12:46 AM
There's only one true Laplacian
$\Delta \phi(r) = \phi(r + dr) - \phi(r)$ after all ;)

1:22 AM
"nappla operator"
3
I've heard it called many things, but certainly not that

1 hour later…
2:34 AM
@EmilioPisanty No. I observed, researched and then came to a conclusion. User A was borderlining on disruptive behaviour, not to be confused with being disruptive. User B did not give a kind reminder. But that's not the issue. The issue is the moderator is seemingly stretching a little bit too far. Its best to stay at bay until a line has been crossed. The line being disruptive.
@EmilioPisanty User A has not broken any rules or regulations yet. And I hope user A doesn't either. I looked and contacted the site to ask for these rules and guidelines for this specific chat room. They told me and I wrote them down as they were said and repeated to me over and over again. I did my homework very well.

Are you guys familiar with Algebra/Trig combo books? I'm trying to find a book that'll give me an understanding of the two so I can advance to higher mathematics in order to study physics.

@EmilioPisanty I am not launching an aggressive tirade against user B. But I see something coming. And I've been through situations just like this so many times, its almost always the same. So I'll not be responding to any other pings, or comments about this specific matter from this message onward. Its in no way to cause harm, it's to let things cool down.
But I am happy to be pinged on other things.
@Sermo I've actually never heard of Algebra and trigonometry combo books. So I have no clue. I might have possibly seen one or used one. But I haven't paid enough attention to the titles as much.
@rob Could you remind me of what you were wanting me to get? I know you wanted me to get something, but I've forgotten.

@ScientistSmithYT I'd have to use the transcript to remember.

I work at a university bookstore, and it's pretty standard. We have three titles at our bookstore.
And also, do you think a college algebra textbook would be sufficient, even assuming that I don't have much background in algebra? I haven't taken a mathematics course in 6 years. Stopped at Algebra I and Geometry. I assume it must be, since even remedial college students are obligated to take the college algebra course, and they seem to scrape by. But I prefer to have a thorough understanding.

2:50 AM
@ScientistSmithYT I'm on mobile and can't type very fluently, but please resist the temptation to get into arguments about whether a rule exists that forbids some disruptive behavior. Such discussions are disruptive. We are people here, with feelings, not robots that can only follow rules. Thanks for cooperating.
I wasn't around for the conversation that you're referring to, but you're showing signs of going in a not-good direction in your most recent few messages about rules and moderation.

3:41 AM
Can spatial frequencies be understand by Fourier decomposition of complicated wave ¿

4:08 AM
Pick up a calculus-based physics book, e.g.
Fundamentals of Physics is a calculus-based physics textbook by David Halliday, Robert Resnick, and Jearl Walker. The textbook is currently in its tenth edition (published 2013). The current version is a revised version of the original 1960 textbook Physics for Students of Science and Engineering by Halliday and Resnick, which was published in two parts (Part I containing Chapters 1-25 and covering mechanics and thermodynamics; Part II containing Chapters 26-48 and covering electromagnetism, optics, and introducing quantum physics). A 1966 revision of the first edition of Part I changed the title...
and use it to work backwards on learning the trig and algebra beyond the basics as it comes

4:24 AM
@rob I want to address your last comment. I type on mobile all the time, and I understand it. The reason why I said I am no longer going to respond go that stuff is for the reason of stopping it. I could if I was forced to contact them again, I could ask for other stuff. But I'm not going to. Disruption is a term that can be used for anything. Such as saying a chipmunk climbing up that tree is disturbing. But we all know that's not acceptable for a reason.
@rob As for assuming my cooperation in that manner. That's not breaking any rules, but its not nice to assume and give no choice. From the people at the site there definition of disturbing is not that kind. So its best to respect it and not say it is something else. I kindly thank you for the thought of letting me know it seems I'm not going in a good direction.

The h-bar has been seeing some weird arguments lately....

@AaronStevens I deal with this stuff all of the time at work, at my shop and at my research building. It gets more annoying than tiring at this point in my life.
It's just life though.
I'm calling it quits on that though.
@rob But with that aside and done with. Just let me know when you find it? It's late here again, and its time for some sleep for me. I'll take a look tomorrow to see if I can find what you were asking me about. I did say I would get it to you.
@JohnRennie I have a question for you and I was meaning to ask. But it's late here so I'll write it down and ask you sometime tomorrow. Is that ok?

4:44 AM
@ScientistSmithYT OK ...

@JohnRennie Thank You. (I think you're thinking I'll write it down here. But I meant I'll write it down on my phone then copy and paste it on the chat and ping you in it tomorrow)
@JohnRennie Is that ok? I just want to make sure.

@ScientistSmithYT Yes, I'm just answering question about relativity in a different room :-)

@JohnRennie Oh ok. Sounds good. Thanks again. :)

2 hours later…
7:09 AM
> The issue is the moderator is seemingly stretching a little bit too far. Its best to stay at bay until a line has been crossed. The line being disruptive.
Since I was the moderator in this case:
The concerned user had crossed a line that should be common sense and that is also explicitly mentioned in the guideline of this chatroom.
I asked that user not to ping random users just to get help with a question.
I deleted two rude chat messages of that user.
And I told the user not be so rude.
That was all. I didn’t kick the user from the room, I didn’t suspend the chat account, and I didn’t threat.
If you still think that moderators have abused their privileges in this chat room, I recommend using the “contact” link at the bottom of any page of the main site and sending a message with your complaint, but please stop throwing around baseless accusations in this chat room.

7:39 AM
morgen
"This definition of clock synchronization was first given by Poincaré [10, 11] although atthe time it was already applied by engineers in the calculation of longitudes by means oftelegraphic signals "

7:58 AM
Basically all GR simultaneity conventions assume a static metric
things are too awful otherwise
I guess perhaps it's best to work backward
Take an arbitrary foliation of the manifold, get the simultaneity connection for it, find the observers associated and try to find conditions for that to not depend too much on position

8:43 AM
hey im new to this chat room
so is it just a place where we ask for clarification ?

if you so wish

8:58 AM
morgen @Slereah!
(why is always morgen over morning though)?

9:47 AM
@yuvrajsingh Certainly! For example, the compression algorithm used in JPEG does that, sort of. It breaks the image up into square blocks and performs a 2D DCT (discrete cosine transform, a close relative of the discrete Fourier transform) on each block, discarding the high frequency components. Eliminating that high frequency "noise" saves a lot of space. Video compression algorithms also utilize this technique.

10:06 AM
@ScientistSmithYT I don't want to re-open the conversation that's been happening between you, Emilio and Loong, but since I was a recipient of the excessive pings, I feel I ought to say something. I am not a RO (room owner) here, but I am a RO of the SO Python room, and the rules for The h Bar are partly adapted from that room.
That person has a habit of pinging people out of the blue with his questions, so when he did it to me I felt it was entirely appropriate to tell him to just ask his questions without targeting an individual. Several others, including an elected mod, repeated that info. When he persisted in pinging, Emilio gave him the friendly advice, as one room user to another, that it's not wise to continue doing something when a mod or RO has requested you to stop. There were no threats made.
Besides, excessive pinging is such a minor thing that it wouldn't invoke a chat suspension (unless the person kept doing it every day, despite multiple warnings). At worst, the member would get "kicked", a brief chat ban that only lasts one minute (on the 1st kick). Please see meta.stackexchange.com/q/271267/334566 for details.

Hi all, basic physical question:
the probability current $j$ tells you how many particles hit a screen on a given area in a given time, right? Now $j=\rho v$ with the velocity field $v$.
I try to come up how to express the limit of v=0 such that it gets clear that $\rho$ is then the measure for the particle density "on the screen"
However, just setting $v=0$ in $j = \rho v$ gives $j=0$ ...
So how to do that properly?

10:29 AM
Just integrate over time?

Yeah, I just try it. t->\infity but at the same time v->0 ...
SO how do to it?
$$P = j \cdot d\vec{A} d t$$
$$P = \rho \vec{v} \cdot d\vec{A} d t$$

Why do you need to set v to 0?

now we want $$\lim_{t\to\infty,\vec{v}\to 0} \int \rho \vec{v} \cdot d \vec{A}dt$$
I want to see what happens for a stationary state, or does that mean v=const.?

@user76284 this seems like some jibber jabber stuff that someone who pretends to know physics will say

like for an electron without magnetic field and $H\Psi = E \Psi$
(and without spin)

10:41 AM
Stationary in stationary state doesn't mean v=0

v=const. then?
But $j=0$ in that case

You have your current j, right? Like you already know what it is?

Yes.

Ok. Integrate over time. Don't worry about what you need to do with v.

$\int P dt=(j(T)-j(0))\cdot d\vec{A}$
$= -j(0)\cdot d\vec{A}$

10:49 AM
I don't think I understand. Is j it's own derivative with respect to time?

crap, sorry so stupid ..
wait
its $(\rho(T)-\rho(0))dA$?

So $\rho$ is the anti-derivative of j with respect to t?

The time integral of current should be charge, right?
@AaronStevens: So yes, I think so.

But your units don't work out
I'm not sure why the dA is there either.
If you were treating it as a current of charge you want to end up with charge per area

the area (dxdy)
@AaronStevens sure current of electron = charge

10:59 AM
Right... But you just have j and you integrate it over time. Where is a dA coming in? I thought you wanted the area density. We're you actually just wanting total charge?

We can also ignore it, I just wanted a proper "probability" P = j dt dA
Yes I want the area density
I have to leave to work, bye!

@PM2Ring Ur a room owner of SO Python room :OOO

@Rudi_Birnbaum Right. But your integral of j over t should give you units of charge per area, which is not what rho is. That is why I was saying your units are wrong.

@JohnRennie if you work in chemistry, spill some chemicals on him and make him take an emergency shower

@Slereah throw something pyrophoric on him and turn the fire hose on him! :-)

11:37 AM
As John Clark said of chlorine trifluoride in Ignition!: It is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively.

@PM2Ring that's such an entertaining book :-)

It's a classic.
I suppose ClF3 is a bit extreme as a treatment for BO, but when nothing else works... :)

@PM2Ring puts down that chlorine trifluoride bottle I've been drinking and starts to sweat

Derek Lowe has some good articles on smelly chemicals, eg blogs.sciencemag.org/pipeline/archives/2012/05/15/…

12:00 PM
@AaronStevens OK, rho is charge per Volume.

@Slereah .. need your insights badly on the equivalence principle... And some GR insights too?

12:47 PM
Sep 5 at 21:23, by rob
@ScientistSmithYT Do you have a link to the article?

12:57 PM
@Rudi_Birnbaum Right. Just do the integral of J over some time interval. That will give you the charge per unit area
@Rudi_Birnbaum $$P=\int\mathbf{j}\,\text dt=\int\rho\mathbf{v}\,\text dt$$

2 hours later…
2:42 PM
Is there ever any reason to use Routhian mechanics over other formulations
A chat search for Routhian yields less than 5 results so I'm starting to doubt anyone ever uses it

@SirCumference Whothian mechanics?

@AaronStevens case in point lol

In analytical mechanics, a branch of theoretical physics, Routhian mechanics is a hybrid formulation of Lagrangian mechanics and Hamiltonian mechanics developed by Edward John Routh. Correspondingly, the Routhian is the function which replaces both the Lagrangian and Hamiltonian functions. The Routhian, like the Hamiltonian, can be obtained from a Legendre transform of the Lagrangian, and has a similar mathematical form to the Hamiltonian, but is not exactly the same. The difference between the Lagrangian, Hamiltonian, and Routhian functions are their variables. For a given set of generaliz...
Wiki knows all

@MoreAnonymous Yeah I was making a joke

i heard it mentioned once in my classical mechanics course a few years ago, the prof even mentioned he's never had to use it

2:53 PM
@AaronStevens so was I ... Mine was that theres a wiki page on it :P

@SirCumference I mean there has to be some instance where it is better, right?

@AaronStevens ¯\_(ツ)_/¯

@SirCumference I could see it being useful in certain engineering contexts where you want to handle certain coordinates differently than others
that said, I see little reason for a physicist to care about it

I accidentally pressed post while editing and figuring out a post .. Panicked, tried to edit it in real time,etc ... I'm satisfied with it now .. But it now has $2$ vote to closes and a $-1$ downvote ... I'm sure I can't be the only clumsy person to have ever done this :/ ... Any relevant meta?
Wish there was a hide option for cases like these :/

3:08 PM
dO yUo kNoW BoOGiE WoOgiE?

@NovaliumCompany there was an indian dance show called that ...
Not sure if it still runs
Nope not the only idiot
22

I was composing my question but I accidentally Tabbed to "Post Your Question" and pressed Space. I went to edit my question to write the rest of it, but by the time I was done someone already downvoted my question and voted to close it due to the details being unclear (as I was not done with wri...

Relevant part (which I did do but panicked to much before undeleting it to gauge anything)
"You can absolutely delete the question in the interim while you edit it - to prevent additional downvotes - but reposting essentially the same question looks like you're trying to escape the penalties of the downvotes - which you are, to an extent. If you do this multiple times, it looks really bad and someone will likely notice and flag your posts and you might even get in trouble with the moderators for it.

"

3:28 PM
@MoreAnonymous you can always click the "rollback" button in the edit history to put it back to a previous version.

@AaronStevens I'm soooo stupid :OOO
Obviously panicked waaay to much

3:52 PM
@Aaron I think now that the two experiments j on screen and rho on screen are completely different things that cannot be brought into one formal description?
?->.

4:16 PM
@SirCumference I've never seen in "in the wild" but in theory it is possible that the equations of motion for some generalized coordinates look nicer (i.e. easier to solve or at least like known differential equations) in the Lagrangian formulation and for others in the Hamiltonian formulation.

@Rudi_Birnbaum I don't understand what you mean

Me going AFK ... Hope the post is in a decent enough shape :)

@AaronStevens counting electrons coinciding with the screen when the velocity is=0 seems to be not a special case of an experiment of counting electrons in current that hit the screen.

@Rudi_Birnbaum If v = 0 there is no current.

right then you just could count electrons that "coincide" with the position of the screen.
I initially thought the latter is special case of the former, which maybe is not the case.

4:46 PM
@Rudi_Birnbaum Any specific question on PSE or chat-link I can see to understand the thread of conversation?

@MoreAnonymous no, sorry it was a bit spread out in the chat.

@Rudi_Birnbaum :((((

@MoreAnonymous its just a small thing. the probability current is a measure for the probabilty that an electron hits a screen in a given infinitesimal area and time interval. Now I was wondering if finding an electron on a infinitesimal area was in some way a special case of that or not., s.t. one can formulate a limit of an intergral or something to get from $j = \rho v$ to $\rho$, but now I think its not.

@Rudi_Birnbaum I wanna participate in the conversation too but I think I'll just say redundant stuff :(((
@Rudi_Birnbaum Interesting problem though ... Any motivation?
@Slereah Took me longer to find this in the chat thread than I expected :/ ... Will let u know tales of my adventure with this book

5:03 PM
@Rudi_Birnbaum The $v$ in $j = \rho v$ is not the velocity of the particle(s)! it's the "velocity field" $\frac{1}{m}\nabla \phi$ where $\phi(x,t)$ is the time-dependent phase of the wavefunction.
Unless you're a Bohmian or doing a semi-classical approximation where this becomes actual velocity, it is not connected to any particle's velocity.
Furthermore, your idea of the "probability current" is wrong. It is not "how many particles hit a screen on a given area in a given time"

D-nim Suoiruca

@ACuriousMind I just figured they really meant to be talking about current

The probability current obeys the continuity equation $\partial_t \rho = -\nabla \cdot j$, meaning it is a measure for how the positional probability density is changing with time.
@AaronStevens I'm reasonably certain they aren't because they've been asking other questions relating to probability currents in the last few days.

@ACuriousMind Ah ok. I was thrown by them saying "Current of electron = charge" Maybe they don't realize they are not the same thing?

Very possible. It's easy to want the QM terms to easily relate to ones our intuition can wrestle with ;)
Alas, for an electron $q\rho$ is a charge density (the "electron cloud", if you will) and $qj$ is an electric current. But $v$ is still a velocity field $v(x,t)$ and not a single velocity.

5:17 PM
@ACuriousMind Well when this started they recognized $v$ is a velocity field

Reading back, I think the only issue is really interpreting $j$ as a measure for "how many particles" and not for a single particle. Once you've measured the particle, its state is gone, replaced with whatever is the outcome of the measurement the screen performs on the particle.

@ACuriousMind Right, which is why I thought they really meant to be talking about actual charge current. But if they have also been asking about actual probability currents then I guess more clarification is needed

@ACuriousMind Well for this consideration I want to look at it as the "subobservable" it is. That to treat it as a classical quantity.

Hey, today I experimented some crazy thing in my PC and broke it XD

@ACuriousMind That's the irrelevant bit of it.
I want to consider it like in fluid dynamics, just for this question.

5:31 PM
I coded a Neural Net and some Deep leaning mechanism which can detect computer viruses belonging to any OS and can eliminate it in a single go

@ACuriousMind like that exactly.

It can even decode most of the Ransom there and can help to extract files, so, while testing WC in my PC (downloaded from internet), I broke my PC had to format it
Neural nets are cooooooool!!!

@AbhasKumarSinha Did I tell you I'm a useless data scientist :p

@MoreAnonymous I'm neither useful here :P XD

@Rudi_Birnbaum So, what exactly do you want to compute? You have some state $\rho(x,t)$ (for a single particle) given and you have a screen of some shape and you want to know what the probability is to have detected this state at a certain location of the screen after "infinite time" (i.e. when the experiment is over)?

5:34 PM
@AbhasKumarSinha I get paid to be useful but I only "look" useful :P
The clacking of my keyboard in the office is probably me on stackexchange :P

@MoreAnonymous I even don't XD

@ACuriousMind I don't want to compute anything. I just want to see if a general experiment measuring current can be somehow "specified" to measure density.

I keyboard games only, very rare cases I'm coding... I'm currently busy with mercury, a very very very high level language

My question is if and how the concepts of current and density (in a fluid dynamical sense) can be related (except the equation $j=\rho v$).

It's okay u'll get a job ... On that note if we were in the same company then we would have to fight like this

5:37 PM
@Rudi_Birnbaum Sure it can - start with a region of known density, measure the current out of it, apply the continuity equation - done. (The hard parts are "start with a region of known density" and "measure the current out of it")

@MoreAnonymous I'm pretty sure, I can get a job, but I'll be more interested in startups :)

@Rudi_Birnbaum How "fluid dynamical sense" do you want it to be?
@AbhasKumarSinha Who said I'm not in one :P ...

@MoreAnonymous did I?

@AbhasKumarSinha Though it's a pretty big start up ... So i get away ... Don't go for a small start up u wont get time ... And you will have to "learn"
:P

In a way my question was if the density can be determined from the flow given that we can slow it down arbitrarily. like $\varepsilon v$. But I see now that this is not possible.

5:40 PM
@MoreAnonymous I'm sure I can manage investments of 4-5MN USD

I want to simplify this expression $im[{\hat {H}},{\hat {x}}]=\hbar {\hat {p}},\qquad i[{\hat {H}},{\hat {p}}]=-\hbar V'({\hat {x}}).$ to this $m{\frac {\partial H(x,p)}{\partial p}}=p,\qquad {\frac {\partial H(x,p)}{\partial x}}=V'(x),$.
I used conversion from position to momentum space, $[{\hat {H}},{\hat {x}}] = {\hat {H}}{\hat {x}} - {\hat {x}},{\hat {H}} = {\hat {H}}{i \hbar \frac{\partial}{\partial p}} - i \hbar \frac{\partial}{\partial p}}{\hat {H}}$ then I need to set $\hat {H}}{i \hbar \frac{\partial}{\partial p}} = 0$. But it seems not formal!

@AbhasKumarSinha multiply ur answer x 100 .. thats the order it's off

@MoreAnonymous Bro, AI = profit. That's how it works, very high efficiency, fewer employees, so already too much profit then will look extending business abroad

@AbhasKumarSinha Did I tell u I don't even have a degree in my field of data science or AI :P
?

5:43 PM
@MoreAnonymous lol.

@AbhasKumarSinha I'm doing an online one simultaneously with work ... cough cough .. Sorry I mean simultaneously with "no work"

@ACuriousMind my question was actually inpired by Luboschs answer here: physics.stackexchange.com/questions/105201/…
where he writes: "Even if one calculates the simple question what the density of dots will be on a plate in the double slit experiment, the probability current is directly relevant for that. Somewhat sloppily, one might imagine that the distribution of the dots matches 𝜌. But it's much more accurate that it matches 𝑗𝑛, the normal component (to the plate) of the probability current. "
These two functions of 𝑥,𝑦 are only proportional to each other assuming that the speed of the particle is "constant" everywhere. If it's not, 𝑗𝑛 gives the more correct representation of the "density of dots" than 𝜌."

@Rudi_Birnbaum Sorry, I think I've entirely misunderstood what this was about. Lubos' answer is the correct answer to what I thought you were asking.

5:46 PM
@AbhasKumarSinha If u wanna know which one to do (amongst these online courses) .. I'm not the right guy to ask :((

@ACuriousMind No his answer was just my starting point.

yesterday, by PM 2Ring
@MoreAnonymous BTW, using words like wanna, lemme, and txtspk like u & ur makes you sound like a little kid. As the chat room rules say, we're supposed to avoid txtspk here. The occasional word is ok, and some common internet abbreviations like IIRC & BTW are ok too. But please try to avoid that other stuff.

@MoreAnonymous For me, NPTEL is enough, I already have completed a lot of books related to Deep Learning and I'm updated with journals by different publications...

Let me maybe re-iterate that this was not just a personal request from PM2Ring but we actually expect people in this room to generally avoid text-speak, especially when asked by other users to do so.

@ACuriousMind Totally forgot about this ... My bad .. Also why is kid a negative connotation .. I love the idealism of youth

5:48 PM
@ACuriousMind yrs, k

@ACuriousMind I asked myself if there is any special way to the conduct the experiment such that it in deed measures rather the density than the current.

@AbhasKumarSinha I don't read books (on this subject) ... I just watch an online lecture, take a quiz (4 hours before deadline) and do a project 4 days before deadline ..

@MoreAnonymous I'll be working on an AI to generate Music of it's won (actually whole song) using ML

@MoreAnonymous Try to remember it, then. And while you're at it, stop littering '...' all over the place. Ellipses are not standard punctuation to end every sentence with! It's distracting to read and makes it harder to determine where your sentences actually end.

5:52 PM
@MoreAnonymous From where these genius people come XD heheh :)

@ACuriousMind That's my standard trademark. It actually shows my thought-process I'm pausing and jumping to the next point I wanna make :P

@ACuriousMind Pistaphobia

@AbhasKumarSinha Genius? I thought it was entertaining but c'mon. I was hoping for soooo much more in the title

@MoreAnonymous "Genius" in other way! :P

@Rudi_Birnbaum Be careful to remember that the experiment only measures the current (or rather its integral over time and particular surface) in the limit of infinitely many particles (you can't really reconstruct the $P(x,y)$ probability density on the screen from a bunch of dots, you have to fit it to some guess you get from elsewhere...)

5:55 PM
@ACuriousMind Don't worry I'll use the chatroom as practice to write grammatically correct stuff which reflect my ideas more accurately :((( Anyone who sees me slipping into my old habit feel free to to call me out?
@AbhasKumarSinha So in the IQ distribution one end is "genius" ... The other end is "dud"

ROBOPHOBIA VS TECHNOPHOBIA
@MoreAnonymous Genius in being crap, I meant

@AbhasKumarSinha It's an original joke! Seriously I thought someone would have at least written a quirky article explaining the difference or something ...
@AbhasKumarSinha I'm curious about the origin story. Did you just memorise a lot of phobia words and between R and T words realise some redundancy in meaning?

@MoreAnonymous B4N, I've to complete my chemistry practicals and some homework stuff, I've not even purchased chemistry copy! lol
@MoreAnonymous Just skills like google XD

@AbhasKumarSinha I remember our school teacher bribing the external invigilator as I mixed chemical A with chemical B. Note: both chemical A and B were water :P

@MoreAnonymous btw, you might be interested in this paper - openreview.net/pdf?id=Syx_Ss05tm , this was my approach... use neural nets linearly and use fuzzy sets in both back and front of inputvec and outvec node vectors.
@MoreAnonymous which school?

6:04 PM
@AbhasKumarSinha Well we had boards in 10th and 12th. It happened in both my schools DPS and Amity

@MoreAnonymous Our Practicals will be happening externally, not sure where's the center of examination. Forget bribing, you can't even peek your shoes at the exam center, they'll throw you out of the hall. No belt, no jeans, I'll just wear shorts and a T shirt, that's what I planned
@MoreAnonymous oh, okay, we've boards in 12th
@MoreAnonymous You were very lucky then... I don't like chemistry practicals, chem sucks :(

I remember it was like Chemical types C + D -> E + F.
But sometime E + F gives nothing!
There were too many exceptions didn't like it :(
Loved physics though (remember studying alot of classical mechanics for iit)

for you, hbar:
what happens if you take a High-overtone Bulk Acoustic Resonator and you make it quantum?

the...hbarbar?
Only an hbarbarian would come up with such an idea

@MoreAnonymous that's what I'm doing

6:13 PM

@EmilioPisanty cool. I don't know what it is, or whatever, it's still cool.

@AbhasKumarSinha basically, quantum mechanics with phonons

@EmilioPisanty wow, now it's even cooler :)

@AbhasKumarSinha Ah. Well if your studying for iit my advice I would give myself is "dont study for it". Your efforts are much more well rewarded if you try some other international scholarship and leave for university abroad

@MoreAnonymous Bro, being an IITian is itself a big reward which no other institution can give you.

6:16 PM

@MoreAnonymous seen that, don't care
@MoreAnonymous when you can do something, just don't think. Do it
personally, I don't find IIT Advanced questions very hard.. They are still easy for me

@AbhasKumarSinha Bro. I know how you feel and probably the pressure too. I was one of the top ranking students of my IIT coaching institute. It's really not the endeavor. It comes down to speed in the end and intelligence or insight.

@MoreAnonymous who cares? I'm doing this for fun. The pressure is what I love! Just don't like everyday dull.

@AbhasKumarSinha Any way don't want to dissuade you. Life isn't a race like the indian society makes it seem.

@MoreAnonymous No... I know what you mean by "Indian society". I'm not doing for that reason. I've other secrets (personal) reasons well.

6:20 PM
@AbhasKumarSinha I wanted to be a physicist at the time. IIT did help me get closer but there were other better ways

@MoreAnonymous Good for you. IIT != Physicist. IIT = Startups/innovation/technologies

@AbhasKumarSinha Whatever they are. I hope they make your journey worth it. Regardless of the outcome

@MoreAnonymous appreciate that.

@AbhasKumarSinha I really don't think I had better options at the time. My parents didn't want me to be one and I'd secretly dream of it.

@MoreAnonymous You could have visited IISc

6:24 PM
@AbhasKumarSinha I am aware but my parents wanted IIT with a good rank so Id get a high paying job

@MoreAnonymous cricket ka shaq hai?

Im acutally the one Indian who doesn't like that sport :P
Firangi's would ask me to play with them in the UK and I'd say no :P

@MoreAnonymous how come this man is pure desi! XD :P

Does any think the top Sabine is wearing looks familiar? As though it was used in some hollywood movie or something? youtube.com/watch?v=2EJZkslpoS4
Nevermind, had a closer look. Seems to Indian-y dyed for a Hollywood movie

In proving the Schrodinger equation
I want to simplify this expression

$im[{\hat {H}},{\hat {x}}]=\hbar {\hat {p}},\qquad i[{\hat {H}},{\hat {p}}]=-\hbar V'({\hat {x}}).$

to this

$m{\frac {\partial H(x,p)}{\partial p}}=p,\qquad {\frac {\partial H(x,p)}{\partial x}}=V'(x),$

I used conversion from position to momentum space,

$[{\hat {H}},{\hat {x}}] = {\hat {H}}{\hat {x}} - {\hat {x}}{\hat {H}} = {\hat {H}}{i \hbar \frac{\partial}{\partial p}} - i \hbar \frac{\partial}{\partial p}{\hat {H}}$

6:52 PM
@AbhasKumarSinha I think the problem was I played "Maar-in Piti" (Dodge ball equivalent but with a cricket/leather ball) as a child. This just made me hate the cricket ball dude. I was okay with the bat but was afraid of the ball. So effectively useless and no one wanted the useless player on their team. :P

@Student404Mus That's because it's not true!

> In proving the Schrodinger equation
what?
the Schrödinger equation cannot be "proved".

I mean its derivation

@Student404Mus it cannot be "derived", either

@AbhasKumarSinha you can guess what my first thoughts were when I saw this in the cinema: youtube.com/watch?v=xZ0OUq_kDh8

6:55 PM
@EmilioPisanty look at this en.wikipedia.org/wiki/Ehrenfest_theorem
Derivation of the Schrödinger equation from the Ehrenfest theorems

anybody that tells you that that's what they're doing is... uh... telling you a vastly simplified cover story so they can get to grown-up QM, get you some experience there, and revisit the fundamentals later

@ACuriousMind what is not true?

@Student404Mus that's not a derivation. At best, that's showing the equivalence between the Schrödinger equation and the Ehrenfest theorems. That's a radically different thing.

though frankly, if the most that you can derive is the Schrödinger equation for a hamiltonian of the form $H=\frac{1}{2m}p^2+V(x)$ for a massive particle, then you really haven't done that, either.
"the Schrödinger equation" implies a much broader class, with a much broader set of hamiltonians that do not need to be constrained to that form

6:58 PM
@EmilioPisanty The problem I'm facing is moving from the commutator to the differential form

@Student404Mus Your $H\frac{\partial}{\partial p} = 0$.
And that's because you have not understood how your commutator works.

@ACuriousMind ${\hat {H}}{\hat {x}} - {\hat {x}}{\hat {H}} = {\hat {H}}{i \hbar \frac{\partial}{\partial p}} - i \hbar \frac{\partial}{\partial p}{\hat {H}}$ breaks earlier, I think

The problem is the implicit order of operations. If you apply $[H,x] = Hx - xH$ to a momentum wave function $\psi(p)$, you need to apply the operators from right to left, i.e. $[H,x]\psi = H (\partial_p\psi) - \partial_p( H \psi )$.

or maybe not "break", but isn't supported by anything much.
-1

For example, the wavelength of radio wave ranges from 1 millimeter to 100 kilometers. Does any electromagnetic radiation exist which has wavelength more than 100 kilometers? If not, why?

Can you now spot where you went wrong, @Student404Mus?

7:02 PM
::sigh::

7:18 PM
@ACuriousMind yes, thanks for the hint!

0

I asked this question few months ago- Proof of Ohm's Law I was looking for a particular proof and explicitly mentioned it but still it was mod hammered even though the comments state that the questions being linked are different, unanswered and even not framed properly. Kindly reopen the ques...

2 hours later…
9:23 PM
How do you even begin to address the errors in this answer?

@Loong & @PM2Ring I think we've all come to a good conclusion. I thank both of you for your input and responses. I also appreciate the kind regards to help to not re-open the conversation. I know about the pinging problem. And I agree it should be used as per agreement, as sparingly and only as necessary. Pinging is not a toy and everyone should understand why.
@rob I just saw your message, if I remember correctly, was it about a star or a black hole?

@PM2Ring Flag as "very low quality"?

@Loong & @PM2Ring I kindly thank you for the courtesy. As I'm am sure other do.

@PM2Ring Sometimes I wonder if such accounts are troll accounts by users who love Stack Exchange. But then again who would waste their time creating a one time account for such purposes.

9:40 PM

### share an orbit

Sep 5 at 18:47, 2 hours 41 minutes total – 19 messages, 3 users, 0 stars

Bookmarked 13 secs ago by rob

9:53 PM
@PM2Ring Looks like an answer made by a machine learning algorithm trained on poor physics SE answers.

10:03 PM
@AaronStevens There's already plenty of that on the internet: wisdomofchopra.com
I feel Deepak Chopra can do the reverse-Chinese room by convincing a machine it's talking to a dumber machine
It also pays a million dollars
And for those of you who think the Clay prize is too easy I have just the sort of challenge you need: improbable.com/2014/07/09/…

@MoreAnonymous what pays a million dollars?

"Ig Nobel Prize winner Deepak Chopra is offering $1,000,000 (a million dollars) to any critic who can explain — to Dr. Chopra’s satisfaction " @MoreAnonymous oh ok. it reminds me of SAs$100K prize for QC impossibility proof lol (also recently cited by you)

10:22 PM
@vzn don't waster your time with this dude unless you have a sense of evil humor and like to see "Sam Harris" and "Richard Dawkins" at a sense of loss on how to explain anything to someone who believes the word is non-local and acausal because my version of quantum mechanics says so
I am under the impression after this one encounter they decided to limit their atheism movement away from India :P

@MoreAnonymous lol saw him live ~2007 boulder CO with a gf, my head didnt explode :P

10:47 PM
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