The h Bar - 2019-03-16 (page 1 of 2)

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user351417

12:37 AM

Well, I'm still the only person I know who hasn't gotten into college :(

user351417

There's this annoying thing where you really want to do a binding (Early Decision) application to a certain place, but your parents don't like the place so you go ant get waitlisted in the regular pool and subsequently feel like throwing things around.

user351417

Or maybe I should have just mentioned Physics SE in the app and tried my luck. Perhaps that would have tipped things over. </rant>

1:08 AM

@Chair Sorry to hear that. :( Maybe you should have mentioned Physics SE.

user351417

Now that I think of it, the time I spend on Physics SE is more than the time I've written for any of the other activities I mentioned, but whatever.

user351417

Most of that is reading, not actively doing stuff.

But you still have other college options, right?

user351417

Yep, eight of them :P

Oh, good. :)

user351417

1:14 AM

(well, I have eight applications which I haven't gotten responses for)

user351417

But anyways, it's a waitlist, so I'll get an update on it after a couple of months.

Ok. So there's no point getting stressed over it.

user351417

1:41 AM

Well, it was the second most competitive place I applied to, so a waitlist (as opposed to a rejection) does make me feel a bit more confident about the others.

user351417

2:32 AM

@AvnishKabaj Well, it wasn't exactly a random ping because I had said something about the IB to that user a while back, but yes, the contents were as random as they get.

@Chair what a joke man , am I not even allowed to have some fabulous conversation ( I mean to get my mood back ) sorry if u strange . My bad IAM the guy of simple taste. Now I'm no more traubling you >.<

2:52 AM

I am not regular here . So feel not hassle when I am here the stuff you guys do isn't so good as I thought (except John Rennie) who is around the corner of his life and done with most part of his life but not sure about who are still young and got some real potential . And finally good bye everyone

1 hour later…

user351417

3:53 AM

Does anyone understand why the author of this scientific american article cites Hossenfelder's "lost in math" arguments? While they aren't unrelated, I don't see how different the article would be without those bits. It's generally a bit of a chaotic article IMO.

user351417

Like it starts with a stock image with glowing lines (or at least I don't understand any direct connection between monism and the diagram), and then there're tonnes of name-dropped terms (including 'quantum mechanics') which receive poor descriptions in arbitrary places.

user351417

Interesting... apparently Einstein has contributed to Scientific American before.

user351417

> Somehow, however, our daily life seems to be protected from experiencing too much quantum weirdness.: Nobody has ever seen an undead cat, and whenever you measure the position of a particle you get a definite result.

user351417

Perfectly misphrased because we all love the word 'undead'.

user351417

4:13 AM

user image

4:51 AM

@DanielSank I guess it's been an year

@Chair Where was your early?

5:05 AM

@Chair Hey, at least they didn't round it off to the nearest lakh. ;)

5:29 AM

@AvnishKabaj Some time before that, I was accused of being a psychopathic monster and running this entire site through a set of sock puppet accounts.

So your comment was funny to me.

@Blue Meh, why do we need a mod in the chat room?

Moderators' job is to handle all the moderator stuff, not debate policy in the chat room, right?

user351417

@PM2Ring I didn't realize that I was that rusty with my Hindi numbers though.

user351417

@AvnishKabaj I didn't do an early binding thing anywhere eventually.

user351417

I really wanted to do one to Chicago though; I got waitlisted with regular, so I may have had a better shot if I'd done the binding one.

5:45 AM

Late 19th - early 20th century physics brought us amazing new technology, and led to a radical change in our view of the universe. It revealed that the cosmos is far larger than we once believed, and much older than was generally accepted by (Western) religion.

Traditionally, science was called natural philosophy. It not only told us how stuff worked, but it also helped us to understand the world, and gave us a perspective on our place in it, complementing rather than competing with religion. But gradually science introduced ideas and information that clashed with many traditional Western …

The multiverse theories in conjunction with the anthropic principle undermine our specialness. For some, the austere beauty of the mathematics underlying the physics is sufficient "spiritual" sustenance. But Sabine Hossenfelder warns us that even that may not be a safe refuge.

But fear not! Quantum Monism can restore us to a state of grace. Maybe. ;)

Now playing on my random MP3 list: Echoes, by Pink Floyd.

user351417

@PM2Ring Ooh I used to love drumming for that. I think I tried to perform that one with my neighbors, a couple of years back, but we couldn't do the sounds in the middle.

user351417

Also, we had no singer, no bassist, and one guitarist.

Anonymous

@DanielSank That's not what I meant.

user351417

I don't think it's about debating policy in chat. Isn't it about actually moderating chat?

@Chair You could probably get by with no bass, if the keyboard player's good. But the guitarist needs to be pretty spot on. And the vocals turn it from a prog-rock jam piece into something deep & mystical.

@DanielSank It's not a matter of need

Anonymous

5:55 AM

@Chair No, I'm not even concerned about chat moderation. That's being handled well enough. The main reason I said that is availability. If someone (any user) is facing any trouble or wants to ask about any specific moderation policy, it's nice if they can speak to one of the mods directly rather than through the flag system.

@Chair I'd guess the point is that if a mod hangs out on chat they can be contacted quickly when urgent action is needed.

Anonymous

Yup, that too. ^

It"s just nice to be able to hang out with mods & discuss stuff informally from time to time.

user351417

@JohnRennie Yeah, for instance yesterday, I noticed something not-so-nice which involved resurrection of a certain user, but whatever.

OTOH, for serious stuff, mods do like it when we use the flag system, since it creates a trail, and keeps everything honest. And lets the mod know they've handled it. :) They might forget, or not think it's urgent, if you just casually mention it in chat.

Anonymous

5:59 AM

One of the things I hate about some websites, for example Quora is that their moderation is extremely obscure and you don't really have anyone to question if you notice something unfair. If you send them an email, you'll get one of their canned responses. There's absolutely no way to debate your stance! That sucks and I don't want SE to ever become like that.

Anonymous

While handling flags is certainly a duty, staying at the ground level and actually interacting with users should also be a duty for mods.

user351417

@Blue I used to use quora. People would joke that quora developers had a policy "if it ain't broke, break it".

Anonymous

After all, mods are supposed to be exemplary users first; diamond users second.

user351417

I think there was this huge uprising when they randomly removed the provisions for question descriptions.

6:14 AM

@DanielSank Oh

Nice

@Chair applies to any ivy

user351417

@AvnishKabaj I applied to one, and the parents are damn pissed that I didn't do more.

user351417

They have this notion that ivies are the only good colleges other than Stan and MIT.

@Chair Speaking of bass players, Mohini Dey is pretty special. She's already good, but she has the potential to be seriously great, if she doesn't get caught in the trap of flashy technique for technique's sake

user351417

@PM2Ring I think I've only seen one thing with her. It was AR Rahman's Berklee performance.

@Chair I mean you could have applied for more nothing you lose other than a couple of hours writing essays

user351417

6:19 AM

@AvnishKabaj And a hefty-ish sum :(

user351417

And a lot of thought. and filling out a bunch of different forms.

@Chair In 9th grade my parents were like you're only going to the states if you make it into an invy

user351417

And coping with a lot of rejection letters.

True

user351417

Eh most of my good places are non-ivies actually.

user351417

6:20 AM

I don't really know how that happened, but it just... did.

@Chair I've seen maybe half a dozen YouTube clips. Her best work is when she's not trying to show off. A computer can churn out a fast sequence of notes. I want music to capture my soul. ;)

user351417

@PM2Ring We have this meme at school about how during our concerts, the recording people kept focusing on our bassist during the guitar solos. Our bassist does this mad stage presence thing. He's a flea fan, but fortunately, he wears clothes and doesn't do drugs or whatever before going on stage.

user351417

So when our lead guitarist left the group, someone suggested "maybe [bassist] can do bass because the way he flexes on stage he looks like he's playing lead"

:D It's nice that kids today appreciate the music from 30+ years ago. That didn't happen much in the 1960s & 70s. The modern sound just pushed the old popular music aside, and only parents & grand parents listened to it.

user351417

@PM2Ring There's a drummer called Jojo Mayer who talks a lot about electronic music. He plays electronic-ish stuff with incredibly technical drumming, and he has a TED (x?) talk about exploring subdivisions in ways which computers can't.

user351417

6:26 AM

@PM2Ring Huh, weirdly enough I've been getting a bit more interested in big band stuff from a while back too. But this interest in older music (from the 80s and before) is only noticeable among people who play instruments.

user351417

There's actually some nice jazz around now too... I'm obsessed with this guy called Yussef Dayes. His music doesn't sound particularly modern, but it isn't like any of the fusion stuff from the 80s either.

user351417

If you limit yourself to modern music, there're very few interesting instrumental stuff to cover.

user351417

And with the way our schools work here, we have a huge number of singers at our disposal, so the instrumentalists who're hot property (drummers and bassists/guitarists) kinda take over and heavily influence song choices for concerts.

Well, computers can, if you know how to program them. But in the end, it's just an instrument, a means for a person to communicate to other people. If there isn't a person behind the instrument, try to connecting with other people, it has limited attractiveness.

user351417

I've tried composing drum parts by writing sheet music with a tool called musink, and it's much harder than improvising something while playing: though the sheet music/computer program can obviously eventually be used to reconstruct the patterns, the intricate and odd bits definitely don't come naturally and are quite a bit harder to put together.

6:36 AM

Here's one of my favourite young guitarists, a Yorkshire lass named Chantel MacGregor, playing a prog rock piece called Daydream. I'm currently listening to the studio version, from her 1st album, but it's nice to see her live work, even if it isn't quite as tight as the studio version.

@Chair For sure!

3 hours later…

user351417

9:50 AM

Duplicate HNQ: physics.stackexchange.com/q/466738

user351417

3

Q: Why does electron(-) keep rotating round the nucleus (+) even they are attracted?

I'm a secondary school pupil, my physics textbook discussed atomic physics without deep details because we are young boys, to explain electron motion we first learn about rotational motion. The main problem is that why the electron dose not fall on the nucleus, my textbook said that it doesn't b...

rotational-dynamics electrons atomic-physics subatomic

@Chair ah, I can't dupehammer that

user351417

I'll add the qm tag :P

user351417

it's applicable

Too late unfortunately, I had already voted to close. I should have waited.

Annoyingly the SE doesn't allow you to unclose vote then close vote again.

user351417

9:54 AM

::screams for help::

user351417

@JohnRennie Dupehammer should really have that backward effect though.

mornin'

user351417

@ACM thanks =)

user351417

(for the duplicate)

user351417

Also, good morning!

11:08 AM

Hello everyone , I think it's pretty good place to cover up my doubts so what all stuff do we talk here.

user351417

@Liquid Don't ask about asking, just ask :)

Anonymous

12:45 PM

@Chair Wouldn't work. Closing/dupehammering (for gold badge holders) is restricted to v1 only.

0

Q: Energy of a Harmonic Progressive Wave

In a harmonic Progressive wave all the particles of the medium perform Simple Harmonic Motion. In case of SHM, when the kinetic energy is maximum the potential energy is minimum and vice versa. Is the case same in wave too? How does energy transfer in wave?

energy waves harmonic-oscillator

Can anybody please help with this question?

user351417

1:25 PM

@Blue Interesting. I was just thinking about how that would be a loophole in the hammer system.

user351417

But the post close message indicates that ACM used the gold badge, not the mod power.

user351417

I'll check meta.

user351417

@user8718165 That isn't your question, right?

No it isn't

user351417

2

Q: Why is the potential energy of a particle in a travelling wave maximum at the mean position?

I mean, we calculate the speed of a wave (in a string) by considering the tensional force as a centripetal one (that's obviously an approximation), so shouldn't potential energy decresase in the direction where it acts? Shouldn't it be maximum at the position of maximum displacement?

user351417

1:27 PM

is related

@Chair I think it always shows the gold badge when a user closes a question unilaterally as dupe and they have a gold badge in the tag

There's no extra logic for not showing it when the user is a mod

user351417

Weird. There should be, IMO, but whatever.

@Chair sometimes such small cosmetics can take surprisingly large development effort

@Chair ok I'll see that thanks... Also this question didn't gain any attention I think...

user351417

@user8718165 They're different cases, but off the top of my head, similar principles should apply.

user351417

1:33 PM

physics.stackexchange.com/posts/466785/revisions v3 is one weird edit.

user351417

Actually even that question is pretty far out there.

user351417

It's uncomfortable to read such oddly specific stuff.

user351417

I'm going to bounce physics.stackexchange.com/q/466785 off @EmilioPisanty because We just need a solar panelled SPAIN to power the world.

Anonymous

10

Q: The powerfullest ever mod, or: do we really need to display the gold badge icon after a user receives a diamond?

That's what happens if a user who is gold-badge-holder dupehammers a question and then finds somewhere a spare diamond: Looks great, I must say. But what's the need? I think that the badge icon should be removed then.

feature-request bug status-declined dupehammer

user351417

@Blue Isn't that answer saying the opposite thing though? The reality is that it was the diamond which did the job (because the original didn't have the QM tag), but that answer says that the diamond is only and indication of the user having mod powers at the time.

user351417

1:49 PM

Like if ACM steps out of the mod shoes, it'll look like ACM used a gold badge there when the gold badge shouldn't have been applicable.

user351417

Eh whatever, nobody really cares about this case; we'll talk about it if there's actually some problem.

Anonymous

@Chair Sure, it's a bug...but they'll probably status-decline even if you report it. Anyway, the thing is: it's well known. :)

@Chair Given that the request to show binding mod votes has been pending for four years, you shouldn't expect any improvements there soon :P

user351417

@ACuriousMind Looks like some people aren't happy with this closed question. IMO it's a pretty terrible question and it is clearly a homework-type calculation, even if people disagree with the engineering background.

user351417

What do the others think?

user351417

1:55 PM

I don't particularly want to put a reopen vote on that one, and there don't seem to be any pending votes.

@Chair People can vote to reopen if they want. I think it's clearly engineery - the problem is supplying the world with power, and it's asking how to design a solar panel to do that.

If someone asked us "how large does a solar panel need to be to power my house?", it would be the same type of question just on a smaller scale, but somehow I don't think as many people would think it to be on-topic.

user351417

Yep, that's cool. I left a comment pointing to meta.

2:15 PM

Skeptics love that sort of question

218

Q: Does hot water freeze faster than cold water?

Is it true that hot water freezes faster than cold water and if so, what practical applications have there been found for this phenomenon?

-3

A: Why hot water freezes faster than cold water?

This phenomenon is called the mpempa effect. There is a research paper which explains this using hydrogen bonding The paper is slightly difficult to understand which can be found here This is a simpler version which I found here Now Xi and co say hydrogen bonds also explain the Mpemba effe...

Godamn them chemists

2:36 PM

@AvnishKabaj That's not the only case of lazy stupid homework question that was upvoted by the HNQ effect on Skeptics. :-(

111

Q: Are 19.6 pounds of CO2 produced from burning a gallon of gasoline?

According to the U.S. Energy Information Administration, About 19.6 pounds [8.89 kg] of CO2 are produced from burning a gallon of gasoline that does not contain fuel ethanol. About 12.7 pounds [5.76 kg] of CO2 are produced when a gallon [3.8 litre] of pure ethanol is combusted. I am not a ...

chemistry climate-change

would be shot down quickly on Chemistry, and rightfully so

it's even off topic on Skeptics

3:22 PM

physics.stackexchange.com/questions/466808/huygens-s-principle plz suggest something if am wrong

Captain Bohemian

3:45 PM

what's the difference between scalar invariance and coformal invariance?

scalar invariance seems to from the perspective of physics while coformal invariance is from the perspective of geometry, but I see in a lot of places one seems to indicate the other, but that's not necessary. I wonder when one doesn't indicate the other.

@Chair interesting article thx for sharing. think physics is in midst of a shifting/ crossroads stage and different authors are struggling with (new) vocabulary/ concepts and thats reflected in the grasping aspect/ theme of the article. hadnt heard of quantum monism but it does sound/ remind me a lot of the fluid paradigm, there are strong parallels :)

Captain Bohemian

does scalar invariance encompass coformal invariance?

in theory salon, 12 secs ago, by vzn

A quantum experiment suggests there’s no such thing as objective reality / MIT tech review

Hi everybody.

I'm here to advertise that I could use some help on this one.

4:01 PM

@Qmechanic @Chair what's with this closure?

0

Q: How does one convert from $\rm mmol/m^3$ to $\rm mmol/L$?

I recently found this conversion table for the unit conversion $\rm mmol/m^3 \ \leftrightarrow\ \rm mmol/L$ (millimoles per cubic meter to millimoles per liter) My physics is very rusty, but just to be sure, is it true that a liter of liquid always corresponds to a particular volume? (i.e.: Does...

homework-and-exercises pressure unit-conversion

user351417

@EmilioPisanty I was thinking of insufficient research.

user351417

Both units are literally called units of volume, which is quite suggestive of the answer.

@Chair ... so you closed as homework?

@Chair OP is explicitly asking whether a liter is a unit of volume

user351417

@EmilioPisanty The show some effort part applies, doesn't it?

it's a basic question, but that doesn't mean we shouldn't answer it

4:04 PM

I agree with Emilio. That question is very basic, but it's well posed.

user351417

google.com/… gives a pretty definite "yes, it's a unit of volume", and that's a straightforward search.

Downvote if you want, but don't close it.

@Chair No. Closing non-homework questions as homework, when the real problem is something else, is just misleading OPs, and creating a whole lot of confusion and anger that can easily be avoided by using the correct closure reasons.

If you feel it's unresearched-enough that it should be closed, then use a custom close reason and say that it's lacking prior research

^ That

Captain Bohemian

sorry, it's conformal invariance above. I don't know why I overlooked the blatant spelling error.

4:05 PM

ideally, link them to the relevant meta post while you're there

Which is why, as I've argued a lot in the past, we need to change the %*@& homework close reason text.

user351417

@EmilioPisanty Hmm, gimme a moment. I'm sure that I've seen a meta post about whether we should close insufficient research questions or not (it's not David Z's what counts as sufficient prior research)

user351417

Gimme a moment to read physics.meta.stackexchange.com/q/6001

41

Q: What counts as sufficient prior research when asking a question?

On Physics Stack Exchange, people asking questions are expected to demonstrate that they've put a certain amount of effort into answering the question themselves. What exactly counts as sufficient effort?

discussion faq questions

What does "It's not David Z's what counts as sufficient prior research" mean?

BTW @EmilioPisanty any help on the question I linked above?

Seems like something you'd know how to do...

4:08 PM

@DanielSank I'm not completely sure of what the goal is

but what I can say is that hermiticity is never incidental

it sounds simple to say, but it is super super important

I have a pair of coupled equations that lack a certain symmetry and I'm trying to get that symmetry back. Maybe that's not possible.

it generally is there as the embodiment of some form of conservation of energy

the fact that your equations aren't formally hermitian doesn't mean that they don't conserve energy

it just means that you're phrasing them in an awkward basis

and, in particular, that in your awkward basis, the energy isn't a cleanly symmetric quadratic form made of multiples of $(V_1^2+V_2^2)$ and $(\dot V_1^2+\dot V_2^2)$

so

user351417

@EmilioPisanty As I mentioned earlier, that is meant as a direction for OPs who're about to ask. It doesn't say whether or not we should close the questions. However, the post I just added a link to has a well-received answer which says "I sometimes vote to close if I think the OP has dashed out the question without thinking about it." I think this qualifies as such a case, and I showed you the google search which I thought explained my point of view.

user351417

If a few people vote to reopen it, that's fine. But I agree that the homework reason is out-of-order, and I should have put a custom reason.

find an expression for the energy of the system

4:11 PM

Yes this sounds like the right line of reasoning...

and find a transformation that will transform that quadratic form into a symmetric canonical form

then that transformation should 'magically' take your equations into a hermitian form

Last night dream, something extremely screwy in logic:
There are people who are being hypnotised, without aware that they are being hypnotised

this is actually some security system in a vault in order to disorient any thieves

Ok...

However, there's one guy who managed to steal the gold and fool the security system by doing something that sounds very meta:

user351417

Ooh, but if that question gets reopened, I wonder if someone'll run of on a tangent by addressing "Doesn't change with regards to temperature, pressure, etc?" with Boyle's law and Charles's law and stuff.

user351417

4:14 PM

That would be pretty bad.

He fooled himself that "he is being hypnotised, without awaring that he is being hypnotised". As a result, the security system thought he is already hypnotised and he is unaware, but in reality, he is aware that he is actually not hypnotised, thus allowing him to steal the gold

@EmilioPisanty I can get most of the energy in terms of $V_1$ and $V_2$, but the inductor energy can't be expressed in terms of voltage.

@DanielSank it'll be in terms of a current that you can relate to the voltages or their time derivatives, right?

yeah

so put in the time derivatives

they're crucial

I mean, you've got a full-blown Hamiltonian system

treat it as such

=)

4:17 PM

This may be an important point.

The way I've been working with this system, it's all second order equations. No Hamiltonians anywhere. In the case where the oscillators are identical, I can easily find the eigenvalues of that matrix, which is nice because they're equal to $1 / \omega_\pm^2$.

In other words, I can find the normal frequencies without much trouble.

Now I do know what the Hamiltonian of that system is, but I don't know how to get normal modes from the Hamiltonian.

I actually posted a question about that a long time ago that nobody ever answered.

yeah, I remember seeing a similar question but with more hamiltonian

Ah yes here it is, with an answer!

5

Q: Is there useful information about normal modes/frequencies in the Hamiltonian matrix of a coupled system?

Single mode Suppose I have two $LC$ oscillators, one with $L_1$ and $C_1$, and the other with $L_2$ and $C_2$. If uncoupled, each oscillator has resonant frequency $\omega \equiv 1/\sqrt{LC}$. Using the flux in the inductor as the coordinate, the equation of motion for each oscillator is $$\ddo...

hamiltonian-formalism normal-modes

Not sure why I accepted that answer :-(

@DanielSank 👍

@DanielSank it's not useful?

It's useful (deserves upvote) but I'm not sure it answered the question.

ah

4:22 PM

Then again, my questions tend to be a bit open-ended.

@DanielSank you don't say

Whatever, dude. They're good questions.

@DanielSank oh, no, that's for sure

;-)

but they are generally quite open ended. which is what makes them good. and also hard.

4:24 PM

Alright so back to expressing the energy...

The energy in the capacitors is $C_1V_1^2 / 2 + C_2V_2^2 / 2 + C_g(V_1 - V_2)^2 / 2$.

Anonymous

@DanielSank I use the accept mark to denote the most helpful answer; they need not necessarily indicate that the question has been answered to my full satisfaction. If a better answer comes along, I shift the tick. But then again, by accepting an answer you lower the chances of your question receiving more answers. So...different people use it in different ways. :P

indeed true

@DanielSank btw on this, my experience is pretty different - I've found them generally quite well received, even when the formal scores have been low

I'd definitely want to see more of yours :-)

Good to know.

There's some correspondence between my self-answered Stack Exchange posts and this GitHub repository.

The repository is too big to convert entirely to Stack Exchange though.

@Blue btw, you can have my can of spray, turns out I won't be needing it =)

Anonymous

4:29 PM

@EmilioPisanty Congrats! :D

Anonymous

Is it published already?

journals.aps.org/prl/accepted/…

accepted

2

I got the proofs yesterday

Congradulations!

@Blue & @DanielSank thx =)

even better, this bad boy is officially heading for Nature Photonics :-D

Nice!

4:32 PM

yeah, I'm pretty chuffed about it =)

Plz write a Light Knots for Physicists Who Know Stuff but not Light Stuff paper.

2

I'll wait right here.

@DanielSank what?

::scratches head::

::waiting intensifies::

::starts dancing, slowly::

"physicist who doesn't know optics" sounds like a contradiction in terms to me

=/

=P

user351417

Light stuff=optics?

4:35 PM

@Chair I think? if it's not that, then I don't know what 'light stuff' is

user351417

Interestiingo. I thought you'd block such tame definitions.

@Chair about fight :0

@EmilioPisanty Yeah well, funny how that works, eh?

@DanielSank admittedly I fall into the box of "physicist who doesn't really understand thermodynamics", so there's that

I work with a PhD holding physicist who never learned Hamiltonian mechanics. These things happen.

@EmilioPisanty Secret: none of us really do.

4:36 PM

@DanielSank ::scratches head::

@EmilioPisanty Yep.

user351417

Is there anyone comfy enough with newtonian mechanics to revisit that carpet jazz?

Heck some times I feel like I don't understand Hamiltonian mechanics. Just last night I was working on coupled oscillators and realized that I don't know what happens when you change from $X$ and $Y$ to $a \equiv X + iY$ and $a^* \equiv X - i Y$.

I don't know how Hamilton's equations of motion work in that case since the transformation isn't canonical.

The interesting thing is that $a$ and $a^*$ diagonalize the matrix representation of Hamilton's equations of motion... but annoyingly that matrix doesn't even seem to have a name!?!?

Quantum entanglement has been experimentally verified, but to me, it is difficult to understand conceptually. How can the measurement of a particle directly change the state of its entangled partner when separated by great distances? How do the various interpretations of quantum mechanics account for this phenomenon? Can groups of particles be entangled with other groups or does it only apply to pairs?

Entanglement can happen between groups. This has been shown in the laboratory.

Anonymous

4:44 PM

@Rico Is that question copied from RG?

Anonymous

Seems so.

Jeez good find, @Blue.

Captain Bohemian

@Rico my problem with experimental quantum entanglement is I feel it's very difficult to actually create quantum entangled states.

Lemme be little brief about this guy Rico . First he had somethin to do with IB and then to some real freaking guy and now turned to a real physist

@Blue eagle eye

user351417

This is getting a bit out of hand now.

user351417

4:53 PM

There's even a star on that particular copied message.

@EmilioPisanty ::chuckle:: Every time I start look at some part of the discipline that I'm not strong on I end up questioning my right to identify myself as a physicist.

@CaptainBohemian It's really not that hard. My lab does it every day, millions of times.

For the last few years I've been trying to shore up my understanding of thermal physics in the corners of free time I find. I guess I'll put optics next on the list.

@EmilioPisanty @dmckee Optics is inherently 3D, or at least 2D, so I don't do it.

I'm a 0D and 1D physicist :-)

Microwave circuits 4 lyf.

@Chair it's me sorry I wanted to flag that post :-|

4:55 PM

@EmilioPisanty See I don't even know stuff like this.

Any
way. Everyone (especially our younsters) here is aware of [the imposter syndrome](https://en.wikipedia.org/wiki/Impostor_syndrome), right?

Don't worry about what other people know, just worry about being as good as you can be.

@dmckee Dude, yes.

user351417

Can we star that message? ;)

For the last six moths I've been so discouraged about my ability to contribute at work that I keep thinking of quitting.

One of my colleagues was in tears because of that feeling yesterday. It's everywhere.

Anonymous

@Liquid If you want to say something specific about about a message that's neither spam nor offensive per se, it's better to raise a custom mod flag. Note the option "flag for moderator".

4:57 PM

@dmckee More than that, we have to talk about it so we see just how insecure our friends are. It helps a lot because you 1) support each other and 2) realize you're not alone.

I actually sent a student off to grad school unaware that the imposter syndrome was a thing. I got the first teary phone call at the beginning of October.

Captain Bohemian

@DanielSank really? I have read several times (ways) how entangled states are created for several materials, but I imagine that sounds very difficult and decoherence may occur easily.

@Blue just kick him out . I think that dude is somewhat puzzling us .

@CaptainBohemian It's not easy but it's not really that hard either. People have shown violations of the Bell inequality many times, and that requires entanglement.

Now she's the star student researcher in her group and they keep sending her to overseas conferences to deliver talks.

4:59 PM

@dmckee Please support that person.

@dmckee good

danielunderwood

@dmckee is imposter syndrome kind of the reverse of the Dunning-Kruger effect or something entirely different?

@danielunderwood Dunning Kruger is different.

The thing is, I go give talks too, actually probably more than most of my colleagues because I have a reputation as a good pedagogical speaker. Despite that, when it comes to getting work done on a daily basis, I feel like a failure more often than not.

@danielunderwood It's the "everyone else here knows what they're doing and I'm just hanging on by my fingernails and eventually they're going to find out and I'm be ruined and humiliated and never amount to anything" feeling.

Not that I've every had that problem. Or anything.

Dunning Kruger is when people are confident about themselves, in imposter they are themselves insecure.

5:01 PM

Woah! A polar bear!

Hi!

Polar bears are awesome.

0

Q: My question was put on hold

My question was put on hold because "homework-like". I would like some clarification on this please. I am not asking anybody to do a conversion of me, I am asking whether the conversion mol/mm3 <-> mol/L is always the same and independent of other features such as temperature, pressure, etc. Can...

discussion scope

There is a good question about it over on Academia: academia.stackexchange.com/questions/11765/…

@DanielSank Hallo! Greetings from Antarctica!

@PolarBear Greetings from the sea!

@PolarBear Waaaaait a minute... polar bears don't live in the antarctic...

@DanielSank Hahaha, came here to meet my friend Penguin

5:04 PM

Hmmm, ok story checks out.

danielunderwood

"friend"

@Loong I wonder what were 111 users doing in their chem classes

@DanielSank They don't ordinarily use internet chat, either.

Anyway, I'm sorry that we're destroying the planet's ecosystems and melting the ice. Hopefully humans will all be dead in a few hundred years and those of you who survive it can get back to living in a balanced biosphere.

Seems like an exceptional bear.

5:05 PM

Smarter than the average bear, you might say.

Yeah lliquid's rico's sock

@DanielSank Thank you for caring :'(

@rob :D

2 days ago, by Avnish Kabaj

Eyo polar baer

2 days ago, by Avnish Kabaj

Study 65 days to go

65 64

danielunderwood

@dmckee oh good. I don't believe that I'm the only clueless one!

Meh

anyhow 63 days

5:12 PM

Suddenly realized that the student mentioned above is researching solar physics, which means that I missed a great opportunity to have intended a pun. ::sigh::

Star student. Get it? Get it?

3

ow

That star just made me a pun god

that comment is pun-godly

Captain Bohemian

@dmckee what a syndrom! I think I am in a syndrom completely opposite to it.

@dmckee that's the daddy of all dad jokes

oooooooooooooohhhhhh I kill me =P

5:17 PM

@CaptainBohemian People who sail through their early life experiences are particularly prone to the syndrome once they rise to the level where they start to encounter challenges.

At that point many of your peers have good habits and coping skills that you have yet to develop. Ask them to help you out.

user image

(not that it's only applicable to PhD students, either)

Among the symptoms: "Increased Eating. Decreased eating." Isn't it wonderful to be human?

Captain Bohemian

I think what I appear to others is usually detracted from my real intelligence because I tend to feel nervious in exams or presentations.

Anyone here know Hamltonian mechancis?

Suppose I have a Hamiltonian $H(X, Y)$ such that $\dot{X} = \partial H / \partial Y$ and $\dot Y = -\partial H / \partial X$.

Now we define new variables e.g. $a_\pm = X + i Y$.

Is there a sensible recipe for the new Hamiltonian equations of motion?

I guess I'm asking if there's a recipe for finding equations of motion when you change coordinates.

@DanielSank I think that Qmechanic is pretty sharp on variational mechanics. I'm barely better than rubbish on the subject. Another item for that list.

5:28 PM

Paging @Qmechanic

@DanielSank That's not a well-defined action in Hamiltonian mechanics because the symplectic manifolds the Hamiltonian lives on are not required to carry a complex structure.

@ACuriousMind o_O

But we do this all the time!

I don't think that we multiply phase space variables by $\mathrm{i}$ "all the time"! I'm pretty sure I've never done that :P

In QM, it is allowed because your operators live on a Hilbert space over the complex numbers. But it's not allowed in the classical case unless you explain what space $X+\mathrm{i}Y$ is supposed to live on

@ACuriousMind Uh, it lives on the space of useful quantities that make the equations of motion really simple.

For a harmonic oscillator, you get $\dot a = \omega a$ which has an obvious solution.

Coupled systems tend to have terms in the Hamiltonian like $(X_1 - X_2)^2$. Converting to $a_\pm$ gives you e.g. $ab + a^* b^* + ab^* + a^* b$, which is nice because in the rotating wave approximation you can ignore the first two terms.

Here $a$ corresponds to $X_1$ and $b$ corresponds to $X_2$, and I switched to $a$ and $a^*$ instead of $a_\pm$ for maximum confusion.

@ACuriousMind Strictly speaking the determinant of the transformation proposed by @DanielSank is 2i, so a simple scaling and adding an "i" somewhere would produce a transformation matrix of det=1, which in 2d phase-space is necessary and sufficient to make the transformation canonical.

5:34 PM

@DanielSank To illustrate what I mean: The usual phase space for one generalized coordinate is $\mathrm{R}^2$. Your complex variables are complex combinations of the coordinate and the momentum, so they must (at least) live in $\mathrm{C}^2$

granted it's not a real transformation so maybe that's the weakness of the argument here...

@ZeroTheHero My point is that you can't just randomly add $\mathrm{i}$s in classical Hamiltonian mechanics!

But, but... it works!

If Hamilton's equations of motion are $$\frac{d}{dt} \left( \begin{array}{c} X \\ Y \end{array} \right) = \left( \begin{array}{cc} 0 & 1 \\ -1 & 0 \end{array} \right) \left( \begin{array}{c} X \\ Y \end{array} \right)$$

then the coordinate transformation I gave above diagonalizes that matrix.

@DanielSank Can I ask a dumb question: basically you have a system of coupled equations so you solve it by going to the "normal" coordinates, i.e. you would diagonalize the matrix...

@ZeroTheHero Yes.

5:38 PM

@DanielSank we were thinking along the same lines...

@DanielSank Ah, yes. In that case, what you're seeing that's making the equations "simpler" is that more matrices are diagonalizable over the complex numbers than over the reals!

@ACuriousMind True.

So I'm asking if there's a Hamiltonian-y way to talk about that.

The problem I'm really trying to solve is this: I have a Hamiltonian $$H = \frac{\Phi_1^2}{2 L_1} + \frac{\Phi_2^2}{2 L_2} + \frac{Q_1^2}{2C_1} + \frac{Q_2^2}{2C_2} + \frac{Q_1 Q_2}{C_g}$$ where $\Phi$ and $Q$ are canonically conjugate.

I just want to find the normal modes.

@DanielSank You're at least not the only person having noticed this: people.umass.edu/bvs/605_ham.pdf

I can pretty easily find the normal modes by using the second order equations as shown here, but only in the case that the oscillators are identical, i.e. $L_1 = L_2$ and $C_1 = C_2$.

I'm pretty sure that the Hamiltonian (i.e. first order) approach makes it easier to deal with asymmetry, i.e. when $L_1 \neq L_2$.

@DanielSank hmmmm

so, first up, re-scale the $\Phi_i$s to make sure the flux part symmetric

5:45 PM

Ok wait.

then re-scale the $Q_i$s to make sure the transformation is canonical

Ah

that's going to give you a new quadratic form on the charge side

I was going to complain about losing conjugate-ness :-)

I like where this is going.

then rotate the charges in the $(Q_1,Q_2)$ plane so that the charge quadratic form is in canonical (diagonal) form

make sure that this transformation is orthogonal

and this will naturally keep the diagonal form of the flux quadratic form

that should work seamlessly

5:47 PM

@DanielSank I don't know if it's equivalent to @EmilioPisanty but the first thing I would do is use one of the $\omega_i$ as inverse unit of time, i.e. rewrite your DEs in terms of $\tau=\omega_1t$ to obtain everything in terms of the single ratio $\omega_2/\omega_1$...

@EmilioPisanty I don't exactly understand that last part, but I think I get what you're saying.

@ZeroTheHero That's probably a good idea too, and I think it works independently of what Emilio suggested.

@DanielSank I mean

you also need to rotate the fluxes

using the same matrix you use for the charges

that is required to keep the conjugateness

but once you put it all together, you'll have one big canonical transformation that gives you a canonical form with two uncoupled harmonic oscillators at different frequencies

@ACuriousMind Ah! Very nice. Thank you.

@ACuriousMind Yes this is quite nice as a matter of fact.

@EmilioPisanty Ok I think the insight here is to rescale the fluxes and then fix the changes to keep canonicalness.

I guess that comes down, geometrically, to squashing an ellipse into a circle. Then the second step you mentioned is rotating the circle.

Thanks @EmilioPisanty, @ACuriousMind, and @ZeroTheHero. I'll report back when I have a result.

Bye, everybody.

5:56 PM

@DanielSank yep, that's the idea. Hope it works without a hitch =).

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