The h Bar

heather

3:05 PM

what does the term "modes" mean in the context of optics (as in, "two modes propagating through the medium")?

John Rennie

@heather The term tends to be used with waveguides rather than a free wave ...

Is in the context of optical fibres?

heather

nope, photons and non-linear kerr media.

and that discussion is in the context of optical photon quantum computing.

Sid

Wimbledon's about to end. Dunno what I will do with my time after it ends. :(

AccidentalFourierTransform

0

Q: What is meant by the term "Fourier mode"?

In physics, whenever Fourier analysis is utilised to analyse a problem the term "Fourier mode" is often used, e.g. "a given function can be represented in terms of its Fourier modes". My question is, what exactly is meant by the term "Fourier mode"? Is it in reference to a given wave oscillating...

Mostafa

3:34 PM

@heather a mode is just a field distribution. when you solve the wave equation with some boundary conditions, you usually get a discrete set of solutions, each of which represents a possible distribution of light in the system.

All other field configuration of light in the system can be written as a sum of these (eigen)modes.

Just win baby

\o @Mostafa

Mostafa

For example, these are the modes (possible solution sets) of the paraxial wave equation (in Cartesian coordinates):

Dumb question: how is spinor-momentum coupling different from spin-momentum coupling?

@AccidentalFourierTransform ^

heather

@Mostafa so, is it just the representation of the wave equation for a photon (or whatever)?

AccidentalFourierTransform

@Mostafa as in $\boldsymbol S\cdot \boldsymbol L$ vs. $\boldsymbol S_1\cdot \boldsymbol S_2$?

user228700

@JohnR: I've sent u a friend request on Fb!

John Rennie

3:44 PM

@Kaumudi.H you've got your own account now?

user228700

Yep. I joined 20 minutes ago in order to follow M.E.C's page.

user228700

...and I have sent friend requests to only 5 people. I plan to keep up this number :-P

user228700

Ah, you've accepted! :-) Thanks.

Sid

Oh, JR is on facebook? Didn't know older guys used facebook. :P

John Rennie

@Kaumudi.H Once you're at MEC and meeting lots of other ~~nerds~~ students I bet your Facebook friend list will expand a bit :-)

Mostafa

3:47 PM

@heather Yeah. kinda

Sid

Actually, now that I see it, only older guys tend to use facebook anyway.

John Rennie

@Sid Yes we like it without you pesky kids! :-)

Sid

He he. :P

AccidentalFourierTransform

Confirmed: Cowsmoothie is an old lady

John Rennie

@Sid Away to Snapchat with you (I'm sure Snapchat is old news these days too...)

user228700

3:48 PM

@AccidentalFourierTransform And not Dhinchak Pooja?

Sid

@JohnRennie Nah, no snapchat for me.It's boring

AccidentalFourierTransform

:-P

user228700

@AccidentalFourierTransform At least u spelled my name right! :-P

Mostafa

@AccidentalFourierTransform I don't know what is that....

Is spin-momentum coupling effects expressed differently for fermions and bosons?

AccidentalFourierTransform

@Mostafa you are talking about non-relativistic QM, right?

Mostafa

3:50 PM

I'm very confused (hence the dumb question)

@AccidentalFourierTransform Not necessarily. photons are involved too

AccidentalFourierTransform

that makes it way more involved

Physics Guy

@AccidentalFourierTransform has anyone ever told you that your profile picture is funny? Because it is indeed funny.

I like mathematical jokes.

AccidentalFourierTransform

e.g., in relativistic mechanics, spin vs orbital angular momentum is undefined

you just have angular momentum

you cannot split it into those two parts

Mostafa

AccidentalFourierTransform

@PhysicsGuy lol thanks :-D

Mostafa

3:53 PM

From a talk ^

AccidentalFourierTransform

hmm that looks like condensed matter physics

i.e., not my thing :-S

let me think

Mostafa

I mean the third (last) sentence. (It differs in its origin from the QSHE....)

user228700

@JohnR: And now I can see photos of ur lunch on Fb as well! ...and other stuff like a broken egg? What's that about?

AccidentalFourierTransform

yeah, the language is way too condensed matter for my taste

I dont really know what they mean

but it could be a good question for main, if you really want to know the answer

John Rennie

@Kaumudi.H Each summer I get birds called swifts nesting in the roof of my house. I feel somewhat protective towards them because swift numbers are declining in the UK, so it's always nice when they successfully raise chicks.

user228700

3:57 PM

Ooh, they're pretty!

John Rennie

@Kaumudi.H but last week I found an egg on the drive that had obviously fallen out of the nest. So that's one less baby swift this year.

user228700

Ah :'-(

Mostafa

@AccidentalFourierTransform I have tens of similar questions as I'm trying to understand topological insulators ...but aren't they too dumb to be asked on the main?

AccidentalFourierTransform

I dont think so

Mostafa

@AccidentalFourierTransform When you study high energy physics, it means you understand all of the physics

AccidentalFourierTransform

3:58 PM

that question seems good or at least decent to me

John Rennie

@Kaumudi.H In fact a while ago I found a dead chick that had fallen from the nest, so it hasn't been a good year.

AccidentalFourierTransform

@Mostafa lol u wish

Sid

@JohnRennie I have seen a baby pigeon getting killed. I was almost terrified

John Rennie

@Kaumudi.H Ignore the sad pictures and concentrate on the food (though some would consider that sad too :-)

user228700

Haha :-)

John Rennie

3:59 PM

@Sid what killed it?

user228700

@JohnRennie Oh, no :-(

John Rennie

@Kaumudi.H it happens. There's always next year.

user228700

@JohnRennie Hmm. My only direct encounter with birds in the house is when that crow got stuck in our balcony, remember? Here.

Sid

@JohnRennie There was a pigeon which laid its eggs on our balcony. The eggs would hatch and the baby pigeons would come out. I was generally protective of them. Once, A huge male Cat(I think it was male) entered into our house by jumping through windows or something(we were in the 3rd floor), entered into the balcony, chased away the mother pigeons and stuffed the baby pigeons into its mouth

user228700

...that is, indeed, the most terrifying and disgusting thing to witness. I'm sorry.

Sid

4:02 PM

duh, no need to be sorry. The Cat was probably hungry. It's a predator. What else is it supposed to do?

John Rennie

@Kaumudi.H oh yes. What became of the crow?

user228700

Nov 17 '16 at 4:52, by Kaumudi

For anybody interested in the story of that poor crow of mine: the crow had been climbing up a small water can now and again, all day yesterday. Today, we placed a taller cardboard box near the ledge of the balcony and huzzah, using the support of the box, it was able to stand on the ledge. Then, it took off, but it fell down into another garden. Thanfully, nothing happened to it. This is him/her now: (The one on the right)

user228700

Nov 17 '16 at 4:53, by Kaumudi

John Rennie

@Sid I saw a hawk take a pigeon in my back garden. It was amazing. The pigeon was on my lawn (presumably looking for worms) and the hawk stooped on it from above.

Sid

Predators on hunt!

Balarka Sen

4:10 PM

I finally watched Get Out. That's a really scary movie.

Semiclassical

I haven't the nerve to watch that movie.

user228700

@BalarkaSen Scary even by your standards?! Must be terrifying, then.

Semiclassical

My tolerance for scary movies isn't that high, though.

Balarka Sen

@Semiclassical It's super super political; there's not much jump/gore stuff in it.

"racial terror" would be a good description

@Kaumudi.H Eh, Cronenberg once said his movies are comedy compared to what happens on the newspapers, so

Mostafa

@BalarkaSen How much terrifying is this to you?

(warning: part of a horror movie)^

Balarka Sen

4:14 PM

The Ring is just full of jump and thrill scares. It's not a good horror movie.

Paranormal horror movies are rarely ever any good

Mostafa

I haven't watched it. Just this scene. I don't like horror movies.

watched Psycho recently though

Semiclassical

yeah, I don't like jump scares

Balarka Sen

I mean, you get a lot of popcorn flying

in the words of John Carpenter

Semiclassical

I'm okay with watching playthroughs of horror games, though.

not sure why that's different

Mostafa

Psycho wasn't really scary.

Semiclassical

4:17 PM

but watching a horror movie != watching a horror game != playing a horror game

John Rennie

@Semiclassical I had to accompany my niece to see The Woman in Black, and that had some real big time jump scare moments. People in the cinema were screaming out loud.

Semiclassical

yikes

Balarka Sen

@Mostafa I liked "Birds" from Hitchcock

John Rennie

@BalarkaSen hmm, there's a fine line between suspense and tedium, and I'm not sure The Birds always stays on the right side of that line.

Mostafa

The last time I watched a horror movie (Grudge, I think), for one week I always felt like someone's following me

Balarka Sen

4:20 PM

@JohnRennie well, it's strictly speaking a horror movie, but not a "horror entertainment movie"

Mostafa

@JohnRennie Psycho is suspense

John Rennie

@BalarkaSen I think back in the 60s when it was made audiences were more easily scared. These days it just seems a bit ho hum.

Balarka Sen

I think a generic viewer would end up confused than scared at the end of Birds. It's a philosophical movie

John Rennie

@Mostafa well, there's the jump scare when the girl is murdered ...

Balarka Sen

there are several feminist (anti-feminist? eh) interpretations of Birds

Slereah

4:23 PM

Bird, bird, bird

The bird is the word

Don't you know about the bird

Everybody knows that the bird is the word

Mostafa

Full Metal Jacket - Bird is the Word

►

Just win baby

@JohnRennie I'll have to agree with @BalarkaSen on The Birds.

Classic Thriller.

I never looked at a crow the same way.

user228700

Say @JohnR: I could check if it's possible to watch Beauty & The Beast using ur account...

Balarka Sen

i must say i never understand the thin distinction between a horror and a thriller

i mean crime thrillers are obviously not horror

Slereah

a thriller has Michael Jackson in it

John Rennie

4:32 PM

@Kaumudi.H gchat ...

Secret

[Reading the arxiv Emilo referred to me]

arxiv.org/pdf/1111.3328v3.pdf

Just win baby

10

Q: Is there a criterion to differentiate "thriller" from "horror"?

The genres, in my opinion, have a very slim boundary separating one from another. I see a lot of movies being categorized as thriller or horror almost interchangeably, which might seem like lack of thought or criteria. However, is there a true criterion used to differentiate between the two film ...

horror thriller genre

Secret

Unless I am missing something, I don't quite agree with their contradiction argument. Since for each of the 4 product state cases, one out of the 4 bell state is orthogonal and hence cannot occur, and that the two physical states are comparable with one of the 4 product state configurations, then what prevents interpreting that as a mixed state and thus all probability amplitudes that are comparable will survive and thus ensure the probability zero case will never be hit?

(My opinion is subjected to change when I get to the section where experimental noise is involved)

Just win baby

You can have a positive "thrill," as in the thrill of victory, but not so for a "horror."

Secret

Or perhaps, my argument is invalid because we cannot have spontaneous mixed state formation by performing a joint measurement. However that seemed to only ruled out the ontic case. If the quantum state is really epistemic, then based on the measurement outcomes obtains, I don't see why we cannot interpret the region where the probability distribution overlap to be like a mixed state

Jaime Gallego

4:48 PM

Zeroing my laptop's hard drive right now, this is going to take a while...

Secret

[Unrelated tangent] Countably infinite tensor products and continuumly infinite tensor products $\lvert 0000\cdots\rangle$, $\lvert x(i)\rangle,i\in \Bbb{R}$

Jaime Gallego

Entertain me, physicists!

ACuriousMind

@JaimeGallego ...why?

Slereah

You can't take the continuum limit.

Sid

@JaimeGallego How would thee want to be entertained? :P

John Rennie

4:49 PM

@JaimeGallego your pictures of the red spot are out ...

Slereah

Otherwise the Hilbert space isn't separable

Jaime Gallego

@ACuriousMind I am trying to erase every trace of Windows, then implement full-disk AES.

@JohnRennie They are? Let me check that out

Secret

Do hilbert space need to be separable to have a physical meaning. Put it in another way, what is the physics property that correspond to the requirement that (rigged?) hilbert space are separable?

Jaime Gallego

Wow, these are beautiful

Slereah

4

A: Separability of a Hilbert space and its implications for the formalism of QM

As showed by Solovay here, in a non-separable Hilbert space $H$ there may be probability measures that cannot be written, for any $M$ closed subspace of $H$, as $\mu (M)=\mathrm{Tr}[\rho \mathbb{1}_M]$, for some positive self-adjoint trace class $\rho$ with trace 1 (density matrix). Here $\mathbb...

0celo7

5:01 PM

@yuggib "ultraweakly positive continuous functional"

what is that supposed to mean

Semiclassical

Well, google does give this: en.wikipedia.org/wiki/Ultraweak_topology

0celo7

oh, wk*

Semiclassical

Relevant bit: "The ultraweak topology can be obtained from the weak operator topology as follows. If $H_1$ is a separable infinite dimensional Hilbert space then $B(H)$ can be embedded in $B(H\otimes H_1)$ by tensoring with the identity map on $H_1$. Then the restriction of the weak operator topology on $B(H\oplus H_1)$ is the ultraweak topology of $B(H)$."

Secret

hmm ok, so we cannot assign any physical making to these probability measures that has no relation to a density matrix?

I am not sure why is that a problem, cause one reason we make density matrices is because state vectors cannot describe mixed states. So it should not be too much of a stretch to include these exotic measures as a new type of quantum state (unless experiment said we never have seen them yet?)

0celo7

@ACuriousMind does this game ever end?

I have things to do

Secret

5:08 PM

the solvery paper had not explain why we cannot give physical interpretatons to the exotic gleason measures

10

Q: Nonseparable Hilbert space

What kind of things can go wrong if we try to do quantum mechanics on a nonseparable Hilbert space? I have heard that usual mathematical manipulations that we take for granted will no longer hold. What I am looking for is either a general high-level argument explaining why things would go wrong o...

quantum-mechanics mathematical-physics hilbert-space

Ah fine, you guys want a countable orthonormal basis set in order to do calculations, and physically meaningful quantum fields don't exist that far out in hilbert space

Semiclassical

The remarks in Frederico's answer seem worthwhile

(the typos not withstanding)

Secret

Guess I might need to read more into stone von neummn stuff when I get to representation theory, perhaps a lot of my answers about "infinite case + quantum" lies in there

Secret

5:27 PM

[Another unrelated tangent] Dynamics involving probabilistic processes with intrinsically nonunitary processes

->pretty sure that is sufficient to imply the process is nonlinear...

Balarka Sen

5:59 PM

@JaimeGallego Looks superficially like the Reeb foliation.

The textures at the top, say

Just win baby

chat.stackexchange.com/rooms/info/71/the-h-bar?tab=schedule

Jim's AMA^

Slereah

Mostafa

6:25 PM

It's too hot

Balarka Sen

the heat goes on

Mostafa

130F (54C) in a city here (Ahvaz)

Sid

Oh my

That sucks..

@Mostafa Humidity?

Mostafa

usatoday.com/story/weather/2017/06/29/…

Sid

Is Humidity high too?

Mostafa

6:31 PM

Usually yes

Sid

Okay, that definitely sucks then.

Mostafa

This is what happened to a car near Ahvaz a few days ago (while moving)

Sid

How is that possible? Someone burnt it from the inside? Suicide?

AccidentalFourierTransform

car suicide

Mostafa

@Sid No. The tire caught on fire

and then the whole car

AccidentalFourierTransform

6:42 PM

good thing the car was empty

Mostafa

In this situation, what should you do if your car doesn't have air conditioning even as an option?

AccidentalFourierTransform

buy a better car

Mostafa

Why not upgrade it yourself?

Slereah

Heyyyy

Jaime Gallego

Slereah

6:47 PM

The Geroch Kronheimer Penrose formalism has a definition of horizons!

Sid

@JaimeGallego Translate that.

AccidentalFourierTransform

@JaimeGallego ^_^

the Calvin & Hobbes of Spanish-speaking countries

Emilio Pisanty

Rolling Shutter Explained on the Cheap

►

fantastic

also savage as hell

Jaime Gallego

@Sid It isn't as funny when I translate it.

Although some have been translated to English

Emilio Pisanty

@Sid yeah, no, you'd just be disgusted at the blonde girl

Sid

6:56 PM

gah

Emilio Pisanty

which I guess was the point, but still

ACuriousMind

@EmilioPisanty C'mon, you can't tease like that and then not explain what it's about :P

Emilio Pisanty

@ACuriousMind it only makes sense in a specific sociocultural context. She's blasting poor people for having bad taste.

Slereah

Hugh Everett III

Hugh Everett III (; November 11, 1930 – July 19, 1982) was an American physicist who first proposed the many-worlds interpretation (MWI) of quantum physics, which he termed his "relative state" formulation. Discouraged by the scorn of other physicists for MWI, Everett ended his physics career after completing his Ph.D. Afterwards, he developed the use of generalized Lagrange multipliers for operations research and applied this commercially as a defense analyst and a consultant. He was married to Nancy Everett née Gore. They had two children: Elizabeth Everett and Mark Oliver Everett, who became...

"Everett's daughter, Elizabeth, committed suicide in 1996 (saying in her suicide note that she wished her ashes to be thrown out with the garbage so that she might "end up in the correct parallel universe to meet up w[ith] Daddy")"

wait what

"At the age of 51, Everett, who believed in quantum immortality,[5][16] died suddenly of a heart attack at home[7] in his bed on the night of July 18–19, 1982."

So much for immortality!

Mostafa

@EmilioPisanty Look at the pattern at 05:00. It's is exactly similar to a fork hologram generated by interfering a plane wave with a twisted beam

Emilio Pisanty

7:09 PM

Jaime Gallego

@Sid The blonde girl above (Susanita) is the smug girl. The black-haired one is Mafalda (hence the comic's name). And this guy is the hypercapitalist one:

Slereah

Mostafa

【・_・?】
Go ahead and ask! This is really interesting!!

ACuriousMind

@Slereah One of the worse uses of Venn diagrams I've seen lately :P

Slereah

Also what is Conscio us-ness

Sid

7:14 PM

@Slereah That would be philosophically speaking a wonderful question

0celo7

7:27 PM

@ACuriousMind Ayy, the sword you get for the tourney is so fugly

Emilio Pisanty

7:41 PM

0

Q: Is there an explicit connection between rolling-shutter images of rotating propellers and interference patterns with optical vortices?

The rolling shutter effect is a neat fact of the geometry of modern CCD cameras and how they interact with objects that move faster than the camera can handle, and it's been beautifully explained by a couple of youtube videos, one at SmarterEveryDay (with a cool behind-the-scenes video to back th...

optics kinematics vortex

Mostafa

@EmilioPisanty ʘ̚ل͜ʘ̚

upvoted

heather

8:27 PM

hello

@Mithrandir24601 rytsas =)

if i have the luminous transmittance of a material, and a number of photons being emitted from a source, how do I calculate how many will make it through?

basically, with a laser of 515 nm, the energy per photon is $E = \hbar c/515 \text{ nm} = 6.13888684\times 10^{-20}\text{ J}$

ACuriousMind

@heather Isn't "transmittance" basically defined as the ratio of photons transmitted to photons incident?

heather

@ACuriousMind i don't know - i'm working off a datasheet for a laser and some equations I found while googling =)

and then $E = nh\nu$, (this is a 1 mW laser, or 1/1000 J/s) so $(\frac{1}{1000}\text{ J/s})/h/5.8212\times 10^{14} \text{ Hz} = n$

ACuriousMind

@heather Okay, so the first thing here is to figure out what that transmittance actually denotes (it could be one of several related quantities). What units does it have?

Or rather, how is it given? Is it a function of frequency? A number? A graph?

heather

it doesn't provide units, but in a table it says "Luminous transmittance ($\tau_v$) - 0.0002%"

@heather no, that's not right - the units are wrong...

AccidentalFourierTransform

8:44 PM

Optical depth

In physics, optical depth or optical thickness, is the natural logarithm of the ratio of incident to transmitted radiant power through a material, and spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material. Optical depth is dimensionless, and in particular is not a length, though it is a monotonically increasing function of path length, and approaches zero as the path length approaches zero. The use of the term "optical density" for optical depth is discouraged. In chemistry, a closely related...

heather

the laser data sheet

the filter data (see pg 6)

Mithrandir24601

@heather Rytsas! :) I have internet access again! :D

ACuriousMind

@heather Hm, okay. So that's probably an annoying quantity to try to compute the "number of photons" from because it's based on luminous fluxes, not "proper" radiant fluxes

Computing luminous flux from spectral radiant flux is easy, the converse is not (in fact I'm pretty sure it's impossible)

I.e. I surmise we have an XY problem here: Whatever you're trying to do is not what you're supposed to do with the data you have.

(Bernardo would make some chocolate banana reference here :P)

0celo7

@ACuriousMind do I need a billion bucks for the house quest in the blue dlc?

the mirror guy said I should bring money

I have zero money

ACuriousMind

@0celo7 Nope, you don't need money

dmckee

9:01 PM

At times I feel like a broken record on the matter of s-orbitals and points (rather than radii) of maximum probability.

Emilio Pisanty

@dmckee I feel like a broken record on the shapes of orbitals

ACuriousMind

I just feel broken.

Emilio Pisanty

0

Q: Does orbital refer to a locus where the probability of finding an electron is maximum?

If I want to draw a certain circle or parabola, I will need an equation from which I can plot points on a polar or cartesian co-ordinate. If orbitals refer to locus of equipotential points where the probability of finding an electron is maximum, there must be an equation for locus from which I ...

quantum-mechanics atomic-physics

dmckee

I'm getting more and more convinced that there are no short cuts in the matter and the subject can-not be approached until the student is ready to perform integrals on the solutions (spherical harmonics times <some French guy>-polynomials).

@EmilioPisanty That is what set me off this time.

Of course, the student being ready to at least verify that the proposed solutions are correct would be even better.

Emilio Pisanty

@dmckee ah, so we are in agreement then =)

cf. also

9 hours ago, by Emilio Pisanty

@ACuriousMind for me it's more "and then you realize that spherical harmonics are taught in the wrong way all the time for unknowable reasons". What they are is just those polynomials and it's a disservice to students to go in through the associated-Legendre-function door

yuggib

9:33 PM

@0celo7 functional that is continuous wrt the weak* (aka ultraweak) topology

and a state in a C*-algebra is positive if it preserves positivity

0celo7

9:48 PM

@yuggib yeah I had never heard weak* called ultra weak before

rob

0

A: Why doesn't the deuterium nucleus have spin 0?

I am bit confused by Rob's reasoning above, he does not talk about the parity of the strong wave function and the color degree of freedom and confinement which seems to me the key of the argument. Please let me know if there is any mistake about my reasoning below. This is how I would argue. The...

Is the above an answer to the original question, or a follow-up question based on my answer? If it's not an answer, I would prefer that someone other than me did the flagging. I'd like to respond, but not in a comment.

AccidentalFourierTransform

10:05 PM

it looks like an answer to me, though I cannot speak to its correctness

yuggib

@0celo7 I have seen it called like that in some older works

rob

@AccidentalFourierTransform Thanks.

Las Vegas Raiders

\o @yuggib

0celo7

10:33 PM

@ACuriousMind this game is amazing

Las Vegas Raiders

@dmckee how goes the the first week of fatherhood?

dmckee

We're starting to figure out how she works well enough to be able to sleep as much as two hours at a time. I suppose that means pretty well.

Las Vegas Raiders

:-D

no_choice99

10:55 PM

hi people im trying to understand a paper arxiv.org/abs/quant-ph/0202038 im stuck on a simple thing in the intro

basically they use an AC through a wire and this causes it to heat and its temperature oscillates with some frequency and so does its voltage

they assume that the resistance of the wire is proportional to rho_0 + rho_1 * T where T is the temperature

so they input a current density J = J_0 cos(omega*t) , this has freq. omega.

apparently the temperature has a frequency 2 omega and the voltage, 3 omega. what im not able to derive is that the temperature has a freq of 2 omega

if I assume it has a freq of 2 omega then i could show that the voltage oscillates at 3 omega

so i started with the joule heating I^2R where I^2 goes as cos^2(omega*t) which indeed has a freq of 2 omega.... but then R depends on T. so there's no way that the joule heating oscillates at 2 omega, yet it does and this apparently implies that T goes as 2 omega

can someone help me out to understand what's going on

heather

11:18 PM

@ACuriousMind I've been looking around for more data and not finding much...is there a specific value I should be looking for?

Transcript for