5:00 PM
yeah, I wanted the intrinsic definition

@vzn yes

@0celoñe7 youre saying you met JR F2F? (his pic is in his av...)

@vzn I'l say no more.

Skype session

5:01 PM
@JohnRennie lol was guessing that. (oops, 007celo7 secret/ cover blown) ... or 0cel07? :P

The avatar picture really is me, but it's 20 years old. I no longer have a beard and have acquired many more wrinkles.

@JohnRennie yes. right. some from driving motorcycles in the sun.

Hey look it's our friend JD

@vzn Basically it means that the forwards and backward propagation directions correspond to left and right polarization handedness (propagation direction is locked to polarization)

@vzn Most from just getting old :-)

5:03 PM
@Slereah I'm going to dedicate my thesis to JD

To John Duffield, Albert Einstein and the Evidence

@Mostafa does that mean the "same" photons shooting out both ways have different polarization directions?
@JohnRennie alas know the feeling :|

@BalarkaSen Are you alive?
Has anyone seen Balarka?

@0celoñe7 Didn't he have some sort of seminar to attend to or something?

Maybe

Anonymous
5:07 PM
Now that I'm in Kolkata I should meet up Balarka sometime :P

@0celoñe7 Also, that line reminds me of my old friends. Whenever I would miss a meeting between friends or something, they would call and spew out some slangs and end with "Are you alive?" (in native language, of course)

Anonymous
@BalarkaSen Where do you stay in Sodepur?

@vzn yes, right and left propagating photons necessarily have different polarizations. (what do you mean by "same" photon?)

@Mostafa (understand inherent QM ambiguity here...) they seem to be able to detect individual photon events at each side, that seems to be a major pt of the experiment... are all the "dots" in the diagrams capable of shooting out photons?

@vzn What diagram?

5:10 PM
@Slereah I don't understand plane geometry

Acuriousmind have left for the day, I guess I need to wait for his reply tomorrow. I hope my proposed realistic setup is sound enough to demonstrate my argument that those coefficients are to be interpreted as probabilities...

@Mostafa will have to work from arxiv version, cant get access to Nature version, but how many photon sources are there? each dot is a photon source right? trying to follow how many dots there are (oh Nature figs are open, let me get to that...)

Sometimes I wonder whether I should change my username to "accidentally left mainstream physics" because this is too common of an error of me

What geometry thing has you mystified

5:12 PM

ok fig 4a, each little gray circle is a quantum dot right? of say a few hundred atoms or something? nature.com/nature/journal/v541/n7638/fig_tab/…

There's a lot wrong with that paragraph...

@vzn No
That's a photonic crystal
There's only one quantum emitter

@Mostafa is the emitter in the center and the gray (hollow) dots are waveguides?

Yes

5:15 PM
@Mostafa the emitter is a quantum dot? of multiple atoms?

The emitter is denoted by $\sigma_{+}$ and $\sigma_{-}$

@vzn They're most likely holes in the structure of the material - they way that the holes are 'placed' creates (in this case) a wave guide, so each hole isn't by itself a waveguide, but the location of each hole forms a waveguide overall

@JohnRennie pls suggest a veg

those cylinders (circles) are the meta-atoms of the periodic structure of the waveguide

@Mithrandir24601 ok, is there a single quantum dot in the center? it doesnt seem to show up in diagram 4a which only shows waveguides/ waves

5:18 PM
@0celoñe7 AccidentalFourierTransform

@0celoñe7 I suspect that a spacetime is causally closed if and only if it contains no naked singularities

3 mins ago, by Mostafa
The emitter is denoted by $\sigma_{+}$ and $\sigma_{-}$

@0celoñe7 To go with what?

@JohnRennie Chicken and potatoes

5:19 PM
Peas!

@Mostafa yes saw that but its just a notation/ symbol placed outside of the actual rectangular diagram

@JohnRennie do I have to put mint in them?

Peas have a slight sweetness that works really well with chicken
No mint.

Thanks for the grammar lesson @JohnRennie :P

isn't mint a thing Brits put on peas

5:20 PM
Just buy good quality frozen peas and careful not to overcook them.
@0celoñe7 I've never had mint with peas ...

@JohnRennie How should I prepare the peas?

@vzn At a very quick look, there doesn't seem to be a dot 'hard-made' into the structure of the top layer of the material, but it could very easily be a dot above or below - is it a simulation?

@0celoñe7 You can put mint and peas on chaat but that's just us.

I'd use frozen peas. Just cook them according to the instructions on the pack. Drop them into boiling water and cook for whatever the pack says - about 5 mins I think.

@Mithrandir24601 yeah wondering about that myself. anyway that diagram is showing a single "photon event" right? or can they control which direction (left/ right) the dot emits in? or is it random?

5:22 PM
@JohnRennie Yes I know how to boil peas...
But do I put a sauce or something on them?

:-) sorry

What spices?

@ACuriousMind well, I'd say the purported approach goes against the purpose of the measurement postulate: probabilities arise in QM only when one takes a measurement

Just the peas. No sauce or spices.

@JohnRennie No spices or sauce? That would be very bland

5:23 PM
@Semiclassical I though you said measurement gives you a headache :P

@vzn haven't read that paper yet (don't know what exactly is that emitter) but all that matters is that it emits RCP or LCP photons.

@vzn There are (if I'm remembering correctly) things you can do to help make the dot emit in a certain direction, but in general, you can't arbitrarily control the direction a dot emits a photon in

I'm more concerned with its (classical) photonic aspects (at least yet).

@Sid he isn't just eating peas. They are to go with chicken and potatoes, and I assume there's gravy or some other sauce for the chicken.

@JohnRennie I hadn't planned a gravy as of right now. I'll take suggestions

5:24 PM
meh, understanding the content of the measurement postulate isn't headache inducing

Well just chicken and potato is going to be a bit dry ...

Due to the circular nature of the definition of measurement.

I could make some more garlic creme sauce

@Mithrandir24601 In this setup you can. Because each propagation direction is locked to a polarization (LCP or RCP)

@Mithrandir24601 so anyway isnt the main thrust of the advance that they can control polarization direction of the emitter?

5:24 PM
@0celoñe7 that will go really well with the peas.

Understanding why the measurement postulate is appropriate? That's where the headache enters

@0celoñe7 Have you ever tried Butter Chicken?

@JohnRennie Dry as in bland or dry as in dry?

Dry as in not enough moisture

@Mostafa Wow, wow, wow - once a photon is coupled into the waveguide, then you can force it to go in a certain direction. Coupling into the waveguide is the harder bit :P

5:25 PM
@Semiclassical how will you write down a hamiltonian for the system of 3 polarisers controlled by a random number generator that I proposed above as an argument that the hamiltonian is to be interpreted as an ensemble of hamiltonians?

@JohnRennie I have a special recipe for chicken...it literally oozes moisture on the plate.

I see @Semiclassical thanks

Or maybe I am buying mutant chicken. Either way.

@0celoñe7 Should be fine then.

@JohnRennie The potatoes will be fried anyway, with onions and garlic. Certainly not bland.

5:27 PM
@Mostafa do they control LCP vs RCP somehow?

Bland is good.

@vzn I haven't read the thing, but it appears that you can 1. Make different polarisations go in different directions (i.e. polarising beam splitter) and 2. have different polarisations have different coupling strengths to the waveguide

(Bland is good for your stomach. Not so great for the tongue)

Yup.

My stomach basically wilted
Was very good though!

5:29 PM
My dinner tonight will be all american
Burger and fries

Variety is the spice of life.

@Slereah Damn, that does sound good...
I could get some burger supplies

1) buns
2) meat

3) cheese
4) onions

only for a cheeseburger

5:30 PM
5) mushrooms
6) lettuce
7) tomato
8) mustard

don't put a girl in your burger

9) jalapenos

10) A fuck ton of ketchup

@AccidentalFourierTransform You savage

Ketchup is more for the fries, imo

5:31 PM
ketchup is the best thing ever, period
ketchup on everything, pls

@JohnRennie Vegetable for burger?

it is pretty good

I may offend purists, but sometimes I eat spaghettis with ketchup

@Slereah I thought that was just a meme

5:32 PM
0) appetite

I am the meme

@vzn This paper arxiv.org/abs/1502.01549

(I don't see how burger makes a dinner. But okay)

-1) money

Burger and fries

5:33 PM
@0celoñe7 to go with fries?

@JohnRennie i wouldn't make fries, just make the same potato thing

Sometimes I'll do an all burger dinner if I'm really lazy

I boiled some last night and used a third for dinner then

In which case I make two burgers

@Mithrandir24601 This is a near-field effect. I think coupling is not a big problem here

5:33 PM
@0celoñe7 OK so you have burgers and potato/onion/garlic ...

I could make fries...but meh. The potatos are sliced incorrectly.
@JohnRennie I would probably cut out the garlic.

Making good fries is a complicated process

Garlic doesn't go with burger, imo.

At least from scratch

@Mostafa (thx!) wonder what they mean by "nonreciprocal nanophotonics"... still confused about chirality, is it basically circular polarization?

5:34 PM
I just use store bought fries

10.333...) drink

@skullpatrol <21

I believe the drink of America is the Coke
sometimes if they're feeling fancy, they'll put some wine in their coke

@Slereah Vanilla Coke Zero ftw
@Slereah You mean whiskey

5:35 PM
@Mostafa coupling itself may (or may not) have a high probability of occurring, but often, getting the dot to emit a photon so that the photon reaches the waveguide is where there are going to be further coupling losses

@JohnRennie So, veg?

I'm more of a vodka and fruit juice fellow

@0celoñe7 Beans in a tomato or BBQ sauce?

Don't drink Coke. It destroys your teeth

You mean baked beans?
That is a good idea
+1 for JR
@Sid nonsense
I drink a liter every day and am fine

5:36 PM
One annoying thing about making fries, though
I use beef tallow
Throwing it out is complicated

is that kosher?
halal?

I do not know
Probably?

@Slereah why?

you cannot throw that into the sink

@0celoñe7 either I scrape it out, or I have to melt it and pour it in a container

5:37 PM
Put it in the trash

Because yeah, it will congeal in the pipe if I throw it in the sink

take a paper towel, wipe it out
throw the towel in the trash

That is what I do, yes, but I can't pour boiling oil into a trashbag

am I missing something?

when in doubt, wipe it out

5:38 PM
There's 1 kg of it

@Slereah does it get really hard when it's cold?

I can't just wipe it
Yes

@Slereah lol, wtf

Well, not completely solid

like butter?

5:39 PM
A bit softer than butter

@vzn nonreciprocal means having different behaviors for different propagation directions. like a diode. (It absorbs light that goes from left to rigtht, but not right to left)

Although
It's harder than butter at room temperature

:: shudder ::
how can you eat that!?

I don't
I just fry things in it

butter is pretty disgusting

5:40 PM
I tried doing fried chicken once
It was alright, but not great
I don't have the good recipe yet

@vzn what kind of clickbait hellhole is this
I never read an article if I have to manually click it for every part of a list

@Slereah lol thats why just went thru 20 pages just to find that one for you guys :P
@Slereah this chatroom is a "clickbait hellhole" :P

Ketchup is indeed the best thing ever, Ill pour it on everything, literally

@vzn and "chiral" here means left and right propagating modes necessarily have opposite polarization directions. By coupling this waveguide to atoms that interact with only one polarization type (LCP or RCP) you make this chiral waveguide a nonreciprocal one which can be used as an optical isolator.

5:43 PM
Ten spacetimes you didn't know existed!

@AccidentalFourierTransform You put Ketchup on a med rare steak?

I dont eat meat

@Mostafa thx they seem to be borrowing/ overloading the term "chiral" from some other area of physics

Jun 13 at 15:30, by AccidentalFourierTransform
I smell lovely cause I don't eat meat

Can I smell you
to check

5:45 PM
@AccidentalFourierTransform Oh god, you're a veg?

@0celoñe7 that works perfectly

disgusting

@0celoñe7 not really, I do love some good steak
but I use BBQ sauce instead of ketchup

Hello h Bar: Perhaps you can help develop a half-baked idea of mine. A handful of tags are prone to misuse and overuse, most notoriously perhaps the tag. Idea: "Protect", say, the tag with, say, a plus in the end. (I put the word "protect" in quotation since there are no actual reputation restrictions on the use of tags.) All appropriate mathematical-physics question should be tagged with this new "protected plus" tag.
6
No questions should be tagged with the old "unprotected" tag. Next let the "unprotected" tag be a synonym of a master tag, say, . The idea is that experienced users will soon learn to add the plus to "protected" tags (it is suggested from the pop-up menu), while questions with tag may need attention from editors. See also this meta post.

@AccidentalFourierTransform Interesting tidbit: there is a harmonic function on $B(0,1)\subset\Bbb R^2$ such that $\frac{1}{2}\int_{B}|Du|^2\,dx=\infty$

5:51 PM
bc $u$ diverges on the boundary, right?
rather, $Du$ diverges
otherwise, that's impossible

The derivative diverges, yeah
It's actually in $C^\infty (B)\cap C^0(\bar B)$

huh, that doesnt look good from a physicist pov
I like to think harmonic functions are perfectly well behaved
@Qmechanic that would take quite some time to get used to, but it could be interesting to give it a try

@AccidentalFourierTransform Yeah. It goes to show that the correspondence "variational problem" $\leftrightarrow$ "Euler-Lagrange PDE" is not perfect.

@Mostafa anyway really nice find, have been tracking this area fairly closely for years... are you doing experiments in this area? trying to remember do you have undergrad degree?

@Qmechanic path-integral should probably be protected as well - I have seen people use it as a synonym for line-integral many times

5:56 PM
@AccidentalFourierTransform That is our bad...many mathematicians call line integrals path integrals.
We never deal with path integrals, so it is not an issue.

No. (unfortunately) no experimental work.

@0celoñe7 which really sucks, bc there is a certain consensus that $\text{variational problem}\equiv \text{oasis of PDE's where everything works just fine}$
oh well
its physics, we dgaf

Speaking of food, how's this for a cherry cake:
Lots of cherries!

yeah, but cake fruits never taste good :-(

@Mostafa think DS will like it, "right down his alley," maybe will mention it to him someitme (havent seen him for awhile)... seems like it could be quite applicable to his area etc

5:58 PM
I always feel deceived

@AccidentalFourierTransform It tasted pretty good to me! They were glacé cherries not fresh cherries. You can't cook fresh cherries in a cake. They just go mushy.

"choose a sequence of smooth domains $\Omega_\epsilon\subset\Omega$ with $\Omega_\epsilon\uparrow\Omega$ and $\mathcal H^{n-1}(\partial\Omega_\epsilon)\to \mathcal H^{n-1}(\partial\Omega)$ as $\epsilon\downarrow 0$"

@JohnRennie yeah, its glacé stuff I have a problem with

Is this trivial?

it never tastes good

6:00 PM
Then you're buying the wrong glacé cherries!

@vzn I'd like to know more about its possible implications in qunatum information and related areas. every papers talks about how important this could be in that area but I don' know why and how.

probably, yes :-P

@AccidentalFourierTransform : If the Phys.SE community thinks it a good idea we could try it out with a few selected tags.

Anonymous
Most fruit cakes I had are too sweet. I don't like much sweet.

Anonymous
6:02 PM
(Dark Chocolates are an exception though) :P

@Mostafa dont quite follow whole thing myself but basically polarization direction is not considered controllable in QM, it seems they are nearly controlling it. they are talking about a (eg) "deterministic CNOT gate" which almost sounds like an oxymoron wrt (prior) QC theory.

@Qmechanic lets wait and see what others think
@Qmechanic in the meantime, here there is a lot of interesting information

@Blue Fats, starches (grains, potatos, ...) and sugars, and meat are bad for your health.
All others seem to be OK

@Secret Quantum mechanics doesn't allow you to say "I have a device controlled by a random number generator". There are two possible descriptions of the system you have set up here: 1. You don't care about the quantum mechanical description of the random number generator and just care about the output state of your polarizing device. Then you just start with the density matrix that's given by the mixed state defined by the probabilities for the electron state you've written down.
2. You care about the quantum mechanical description of the random number generator, in which case you have the generator and the electrons unitarily evolving as an interacting system, resulting in an entangled state. Tracing out the state of the generator then reproduces the mixed state from approach 1. In practice, it is impossible to give a full quantum mechanical description of your "random number generator", so you just go with approach 1.

Anonymous
@Mostafa In short: Everything that is tasty is bad for your health :D

6:09 PM
@Qmechanic I'm not entirely sure what this is supposed to achieve - what will stop the same hapless users that currently tag the wrong questions with math-phys from tagging the wrong questions with math-phys+?

@ACuriousMind Ah I see, that really cleared things up. Thanks!

> Everything that kills me makes me feel alive metrolyrics.com/counting-stars-lyrics-onerepublic.html guitarhero.com

@ACuriousMind I have simulated a system where I have a section of gates (currently only Paulis for testing purposes, but if I can get time, I plan to extend this to a different set of gates), with the gate operation to be performed depends on the outcome of a QRNG, so it does require interaction of quantum-classical-quantum, but it is 'a device controlled by a random number generator' to some extent...

@Mithrandir24601 I'm not saying such systems don't exist. I'm saying the proper theoretical description in quantum mechanical terms is either my option 1 or my option 2, and not the strange hybrid that Secret tried to do.

@ACuriousMind do you know the answer to my doubt?

6:15 PM
@0celoñe7 Which one?

15 mins ago, by 0celoñe7
"choose a sequence of smooth domains $\Omega_\epsilon\subset\Omega$ with $\Omega_\epsilon\uparrow\Omega$ and $\mathcal H^{n-1}(\partial\Omega_\epsilon)\to \mathcal H^{n-1}(\partial\Omega)$ as $\epsilon\downarrow 0$"

Also, can you perhaps stop using "doubt" in that way? It just comes across as you making fun of Indians to me.
@0celoñe7 ...and what is the question?

@ACuriousMind They tell me it is acceptable usage in their dialect...

@ACuriousMind Ah, I'm just reading that now - I get what you're saying now

@ACuriousMind How would one obtain such a sequence. Assuming $\partial\Omega$ is bounded and $C^1$.

Anonymous
6:17 PM
0celo finally learnt using doubt :P

@Qmechanic I like where you're going with this but my concern is that, in this example, people who want to use will just start typing it and choose what appears in the autocompletion popup, which will be . The effect being that it's not really going to solve the problem.

Yeah, shame that we have to teach them how to use words. :P

@0celoñe7 What are the $\mathcal{H}^{n-1}$?

(cont. from above) Perhaps a better approach (for now) is to pipe the tag feed into this chat room, or another room dedicated to posts to review. We get the same effect of putting questions where people have tried to use the tag in front of reviewers who can tell whether it's appropriate, without introducing an extra level of indirection.

@ACuriousMind Also, in case it isn't clear, I don't think either blue or me or Yashas take any offence to that. (We are obviously not the ultra-nationalist type of guys)

6:22 PM
@Sid ::shrug:: Okay, then. I was just airing my impression.

we're ALL Indians on this blessed day :)

@Sid Quick reminder: just as a general principle, even if people here don't take offense to something, that doesn't automatically make it appropriate for chat. (Though I don't mean to imply that this particular usage is or isn't appropriate.)

Anonymous
Nah, we are citizens of the world :P

6:38 PM
@ACuriousMind and @David Z : Yeah, like I said: A half-baked idea. Your inputs needed. Or perhaps it in practice slows down the tag misuse just enough...Should we test it?
@DavidZ : Interesting idea.

Hm, are naked singularities always timelike, null and spacelike singularities?
I think so

6:56 PM
@Qmechanic Oh, I missed that @ACuriousMind raised much the same objection I did. Whoops. Well, I'm always up for testing, I just have my doubts that it's going to fix things.
For a test, I suppose we create the new tags and , then set up the synonym, but do not convert existing tags. Then we can let things sit for a while and see how the tag usage patterns after the switch compares to the frequency at which was used before it.
If we decide that it's not working, we can reverse the changes with our existing tag-mapping tools, as long as no other synonyms point to .
For testing purposes, I think it makes sense not to make any special effort to expose to reviewers just yet. That way we can get a baseline comparison of tag usage patterns.

also, it would be nice to know how other sites deal with this issue
i.e., to perhaps bring it up on (mother) Meta

7:13 PM
I know other sites have tag notices (I forget the real name), i.e. popups that show up when someone tries to use a tag, containing some information or warnings about the tag usage.

Does the causal part of the exponential map cover the entire manifold if there are no naked singularities?

14

What are tag warnings? Tag warnings are meant to provide users with just-in-time information to help them avoid mistakes that are common for the tag they’re using. Here’s what they look like: To see a tag warning in action, begin asking a question on Stack Overflow and tag it with sql. (Mor...

7:30 PM
Hm, let's see
What I want is $\mathcal{D}_p \cap \mathfrak{T}^\pm = \mathfrak{T}^\pm$
Intersection of the domain of the exponential map and the light cones are the light cones

@Loong nice, thanks

wait no, that's not true
Hm
I'm sure there's a condition on naked singularities and the exponential map
not quite sure what

7:50 PM
@Qmechanic That doesn't feel that likely to work to me
It feels a bit underhanded and somehow wrong.
For a confused new user, we just made the system even more confusing instead of teaching them the rules
For a casual user who is using the tag correctly, we just added another hoop to jump through
plus a huge overhead in curation of that tag

@ACuriousMind surface area
I'm thinking a small inward geodesic flow using the normal vector.

And, it's plenty easy to game
and the two tags will show up on the autocomplete anyway, with one of them synonym'ed to please-delete
If I was a new user, I know which one I'd choose
That said, tag warnings on mathematical-physics and mathematics sound like really good ideas
You know what would really be great, though? A review queue for that kind of thing
3
I.e. if a user has three positive-score questions on (tag), then they can use it without problems. Until they do, though, all their posts get sent to the first-posts queue with a notice that says "This post uses the watched tag (tag). Please ensure that it's being used correctly."

$[d\phi],\mathscr D \phi,\dots$ is just stupid notation

and then possibly with some restrictions (like having three positive-score posts on the tag) on who can review those posts

the correct notation for functional integrals is $\delta\phi$
bc functional derivatives are $\frac{\delta}{\delta\phi}$
so $\delta\phi$ for the measure is the correct notation

7:59 PM
The correct notation is $d\mu[\phi]$

ok, you win
but $\mathrm d\mu[\phi]$, pls

Hm, what notation does Jaffe use
Let's see

$\mathrm{d}\phi_C$

DeWitt uses $[d\phi]$
what is wrong with him!?
what is the $C$? the covariance?

8:02 PM
I think it's canonical
Oh no
$C$ is a bilinear form on the set of Schwartz functions
$\mathrm d\phi_C$ is the Gaussian measure of covariance $C$

DeWitt pls
why you gotta be like that

@JohnRennie Nah - it's nice to hear what it was like a few decades ago :)

DeWitt also uses that weird index notation
Where $\phi_i$, the $i$ means everything

his notation is the best thing ever, and, at the same time, the worst thing ever

Spacetime indexes, Hilbert indexes, position, etc etc
So $\phi_i \phi^i$ is a sum on EVERYTHING

8:06 PM
oh no

What the hell
Can we stick to rigorous math here please

Stop

what the hell, DeWitt
ugh

That notation was brought up in a lecture in QFT last year. I point blank refused to use them and the lecturer's response was along the lines of "I don't blame you - I find it ridiculous as well"

8:10 PM
well, when you want to do things with fermions, you are kind of forced to use it
otherwise, keeping track of the signs can be a real pain in the neck
but yeah, the notation sucks

@DavidZ/@Qmechanic/@ACuriousMind I think the ideal thing sounds like a feed into this chatroom - new tags will get misused like the old. I think @EmilioPisanty's idea of a review queue is best, and it's the feed into this chatroom idea that sounds closest to that.
Tag notices sound good too.
But if I recall correctly, the tag excerpt already has a warning.

@EmilioPisanty and others: Thanks for the feedback. Perhaps you are right. I have created a test for the and tags.
A review feed is an interesting idea. Concening tag notices: Versions of this have already been long in place (in tag wikis/info) with seemingly no visible results.

8:33 PM
Ahhh the sweet smell of nitrogen

@AccidentalFourierTransform : The DeWitt's index notation before and after the symbol shines when working with theories with fields of arbitrary Grassmann-parity.

@Qmechanic I always thought that DeWitt's notation is very good but quite daunting. I've never seen anyone use it but DeWitt himself.