiny bit.

Bernard Meurer

Partial derivatives?

That's calc aint it?

DanielSank

@BernardMeurer That was me. It will definitely help understand applications of quantum, and give you some real estate to try out problems. But, quantum does not need E&M from a logical point of view.

Bernard Meurer

Ah, I see

DanielSank

@BernardMeurer You do not need partial derivatives to understand quantum.

Bernard Meurer

@DanielSank My life is a lie, what do I need to understand quantum?

You say I don't need linear algebra I'm flipping out

DanielSank

4:35 AM

Quantum mechanics is a funny kind of theory. It's not like solid state physics, or E&M, or anything like that. It's not the physics of any particular subsection of nature. It is the general framework of how to describe the information involved in any physics theory.

@BernardMeurer You need linear algebra. No question.

Statistical mechanics is the other thing in physics that's a bit like quantum in the sense that it applies to everything.

Bernard Meurer

@DanielSank Good, at least I got that right

DanielSank

Statistical mechanics is absolutely amazing. It changed my understanding of Nature, human interaction... everything.

Bernard Meurer

I don't know that either :(

I'm literally physics' Jon Snow

DanielSank

@BernardMeurer You're still a physics infant. Don't worry about it.

When you get to a statistical mechanics course, pay attention.

It's the bridge between kid physics and grown-up physics.

Bernard Meurer

When do I get to that?

DanielSank

4:40 AM

@BernardMeurer Usually year 2 or 3

Some 1st year courses do a bit of thermodynamics, but I actually think that's a mistake.

Bernard Meurer

Why are things so slow Dan?

DanielSank

You need stat. mech. to derive thermo.

Bernard Meurer

I want NAWLIDGE

DanielSank

@BernardMeurer A lot of it is because people don't know enough math.

Bernard Meurer

Bloody mathematics

DanielSank

4:41 AM

Teaching physics without linear algebra and calculus is like trying to make love with a raincoat on.

Bernard Meurer

@Danu This is all your fault!

@DanielSank Have you tried that?

DanielSank

@BernardMeurer No.

Bernard Meurer

That ought to be interesting

I'll add it to my list, nice one, thanks dan!

DanielSank

Add what to your list?

Bernard Meurer

Having sex with a raincoat on

DanielSank

4:44 AM

@BernardMeurer Your list of what?

Bernard Meurer

@DanielSank I keep many many lists at a notebook I carry around

this is going into the "Is it doable? Is it nice?" list

DanielSank

@BernardMeurer I see.

How's Isabel?

Bernard Meurer

I dropped that ball accidentally, I have forgotten how this works dan. Now I need a new Isabel

Hopefully Isabel will be a nice fat scholarship

We'll know on the 25th

Gonna hit bed now, goodnight Dan!

DanielSank

4:59 AM

ciao

Danu

6:04 AM

@BernardMeurer ?

@DanielSank that severely restricts one---you won't be able to do much concrete calculating: no wave mechanics without calculus.

John Rennie

6:41 AM

@Danu Daniel is keen on the more fundamental approach to QM (a view that I have considerable sympathy with!) rather than starting by writing down a differential equation. Calculus isn't as important in this approach, though obviously it would be to actually do any calculations.

Having said this, I'm unsure how accessible this approach is for students without the experience we old timers have. Abstract approaches can be hard to get a grip on i.e. it can be hard to see where you're going with them.

user116211

WTH did the price drop after I ordered Grillet ;_;

user116211

@JohnRennie Yeh... I never seen Feynman cracking some hard maths in his lectures in vol 3 although the book is an excellent piece of introductory QM; however it is not self-contained ;/

user116211

0

Q: stern-gerlach experiment (deflection of silver atoms)

Determine the distance between $P_2$ and $P_3$ for the stern-gerlach experiment with silver atoms and the following conditions: $\frac{\partial B_z}{\partial z}=10^3$ T/m , $L=10$ cm, $l=1$ m and a temperature of 600 K. Assume that the average velocity of the silver atoms is $(\frac...

user116211

The question at first sight seems to me HW type. What do you think @JohnRennie?

user116211

@yuggib: o/

yuggib

6:56 AM

\o

John Rennie

@MAFIA36790 yes it's a homework question, but my answer is conceptual i.e. it discusses the forces on a dipole. This is one of those borderline cases where I think an answer can help the OP understand physics better (as well as helping with their homework :-)

user116211

@JohnRennie Thanks, but I'm going to CW it unless OP modifies it to the more conceptual one.

David Z

I closed it

user116211

@DavidZ T__T thanks

user116211

Damn, I wrote CW ;_;

Danu

7:05 AM

@JohnRennie I also sympathize, but I still want to solve the harmonic oscillator (without slick tricks). It's easy to take a "fundamental point of view" when you're already knowledgeable.

John Rennie

@MAFIA36790 ah, having checked I has also VTC'd but given a hint in the comments

user116211

@vzn: Did Lumo respond?

John Duffield

@BernardMeurer : I just talk physics. Sometimes it turns into a lively discussion, but do note that I don't go round being unpleasant to people and calling them names.

@vzn : I have some "unorthodox" views because I've read the Einstein digital papers and some old electromagnetism material.

David Z

7:26 AM

@JohnDuffield again, that's the sort of thing we'd rather you not post

John Duffield

@David Z : and again, why should I be subject to your censorship? 0celo7 has served his time, why should I suffer a life sentence that came with no warning? Especially when you suggest to people like Obliv that it's because I'm unpleasant, when I'm not: "That being said, any time someone gets suspended from chat, you can be fairly confident it has to do with violations of the "be nice" rule".

Your ongoing lack of response to this point speaks volumes.

user116211

8:01 AM

Okay, this is giving me a shit.

user116211

Purcell says in order to get a dipole configuration, you have to make a singular abstraction.

user116211

But he ends the discussion:

user116211

> Fortunately, we shall not do.

user116211

._.

David Z

1

Q: Subtracting Audio from a Song with Multiple Forms

This question may start oozing into the realm of copyright infringement, but let's discuss the theory first and foremost. I have a song with vocal and orchestral accompaniment from a well-known movie in two different languages. The orchestral accompaniment only of the song has never been publish...

waves acoustics vectors

Thoughts on whether that's off topic?

user116211

8:15 AM

@DavidZ really the intention of OP doesn't seem to be related with physics anyway.

user116211

I would better go with Chris White; so I would CV it.

yuggib

I put a mathematics paper on the arXiv, and a damn physicist asks me to put 12 completely unrelated references to his work on the paper... T__T

some people is nuts

and in general this practice, very usual in physics (but luckily not in maths), is really unethical

especially when, as a referee, you ask to add references to your own (completely unrelated) work

user116211

8:44 AM

@yuggib Is not it a blunt begging? Really it sounds off-tune to me, let alone unethical.

David Z

9:26 AM

@MAFIA36790 and yet you didn't...

user116211

@DavidZ Fine; I'm retiring ;_;

user116211

10:17 AM

@ArtOfCode: o/; after long time.

ArtOfCode

@JohnDuffield If you want response, here's one: you've been asked to stop talking about physics because many of your past discussions about physics have resulted in flame wars, nastiness, and suspensions. Not all from or to you, it's true, but it's been observed that you're a central figure in this pattern, so you've been asked to stop to keep the peace.

You're welcome to continue such discussions in other chatrooms.

Additionally, if David Z isn't responding, that's likely because you've been told all this before and refuse to accept it. It's truth; I can verify any of it for myself with mod tools. That's how it is, and that's how it needs to stay unless and until the Physics mods say otherwise.

That's as much as it needs to be discussed; I won't say more on the matter.

user116211

WoW! \o/ @ManishEarth.

ManishEarth

o/

ArtOfCode

@MAFIA36790 evening

yuggib

10:39 AM

@MAFIA36790 well, it surely is unethical; and I will surely not cite completely out of context papers

luckily it is the first time it happens to me

user116211

@yuggib yes and that is correct attitude to deal with such crap.

Slereah

11:16 AM

Ask for money at least

user116211

or Bitcoins.

yuggib

11:51 AM

@Slereah nah...I will just ignore the physicist

as it is always sensible to do ;-P

John Duffield

12:26 PM

@ArtOfCode : only it isn't true. I was barred from discussing physics here because Danu had it in for me, particularly after I corrected him on a physics point. See this. As for suspensions. you suspended me for a week without warning, for flagging abusive posts.

John Duffield

12:44 PM

The truth is that I get censored because I get abuse for challenging some self-appointed "expert" and referring to Einstein to support my case. It even happened yesterday, with Motl. And then comes the insinuation that it's all because of some unpleasantness from me, in posts that have now been deleted. Or that you've been told all this before when I haven't. I have to say, all this rather colours my experience of physics.

user116211

1:01 PM

> postmodern feminist philosophers

user116211

I like that.

ArtOfCode

@JohnDuffield page not found. If your experience here is bad, you're entirely free to leave the chatroom, or even the site. If you think you're being treated unfairly, I invite you to contact the team using /contact.

yuggib

1:18 PM

@ArtOfCode He seems to have a rather bad experience with all physicists he ever interacted with; and even most of dead ones. But his reaction up to now has always been to consider all the aforementioned people always wrong, and himself always right.

user116211

@yuggib Let's talk about physics ;)

yuggib

@MAFIA36790 let's talk about mathematics ;-P

or physics from a mathematical perspective

user116211

@yuggib I would after reading Grillet :) Just one day away ;))

yuggib

well, reading Grillet you will talk about abstract algebra; and I am surely not qualified to answer

:-D

at least to high-level questions ;-)

user116211

@yuggib: If you are bored, BTW, read Lumo's blog.... no objection to his physics (it's beyond my scope) but the way he presents.... ;)))

yuggib

1:24 PM

let's say that reading his blog I would be more bored than before :-D

user116211

23 mins ago, by MAFIA36790

> postmodern feminist philosophers

yuggib

he likes to express thoughts in a colourful manner

user116211

I would be banned if I add some other beautiful remarks he uses to attack his opponents ;/

yuggib

the point is that, as almost any physicist, he is so full of mathematical inaccuracies that simply make me mad

user116211

So, what should be the ideal way to explore both mathematics and physics @yuggib? This would help me surely in framing my career :)

user116211

1:26 PM

Double major?

yuggib

no, I don't think so

it surely depends what you want to do

a recurring pattern in the career of mathematical physicists is that they have a degree in (theoretical) physics, and then do a phd in mathematics

user116211

@yuggib Well, I can't tell about my future but really it would be great if I go with mathematics at the ultimate end.

user116211

@yuggib Thanks, sir!

yuggib

if you're interested in pure mathematics, there is no need of studying physics

or maybe only studying it marginally

ACuriousMind

@yuggib Some physicists seem to apply the converse - "to do pure physics, you don't need to study mathematics" ;(

yuggib

1:30 PM

@ACuriousMind well, that is disputable if you see mathematics as a language for many things (among which physics)

as I do by the way

but if you see it as a "game" (I've seen people saying that) or some almost sophistic speculation, then you probably think it is not necessary

AccidentalFourierTransform

-1

Q: Partial Derivative in FeynCalc

I try to compute some loop diagram in mathematica with FeynCalc package. In the nominator, I have a huge trace and it shows the right solution but in the next step I need to find the solution of a partial derivative such as simply FieldDerivative[FV[p,\[Mu]]. DiracMatrix[\[Nu]],{FV[p,\[Nu]]}] ...

computational-physics feynman-diagram algorithm

^ is it really off-topic?

user116211

@AccidentalFourierTransform Damn off-topic ;(

user116211

okay, seeing

AccidentalFourierTransform

I mean, it's not a question that I find particularly interesting, and when I first saw it I thought it was slightly off-topic but I was unsure

yuggib

@AccidentalFourierTransform it is borderline, for it is indeed about a software, but one that is used only/mostly by physicists

nevertheless, it is maybe more appropriate for the mathematica help center

AccidentalFourierTransform

1:34 PM

@yuggib exactly. Where else could anyone discuss about FeynCalc but here

yuggib

or the feyncalc support (if there is one)

AccidentalFourierTransform

yeah I guess youre right

yuggib

maybe it would have been better as a chat question

AccidentalFourierTransform

definitely

but OP is a <20 user :s

yuggib

there is indeed a mailing list for feyncalc

yeah I see...

AccidentalFourierTransform

1:37 PM

mathematica.stackexchange.com/questions/tagged/feyncalc

^ the question should be migrated to mathematica.SE

user116211

@AccidentalFourierTransform: Advise OP to do that.

yuggib

only mods can do that probably

ACuriousMind

@AccidentalFourierTransform The world won't end if it stays open, but I think it is off-topic - particularly because it's not even clear what the question actually is asking: Is it asking for the correct function to use? Is it asking whether the expected result is correct? If it said what "FieldDerivative" does, maybe someone could answer this without any knowledge of FeynCalc?

user116211

Where is 0celot??

AccidentalFourierTransform

@ACuriousMind I guess I empathised with OP: feyncalc can be a real headache :P

user116211

1:50 PM

This is the most frustrating thing:

user116211

You see there is an suggested edit; but when you go it is cleared ;_;

dmckee

2:01 PM

@yuggib We could wish that other games turned up so many profoundly useful tools.

I wouldn't use the word "game" myself because of the dismissive tone that could be read into it, but there is a kind of freedom to change the starting rules on whim and just look to see if the result is in someway interesting. If it is you win.

yuggib

@dmckee Maybe you're right. However I think that the most important (and appreciated) theorems of mathematics are about general characterization of structures: you define some structure by its (usually very general) properties, and try to describe the features that are true for all the objects in the structure.

Of course, you have a lot of freedom in defining the structures ;-)

But the toughest areas of mathematics are those where you are not able to have such a general characterization, and you're forced to study each singular case by itself.

One of the most relevant examples is, in my opinion, the study of non-linear PDEs

where if you change very slightly the non-linear interaction, or the dimension of the underlying space, you often obtain radically different behaviors

Physics Meta

3:45 PM

0

Q: Scratch area where I can try formatting my equations

Is there a sandbox area where I could test the formatting of my equations without the 5 minute reply limit kicking in? I have a long set of equations to type and I'm trying to learn how to format stuff on StackExchange.

support

DanielSank

@Danu I use quantum mechanics in a practical setting in my work on a regular basis. I have almost never needed to use the wave picture for anything.

@JohnRennie I don't see the problem. If someone can understand time dependent x and p in classical mechanics then introducing the Heisenberg picture in quantum should be easier than introducing the Schrodinger picture.

Danu

@DanielSank I still maintain that it's very hard to deal with the harmonic oscillator, then. This is barring slick tricks (even the $a$, $a^\dagger$ stuff is pretty hard to come up with)

And I'm not really willing to say anyone understands quantum mechanics without dealing with at least e.g. finite well, harmonic oscillator, Dirac potential (just listing the ones Griffiths does off the top of my head)

Also aren't you big on Fourier transforms? Those come in pretty handy in QM: They may even be essential, I'm not sure!

@DanielSank Still, you can't get away from differential equations in the Heisenberg picture either.

I do agree that the non-calculus oriented component of QM is the actually insightful one, in most cases. In that sense, you're right. But I think it's essential to grind through the nasty calculations first.

Obliv

can someone help me with a math proof?

John Rennie

4:01 PM

@Obliv probably not unless it's a very simple one, but post it and I'll have a look

Obliv

thanks john

wait quick question: if the identity of a group is always self-invertible then is its order always 2?

Danu

No, its order is always 1

Look at Wikipedia for a definition of order.

Obliv

well that would have to mean the identity is always $1$ which I'm skeptical about

Danu

"is always 1"

That statement makes no sense

A group is defined abstractly

There are no numbers associated to its elements

Obliv

the order $n$ of an element $g\in G$ is $g^n = 1$ where $n = |g|$

Danu

4:06 PM

No

Obliv

for the order of the identity to always be 1 then $g^1 = 1$ so $g = 1$?

Danu

The order of an element $g\in G$ is defined as: $n=|g|\Leftrightarrow g^n=e$, where $e$ denotes the identity element.

Obliv

OH

Danu

There are no numbers associated to groups, in general.

Obliv

wow my book didn't show that notation

probably assumed it was $e = 1$

Danu

4:08 PM

Then your book is either very non-abstractly oriented, or very bad.

Obliv

hey man i heard good things about it

John Rennie

What does self-invertible mean? Do you mean $(x*y)*y=x$ for all $x$ and $y$ in the group?

Danu

It's important to note that groups are not defined in terms of numbers!

@JohnRennie Invertible (in groups) means $\forall g\in G$, $\exists g'\in G$ such that $g g'=g'g=e$

$g$ and $g'$ are then called each other's inverses.

Obliv

alright so I have to prove that any finite group $G$ of even order contains an element of order $2$. Aka, $g^2 = e$ so $g = g^{-1}$

yuggib

especially with multiplicative notation, it is not uncommon to denote the identity element of a group by $1$. That symbol is not however necessarily the natural number one.

Obliv

4:11 PM

if it was an odd group there would have to exist at least 1 element that is self-invertible but since it's even I don't know of any way to deduce such an element exists

WAIT

@danu is the identity self-invertible or no?

$e*e = e$ seems to be self-evident no?

if I use the idea that the identity is self-invertible, then there has to be at least 1 element that doesn't have another element as an inverse.

Danu

@yuggib But to introduce it as 1 seems very bad to me

@Obliv Eh... no.

Every group element is invertible by definition of a group.

Obliv

yes it's still invertible but it must be self-invertible in this case

Semiclassical

I take your point as such. Let $F(g)=g^{-1}$. Then $e$ is a fixed point of $F$, and the question is whether there are any others.

Obliv

there should be others unless two elements could share an inverse

at least 1 other for an even ordered group

Semiclassical

If two elements have the same inverse, they're the same element.

Obliv

4:21 PM

ah ok

Danu

your book should prove these basic propositions

Semiclassical

@danu or at least give the tools to prove them as exercises

Obliv

that if two elements have the same inverse, they're the same element? @danu

Danu

Things like uniqueness of identity etc etc

Obliv

yeah i proved those

DanielSank

4:35 PM

@Danu Grinding through "nasty" calculations without understanding wtf is going on seems like a bad idea, and I think making students do that is one of the reasons people drop science/math for other things.

Doing hard calculations is essential, but the way e.g. Griffiths drops the Schrodinger wave equation on your head on page one and says "quantum mechanics means solve this equation" seems totally wrong to me.

@Danu True, but they're very, very simple compared to e.g. the radial and angular equations for the hydrogen atom wave function.

Danu

@DanielSank I agree that that... pretty lame :P

Bernard Meurer

@JohnDuffield I'm not accusing you or anything, I'm in no position to do that after all, I was just making a statement from observation

@Danu It was your fault because you're a pesky maths person

Danu

5:49 PM

@BernardMeurer I'll take that as a compliment.

Bernard Meurer

@Danu It's meant as such :)

3075

@BernardMeurer quest? :p

Bernard Meurer

@3075 Just checked, nothing :p

3075

fyi I received mine sometime between 11:00 am and 11:30 am my time.

vzn

6:08 PM

@DanielSank lol aka "shut up and calculate"

yuggib

@vzn aka (theoretical) physicist's way

Bernard Meurer

@3075 This is killing me

yuggib

@BernardMeurer junk food, carbonated drinks and alcohol are more likely killing you...

vzn

@yuggib uh, depends which "theoretical physicist" you are talking about. does it include bell? bohm? einstein? etc... :|

Bernard Meurer

@yuggib Alcohol is what's keeping me alive you fool

yuggib

6:22 PM

@BernardMeurer you've a strange definition of life

Bernard Meurer

@yuggib My definition of fun is microwaving grapes, what did you expect?

yuggib

@vzn yes... ;-P

maybe someone of them to a lesser extent

but every theoretical physicist did some (or probably a lot) of mindless calculations at some point of his career

vzn

@yuggib this reminds me. had a long "colorful" chat with @innisfree once in here about sociology/ philosophy of science. now wonder what he thinks of copenhagen interpretation... o_O

highlight: he denied the existence of the so-called "scientific method" on philosophical grounds. wow, seems almost/ verging on nihilist to me, 0celo7 would be proud... (er, if its possible for nihilists to be proud) :|

Bernard Meurer

@0celo7 is basically Nietzsche

yuggib

he denied the existence of falsifiable statements?

vzn

6:32 PM

@yuggib wow lol exactly something like that. my head was spinning some )(, had not heard that one before.

... who is 0celo7s new av? he chgd it, is that a rapper?

0celo7, USA

4.5k 1 8 31

general-relativity differential-geometry homework-and-exercises quantum-mechanics metric-tensor lagrangian-formalism quantum-field-theory

would not really "blame" him much if he left/ decided to leave. :(

yuggib

he may return some day

vzn

@BernardMeurer "@0celo7 is dead," RIP for now, not banned, but/ yet unresponsive :(

DanielSank

@BernardMeurer <3

John Duffield

@ArtOfCode : re page not found, it's there, I'm sure David Z will show it to you if you ask. After all, he's got nothing to hide, has he? As for if you think you're being treated unfairly, I invite you to contact the team using /contact, I did. I didn't hear back.

Obliv

lol... physics.stackexchange.com/questions/256870/rail-gun-launcher

@johnR did you get started on the bot?

Danu

6:43 PM

@0celo7 You misspelled Leibniz here.

Obliv

man I don't think he gets how to use this website physics.stackexchange.com/questions/256869/rail-launcher-system

DanielSank

@Danu LOL the title of that blog.

Danu

@DanielSank No comment.

John Duffield

@DavidZ : Here's another example of what I have to put up with. And here we go, wink wink chuckle because Motl called me a psychopath. Only if I were to reply in kind, I'd be on a holiday, with my post deleted and tut-tut troublemaker insinuations made: he must have said something really bad.

ACuriousMind

@BernardMeurer He has syphilis?

Danu

6:45 PM

@JohnDuffield Would you like a separate chat room for your complaints? In this room, they just distract from the other conversations.

Obliv

@danielS do you think him asking if his idea would work be salvageable enough to not close the post?

like if he was more specific with his idea and his definition of "work"?

user116211

@DanielSank Ask JD for that.

Danu

@ACuriousMind Do you know about the IIA and IIB superstring theory particle spectra?