The h Bar

Semiclassical

4:00 PM

if not, though, it tends to be chewy and that's not so great.

0ßelö7

My bitterness taste buds are deficient.

Semiclassical

roasted broccoli is really good

bolbteppa

"A number of important properties of the scattering amplitude can be established by considering it as a function of the energy $E$ of the particle undergoing scattering, the energy being formally regarded as a complex varriable."

John Rennie

@Semiclassical I like all the brassicas.

0ßelö7

There's a giant football game tomorrow so the town will be gridlocked

Not fun

Semiclassical

4:01 PM

@bolbteppa sure. you'd expect to have poles at the bound state energies, if memory serves.

@0ßelö7 and if you're doing scattering in a periodic potential, then you'll have bands of allowed/ forbidden energies. I think in that case the scattering amplitude has square root branch points at the band edges? I'm not certain that's right, though.

0ßelö7

@Semiclassical what?

John Rennie

-1

Q: Why am I still alive?

Ive tried everything, but im still breathing! WHY? does anybody have an idea, ive tried trains, nooses guns, and even burying myself alive.

half-life

Beats me :-)

Semiclassical

... D:

John Rennie

Someone upvoted that!

bolbteppa

Alright not so strange now

Semiclassical

4:09 PM

ugh, brain work now

Emilio Pisanty

4:22 PM

@JohnRennie that's...

wow

John Rennie

@EmilioPisanty Jon Ericson has just deleted it

Emilio Pisanty

@JohnRennie curious

the roomba was going to get it anyways, no?

this is curious, though

> This question was marked as spam or rude or abusive and is therefore not shown - you can see the revision history for details.

has it, really?

and if so, how?

were there rude-or-abusive flags on it?

John Rennie

I doubt there's any significance to that. Presumably spam/abusive was the closest of the available reasons for deletion.

Emilio Pisanty

(CC @ACuriousMind)

@JohnRennie you don't need a reason, no?

John Rennie

It is a bit odd Jon Ericson got involved. I wonder if someone notified the SE mods that it was a suicide post.

Emilio Pisanty

4:29 PM

cf e.g. physics.stackexchange.com/questions/359815/…

@JohnRennie maybe there's an automated alarm system hooked up to mentions of suicide?

Balarka Sen

yeah the head mod shouldn't meddle himself with such petty affairs

John Rennie

@EmilioPisanty entirely possible ...

Emilio Pisanty

I'm not sure why this merited any more attention than just closure and five downvotes tbh

Balarka Sen

@EmilioPisanty interesting

John Rennie

@EmilioPisanty could we have an automated system to warn of posts about career suicide e.g. questions about the interpretation of quantum mechanics :-)

Emilio Pisanty

4:32 PM

hiya @JonEricson

John Rennie

Ah, here's the man.

Jon Ericson

@JohnRennie We ask the mods to contact us if they see them.

Emilio Pisanty

just wondering why this caught your attention

in Tavern on the Meta on Meta Stack Exchange Chat, 59 secs ago, by E.P.

is @JonEricson around? if so, we've got a couple questions for ya over at hbar

=P

John Rennie

@JonEricson aha, thanks. That makes sense in case the post is a genuine plea for help.

Jon Ericson

I sent a personal email and deleted the post.

Emilio Pisanty

4:33 PM

@JonEricson was there a flag of some description? or why hide the content even when it was already deleted?

Jon Ericson

@EmilioPisanty I think there was a flag. We delete these posts quickly because there's a documented copycat phenomena.

Emilio Pisanty

@JonEricson ok, fair enough

0ßelö7

Interesting.

Jon Ericson

We can never know if someone is in real danger or just pulling our leg. But it never hurts to treat it as real.

6

Balarka Sen

so, if i post an answer to a homework question on the main site expression frustration towards OP's zero attempt and say "i have level 4 cancer; i want to die now", do i get to have a personal email?

i am a depressed fella

the homework spams depress me

Emilio Pisanty

4:35 PM

I'm not sure I would really read it as actual suicide talk (looks more like taking the mickey than anything else), but yeah, there's no harm in treating it in full seriousness

@JonEricson that.

beat me to the punch

thanks for clarigying =)

0ßelö7

but then you let the "leg pullers" win

John Rennie

@0ßelö7 well, no, the post gets deleted anyway.

0ßelö7

@JohnRennie getting a personal email from an internet celebrity is neat

Jon Ericson

@BalarkaSen Maybe. Sometimes mods jump the gun and take things the wrong way. But then the user has a chance to talk about it with a CM.

0ßelö7

@BalarkaSen stage 4

Jon Ericson

4:37 PM

@0ßelö7 Attention from one person isn't nearly as satisfying as attention from an entire site. So delete, delete, delete. ;-)

Or flag.

Emilio Pisanty

@JonEricson yeah, that's an interesting point. My instinct was just to let it lie (closed + deep negative score) until the roomba got it.

but I guess if someone is just out for attention then deleting does help

Balarka Sen

@JonEricson I was being silly, but yeah, I actually applaud the email policy.

Jon Ericson

Cool. I imagine someone wants to talk Physics now? ;-)

Emilio Pisanty

@JonEricson I was going to bring up that woman, but yeah, physics sounds like a better idea.

Balarka Sen

@0ßelö7 Let's talk about topological quantum field theories

which are allegedly the very mathematical model of physics

0ßelö7

4:40 PM

@BalarkaSen I was just looking at Folland's QFT for Math People book

Balarka Sen

Is it good?

0ßelö7

I think my advisor wants to read it, he randomly talked about it the other day

@BalarkaSen I'm not a physicist, I dunno

Semiclassical

@JonEricson How about a nice game of physics

0ßelö7

you might need to be fairly familiar with QM first

Balarka Sen

@0ßelö7 chat.stackexchange.com/transcript/71?m=40271553#40271553

boi aren't you confusing today

Semiclassical

4:42 PM

well, this is QM we're talking about

he's in a superposition of being and not being a physicist until he observes himself working on a physics problem

Balarka Sen

lol

I should have seen this coming

Semiclassical

yep

Emilio Pisanty

@JohnRennie there's also this, fwiw

John Rennie

@EmilioPisanty just a dickhead then, not a suicidal dickhead

Jon Ericson

@Semiclassical "There's no way to win. The game itself is pointless!" (The second law of thermodynamics is so depressing.)

John Rennie

4:45 PM

And gravity sucks!

Emilio Pisanty

@JohnRennie well, we are all nerds here, mostly

but still

=P

@JonEricson well, that's why we invented quantum thermodynamics

and quantum quantum thermodynamics

John Rennie

Aug 5 at 9:52, by John Rennie

@BalarkaSen nonsense, you can't have too many nerds. It is a noble and honourable calling :-)

0ßelö7

0

Q: What is a multiple characteristic of a hyperbolic PDE?

In section 3.1 of The Wave Equation on a Curved Spacetime, Friedman defines what a characteristic hypersurface for the wave equation $$\Box u+a\cdot\nabla u+bu=f$$ is, and then shows that these are precisely the null hypersurfaces of the Lorentzian manifold. He also talks about tensor wave equati...

differential-geometry pde riemannian-geometry mathematical-physics

pls

Semiclassical

@EmilioPisanty what?

Balarka Sen

upboated

Emilio Pisanty

4:48 PM

@Semiclassical =P

it's a thing

ifisc.uib-csic.es//qtd2/presentations/M_Lostaglio.pdf

ook

hello @JohnRennie

Hi

I have doubt in array

int input[i],i;
    for(int i = 0; i < 2; i++)
    {
        printf("Please enter an integer: ");

        scanf("%d", &input[i]);

    }

Can I use it like this

John Rennie

Does it compile?

Koolman

4:55 PM

also can I take the input value of 'i' from user ?

actually it is working on terminal but not on hacker rank

Abcd

@JohnRennie Seriously?

Does anyone know the derivation of the Arrhenius equation? I couldn't find it on the internet. Or, are we simply supposed to learn it without deriving it?

I saw one here: ww2.d155.org/clc/tdirectory/JSayles/Shared%20Documents/… ..but it's really vague/informal.

John Rennie

when I try to compile it on MSVC I get:
error C2065: 'i': undeclared identifier
rat.c(6): error C2057: expected constant expression
rat.c(6): error C2466: cannot allocate an array of constant size 0
rat.c(6): error C2133: 'input': unknown size

Abcd

@JohnRennie Is it possible to reply without tagging/pinging the person just as you did?

Koolman

when I searched on internet , I found that 'i' is uninitialized

but I could not understand how to initialize it

John Rennie

@Abcd it was just a normal reply, but with multiline posts it hides the name of the person you're replying to

Abcd

4:59 PM

Ok.

Alex K Chen

Hmm..well if you add the iterator of Reinman function and couple it with dimensional instability of Wittenian manifolds, it gives you a globally stable field.

Abcd

Please let me know (by pinging me) if there's a derivation of arrhenius equation. Bye.

John Rennie

@Koolman in standard C or C++ you cannot declare an array with a variable length. You need to allocate the memory for the array using malloc or for C++ new

I believe GCC has extensions that do allow for variable length array declarations

Koolman

okay , then I should learn malloc

John Rennie

int* input = malloc(i*sizeof(int));

Alex K Chen

5:04 PM

Oh and you also need to integrate the charge over the 5 dimensional manfold

John Rennie

Or in C++ int* input = new int[i];

Alex K Chen

It then produces a symmetric locally invariant gauge, doesn't it ?

Koolman

@JohnRennie No , I will first learn C

tutorialspoint.com/c_standard_library/c_function_malloc.htm

is it fine to learn from here

codesdope.com/c-dynamic-memory

I will learn from there

@JohnRennie thank you

John Rennie

@Koolman: I used this book

Abcd

@JohnRennie Just wanted to ask you whether I can ask my question on Chemistry.SE.

Koolman

5:07 PM

@JohnRennie Is it good for begineers

John Rennie

@Abcd Derivation of the Arrhenius equation?

@Koolman Yes

Abcd

@JohnRennie yes

Koolman

okay, thanks

John Rennie

0

Q: Arrhenius equation derivation

I couldn't find the derivation of Arrhenius equation. So, How can we derive the Arrhenius equation: $k = A \mathrm e^{-E_\mathrm a/(R T)}$?

kinetics

0ßelö7

Only one upvote? Wow

@BalarkaSen has my back

John Rennie

5:09 PM

@Koolman it's bound to be downloadable from the Internet somewhere. The book is 50 years old!

Abcd

@JohnRennie Bad treatment of that question by Chem.SE.

They shouldn't have migrated it to hsm.SE.

Derivations are science and not history IMO.

Alex K Chen

You also need to make sure the function is locally integrable, though.

Qmechanic

@JohnRennie : I did inform the SE team, in case it was real.

Abcd

Anyway, I understood that it doesn't have any derivation.

Oh, they didn't migrate it. I misread :P.

John Rennie

@Abcd I think it can be derived if you make various assumptions. The problem is that those assumptions may not be true of real eqautions.

Abcd

5:12 PM

But there could be a better answer..

@JohnRennie Yes, understood.

John Rennie

As I recall it ultimately comes from the Boltzmann distribution

Alex K Chen

No well often time the stuff is topologiacally inconstant, and applying Thue-Witten-Morse theory, we often see that mesons keeps inhalting in and out.

@JohnDvorak Hmm...still not :P

John Rennie

@Qmechanic Jon was saying they have a policy of responding to all posts that look related to suicide, and it makes sense to assume they're real. If they aren't there's no great harm done.

Qmechanic

@JohnRennie : Agree.

0ßelö7

5:30 PM

@ACuriousMind Where would I learn about the classical theory of constrained Hamiltonian systems with applications and PDE in mind?

Sid

To what email do the ~~overlords~~ CMs send the personal email? The one the users registered with?

0ßelö7

I emphasize classical. If I see BRST I will not be happy.

ACuriousMind

@0ßelö7 Just about to head out the door. The only thing I've really read on constrained systems is QoGS

@0ßelö7 The BRST-BV formalism is not necessarily quantum

@Sid Yes

0ßelö7

@ACuriousMind Is QoGS of independent mathematical interest?

I don't really care about constrained quantization.

Sid

@JohnRennie I love the tag on that question. "half-life". lol

Koolman

5:43 PM

@JohnRennie thanks I have downloaded it

Alex K Chen

(Sorry for spamming the chat with nonsense theories. It was part of a inter-chatroom experiment)

David Z

@AlexKChen Ah, the old XKCD experiment

Sid

@DavidZ XKCD has everything relevant to life. :-)

Randall Munroe for President, anyone?

David Z

This may be an instance of anyone qualified to be president being smart enough not to take on the job

dmckee

7:15 PM

@Koolman I would say that Kernighan and Ritchie is good for newcomers to C that already have at least a little of the programmer mindset. It often overwhelms complete newbies.

In any case you have to read the book carefully as there are many places where each word is chosen for a reason (as is each word left out).

Also do the exercises—all of them.

0ßelö7

@dmckee that sounds long

dmckee

@0ßelö7 It is a bit long, but c is full of traps for the unwary and the exercises expose many of them to clear view.

Semiclassical

7:32 PM

@Abcd I think it depends on what you count as a 'derivation.' One can certainly obtain it by starting from certain assumptions/approximations, e.g. Arrhenius's logic about activation energy. But if you don't include those approximations then you probably won't get such a simple result. (And you can find systems that will violate it; google 'non-arrhenius behavior' for examples.)

It's a bit like Ohm's law in that regard, I suppose.

see for instance the notes/slides here: www1.udel.edu/pchem/C444/Lectures/Lecture5.pdf

Phase

8:00 PM

hi

what's the term for diagonalising a hermitian / breaking it down into it's vector images

Emilio Pisanty

I think it was Jeff Atwood that said "there's three truly hard problems in programming: garbage collection, and off-by-one errors"

I have a bad case of the latter =/

@Phase you mean "diagonalising"?

if not, what do you mean by "a hermitian"? (i.e. a hermitian what?), and what do you mean by "images"?

Phase

Images

like

preimages and images

$f:a \to b$

nevermind, it's probably just another poorly formed question

Physics Meta

8:19 PM

0

Q: "Repeated Deletion of Answered Questions"

What exactly does this mean? Could I be banned from asking questions just for clearing out trash / malformed questions that received answers that are just of the form "Your premise is wrong" or Duplicates? I could maybe understand the virtue of leaving the former up so anyone else caught in the s...

support

Kristina L

Hello! I have a professor that described one stream of light traveling through a birefringent medium as going "slower" than the other, but this is making no sense to me. Is there another word besides slower that would better describe this?

Semiclassical

The tricky word in here is really velocity and what that means for a ray of light

citing WP for convenience: "The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, and the phase velocity v of light in the medium, i.e. n=c/v. The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves."

Kristina L

I was not aware that there was a phase and group velocity... this is probably why I was lost. Would one of these velocities stay constant? For example: the phase velocity of light is always the same, but the group velocity can differ when passing through different materials.

Semiclassical

well, if you look at that definition, you'll note that the index of refraction is c divided by the phase velocity

Emilio Pisanty

@KristinaL the phase-velocity argument is a bit of a red herring. What you care about is the group velocity and that can also be slower.

Light in a medium need not travel at the speed of light in vacuum.

This is true for both phase and group velocity.

Semiclassical

8:27 PM

right.

the phase velocity bit is really a further subtlety

Emilio Pisanty

@KristinaL To answer your core question: no.

Here the word "slower" describes something that gets from A to B in more time than something else.

@PhysicsMeta @Phase This is unanswerable without examples.

Semiclassical

the point, I suppose, is that while light doesn't have a medium, it does interact with its environment. hence light propagating in vacuum need not behave the same as light propagating through glass, for instance.

mercifully, in the case of glass it mostly behaves the same, but with a lower velocity than you'd get in vacuum

there are other media which are weirder in that regard.

Kristina L

@Semiclassical I just started in a mineralogy course, so I might see these weird ones soon. Do you know of any examples off the top of your head?

And thank you, @EmilioPisanty and @Semiclassical for the explanations!

Semiclassical

the fashionable example nowadays are metamaterials, but that would definitely be outside the context of mineralogy

hmmm

ah, actually, your birefringent query originally is an example:

"Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light."

setting aside the polarization part, the propagation direction bit is clear enough: if you send in the light horizontally, it can take longer to pass through the medium than if you did so vertically.

vzn

@KristinaL we were discussing this in here relatively recently, there is a material known as BBO (Beta Barium Borate) used in QM bell experiments for its birefringence properties. en.wikipedia.org/wiki/Birefringence en.wikipedia.org/wiki/Barium_borate

Semiclassical

8:40 PM

There's a macroscopic vs. microscopic question here, though. Macroscopically it's enough to say that, for whatever reason, a birefringent material exhibits a difference index of refraction for light entering vertically vs. horizontally.

0ßelö7

@Semiclassical Colloquium about nonlinear nonlocal elasticity was...complicated

Semiclassical

@0ßelö7 What a surprise :P

0ßelö7

Pretty good though. Lots of jokes, some at the expense of engineers

Semiclassical

microscopically, though, you'd want someone to explain why light interacts with the medium in that way

oh those silly engineers

too busy making sure things don't collapse to worry about proving theorems

Kristina L

@Semiclassical With two different rays entering the object, the propagation direction difference makes sense. From what I understood from the lecture, one ray of light was entering at the same position, separating into two different rays, and then recombining to form an interfering wave that was different from the original. Would this be where the microscopic explanation would be of use?

Semiclassical

8:50 PM

not really. that's still macroscopic

shai horowitz

hey, simple question i think, are mass and velocity commuting variables?

Semiclassical

but this goes to a word that I put aside earlier: polarization

one usually talks about either linear or circular polarization of light; the latter is more annoying, so I'll only address the former.

the basic point is that what constitutes light, at the macroscopic scale which matters for crystals, are electric and magnetic fields which vary in space and time

Avantgarde

@shaihorowitz yes, though the (rest) mass isn't a variable

Semiclassical

see for instance this picture:

the propogation direction of the light would be to the right, and it's constituted by the electric and magnetic fields.

that's an example of polarized light: the electric field always point up/down, and the magnetic field points left/right

shai horowitz

@Avantgarde why cant rest mass be a variable? for refrence i'm considering the equation $E^2=m^2c^4+((1/sqrt(1-v^2/c^2)mv)^2c^2$ which seams to accept m as a variable

Semiclassical

8:56 PM

if you're just doing special relativity then commutativity is irrelevant. you don't have operators

shai horowitz

i realize this. i'm doing a no no and playing in both realms

Semiclassical

(continuing from above): but nothing is stopping us from having the electric field pointing in a different direction; we could swap the blue and red vectors and that'd still be a valid light wave, just with a different polarization

Mithrandir24601

@Semiclassical I've got such an explanation sitting in a book just a few metres away...

Semiclassical

Which book?

Mithrandir24601

@Semiclassical Boyd Nonlinear Optics

Semiclassical

9:00 PM

ah, that figures

Mithrandir24601

Kind of hinted at by the title, yeah :P

Semiclassical

(continuing) Additionally, we could take two waves with different polarizations and take their superposition. Then we'd get a light wave which is a mixture of the two polarizations

shai horowitz

side really bizzare question. do entropy and temperature commute i.e. a ST diagram.

Semiclassical

if it's an equal mixture of all possible polarizations, the light in that case would be unpolarized.

Avantgarde

@shaihorowitz I think you mean the 'relativistic mass', which is different from the rest mass. Some people don't like talking in terms of relativistic mass because it can provide an incorrect picture of what happens to a particle's energy content at different velocities. In any case, you're right, this is classical mechanics (with special relativity) and there are no operators here, so commutability follows.

bolbteppa

9:03 PM

Anybody know why \tableofcontents takes like 2 builds before the actual toc updates?

Semiclassical

now suppose we shine unpolarized light on an optical medium. if the material isn't birefringent, then nothing terribly weird happens: each polarization of light has the same velocity in the medium, and so they all refract in the same way.

but if it's birefringent, then that's not the case and each polarization can have a different index of refraction.

shai horowitz

in the end, i'm trying to consider a mass-less particle gaining mass. so i have to worry about quantum commutabillity only in the sense that i need to make sure i'm not leaving out a part of the system. in that sense i care about the variables (m,v) and (S,T)

Semiclassical

and therefore the different polarizations will refract with slightly different angles at the interface of the medium

now, why different polarizations of light behave differently in that that question is another question entirely. but if it can happen, then you get various experimental consequences

shai horowitz

ew bell...

Semiclassical

just characterizing these different ways the medium can respond can be a hard enough task. (oh god, flashbacks of stokes parameters)

shai horowitz

9:09 PM

but really does anyone know if (S,T) temperature and entropy commute in quantum mechanics

Semiclassical

you're acting as though entropy and temperature are quantum mechanical operators.

with entropy, at least, you can write it in terms of sums over probabilities. so that's fine

shai horowitz

same with Temp as average kinetic energies

Semiclassical

That's not the definition of temp, though. Temp is just $T=\frac{\partial U}{\partial S}$

shai horowitz

its a definition of temp

Semiclassical

you can relate the temp to the average kinetic energy if you have a boltzmann distribution, but that's not it's definition.

the questions you're asking sound to me like the equivalent of asking what the color blue tastes like.

or what color the letter e has.

Kristina L

9:15 PM

@Semiclassical You guessed correctly what my next question would be... but considering that this topic is now delving into the realm of "oh god" flashbacks, I won't harass you any further. You already helped me understand polarization of light much better. Are there any good books I could pick up to understand the details better?

Semiclassical

I don't know any off the top of my head.

what i know is mostly dim recollections of undergrad physics and grad-level E&M.

shai horowitz

i'm saying you can define temp that way. and entropy as a measure of macro states. in this sense they become quantum operators. i'm asking if these specifically commute

Semiclassical

this would be a good question for your prof @kristina

@shaihorowitz and I'm saying that I doubt that such a definition is meaningful.

shai horowitz

can you give me a situation in which its not meaningful?

Kristina L

@Semiclassical I think I'll do that. Thanks!

Mithrandir24601

9:21 PM

@KristinaL I've missed most of the conversation, so what is it that you're looking to know/find out?

Ah, I've found the start, I'll just have a reread :P

shai horowitz

:p

in the end. i'm writing a paper on the mass of information by the way

Kristina L

@Mithrandir24601 Why different polarizations of light refract differently on a birefringent medium

Avantgarde

@shaihorowitz As far as von Neumann entropy is concerned, then yes, because it's just a number (as the trace of an operator)

Mithrandir24601

@shaihorowitz First thing is that the Boltzmann distribution starts by assuming a gas, so... Would it work in a liquid or solid?

shai horowitz

in my paper i'm assuming a gas but i believe it has been recreated in other mediums

yeah i looked that up, it has the thing that changes is the degrees of freedom of the molecules in a solid

0ßelö7

10:14 PM

@Semiclassical oh god I have a month to prepare three talks

Can I fake my death and transfer universities?

Emilio Pisanty

> Do not multiply entities without necessity

ah, wikipedia, I see your grammar is ship-shape today

I guess it makes sense, just

0ßelö7

@EmilioPisanty not without contex

What's it supposed to say

Emilio Pisanty

Occam's razor

Razor (philosophy)

In philosophy, a razor is a principle or rule of thumb that allows one to eliminate ("shave off") unlikely explanations for a phenomenon. Razors include: Occam's razor: When faced with competing hypotheses, select the one that makes the fewest assumptions and is thus most open to being tested. Do not multiply entities without necessity. Grice's razor: As a principle of parsimony, conversational implications are to be preferred over semantic context for linguistic explanations. Hanlon's razor: Never attribute to malice that which can be adequately explained by stupidity. Hume's razor: "If the cause...

I initially read

> Do not multiple entities without necessity.

but it's not like correcting it makes it that much better

0ßelö7

That seems like an old-English phrasing.

Semiclassical

@0ßelö7 ooof

Is there anything the three talks have in common?

0ßelö7

10:22 PM

@Semiclassical Two are about different aspects of the same problem (geometric/analytic) and one is related to the geometric part

I could roll two up into a coherent 1.5-hour talk, in other words

Semiclassical

Hmm. Split it in two, abd spend some time in the second talk reminding people about the first one?

0ßelö7

@Semiclassical Different audiences.

Semiclassical

Hrm

Emilio Pisanty

-1

Q: Angular momentum ladder operators give inconsistent results

Refer to picture below for specifics (uploaded as .jpg file.)

quantum-mechanics homework-and-exercises angular-momentum hilbert-space spherical-harmonics

bejeesus, some people

Semiclassical

Board talk or slide talk?

0ßelö7

10:25 PM

The analytic one will be for my PDE class and the geometric one at the geometric analysis seminar

@Semiclassical Now that I don't know. I need to ask.

Semiclassical

Yeah

0ßelö7

@Semiclassical I told the organizer for the seminar that I'd have a somewhat outline by Monday. These talks aren't out of the blue and it's well within my field.

It's just daunting now.

Mithrandir24601

@0ßelö7 Enjoy your weekend!

0ßelö7

@Mithrandir24601 not possible

Mithrandir24601

;)

0ßelö7

10:29 PM

@Semiclassical my advisor said I should get two talks for the PDE class. That would be four talks.

IcE my bReaD

are these talks being graded?

0ßelö7

@Semiclassical how does a board talk differ from a slide talk

IcE my bReaD

in the former people don't fall asleep.

0ßelö7

@IcEmybReaD no

@IcEmybReaD I've fallen asleep in board talks

IcE my bReaD

maybe I should rephrase that, you also won't fall asleep in board talks.

Emilio Pisanty

10:31 PM

No offense, but mathematicians should be worth less points. — AbleArcher 7 hours ago

lolz

Balarka Sen

This is beautiful

Secret

0celo will like this mathematical rigor:

0

Q: Physics terminology about smeared and unsmeared fields

Let $M$ be a smooth manifold and denote $C^\infty_0(M)$ the space of smooth functions with compact support. In Mathematics a distribution is defined to be a continuous linear functional $\phi : C^\infty_0(M)\to \mathbb{R}$. The space of distributions is usually denoted $\mathfrak{D}'(M)$. So a d...

quantum-field-theory mathematical-physics terminology dirac-delta-distributions

IcE my bReaD

Secret

> Quantum (unsmeared) fields are often referred to as operator-valued distributions in mathematical physics.

They surely are linear maps from some symplectic linear space of test functions to the self-adjoint operators affiliated to a W*-algebra.

Hmm, so that would meam: $\phi \to \hat{O}$

0ßelö7

W* algebra seems quantum

Secret

10:47 PM

Wikipedia said it is von neumann algebra, a subset of $C^*$ involving only bounded hermitian operators

bolbteppa

10:58 PM

Is there like a children's book for systems of equations in infinite dimensions or something, like some old crazy book on them anybody knows about?

Secret

I don't think there exists something like infinite dimensions for dummies, because infinite sets and functional spaces requires quite high level maths to understand

bolbteppa

Yeah, I'd still say there's some good stuff from people around the 1920's or so before they used words like operator on this stuff, just can't find it

Secret

Unrelated, but I also suspect had we humans need to deal with infinite sets on a daily basis, then finite number mathematics will still be easier to us. If we had already being able to count to infinity, then finite is a very very small number and possibly all finite maths will have been done in an instant

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