The h Bar

now terminating that exam

user228700

:-P OK.

Terminate the students, stream if possible

6:02 PM

I'm expecting a low average on this exam

Q: could a non linear transformation be orthogonal?

0

Could a non linear transformation be orthogonal? Or in other words, could the Jacobin matrix of an orthogonal transformation be dependent of the coordinates (does not contain constant values only)?

linear-algebra

for math se?

0

Q: Find anomaly media, knowing true anomaly?

I know how to find the true anomaly by knowing the eccentric anomaly and finding eccentric anomaly by knowing the mean anomaly. $M$ ->> $E$ ->> True anomaly ... ok. But how to find eccentric anomaly and anomaly media only knowing true anomaly? True anomaly ->> $E$ ->> $M$? (inverse)

astronomy

unclear?

No, don't migrate garbage questions

I love India. So sad about the pollution there !

VTC as low quality

I can't flag for close becaz I have ran out of votes.

user228700

6:05 PM

@Cham Pollution is waaay down my list of troubles I have about India.

What is worse?

a pro-fascist government

user228700

^^^

Oh please. That word is so overused

What have they done?

user228700

Well, for the most part.

6:06 PM

@Kaumudi.H, why ? what other troubles ? I know women are baldy respected there

I won't discuss that here.

user228700

@Cham Yep, that's one of my major concerns.

India has a pro-fascist government? o0

@BalarkaSen politics is not banned here

Pollution is the worst thing

6:07 PM

I know. I just don't want to go in a tedious discussion about the politics of India.

Pollution will kill you all

@Kaumudi.H can you explain?

Women, men, children, animals,... pollution will trash everything

Hunger kills faster at least

user228700

@Cham ...I too don't want to go into an extensive discussion about our failings as a country but let me submit that rape also kills.

6:09 PM

yep, I know rapes and violence against women is terrible. But pollution in big cities is worst, I think

Now I had heard about that problem in India

@Cham As a matter of fact, the rape rate is 6 times lower than U.S.

Nice

The total number of rapes is high but you should keep in mind that India houses 1.3 billion people.

@Cham just a bit of violence is worse than the worst pollution

6:11 PM

Then you guys need to recite more mantras

user228700

@AccidentalFourierTransform ^ This is how I also feel. Chennai is one of the safest cities in India but I still don't feel safe walking around after 9 PM here.

others will also start recitating mantras, and the world will go better

Ananda Marga is the way to go

Communism > Mantras

LOL !

user228700

@Cham That is much easier said than done. In the first place, not everybody will also join. Some believe that mantras are exclusive to the Hindu community and still others don't buy the scientific evidence, etc.

6:13 PM

Buddhists recite mantras too, and the jains, and the sikhs

Physics is the largest mantra of all

Hum,... maybe not

I plan to go to India,. maybe, this summer (in jully), in the north.

user228700

Just BTW, there are so many articles like this out there:

@BalarkaSen are you a communist?

user228700

dnaindia.com/india/…

Kushinagar, Bodhgaya

@0celo7 I always wanted a "Karl Marx is my homeboy" T-shirt.

Other than that, no.

6:16 PM

So you're just an edgy teen? ;)

user228700

And I am guilty of not having caught up with all the science. I've found that we youngsters are much more dismissive of these aspects of our history.

I'm a nutty chap

Siva, Çiva, Shiva is the lord of the cosmic dance. Cosmic rays falling down, equilibrium of all forms of energy...

user228700

@Cham Hinduism is more complex than my brain can handle at the moment. I plan to study it some more before making any conclusions/dismissing stuff.

Hinduism is complex because of its very long history. Like Buddhism, it's an India's jewel that you should cherish, protect and show to the world

6:19 PM

Hinduism is indeed a complex religion, but the Hindu philosophy garbage thrown around a lot these days irritates me

user228700

Also, @Cham, surely, u've seen this before:

user228700

...alrighty, it's taking too long to upload.

??

user228700

@Kaumudi.H Shouldn't you take the time to investigate every religion?

6:21 PM

Hinduism/Buddism aren't religions. They're spiritualities. So much better than "religions" !

user228700

@Cham I agree with this to a certain extent.

Good for them?

@Cham Hindu spiritualism seem to be a part of Hindu religion to me.

Seems like nonsense either way but I'm not here to start a fight.

user228700

@0celo7 Surely, I must and I do plan on it.

6:22 PM

@0celo7 yeah man who cares.

Why Religious Beliefs Aren't Just Silly

ACM is not here. It's unusual.

user228700

I'm not cynical about religion because this is my stand:

user228700

►

Does Hinduism have honor killings?

I think it did

6:23 PM

@0celo7 Why?

Does Hinduism categorically denounce a class of people?

I think it does

Then it's probably garbage. @Mostafa

Definition of Science : path of knowledge of the exterior world.Definition of spirituality : path of knowledge of the self.

Does Hinduism categorically dismiss some simple quantum models?

6:25 PM

@AccidentalFourierTransform That question :)

user228700

@0celo7 I'm not nearly as educated as I'd like to be regarding this because of which I'm refraining from answering this question in depth but yes, oftentimes, Hindiusm does discriminate b/w different classes of people and that's all I'm saying about that.

Castes. It's officially off now

@Kaumudi.H How you could complain about discrimination against women while wanting to learn more about a descriminatory religion is beyond my understanding.

But castes are so old, it can't be erased so easily

@0celo7 You dont have to agree with something to study it.

actually, quite the opposite

6:27 PM

Spiritualism does not need to go through a veil of religion. Watch Tarkovsky.

user228700

@0celo7 I have learnt not to take everything at face value. There is much more to Hinduism than I know at the moment and I also know that there might be something to learn there.

user228700

On the other hand, discrimination against women is just that--there isn't any more to it.

Discrimination against women is a social problem everywhere all around the world, these days. Not just in India.

user228700

Yep.

It's unrelated to religion/hinduism, etyc.

user228700

6:29 PM

Oh lord, this discussion could go just about anywhere ::Slowly backs away; too tired::

I don't think this is going anywhere

I think the basic origin of this problem is anxiety. Men are unconsciously anxious about the future.

I just drew a beautiful psi

we're just expressing our idle opinions and garbage

user228700

@BalarkaSen ^ Trust me, this is going places :-P

6:30 PM

How do I upload a picture on my phone?

\Psi

lol 0celo7s "non" religion is nihilism :P

David Bowie - Looking For Satellites

►

Nihilism is stupid

3

user228700

@BalarkaSen Garbage? I must admit, I haven't met anybody quite as cynical as u before :-P (I don't mean offence by this, please don't hate me)

6:31 PM

@0celo7 agreed! :P

I'm sure Kaumudi is a very nice girl, and she deserve all respect. Girl, you are a jewel of the universe !

Strong language, whoops

@BalarkaSen How do you know?

@Cham agreed, like shakti + shiva :)

user228700

@Cham Lol, I myself haven't faced that much discrimination but thanks for ur open-mindedness :-)

6:32 PM

@Kaumudi.H I know I am, it's something I gotta work on. I didn't take it as an offence, don't worry.

Okay, what physics are you currently studying ?

user228700

@0celo7 Have u learnt everything there is to know about Nihilism? Have u engaged in productive conversations with nihilists?

@Kaumudi.H I have

user228700

@Cham I'm preparing for entrance exams :-)

user228700

@0celo7 Alright then.

6:33 PM

Well, no productive conversations

entrance to what subject ?

They're nihilists

@Mostafa Well cast-ism is a standard issue in Hinduism. I don't know the depth of it, hence why the "I think"

It's impossible to reason with them

@0celo7 lol

user228700

6:34 PM

@0celo7 Having conversations is important to understand where other people are coming from, even if u don't agree with their particular philosophies. Otherwise, u're just shouting in ur own echo chamber and of what good is that?

user228700

@Cham Engineering.

ok lets practice a bit : what's the general solution of this differential equation : $\frac{d^2 x}{d t^2} + \omega^2 x = 0$ ?

@Kaumudi.H "conversations?" 0celo7? o_O :P

Speaking of differential equations

c'mon : $x(t) = ?$

user228700

6:36 PM

@Cham x'D I'd be happy to go on a revision trip with you, but I'm tired and also multi-tasking.

@BalarkaSen the other day an engineering professor of mine did the old "dx/dt is a fraction" trick and then commented and said "this is wrong but it works"

LOL. Women are god at multi-tasking

user228700

Plus, the woes of typing in LaTeX :-P

@0celo7 I like that.

usually people are surprised that it's wrong

user228700

6:37 PM

@0celo7 I spent about an hour discussing this here last year :-P

$\frac{d x}{d t} = \lim_{\Delta t \rightarrow 0} \frac{\Delta x}{\Delta t}$

Q: Can you touch something which is massless?

4

can one touch mass-less things? If not then why the light get refracted by the tiny particles present in air $$**OR**$$ The light do not need any medium to travel then why it changes its path by changing medium

visible-light mass refraction

lol

that guy gave choices

:D

Jaime Gallego

@0celo7 Ooooh that reminds me of smbc-comics.com/comic/2012-07-17

user228700

Alright, I'm off. It was nice meeting (well, sort of meeting :-P) you, @Cham. Bye, everyone.

Bye Kau

6:40 PM

@BalarkaSen I think the problem here is that some of you have just read/heard some criticism on the subject (religion, Hinduism,...) without first studying it yourself! That's stupid.

You first read a book, watch a film, etc. then read the critiques.

@Mostafa Dude I was expressing opinions. Everyone's free to express their opinions

@JaimeGallego that's a good one

@Mostafa there are (extreme!) "castes" in the US! its called inequality...

otoh you're free to not listen to it

(also I personally don't believe in critiques and have never read one in my life)

@DanielSank There's a book about stochastic processes on manifolds

Wonder what they talk about

6:44 PM

and I was just saying my opinion on why this discussion apparently doesn't go anywhere.
Of course you're free to express your opinion.

no idea what you're talkin' about man

@Mostafa can you say anything more on the photonics experiments?

@ACuriousMind ::quantum bat signal::

@BalarkaSen I think I was clear but if not, sorry, I'm bad at multitasking. :(

(dinner!)

@vzn What experiment?

@Mostafa you are doing photonics for masters? angular momentum? aka spin?

6:48 PM

I mean I have no idea what you're replying to if you were expressing opinions. Of course I haven't read Hinduism in any nontrivial level of depth and have never claimed to have. So the point you're trying to make is void.

@vzn photons don't have spin

No experiments :(
Just simulations and some theory

@0celo7 What is spin?

@0celo7 huh?

@vzn for photons you look at the little group. They have nonzero helicty, not spin

Spin only makes sense for massive particles (they have rest frames)

← has studied hinduism in nontrivial level of depth and now claims to have

6:53 PM

@Mostafa no clue, there's an obligatory xkcd that I'm too lazy to find

@0celo7 its an analogous QM concept afaik.

@vzn photons are not purely QM objects, you have to take relativity into account

It's an abuse of terminology to call it spin

depends how you define "spin"

dmckee

@0celo7 There is a better abstrusegoose.

abstrusegoose.com/342

eg photons have a singlet state & count 46 instances of word "spin" here en.wikipedia.org/wiki/Singlet_state

6:54 PM

What does physical spin have to do with the spin group?

@dmckee I meant that one. Thanks

@BalarkaSen you measure spin using a representation of the spin group, roughly

ah.

You can also define spin as a part of the Noether current for angular momentum

in which case photons have spin

Representation of the spin group in what exactly, though?

@BalarkaSen unitary operators on a Hilbert space

6:56 PM

@Mostafa can you elaborate on that?

It's not a linear representation

Hmm, interesting.

There are linear reps too. It's hard to keep track unless you're really into it.

It's basically manipulation of light based on its helicity.

science.sciencemag.org/content/348/6242/1448

@Mostafa right. increasingly used in eg fiber optics. so is your masters more applied or theoretical? are you writing code/ simulations? what language? etc

7:02 PM

applied

no languages :)

Time for sum dinner

Steak and fries

just simulations using commercial packages

@Mostafa interesting, 11 matches on "spin" :)

@Mostafa like what kind of packages?

CST studio, COMSOL, etc.

(sorry for the very short answers. busy with a homework for tomorrow)

@vzn >free-space light exhibits an intrinsic quantum spin Hall effect

@Mostafa was just reading that. would all make a great guest speaker session am sure, plz consider it, no pressure :)

7:09 PM

@BalarkaSen You can instead consider projective reps of SO

@vzn I'm ultimately interested in the theoretical aspects of it, but for now just trying to finish my Master's :)

That does make sense.

Projective meaning a representation on the projective unitary group, meaning unitary mod phases

I got that.

I have no idea what all those, geometrically, mean however :)

@BalarkaSen agreed

7:12 PM

My intuition for Spin(n) comes from spin structures

You might be interested in this too:
[Chiral nanophotonic waveguide interface based on spin-orbit interaction of light](http://science.sciencemag.org/content/346/6205/67)

what's wrong with my links :/

@BalarkaSen ACM once said that Spin is what you get if you naviely exponentiate so

@0celo7 My guess would be that they talk about stochastic processes, but on manifolds.

@Mostafa We use COMSOL too.

> Want it tomorrow, March 1? Order within 0 mins and choose One-Day Shipping.

Hmm.

the amazon book preview is freezing

@0celo7 Exponentiate the tangent space of SO you mean?

7:16 PM

@BalarkaSen yeah, the Lie algebra

I am confused. Spin does not live inside SO, it covers SO.

yeah, so?

yeah, SO?

so(n) is a matrix Lie algebra

so you can always exponentiate it

@vzn By just putting a nano-particle near a fiber, you can efficiently couple light into it, and direct the light in you preferred direction just by controlling its helicity!! Very interesting! (the above paper)

7:17 PM

via the

e x p o n e n t i a l m a p

Exponentiating gets me a submanifold of SO, right?

@BalarkaSen negative

a submanifold of GL(N)

Ahh.

Fair enough.

@Mostafa yeah wonder if there are commercial fiber optic spin-exploiting devices yet...? heard about it as research topic a few yrs ago, theres a huge market for that...

Not commercial yet.

Using vortex beams one can add another DOF for sending information over a fiber.

7:21 PM

> theres a huge market for that...

@Mostafa think itll be worth a ton of $$$ to whoever figures out how to "productize" it...

Define "that".

@vzn Why?

You're saying that you can make money by productizing a physical phenomenon?

I think it usually works the other way around: you have a market need for a product and you make $$ by figuring out how to fill that need, right?

Certainly new technology enables new products (i.e. the laser), but the folks who figure out that technology aren't the folks manufacturing products, in all cases.

@DanielSank lol here to argue? think of cpus/ chip fabrication etc./ fiber optics is a massive billion $$$ industry wrt data transmission/ networking. currently not utilizing photon spin. but many researchers are working to chg that asap...

@DanielSank I think he means photonic products enabled by exploiting angular momentum of light

@Mostafa Sure but why is it obvious that there's a huge market for products that use angular momentum?

7:24 PM

@DanielSank its a new degree of freedom for transmission aka one could compress more data per time etc

@DanielSank Because currently there's a real urgent need for increasing the capacity of optical fibers

@vzn Angular momentum can carry more information per time than what we have now? Please explain!

Orbital angular momentum multiplexing

Orbital angular momentum (OAM) multiplexing is a physical layer method for multiplexing signals carried on electromagnetic waves using the orbital angular momentum of the electromagnetic waves to distinguish between the different orthogonal signals. Orbital angular momentum is one of two forms of angular momentum of light. OAM is distinct from, and should not be confused with, light spin angular momentum. The spin angular momentum of light offers only two orthogonal quantum states corresponding to the two states of circular polarization, and can be demonstrated to be equivalent to a combination...

@DanielSank have you heard some theory about fiber optic data transmission? its just light pulses right now.

@vzn That doesn't answer my question, does it?

7:26 PM

@DanielSank lol mostafa answered it with a wikipedia article try it (thx man)

Ah, it requires multimode fiber. That makes sense.

So @Mostafa, it sounds like the cable has to be replaced to use OAM multiplexing. That being the case, wouldn't there be other improvements that could be made at similar cost?

Sounds like OAM would be useful, but there's a barrier there in the fact that the cable needs to be changed.

@DanielSank its new technology. the actual cost is TBD. (agreed the fiber could be more expensive)

@vzn That doesn't answer my question.

@vzn I'm not worried about the cost of the fiber. Isn't the cost in the labor of laying entirely new long-haul lines?

Optical fiber is really cheap, I think.

Again, I'd like to understand how the push for OAM fits in with the fact that actually using it requires laying new long-haul bundles.

@DanielSank not a simple topic. economics is not the same as technology...

@DanielSank google was laying (new!) fiber across the ocean recently werent they?

All other easy degrees of freedom for multiplexing information over a fiber are already used...time, freq. , polarization, ...

There is spatial multiplexing but that also requires very complicated fibers

7:31 PM

@Mostafa so orbital angle multiplexing is different than polarization?

Yes

In polarization MUX you can only double the capacity (left and right hand polarization)

but polarization and spin are the same D:

but in OAM multiplexing you (theoretically) have infinitly many orthogonal channels

@vzn Indeed. Yet you're comfortable making claims like:

12 mins ago, by vzn

@Mostafa think itll be worth a ton of $$$ to whoever figures out how to "productize" it...

@Mostafa yeah cant OAM be thought of as a "larger" polariation spectrum?

7:34 PM

@vzn Sort of.

@vzn I have no idea.

@Mostafa Right but if we're going to replace all the fiber with multimode, why not just lay more fiber?

@DanielSank intel makes a ton of $$$ of their chips. cisco does off their routers. some are fiber optic. etc! youre upset by the phrase "ton of $$$"? google makes a ton of $$$ off internet advertising/ search. etc

@vzn Please don't throw emotional characterizations like "upset" into this.

@DanielSank the pt is OAM will likely lead to a very large class of devices worth a lot of $$$... presumably someone sharp at google is already looking into it! :P

@vzn So economics is complex, but not too complex for you to make general speculations? I guess that's reasonable.

@DanielSank think moores law applied to photonics. the photonics field is still evolving. think cpus in the 1970s. even ~~boring~~ conservative engrs were predicting a glorious future.

7:38 PM

@DanielSank As I said there's no limitation on the number of OAM channels theoretically. The challenge is to produce vortex beams with very high vorticities efficiently (which is related to my research)

@Mostafa Sure there is.

Those statements "There is no limit in theory" are only true in a theory without effects such as noise etc.

In other words, your're right that there's no limit in theory, but only it pretty feeble theory!

@DanielSank ofc they will be limited but nobody knows what the limits will be (yet). much like QM computing :P

Also i'm pretty sure uncertainty will limit the theory at some point

@Mostafa Oh you're working on this!?

7:40 PM

@DanielSank Yes. On metasurfaces that produce vortex beams.

@Mostafa Experiment/theory?

Theory/simulation only :(

@AccidentalFourierTransform I'm discovering that washing my hair more too much is really bad for it.

@Mostafa ah. We need good theorists!

A theorist who understands hardware is a valuable and rare animal.

http://chat.stackexchange.com/transcript/message/35742552#35742552
You see, here beams with different *twist* don't interfere.

@DanielSank maybe a hair salon might have a good product for your sensitive needs

7:42 PM

@vzn Nah, I just wash it less often nowadays and let the natural oil do its thing.

@Mostafa Yeah, I get it. Orthogonal modes.

and once you can produce vorticites up to some number $l$, you get a X2 bonus because you can use modes with negative $l$ too :)

← picturing DS getting hair done at elite salon by gorgeous babe

@vzn o_O

@DanielSank cherish those natural oils. They're the best for your hair

@AccidentalFourierTransform Yeah. I figured that out the hard way.

7:43 PM

lol what happened?

As a child, my mother told me to wash my hair with every shower! This was not a good habit as I grew up and got longer hair, etc.

that is what is refered to as "mom science"

lol reminds me, did anyone see 50shades darker? how about kim basinger as ~~evil~~ ~~villain~~ hairstylist? :)

Well, I had really bad dandruff from a combination of swimming all the time in chlorinated pools and having naturally well-oiled skin. Then when I stopped swimming I still had bad dandruff probably because I was washing my hair too much and drying the crap out of my scalp with anti-dandruff shampoo.

@DanielSank IIRC you have slightly long and curly hair

right?

7:45 PM

@AccidentalFourierTransform It's pretty long now, actually...

Longest it's ever been, I think.

cool! long hair is the best