The h Bar

Jake Rose

00:25

Anybody any good with diffraction gratings?

Secret

00:54

I wonder if there is more to learn about nuclear atomic interactions. Also the possibility of a nuclear battery that is not radioactive is interesting

DanielSank

01:13

@Blue wat? This article doesn't show that the expected result is wrong. It shows that the student had crappy equipment and/or insufficient instruction.

vzn

01:46

Viewpoint: Quantum Computer Simulates Excited States of Molecule / APS physics

loocsieulb

@Phase it doesn’t really matter. lol

Phase

@Blue ya cant just ignore your comrade in blue

DanielSank

sigh

loocsieulb

02:28

science people let’s see you figure this one out. i turned off the heat in my apartment and my vents are not working but it does not drop below 17 degrees C even when it’s -15 outside.

why is it like this

i want cold

vents are not working because i closed them*

dmckee

04:54

But odds are that your neighbors don't and if you live in a affordable unit the adjoining walls and ceilings probably have little deliberate insulation in them.

So you're inadvertently driving their heating bills up.

Anonymous

05:33

@DanielSank 1) that my equipment is crap, as are all the available texts on the subject and 2) that this whole exercise was a complete waste of my time

Anonymous

@Phase What comrade ?

Cows

ok now I know why linked lists are important. I can move on now

loocsieulb

06:25

@dmckee am I though? because my unit is indented off from others. i don't have anyone beside me on any side (except for the hallway) but someone is below.

that's the weird bit

i would expect it to get cold because of that

John Rennie

06:42

@SirCumference No, energy isn't conserved in an expanding spacetime. This follows from the lack of time shift symmetry courtesy of Noether's theorem. Though having said this, it does depend on how you define energy.

Secret

06:55

I don't know how legitimate that post is, but what I learnt from a cosmology seminar is that gravitational entropy does weird things such as stars collapse further as it increases

Balarka Sen

07:05

@loocsieulb \o

dmckee

@loocsieulb Well, I was just guessing, but if there is little insulation between you and the unit below, you can get quite a lot of heating from them.

loocsieulb

07:22

@BalarkaSen heeeello

have to sleep now

@dmckee thats probably what it is

Slereah

07:52

mornin

Sir Cumference

@JohnRennie I know?

@Shing Oh wow...I meant to reply that to this, @JohnRennie...

John Rennie

Ah :-)

Cows

08:13

@JohnRennie I just discovered that linked lists are used almost everywhere you look

John Rennie

@Cows linked lists are something that IT beginners find cool when they first learn about them, and to be fair they do have their uses. However I think they are over used. There are lots of other ways of achieving the same end result.

You'd be surprised how often hardened ITers just use good old fashioned arrays :-)

Slereah

"Let $N^\pm$ be $C^3$ manifolds with boundary carrying $C^2$ metrics $g^\pm_{ab}$ of Lorentzian signature. Denote the boundaries by $\Sigma^\pm$ and let $\phi: \Sigma^- \to \Sigma^+$ be a $C^3$ diffeomorphism such that $$(i^+ \circ \phi)^*g^+_{ab} = (i^-)^*g^-_{ab} = {}^3g_{ab}$$where $i^\pm : \Sigma^\pm \to N^\pm$ are the inclusions. Assume further that the signature of ${}^3g_{ab}$ is constant.
Let $M$ denote the disjoint union of $N^\pm$ with $\phi$-related points identified; we will henceforth identify $N^\pm$ with their images in $M$ and denote the $(C^3)$ of $\Sigma^\pm$ in $M$ by $\S…

Gee talk about a mouthful

Although... Is it a sufficient condition or a necessary condition, too

I have an inkling that if one wormhole accelerates wrt the other, the two mouthes may not be isometric

at least as far as the timelike components go

Mithrandir24601

09:22

@JohnRennie Arrays are fast and easy to use - for many applications, what more could you want?

:)

Dawood ibn Kareem

@JohnRennie In the Java community, ArrayLists are used more commonly than ordinary arrays or LinkedLists.

Secret

09:35

Finally, math chat has gone [data expunged]. Release the demons!

I have been waiting for this forever

Slereah

10:34

I think by adding the requirement of isometry, you indeed get a time-shift from accelerating wormholes.

Given some generous simplifications, if two mouthes have positions $q_1(t)$, $q_2(t)$, then the time shift should be \begin{equation}
\dot{b} = \sqrt{\frac{(-1 + (\dot{q}_1^x(t))^2)}{(-1 + (\dot q^x_2(t))^2)}}
\end{equation}

The time shift being $b(t) - t$

Hence for stationary mouthes, $\dot b = 1$ so that $b(t) - t = 0$

That's the only gluing (given the simplifications) that is isometric

0celo7

13:38

@Slereah what on earth are you reading

Slereah

@0celo7 iopscience.iop.org/article/10.1088/0264-9381/4/2/010/meta

0celo7

Ok, CQG, carry on

Slereah

CQG?

0celo7

Class. Quant. Grav.

Slereah

o

0celo7

13:50

@Slereah I have 19 pages of the thesis done

it's coming along nicely

and by done I mean "done", like it's unlikely those pages will change much

I finally figured out how to format this thing

Slereah

All is good

Slereah

14:11

0

A: Wormholes & Time Machines - for *experts* in GR/maths

Let's consider the case of a thin-shell wormhole in Minkowski space $M = \Bbb R^{2,1}$ (We need at least two spatial dimensions for a proper wormhole without getting topology change involved). First we need to define two spacelike hypersurfaces $S_1$ and $S_2$. To simplify things, we'll conside...

Hopefully not too wrong

0celo7

@Slereah do you have a legal copy of wall

Slereah

it is available

Not too much interesting stuff for me but one of the only place with a decent chapter on gluing

0celo7

huh, there it is

last time I checked it wasn't there

but that was a year or more ago

Semiclassical

hrm. I'm having one of those moments where the result I have seems too strange to be right.

Mathematically, I think I can justify it.

But physically I'm at a loss.

Slereah

what is it

Semiclassical

14:26

So, I've got a spin-1/2 particle on a ring ($\theta\in[0,2\pi)$ with periodic boundary conditions on any solution)

The hamiltonian is $\hat{H}_\Delta=\hat{H}_0+\Delta \sigma_z$ where $\hat{H}_0=\hat{p}^2 I_2+(2\alpha\cos\theta )\sigma_z+\Delta \sigma_z$

ugh, I'll just take m=1/2 for convenience

oh derp. Should've had one of those pauli matrices be $\sigma_x$

yeah, let me have $\hat{H}_0=p^2I_2+(2\alpha \cos\theta)\sigma_x$

Since it's a periodic system, I can work in a basis of Fourier modes $\{e^{ik\theta}|m \rangle\}$ where $k\in\mathbb{Z}$ and $m=\pm \frac12$

ugh, why do I have to keep editing myself blaaagh

Anyhow. That gives
\begin{align}
\hat{H}_\Delta e^{ik\theta}|\uparrow\rangle
&= (-k^2+\Delta) e^{i k\theta}|\uparrow \rangle +\alpha e^{i(k+1)\theta}|\downarrow\rangle+\alpha e^{i(k-1)\theta}|\downarrow\rangle\\
\hat{H}_\Delta e^{ik\theta}|\downarrow\rangle
&= (-k^2-\Delta) e^{i k\theta}|\downarrow \rangle +\alpha e^{i(k+1)\theta}|\uparrow\rangle+\alpha e^{i(k-1)\theta}|\uparrow\rangle
\end{align}

not sure why that look so bad, bleh

If i go to an infinite matrix representation, I can write that as...

\begin{pmatrix}
\ddots\\
\cdots & -k^2+\Delta & 0 & 0 & \alpha & \cdots \\
\cdots & 0 & -k^2-\Delta & \alpha & 0 & \cdots \\
\cdots & 0 & \alpha & -(k-1)^2+\Delta & 0 & \cdots \\
\cdots & \alpha & 0 & 0 & -(k-1)^2-\Delta & \cdots \\
\ddots
\end{pmatrix}

agh

...okay, this is just too tedious

vzn

16:08

Picture of a Single Atom Wins Science Photo Contest / petapixel

2

Interpretive cards (MWI, Bohm, Copenhagen: collect ’em all) / aaronson blog

↑ aaronson retackles QM interpretations in his distinctive style. very lively debate by audience, over 300 comments! o_O

Semiclassical

my main problem with a discussion like that is that it's tough to sort the wheat from the chaff

Slereah

Semiclassical

16:26

the other trouble is that a discussion like that is less a chain (each post responding directly to the one previous to it) than a tree (multiple chains in parallel)

vzn

@Semiclassical lol sometimes science is messy :P

Semiclassical

eh, this isn't even science being messy

dmckee

Offered without comment:

0

Q: How to start on General Relativity

I know the basics of General Relativity and most of the theory, but I want to understand how to prove it mathematically, most exactly I want to understand the Einstein equation (and all that implicates) and gravitational field; and which could be the relative similar for Newton's gravity equation...

Semiclassical

it's that the message structure enforced by that particular forum is in conflict with how the discussion is practiced

vzn

@Semiclassical uh, look at the core topic. ("the one that shall not be named") think its unresolved among pro physicists for decades. even nearly a century at this pt.

Semiclassical

16:31

...ok? that's not what I was addressing

I was addressing why it's hard to follow the conversation there

vzn

@Semiclassical a large melting pot of views is hard to view almost anywhere. maybe reddit has the best interface possible for such a variegated/ diverse stew. (with the indented replies, comment voting, ranking etc, fmt evolved over many yrs now)

Semiclassical

Yeah, the reddit format would be more useful here

vzn

signal vs noise is a general challenge on the internet/ cyberspace all over. and its reaching (very) high degrees of significance eg facebook/ election influence etc

Semiclassical

The other problem I have is that, while I'm broadly sympathetic to the dBB point of view, I feel like the main representative of dBB in that conversation comes off as rather polemical

vzn

yes unf different ideas are espoused by people, who have personalities... and sometimes that all gets mixed up... although, sometimes not a bug, but a feature... ps really appreciate your not-so-common openmindedness on the subj... :)

Semiclassical

16:35

it's a fact of life

vzn

@Semiclassical think aaronson is lucky to have such a lively following...! but hes put a lot of energy into blogging over the yrs... (not entirely unlike other colorful personality lubos motl in that regard!) occasionally maybe even at some significant personal expense...

Semiclassical

@vzn with one principal difference being that of personality :P

I could imagine having a productive conversation with SA. Not so much with LM.

vzn

@Semiclassical lol think they are not so dissimilar in various ways...

Semiclassical

eh. the level of vitriol is very different.

vzn

@Semiclassical lol he (LM) flamed me a few mos ago in comments for espousing the significance of P vs NP :P

Semiclassical

16:45

lol

0celo7

@Semiclassical but LM would be much more fun

Semiclassical

@0celo7 for you, maybe.

0celo7

He’d be great to have a beer with, provided you have an escape plan ready

vzn

@Semiclassical SA can be quite searing also. eg wrt Dwave, academics he thinks are NOT EVEN WRONG, etc... actually was just thinking, maybe a debate between LM and SA would be amusing... surprised they have not ~~attacked~~ challenged each other already... maybe missed it?

Semiclassical

they have.

at least at the blog level

vzn

16:48

Godzilla vs King Kong? Batman vs Superman? :P

Slereah

SA?

Semiclassical

scott aaronson

vzn

Shark vs Gorilla? stackoverflow.blog/2011/08/16/gorilla-vs-shark :P

Semiclassical

MONKEY VERSUS ROBOT

vzn

← flamed by LM over P vs NP... badge of honor! =D

Slereah

17:02

@0celo7 I have a doubt

0

A: Wormholes & Time Machines - for *experts* in GR/maths

Let's consider the case of a thin-shell wormhole in Minkowski space $M = \Bbb R^{2,1}$ (We need at least two spatial dimensions for a proper wormhole without getting topology change involved). First we need to define two timelike hypersurfaces $S_1$ and $S_2$. To simplify things, we'll consider...

Should it be

\begin{equation}
\dot{b}^2 = \frac{1}{1 - \dot{\vec{q}}_2(t) \cdot \dot{\vec{q}}_2(t)}
\end{equation}

Or

\begin{equation}
\dot{b}^2 = \frac{1}{1 - \dot{\vec{q}}_2(b(t)) \cdot \dot{\vec{q}}_2(b(t))}
\end{equation}

0celo7

No idea

I dont know what those are

Slereah

Well for an isometry $f$, is the formula $$g_{ab}(p) = g_{cd}(f(p)) \frac{\partial f^c}{\partial x^a} \frac{\partial f^d}{\partial x^b}$$

I guess so?

I'm not sure how it applies here, I should check some more

0celo7

It’s either that or the opposite lol

I’m in class rn

Slereah

np

0celo7

I can answer you in 8 hours

Slereah

17:07

I'll be dead in 8 hours

0celo7

Oh well

Slereah

fortunately in my answer I just used $\dot q$ as a constant so it doesn't change the result

DanielSank

@Semiclassical Agreed. Blog comment sections are usually pretty worthless.

Slereah

I should try to find out what the results are like for variable radius

I suspect that there's this Thing where the wormhole mouth closes too fast to cross

vzn

@DanielSank maybe thats why you have none? (blog comments)

Slereah

17:10

Or maybe not, I dunno

no_choice99

17:21

@EmilioPisanty which answer is exemplary in this question? physics.stackexchange.com/questions/295365/… both answers seem over the top of the mountain to me

I upvoted the least voted answer as I think it's the best

am I missing something. both are utterly good

ciao @EmilioPisanty ci sei?

DanielSank

17:42

@vzn I don't like the format. I'd rather let others link to the posts on better discussion sites (reddit, Stack Exchange, etc).

vzn

@DanielSank dont blame you. however SE is not so great for "discussion" (expressly/ generally rejected outside of chat) and reddit(tors) often doesnt/ dont like blogs. etc...

Emilio Pisanty

@ACuriousMind wait, the guy who came up with continental drift was called Wegener?

Alfred Wegener

Alfred Lothar Wegener (1 November 1880 – November 1930) was a German polar researcher, geophysicist and meteorologist. During his lifetime he was primarily known for his achievements in meteorology and as a pioneer of polar research, but today he is most remembered as the originator of the theory of continental drift by hypothesizing in 1912 that the continents are slowly drifting around the Earth (German: Kontinentalverschiebung). His hypothesis was controversial and not widely accepted until the 1950s, when numerous discoveries such as palaeomagnetism provided strong support for continental drift...

::savours the poetic coincidence::

or was it just a Name Is Fate thing?

Anonymous

@EmilioPisanty What is the coincidence?

Emilio Pisanty

@Blue dict.leo.org/englisch-deutsch/weg

DanielSank

17:58

> expressly/generally rejected outside of chat

Right, but then there's chat...

vzn

@DanielSank oh yeah, and blogs refs are frowned on sometimes in chat too :| guess blogs are the rodney dangerfield of cyberspace :P

Anonymous

@EmilioPisanty Ah, so Weg means path in path/road in German. I still don't get how that is related to continental drift :P Must be missing some reference

Slereah

Can't get no respect?

i am told that in his family tree, Rodney Dangerfield was the sap

Emilio Pisanty

@Blue well, 'path' with a bit of an emphasis on 'movement'

Anonymous

Oh, hehe

vzn

18:03

← (lol) relieved at least 1 person in room recognizes very dated humor "meme"

Slereah

I believe that back then they were still called "jokes"

vzn

@Slereah suspect you might be too young to have experienced his "jokes" 1sthand! but your extensive grasp of semi-obscure americana shines thru :)

Slereah

I'm afraid I had to watch him on the youtube!

Since I'm not a skeleton man yet

vzn

@Slereah RD might nowadays be nicknamed the low self esteem comic :P

Slereah

One thing I noticed is that he wasn't really the type of comic to weave intricate narratives

It was more of a ten jokes a minute kind of thing

vzn

18:07

@Slereah yeah there are somewhat like 2 separate styles wrt comics that way. so whos your fave american comic anyway?

Slereah

Carlin I guess?

vzn

wow, was just thinking of carlin myself. yeah one of the greats... very cynical/ jaded tho... (would fit right in around here) :o

Slereah

Yeah the edgy act gets a bit old by today's standard

but he has plenty of fine skits

(Favorite French comic is of course Pierre Desproges)

vzn

@Slereah BaSe/ 0celo7 seem to be carrying that on wrt the new generation™

Slereah

that is why it's old

I'm sure Carlin's stuff was very fresh in the 70's

But by the 90's everyone was doing that kind of humor

vzn

18:10

yeah he was very innovative in his style at the time

Slereah

And by now it can get a bit grating

vzn

"grating"? kinda like the h bar? :P

Slereah

The hbar is fine

although

"This user is suspended on the parent site and cannot chat for 12 days."

Tic toc

it's getting nigh

vzn

t minus 12 and counting... o_O

Emilio Pisanty

@JohnRennie duplicate?

0

Q: How can the antiparticle of Hawking radiation fall into the black hole?

According to the theory, when quantum fluctuations occur near the event horizon, one is absorbed and the other is emitted as hawking radiation But in order to conserve the energy the fallen particle must've been of negative mass We know that negative mass particles move in the opposite direction ...

black-holes antimatter event-horizon hawking-radiation qft-in-curved-spacetime

Cows

19:08

I'm going to sit here all day and go over every algorithm a cs major learns and corresponding interview questions

dmckee

::boggles:: Does anyone know when Stack Overflow started plastering your job title (presumably from Jobs) across the top of your profile?

Not that I've taken a lot of care to hide my Secret Identity (tm), but I generally like to keep a nominal line between my on-line and real-world identities as a signal that I don't want to contacted out of band.

Slereah

If you wanted to hide your secret identity maybe it was a bad idea to put your real name as a handle

skullpatrol

19:25

he's got a good point :P

(never too late to change)

no_choice99

19:38

sorry to be redundant @Slereah but can someone tell me whether this physicist is a crank or not? scholar.google.com/… he solved the solar neutrino problem, high Tc superconductor, introduced a new QM theory, a new thermodynamics theory, all within a year or so

he's highly cited

Cows

@dmckee damn I checked and they used big fat giant fonts too lolz. hehe. It's alright though I'm sure none will notice :P

dmckee

@Cows Interestin. I don't see your job title.

SO that may be something that is only presented to you. Or there may be a switch somewhere to toggle showing it.

Cows

@dmckee well, I'm a small potato so my job info isn't up there. I think perhaps it might be a feature for professors (and academics in general maybe) or something

dmckee

@Cows Ah. I take it you don't have a Jobs profile (or perhaps a Developer Story or whatever the newest whing-ding is)?

Loong

Reminds me that I should update mine

no_choice99

19:54

what do you mean @Slereah, where did I use my name

dmckee

@no_choice99 He means that my username consists of my first initial and last name. Which shows you exactly how much care I have put into hiding my secret identity.

Like I said, the nominal line is a social signal not a security measure.

no_choice99

ah ok, thanks a lot @dmckee

Emilio Pisanty

@dmckee I do see your title in your SO profile

no_choice99

why do I sometimes see the number of points a user has ever gained on the left of this chatroom

but not always

dmckee

@no_choice99 The neutrino paper is from 2016 (14 years after the Nobel for demonstrating that the solar neutrino problem really was a thing and 1 year after the prize for demonstrating the neutrino oscillation really was a thing). And it appears to be a thoroughly alternative treatment.

Emilio Pisanty

20:07

@no_choice99 it's compressed if there isn't enough room to display it

dmckee

Also 0 citations for that.

Emilio Pisanty

presumably the threshold is four lines and/or a oneboxed item

no_choice99

thanks guys

but it's strange that instead of showing the current number of points, the total ever gained is displayed instead

Emilio Pisanty

@vzn Gorilla

no_choice99

@dmckee he also came up with a new thermodynamics theory and wrote a lot of papers afterwards

for instance @EmilioPisanty you earned 88.2k points and your current is 67k points

Emilio Pisanty

20:10

also Gorilla vs (shark + hippo + crocodile + condor + another shark)

dmckee

So just clicking some links at random I see a lot of self-citations. Of course there is nothing wrong with self-citations (you should cite the work you are building on, after all), but when there are more of them than citations by others it looks like you are working in a back-water. Or worse.

Anonymous

@no_choice99 I guess it shows total rep (summed over all SE sites)

Anonymous

All the SE sites share the same chat system, so...

dmckee

Also the breadth of the topics is unusual. I would guess that this guy does some real science, but that doesn't mean that every one of those papers is good.

Emilio Pisanty

hmmmm, can't find the original image

there 'e is

winning

skullpatrol

20:18

is it blank on the back?

Anonymous

I want that t-shirt

Emilio Pisanty

@skullpatrol yes

Anonymous

@skullpatrol What are you expecting? :P

skullpatrol

dunno

Emilio Pisanty

@Blue the keyword you're looking for is 'sasquatchtron'

skullpatrol

20:21

I would put some sort of "slogan" on the back...

Anonymous

Goddamn, it's famous!

Semiclassical

@Blue what

@EmilioPisanty what

what

Anonymous

This is cool

Emilio Pisanty

@Semiclassical that is a drawing of a sasquatch being attacked by a condor, two sharks, a hippo and a crocodile, and looking rather unfazed by the fact

Semiclassical

20:23

i initially read that as "sasquatchton"

which I guess would be a very short-lived mythical particle?

Emilio Pisanty

I personally think it is quite obvious but the question "what?" does get asked quite often

Semiclassical

"Forget the God particle, I want to find the sasquatchton"

skullpatrol

yeah, the condor is not obvious :P

Anonymous

That fight is a bit unfair though. They put a baby shark in front of a gigantic gorilla

Emilio Pisanty

@skullpatrol it's clearer in person. the claws and beak are visible at the shoulders and head of the sasquatch

skullpatrol

20:25

I see.

::zooms it::

Emilio Pisanty

@skullpatrol if I recall correctly the original version was sans the condor, and that was added for the t-shirt

I can't find it in the original site, though

skullpatrol

yup, the original fades fast once these things go viral

Emilio Pisanty

@skullpatrol no, it's still quite tightly linked to The Best Page In The Universe, but I can't be bothered to take a deep dive into those archives

I used to find maddox funny when I was a teenager

that's kinda faded over the years

skullpatrol

Here's a Valentine’s Day Physics Poem

Semiclassical

@EmilioPisanty I think there's a lot of things one can replace 'maddox' with in that statement (and the next one) and have it remain true :P

Emilio Pisanty

20:34

@Semiclassical sure

but I mean, who doesn't miss 2003?

Semiclassical

lol

Emilio Pisanty

I mean, other than "bejeesus, it's been fifteen years since the Iraq war fiasco!!!???"

Semiclassical

oh, for the days when I felt like I could laugh at the president

the present scenario feels more like an old Lincoln line, that he felt "like the boy that stumped his toe,—‘it hurt too bad to laugh, and he was too big to cry.’” @EmilioPisanty

Slereah

Because it's not. — Slereah 9 secs ago

Best comment so far

skullpatrol

hmm, yesterday was Lincoln and Darwin's birthday

loocsieulb

20:43

@Slereah what about now?

Emilio Pisanty

@Semiclassical well, we've been in a 10-to-15k-dead-a-year civil war since the Bush years, so I sometimes struggle finding the US's present troubles all that terrible

Pieter

@dmckee Let's hope that he won't discover PSE...

skullpatrol

> Both lost their mothers at a young age: Darwin at 8 and Lincoln at 9. As adults, both watched children of their own die -- and suffered terribly over the losses.

no_choice99

@Blue I see! Thanks again

skullpatrol

@DavidZ isn't it a little late to be still wearing a christmas hat :P

but he got impeached

Semiclassical

20:49

uh

Emilio Pisanty

@Semiclassical yeah, I guess you can say the same about Vicente Fox

heck, he's even sorta come out and owned it, to a point

I mean

A New Message for Donald Trump from Former Mexican President Vicente Fox

►

that is just magic

Semiclassical

lol

skullpatrol

oops, that was Clinton

Phase

21:32

side note I have a bit of a dumb question but: is the reason for the position operator being $\hat X \vert \psi \rangle = x \vert \psi \rangle$ just because normally we work in a basis of position eigenvectors?

Semiclassical

i actually wouldn't write that. $\hat{x}\psi(x)=x\psi(x)$, sure

Since then psi(x) is explicitly the representation in position space

ArtOfCode

→ 6 messages moved to Trashcan

Semiclassical

But there’s no particular reason to assume that $|\psi\rangle$ is in position space

Phase

Oh right

ArtOfCode

→ 5 messages moved to Trashcan

When I say "done", I mean "done". Any further messages on the topic will also find their way to the trashcan.

Phase

21:39

You literally just deleted my response to Semiclassical

That wasn't even in response to the issue

I'd like my response to semiclassical back please

ArtOfCode

← 1 message moved from Trashcan

Phase

Thanks.

loocsieulb

@Phase hey now you're like vzn

Phase

@loocsieulb Idk man you're the one getting chatbanned

loocsieulb

the arrow dude

calm down

Phase

21:42

No, challenge me to a duel I shall defeat you

I play Little D, face down

loocsieulb

← is ready to "duel" (surprised you're asking for this)

Anonymous

@Phase Keep your nose safe ;)

Semiclassical

@phase you also see stuff like $\psi(x)=\langle x|\psi\rangle$ in texts though @0celo7 will protest (justifiably) that bra-x isn’t meaningful unless you change the rules a bit

Slereah

$\langle x | \psi \rangle$ is meaningful

As long as both are part of the Gel'fand triple

bolbteppa

(Time better spent ignoring this ridiculous notation and solving the Hydrogen atom in an external field in parabolic coordinates to look at the Stark effect :p)

I really hate quantum notation, ultimately just conventions

Semiclassical

21:50

It depends what you’re doing.

What I find convenient about Dirac notation is that I can avoid using so many subscripts

Anonymous

I found the bra-ket notation quite useful though while first learning. It's sort of "self-correcting" at times

Anonymous

@Semiclassical Exactly

Anonymous

@bolbteppa That wouldn't provide mental satisfaction to math students :P

Semiclassical

one thing I notice is that QM doesn’t use index notation nearly as much as GR for instance

It’ll use indices for components of classical vector quantities

Anonymous

I personally find the index notation very difficult to handle. Even for basic matrices I end up getting confused at times

Anonymous

21:54

Probably I need more practice

Semiclassical

It takes practice, yeah

I sorta like the idea of diagrammatic notation but in practice I dunno

Slereah

@Semiclassical you can use index notation in QM

It's rarely done but i've seen it

Semiclassical

Sure. It’s the status quo that I had in mind

Slereah

the big difference is that it's infinite dimensional

bolbteppa

It's a shame how complicated things get when you leave the realm of baby wave functions, e.g. the Harmonic oscillator path integral, getting the wave functions from this is pretty insane, haven't tried to write it up yet but it looks huge

and the hydrogen atom path integral, impossible

Semiclassical

21:57

The concept of the path integral is lovely

The technical details are not

Slereah

Feynmann Hibbs does the harmonic oscillator path integral

bolbteppa

Yeah, he makes a comment about how it's tedious to get the wave function directly, then gives a trick which is still crazy heh

Slereah

They do the general case $L = a \dot x^2 + b x^2 + c x + d$

Semiclassical

Thank goodness for Gaussian integrals

Slereah

yeah things become tricky once you leave the Gaussian case

ie impossible

bolbteppa

22:00

'Feynman told me during a discussion how embarrassed he was, not being able to solve the path integral of this most fundamental quantum system' (hydrogen)

Slereah

I think Kleinert does it for hydrogen

Or Grosche

the tricky part is doing it in spherical coordinates

there are technical pitfalls

Hans

Guys you know how to answer this question physics.stackexchange.com/questions/386119/… ?

It has been bugging me for quite some time

bolbteppa

users.physik.fu-berlin.de/~kleinert/kleiner_re65/65.pdf

Slereah

Yep

Good old Kleinert

He wrote a giant brick on path integrals

Semiclassical

I’d like to know more about the coherent state path integral

There’s nice stuff there, but it’s beyond me

bolbteppa

22:15

Up to equation 8 I can vaguely follow, but from 9 on wtf

Slereah

22:31

Apparently Poisson's notes on the junction condition seem alright

peterh

23:27

Anyone has an idea, what makes this question homework-like?

2

Q: Dependency of $\mathrm{H_2O}$ surface tension on vapour pressure

How is does the surface tension between: liquid water, and humid air depend on $\mathrm{H_2O}$ partial pressure in the air, and temperature? Edit: I assume that temperature and humidity will both lower the surface tension. But I'm searching for equations to quantify this effect. I was t...

thermodynamics surface-tension

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