The h Bar

GPhys

13:00

oh well then my solution would still be fine

although I still don't understand how to go from such inner product to that being the component up to a sign

0ßelö7

@GPhys because you select the component of e_1 by orthogonality, but with a factor +-1 because of the inner product involved

I'm sure @ACuriousMind can explain, I'm in class

Secret

-1

Q: What would happen if the delayed choice quantum eraser experiment was both observed and unobserved?

What I was wondering is if this experiment was conducted, but two people chose the results. The two people would be completely isolated with no knowledge of eachother, and would each choose to observe or not observe the data. Would the results instantly be those of a particle for both if one pe...

It really depends on whether the entangled state is projected away

also c.f. Wigner's friend

Semiclassical

13:22

so, this question is over on MSE:

1

Q: Why Fokker–Planck equation and path integral are equivalent and when?

Why is Path integral equivalent to Fokker–Planck equation, the notion here is unclear to me. Under what assumptions does it hold and why they are similar? In here it says that it's equivalent to Schrodinger equation which makes me even more confused.

mathematical-physics stochastic-pde

i'm trying to decide whether to vote to close, or whether it should be transferred to Physics.SE. as written, it's quite thin and not motivated.

(I haven't done any votes period yet.)

GPhys

He talks about the norm of the g(V,e_(1)) in a way that must mean the parts in the -1 part of the metric pick up a negative sign - is it correct notation to write the magnitude of the |g(V,e_(1))|^2? How should I write it

Semiclassical

@JohnRennie "...for tomorrow we go back to grading" is the TA version of that.

GPhys

I was going to write something like $g_{11}V^1V^1$ and then write below it that it was in the e basis

ACuriousMind

@Semiclassical Since it gives no physical context whatsoever, we would probably debate whether to send it to math.SE if it was posted here. If you'd vote to close it for any reason other than "it's physics", then just vote to close - remember the golden rule of migrations.

0ßelö7

@ACuriousMind Someone commented on my wave equation question with exactly what I had in mind. Guess I don't suck at GR after all.

Secret

13:27

The Fokker-Planck equation looks like stochastic process stuff. In addition, the path integrals don't look like those in QFT

user307388

The torus is $\mathbb R^2/ \mathbb Z^2$ ?

Secret

so the path integrals are likely stochastic path integrals instead of the QFT ones

0ßelö7

@MathAminPhysics yes

user307388

Why?

0ßelö7

@GPhys what you're doing sounds right, I think, but trying to figure it out on a phone isn't working. I'll take a look when I get home

Feel free to just send me the LaTeX solutions, I'm always happy to read GR

ACuriousMind

13:29

@Secret The QFT ones are stochastic ones (where they are rigorously defined).

GPhys

I'm almost completely certain the proof concept is right, but I'm just trying to figure out my notation

Semiclassical

@ACuriousMind Well, I actually like the question (despite the poor framing of it).

0ßelö7

@MathAminPhysics That's literally the definition.

Semiclassical

And I do consider it to have physical content...just not well-explained at all

ACuriousMind

@Semiclassical Then you could consider editing it to make it better, then vote to migrate

0ßelö7

13:30

Do you know the polygon construction of 2-surfaces?

Semiclassical

Yeah, that's fair.

I don't care enough to do that, alas.

user307388

No.

Semiclassical

So it's a moot point :P

Secret

@ACuriousMind Ok nvm, I must have mixed them up with this:

chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/…

0ßelö7

ACM is ignoring me so he won't help. Google "torus via gluing" or something @MathAminPhysics

ACuriousMind

13:33

@Secret Huh? That's precisely the kind of path integrals that appear in QM/QFT. The point is that these are the same as the stochastic ones - the standard QM integral integrates over the Wiener measure, which is the stochastic integral of the Wiener process (better known to physicists as Brownian motion).

user307388

I know its definition via gluing. But I do not know why that definition equals to $\mathbb R^2/ \mathbb Z^2$ .

0ßelö7

You're just periodically identifying parts of the plane. @MathAminPhysics do you understand what the implied action of Z^2 is?

And what a quotient group is?

Semiclassical

The Wikipedia link provided by the poster of said question is relevant: en.wikipedia.org/wiki/Langevin_equation#Equivalent_techniques

Secret

I guess I have a poor background on them (and statistics in general), I thought that those that is used in chemistry don't contain field (operators) and thus they are different from those in QFT (which has fields in them)

ACuriousMind

@Secret The path integral formalism is precisely the formalism in which the fields are not operators.

user307388

13:36

identifying the $\mathbb Z^2$ in $\mathbb R^2$ with the identity element

Secret

Aren't the creation and annhilation operators that appeared in QFT integrals part of the field.
.... nvm, I need huge revision

0ßelö7

Not quite, you identify points that differ by an element of Z^2

Semiclassical

I'm forgetting stuff as well, unfortunately. I imagine there's a dictionary to be made

user307388

The set of those points is isomorphic to $ \mathbb Z^2$, I think.

0ßelö7

No.

Semiclassical

13:41

something like QM : statistical physics :: Schrodinger equation : Langevin equation

But I'm not sure about that, and I don't remember what the analogue of Fokker-Planck would be.

user307388

My definition of that quotient group was wrong?

Semiclassical

or maybe FP is what's analogous to the Schrodinger equation? Ugh, it's been a while since I thought about this stuff

0ßelö7

That set is uncountable, it's not going to be isomorphic to a countable group.

Semiclassical

pah, I mutter that nonsense out loud and then I find this remark on the Fokker-Planck page: "A derivation of the path integral is possible in the same way as in quantum mechanics, simply because the Fokker–Planck equation is formally equivalent to the Schrödinger equation"

Secret

well.... I don't even know what Langevin equation is. Are physics graduates supposed to know about stochastic stuffs when they learn statistical mechanics?

If yes, then my old uni does a very poor job at teaching it because they said nothing about stochastics

0ßelö7

13:45

I would think a proper course in stochastics goes well beyond the math that physicists know.

Semiclassical

I think it's usually reserved for grad-level treatments

user307388

Thanks.

0ßelö7

@MathAminPhysics I think you need to draw a picture

Secret

Even though I always ramble about how hard number theory is to me, the maths subject that I have litterally no background on is nearly all of stochastics

0ßelö7

Draw R^2 and Z^2, then pick a point and check which points end up in the same equivalence class when you take the quotient.

Jasper

13:48

@0ßelö7 The book Knowing the Odds by Walsh treats elementary probability, measure-theoretic probability, discrete stochastic processes and continuous stochastic process all in one, if you are interested.

Semiclassical

What one counts as 'knowledge of stochastics' also varies quite a bit

for instance, most physicists will certainly not have seen a rigorous treatment of it

Secret

Sounds a nice thing to add to my reading list

Semiclassical

by contrast, I think a lot more physicists would know there's a relation between statistical field theory with temperature T is related to a quantum field theory over an imaginary time $iT$.

e.g. the answer here: physics.stackexchange.com/a/35136/55641

0ßelö7

@Jasper no time for more books

Anonymous

14:17

@0ßelö7 That's what I tell people nowadays when they suggest me new books :P

0ßelö7

@Blue have you read 5 volumes of spivak and 4 volumes of Reed and Simon yet?

Anonymous

@0ßelö7 Yeah, but in another universe.

Mithrandir24601

@0ßelö7 Always time for more books

Anonymous

I wonder which textbook I fully completed reading...

Anonymous

Probably not in the last 5-6 years...

Mithrandir24601

14:39

@Blue I think the only textbook I ever read cover to cover was the one I got for A level further maths

John Rennie

@Semiclassical :-)

@Blue disk is in the post!

Anonymous

@JohnRennie Wow! :D Did they give any link to track the parcel? :)

John Rennie

@Blue no. I sent it using the el cheapo post. It you want tracking it increases the price a lot. Give it ten days. If it never turns up then well, I tried.

Anonymous

@JohnRennie Oh, that's fine. I hope you weren't troubled much. :)

Anonymous

I informed my parents. They'll collect it in case I'm not at house at the time of delivery

John Rennie

14:45

It's just in an envelope, so if you're not in presumably the postman will just put it through the letterbox. It doesn't need to be signed for.

Phase

What's Mathjax for the font used in the Laplace transform?

Anonymous

@JohnRennie Oh, cool!

Anonymous

@JohnRennie My mom was shocked when she heard someone from Europe is sending me a SSD :P She thought you might be a kidnapper or something who is tricking me into revealing my address. lol :'D

John Rennie

I'm secretly a supervillain!! :-)

Semiclassical

what a tweest!

0ßelö7

14:54

@Blue that's what my family thinks Bernardo is

@Blue there's not a lot of reason to read a book absolutely 100%

Anonymous

@0ßelö7 Oh, I'm pretty sure @BernardoMeurer kidnaps people and asks for booze as ransom.

2

Balarka Sen

@Semiclassical what brings you to this broken place

go back to where you came from outlander

Semiclassical

pfff

Balarka Sen

this is the place for the dying men, the diseased men

go back

Semiclassical

tsk, you missed an opportunity for a TS Eliot line

"we are the hollow men/ we are the stuffed men"

Balarka Sen

15:04

that's what brought me the idea but i didn't want to quote him :P

Semiclassical

fair enough

John Rennie

@Semiclassical it's certainly a wasteland :-)

Balarka Sen

that's from the hollow men actually

Semiclassical

[insert reference to particle physics desert here]

0ßelö7

@BalarkaSen implying math chat is better

Why are you here anyway?

John Rennie

15:07

@BalarkaSen Shrug. The only bit of the wasteland I've actually read is the Consider Phlebas bit, and only then because I'd read the Iain M. Banks novel and was curious about the quote.

0ßelö7

At least if you did something like TQFT you'd belong here

Balarka Sen

@JohnRennie I actually retroactively like "Death by Water"

Semiclassical

hard to top 'what the thunder said', though

Balarka Sen

Of course

I'd probably list that bit at the last if I had to rank all the chapters

Semiclassical

at the top or the bottom? it's probably at the top for me

Balarka Sen

15:08

by "that" I mean "Death by Water"

Semiclassical

ah

I like Death by Water more than I like the Fire Sermon, if only because the latter feels like it goes on for a bit too long

Balarka Sen

Fire Sermon is amazing to me, especially the paranoid conversation at the end

Semiclassical

though there are bits of the Fire Sermon which do stick out to me, especially near its end

which?

"my feet are at moorgate, and my heart under my feet" ?

Balarka Sen

Ah sorry I confused with A Game of Chess

Semiclassical

I wondered if you had, heh

Balarka Sen

15:10

actually I like the beginning of Fire Sermon

Semiclassical

like I said, I mostly remember the end of it

Balarka Sen

but yeah I probably agree with you that it sticks with me less than the other things

Semiclassical

the Tiresias part never really stuck for me

Balarka Sen

right

that part is pretty horrid

Semiclassical

I think that part of the poem reflects less Eliot as poet and more Eliot as...eh, how to put it.

class prejudices, I guess.

plus a general discomfort with human intimacy

Balarka Sen

15:15

I agree

Semiclassical

he's comparable to HP Lovecraft in that regard, except that Eliot moved out of that mindset more as time went on (compare his first and second marriage)

(I think one could make a good article out of comparing Lovecraft and Eliot, though the differences between them are also pretty clear)

Balarka Sen

I haven't read a lot of Lovecraft but I do know he's a luminary in the horror world

Semiclassical

which is funny if only because Lovecraft also wrote this: hplovecraft.com/writings/texts/poetry/p228.aspx

Balarka Sen

lool

what is that

Semiclassical

a parody of the Waste Land, and a rather mean-spirited one at that

Balarka Sen

15:19

is that really a parody of The Waste Land

Semiclassical

check out the last line if you're skeptical

Balarka Sen

snip'd

oh man why

@Semiclassical yeah I did

Semiclassical

looks like there's a senior thesis comparing them here: commons.emich.edu/cgi/…

first page of text has some relevant biographical comparison

Balarka Sen

recite this at my funeral, this is an insane piece of poetry loool

Semiclassical

lol

skullpatrol

15:24

lo

John Rennie

I've read everything HPL wrote, and very entertaining it is even though it's complete rubbish (clichéd rubbish at that!).

I've read snippets of T S Eliot, but it's so far up its own alimentary canal that I found it completely opaque.

To compare the two in an essay seems a curious task to attempt.

Balarka Sen

loool

Semiclassical

Eh, there's some good basis for it IMO

user228700

@BalarkaSen Thanks.

Balarka Sen

well you have the literary taste of a hipster so there's that

John Rennie

15:26

Rarely have I been accused of any hipster qualities :-)

Secret

[Autoupdate lagrangian] Turns out trying to write a lagrangian that builds itself some time interval later when a certain time interval is reached is harder than I expect... hmmmmm

Semiclassical

for one, they both came from old New England families, so there's a similitude in cultural perspective. (though Eliot definitely came from a bit higher strata in that regard, and Lovecraft was a bit older)

Balarka Sen

@Kaumudi.H Sorry about that :P

user228700

:-P It's OK.

user228700

I'm going back tomorrow! :'-(

Balarka Sen

15:28

I haven't really read a lot of classic horror fiction actually; my knowledge on that is restricted to Poe, which I love and adore

I should maybe

Semiclassical

That essay mentions Poe as a common influence, amusingly enough

Balarka Sen

yup

Eliot has a critique review on Poe that I found entertaining

user228700

@JohnRennie Oh, why must you be so impressively eloquent while I remain a babbling, bumbling, babboon?

Balarka Sen

and he literally influenced nearly all the horror writers through the century so no wonder it was an influence for Lovecraft

Semiclassical

yeah

you should read that article, you'd probably appreciate it

Balarka Sen

15:31

Let me bookmark it

Semiclassical

kk

John Rennie

@Kaumudi.H (a) I've been practising for 56 years and (b) it's my native language. I doubt I'd be eloquent in Hindi. Actually the only words I know in any Indian language are some Urdu swear words that my father taught me :-)

Balarka Sen

Semiclassical

it's not as fully developed as I would like, but it's not bad

Secret

One of the things I want to do is something that is like this:

(In pseudocode)

Balarka Sen

15:32

I don't know why I have so many Poe memes in my meme stashes

user228700

@JohnRennie Ah, but I wish that it were my native language as well!

Sid

@JohnRennie Are there words that you don't know? :P

Semiclassical

As a very thin gloss, what I think unites Lovecraft and Eliot is an appreciation for mythology

user228700

And I'm not at all anything remotely close of eloquent in Hindi!

user228700

My only hope is to become eloquent in English, for my Malayalam also sucks.

Semiclassical

15:34

Whereas what divides them is that Eliot ultimately is a Christian and Lovecraft an atheist, both avowedly so

Sid

Also, for some reason, my seniors told me I am pretty good in English and Hindi although neither is my native language

Balarka Sen

@Semiclassical It seems to reference the essay review on Poe that Eliot wrote, "From Poe to Valery"

Semiclassical

@BalarkaSen makes sense

One thing that the both have in common, unfortunately, is varying degrees of prejudice

Balarka Sen

yikes

user228700

@JohnRennie Here, let me teach you some Malayalam: Nah-ma-scar-um is "Hello" :-)

John Rennie

15:35

@Kaumudi.H നന്ദി

Sid

@Kaumudi.H Isn't Malayalam basically adding "Um" to the end of normal hindi words? Or is that Sanskrit?

Semiclassical

both of them were responding to what horrified them about the modern world, and that sometimes clashes pretty badly with modern sensibilities

user228700

@JohnRennie Ah, haha, yes, you're welcome! :-)

Semiclassical

(in lovecraft it's evident in his published works. in eliot it's less so, but in his unpublished work there's some pretty bad stuff.)

user228700

@Sid It is strikingly similar to Sanskrit, yes, but that rule doesn't apply, no x'D

Balarka Sen

15:37

I haven't read any of his unpublished works but I can easily see what you mean

John Rennie

@Kaumudi.H my Knowledge of Google somewhat outweighs my knowledge of Malayalam :-)

user228700

Of course :-)

Anonymous

@Sid Your name would have been Sid-um and mine would be Blue-um in that case. :P

user228700

@Blue -_-

Anonymous

The best ones would be John Rennieum and Kaumudium

user228700

15:38

@Blue No, both of you would have been immediately nicknamed one of Appu, Kanna or Unni.

Anonymous

@Kaumudi.H :D

Sid

@Blue LOL. Yeah yeah...

Balarka Sen

irrelevant quibble: there's a renowned Bengali poet which started poetic modernism in Bengal and was very influenced by Eliot.

ACuriousMind

@Blue These are clearly the names of new chemical elements, not words.

John Rennie

Kaumudium - element number 120

user228700

15:39

Lol.

Secret

Define L(t) as lagrangian
#Initialisation
t=0
t_1,t_2,...
U_i(t) for i in {1,2,3,...}
L(0)=1/2mv^2
if t = t_1
L(t_1)=L(0)+U_1(t_1)
if t = t_2
L(t_2) = L(t_1)L(0)+1/2mv^2
increment t

Sid

Isn't that supposed to be Unbinium or something similarly weird? :P

Balarka Sen

Unbinilium I think

John Rennie

Unbinilium

Unbinilium, also known as eka-radium or simply element 120, is the hypothetical chemical element in the periodic table with symbol Ubn and atomic number 120. Unbinilium and Ubn are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkaline earth metal, and the second element in the eighth period. It has attracted attention because of some predictions that it may be in the island of stability, although newer calculations expect the island to actually occur at a slightly lower...

user228700

^

user228700

15:41

@Blue And if either of you are secretly girls, equivalent nicknames would be Ammu and ponnu.

Secret

basically, the idea is to define some initial guess lagrangian at step 0, then after some time t1, update the old lagrangian with a potential energy term starting at t1

user228700

I, for one, am called Ammu at home. It makes no sense at all. ::Facepalm::

Balarka Sen

(I wonder if @blue can guess which poet I am talking about up there, given that he's almost a bengali)

Secret

and then when time is reached t2, the new lagrangian is constructed by adding the lagrangian at t0 and that at t1

Sid

@Kaumudi.H Well, i am not. And Unless @blue is a wonderful liar and takes real pain to fool people, blue is a "he" too.

Secret

15:44

So the dynamics should be numerically calculated by starting with a simple lagrangian, and then update it with more and more complicated potential energy terms as time progress

user228700

@Sid OK :-P

Anonymous

@BalarkaSen Tagore I suppose (?)

Secret

So, even though the whole dynamics took place in the interval [t0,tn], the lagrangian in that interval will change in the computation because it is recursively updated by solving some equation numerically

Balarka Sen

lol naw tagore is far from modernism

he's a romanticist

user228700

@BalarkaSen Ewww (:-P)

Anonymous

15:46

Well, Tagore did mention Eliot in some essay iirc

Secret

Let me check if there are examples...

Balarka Sen

@Blue Yeah

Anonymous

@BalarkaSen :P Then I need to think

Balarka Sen

but he had very little influence on him

@Kaumudi Well there are some good Romanticist poets out there

Wordsworth is one

most of it is just too corny for me

John Rennie

I wandered lonely as a soliton

4

Balarka Sen

15:47

lol

user228700

x'D

Balarka Sen

@Blue I had ya boi Jibanananda

in mind

user228700

@BalarkaSen Presumably, for me as well.

Anonymous

@BalarkaSen Huh. Too hard for me to guess. Have been out of touch with Bengali literature for atleast 2 years :P

Balarka Sen

@Kaumudi.H I like Blake instead, who declared major war against the Romanticism in 19th century

10/10 stuff

user228700

15:50

I haven't read very much of his poetry.

John Rennie

My favourite poet is Ogden Nash. Which figures I suppose :-)

user228700

@JohnRennie It does :-) Some of his poems are quite amusing, I must admit.

Semiclassical

@BalarkaSen Eliot was also a bit of anti-Romantic, if memory serves

user228700

@BalarkaSen Recommend me a poem or two.

Anonymous

I used to read Roald Dahl's poems. They used to be funny.

user228700

15:53

Aug 30 at 16:16, by Balarka Sen

@Kaumudi.H Why don't you read books and watch movies

Balarka Sen

my favorite poetic work is James Joyce's "Chamber Music", which has title based upon the sound of urine tinkling in the chamber pot in Joyce's own words

John Rennie

@Kaumudi.H Hilaire Belloc - The Microbe

Balarka Sen

@Blue Roald Dahl is great

amazing guy

user228700

A+ advice. I'm taking my pile of books back with me.

Semiclassical

ah, Roald Dahl

pretty good books, pretty bad human being

Balarka Sen

15:54

lool

Anonymous

John Rennie

@Semiclassical Was Roald Dahl a bad person?

Balarka Sen

@Kaumudi.H what kind of things do you like

I can give you super hipster stuff which you might not necessarily enjoy

user228700

@BalarkaSen The vaguest question of all! :-P

Balarka Sen

@Semiclassical yeah he was more influenced by French surrealism

Secret

15:56

@Semiclassical Is there any context where one need to numerically estimate the lagrangian thus requiring some recursive updating algorithm to compute the lagrangian hence dynamics?

user228700

@JohnRennie No, no, I meant by William Blake! Still, I will look it up, thanks :-)

Balarka Sen

Rimbaud's "A Season In Hell" has had a great influence on The Waste Land

Semiclassical

@JohnRennie well, for instance: independent.co.uk/news/people/…

user228700

@BalarkaSen And Ruskin Bond? Dyou like his stuff?

Balarka Sen

@Kaumudi Oh you wanted Blake recommendations

user228700

15:57

Yeah.

Balarka Sen

"Visions of the Daughters of Albion"

user228700

Oh, that's mighty long!

user228700

I've bookmarked it :-P

Balarka Sen

very disturbing content, but it's a critique of the hedonism in 19th century, which is a surprising thing because Blake himself rooted for the free love movement

John Rennie

@Kaumudi.H The Tyger then. We all learned that at school.

Balarka Sen

15:59

I like that

Transcript for